P H A S E T R A N S I T I O N S A N D S T R U C T U R A L M O T I F S O F I N O R G A N I C - O R G A N I C L E A D H A L I D E H Y B R I D S Andreas Lemmerer A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, 2007 ii Declaration I declare that this thesis is my own, unaided work. It is being submitted for the Degree of Doctor of Philosophy in the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other University. __________________________________________ (Signature of Candidate) _______________day of____________________2007 iii "But to what extent can we really know the universe around us? ...Let us approach a much more modest question: not whether we can know the universe or the Milky Way Galaxy or a star or a world. Can we know, ultimately and in detail, a grain of salt? Consider one microgram of table salt, a speck just barely large enough for someone with keen eyesight to make out without a microscope. In that grain of salt there are about 1016 sodium and chlorine atoms. This is a 1 followed by 16 zeroes, 10 million billion atoms. If we wish to know a grain of salt, we must know at least the three-dimensional positions of each of these atoms. (In fact, there is much more to be known-for example, the nature of the forces between the atoms-but we are making only a modest calculation.) Now, is the number more or less than the number of things which the brain can know? How much can the brain know? There are perhaps 1011 neurons in the brain, the circuit elements and switches that are responsible in their electrical and chemical activity for the functioning of our minds. A typical brain neuron has perhaps a thousand little wires, called dendrites, which connect it with its fellows. If, as seems likely, every bit of information in the brain corresponds to one of these connections, the total number of things knowable by the brain is no more than 1014, one hundred trillion. But this number is only one percent of the number of atoms in our speck of salt. So, in this sense this universe is intractable, astonishingly immune to any human attempt at full knowledge. We cannot on this level understand a grain of salt, much less the universe. But let us look a little more deeply at our microgram of salt. Salt happens to be a crystal in which, except for defects in the structure of the crystal lattice, the position of every sodium and chlorine atom is predetermined. If we could shrink ourselves into this crystalline world, we would see rank upon rank of atoms in an ordered array, a regularly alternating structure - sodium, chlorine, sodium, chlorine, specifying the sheet of atoms we are standing on and all the sheets above us and below us. An absolutely pure crystal of salt could have all the positions of every atom specified by something like 10 bits of information. This would not strain the information- carrying capacity of the brain. If the universe had natural laws that governed its behaviour to the same degree of regularity that determines a crystal of salt, then, of course, the universe would be knowable." From "Broca's Brain" by Carl Sagan. "Ever since I began working on X-rays, I have repeatedly sought to obtain diffraction with these rays; several times, using narrow slits, I observed phenomena which looked very much like diffraction. But in each case a change of experimental conditions, undertaken for testing the correctness of the explanation, failed to confirm it, and in many cases I was able to directly show that the phenomena had arisen in an entirely different way than by diffraction. I have not succeeded to register a single experiment from which I could gain the conviction of the existence of diffraction of X-rays with a certainty which satisfies me." From W. C. R?ntgen's Third Communication, March 1897. iv Abstract Layered inorganic-organic hybrid compounds have been widely studied as new potential sources of semiconductors and other optical devices. They simulate natural quantum well materials, where the inorganic part acts as semiconductors, separated by an organic part. This class of hybrid materials has no covalent bonds between the inorganic and organic parts; instead, weak hydrogen bonds and van der Waals forces bind and stabilise the overall structure. The inorganic part is made up of layers of corner-sharing metal halide octahedra, MX6, where the metal must be in a divalent state and the halides are Cl, Br or I. The 2-D layers extend infinitely in two directions and are separated themselves by layers of primary ammonium cations, with only one ammonium group at one end of the chain, [(R-NH3)2MX4], or two ammonium groups at either of the chain, [(H3N-R-NH3)MX4]. Due to its similarity to the cubic perovskite structure, this inorganic motif is referred to as "layered perovskite-type". Depending on the choice of the organic ammonium cation, the materials can display phase transitions and / or have optical and electronic properties. Various investigations of inorganic-organic hybrids have concentrated on the phase transitions of the hybrids of general formula [(CnH2n+1NH3)2MX4] and [(NH3CnH2nNH3)MX4] (n = 1-18; X = Cl, Br, I; M = Cu2+, Mn2+, Cd2+) to elucidate their mechanism. There are two types of displasive transitions, a minor one were small conformational changes within the alkylammonium chain occurs, and a major one, when the entire alkylammonium chain becomes disordered along its long axis. The interlayer spacing between the inorganic layers increases with temperature and during the major phase transition. The methods used to identify the temperatures and the enthalpies of the phase transitions are Differential Scanning Calorimetry (DSC); and Single Crystal X-ray Diffraction (SC-XRD) as well as Powder X-Ray Diffraction (P-XRD) to follow the structural changes. In contrast, only a few reports on investigations of the lead iodide hybrids, [(CnH2n+1NH3)2PbI4] were found in the literature, with only two single crystal structures previously reported. Due to the difficulty in growing good quality crystals, the previous studies on the lead iodide hybrids have been only researched using DSC and P-XRD. The phase transition behaviour has been found to show the same trends as the previous hybrids. The primary aim of this study was to follow the same phase transitions via SC-XRD, ideally single-crystal to v single-crystal, and to determine the detailed structural changes with the hopes of elucidating their detailed phase transition mechanism. A secondary aim was to synthesize as many inorganic-organic hybrids as possible using a variety of primary ammonium cations to find different inorganic motifs apart from the layered perovskite-type. Other inorganic motifs can have purely corner-, edge or face-sharing octahedra or combinations thereof to give 2-D net-type networks or 1-D extended chains. The effect that the identity of the ammonium cation has on the type of inorganic motif and the effect on the detailed structural geometry within the inorganic motif are investigated. Examples of structural geometries within the layered perovskite-type inorganic motif that can differ from compound to compound are the relative positions of the inorganic and organic moieties; the N---H?.X hydrogen bonding geometry between the halides and the ammonium group; and the relative positions of successive inorganic layers. vi Acknowledgements My supervisor, Dave, for showing me a picture of a packing diagram that I did not understand at all when I was in honours. It was the first packing diagram I have ever seen. Also, he helped shape my life philosophy by sharing his views with me. Manuel Fernandes for being my idol and mentor and teaching me everything I know about crystallography and helping me to solve those difficult structures. Demetrius Levendis for being a patient consultant, who never charged for his services when I went to his office next door to me. Bernard for not playing his annoying Kenyan music whenever I was around and being the most mature PhD student ever, raising a family already. Gert Kruger at the University of Johannesburg for the use of his Mettler Toledo Calorimeter and Melanie Rademyer at the University of KwaZulu-Natal for helpful encouragement. Susan Travis for casting her expert eye on various drafts of this manuscript. The Beacon? company for their delicious Sparkles? and all the chocolate manufacturing companies, especially Milka? and Cadbury?. The Toshiba? computer company for manufacturing the laptop I wrote my thesis on. And my family. And lastly, to Bruker? AXS in South Africa for their incomparable technical support in maintaining our beloved SMART and APEX II diffractometers. vii Presentations and Posters 1) Oral Presentation: "Structural motifs of lead halide inorganic-organic hybrids", South African Chemical Institute, Young Scientist, Pretoria, 2005. 2) Oral Presentation: "Phase transitions and structural motifs of inorganic-organic lead halide hybrids", Departmental Seminar at the School of Chemistry, Johannesburg, 2007. 3) Poster Presentation: "Synthesis and Characterization of Organic-Inorganic Hybrid Perovskites", Indaba IV Conference, Skukuza, Kruger National Park, 2003. 4) Poster Presentation: "Synthesis and Characterization of Organic-Inorganic Hybrid Materials", European Crystallographic Meeting 21, International Conference Centre, Durban, 2003. 5) Poster Presentation: "Temperature Dependant Phase Transitions of Organic-Inorganic Hybrid Perovskites", International School of Crystallography?s 35th Course: Diversity Amidst Similarity: A multidisciplinary Approach to Polymorphs, Solvates and Phase Relationships, Erice, Sicily, 2004. 6) Poster Presentation: "Temperature Dependant Phase Transitions of Organic-Inorganic Hybrid Perovskites", South African Chemical Institute, Pretoria, 2004 (Won RSC Poster Prize). 7) Poster Presentation: "Structural Transitions of the Layered K2NiF4 Type System (CnH2n+1NH3)2PbI4; n = 12, 16, 18", Carman Symposium, Pretoria, 2005 (Won IUPAC Poster Prize). 8) Poster Presentation: "Structural Transitions of the Layered K2NiF4 Type System (CnH2n+1NH3)2PbI4; n = 12, 16, 18", European Crystallographic Meeting 23, Leuven, Belgium, 2006 (Won IUCr Poster Prize). 9) Poster Presentation: "Structural Transitions of the Layered K2NiF4 Type System (CnH2n+1NH3)2PbI4; n = 12, 16, 18", Indaba V conference, Berg-en-Dal, Kruger National Park, 2006. viii Preface The entire thesis has two styles of writing. The chapters of the introduction (Chapter 1), literature survey (Chapter 2) and experimental methods (Chapter 3) are detailed and exhaustive and written in a uniform style. The results chapters (Chapters 4-6) consist partly of published work in crystallographic specific journals such as those of the International Union of Crystallography and the Royal Society of Chemistry, and work that will be submitted or is currently under review. All the results chapters are subsequently written up in styles required for the different journals. The advantage is that a large amount of work, 76 new compounds and their single crystal structures, can be discussed concisely and the most important and relevant features described. Crystal structure determination has become a routine exercise as detector technology and computing speed has improved. Each structure is viewed more as a data point whereas previously, a whole thesis consisted of only a few single crystal structures. The figures in the literature survey are all in grey-scale, indicating that they are results published from previous work. The figures in the results chapters are all in colour, differentiating them explicitly as new work, except those in journals that do not usually publish in colour, specifically Acta Crystallographica C. The Cambridge Structural Database (CSD) (Version 5.27, August 2006 release; Allen, 2002) contains an inventory of all reported single crystal structures and is used throughout the literature survey. The reference codes for those structures as they appear in the CSD are given throughout. Reprints of published work are supplied in the attached Compact Disc as pdf files. Crystallographic Informations Files (CIF) and CIF Tables of all structures are also supplied on the disc under the relevant chapters. Finally, the complete electronic version of the thesis can also be found on the disc. ix Table of Contents Page Abstract iv Acknowledgements vi Posters and Presentations vii Preface viii Table of Contents ix List of Figures xii List of Tables xx List of Schemes xxi Abbreviations xxii Section A: Background and Literature Survey Chapter 1: Introduction 1.1 Overview 1 1.2 Basic cubic perovskite motif 2 1.3 Two-dimensional layered perovskite-type motif 3 1.4 Lower dimensional motifs on inorganic-organic hybrids 8 1.5 Zero-dimensional motifs 11 1.6 Hydrogen bonding in inorganic-organic layered perovskite-type hybrids 11 1.7 Hydrogen bonding in non layered perovskite-type inorganic-organic hybrids 14 1.8 Aims 14 Chapter 2: Literature Survey 2.1 First synthesis and structure determination 15 2.2 Inorganic-organic layered perovskite-type hybrids [(CnH2n+1NH3)2MX4] 21 with simple alkylammonium chains 2.2.1 Phase transitions in inorganic-organic layered perovskite-type hybrids 23 [(CnH2n+1NH3)2MX4] with n ? 3 and M = Mn and Cd 2.2.2 Phase transitions in inorganic-organic layered perovskite-type hybrids 28 [(CnH2n+1NH3)2MX4] with n ? 4 2.2.3 The lead halide inorganic-organic hybrids [(CnH2n+1NH3)2PbX4] 37 with the layered perovskite-type motif 2.2.4 Phase transitions in inorganic-organic layered perovskite-type hybrids 38 [(CnH2n+1NH3)2PbX4] x 2.2.4.1 Alkylammonium chains with n = 1 38 2.2.4.2 Alkylammonium chains with n ? 4 38 2.3 Aromatic R groups and their photoelectric behaviour 42 2.4 Inorganic-organic layered perovskite-type hybrids [(H3N(CH2)nNH3)MX4] with 51 simple alkyldiammonium chains 2.4.1 Lead(II) halide inorganic-organic layered perovskite-type hybrids 52 [(H3N(CH2)nNH3)PbX4] and [(H3N-R-NH3)PbX4] 2.4.2 Other divalent metals reported to form inorganic-organic layered 58 perovskite-type hybrids [(H3N(CH2)nNH3)MX4] with diammonium alkyl chains 2.4.3 Structural phase transitions of inorganic-organic layered perovskite-type 61 hybrids [(H3N(CH2)nNH3)MCl4] (M = Cd and Mn) with diammonium alkyl chains 2.5 Inorganic-organic layered perovskite-type hybrids [(H3N-R-NH3)MX4] containing 63 aromatic diammonium cations 2.6 Inorganic-organic layered perovskite-type hybrids with triammonium cations 64 2.7 Other metals and more complex ammonium cations contained in 66 inorganic-organic layered perovskite-type hybrids 2.8 Multilayer inorganic-organic layered perovskite-type hybrids 75 2.9 Photopolymerization 77 2.10 Two-dimensional inorganic motifs 80 2.10.1 Two-dimensional motifs - NET 80 2.10.2 Two-dimensional motifs - based on corner-sharing layers 83 2.10.3 Two-dimensional motifs - based on face-sharing 84 2.11 One-dimensional inorganic motifs 86 2.11.1 Purely corner-sharing, edge-sharing and face-sharing 86 2.11.1.1 Motifs based on trans corner-sharing 86 2.11.1.2 Motifs based on cis corner-sharing 88 2.11.1.3 Motifs based on face-sharing 91 2.11.1.4 Motifs based on edge-sharing 94 2.11.2 Motifs based upon combinations of edge- and face-sharing 97 2.11.3 One-dimensional "Ribbon" type motifs 97 2.12: Zero-dimensional inorganic motifs 102 2.13: Summary and Conclusion 107 Chapter 3: Experimental 3.1 Synthesis 109 3.1.1 Slow cooling 109 3.1.2 Slow evaporation 112 3.1.3 List of compounds prepared with corresponding chapter reference in 112 this thesis 3.2 X-ray diffraction 119 3.2.1 Instruments used 119 3.2.2 Face-indexed absorption corrections 120 3.3 Thermal analysis 122 3.4 Elemental analysis 122 3.5 Hot Stage Microscopy xi Section B: Results and Discussion Chapter 4: Structural Motifs of Inorganic-Organic Hybrids 4.1 Introduction 125 4.2 Synthesis and crystal structures of inorganic-organic hybrids incorporating an 126 aromatic amine with a chiral functional group 4.3 Inorganic-organic hybrids incorporating a chiral cyclic ammonium cation 139 4.4 Inorganic-organic hybrid materials incorporating primary cyclic ammonium 153 cations: The lead iodide series 4.5 Inorganic-organic hybrid materials combining primary cyclic ammonium 164 cations with bromoplumbate and chloroplumbate anions 4.6 Effect of heteroatoms in the layered perovskite-type system 185 [(XCnH2nNH3)2PbI4], n = 2, 3, 4, 5, 6; X = OH, Br and I; and [(H3NC2H4S2C2H4NH3)PbI4]. 4.7 Inorganic-organic hybrids incorporating diammonium cations 204 Chapter 5: Phase Transitions of Inorganic-Organic Layered Perovskite-type Hybrids 5.1 Introduction 220 5.2 Synthesis, characterization and phase transitions in the inorganic-organic layered 221 hybrids [(CnH2n+1NH3)2PbI4], n = 4, 5 and 6 5.3 Synthesis, characterisation and phase transitions of the inorganic-organic layered 247 hybrids [(CnH2n+1NH3)2PbI4], n = 7, 8, 9 and 10 5.4 Structural transitions of the inorganic-organic layered perovskite-type hybrids 277 [(CnH2n+1NH3)2PbI4]; n = 12, 14, 16, 18 Chapter 6: Miscellaneous Structures and Motifs 6.1 Introduction 293 6.2 Bis[(S)-?-phenethylammonium] tribromoplumbate(II) 295 6.3 Bis(pentane-1,5-diammonium) decaiodotriplumbate(II) 299 6.4 p-phenylenediammonium tetraiodozincate(II) dihydrate 303 6.5 1-Naphthylammonium triiodoplumbate(II) 307 6.6 catena-Poly[tetrakis(3-phenylpropylammonium) 311 [iodoplumbate(II)-tri-?-iodo-plumbate(II)-tri-?-iodo-plumbate(II)-di-?-iodo]] 6.7 Bis(propane-1,2-diammonium) hexaiodoplumbate(II) trihydrate 315 6.8 Octakis(3-propylammonium) octadecaiodopentaplumbate(II): a new layered 319 structure based on layered perovskites 6.9 catena-Poly[bis(tert-butylammonium) [plumbate(II)-tri-?-iodo] iodide dihydrate] 323 6.10 Poly[bis[2-(1-cyclohexenyl)ethylammonium] di-?-iodo-diodoplumbate(II)] 328 6.11 Two packing motifs based upon chains of edge-sharing PbI6 octahedra 332 xii Chapter 7: Conclusion 7.1 Concluding remarks 339 7.2 Future work 340 Chapter 8 References 343 Appendix 357 xiii List of Figures Page 1.1: Ball and stick model of the basic AMX3 perovskite showing the unit cell 3 structure and the polyhedral representation of how the structure extends in three dimensions. 1.2: The unit cell of the inorganic compound K2NiF4, that is the archetype for the 5 2-D layered perovskites that have staggered layers (left), and RbAlF4, that is the archetype of the eclipsed inorganic layers (right). 1.3: Schematic Representation of single-layer perovskites with (a) monoammonium 5 (R-NH3+) or (b) diammonium (+H3N-R-NH3+) organic cations. 1.4: The area generated by the four terminal halides, viewed perpendicular to 7 the 2-D layers. (a) shows the biggest possible scenario of a square, when there is no tilting of the octahedra. (b) shows the actual scenario, when both ? and ? tilts are observed. 1.5: Schematic Representation of the two commonly encountered tilts in 7 the layered perovskites. (a) (0?0) tilt, leading to a corrugation of the sheets in one direction; (b) (00?) tilt, leading to a rotation of adjacent octahedra relative to each other. 1.6: A space-filled representation of the packing arrangement of a typical 8 inorganic-organic layered perovskite-type hybrid with atoms drawn with their van der Waals radii. The terminal iodides are shown as red coloured spheres. 1.7: An illustration of the n = 3 [Pb3I10]n4n- 2-D net. 9 1.8: Example of a corner-sharing chain and the classification of the halides 10 within the octahedra. 1.9: Example of an edge-sharing chain and the classification of the halides 10 within the octahedra. 1.10: Example of a face-sharing chain and the classification of the halides 11 within the octahedra. 1.11: Two hydrogen bonding configurations typically observed in the 12 [(R-NH3)2MX4] and [(H3N-R-NH3) MX4] type structures: (a) the bridging halogen configuration, and (b) the terminal halogen configuration. 1.12: Two types of terminal halogen configuration: (a) equilateral configuration, where 13 the three halides involved in hydrogen bonding are at the vertices of an equilateral shaped triangle (dashed blue lines) and (b) right-angled configuration, where the halides are at the vertices of a right-angled triangle. The obtuse xiv angled position is shown in (a) and the acute angled position in (b) relative to the parallelogram (green lines). 1.13: The correlation between the hydrogen bonding interactions and the tilting 14 of the PbI6 octahedra in the layered perovskite-type hybrid [(C3H5NH3)2PbI4]. 2.1: The tilted and non-interdigitated decylammonium chains in C10MnCl (left). 22 The non-tilted and interdigitated nonylammonium chains in C9PbI (right). 2.2: The effect of the identity of the metal on the ? tilt of the octahedra is seen 23 in the compounds C4GeI (left) and C4SnI (right). The (OO?) tilt is 13.73? in the layered perovskite-type hybrid with Ge and 20.39(5)? with Sn. 2.3: The hydrogen bonding interactions of the layered hybrid with 25 methylammonium and cadmium(II) chloride in phase II. 2.4: Phase II of C2CdCl and its terminal halogen configuration. The ethylammonium 25 cation is ordered in this phase. Phase I has the same ethylammonium cation disordered over two positions. The SC-XRD structure of phase III has not been determined. Figure adapted from Peyrard and Perret, 1979. 2.5: The two SC-XRD structures of phases III and I of C3CdCl. 27 2.6: Schematic representation of DSC results of the homologous CnCdCl4 series 33 for n = 6 - 18. Inset: Transition enthalpies for n = 7-12. Asterisk represent the chain melting transition and filled circles the minor transition. Figure taken directly from Schenk and Chapuis, 1988. 2.7 The herringbone arrangement of the tilted decylammonium chains in C10CdCl 36 in the monoclinic phase III (left) and the two independent chains in this phase (right). Taken from Kind et al, 1979. 2.8: Electron density contours from the orthorhombic phase I of C10CdCl. Taken 36 from Kind et al, 1979. 2.9: A schematic of the various phases of C6PbCl and their unit cell parameters as 39 determined by P-XRD. Adapted from Kammoun et al, 1996a. 2.10: DSC curve of C9PbCl. Taken from Kammoun et al, 1997. 40 2.11: A schematic of the two possible packing arrangements, parallel (left) or 41 herringbone (right), of the alkylammonium chains in CnPbI (n = 12, 16, 18). All the bonds in the chains are in an all-trans conformation. Taken from Venkataraman et al, 2002. 2.12: A schematic of the phase transition of CnPbI (n = 12, 16, 18). Taken from 42 Venkataraman et al, 2002. xv 2.13: The hydrogen bonding interactions of the layered hybrid with anilinium and 44 the two long and four short Cu-Cl bonds of the copper(II) chloride octahedra. 2.14: The packing arrangement of a complete unit cell of [(p-Ph-C6H4NH3)2CuCl4]. 44 2.15: Hydrogen bonds in [(C6H5CH2NH3)2PbI4]. 46 2.16: The bridging halogen configuration of [(C6H5(CH2)2NH3)2CuCl4]. 47 2.17: The simplest repeating unit of the perovskite sheets in 48 [(C6H5(CH2)2NH3)2PbCl4]. The four phenethylammonium cations adopt a J-shaped conformation. 2.18: A schematic of the organic-inorganic heterostructure electroluminescent 50 device with approximate thickness of the layers and the structure of the organic component, OXD7, used. Figure adapted from Era et al (1994). 2.19: A schematic of the three-layered heterocontact organic-inorganic light emitting 50 diode with a chiral layered-perovskite. Figure adapted from Gebauer and Schmidt (1999). 2.20: Optical absorption spectra of (a) [(RNH3)2PbBrxI4-x] and 51 (b) [(RNH3)2PbClxBr4-x] films measured at room temperature. Taken from Kitazawa (1997). 2.21: The packing diagram of a single unit cell of [(H3N(CH2)3NH3)PbCl4] shown 52 side-on (left) and from the top (right). The inorganic layer shown as light grey octahedra is staggered relative to the inorganic layers shown as dark grey octahedra. 2.22: Half of the unit cell of [(H3NCH3CH(CH3)(CH2)3NH3)PbCl4] showing a 53 magnified view of the arrangement of the cations between the layers. The methyl group has a repulsive effect on the cations in the crystallographic c direction. 2.23: The structure of phase II of [(H3N(CH2)4NH3)PbCl4] showing a magnified view 54 of the left-hand conformation of the cation between the layers. 2.24: The structure of [(H3N(CH2)6NH3)PbI4]. The cation is centrosymmetric and the 55 two halves are related by the symmetry operator (1-x, 1-y, 1-z), shown as atoms marked with dashes ('). 2.25: The molecule 5,5'''-bis-(aminoethyl)-2,2':5',5'',2'''-quaterthiophene, AEQT. 56 2.26: The unit cell of [(AEQT)PbCl4]. The ethylammonium groups and the bridging 57 bromides are disordered over two positions. 2.27: The molecule BAESBT. 57 xvi 2.28: The molecule AETH. 58 2.29: The hydrogen bonding configurations of [(H3N(CH2)4NH3)HgCl4] 59 (left) and [(H3N(CH2)3NH3)HgCl4] (right). 2.30: The packing diagrams of phase II (left) and phase I (right) of 63 [(H3N(CH2)4NH3)MnCl4]. The two equivalent positions of the atoms are shown as light grey and dark grey spheres in phase I. 2.31: The packing diagrams of [(H3N-C6H4-NH3)CdCl4] (left) and 64 [(H3N-C6H4-C6H4-NH3)CuCl4] (right). The C-H...? interactions are shown as dashed black lines. 2.32: Half of the unit cell of [((H3NCH2CH2)2NH2)CuCl4]?Cl. Figure is taken 65 from Ferguson and Zaslow (1971). 2.33: Half of the unit cell of [((H3NCH2CH2)2NH2)MnCl4]?Cl. The hydrogen bonds 66 to the interlayer chloride are shown as dashed black lines. 2.34: The packing diagram of [(4-F-C6H4C2H4NH3)2SnI4]. The aromatic rings are 68 parallel to each other. 2.35: The carbozole chromophore, n = 3-8, 12. 69 2.36: The packing diagram of [(Cu(O2C-(CH2)3-NH3)2PbBr4]. The PbBr6 octahedra 71 are shown as dark grey octahedra and the CuO4Br square-planar pyramids are light grey. 2.37: The packing diagram of [(HO2C(CH2)3NH3)2PbI4]. The R groups have a 73 carboxylic functional group that interacts strongly with adjacent R groups via O-H...O (d(O...H) = 1.8 ?) hydrogen bonds to strengthen the overall structure. 2.38: The packing diagram of [(C6H8N4)PbI4]. There are only four hydrogen bonds 74 between the individual cations and the inorganic layers. 2.39: The packing diagram of [((CH3)3N(CH2)2NH3)SnI4]. 75 2.40: The packing diagram of the bilayer hybrid 76 [(CH3NH3)(H3CC6H5(CH2)NH3)2Pb2I7] (Papavassiliou et al, 2000; CSD ref. code: MEMYAE). 2.41: The packing diagram of the trilayer hybrid [(CH3NH3)2(C4H9NH3)2Pb3I10]. 76 The CH3NH3 cations are not shown as their positions were not accurately determined in the crystal structure (Mitzi et al, 1994; CSD ref. code: PIVCUS). 2.42: The basic idea of solid-state polymerization within layered type structures. 78 Taken from Takeoka et al, 2001. 2 xvii 2.43: The geometries of the closest propargylammonium cations in the hybrid structure 79 that undergoes possible photopolymerization. The octahedra consist of CdCl6. 2.44: The 2-D net of [(Me2HN-C2H4-NHMe3)Sn3I8]. The cations are omitted for clarity. 81 2.45: 2-D net of [(Pr3N-C2H4-NPr3)Pb(dmf)6Pb5I14] ? DMF. The cations and 82 [Pb(dmf)6] anions are omitted for clarity. 2.46: The 2-D net of [(Me3N-C3H6-NMe3)3Pb3I9]. The cations are omitted for clarity. 83 2.47: The [SnI4]2- 2-D layers. The cations are omitted for clarity. 84 2.48: The twin 2-D layers of face-sharing PbCl8 square antiprisms, 85 separated by a monolayer of p-phenylenediammonium. The hydrogen bonds are shown as dashed black lines. 2.49: The mono 2-D layers of face-sharing [PbCl8], separated by bilayers 86 of H3N-C2H4-NH3. The two different orientations of the cations are labelled I and II. 2.50: The quasi 0-D chains of [(CH3SC(=NH2)NH2)3SnI5]. The activity 87 of the stereochemical lone pair is in the direction of the chains. 2.51: The 1-D chain of corner-sharing octahedra is shown in light grey as cut-outs of 88 the layered perovskite structure. The PbI2 deficient sites repeat themselves every third row along the b-axis and are shown in dark grey. 2.52: The 1-D chains of [(H3N(CH2)6NH3)BiX5]. 90 2.53: The 1-D chains of [(Na3(OCMe2)12)Pb4I11(OCMe2)]3-, which has 92 face-sharing involving three I atoms or alternately, two I atoms and one O atom from an acetone solvent molecule. 2.54: The twin 1-D chain of face-sharing PbI6 octahedra. 93 2.55: The 1-D chain of [(Me3N(CH2)6NMe3)PbI3]2. The face-shared 94 octahedra are alternatively cis and trans related. 2.56: The 1-D chain of the hybrid [(Pr4N)PbI3]. 95 2.57: The 1-D chain of the hybrid [(4-(CH3)C5H3NH)CdBr3], which has a single hydrogen bond between the anionic chain and the organic cation. 96 2.58: The 1-D chain of the hybrid [((CH3)3NH)HgCl3]. 96 2.59: A single layer cutout of the CdI2-Structure type. The octahedra in light grey 98 show the twin anionic chains seen in lead iodide inorganic-organic hybrids. xviii 2.60: The packing diagram of [(C10H7CH2NH3)PbI3] is shown on the left together 98 with the hydrogen bonds in dashed lines. On the right is an illustration of the anionic twin chains of edge-sharing PbI6 octahedra (Papavassiliou et al, 1999b; CSD ref. code: COTVUC). 2.61: The anionic polymeric chains of [(Ph4P)Sb3I10] (a) and [((Me2N)3C3)Sb3I10] 99 (b) shown schematically (light grey octahedra) as cut-outs of the layer structure of CdI2 (dark grey octahedra). 2.62: The cut-out of the K2NiF4 type inorganic motif that gives rise to the 1-D 100 inorganic ribbons, shown as light grey octahedra. Every fourth row is missing, shown as dark grey octahedra. 2.63: Two inorganic ribbons, connected by hydrogen bond interactions between 101 the terminal bromides and the oxygen molecules between them. 2.64: Twin anionic chains of face- and edge-sharing lead(II) iodide. 101 2.65: Twin anionic chains of edge- and corner-sharing Sn(II) bromide. 102 2.67: Twin anionic chains of lead(II) iodide, that has the three types of sharing in one 102 structure. 2.68: Alternating organic and inorganic layers bridged by hydrogen bonds in 103 [(H3N-C6H4-C6H4-NH3)2PbCl6]. 2.69: Incomplete part of the unit cell of [(Cl-C2H4-NH3)6PbCl6]?2Cl, showing only 104 a single ribbon of the hydrogen bonded interactions between the alternating PbCl6 octahedra and the cations. 2.70: Two views of a filled unit cell of [(CH3NH3)4PbI6]?2H2O. The cif file did not 105 contain any hydrogen atom coordinates so the interactions are shown as dashed lines between the various acceptor and donor atoms. 2.71: The anions and cations of [(Ph4P)2Pb2I6] (left), [(Pr4N)2PbI4] (middle) and 106 [(Bu3N-(CH2)3-NBu3)PbI4] (right) that contain tetra-coordinated lead atoms. 2.72: The cluster anion [Pb18I44]8-. 106 3.1: The basic experimental setup used to grow crystals of the inorganic-organic 110 hybrids. 3.2: The pictures show the important stages of the slow cooling technique. An 111 orange precipitate of the layered perovskite-type hybrid [(C8H17NH3)2PbI4] at room temperature slowly dissolves as the temperature of the solution increases to 100?C and then becomes a clear solution after a few hours. As the cooling takes place, orange plate-like crystals grow first at the surface of the solution xix and then at the bottom. 3.3: The CCD instruments used. (a) SMART 1K with Kryoflex. (b) The Bruker 120 APEX II with an Oxford Cryostream. (c) Close-up picture of the APEX II showing the centering video camera, CCD detector plate, collimator and heating tube. 3.4: Typical crystal shape of hybrid with the layered perovskite-type motif. 122 3.5: Locally modified Koffler Hot Stage. 123 7.1: The hexylammonium cations and the arrangement of the inorganic layers in the 341 two phases of [(C6H13NH3)2SnI4]. xx List of Tables Page 1.1: Mean distances (?) in N?H---A- hydrogen bonds to halide ions 12 with <(DHA) > 140?. 2.1: The composition of various CuCl inorganic-organic hybrids with 16 simple alkylammonium chains. 2.2: Summary of [(CnH2n+1NH3)2MX4] and [(NH3CnH2nNH3)MX4] (n = 1-10) 18 inorganic-organic layered perovskite-type hybrids in the literature. Numbers in superscript refer to the references listed at the end of the table. 2.3: Summary of [(CnH2n+1NH3)2MX4] and [(NH3CnH2nNH3)MX4] (n = 11-18) 29 layered perovskite-type hybrids in the literature. Numbers in superscript refer to the references listed at the end of the table. 2.4: Summary of interlayer spacing, c, from X-ray spectra of powders for 31 CnMCl (1). 2.5: Summary of phase transition temperatures, enthalpies and entropies from 32 DSC heating and cooling scans for CnHgCl (1). 2.6: Summary of unit cell parameters of CnCdCl inorganic-organic layered 34 perovskite-type hybrids in their various phases, n = 8 - 16. 2.7: Unit cell constants of the layered perovskite-type hybrids CnPbX at room 37 temperature. 2.8: Unit cell constants and other structural data of the various phases of the 38 hybrids [CH3NH3PbX3] that have a 3-D cubic perovskite motif (1). 2.9: The most common aromatic R groups that form inorganic-organic layered 43 perovskite-type hybrids. 2.10: Structures of compounds that appear in the CSD. 60 2.11: [(x-F-C6H4C2H4NH3)2SnI4], x = 2, 3, 4. 68 2.12: [(2-X-C6H4C2H4NH3)2SnI4] (X = Cl and Br) (1). 68 2.13: Other bilayer inorganic-organic layered perovskite-type hybrids with their 77 reported single-crystal structures if reported. 7.1: Summary of the inorganic motifs of the 76 inorganic-organic hybrids that 340 were made in this thesis. xxi List of Schemes Page 2.1: The inter-relationship between the four phases of C1CdCl and C1MnCl as a 24 function of temperature. 2.2: The phase sequence of C3CdCl and their unit cell parameters (?). 26 2.3: The phase sequence of C3MnCl and their unit cell parameters (?) with CSD 27 reference codes. The greek numbering for the phases is taken from the literature. xxii Abbreviations ap Cubic perovskite lattice parameter CCDC Cambridge Crystallographic Data Centre CSD Cambridge Structural Database 2-D two-dimensional 1-D one-dimensional 0-D zero-dimensional dmf dimethylformamide DSC Differential Scanning Calorimetry IR Infrared NMR Nuclear Magnetic Resonance NQR Nuclear Quadropole Resonance P-XRD Powder X-Ray Diffraction SC-XRD Single Crystal X-Ray Diffraction xxiii Chapter 1 Introduction 1 Chapter 1 Introduction 1.1 Overview Inorganic-organic hybrid structures are able to combine excellent features from both types of constituents. Inorganic compounds have different band gaps and hence their electrical properties can vary from insulators to semiconductors right the way through to superconductors. Furthermore, they supply the hybrid structure with thermal stability and hardness as well as magnetic and dielectric properties. Organic materials can offer highly efficient luminescence and can show conducting properties. Their biggest advantage however is a structural diversity that enables us to produce a range of different compounds to suit our needs. This property can best be described as essential to crystal engineering. As is sometimes the case, nature has long been aware of these materials and has incorporated the hybrid character into mollusc shells, and mammalian teeth and bone. The inorganic layer in sea shells consists of CaCO3 crystals and alternates with proteinaceous organic matter. The strength comes from the contrasting properties of the two: the hard and brittle inorganic part and the softer, more plastic-like organic part. The inorganic phase in teeth consists of calcium phosphate, Ca10(PO4)6(H2O), and the organic constituent of various protein matter. The resulting hybrid gives teeth their protective outer enamel shell with excellent wear resistant properties. Bone has the same inorganic compound but in this case alternates with fibres of the protein collagen. The softness of the organic constituent gives bone its flexibility; otherwise if it where only made up of the calcium phosphate it would shatter much more easily. In all three cases, the resultant strength is a case of the whole being greater than the sum of its parts, mainly due to the strength of the bonds that hold the framework together. The inorganic part of inorganic-organic hybrids consists of metal halide octahedra, which can be corner-sharing to form a 3-D network based on the distorted cubic perovskite structure [ABX3] or they can form 2-D layers based on the [A2BX4] or [ABX4] type families. Lower dimensional systems consist of simple 1-D chains of octahedra extending in one direction or completely isolated octahedra (0-D). Chapter 1 Introduction 2 The bonding properties are another point of interest. The organic part makes use of covalent bonds whereas ionic attractions keep the inorganic framework of the hybrid intact. Between the inorganic and organic parts there exist ionic interactions between the R-NH3+ and I- moieties, hydrogen bonding and other van der Waals interactions. The ultimate strength of the hybrid is a combination of all the various types of bonding present. 1.2 Basic cubic perovskite motif The basic perovskite structure [AMX3] consists of corner-sharing octahedral MX6, where M is a divalent metal and X a halide. The cation A sits in the voids of this 3-D network (Figure 1.1) and hence has a limited radius. The formula that determines this maximum radius was derived by Goldschmidt (1926) and assumes that we have a perfect cubic perovskite structure and that all the spheres are in contact. If RA, RM and RX are the ionic radii for the spheres, then the geometric limit imposed on RA is RA + Rx = t 2 (RM + Rx) where t is the tolerance factor and lies between 0.78 and 1.05 for compounds in the perovskite family (Randall et al, 1990). For the inorganic-organic hybrids using the metal Pb2+ and the halide I-, with RPb = 1.19 ? and RI = 2.20 ? respectively (Shannon, 1976), a large cavity for A is created. If t = 1.0, then RA = 2.6 ? and hence A can only consist of at maximum one C-C or C-N bond. This restriction is only fulfilled by the methylammonium cation and compounds with the general formula [CH3NH3MX3], where M is Sn or Pb and X is Cl, Br and I have been synthesized (Poglitsch and Weber, 1987). The unit cell lattice constant varies from ap = 5.657 (2) ? for [CH3NH3PbCl3] to ap = 6.3285 (4) ? for [CH3NH3PbI3] and for the tin analogue, ap goes from 5.89 ? to 6.24 ? (Mitzi, 1999a). Chapter 1 Introduction 3 Figure 1.1: Ball and stick model of the basic AMX3 perovskite showing the unit cell structure and the polyhedral representation of how the structure extends in three dimensions. 1.3 Two-dimensional layered perovskite-type motif For larger organic molecules, where the A cation is replaced by an ammonium cation with two or more C-C or C-N bonds, the stable configuration requires layered octahedra that are based on the [A2BX4] or [ABX4] structure type. The former structure type has staggered layers of corner- sharing BX6 octahedra, as in [K2NiF4] or [K2MgF4] (Hatch et al, 1989), and the latter structure type has eclipsed layers of BX6 octahedra, e.g. [RbAlF4] and [TlAlF4] (Hatch and Stokes, 1987) (Figure 1.2). In the inorganic-organic hybrids described in this thesis, the A cation gets replaced by the organic ammonium cation and sits in the interstitial sites between the layers. The organic cation can form bilayers between these inorganic layers if it has only one ammonium group or a monolayer for two ammonium groups on the same cation (Figure 1.3). The inorganic layer consists of [MX4]2- corner-sharing metal halide octahedra. The four halides that are involved in the corner-sharing to adjacent octahedra are called 'bridging halides' and the two remaining halides that are above and below the inorganic layer are called 'terminal halides' as they undergo no sharing. To keep these larger cations effectively in place, there must exist hydrogen bonding Chapter 1 Introduction 4 between one end of the organic molecule and the halide on the metal. This 'head' of the molecule is the primary ammonium -NH3+, and the rest of the molecule R is the tail. If the organic tail is very long, for example in the longer straight-chain alkylammonium chains, a large degree of interdigitation is possible for the spacious PbI6 framework. The chloride and bromide transition metal analogues exhibit less interdigitation. If the organic cation has an -NH3+ group on both terminal ends of the molecule, both ammonium groups hydrogen bond to the inorganic layers that sandwich it. Furthermore, looking down the c-axis of the unit cell, the organic molecules have two different relative packing arrangements, similar to the inorganic layers. They can eclipse the next layer or be staggered. This depends on the size of the halide: the smaller chlorine and bromine enable staggered whereas the larger iodine atom can allow eclipsed. Also the monoammonium cation usually has a staggered and the diammonium cation an eclipsed conformation. The general formula then becomes [(R-NH3)2MX4] or [(NH3-R-NH3)MX4], where R can be aliphatic or aromatic. The two unit cell parameters that are parallel to the inorganic layers are of a length that is comparable to the cubic perovskite lattice parameter ap. There are two different factors observed, the more common one being ?2 x aP and the lesser one 2 x ap. Inorganic-organic hybrids are classified as having either the 2ap x 2ap or ?2ap x ?2ap superstructure (Mitzi, 1999a). The 2-D corner-sharing layers can also be viewed as "single layers of <100> orientated perovskite sheets separated by bilayers of organic ammonium cations" (Mitzi, 1999a). Hence, when discussing inorganic-organic hybrids that have either staggered or eclipsed 2-D layers, they will be referred to as having the layered perovskite-type motif. Inorganic-organic hybrids that have this motif have the potential of forming natural quantum well structures1 when combined with Pb2+ and I- (Papavassilliou et al, 1994; Hong et al, 1992a; Tanaka et al, 2005). 1 Quantum well structures, also known as multiple quantum well structures (Atkins et al, 2006), are materials that combine different bandgaps within a structure, that alternate in a regular fashion. Here, the lead iodide forms a 2-D semiconductor layer, which alternates with the dielectric RNH3 layer (Era et al, 1997) Chapter 1 Introduction 5 Figure 1.2: The unit cell of the inorganic compound K2NiF4, that is the archetype for the 2-D layered perovskites that have staggered layers (left), and RbAlF4, that is the archetype of the eclipsed inorganic layers (right). Figure 1.3: Schematic Representation of single-layer perovskites with (a) monoammonium (R- NH3+) or (b) diammonium (+H3N-R-NH3+) organic cations. As in the 3-D cubic perovskite case, we can determine numerically the size of the organic cation we can fit in between the inorganic layers. The boundary is defined not by volume but by the cross sectional area of the quadrilateral formed by the four axial or terminal halides of the K2NiF4 Chapter 1 Introduction 6 or RbAlF4 structure, labelled as the quadrilateral ABCD in Figure 1.4a. If this quadrilateral is shaped like a square in the case of the K2NiF4 or RbAlF4 structures, then the side of the square is simply twice the length of the largest possible bond length between the lead and the halide. If we consider the bond to be ionic in character, then, using the values for ionic radii of Pb2+ (1.19 ?), I- (2.20 ?), Br- (1.96 ?) and Cl- (1.81 ?) (Shannon, 1976), we get an area of 46 ?2 for lead iodide. The analogous areas for PbCl2 and PbBr2 are 40 ?2 and 36 ?2 respectively. In general however, this area described by the quadrilateral is much greater than required by the organic cation and the adjacent octahedra undergo various tilts to reduce the area and pack more efficiently. For the layered perovskite-type hybrids, two out of three possible tilts are encountered (Hatch et al, 1989); a tilt perpendicular to the inorganic sheets (? tilt), so that adjacent corner-shared octahedra are rotated relative to each other. A geometric consequence is that the bond angle Pb-I(bridging)-Pb deviates from 180? (Figure 1.5b). If the layers are normal to the c-axis, then the notation would be (00?), a tilt around the c-axis. The second kind of tilt is away from the perpendicular to the layers (? tilt) so that the layers are corrugated in one direction. If the corrugation is along the a-axis as in Figure 1.5a, then the ? tilt is around the b- axis, abbreviated (0?0). The net effect of a combination of these two tilts is to create a quadrilateral with a smaller area (Figure 1.4b). These distortions from the ideal square K2NiF4 or RbAlF4 arrangement results in the closest possible packing arrangement (Figure 1.6). The tilting of the octahedra also facilitates the hydrogen bonding interactions between the ammonium group and the terminal halides. The area of the quadrilateral ABCD shown in Figure 1.4b is half of the product of the two diagonals AC and BD, measured in Angstroms (See appendix for derivation of formula). Chapter 1 Introduction 7 Figure 1.4: The area generated by the four terminal halides, viewed perpendicular to the 2-D layers. (a) shows the biggest possible scenario of a square, when there is no tilting of the octahedra. (b) shows the actual scenario, when both ? and ? tilts are observed. Figure 1.5: Schematic representation of the two commonly encountered tilts in the layered perovskites. (a) (0?0) tilt, leading to a corrugation of the sheets in one direction; (b) (00?) tilt, leading to a rotation of adjacent octahedra relative to each other. Chapter 1 Introduction 8 Figure 1.6: A space-filled representation of the packing arrangement of a typical inorganic- organic layered perovskite-type hybrid with atoms drawn with their van der Waals radii. The terminal iodides are shown as red coloured spheres. 1.4 Lower dimensional motifs of inorganic-organic hybrids The most common structure type encountered in the family of inorganic-organic hybrids is the 2- D layers of corner-sharing octahedra as discussed above. However, it is possible to get motifs that comprise the sharing of two or three halides, otherwise known as edge- and face-sharing motifs. Combinations of any of the three types of sharing give a multitude of different motifs. One of the possible structural motifs also forms 2-D layers, where chains of two or three face- sharing octahedra are connected via corner-sharing on both ends (Figure 1.7). This situation can be summarized by the formula [MnX3n+1](n+1)-. Chapter 1 Introduction 9 Figure 1.7: An illustration of the n = 3 [Pb3I10]n4n- 2-D net. If the space required by the R group is greater than the area provided by the 2-D type lead(II) iodide framework, then a different structural arrangement of the inorganic component is preferred, e.g. 1-D chains of inorganic metal halides. In this case, long chains of corner-sharing, edge-sharing or face-sharing MX6 octahedra create channels within which the organic ammonium cations sit. The relative position of the halides within the octahedra is classified differently to that of the layered perovskite-type hybrids. For the corner-sharing chains, the two halides that bridge to two adjacent octahedra and the two halides that are trans to them are labelled the "equatorial halides". The last two halides extend out of the plane of the corner-sharing chain and are thus labelled as "axial halides" (Figure 1.8). In the edge-sharing chains, the four halides that bridge to adjacent octahedra all lie in a plane and are thus labelled as "equatorial halides". The "axial halides" are labelled in the same way as in the corner-sharing chains (Figure 1.9). In the face- sharing chains, the "equatorial halides" and the "axial halides" are labelled in the same way as in the edge-sharing chain case except that the axial halides also bridge to adjacent octahedra (Figure 1.10). Chapter 1 Introduction 10 Figure 1.8: Example of a corner-sharing chain and the labelling of the halides within the octahedra. Figure 1.9: Example of an edge-sharing chain and the labelling of the halides within the octahedra. Chapter 1 Introduction 11 Figure 1.10 Example of a face-sharing chain and the labelling of the halides within the octahedra. 1.5 Zero-dimensional motifs It is also possible to get 0-D structures where the octahedra and the organic cation are isolated from another. An example is [(CH3NH3)4PbI6 ? 2H2O], which has the anions PbI64- and cations (CH3NH3)+ isolated from one another and from water (Mitzi, 1999). 1.6 Hydrogen bonding in inorganic-organic layered perovskite-type hybrids Another important determinant of the arrangement of the inorganic layers apart from the choice of the organic molecule, is the hydrogen bonding scheme between the primary ammonium head and the halides. There are four terminal and four bridging halides available to bond to the three hydrogens on the ammonium cation. However, the size of the ammonium group prevents the hydrogens from penetrating deeply into the "box" formed by the eight halides and hence only three halides are close enough to form hydrogen bonds. There are two possible scenarios: Two hydrogens can bond to the terminal halides and the third to the bridging halide (terminal halogen configuration) or the reverse case with two bridging and one terminal hydrogen (bridging halogen Chapter 1 Introduction 12 configuration) (Figure 1.11). This classification of hydrogen bonding is taken from Mitzi (1999a). The length of the N---X interaction is greater than 2.2 ? and hence is classified as a weak hydogen bond (Jeffrey, 1997) with bond angles greater than 90?. Table 1.1 below gives the average distances for the three possible halides that are used, Cl, Br and I. The values where obtained from a study of the Cambridge Structural Database (CSD, June 1997 update with 167 797 entries; Allan and Kennard, 1993) done by Steiner (1998) of hydrogen bonds in organometallic crystal structures. The author excluded strongly bent geometries. Table 1.1: Mean distances (?) in N?H---A- hydrogen bonds to halide ions with <(DHA) > 140?. N?H donor Cl- Br- I- D(H?A-) 2.247(5) 2.49(2) 2.72(2) D(N?A-) 3.207(4) 3.44(1) 3.68(2) From (Steiner, 1998). Figure 1.11: Two hydrogen bonding configurations typically observed in the [(R-NH3)2MX4] and [(H3N-R-NH3) MX4] type structures: (a) the bridging halogen configuration, and (b) the terminal halogen configuration. However, there are two ways that the hydrogens can adopt either the terminal or bridging halogen configuration: The three halides to which the hydrogens bond can be at the vertices of either an equilateral triangle (equilateral configuration) or a right-angle triangle (right-angled configuration). Figure 1.12 shows the equilateral and right-angled configuration as observed in the terminal halogen configuration. Chapter 1 Introduction 13 It is also important to be able to specify the position of the ammonium group relative to the inorganic layer. Due to the rotation of the MX6 octahedra relative to each other, the area enclosed by four bridging halides is shaped like a parallelogram. In projection, the ammonium group is contained within this parallelogram defined by the four bridging halides, shown in green in Figure 1.12. By projection onto this parallelogram the ammonium group is found in proximity to either an acute or an obtuse angle of the parallelogram. There is a correlation between the position of the ammonium group and the type of hydrogen bonding configuration: If the ammonium group is in the acute angled position, the ammonium group has the right-angled configuration and if the ammonium group is in the obtuse angled position, the ammonium group has the equilateral configuration. Figure 1.12: Two types of terminal halogen configuration: (a) equilateral configuration, where the three halides involved in hydrogen bonding are at the vertices of an equilateral shaped triangle (dashed blue lines) and (b) right-angled configuration, where the halides are at the vertices of a right-angled triangle. The obtuse angled position is shown in (a) and the acute angled position in (b) relative to the parallelogram (green lines). From the picture in Figure 1.13, it is clear that the hydrogen bonding is associated with the corrugation of the MX6 octahedra along a given direction. The bridging halides deviate from the plane and the terminal halides tip the octahedra towards the ammonium group. Chapter 1 Introduction 14 Figure 1.13: The correlation between the hydrogen bonding interactions and the tilting of the PbI6 octahedra in the layered perovskite-type hybrid [(C3H5NH3)2PbI4]. 1.7 Hydrogen bonding in non layered inorganic-organic hybrids The classification of hydrogen bonds in inorganic-organic hybrids that do not have the layered perovskite-type motif is performed in a similar manner. If the acceptor halide atoms are predominantly in the axial position of the octahedra, then this geometry is referred to as "axial halogen configuration" and vice versa, if there are more hydrogen bonds to halides in equatorial than in axial positions, "equatorial halogen configuration". Bifurcated and trifurcated hydrogen bonds exist in these compounds. 1.8 Aims The aims of this study was to use the structural diversity offered by organic ammonium compounds and observe how the supramolecular structure of the resulting inorganic-organic hybrid gets influenced. For simplicity, the inorganic framework was chosen to consist of the metal lead and the halides chlorine, bromine and iodine only. When the organic ammonium cation consisted of simple alkylammonium or alkyldiammonium compounds, (CnH2n+1NH3) and (H3NCnH2nNH3), then the halide used was restricted to I, and when the R group consisted of aromatic and other hydrocarbons, (R-NH3), then all three halides were used. Chapter 1 Introduction 15 Chapter 2 Literature Survey 16 Chapter 2 Literature Survey 2.1 First synthesis and structure determination The first reported synthesis of compounds with the general formula [(R-NH3)2MX4] was by Remy and Laves (1933). They prepared a series of compounds containing copper chloride and short alkyl chains with amino groups. The compounds made are listed in Table 2.1, which is adapted from their paper. Table 2.1: The composition of various CuClx inorganic-organic hybrids with simple alkylammonium chains. Ratio of the two components in aqueous solution CuCl2:AmCl = 1:1 1:2 1:3 1:6 Am = CH3NH3, CH3CH2NH3 CH3CH2CH2NH3 CH3CH2CH2CH2NH3 [(Am)2CuCl4] Am = (CH3)2NH2 [(Am)CuCl3] [(Am)2CuCl4] [(Am)3CuCl5] Am = (CH3)3NH [(Am)CuCl3]?H20 or [(Am)CuCl3] [(Am)3CuCl5] Am = (CH3)4N [(Am)2CuCl4] The molecular formula of the resulting crystals reported in the paper was determined; electrolytically for copper, gravimetrically for chlorine and via titration for the ammonium component. More compounds were made by the authors from a non-aqueous solution containing alcohol or acetone which were not reported previously but confirmed to be [((CH3)3NH)3Cu2Cl7], [((CH3)3NH)2CuCl4], [((CH3)3CHNH)CuCl3] and [((CH3)3CHNH)2CuCl4]. The results of the combination of the mono-ammonium compounds with copper(II) chloride are significant as they all have the molecular formula [(Am)2CuCl4], regardless of the ratio of the reactants, and are possibly all layered perovskite-type hybrids. The unit cell constants of the layered perovskite-type hybrid [(CH3NH3)2CuCl4] were determined in 1933 by Greenwood (1933). They are a = 18.55 ?, b = 7.30 ? and c = 7.54 ?. The results were confirmed by Willett (1964) from Weissenberg and precession camera photographs. From the systematic absences, the two possible space groups were either Cmca or C2ca (Aba2). The Chapter 2 Literature Survey 17 values for the b-axis and c-axis are characteristic of copper(II) chloride layered perovskites and the value for the a-axis suggests two complete inorganic layers per unit cell. The lattice constants for [(C2H5NH3)CuCl4] were reported by Willett in the same paper to be a = 21.18(2) ?, b = 7.47(1) ? and c = 7.35(1) ? with the space group Pbca, which is commonly encountered in lead(II) iodide layered perovskites. The increase in the interlayer spacing is due to the extra carbon atom in the alkyl chains. The first reported fractional coordinates and structure solution was done for the compound [(NH4)2CuCl4] (Willett, 1964). The lattice constants were a = 15.46(2) ?, b = 7.20(1) ? and c = 7.20(1) ?. The space group was Cmca and 187 reflections were recorded, 173 of which were unique. The structure of the compound was presumed to be similar to K2CuF4, which contains infinite sheets of corner-sharing CuF6 octahedra. There are three unique Cu-Cl bond lengths of 2.300(5) ?, 2.332(4) ? and 2.793(5) ?. The individual octahedra are not rotated relative to each other as the Cu-Cl-Cu bridging angle is 180.0(2)?. The distances between the chlorine and nitrogen atoms are in the range 3.34 ? to 3.61 ?, which could be indicative of hydrogen bonded interactions between the eight chlorine atoms that form the "box" within which the ammonium group sits. From a detailed literature survey it is clear that the simplest and most studied inorganic-organic hybrids with the layered perovskite-type motif are the straight chain alkylammoniums with general formula [(CnH2n+1NH3)2MX4] and [(NH3CnH2nNH3)MX4] (n = 1-18; X = Cl, Br, I; M = Cu2+, Mn2+, Cd2+, Sn2+, Pb2+, Hg2+ and Cr2+ (see Table 2.2 and Table 2.3) Chapter 2 Literature Survey 18 Table 2.2: Summary of [(CnH2n+1NH3)2MX4] and [(NH3CnH2nNH3)MX4] (n = 1-10) inorganic- organic layered perovskite-type hybrids in the literature. Numbers in superscript refer to the references listed at the end of the table. Cu2+ Mn2+ Cd2+ Sn2+ Pb2+ Hg2+ Cr2+ CH3NH3 Cl9, 31, 49, 86, 109, 116, 118, 123, 125, 126, 127, 141 Br109, 125, 126 Cl16, 35, 37, 71, 72, 73, 76, 85, 92, 114, 117, 120, 128, 135, 136 Cl34, 37, 39, 69, 70, 71, 88, 89, 90, 113, 127 I54 Cl62 Br40, 55, 62 I62, 61, 55 Cl83, 132, 133 NH3CH2NH3 C2H5NH3 Cl2,49, 109, 116, 118, 121, 123, 125, 126 Br109, 125, 126, 140 Cl16, 18, 19, 27, 41, 71, 72, 114, 119 Br137, 142 Cl36, 69, 70, 71, 91, 107 Cl 26 Cl5 Cl108 Cl132, 133 NH3C2H4NH3 Cl24, 68, 77 Br24 Cl 65, 130 Cl69, 70, 71 C3H7NH3 Cl4, 14, 48, 49, 75, 109, 125, 126 Br109, 125, 126, 140 Cl3, 15, 16, 19, 20, 21, 23, 28, 60, 72, 87, 93, 114, 134 Br134, 142 Cl12, 17, 69, 70, 87 Br53 Cl6 Cl131 NH3C3H6NH3 Cl1, 50, 74, 77 Br24, 78, 140 Cl67, 122, 130, 138 Cl25, 69, 70, 71 Br53 Cl 7 Cl63 C4H9NH3 Cl42, 57, 77, 109, 118, 125, 126 Br109, 125, 126 Cl13, 72, 60 Cl 26 I10 I10, 40 Br44 NH3C4H8NH3 Cl22 Br22, 78 Cl 66, 124, 138 Cl69, 70, 71, 130 Cl 33 Br45 Cl 64 C5H11NH3 Cl109, 125, 126 Br109, 125, 126 Cl 32, 72, 60 Cl131 NH3C5H10NH3 Cl22, 77 Br22 C1138 Cl69, 70, 71, 130 Chapter 2 Literature Survey 19 Cu2+ Mn2+ Cd2+ Sn2+ Pb2+ Hg2+ Cr2+ C6H13NH3 Cl109, 126 Br109, 125 Cl82 Cl26 Cl29, 30, 52 Br45 I99-105 NH3C6H12NH3 Cl118 Cl8 Br8, 45 I8, 43 C7H15NH3 Cl 32, 84, 60 Cl84 NH3C7H14NH3 C8H17NH3 Cl60 Cl56, 80 Cl26 Cl52 Br58 I41 Cl115 Cl133 NH3C8H16NH3 Br45, 58 C9H19NH3 Cl47 Cl32, 41, 60, 110 Cl29 Cl29, 46 I11 Cl 115 NH3C9H18NH3 C10H21NH3 Cl79, 109, 125, 126, 139 Cl59, 72, 89, 106, 111, 139 Cl 51, 81, 139 Cl26 Cl52 Br45 I94-98 Cl112 NH3C10H20NH3 Cl133 Chapter 2 Literature Survey 20 Key to references in Table 2.2 1) Phelps et al, 1976. 2) Steadman and Willett, 1970. 3) Peterson and Willett, 1972. 4) Barendregt and Schenk, 1970. 5) Geselle and Fuess, 1997. 6) Meresse and Daoud, 1989. 7) Corradi et al, 1999. 8) Mousdis et al, 1999. 9) Pabst et al, 1987. 10) Mitzi, 1996. 11) Nagapetyan et al, 1988. 12) Doudin and Chapuis, 1988. 13) Depmeier and Chapuis, 1979. 14) Doudin and Chapuis, 1990. 15) Depmeier, 1981. 16) Depmeier et al, 1977. 17) Chapuis, 1978. 18) Depmeier, 1977. 19) Brunskill and Depmeier, 1982. 20) Steurer and Depmeier, 1989. 21) Harris et al, 1994. 22) Garland et al, 1990. 23) Depmeier and Mason, 1983. 24) Halversen and Willett, 1988. 25) Willett, 1977. 26) Yin and Yo, 1998. 27) Depmeier and Heger, 1978. 28) Depmeier and Mason, 1978. 29) Kammoun and Daoud, 1997. 30) Kammoun et al, 1996a. 31) Pabst et al, 1996. 32) Flandrois et al, 1995. 33) Courseille et al, 1994. 34) Chapuis et al, 1976. 35) Heger et al, 1976. 36) Chapuis, 1977. 37) Couzi et al, 1977. 38) Peyrard and Perret, 1979. 39) Kind, 1977. 40) Matsuishi et al, 2004. 41) Wortham et al, 2002. 42) Xiao et al, 2005. 43) Goto et al, 2003. 44) Kato et al, 2003. 45) Matsui et al, 2002. 46) Kammoun et al, 1996b. 47) Ning, 1995. 48) Jahn et al, 1994. 49) Jahn et al, 1989. 50) Phelps et al, 1976. 51) Kind et al, 1979. 52) Lee et al, 2000. 53) Ishihara et al, 1996. 54) Mitzi et al, 1995. 55) Tanaka et al, 2003. 56) Chanh et al, 1983. 57) Yamazaki, 1977. 58) Kitazawa et al, 2006. 59) Guillaiume et al, 1989. 60) Depmeier, 1979. 61) Hirasawa et al, 1994. 62) Poglitsch and Weber, 1987. 63) Spengler et al, 1998. 64) Amami et al, 2002. 65) Tich? et al, 1978. 66) Tich? et al, 1980. 67) Crowley, et al, 1982. 68) Birrell and Zaslow, 1972. 69) Levstik et al, 1976. 70) Blinc et al, 1977. 71) Tello et al, 1977. 72) Arend et al, 1973. 73) Knorr et al, 1974. 74) Soos et al, 1977. 75) Kempen et al, 1977. 76) Kind and Roos, 1976. 77) Snively et al, 1981. 78) Snively et al, 1982. 79) Ko?elj et al, 1981. 80) Ricard et al, 1985. 81) Ricard et al, 1984. 82) Van Oort and White, 1985. 83) Rahman et al, 1982. 84) White et al, 1983. 85) White et al, 1982. 86) White and Staveley, 1982. 87) White et al, 1981. 88) Blinc et al, 1978. 89) Seliger et al, 1976. 90) Chapuis et al, 1975. 91) Peyrard and Perret, 1979. 92) Heger et al, 1975. 93) Depmeier and Mason, 1982. 94) Xu et al 1991a. 95) Xu et al, 1991a. 96) Xu et al, 1991c. 97) Ishihara et al, 1989. 98) Hirasawa et al, 1993. 99) Kataoka et al, 1993a. 100) Kondo et al, 1998a. 101) Shibuya et al, 2002. 102) Tanaka et al, 2002. 103) Kondo et al, 1998b. 104) Kataoka et al, 1993b. 105) Tanaka et al, 2005. 106) Ciajolo et al, 1976. 107) Moral and Rodriuez, 1997. 108) Salah et al, 1983a. 109) Colpa, 1972. 110) Vacatello and Corradini, 1974. 111) Vacatello and Corradini, 1973. 112) Busico et al, 1979. 113) Seliger et al, 1976. 114) Bocanegra et al, 1975. 115) Busico et al, 1979. 116) Willett et al, 1967. 117) Lehner et al, 1975. 118) Whealy et al, 1959. 119) Depmeier, 1976. 120) Foster and Gill, 1968. 121) Mostafa et al, 1977. 122) Baberschke et al, 1977. 123) Heygster and Kleeman, 1977. 124) Hagen et al, 1977. 125) Bloembergen, 1977. 126) Bloembergen, 1976. 127) Stoelinga and Wyder, 1976. 128) Brinkmann et al, 1976. 129) Arend et al, 1976a. 130) Arend et al, 1976b. 131) Stead and Day, 1982. 132) Bellitto and Day, 1978. 133) Bellitto and Day, 1976. 134) Groenendijk et al, 1979. 135) Heger et al, 1973. 136) van Amstel and de Jongh, 1972. 137) Riedel and Willett, 1975. 138) Guillaume et al, 1989. 139) Wang et al, 1999. 140) Willett and Extine, 1973a. 141) Drumheller et al, 1972. 142) Willett and Extine, 1973b. Chapter 2 Literature Survey 21 2.2 Inorganic-organic layered perovskite-type hybrids [(CnH2n+1NH3)2MX4] with simple alkylammonium chains The [(CnH2n+1NH3)2MX4] materials, abbreviated CnMX, often exhibit a range of temperature- dependant structural transitions that can be associated with changes in the ordering and hydrogen bonding of the organic cations. Further, the conformation of the inorganic layers can change between eclipsed and staggered at the phase transitions and the degree of distortion of the octahedral geometry decrease with increasing temperature. The structural phase transitions observed can be displasive phase transitions, associated with conformational changes within the ammonium chains or order-disorder transitions of the alkyl ammonium chains along their longitudinal axis. The latter ultimately leads to a "quasi-melting" of the hydrocarbon part (Chanh et al, 1989) in the highest temperature phases. The order-disorder transition is the only one observed when n ? 2 and both types of transition have been reported in chain lengths when n ? 3. The chain-melting transition is the major transition, usually the last one observed and with the highest enthalpy. Strikingly the crystal system of the structure often changes from monoclinic at the low temperature to orthorhombic at room temperature and finally tetragonal at the high temperature (Mitzi, 1999a). The sequence generally holds for most alkyl chain lengths. The nature of the phase transitions also depend on the packing arrangement of the alkyl chains. They can be either interdigitated or non-interdigitated and can be tilted at various angles and directions relative to the inorganic layers. The packing of the chains is often metal dependant, as in C10CdCl, where the non-interdigitated chains on opposite sides of the [CdCl4]2- layers are tilted at +40? and -40? relative to the normal of the inorganic layers in the compounds lowest temperature phase (Kind et al, 1979). This type of packing is not seen in the analogues compounds C10MnCl (Ciajolo et al, 1976) (Cambridge Structural Database (CSD) ref. code: DECAM) and C10CuCl (Ko?elj et al, 1981), where the chains are all parallel in one direction, tilted at approximately +40? relative to the inorganic layers. Interdigitated chains are present in the compounds that offer the largest separation between the metal atoms in the corner-sharing octahedra and have long chain lengths, as in C9PbI (Nagapetyan et al, 1988) (CSD ref. code: KECKOS), which has a separation of 8.708(1) ? and 9.034(1) ? (See Figure 2.1). In C10MnCl for example, the separation is only 7.213(8) ? and 7.337(2) ? (Ciajolo et al, 1976). Chapter 2 Literature Survey 22 There are three different systems of nomenclature used in the literature to designate the various phases. Some authors designate the phase stable at highest temperature with either Roman Numeral I or the greek letter ?, the next lowest temperature phase II or ?, and so on. This method works well when there are many phase transitions, as in C3MnCl, which has six phases identified (Depmeier et al, 1977). In this survey, roman numerals will be used throughout. Figure 2.1: The tilted and non-interdigitated decylammonium chains in C10MnCl (left). The non- tilted and interdigitated nonylammonium chains in C9PbI (right). The rotation of the octahedra within the plane of the inorganic layers, the ? tilt, and the distortion of the octahedral geometry (bond lengths and bond angles) are both heavily dependant on the identity of the metal. The transition metals, that form the layered perovskite motif are divalent, the group 14 cations Ge, Sn and Pb and have a stereochemically active lone pair where the strength of the stereoactivity increases from Ge to Pb (Mitzi, 1996). In the layered perovskites C4MI (M = Ge, Sn and Pb), the geometry of the GeI6 octahedra (Ge-I: 2.837(2) ? to 3.217(2) ?; I-Ge-I: 174.46(7) to 175.38(9)?) is more distorted compared to PbI6 (Pb-I: 3.175(2) ? to 3.200(2) ?; I-Pb-I: 180?) and SnI6 (Sn-I: 3.133(1) ? to 3.160(2) ?; I-Sn-I: 180?) (Mitzi, 1996). The trend in the bridging angle between adjacent octahedra, which defines the ? tilt, is a decrease in the angle from 166.27(8)? (I-Ge-I) to 159.61(5)? (I-Sn-I) to smallest 155.19(6)? (I-Pb-I). Chapter 2 Literature Survey 23 Figure 2.2: The effect of the identity of the metal on the ? tilt of the octahedra is seen in the compounds C4GeI (left) and C4SnI (right). The (OO?) tilt is 13.73? in the layered perovskite-type hybrid with Ge and 20.39(5)? with Sn. Another structural feature that is dependant on the chain length is the type of hydrogen bonding configuration. For n = 1, both the terminal halogen configuration and bridging halogen configuration are possible. However, for n ? 2, the bridging halogen configuration is sterically unfavourable as it would bring the second carbon atom too close to a terminal halide and hence the terminal halogen configuration is the only configuration observed for longer alkyl chains. 2.2.1 Phase transitions in inorganic-organic layered perovskite-type hybrids [(CnH2n+1NH3)2MX4] with n ? 3 and M = Mn and Cd The complete sequence of phase transitions for [(CH3NH3)2CdCl4], C1CdCl, has been elucidated by many techniques and is summarized in Scheme 2.1 below. The compound has three phase transitions and the phases are labelled I through IV with decreasing temperature. The phase sequence is unusual as it goes through a tetragonal phase, III, before terminating at the lowest temperature monoclinic phase, IV. Only the single crystal data for the orthorhombic phase (II) (CSD ref. code: MATCCD) and tetragonal phase (III) (CSD ref. code: MATCCD01) are reported in the CSD. The details of the structural phase transitions between the four different phases were summarized by Couzi et al (1977) and are detailed below. In the highest temperature tetragonal phase I, the ammonium group has a bridging halogen configuration. The methylammonium cations are tilted randomly in four different directions, with a 1 in 4 probability of being in any particular direction. The methylammonium cations are disordered over the four potential wells. A disorder-order phase transition occurs at 484 K from phase I to Chapter 2 Literature Survey 24 phase II, where the methylammonium cation is locked or "frozen" in one potential well, which is then favoured. There is no change in the hydrogen bonding configuration during this second order phase transition from I to II. The transition to phase III is first-order and such that there is now a 1 in 2 probability of the methylammonium cation being oriented in any one direction. SC- XRD results show a superposition of two orientations of the CH3NH3+ cations. The X-Ray results give no indication of the type of hydrogen bonding configuration due to the five hydrogen positions in the structure. However, by performing 14N NMR and Raman investigations (Blinc et al, 1978), the authors conclude that no changes in the hydrogen bonding configuration occur. Finally, the third phase transition to the monoclinic phase IV is first order and the cations are "frozen" into the terminal hydrogen bridging configuration. The manganese analogue, C1MnCl, exhibits the same sequence and has been studied via neutron diffraction (Heger et al, 1975), optical birefringence (Knorr et al, 1974), 35Cl Nuclear Quadropole resonance (Kind and Roos, 1976) and P-XRD (Depmeier et al, 1977). Scheme 2.1 The inter-relationship between the four phases of C1CdCl and C1MnCl as a function of temperature. Chapter 2 Literature Survey 25 Figure 2.3: The hydrogen bonding interactions of the inorganic-organic layered perovskite-type hybrid with methylammonium and cadmium(II) chloride in phase II. The ethylammonium layered perovskite, [(CH3CH2NH3)2CdCl4], C2CdCl, displays only two phase transitions, at 114.2(9) K and 216.2(5) K, and decomposes at 450 K. Only the second phase transition has been studied by SC-XRD and corresponds to a first order transition from an orthorhombic phase, II, with space-group Pcab, to an orthorhombic phase, I, with space-group Bmab (Chapuis, 1977). C2CdCl has no higher temperature phase with tetragonal symmetry. The structures of both phases I and II are reported in the CSD (EAMCDC01 and EAMCDC respectively), i.e. the structure of phase III has still to be determined. In phase II, the CH3CH2NH3+ cation is ordered (Figure 2.4). In the highest temperature phase I, the carbon atoms of the CH3CH2NH3+ cation become disordered over two positions, along the mirror plane inherent in the space group Bmab. The unsplit nitrogen atom has a large anisotropic displacement parameter perpendicular to the mirrorplane, about 0.28 ? (Chapuis, 1977). The two individual molecules influence the position of the terminal chlorides in the octahedra through their hydrogen bonding interactions. The anisotropic displacement parameters of the terminal chlorides are significantly elongated along the crystallographic a-axis (Figure 2.4). The ? and ? tilt of the Chapter 2 Literature Survey 26 CdCl6 octahedra increase by 1? and decrease by 5.5? respectively when changing from phase II to phase I. Phase I has a more regular, almost checkerboard-like pattern of CdCl6 octahedra. Figure 2.4: Phase II of C2CdCl and its terminal halogen configuration. The ethylammonium cation is ordered in this phase. Phase I has the same ethylammonium cation disordered over two positions. The SC-XRD structure of phase III has not been determined. Figure adapted from Peyrard and Perret, 1979. Chapter 2 Literature Survey 27 C3CdCl has two phase transitions, summarized in Scheme 2.2 below. Phase II that exists between 180 K and 158 K is unique, as it is an intermediate modulated phase (Doudin and Chapuis, 1988). This intermediate phase is also observed in C3MnCl (Depmeier and Mason, 1982). The orthorhombic phase I of C3CdCl (Chapuis, 1978) (CSD ref. code: PRACDC) has two carbon atoms disordered across a mirrorplane along the a-axis (Figure 2.5). The incommensurate phase II shows large displacement amplitudes of the Cd and Cl atoms along the c-axis (Doudin and Chapuis, 1988) (CSD ref. code: PRACDC02). The final phase transition is a disorder-order transition at 158 K, where the propylammonium cation is now "locked" into one of the previous two equivalent positions. However, the middle carbon atom remains disordered in phase III (Chapuis, 1978) (CSD ref. code: PRACDC01). Scheme 2.2: The phase sequence of C3CdCl and their unit cell parameters (?). Figure 2.5: The two SC-XRD structures of phases III and I of C3CdCl. Chapter 2 Literature Survey 28 The phase behaviour of the layered perovskite C3MnCl is unique in that it has the most phase transitions identified to date, three more than it's Cd analogue (Scheme 2.3 below), and a number of these are unusual, e.g. the phase transition from IV to V leads to a superstructure with a three- fold increase of the b-axis, V to VI is incommensurate to commensurate (Depmeier and Mason, 1983; Harris at al, 1994), IV to III goes from a commensurate to an incommensurate phase and III to II is incommensurate to commensurate (Depmeier and Mason, 1978). Scheme 2.3: The phase sequence of C3MnCl and their unit cell parameters (?) with CSD reference codes. The greek numbering for the phases is taken from the literature. 2.2.2 Phase transitions in inorganic-organic layered perovskite-type hybrids [(CnH2n+1NH3)2MX4] with n ? 4 The phase transitions of the compounds with longer alkyl chains, were n ? 10, are of interest as they can act as models for the phase behaviour of lipid bilayers (Needham et al, 1984). Very little single-crystal work has been done on the structures of the various phases. The changes in unit cell parameters have, in general, only been inferred from P-XRD. Chapter 2 Literature Survey 29 Table 2.3: Summary of [(CnH2n+1NH3)2MX4] and [(NH3CnH2nNH3)MX4] (n = 11-18) layered perovskite-type hybrids in the literature. Numbers in superscript refer to the references listed at the end of the table. Cu2+ Mn2+ Cd2+ Fe2+ Pb2+ Co2+ Hg2+ Cr2+ C11H23NH3 Br15 Cl19 Br15 Cl 20 NH3C11H22NH3 C12H25NH3 Cl3,12, 21, 24 Br15 Cl3, 18, 21, 24 Br15 Cl3, 11, 14, 24 Cl 21 I2, 4, 5 Cl20, 21 Cl23 NH3C12H24NH3 C13H27NH3 Br15 Cl19, 22 Br15 Cl 20 NH3C13H26NH3 C14H29NH3 Cl3, 24 Br15 Cl3, 6, 18, 22, 24 Br15 Cl3,16, 24 Cl20 NH3C14H28NH3 C15H31NH3 Br15 Cl19 Br15 Cl20 NH3C15H30NH3 C16H33NH3 Cl21, 24 Br15 Cl18, 21, 24 Br15 Cl 9, 14, 24 Cl21 I2, 4, 5 Cl7, 8 Cl20, 21 NH3C16H32NH3 C17H35NH3 Cl19 Chapter 2 Literature Survey 30 Cu2+ Mn2+ Cd2+ Fe2+ Pb2+ Co2+ Hg2+ Cr2+ NH3C17H34NH3 C18H37NH3 Cl24 Cl1,10, 24 Cl17, 24 I2, 4, 5 NH3C18H36NH3 Key to references in Table 2.3 1) Lee and Lee, 2003. 2) Venkataraman et al, 2002a. 3) Needham and Willett, 1984. 4) Barman et al, 2003. 5) Venkataraman et al, 2002b. 6) Almirante et al, 1986. 7) Ning et al, 1992a. 8) Ning et al, 1992b. 9) Chanh et al, 1989. 10) Lee at al, 2003. 11) Chanh et al, 1985. 12) Kang et al, 1993. 13) Chanh et al, 1983. 14) Ricard et al, 1985. 15) Vacatello et al, 1981. 16) Schenk and Chapuis, 1988. 17) White, 1984. 18) Vacatello and Corradini, 1973. 19) Vacatello and Corradini, 1974. 20) Busico et al, 1979. 21) Landi et al, 1977. 21) Landi et al, 1977. 22) Carfagna et al, 1977. 23) Stead and Day, 1982. 24) Wang et al, 1999. DSC, IR and P-XRD studies on the series of compounds [(CnH2n+1NH3)2MX4] (M = Mn, Hg, Fe and Cu, X = Cl and Br, n = 9 - 17) has been done by Vacatello and co-workers (See Table 2.2 and Table 2.3 for details). The focus of their work was to determine the mechanism of the phase transitions and the conformations of the chains by measuring the changes in the interlayer spacing between the low- and high-temperature phases. Table 2.4 summarizes the changes in the interlayer spacing for two chain lengths and different metals. In general, they concluded that the low temperature phase has an ordered arrangement which changes to a disordered arrangement at the high temperature phase. The integrity of the inorganic layers remain practically unchanged during the solid-state phase transitions from the ordered to disordered phases (Landi et al, 1977). The disorder is mainly due to the "thermal liberation of movements around C-C bonds" (Vacatello and Corradini, 1973). Their systematic studies also show that the transition temperatures increase as the chain length increases and that the phase transitions are often reversible, with some thermal hysteresis observed (Table 2.5). The room temperature structure of Chapter 2 Literature Survey 31 the layered perovskite C10MnCl is the only reported structure in the CSD that includes fractional coordinates (Ciajolo et al, 1976) (CSD ref. code: DECAM). Table 2.4: Summary of interlayer spacing, c, from X-ray spectra of powders for CnMCl (1). n M c, ?, at 25?C c, ?, at 120?C 12 Mn 30.28(5) 33.4(1) Cu 29.09(5) 32.0(1) Fe 30.23(6) 34.2(3) Hg 27.00(6) 29.7(2) 16 Mn 36.71(5) 41.8(1) Cu 36.12(5) 40.4(1) Fe 37.20(6) 43.3(3) Hg 32.96(6) 36.9(2) (1) Taken from Landi et al, 1977. Chapter 2 Literature Survey 32 Table 2.5: Summary of phase transition temperatures, enthalpies and entropies from DSC heating and cooling scans for CnHgCl (1). Heating Cooling n T, K ?S, J K-1 mol-1 ?H, kJ mol-1 T, K ?H, kJ mol-1 ?S, J K-1 mol-1 8 297 0.6 2.0 289 0.6 2.1 314 6.6 21.0 305 6.8 22.3 9 292 5.9 20.2 282 5.1 18.1 303 6.1 20.1 296 5.4 18.2 10 318 18.3 57.5 311 19.0 61.1 11 323 19.9 61.6 317 19.4 61.2 336 0.7 2.1 331 0.7 2.1 476 24.6 51.7 472 17.9 37.9 12 332 27.9 84.0 326 29.3 89.9 475 24.7 52.0 472 26.1 55.3 13 340 34.6 101.8 334 32.4 97.0 473 26.5 60.3 470 24.5 52.1 (1) Taken from Busico et al, 1979. The phase transitions of the CnCdCl series have been extensively investigated via DSC for n = 6 - 18. Figure 2.6 summarizes some of the DSC results. Schenk and Chapuis (1988) found that for n ? 13, there are four phase transitions, for 7 ? n ? 12, two phase transitions, and there are several phase transitions for n ? 6. Chapter 2 Literature Survey 33 Figure 2.6: Schematic representation of DSC results of the homologous CnCdCl4 series for n = 6 - 18. Inset: Transition enthalpies for n = 7-12. Asterisks represent the chain melting transition and filled circles the minor transition. Figure taken directly from Schenk and Chapuis, 1988. The phase transitions of C10CdCl, C12CdCl, C14CdCl, C16CdCl and C18CdCl in particular have been followed via X-ray powder diffraction to determine the unit cell parameters of their various phases (Table 2.6). Chapter 2 Literature Survey 34 Table 2.6: Summary of unit cell parameters of CnCdCl inorganic-organic layered perovskite-type hybrids in their various phases, n = 8 - 16. I II III IV V Ref. C8CdCl Orthorhombic T = 353 K a = 7.49(1) ? b = 7.58(1) ? c = 47.88(9) ? Z = 4 Amaa Undetermined Monoclinic T = 243 K a = 7.41(2) ? b = 7.53(2) ? c = 45.34(20) ? ? = 96.55(28)? Z = 4 P21/n N/A N/A 1 C10CdCl Orthorhombic T = 318 K a = 7.460(2) ? b = 7.546(2) ? c = 54.64(2) ? Z = 4 Amaa Orthorhombic T = 308 K a = 7.40(2) ? b = 7.54(2) ? c = 51.62(6) ? Z = 4 Pmnn Monoclinic T = 294 K a = 7.354(1) ? b = 7.545(1) ? c = 51.620(3) ? ? = 91.74(1)? Z = 4 P21/n N/A N/A 2 and 3 C12CdCl Tetragonal T = 360 K a = 5.310(1) ? b = 5.310(1) ? c = 64.31(4) ? Z = 2 Orthorhombic T = 334 K a = 7.470(7) ? b = 7.553(7) ? c = 63.50(4) ? Z = 4 Amaa Monoclinic T = 293 K a = 7.463(1) ? b = 7.523(1) ? c = 59.152(8) ? ? = 96.54(2)? Z = 4 P21/n N/A N/A 4 C14CdCl Orthorhombic T = N/A a = 7.46(1) b = 7.54(1) c = 35.77(6) Z = 2 Undetermined Monoclinic T = N/A a = 7.32(3) b = 7.45(2) c = 33.60(7) ? = 92.2(2) Z = 2 Undetermined Triclinic T = 298 K a = 7.329(2) b = 7.482(1) c = 33.188(5) ? = 98.19(1), ? = 92.2(2), ? = 90.04(2) Z = 2 1P 5 C16CdCl Tetragonal T = 360 K a = 5.298(2) ? b = 5.298(2) ? c = 80.03(7) ? Z = 2 Orthorhombic T = 354 K a = 7.383(18) ? b = 7.641(15) ? c = 76.45(11) ? Z = 4 Orthorhombic T = 348 K a = 7.437(10) ? b = 7.590(10) ? c = 75.24(8) ? Z = 4 Monoclinic T = 293 K a = 7.384(5) ? b = 7.546(11) ? c = 73.58(3) ? ? = 96.27(6)? Z = 4 P21/n N/A 6 Key to references in Table 2.6 1) Chanh et al, 1983. 2) Kind et al, 1979. 3) Ricard et al, 1984. 4) Chanh et al, 1985. 5) Schenk and Chapuis, 1988. 6) Chanh et al, 1989. The most accurate structural data on the phase transitions of the long chain layered perovskite- type hybrids is found for C10CdCl (Kind et al, 1979) and can be used as a model for other long chain alkylammonium layered perovskite-type hybrids. The compound has two closely spaced first-order phase transitions, a minor one at 308 K and a major one at 312 K. In the monoclinic phase III (CSD ref. code DECACD), the decylammonium chains are ordered and are tilted at Chapter 2 Literature Survey 35 +40? and -40? relative to the inorganic layer, which gives an overall herringbone-type arrangement of the chains (Figure 2.7). The asymmetric unit contains two unique decylammonium chains; chain A which has a gauche bond between the first and second carbon atom, beginning after the nitrogen atom in the chain, and chain B, which has the gauche bond between the second and third carbon atom. The remainder of the bonds within the chains have an all-trans conformation. In the intermediate orthorhombic phase II, both chains continuously switch between two equivalent positions along their long molecular axis, separated by 90? from each other. They still retain their tilting in this phase as the interlayer spacing between the layers has remained the same. This phase transition from phase III to phase II at 308 K is similar to the order-disorder transition seen previously in the short chain alkylammonium hybrids. The second phase transition at 312 K to the orthorhombic phase I (CSD ref. code: DECACD01) shows the "melting" transition, seen generally only in the longer chain alkylammonium hybrids and is generally the transition in the DSC scans with the greatest enthalpy, referred to as the "major" transition. This phase transition is called the "melting" transition as the bonds within the chains now have conformational freedom, akin to repeated diffusion of their gauche bonds through the whole chain. The decylammonium chains are disordered over two equivalent positions in phase I, related by a mirrorplane in the space group Amaa. The disordered chains are now tilted almost perpendicular to the inorganic layers, increasing the interlayer spacing by 1.5 ?. The electron density map in Figure 2.8 shows the positions of the carbon and nitrogen atoms in the chains. In summary, the major transition in C10CdCl is the chain melting transition, where the interlayer spacing increases significantly due to changes in the tilt angle of the chains; and the minor transition, where no change in the interlayer spacing is observed, a positional disorder of either the entire chain along its axis occurs or a torsional disorder of parts of the chain is observed (Needham et al, 1984). Chapter 2 Literature Survey 36 Figure 2.7 The herringbone arrangement of the tilted decylammonium chains in C10CdCl in the monoclinic phase III (left) and the two independent chains in this phase (right). Taken from Kind et al, 1979. Figure 2.8 Electron density contours from the orthorhombic phase I of C10CdCl. Taken from Kind et al, 1979. Chapter 2 Literature Survey 37 2.2.3 The lead halide inorganic-organic hybrids [(CnH2n+1NH3)2PbX4] with the layered perovskite-type motif The inorganic-organic hybrids CnPbX that have the layered perovskite-type motif are the most recently studied of the inorganic-organic layered perovskite-type hybrids, as opposed to the Cd and Mn hybrids, which were the main focus for physicists and materials scientists initially. Very few single-crystal structures have been determined for the CnPbX hybrids (See Table 2.7). Table 2.7: Unit cell constants of the layered perovskite-type hybrids CnPbX at room temperature. X n a / ? b / ? c / ? CSD Reference Cl 3 7.815(1) 25.034(3) 7.954(1) JADLUV Meresse and Daoud, 1989. 6 7.78(6) 7.93(3) 38.1(4) N/A Lee et al, 2000. 8 7.82(9) 7.96(3) 43.5(5) N/A Lee et al, 2000. 10 7.86(2) 7.98(9) 49.0(9) N/A Lee et al, 2000. I 4 8.863(2) 8.682(1) 27.570(2) TECFAI Mitzi, 1996. 9 9.034(1) 8.708(1) 39.785(3) KECKOS Nagapetyan et al, 1988. 10 8.968 8.667 42.51 N/A Ishihara et al, 1990. 12 8.882 8.529 49.02 N/A Ishihara et al, 1990. Interest in the CnPbI compounds is due to their excitons2, which are significantly enhanced as compared to CH3NH3PbI3 and PbI2. The exciton binding energy varies from 170 meV to 330 meV, while it is only 45 meV in CH3NH3PbI3 and 30 meV in PbI2 (Ishihara et al, 1990; Muljarov et al, 1995). The hybrids C6PbI and C10PbI have been the most studied (Table 2.2) by measuring their electro-absorption, reflection, luminescence, magneto-absorption, magneto-reflection, absorption and emission spectra (See ref 99-105 in Table 2.2). 2 An exciton is a "fundamental quantum of electronic excitation in condensed matter, consisting of a negatively charged electron and a positively charged hole bound to each other by electrostatic interaction. Typically, an exciton is created when a photon is absorbed in a solid; the exciton then moves through the crystal; and finally the electron and hole recombine, resulting in the emission of another photon, often at a wavelength different from the original photon." (McGraw-Hill, 2005) Chapter 2 Literature Survey 38 2.2.4 Phase transitions in inorganic-organic layered perovskite-type hybrids [(CnH2n+1NH3)2PbX4] 2.2.4.1 Alkylammonium chains with n = 1 The C1PbI hybrids display a similar sequence of phase transitions as the Mn, Cu and Cd hybrids with methylammonium, being orthorhombic in the lowest temperature phase, tetragonal in the intermediate phase and finally cubic at the highest temperature (Table 2.8). Due to the larger ionic radii of the Pb2+ and I- ions, the motif of the C1PI hybrids is based on the cubic perovskite motif, described in Section 1.2 previously. Table 2.8: Unit cell constants and other structural data of the various phases of the hybrids [CH3NH3PbX3] that have a 3-D cubic perovskite motif (1). X T / K Crystal System (Phase) Space group a / ? b / ? c / ? Z Cl >178.8 Cubic (I) Pm3m 5.675 5.675 5.675 1 172.9-178.8 Tetragonal (II) P4/mmm 5.656 5.656 5.630 1 <172.9 Orthorhombic (III) P2221 5.673 5.628 11.182 2 Br >236.9 Cubic (I) Pm3m 5.901(1) 5.901(1) 5.901(1) 1 155.1-236.9 Tetragonal (II) I4/mcm 8.322(2) 8.322(2) 11.832(7) 4 149.5-155.1 Tetragonal (III) P4/mmm 5.894(2) 5.894(2) 5.861(2) 1 <144.5 Orthorhombic (IV) Pna21 7.979(1) 8.580(2) 11.849(2) 4 I >327.4 Cubic (I) Pm3m 6.3285(4) 6.3285(4) 6.3285(4) 1 162.2-327.4 Tetragonal (II) I4/mcm 8.855(6) 8.855(6) 12.659(8) 4 <162.2 Orthorhombic (III) Pna21 8.861(2) 8.851(2) 12.620(3) 4 (1) Adapted from Mitzi, 1999a; Poglitsch and Weber, 1987. 2.2.4.2 Alkylammonium chains with n ? 4 The phase transitions in the CnPbI inorganic-organic layered perovskite-type hybrids are characterized by thermochromic behaviour. The lowest temperature phase is yellow coloured and the highest orange. The temperature at which this colour change occurs is dependant on the chain length. For n = 4, 8, 9, 10 and 12, this critical temperature is 250, 235, 240, 275 and 310 K Chapter 2 Literature Survey 39 respectively (Ishihara et al, 1990). The authors associate the phase transitions with "rearrangements of the alkylammonium chains". Furthermore, C6PbI shows no phase transitions or colour change below room temperature. C10PbI has the most complex phase behaviour, with no less than three phase transitions and four distinct phases (Xu et al, 1991c). Two very comprehensive studies on the phase transitions of C6PbCl and C9PbCl can be used as models for the phase transitions of other Pb hybrids. C6PbCl has three phase transitions, all first- order and C9PbCl, two phase transitions. The phase stable at the lowest temperature, phase IV in C6PbCl and phase III in C9PbCl, is completely ordered and has a gauche bond near the ammonium head group and the rest of the bonds within the chains are in an all-trans configuration. The first transition, with has the smallest enthalpy, involves the appearance of gauche bonds at the opposite end of the chains, near the methyl group. The last transition to phase I is the same as in the other layered perovskite-type hybrids, a complete chain melting and rotational disordering and the interlayer spacing increases, indicative of changes in the tilt angle of the alkylammonium chains (Figure 2.9). The DSC curves show a small thermal hysterises, especially in C9PbCl. Smaller, second order transitions are also observed in the DSC curves of C6PbCl and C9PbCl (Figure 2.10). Figure 2.9: A schematic of the various phases of C6PbCl and their unit cell parameters as determined by X-ray powder diffraction. Adapted from Kammoun et al, 1996a. Chapter 2 Literature Survey 40 Figure 2.10: DSC curve of C9PbCl. Taken from Kammoun et al, 1997. The only long chains, n ? 12, alkylammonium inorganic-organic hybrids in the lead(II) iodide layered perovskite-type compounds that have been studied in detail are C12PbI, C16PbI and C18PbI. The packing of the alkylammonium chains was determined by 13C NMR, IR and Raman spectroscopy and found to be in an all-trans configuration at room temperature. The tilt of the long chains in the three compounds relative to the inorganic layer was estimated at 55? from the infrared spectra (Venkataraman et al, 2002a; Venkataraman et al, 2002b). The direction of the tilt can either be the same for all chains to give a parallel arrangement, or alternate, to give a herringbone arrangement (Figure 2.11). The authors found no evidence of interdigitation in their study and classify interdigitated and non-interdigitated alkylammonium hybrids as separate polymorphic groups (Venkataraman et al, 2002a). Chapter 2 Literature Survey 41 Figure 2.11: A schematic of the two possible packing arrangements, parallel (left) or herringbone (right), of the alkylammonium chains in CnPbI (n = 12, 16, 18). All the bonds in the chains are in an all-trans conformation. Taken from Venkataraman et al, 2002. The phase transitions for these three compounds all occur above room temperature (Barman et al, 2003). The authors have assigned the first, minor transition to the premelting transition and the second, major transition to the melting transition. On heating the samples, the two transitions appear as endothermic peaks and upon cooling immediately, only a single exothermic peak of the major transition appears. If the samples are heated immediately again, the premelting endotherm is not seen but returns after leaving the samples standing for a few days. The model according to Barman (2003) of the phase changes is as follows: the chains are in an all-trans, static conformation at room temperature and after the premelting transition, there is an increase in gauche conformers in the chains causing the interlayer spacing to decrease slightly at the premelting transition. In this phase, the NH3+ group becomes rotationally disordered within the cavity of the four terminal iodides. At the melting transition, there is an abrupt increase in the interlayer spacing attributed to a loss of the uniformity of the tilt angle across all the individual chains. There is also a marked increase in the conformational disorder in the chains. The packing of the chains before and after the melting transition is shown schematically in Figure 2.12. Chapter 2 Literature Survey 42 Figure 2.12: A schematic of the phase transition of CnPbI (n = 12, 16, 18). Taken from Venkataraman et al, 2002. 2.3 Aromatic R groups and their photoelectric behaviour Apart from the simple alkyl chains, another common choice encountered in the literature for the R group is an aromatic ring, separated from the ammonium group by short alkyl chain spacers. These have the general formula [(C6H5(CH2)nNH3)2MX4], n = 0-3, and the most common examples are summarized in Table 2.9 below. The most studied inorganic-organic layered perovskite-type hybrid is without doubt [(C6H5(CH2)2NH3)2MX4] as it is the material that has shown the most application potential. Various articles that summarize the application potential of inorganic-organic layered perovskites include Organic-Inorganic Electronics (Mitzi et al, 2001a), Solution-processed inorganic semiconductors (Mitzi, 2004), Organic-Inorganic Hybrid Materials as Semiconducting Channels in Thin-Film Field-Effect Transistors (Kagan et al, 1999), Electronic properties of three- and low-dimensional semiconducting materials with Sn halide and Pb halide (Koutselas et al, 1996), Optical properties of PbI-based perovskite structures (Ishihara, 1994) and Some New Organic-Inorganic Hybrid Semiconductors Based on Metal Halide Units: Structural, Optical and Related Properties (Papavassiliou et al, 1999a) Chapter 2 Literature Survey 43 Table 2.9: The most common aromatic R groups that form inorganic-organic layered perovskite- type hybrids. Numbers in superscript refer to the references listed at the end of the table. Pb2+ Sn2+ Cu2+ Cr2+ Cd2+ C6H5NH3 Cl1 C6H5(CH2)NH3 I2 Cl4, 32 Cl19, 26 Br18, 22 Br 5, 29 C6H5(CH2)2NH3 Cl3, 6, 32 Br6, 3, 7, 28 I8 , 7, 9, 10, 11, 12, 13, 17, 3, 23, 25, 27, 28, 30, 31 I14, 15 Cl 16, 19, 26, 33 Br16, 18 Cl 20 C6H5(CH2)3NH3 Cl19, 26 Br18 C6H5(CH2)4NH3 Cl19 ?-C6H5CH2(CH3)NH3 Cl21 Br21 I24 Key to references in Table 2.9 1) Larsen, 1974. 2) Papavassiliou et al, 1999b. 3) Ueda et al, 1998. 4) Braun and Frey, 1999a. 5) Halepoto et al, 1989. 6) Mitzi, 1999b. 7) Mitzi et al, 1999a. 8) Era et al, 1994. 9) Hong et al, 1992a. 10) Cheng et al, 2003. 11) Kitazawa, 1998. 12) Shimizu et al, 2005. 13) Shimizu and Fujisawa, 2004. 14) Papavassiliou et al, 1994. 15) Kagan et al, 1999. 16) Willett, 1990. 17) Calabrese et al, 1991. 18) Zhou et al, 1992a. 19) Dupas et al, 1976. 20) Groh et al, 1997. 21) Gebauer and Schmidt, 1999. 22) Zhou at al, 1992b. 23) Hong et al, 1992b. 24) Billing, 2002. 25) Era et al, 1997. 26) Dupas el al, 1977. 27) Era et al, 1995. 28) Cheng et al, 2005. 29) Bellitto et al, 1986. 30) Fujita et al, 1998. 31) Fujita et al, 2000. 32) Braun et al, 1999a. 33) Kang and Jeon, 1995. The simplest aromatic amine, aniline, is also the least studied, with only one inorganic-organic layered perovskite-type hybrid structure in the CSD (Ver. 5.27, including May 2006 update). The hybrid is [(C6H5NH3)2CuCl4] (Larsen, 1974) (CSD ref. code: ANILCP) and has the typical 4+2 coordination around the Cu atom and eclipsed inorganic layers. Four Cu-Cl bond lengths are short, 2.3007(5) ? and 2.2804(6) ?, and the other two are long, 2.9178(5) ? (Figure 2.13). If a phenyl group is bonded to the anilinium backbone in the para position, the inorganic layers become staggered. The two aromatic rings in [(p-Ph-C6H4NH3)2CuCl4] (Bourne and Mangombo, Chapter 2 Literature Survey 44 2004) (CSD ref. code: HAJTAO) are twisted by 23.07(9)? relative to each other (Figure 2.14). The effect of smaller functional groups para to the ammonium group on the crystal structure has been systematically investigated using chloro (CSD ref. code: PAYDUO), nitro (CSD ref. code: PAYFAW) and cyano groups (PAYDOI) (Sekine et al, 1996a) together with copper(II) chloride (Sekine et al, 1996b). Other inorganic-organic layered perovskite-type hybrids with nitro groups are [(p-O2N-C6H4NH3)CdCl4] (Azumi et al, 1995) (CSD ref. code: ZIKFOO) (Azumi et al, 1996) and [(p-O2N-C6H4NH3)CuBr4] (Sekine et al, 1996c) (CSD ref. code: VACSAT); and with chloro groups are [(p-Cl-C6H4NH3)2PbI4] (Liu et al, 2004) (CSD ref. code: FIXMOP). Figure 2.13: The hydrogen bonding interactions of the layered perovskite-type hybrid with anilinium and the two long and four short Cu-Cl bonds of the copper(II) chloride octahedra. Figure 2.14: The packing arrangement of a complete unit cell of [(p-Ph-C6H4NH3)2CuCl4]. Chapter 2 Literature Survey 45 The methylene spacer in benzylammonium causes the ammonium head group to adopt the right- angled hydrogen bonding configuration, as in [(C6H5CH2NH3)2PbI4] (Papavassiliou et al, 1999b) (CSD ref. code: COTVIQ) (Figure 2.15), [(C6H5CH2NH3)2PbCl4] (Braun and Frey, 1999a) (CSD ref. code: HORFAV) and [(C6H5CH2NH3)2CrBr4] (Dost et al, 1989) (CSD ref. code: VAVNOV). In the anilinium compounds, the ammonium group has the equilateral hydrogen bonding configuration. The only reported structures with substituents on the benzylammonium backbone are with a methyl group, as in [(p-CH3-C6H4CH2NH3)2PbX4] (X = Cl, Br and I) (Papavassiliou et al, 2000; Makino et al, 2005) (CSD ref. codes: MEMYIM, MEMXUX and MEMYEI respectively); and a flouro group, [(p-F-C6H4NH3)2PbI4] (Kikuchi et al, 2003). The optical absorption spectra contain peaks at 397 nm and 515 nm respectively for the bromide and iodide inorganic-organic layered perovskite-type hybrids. Inorganic-organic layered perovskite-type hybrids with large fused aromatic rings are also able to crystallize out as the perovskite-type layer structure providing it contains a methylene spacer, that prevents a steric interaction with the bulky R group and the terminal halides. Two such structures are known for lead(II) chloride with either 2-napthylmethylammonium (CSD ref. code: HORFEZ) (Braun and Frey, 1999b) and 2-anthrylmethylammonium (CSD ref. code: GOLJOG) (Braun and Frey, 1999c). Fullerene ammonium derivatives, such as N-methyl-2-(4- aminophenyl)-fulleropyroolidene, form a layered perovskite-type inorganic-organic hybrid with lead(II) iodide (Kikuchi et al, 2005). In this compound, the fullerene molecule is bonded to benzylammonium, which acts as the spacer between the bulky fullerene molecule and the terminal iodide halides. Chapter 2 Literature Survey 46 Figure 2.15: Hydrogen bonds in [(C6H5CH2NH3)2PbI4]. The first mention of inorganic-organic layered perovskite-type hybrids in the literature with the phenylethylammonium cation is that of the ferromagnetic compound [(C6H5(CH2)2NH3)2CuCl4] in 1976 (Dupas et al, 1976). The reason its magnetic properties were investigated was to compare them to the magnetic properties of the alkyl ammonium series [(CnH2n+1NH3)2CuCl4] (Dupas et al, 1976). The authors surmised that the packing of the inorganic layers and the phenethylammonium cations is closely related to the structures of [(NH4)2CuCl4] and [(CH3NH3)2CuCl4] after determining approximate values of the unit cell axis for [(C6H5(CH2)2NH3)2CuCl4] from X-ray powder data. The first complete single crystal study was performed by Willett (1990) on both the chloride and bromide inorganic-organic hybrids [(C6H5(CH2)2NH3)2CuCl4] (CSD ref. code: KEJCEH) and [(C6H5(CH2)2NH3)2CuBr4] (CSD ref. code: KEJCIL). Both hybrid compounds have staggered inorganic layers. The ethylammonium substituents on the benzene rings have an approximate all-trans conformation (Torsion angles: 173.5(5)? and 171.5(1)? respectively for X = Cl and Br) and have the bridging halogen configuration (Figure 2.16). Chapter 2 Literature Survey 47 Figure 2.16: The bridging halogen configuration of [(C6H5(CH2)2NH3)2CuCl4]. The crystal structure and conformation of the phenethylammonium cation changes entirely when the metal cation is lead. The inorganic-organic layered perovskite-type hybrid [(C6H5(CH2)2NH3)2PbCl4] (CSD ref. code: MAPBIO) has the rare 2ap x 2ap superstructure, where ap is the cubic lattice parameter of the ideal cubic perovskite [(CH3NH3)PbCl3] (Mitzi, 1999a). The unit cell axes are a = 11.1463(3) ?, b = 11.2181(3) ? and c = 17.6966(5) ? and the space group is triclinic 1P . In this structure, the lattice parameters a and b are parallel to the plane of the inorganic layers and are twice the cubic lattice parameter ap = 5.657(2) ? (Mitzi, 1999a). The related crystal structure of the copper(II) chloride inorganic-organic layered perovskite-type hybrid has the smaller ratio to the cubic lattice parameter, namely ?2ap x ?2ap. The author rationalizes these differences by the degree of distortion of the MCl6 octahedra. If the octahedra were not tilted or rotated relative to each other, the unit cell dimensions within the corner-sharing layers would be simply ap x ap. The deviations from this ideal scenario accounts for the two possible superstructures of the two compounds. The PbCl6 octahedra within the layers are more distorted than the CuCl6 octahedra and the unit cell is larger in the directions parallel to the layers. The basic building block of the corner-sharing layers consists of four corner-sharing squares, as shown in Figure 2.17 below. The asymmetric unit is also correspondingly bigger and contains two lead and eight chloride atoms. Each square has a partner phenethylammonium Chapter 2 Literature Survey 48 cation so that there are four unique cations in the asymmetric unit, labelled N1 to N4. The ethylammonium groups are not in the all-trans conformation seen in [(C6H5(CH2)2NH3)2CuCl4] and have torsion angles of -67.0(7)? (N1-C1-C2-C3-C4), -67.9(7)? (N2-C9-C10-C11-C12), 58.9(7)? (N3-C17-C18-C19) and -60.6(7)? (N4-C25-C26-C27). The resulting shape of the ethylammonium groups is "J-shaped" (Mitzi, 1999b) and is further stabilized by hydrogen bonding with the terminal halogen configuration and having the right-angled configuration. A preliminary single-crystal structure of the bromide inorganic-organic layered perovskite-type hybrid by the same author revealed an almost identical unit cell. However, not all reflections were indexed, suggesting a possible supercell and that the chloride and bromide structures are not isostructural. Figure 2.17: The simplest repeating unit of the perovskite sheets in [(C6H5(CH2)2NH3)2PbCl4]. The four phenethylammonium cations adopt a J-shaped conformation. The crystal structure of the iodide inorganic-organic layered perovskite-type hybrid, [(C6H5(CH2)2NH3)2PbI4] (CSD ref. code: JIMDEO), has the ap x ap structure (Calabrese et al, 1991). The space group is C2/m and the bridging iodides as well as the phenethylammonium Chapter 2 Literature Survey 49 cations are disordered across the mirrorplanes in the unit cell and hence not much structural detail of the tilting and rotation of the PbI6 octahedra and the conformation of the ethylammonium groups can be elucidated. The structure of [(C6H5(CH2)2NH3)2SnI4] (CSD ref. code: POFKOK) is isostructural to the lead(II) iodide inorganic-organic layered perovskite-type hybrid and shows the same disorder and/or superstructure defects (Papavassiliou et al, 1994). The structure of the phenethylammonium cations within the three inorganic-organic layered perovskite-type hybrids [(C6H5(CH2)2NH3)2PbX4] (X = Cl, Br and I) has also been investigated by 13C cross polarization/magic angle sample spinning NMR technique (Ueda et al, 1998). The properties of the phenethylammonium inorganic-organic layered perovskite-type hybrids have excited both physicists and materials scientists. For example, [(C6H5(CH2)2NH3)2PbI4] shows strong photoluminescence (Hong et al, 1992), electroluminescence (Hong et al, 1992a. 201), a very strong exciton absorption at 2.4 eV and a large exciton binding energy of 0.220 eV. For comparison, the position of the exciton for the tin(II) iodide derivative is at 2.0 eV and the exciton binding energy is 0.190 eV (Papavassiliou et al, 1994). To make use of the optical property of the lead(II) iodide inorganic-organic layered perovskite-type hybrid, Era et al (1994) combined the compound with an electron transporting oxadiazole derivative (OXD7) to construct an "organic-inorganic heterostructure electroluminescent device (EL)". A schematic of the device is shown in Figure 2.18. The hybrid [(C6H5(CH2)2NH3)2PbI4] (PAPI) is used as the emitter and OXD7 as the electron transport layer. The two layers were then sandwiched between an indium-tin-oxide anode and a MgAg cathode. The intensity reached a maximum of 10 000 cd m-2 at liquid nitrogen temperatures. To achieve this, a current density of 2 A cm-2 and a voltage of 24 V had to be applied. The colour of the emission was an intense green and peaked at 520 nm, a spectrum that corresponds well to the photoluminescent spectra obtained from a thin film of purely PAPI (Era et al, 1994) laid down. Other layered perovskite-type hybrids which have been studied with identical devices are [(C6H9(CH2)2NH3)2PbI4] and [(C6H5(CH2)4NH3)2PbI4] (Hattori et al, 1996). The maximum electroluminesence reached for these two cases were 4800 cd m-2 (50 mA cm-2, 24 V) and 180 cd m-2 (25 mA cm-2, 30 V) respectively. Two similar devices were constructed using a structural isomer of the phenethylammonium molecule, chiral (C6H5CH(CH3)NH3) (See Figure 2.19) (Gebauer and Schmidt, 1999). The electron transport layer is the n-semiconductor called 'Starburst', the hybrids [(C6H5CH(CH3)NH3)2PbCl4] (diode 1) or Chapter 2 Literature Survey 50 [(C6H5CH(CH3)NH3)2PbBr4] (diode 2) as the p-semiconductor and as a contact between the two semiconductors, a poly(N-vinylcarbazole)-layer doped with Coumarin6. Both diodes started showing green emissions at 7 V. Figure 2.18: A schematic of the inorganic-organic heterostructure electroluminescent device with approximate thickness of the layers and the structure of the organic component, OXD7, used. Figure adapted from Era et al (1994). Figure 2.19: A schematic of the three-layered heterocontact inorganic-organic light emitting diode with a chiral layered-perovskite. Figure adapted from Gebauer and Schmidt (1999). A novel way to tune the position of the exciton absorption and photoluminescence bands is by systematically replacing the halide in the lead(II) halide inorganic-organic layered perovskite- Chapter 2 Literature Survey 51 type hybrids. Kitazawa (1997) prepared thin films of the hybrids [(C6H5(CH2)2NH3)2PbBrxI4-x] and [(C6H5(CH2)2NH3)2PbClxBr4-x] and found that it was possible to smoothly shift the bands towards green-blue-violet regions as a function of x, as shown in Figure 2.20 below, taken directly from the article. Figure 2.20: Optical absorption spectra of (a) [(RNH3)2PbBrxI4-x] and (b) [(RNH3)2PbClxBr4-x] films measured at room temperature. Taken from Kitazawa (1997). To improve the stability of the [(C6H5(CH2)2NH3)2PbI4] thin films against moisture, thermal annealing and photo-irradiation, Kitazawa (1998) prepared nanocrystalline films of the hybrid doped with poly(methyl methacrylate). The exciton binding energy increased to 0.300 eV from undoped films (cf. 0.200 eV for undoped) and the degradation could be suppressed. A similar study was performed on films of [(C6H5(CH2)2NH3)2PbBrxI4-x] (Kitazawa et al, 2004). 2.4 Inorganic-organic layered perovskite-type hybrids [(H3N(CH2)nNH3)MX4] with simple alkyldiammonium chains Compared to the simple straight chain aliphatic mono-amines, fewer inorganic-organic layered perovskite-type hybrids with diamines have been synthesized and characterized. The length of the simple straight alkyl chain studied is generally quite short with a maximum chain length of ten Chapter 2 Literature Survey 52 carbon atoms. Structural phase transitions behave in a similar fashion to the mono-ammonium cations. 2.4.1 Lead(II) halide inorganic-organic layered perovskite-type hybrids [(H3N(CH2)nNH3)PbX4] and [(H3N-R-NH3)PbX4] The compound [(H3N(CH2)3NH3)PbCl4] (Corradi et al, 1999) (CSD ref. code: CAKBUL) has two unique inorganic layers in the unit cell (Figure 2.21). Adjacent layers are slightly offset relative to each other. The 1,3-diammoniumpropane cations are twisted along one end of the chain by 105.2(7)? to compensate for the shift of the layers. In the same study, two related inorganic-organic layered perovskite-type hybrids with the cation H3NCH3CH(CH3)(CH2)3NH3 where prepared with lead(II) chloride (CSD ref. code: CAJXUG) and lead(II) bromide (CSD ref. code: CAJZAO). These two compounds are isostructural and have the same staggered conformation of adjacent layers as the previous structure. The displacement of the layers is due to the steric effect of the methyl group on the 2-position of the pentane chains (Corradi et al, 1999) (Figure 2.22). The methyl groups have a repulsive effect on neighbouring cations and this is mirrored in the layer shift. The bond lengths between the lead and the halide atoms increases as expected with the increasing halide radius. Figure 2.21: The packing diagram of a single unit cell of [(H3N(CH2)3NH3)PbCl4] shown side-on (left) and from the top (right). The inorganic layer shown as light grey octahedra is offset relative to the inorganic layers shown as dark grey octahedra. Chapter 2 Literature Survey 53 Figure 2.22: Half of the unit cell of [(H3NCH3CH(CH3)(CH2)3NH3)PbCl4] showing a magnified view of the arrangement of the cations between the layers. The methyl group has a repulsive effect on the cations in the crystallographic c direction. One layered perovskite-type lead hybrid with a diammonium cation has been reported to display reversible phase transitions, studied via DSC, SC-XRD and P-XRD (Courseille et al, 1994), is [(H3N(CH2)4NH3)PbCl4] (CSD ref. code: YOVXAI). It has a monoclinic room temperature phase II and a monoclinic high temperature phase I. The transition temperature of the endothermic peak is T = 323.8 K when heating, and when cooling exhibits strong thermal hysteresis so that the exothermic peak is at T = 296.9 K. The monoclinic phase II has the unit-cell dimensions a = 7.944(2) ?, b = 7.772(5) ?, c = 19.761(8) ? and ? = 94.84(3)?, space group is P21/c and Z = 4. The structure contains two layers per unit cell that are staggered relative to each other. The 1,4- diammoniumbutane cation is non-centrosymmetric and has a "left-hand" conformation, as defined by the authors, at one extremity, as shown in Figure 2.23. The atoms N1, C1, C2, C3 and C4 form a quasi-perfect all-trans configuration (Courseille et al, 1994) and N2 is clearly bent out of the plane of those atoms. The room temperature structure was determined from SC-XRD data. The structure of the high temperature phase I had its initial unit-cell dimensions determined from precession photographs and refined from 34 peaks from P-XRD data determined at 353 K. The unit-cell dimensions are a = 7.963(5) ?, b = 7.735(6) ?, c = 11.011(1) ? and ? = 102.22(9)?. The Chapter 2 Literature Survey 54 space group is P21/a and Z = 2. The authors surmise that the cation untwists to give a centrosymmetric and stretched conformation where all the atoms are in a planar arrangement and trans to each other. The increase in molecular length consequently results in an increase in the interlayer spacing of the layers. Phase II has a spacing of 19.761(8)/2 = 9.881(8) ? and phase I a spacing of 11.011(1) ?. Not mentioned in the study is the possibility of the layers shifting relative to each other. The unit-cell axis halves in the direction perpendicular to the layers when transforming from phase II to phase I; this could be indicative of a change from a staggered to an eclipsed arrangement of the layers. Figure 2.23: The structure phase II of [(H3N(CH2)4NH3)PbCl4] showing a magnified view of the left-hand conformation of the cation between the layers. Eclipsed layered perovskite-type layers are seen in the series of compounds [(H3N(CH2)6NH3)[PbX4] (X = Cl, Br and I) (Mousdis et al, 1999) (CSD ref. codes: WOGJEH, WOGJIL and WOGJOR respectively). The three compounds are isostructural but only SC-XRD data and structures were reported for the iodide and bromide compounds. Contrary to the diammonium cations discussed above, the 1,6-diammonium cations are centrosymmetric and only half of the molecule is in the asymmetric unit. The molecules pack around inversion centres Chapter 2 Literature Survey 55 located within the unit cell. The carbon atoms form a plane with the nitrogen atoms bent out of the plane. The unit cell contains only one complete layer per unit cell, i.e. two halves at x = 0 and 1 (See Figure 2.24). Synthesized but not structurally characterized are the Sn equivalents [(H3N(CH2)6NH3)SnX4] (X = Br and I). All five layered perovskite-type hybrids show excitonic peaks when optical absorption spectra were recorded and the peak positions are shifted to lower energies in the order I < Br < Cl (Mousdis et al, 1999). The lead(II) iodide hybrid shows a very large exciton binding energy of 0.33 eV, below room temperature, and this is correlated with the fact that it does not undergo any structural phase transitions below room temperature (Goto et al, 2001). Figure 2.24: The structure of [(H3N(CH2)6NH3)PbI4]. The cation is centrosymmetric and the two halves are related by the symmetry operator (1-x, 1-y, 1-z), shown as atoms marked with apostrophes ('). The optical absorption spectra of the series of compounds [(H3N(CH2)nNH3)PbBr4] (n = 4, 6, 8 and 10) (Matsui et al, 2002) were also measured. The structure of the compounds was deduced from P-XRD and confirmed to have the layered perovskite-type motif. The position of the exciton peak is independent of the length of the alkyldiammonium cation and is centred around Chapter 2 Literature Survey 56 390 nm. The interlayer spacing ranges from 10.2 ? (n = 4) to 15.0 ? (n = 10) and separates the inorganic layers sufficiently to cause a quantum confinement effect. In an attempt to enhance the electroluminescence and photoluminescence properties of the inorganic-organic layered perovskite-type hybrids compared to simple alkyl chains and aromatic moieties, a specially synthesized oligothiophene chromophore was incorporated into the layered perovskite-type motif employing the three lead(II) halides (Mitzi et al, 1999b). The molecule, shown in Figure 2.25 below and abbreviated AEQT, has a long, narrow profile and four ?-linked thiophene rings. The ethylammonium groups provide flexibility and anchorage points to the inorganic layer via the hydrogen bonds of the ammonium group. Only the compound [(AEQT)PbCl4] shows relatively efficient room-temperature electroluminescence (Chondroudis and Mitzi, 1999) and strong photoluminescence (Mitzi et al, 1999b). S S S SNH2 NH2 Figure 2.25: The molecule 5,5'''-bis-(aminoethyl)-2,2':5', 2'':5'',2'''-quaterthiophene, AEQT. Of the three compounds synthesized and characterised by optical absorption spectra, only [(AEQT)PbBr4] (CSD ref. code: QEKGES) was structurally characterized by SC-XRD. An interesting feature of this inorganic-organic layered perovskite-type hybrid is that it has the 2ap x 2ap superstructure. The packing of the compound has a herringbone arrangement of the organic dye molecules. The conformation of the quaterthiophene backbone is syn-anti-syn and each ring is essentially planar. The ethylammonium anchors are bent out of the plane formed by the quarterthiophene backbone and adopt a conformation suitable to hydrogen bonding interactions (Figure 2.26). Chapter 2 Literature Survey 57 Figure 2.26: The unit cell of [(AEQT)PbCl4]. The ethylammonium groups and the bridging bromides are disordered over two positions. A related compound that has a bithiophene backbone instead of the quaterthiophene has also been synthesized and characterized (Zhu et al, 2003), the organic cation being 5,5'- bis(ammoniumethylsulfanyl-2,2'-bithiophene, abbreviated BAESBT, and is shown in Figure 2.27. The crystal structure of [(BAESBT)PbI4] (CSD ref. code: BAYHAL) has the ?2ap x ?2ap superstructure (Mitzi, 1999b). The packing is similar to the above mentioned layered perovskite- type hybrid and has an exciton peak at 504 nm. S NH2 S SS NH2 Figure 2.27: The molecule BAESBT. Yet another compound has two thiophene units separated by a hexane chain and two ethylammonium groups on either end similar to AEQT. The compounds name is then 1,6-bis[5'- (2''-aminoethyl)-2'-thienyl]-[hexane], abbreviated AETH, and is shown in Figure 2.28. The hydrocarbon chain lends flexibility to the molecule and has the long, narrow profile the authors deem necessary (Chondroudis et al, 2000) (Figure 2.28). The optical properties of the inorganic- Chapter 2 Literature Survey 58 organic layered perovskite-type hybrids [(AETH)PbX4] (X = Br and I) were measured on thin films that were deposited using a single source thermal ablation method (SSTA). No SC-XRD data was reported but the layered perovskite-type motif was confirmed from P-XRD data. S NH2 SNH2 Figure 2.28: The molecule AETH. 2.4.2 Other divalent metals reported to form inorganic-organic layered perovskite-type hybrids [(H3N(CH2)nNH3)MX4] with diammonium alkyl chains A number of inorganic-organic hybrid materials containing short (n < 6) diammonium alkyl chains have been reported with mercury(II) chloride. The two inorganic-organic layered perovskite-type hybrids, [(H3N(CH2)3NH3)HgCl4] (Spengler et al, 1998) (CSD ref. code: PUVLUN) and [(H3N(CH2)4NH3)HgCl4] (Amami et al, 2002) (CSD ref. code: LOYBEG), both have eclipsed inorganic layers. One would expect the interlayer spacing to be greater for the 1,4- diammoniumbutane compound compared to the 1,3-diammoniumpropane compound but the reverse is observed, where the spacing is 0.4 ? longer in the latter compound. This is due to the conformation of the cations between the layers as the H3N(CH2)4NH3 chain has a gauche-trans- gauche conformation and H3N(CH2)3NH3 is gauche-trans. The shorter cation is also tilted more towards the perpendicular to the layers. The two compounds also differ significantly in their hydrogen bonding configuration. [(H3N(CH2)3NH3)HgCl4] has a terminal halogen configuration and [(H3N(CH2)4NH3)HgCl4] has a bridging halogen configuration (Figure 2.29). Chapter 2 Literature Survey 59 Figure 2.29: The hydrogen bonding configurations of [(H3N(CH2)4NH3)HgCl4] (left) and [(H3N(CH2)3NH3)HgCl4] (right). The most frequently reported metal halide inorganic-organic layered perovskite-type hybrids contain the metals Cu, Mn, Cd, Hg and Ni and the halides Cl and Br. The crystal structures of most of them have been determined via SC-XRD and are listed in Table 2.10. Chapter 2 Literature Survey 60 Table 2.10: Structures of compounds that appear in the CSD. Numbers the last column refer to the references listed at the end of the table. Compound Arrangement of Layers Conformation of Cation CSD ref. code Hydrogen Bonding Configuration Ref. [(H3N(CH2)2NH3)NiCl4] Eclipsed trans NICLEN Terminal 5 [(H3N(CH2)2NH3)MnCl4] Eclipsed trans ENDAMN10 Terminal 6 [(H3N(CH2)3NH3)MnCl4] Eclipsed trans PYDAMN03, PYDAMN Terminal 8, 10 [(H3N(CH2)4NH3)MnCl4] Eclipsed trans BUCLMN BUCLMN01 Terminal 7 [(H3N(CH2)2NH3)CuCl4] Eclipsed trans EDIACU11 Terminal 6, 9 [(H3N(CH2)3NH3)CuCl4] Eclipsed trans PAMTCC Terminal 3 [(H3N(CH2)4NH3)CuCl4] Eclipsed trans-gauche- trans JEPDUK Bridging Bridging 2 [(H3N(CH2)5NH3)CuCl4] Eclipsed trans-trans- trans-gauche JEPLEV Terminal Terminal 2 [(H3N(CH2)3NH3)CdCl4] Eclipsed trans-trans PRDACD N/A 4 [(H3N(CH2)3NH3)FeCl4] Eclipsed trans-trans PYDAFE N/A 10 [(H3N(CH2)2NH3)CuBr4] Eclipsed trans VABDUX Terminal Terminal 1 [(H3N(CH2)3NH3)CuBr4] Eclipsed trans-gauche VABFAF Terminal Bridging 1 [(H3N(CH2)4NH3)CuBr4] Eclipsed trans-gauche- trans JEPLAR Bridging Bridging 2 [(H3N(CH2)5NH3)CuBr4] Eclipsed trans-trans- trans-gauche JEPLIZ Terminal Terminal 2 Key to references in Table 2.10 1) Halvorsen and Willett, 1988. 2) Garland et al, 1990. 3) Phelps et al, 1976. 4) Willett, 1977. 5) Skaarup and Berg, 1978. 6) Tich? et al, 1978. 7) Tich? et al, 1980. 8) Crowley, et al, 1982. 9) Birrell and Zaslow, 1972 10) Willett and Riedel, 1975. Chapter 2 Literature Survey 61 2.4.3 Structural phase transitions of inorganic-organic layered perovskite-type hybrids [(H3N(CH2)nNH3)MCl4] (M = Cd and Mn) with diammonium alkyl chains The alkyldiammonium compounds have been intensely investigated to understand the mechanism of their structural phase changes, if any. The two most discussed systems are cadmium(II) chloride and manganese(II) chloride. The structural transitions were not always analysed only via SC-XRD but through other techniques. The possible phase transitions of [(H3N(CH2)nNH3)CdCl4] (n = 2-5), abbreviated CnN2CdCl, were followed via 1H NMR (Blinc et al, 1977) and changes in the dielectric constant (Levstik et al, 1976) as a function of temperature. The unit cell parameters of the room temperature phases of n = 2 and 4 were found to be monoclinic with space group P21/b and orthorhombic for n = 3 and 5 (space group Imma) (Peterson and Willett, 1975; Arend and Gr?nicher, 1976). The compound C2N2CdCl shows no phase transitions between -150?C and +100?C, probably due to the rigidity of the cation between the layers due to the double hydrogen bonding interactions on both ends of the molecule and the short chain length, which does not allow for much freedom of movement. The longer chain compounds do have transitions at 103?C (C3N2CdCl), 68?C (C5N2CdCl) and multiple transitions at 68?C, 88?C and 91?C (C4N2CdCl). Enthalpies and entropy values for these transitions were determined by a calorimetric study done by Tello et al (1977). The transitions were detected by changes in the second moments M2 of the NMR absorption spectra and the spin relaxation times T1. In summary, Blinc et al (1977) found the transitions to be due to changes in the hydrogen bonding configurations, in conjunction with rotation and motion of the alkyl chains. The single phase transitions of C3N2CdCl and C5N2CdCl were also studied by a variety of techniques, including 35Cl NMR and deuteron quadrupole resonance spectroscopy, and found to be order-disorder transitions (Kind et al, 1981). The motion of the diammonium chains could be followed more accurately as they were deuterated. The manganese analogues, [(H3N(CH2)nNH3)MnCl4] (n = 2-5), abbr. CnN2MnCl, show a very similar phase behaviour compared to cadmium. The same odd / even effect of the room temperature unit cells is seen (Arend et al, 1976b). Again, there are no phase transitions for n = 2 but they exist for C3N2MnCl (33?C and 63?C), C4N2MnCl (110?C) and C5N2MnCl (28?C). The Chapter 2 Literature Survey 62 space groups and crystal structures of C3N2MnCl were determined by SC-XRD and reveal the following phase sequence with increasing temperature: Phase III (Pnma) ? Phase II (Fmmm) ? Phase I (Imma) (Crowley et al, 1982). The results are in agreement with studies done using 35Cl NQR measurements and deuterated NMR-NQR (Kind et al, 1978) where both phase transitions are first-order. Phase III and phase I both have a terminal hydrogen bonding configuration and only differ by a two-fold disorder of the cation in phase I, where the cation tilts by about 40? around the long axis compared to phase III. Phase II has a predominant terminal halogen configuration as one hydrogen bonds to both a bridging and a terminal chloride, also known as a bifurcated hydrogen bond. Phase II has the chain tilted by 20? relative to the inorganic layer, intermediate compared to phase III and phase I. Only the single crystal structure of phase III has been reported (CSD ref. code: PYDAMN03). C4N2MnCl has only one phase transition compared to the three for C4N2CdCl and it is second- order. Complete SC-XRD crystal structures were reported for both the monoclinic room temperature phase II (CSD ref. code: BUCLMN) and the orthorhombic high temperature phase I (CSD ref. code: BUCLMN01) (Tich? et al, 1980). The cation in phase II is very nearly planar and all-trans with a centre of symmetry at the midpoint of the chain. In phase I, the position of the cation is split between two equivalent positions across a mirror plane. The connectivity of the resulting ten atoms, all of them half occupied, and the conformation of the cation can not be determined (See Figure 2.30). 35Cl NMR and NQR measurements on deuterated samples again confirm the order-disorder transition behaviour (Kind et al, 1981). Chapter 2 Literature Survey 63 Figure 2.30: The packing diagrams of phase II (left) and phase I (right) of [(H3N(CH2)4NH3)MnCl4]. The two equivalent positions of the atoms are shown as light grey and dark grey spheres in phase I. 2.5 Inorganic-organic layered perovskite-type hybrids [(H3N-R-NH3)MX4] containing aromatic diammonium cations Diammonium compounds with aromatic R groups are rare. The simplest structure has a single benzene ring, as in 1,4-phenylenediammonium. The ammonium groups have to be para to each other; otherwise they will not be able to hydrogen bond to adjacent layers. Only three such structures have been reported, [(H3N-C6H4-NH3)CdCl4] (Ye et al, 1996) (CSD ref. code: ZITTOL) (eclipsed inorganic layers), [(H3N-C6H4-NH3)CdBr4] (Ishihara et al, 1996) (CSD ref code. NOJQIM) (staggered inorganic layers) and [(H3N-C6H4-NH3)CuCl4] (Bourne and Mangombo, 2004) (CSD ref. code: HAJSOB) (eclipsed inorganic layers. The phenyl rings themselves are almost perpendicular to the plane of the inorganic layers (See Figure 2.31). Both the cadmium(II) chloride and copper(II) chloride hybrids have weak edge-to-face C-H...? interactions between adjacent phenyl rings (Hydrogen...centroid distance is 3.134(17) ? for Cu compound and 3.034(66) ? for Cd compound). The next cation of interest would have two benzene rings connected in a para-fashion, so that the ammonium groups are still para to each other. This organic compound is called benzidine. Only one reported structure of an inorganic-organic layered perovskite-type hybrid exists for this cation. [(H3N-C6H4-C6H4-NH3)CuCl4] (CSD ref. code: HAJTES) has eclipsed inorganic layers with an interlayer spacing of 14.3769(2) ?. For comparison, the interlayer spacing for the single aromatic case is 10.007(5) ?. The hydrogen bonding interactions are the same as those for the previous structures (terminal halogen configuration). The Cu compound with the benzidine cation has two edge-to-face C-H...? interactions which are closer than in the previous compound (H...centroid distance 2.985(2) ? and 3.074(2) ?) (Bourne and Mangombo, 2004) thus further stabilizing the overall structure. The same benzidine cation with lead(II) chloride does not form the layered perovskite structure type but rather a hybrid material with isolated PbCl6 octahedra. This structure is discussed in Section 2.10.1 below. Chapter 2 Literature Survey 64 Figure 2.31: The packing diagrams of [(H3N-C6H4-NH3)CdCl4] (left) and [(H3N-C6H4-C6H4- NH3)CuCl4] (right). The C-H...? interactions are shown as dashed black lines. 2.6 Inorganic-organic layered perovskite-type hybrids with triammonium cations The compound [((H3NCH2CH2)2NH2)CuCl4]?Cl (Ferguson and Zaslow, 1971) (CSD ref. code: AEATCU10) is unique as it contains not only layers of corner-sharing CuCl6, but in between the layers, it has isolated chloride ions as well (See Figure 2.32). The two equivalent ethylammonium groups, consisting of the N2 atom, sit in the holes shaped by the four bridging and four terminal chlorides in the usual manner associated with the layered perovskite-type motif. The NH2 group, to which the ethylammonium groups are attached and contains atom N1, is found on a mirror plane at y = 1/4 together with the chloride anion, Cl(3). There is a short N1...Cl3 distance of 3.06(3) ?, which is indicative of hydrogen bonding. The position of the hydrogen atoms were not reported in this structure. For this reason, a more accurate structure determination was done by Greenhough and Ladd (1977) at room temperature. An accurate crystallographic study of this compound at different temperatures would be useful as it undergoes thermochromic behaviour above and below room temperature, suggested to be due to shifts in the position of the hydrogen atoms involved in hydrogen bonding. The compound also undergoes a phase transition from a paramagnetic to an antiferromagnetic state when cooling to below 11.8 K (Losee and Hatfield, 1974). Chapter 2 Literature Survey 65 Figure 2.32: Half of the unit cell of [((H3NCH2CH2)2NH2)CuCl4]?Cl. Figure is taken from Ferguson and Zaslow (1971). The same amine was also crystallized with manganese(II) chloride and gave the same geometry as the copper(II) chloride inorganic-organic layered perovskite-type hybrid (See Figure 2.33). The compound [(H3NCH2CH2)2NH2)MnCl4]?Cl (CSD ref. code: ETRAMN) shows no structural phase transitions as the hydrogen bonding to the isolated interlayer chloride reduces the mobility of the organic chain (Breneman and Willett, 1981). Chapter 2 Literature Survey 66 Figure 2.33: Half of the unit cell of [((H3NCH2CH2)2NH2)MnCl4]?Cl. The hydrogen bonds to the interlayer chloride are shown as dashed black lines. 2.7 Other metals and more complex ammonium cations contained in inorganic-organic layered perovskite-type hybrids In this section, we look at the compounds that contain unusual metals or that have specially designed cations resulting from crystal engineering type principles. These cations are often only characterized by non-crystallographic techniques to investigate the effect the metal(II) halide and the ammonium cation have on their optical properties. The most studied R group is based on the 2-phenylethylammonium backbone, abbr. PEA. The use of non-transition metals, that are divalent, is an idea that follows on after much work has been done using the metals Cu, Pb, Mn, Fe, Cd, Sn, etc as discussed in the previous sections. The only divalent rare-earth metal reported so far has been europium (Mitzi and Liang, 1997). The synthesis of the inorganic-organic layered perovskite-type hybrid with butylammonium, Eu(II) and I is not trivial as the metal has a tendency to coordinate the solvent molecules to itself when in solution. Single crystals of the inorganic-organic layered perovskite-type hybrids are mostly Chapter 2 Literature Survey 67 obtained from slow cooling or evaporation of solutions using acid halides and some alcohol or other common solvents (See Chapter 3). Furthermore, slow oxidation of Eu(II) is often seen in solution and this does not allow for a long enough crystallization period. Thus, the compound [(C4H9NH3)2EuI4] was prepared by solid state reaction in an inert atmosphere of Argon. The resulting polycrystalline samples were analysed by Powder X-Ray diffraction and the orthorhombic unit cell dimensions determined to be a = 8.913(3) ?, b = 8.759(3) ? and c = 27.793(6) ?. These values are very close to the room temperature unit cell of [(C4H9NH3)2PbI4] (Mitzi, 1996) and confirm that it has corner-sharing layers of EuI6 octahedra. The compound shows a strong blue photoluminescence at 460 nm. The group IVB metals Pb and Sn have been extensively studied. Mitzi (1996) has also prepared [(C4H9NH3)2GeI4] and characterized it by SC-XRD, and additionally shows photoluminescence at 690 nm. The crystal structure is similar to the analogues structures with Pb, Sn and Eu. The conscious design of a particular structure in the inorganic-organic layered perovskite-type hybrids was performed on the system [(C6H5C2H4NH3)2SnI4]. This parent structure has been used to change its electronic properties by changing the organic cation. This was achieved by Mitzi et al (2001) by substituting one of the aromatic hydrogens for a fluorine atom and then changing its position on the ring between the 2, 3 and 4 positions. Table 2.11 summarizes the trends observed in the electronic properties and crystal structures of [(x-flourophenylethylammonium)2SnI4] for x = 2, 3, 4. There is a noticeable correlation between the bridging angle I-Sn-I and the shift of the peak position of the exciton band. The dependence of the absorption and photoluminescence spectra of spin coated films of these three compounds on the position of the fluorine atom was confirmed by Kikuchi et al (2004). The idea was then carried further by exchanging the halide for Br and Cl on the 2-position only and observing the effect of the halide on the peak position. These results are summarized in Table 2.12. Chapter 2 Literature Survey 68 Table 2.11: [(x-F-C6H4C2H4NH3)2SnI4], x = 2, 3, 4. x F...F distance / ? Bridging angle I-Sn-I/ ? Peak of Exciton / nm Superstructure Interlayer Spacing / ? CSD ref. code 0 N/A 156.48 609 ap x ap 16.30 POFKOK (1) 2 > 6.0 153.28(3) 588 ap x 2ap 17.535(3) BAKHAX (2) 3 3.02(1) 154.16(3) 599 ap x 2ap 17.297(4) BAKHEB (2) 4 3.516(2) 156.375(8) 609 ?2ap x ?2ap 16.653(2) BAKHIF (2) 1) Papavassiliou et al, 1994. 2) Mitzi et al, 2001b. Table 2.12: [(2-X-C6H4C2H4NH3)2SnI4] (X = Cl and Br) (1). X I...X distance / ? Bridging angle I-Sn-I / ? Exciton Peak / nm Superstructure Interlayer Spacing / ? CSD ref. code Cl 3.98 154.76(6) 586 ap x ap 16.891(7) RUYDUK Br 4.29 148.71(1) 557 ?2ap x ?2ap 18.540(2) RUYDOE (1) Xu et al, 2003a. Figure 2.34: The packing diagram of [(4-F-C6H4C2H4NH3)2SnI4]. The aromatic rings are parallel to each other. Chapter 2 Literature Survey 69 In another example, an organic chromophore was used as the R group. In principle it can add hole-transporting capability to the overall inorganic-organic layered perovskite-type structure (Era et al, 2005). The distance between the ammonium group and the chromophore was varied by hydrocarbon chains of varying length (Figure 2.35). The inorganic layers were composed of PbBr6 octahedra and the interlayer spacing was determined by P-XRD. The absorption spectra of spin coated films peaked at around 400nm for n > 3 and varied only slightly with the increasing values of n. No exciton absorption peak was seen for n = 3. Figure 2.35: The carbozole chromophore, n = 3-8, 12. Another comparatively common R group has a naphthalene backbone, C10H7, and the ammonium group on its 1-position. The inorganic-organic layered perovskite-type hybrids [(C10H7- (CH2)nNH3)2PbBr4] (n = 1 and 2) and [(C10H7-O(CH2)nNH3)2PbBr4] (n = 3, 4 and 8) show phosphoresence for all compounds and exciton emission for all compounds except where n = 1 (Era et al, 1998a). Another studied chromophore has azobenzene-linked ammonium molecules, [(C6H5-N=N-C6H4-O(CH2)nNH3)2PbBr4] (n= 3, 4 and 6). The absorption peaks for the three compounds are centered around 390 nm (Era et al, 1998b). The 1-naphthalene backbone has also been used to prepare copper(II) chloride inorganic-organic layered perovskite-type hybrids, [(R- NH3)2CuCl4], where R is C6H5CH2-, C10H7-CH2-, C10H7-O(CH2)3- and C10H7-O(CH2)4- (Shikoh et al, 2001). These complexes show ferromagnetism. The values of the Curie temperatures, Tc, are independent of the interlayer spacing but change with the identity of the R group. The absorption spectra show two peaks, around 290 nm and 370-400 nm, which are indicative of Jahn-Teller type distortion. Chapter 2 Literature Survey 70 One of the largest chromophores, reported in the literature, has pyrene as the backbone and methylammonium on the 1-position. Three inorganic-organic layered perovskite-type hybrids were made, [(C16H9-CH2-NH3)2PbX4] (X = Cl, Br and I), by slow evaporation of the DMF solvent containing a 2:1 ratio of the cation salt and PbX2 (Braun et al, 1999b). The identity of the halide affects the emission spectra and phosphorescence decay times. The authors also investigated the inorganic-organic layered perovskite-type hybrids with mixed halide inorganic layers, [(C16H9-CH2-NH3)2PbClnBr4-n] (n = 0-4). The compounds were prepared as spin-coated films on quartz substrates. The ratio of the two halides again affects the peak position of the absorption spectra (Braun et al, 1999b). A significant achievement in the crystal engineering of inorganic-organic layered perovskite-type hybrids was achieved in the compound [(C6F5C2H4NH3?C10H7C2H4NH3)SnI4] (CSD ref. code: AQIMOC), which contains two different ammonium cations in the same structure, the molecules 2,3,4,5,6-pentaflourophenethylammonium (5FPEA) and 2-naphthylenethylammonium (NEA) (Xu and Mitzi, 2003). The structural model was deduced from SC-XRD data. The bilayers of organic molecules within the 2-D inorganic layers each contain one of these molecules, so that the sequence of molecules perpendicular to the layers is [NEA-5FPEA-PbI4-NEA-5FPEA-PbI4- NEA] as the flouroaryl-aryl interactions seem to occur perpendicular to the layers. Hence, both the 5FPEA and NEA molecules hydrogen bond to the layers. The second reported case of mixed organic molecules within the perovskite-type layers involves the compounds [(C6F5C2H4NH3)SnI4]?(C6H6) (CSD ref. code: XIYZEK) and [(C6H5C2H4NH3)2SnI4]?(C6F6) (CSD ref. code: XIYZIO). In contrast to the compound described above, the benzene and flourinated benzene molecule do not have any ammonium groups and hence are intercalated between the bilayers of the 5FPEA and PEA organic cations. The sequence perpendicular to the layers is then [PbI4-5FPEA-C6H6-5FPEA-PbI4] and [PbI4-PEA-C6F6-PEA- PbI4]. The intercalated rings have strong face-to-face ?-type interactions with the aromatic rings of the ammonium cations, thus stabilizing the overall structure (Mitzi et al, 2002). Also mentioned in the article is that when using separately either the flourinated or unflourinated compounds, no stable product compounds were formed. This highlights even further the significance of the flouroaryl-aryl interactions. Chapter 2 Literature Survey 71 The only reported case of an inorganic-organic layered perovskite-type hybrid that has adjacent layers connected by covalent bonds is the compound [(Cu(O2C-(CH2)3-NH3)2PbBr4] (CSD ref. code: EXUNUG), which has Br-Cu-Cu-Br linkages between adjacent layers. The organic cation 4-aminobutyric acid is zwitterionic and is covalently bonded to Cu atoms via the carboxylate groups. Four of these organic cations are bonded to the Cu atoms to form dimeric clusters. The Cu atoms are then covalently linked to the terminal bromides of the PbBr6 layered perovskite layers and to adjacent clusters to form a "covalent bond pathway between adjacent perovskite layers" (Mercier and Riou, 2004) (See Figure 2.36). This makes the overall 3-D structure much stronger than before as the usual interactions observed until now between adjacent layers and cations are weak van der Waals forces. The ammonium groups hydrogen bond to both the three bromides of the inorganic perovskite-type layers and to one of the oxygen atoms intramolecularly. Figure 2.36: The packing diagram of [(Cu(O2C-(CH2)3-NH3)2PbBr4]. The PbBr6 octahedra are shown as dark grey octahedra and the CuO4Br square-planar pyramids are light grey. The search for other non-covalent interactions between the R groups of the organic ammonium cations has had some success. The objective is to use functional groups that strengthen the Chapter 2 Literature Survey 72 interactions between R groups without affecting the desired layered perovskite-type motif. This process is at the heart of crystal engineering. Previously, aromatic interactions between ring systems has shown positive results. However, a stronger interaction can be hydrogen bonds between alcohol and carboxylic acid functional groups. With this objective in mind, the layered perovskite-type hybrids [(HO(CH2)2NH3)2PbX4] (X = I and Br) were made, which have alcohol- based bifunctional ammonium cations (Mercier et al, 2004). There are three different hydrogen bonding interactions in these structures. The usual NH3+...X interaction, but with only two hydrogens bonding to the terminal halide and bridging halide. The second interaction is the one of interest as it involves the third ammonium hydrogen, which hydrogen bonds to the oxygen molecule of the adjacent cation to form hydrogen bonded dimers. The N-H...O bond distance is 2.23 ? in the lead iodide structure and brings the lead(II) iodide layers closer together. The nearest distance between I...I contacts is 4.279(2) ?, which is the second shortest reported for Group IVB divalent metals with the layered perovskite-type motif, helped by the fact that the inorganic layers are eclipsed. This causes a significant red shift of the exciton peak to 536 nm. The shortest Br...Br contact is 4.36(2) ? and the exciton peak is blue shifted to 417 nm. The layers are staggered. The third interaction has an O-H...I hydrogen bond, which means that both ends of the hydroxyethylammonium cations have hydrogen bonded interactions with the halides. The first reported structure with an alcohol functional group was [(HO(CH2)2NH3)2CuCl4] (CSD ref. code: TIRQOQ), which has a two-fold disorder of the HOCH2CH2- moiety (Halvorson et al, 2005). Carboxylic acids form very strong hydrogen bonded dimers, stronger than the alcohols. The first inorganic-organic layered perovskite-type hybrids with carboxylic dimers reported were [(?- alaninium)2CuCl4] (Willett et al, 1981) (CSD ref. code: BEHXIV) and [(?-alaninium)2CuBr4] (Willett et al, 1983) (CSD ref. code: CAYPOH). The inorganic layers consist of square-planar CuX4 anions separated by the organic cations. The cations from adjacent layers form dimeric pairs, adding a 3-D stability to the crystals not seen in other inorganic-organic layered perovskite- type hybrids. The O...O distance is 2.682(3) ? in the copper(II) chloride hybrid. Another inorganic-organic layered perovskite-type hybrid was prepared by Mercier (2005). The bifunctional cation is ammonium 4-butyric acid, which has a carboxylic acid group separated by a propane chain from the ammonium functional group. The compound is Chapter 2 Literature Survey 73 [(HO2C(CH2)3NH3)2PbI4] (CSD ref. code: QARWOW). The carboxylic acid groups form extended 1-D chains of hydrogen bonds. Adjacent cations point in opposite directions to form a ladder-like motif of O-H...O chains (See Figure 2.37). Figure 2.37: The packing diagram of [(HO2C(CH2)3NH3)2PbI4]. The R groups have a carboxylic functional group that interacts strongly with adjacent R groups via O-H...O (d(O...H) = 1.8 ?) hydrogen bonds to strengthen the overall structure. The rare case of an inorganic-organic layered perovskite-type hybrid that does not have a primary ammonium head group is demonstrated in the two isostructural compounds [(C6H8N4)PbI4] (CSD ref. code: QUFBUO) and [(C6H8N4)SnI4] (CSD ref. code: QUFCAV) (Tang et al, 2001). The protonated cation has only one hydrogen on each of the four nitrogen atoms, as seen in Figure 2.38 below. Nonetheless, the molecule can move far enough into the "box" to hydrogen bond to both sandwiching layers akin to the primary, diammonium cations discussed previously. Chapter 2 Literature Survey 74 Figure 2.38: The packing diagram of [(C6H8N4)PbI4]. There are only four hydrogen bonds between the individual cations and the inorganic layers. The inorganic-organic layered perovskite-type hybrid with the shortest interlayer spacing, and hence shortest I...I contact between adjacent layers, is [((CH3)3N(CH2)2NH3)SnI4] (Xu et al, 2003b) (CSD ref. code: LUXJET). It has quaternary and primary ammonium cations and a I...I distance of 4.19 ?. The absorption peak is 630 nm. The structural consequence of the two ammonium cations can be seen in the corrugation of the SnI6 layers. The terminal iodides are bent inward when the NH3 group is in the hole and outward when the N(CH3)3 group is in the hole formed by the four bridging and terminal iodides (See Figure 2.39). Chapter 2 Literature Survey 75 Figure 2.39: The packing diagram of [((CH3)3N(CH2)2NH3)SnI4]. 2.8 Multilayer inorganic-organic layered perovskite-type hybrids A different structural variation of the cubic perovskite structure type is seen in the compounds of general formula [(CH3NH3)m-1(R-NH3)2MmX3m+1] (M = Sn or Pb; X = Cl, Br and I; R = CnH2n+1- or phenethylammonium; m = 1, 2, 3,?). If m = 1, then the hybrids have a monolayer of corner- sharing octahedra, which is then the layered perovskite-type motif already described extensively. If m > 1, then the monolayer is replaced by a bilayer (m = 2) (Figure 2.40 below), a trilayer (m = 3) (Figure 2.41 below), and so forth until m = ?, which is again the 3-D cubic perovskite structure type of [(CH3NH3MX3]. In the bilayer structure type, two monolayers are bonded by one of the formerly terminating iodides. Within the bilayer, the methylammonium cation occupies the cavities in the same manner as in the 3-D [CH3NH3MX3] inorganic-organic hybrid structures, i.e. it fits in the centre of eight corner-shared MX6 octahedra. The bilayers are separated by any other ammonium cation, R-NH3, which is larger than the methylammonium molecule, which fits on the periphery of a set of four corner-shared MX6 octahedra (Tabuchi et al, 2000). Similarly, a trilayer has three monolayers stacked upon each other. Both ammonium Chapter 2 Literature Survey 76 cations form hydrogen bonds to the halides in the usual manner described for the monolayer inorganic-organic layered perovskite-type hybrids. Figure 2.40: The packing diagram of the bilayer hybrid [(CH3NH3)(H3CC6H5(CH2)NH3)2Pb2I7] (Papavassiliou et al, 2000; CSD ref. code: MEMYAE). Figure 2.41: The packing diagram of the trilayer hybrid [(CH3NH3)2(C4H9NH3)2Pb3I10]. The CH3NH3 cations are not shown as their positions were not accurately determined in the crystal structure (Mitzi et al, 1994; CSD ref. code: PIVCUS). As the value for m increases, the behaviour of the hybrid goes from semiconducting to metallic (Mitzi et al, 1994). The electrical properties of these multilayer inorganic-organic layered perovskite-type hybrids can be further modified by varying the length of the alkylammonium chain from n = 2 - 12 and simultaneously varying the thickness of the inorganic layers, as in (CH3NH3)m-1(CnH2n+1NH3)2[SnmI3m+1] (n = 2 - 12, m = 2, 3, 4, ?) (Mitzi et al, 1994) and (CH3NH3)m-1(CnH2n+1NH3)2PbmBr3m+1 (m = 1 and n = 2, 3, 4, 6, 10; m = 2 and n = 2, 3, 4, 6; m = 3 and n = 6) (Tabuchi et al, 2000). In the latter study, the exciton absorption peak undergoes a red Chapter 2 Literature Survey 77 shift as m increases. Only three other single crystal structures of various multilayer perovskites were found in the CSD (Table 2.13). Table 2.13: Other bilayer inorganic-organic layered perovskite-type hybrids with their reported single crystal structures if reported. Compound CSD ref. code Reference [(CH3NH3)(C6H5(CH2)2NH3)2Pb2I7] JIMDIS Calabrese et al, 1991. [(CH3NH3)(HO2C(CH2)3NH3)2Pb2I7] QARWIQ Mercier, 2005. [(CH3NH3)(C4H3SCH2NH3)2Pb2I7] MUBHEW Zhu et al, 2002. [(CH3NH3)(C6H13NH3)2Pb2I7] N/A Kataoka et al, 1994. 2.9 Photopolymerization An exciting possibility in inorganic-organic layered perovskite-type hybrids is solid-state polymerization by irradiating the crystals with an external energy source. Simple alkyl chains that contain triple bonds are brought into close contact and photodimerize, as shown schematically in Figure 2.42 below (taken from Takeoka et al, 2001). The distance between closest triple bonds should be ideally between 3.6 and 4.1 ? (Schmidt, 1964) to form the polyene organic system. Chapter 2 Literature Survey 78 Figure 2.42: The basic idea of solid-state polymerization within layered type structures. Taken from Takeoka et al, 2001. The simplest ammonium cation that has been investigated for possible solid-state reactivity is propargylammonium; it forms the layered perovskite-type structure with cadmium(II) chloride, [(HC?C-CH2-NH3)2CdCl4] (Lartigue-Bourdeau et al, 1992) (CSD Ref. code: LAPDIP). The cations form bilayers between the inorganic layers. The -CH2- spacer is important as it raises the unsaturated part of the cation above the level of the terminal halides, here chlorine, and angles the terminal HC?C- groups within the bilayers towards each other (See Figure 2.43). The distances between the two closest terminal carbon atoms are 3.44 ? and 3.48 ?. When irradiated by u.v. or 60Co-? radiation, the colourless crystals display photoreactivity by changing colour (not specified by the authors). The authors surmise that the observed photoreactivity can possibly be due to a polymerization reaction of the triple bonds. Chapter 2 Literature Survey 79 Figure 2.43: The geometries of the closest propargylammonium cations in the hybrid structure that undergoes possible photopolymerization. The octahedra consist of CdCl6. Longer alkyl chains with butadiyne moieties, H3C(CH2)m-1C?C-C?C(CH2)9NH3 (m = 6 and 14), have also formed inorganic-organic layered perovskite-type hybrids with cadmium(II) chloride. Thin films of both these hybrids were irradiated by a 4-W UV lamp at 254 nm and formed ?- conjugated polymers (Kosuge et al, 2002a). P-XRD patterns of the thin films before and after irradiation show an increase in the interlayer spacing of 0.2 ? and 2.3 ? respectively for m = 6 and 14. The polymerization reactions were also followed by the changes in the absorption spectra of the spin-coated films. The maximum absorption wavelengths after irradiation are 528 nm (m = 6) and 635 nm (m = 14). Takeoka and co-workers (2001) investigated a series of inorganic-organic layered perovskite- type hybrids with lead bromide, [(H3C(CH2)nC?C-C?C(CH2)mNH3)2PbBr4], where n-m = 1-1, 2- 1, 13-1, 15-1, 11-3. The source for the ? radiation was 60Co. They found that photopolymerization only occured when n-m was 13-1 and 15-1, shown schematically in Figure 2.42. If the 11-3 cation is used, where the spacer consist of three methylene units, no reaction took place, even though the total length of the cation is the same as for the 13-1 cation. From this they concluded Chapter 2 Literature Survey 80 that the ideal spacer distance between the butadiyne moiety and the ammonium group should be a single methylene group. The organic cations with n-m equal to 1-1 and 2-1 did not react, i.e. the longer alkyl chains in 13-1 and 15-1 help to orient the butadiyne moieties so that they can undergo a topochemical polymerization. The optical absorption spectra of the layered hybrid, [(H3C(CH2)13C?C-C?C(CH2)1NH3)2PbBr4] was further investigated using spin-coated films on a SiO2 substrate (Takeoka et al, 2002). The inorganic-organic layered perovskite-type hybrid in monomer form is colourless and changes colour to red after ?-irradiation. The exciton peak due to the 2-D quantum well structure of the monomer hybrid is at 378 nm and remains even after irradiation. A second, broad peak appears at 550 nm is attributed to the ?*-? transitions of the formed polydiacetylene. The length of the polymer is estimated to be 22 monomer units, which the authors estimated from the ?*-? peak using an adopted method of Exarhos et al (1976). 2.10 Two-dimensional inorganic motifs 2.10.1 Two-dimensional motifs - NET Most 2-D inorganic motifs seen in the hybrid structures consist purely of corner-sharing octahedra. However, 2-D motifs can also be created by a combination of corner-, edge- and face- sharing. Most common of this type in the literature is the so-called net type motif which has trimeric units of trans face-sharing octahedra, summarised by the formula (MnX3n+1)(n+1)-. The 2- D layers are separated by monolayers or bilayers of organic cations containing primary, secondary or quaternary amine groups. The trimeric units are connected to each other via two corner-shared halides on both ends. To my knowledge, only one structure with n = 2 has been reported in the CSD, [(Me3N-C2H4-NMe3)2Pb2I7 ? I] (CSD ref. code: GEQHAL), which has isolated I- anions between the lead iodide layers (Krautscheid et al, 1998). The organic cation is a quaternary diammonium group and forms a monolayer between two adjacent nets and interacts with the anionic layers purely through coulombic forces. There are numerous cases with n = 3 and this motif has been observed with both lead bromide as in [(PhNMe3)4Pb3Br10] (Wiest et al, 1999) (CSD ref. code: CAQVIZ) and tin iodide [(PhNMe3)4Sn3I10] (Lode and Krautscheid, 2001) (CSD ref. code: RAJMUK). Since the organic cation has only one nitrogen atom, both structures have bilayers of PhNMe3 cations between the inorganic layers. Furthermore, these structures Chapter 2 Literature Survey 81 have the individual building blocks cis related. The 2-D nets can also be corrugated if the trimeric units connect in an alternating trans fashion as seen in [(C6H5NH3)4Cd3Br10] (Ishihara et al, 1994) (CSD ref. code: POPHAD), [(C6H5CH2SC(NH2)2)4Pb3I10](Raptopoulou et al, 2002) (CSD ref. code: IGECIG) and [(AESBT)4Pb3I10] (Zhu et al, 2003) (CSD ref. code: BAYHEP), where AESBT is 5-ammoniumethylsulfanyl-2,2'-bithiophene. These three compounds have primary and secondary ammonium groups and are stacked head-to-tail between the inorganic layers to form a bilayers of organic cations. The bilayers interact with the inorganic layers in the same way as the 2-D layered perovskites via hydrogen bonds to the iodine atoms. A net-type motif which has no face-sharing but only edge- and corner-sharing SnI6 octahedra is found in [(Me2HN-C2H4-NHMe3)Sn3I8] (Lode and Krautscheid, 2001) (CSD ref. code: RAJNEV) (Figure 2.44). Figure 2.44: The 2-D net of [(Me2HN-C2H4-NHMe3)Sn3I8]. The cations are omitted for clarity. Another net-type motif that has only been reported once is that formed in the compound [(Pr3N- C2H4-NPr3)Pb(dmf)6Pb5I14] ? DMF (Krautscheid et al, 1998) (CSD ref. code: GEQGUE), which has pentameric units of five face-sharing PbI6 octahedra, [Pb5I15]4-, that are connected to each other via a shared face to form S-shaped chains along the b-axis. These chains are then connected Chapter 2 Literature Survey 82 to each other via corner-shared iodides along the c-axis to form the 2-D net as shown in Figure 2.45. In between the layers, there are [Pb(dmf)6]2+ and (Pr3N-C2H4-NPr3)2+ cations as well as a DMF solvent molecule. Figure 2.45: 2-D net of [(Pr3N-C2H4-NPr3)Pb(dmf)6Pb5I14] ? DMF. The cations and [Pb(dmf)6] anions are omitted for clarity. The only reported net-type motif that involves all three types of sharing is found in the compound [(Me3N-C3H6-NMe3)3Pb3I9]2 (Krautscheid and Vielsack, 1996) (CSD ref. code: TIDVOR). The [Pb3I9]3- units consist of three face-sharing octahedra shaped as an almost equilateral triangle. The lead atoms are at the vertices of the triangle and the distances between the three lead atoms are in the range 4.2191(9) ? to 4.3046(8) ? (Krautscheid and Vielsack, 1996). These trimeric units are connected via corner-sharing to form 1-D chains along the b-axis. The chains are then further connected via edge-sharing along the c-axis to eventually form the 2-D net-type layers (See Figure 2.46). By changing the identity of the counterion from (Me3N-C3H6-NMe3)2+ to (Me3N-C2H4-NMe3)2+, the chains of face-sharing and corner-sharing units are not connected via edge-sharing so that the inorganic motif simply consists of 1-D zig-zag chains. The molecular formula then becomes [(Me3N-C2H4-NMe3)Pb3I10] (CSD ref. code: TIDVIL). Chapter 2 Literature Survey 83 Figure 2.46: The 2-D net of [(Me3N-C3H6-NMe3)3Pb3I9]. The cations are omitted for clarity. 2.10.2 Two-dimensional motifs - based on corner-sharing layers A 2-D motif that is closely related to the layered perovskite-type motif has corrugated sheets of [SnI4]2- corner-sharing octahedra. The layered perovskite-type motif has the corner-shared iodides always trans to each other. In this new motif, every third octahedron has cis shared iodides in the sequence -trans-trans-cis-trans-trans-cis- as described by the authors (Guan et al, 1999) (CSD Ref. code: DONDUF) (Figure 2.47). The organic counterion is (H3N(CH2)5NH3)2+ and is linked to the inorganic tin(II) iodide sheets via hydrogen bonds. Chapter 2 Literature Survey 84 Figure 2.47: The [SnI4]2- 2-D layers. The cations are omitted for clarity. 2.10.3 Two-dimensional motifs - based on face-sharing One of the few reported cases of lead(II) halide inorganic-organic hybrids that does not have octahedral coordination is found in the compound [(H3N-C6H4-NH3)(PbCl3)2] (CSD ref. code: HAJSUH) (Figure 2.48). Here, there are twin 2-D layers of purely-face-sharing eight-coordinate PbCl8. The coordination geometry is square antiprismatic but the geometry is distorted with the bond lengths to the chloride ligands in the range from 2.805(2) to 3.388(2) ? (Bourne and Mangombo, 2004). Chapter 2 Literature Survey 85 Figure 2.48: The twin 2-D layers of face-sharing PbCl8 square antiprisms, separated by a monolayer of p-phenylenediammonium. The hydrogen bonds are shown as dashed black lines. Another face-sharing 2-D motif has eight-coordinate lead(II) chloride but this time, there are three unique lead atoms in the asymmetric unit compared to the single one in the compound [(H3N-C6H4-NH3)(PbCl3)2] discussed above. In the compound [(H3N(CH2)2NH3)(Pb2Cl6)] (L?fving, 1976) (CSD ref. code: EDAPBC), Pb(1) and Pb(3) each form distorted bicapped trigonal prisms and Pb(2) forms a square antiprism. The mono layers are parallel to the bc-plane. The three lead atoms are at sites with different point symmetries, 1, 2 and m respectively for Pb(1), Pb(2) and Pb(3) (L?fving, 1976). The layers are separated by diammonium ethylene ions and interact in the usual way via N-H...Cl hydrogen bonds (See Figure 2.49). There are two unique cations in the asymmetric unit. Cation I has all the atoms in a plane and is perpendicular to the layers as it is on a mirror plane at z = 1/4. Cation II is on a two-fold axis and is almost parallel to the layers. Chapter 2 Literature Survey 86 Figure 2.49: The mono 2-D layers of face-sharing [PbCl8], separated by bilayers of H3N-C2H4- NH3. The two different orientations of the cations are labelled I and II. 2.11 One-dimensional inorganic motifs 2.11.1 Purely corner-sharing, edge-sharing and face-sharing 2.11.1.1 Motifs based on trans corner-sharing Another very common inorganic motif after the layered perovskite-type, are 1-D chains of either purely corner-sharing or face-sharing octahedra. In the corner-sharing series, the two bridging halides that are shared to adjacent octahedra can either be trans to each other or cis. All the compounds that undergo trans corner-sharing have secondary ammonium groups, =NH2+. The octahedra themselves can be very distorted due to stereochemical activity of the Pb and Sn lone pairs. The compound [(CH3SC(=NH2)NH2)3SnI5] (Raptopoulou et al, 2002) (CSD ref. code: IGEBUR) has the most distorted octahedral geometry and can be considered quasi-zero dimensional as the lead iodide bond lengths to the shared halides are 2.921(1) ? and 4.042(1) ?. The related compound, [(CH3SC(=NH2)NH2)3PbI5] (Mousdis et al, 1998) (CSD ref. code: HIWMOP), has a similar distorted geometry, where the two bridging I-Pb-I bond lengths are Chapter 2 Literature Survey 87 3.037(2) ? and 3.882(2) ?. When the halide is chloride, the extreme distortion is absent. This compound, [(CH3SC(=NH2)NH2)3PbCl5CH3SC(=NH2)NH2Cl] (CSD ref. code: HIWNAC), has two unique inorganic chains in the asymmetric unit. The chains are similar to those in the lead(II) iodide case but the bond lengths to the bridging chlorides are 2.863(12) ? and 2.893(12) ? for the first chain and 2.811(12) ? and 2.941(12) ? for the second chain (Mousdis et al, 1998). The cation, (CH3SC(=NH2)NH3)+, has a resonance delocalised structure in all three compounds as the two C-N bonds are of almost equal length. Figure 2.50: The quasi 0-D chains of [(CH3SC(=NH2)NH2)3SnI5]. The activity of the stereochemical lone pair is in the direction of the chains. Another cation that forms hybrids with trans corner-sharing octahedra is iodoformamidinium, (H2NC(I)=NH2)+. In the paper by Wang et al (1995), the effect of the stereochemical lone pair was investigated in the compound [(H2NC(I)=NH2)3MI5] (M = Sn and Pb, CSD ref. codes: YUVFIE and YUVFOK). Both compounds are isostructural and the three cations in the asymmetric unit are resonance stabilised. In the Sn analogue, the most distortion occurs along the direction of the chains, which is along the (I-Sn-I)n chain. The bridging bond lengths are 2.957(1) ? and 3.484(1) ?. The range decreases to 3.182(3) ? to 3.243(3) ? for (I-Pb-I)n. An interesting phenomenon is observed in the Sn analogue. The compound is made by dissolving cyanamide, Chapter 2 Literature Survey 88 H2N-C?N, and tin(II) iodide in hot, concentrated aqueous hydroiodic acid. If the solution is cooled immediately from 70 to -20 ?C at 2 ?C/h, cyanamide undergoes an addition reaction to form the iodoformamidinium cation and ultimately the compound [(H2NC(I)=NH2)3SnI5] results (Mitzi, et al, 1998). If the same solution is prepared but left at 80 ?C for 24 hours before the same cooling regime, some of the iodoformamidinium is reduced to formamidinium and both cations can be crystallized out in the structure [(H2NC(I)=NH2)2(H2NCH=NH2)SnI5] (Mitzi, et al, 1998) (CSD ref. code: POXNEV). The mixed cations reduce the distortion of the SnI6 octahedra so that the bond lengths range only from 3.140(8) ? to 3.210(6) ?. 2.11.1.2 Motifs based on cis corner-sharing The motif of cis-corner-sharing chains can be considered to be a layered perovskite but with PbI2 deficient sites as shown in Figure 2.51. Figure 2.51: The 1-D chain of corner-sharing octahedra is shown in light grey as cut-outs of the layered perovskite-type structure, i.e. every row of dark grey octahedra is effectively omitted. The PbI2 deficient sites repeat themselves every third row along the b-axis. Chapter 2 Literature Survey 89 The packing diagram of [(C6H5CH2CH2SC(NH2)2)3PbI5] (Papavassiliou et al, 1999b) (CSD ref. code: COTVOW) consists of anionic zig-zag chains of corner-sharing PbI6 octahedra, which are formed via cis iodine bridges. This inorganic motif is encountered for a variety of simple cations and metal halides such as [(H3N(CH2)6NH3)BiX5] (X = I, Cl) and [(H3N(CH2)6NH3)SbX5] (X = I, Br) (Mousdis et al, 1998a) (CSD ref codes: SOWNUN, SOWPAV, SOWQAW, SOWQEA). The equatorial halides, including the two bridging halides, are equiplanar, i.e. when looking down the chains, every second octahedron is eclipsed. These four compounds show excitonic absorption bands in the blue region due to their 1-D character. A more complex cation has been used together with lead(II) iodide, which can form either the layered perovskite-type hybrid [(H3N-R-NH3)PbI4], where R = 5,5'-bis(ethylsulfanyl)-2,2'- bithiophene or the 1-D hybrid [(H3N-R-NH3)(H3N-R-NH2)PbI5] (Zhu et al, 2004). Both compounds were prepared from the same solution mixture of (H3N-R-NH3)Cl2, KI, PbI2 and water. The ratio of the two forms is 1/1 and can be easily identified by the orange colour of the layered perovskite-type hybrid and the yellow colour of the corner-sharing hybrid. [(H3N-R- NH3)PbI4] becomes the sole product if a few drops of HI are added. The 1-D compound, CSD ref. code: EWAZOR, has two unique cations in the asymmetric unit. There are two additional interactions between the R moieties that are unique to this hybrid compound. The distances between S...S atoms on the individual cations is less than 3.9 ?, good evidence for charge transport properties. In addition, there are NH3+...NH2 hydrogen bond interactions between molecules in addition to the usual NH3+...I interaction between the inorganic and organic components. Chapter 2 Literature Survey 90 Figure 2.52: The 1-D chains of [(H3N(CH2)6NH3)BiX5]. The optical properties of inorganic-organic hybrids based on bismuth(III) iodides depend on the dimensionality of the inorganic motif and to this effect, Mitzi and Brock (2001) have investigated more complex organic cations and their effect on the overall structure and properties. Two corner-sharing inorganic-organic bismuth iodide hybrids with the amines 1,6-bis[5?-(2??- aminoethyl)-2?-thienyl]hexane (abbr. AETH) and 1,12-dodecanediamine (abbr. DDDA) were crystallized and their optical absorption spectra measured as thin films. The crystal structures of [(H3NC18H24S2NH3)BiI5] (CSD ref. code: MIKZOV) and [(H3N(CH2)12NH3)BiI5] (CSD ref. code: MIKZOB) have similar Bi(III) coordination. The six Bi-I bond lengths can be subdivided into three pairs according to their lengths. The iodides that bridge the adjacent octahedra, I1, and form the backbone of the inorganic chain are the longest, 3.230(2) ? to 3.2711(4) ?, the iodides that are trans, I4 and I5, the shortest, 2.942(3) ? to 2.9290(6) ?, and the iodides in the axial positions, I2 and I3, which are cis to the long bonds, intermediate in length, 2.989(2) ? to 3.187(2) ?. This distribution of bond lengths is typical of purely corner-sharing compounds of this kind. Chapter 2 Literature Survey 91 1-D chains that contain no six-coordinate metal(II) halide hybrids are also found. The compound [(H3NOC-C5H4N-CH3)CdI3] has corner-sharing CdI4 tetrahedra, which is a rarely reported 1-D inorganic motif, according to the authors (Kosuge et al, 2002b). The deposited cif file in the CSD, AKOKIU, contains no 3-D coordinates. 2.11.1.3 Motifs based on face-sharing Structures containing motifs based on purely face-sharing metal halide octahedra have been reported for a variety of metals, halides and counter ions. Generally, the adjacent octahedra share faces that are trans-related, as in [(H3C-C5H4N-CH3)PbBr3] (Raptopoulou et al, 2002) (CSD ref. code: IGECEC), [(Na4(dmf)14)PbI3]4 (Krautscheid et al, 2001) (CSD ref. code: XEPDOL), [(C8H4S6)2PbI3]?H2O (Devic et al, 2004) (CSD ref. code: ARUWEP), [(Me4N)PbI3] (Contreras et al, 1983) (CSD ref. code: CERBUW) and [(Ph4P)PbI3]?DMF (Krautscheid et al, 1996) (CSD ref. code: TOPZIH). Hybrids that have face-sharing octahedra have been demonstrated to undergo structural phase transitions, as in the compounds [(Me4N)PbBr3] (Van?k et al, 1992) (CSD ref. code: KUBBIS), [(Et4N)PbBr3] and [(Bu4N)PbBr3] (Goldstein and Tok, 1975). The nature of the phase transitions in [(Me4N)PbBr3] was investigated by DSC, polarizing microscopy and dielectric measurements and found to depend on the reorganization of the tetramethylammonium anions (Van?k et al, 1992). All of the anionic counterions described above have quaternary nitrogens, i.e. no hydrogen atoms that can undergo hydrogen bonding interactions with the halides of the extended inorganic chains. MX6 metal halide units can have mixed 6-membered coordination geometries within the face- shared chain. This is observed in the lead(II) iodide hybrid with 1,1?-dimethyl-4,4?-bipyridinium (CSD ref. code: HINYUY), which has four lead atoms in the asymmetric unit, labelled Pb1, Pb2, Pb3 and Pb4. Pb1 and Pb4 have a nearly regular octahedral coordination, Pb2 has a more distorted coordination geometry and leads up to the trigonal prismatic coordination of Pb3 (Tang and Guloy, 1999). The sequence of octahedral (O) and trigonal prismatic (TP) coordination of the trans face-sharing chain is described by the authors as [O-O-TP-O-TP-O]. The ligands bonded to the metal can be different. In the hybrid compound with the cation (Na3(OCMe2)12)+ and the anion [Pb4I11(OCMe2)]3- (CSD ref. code: TOPYUS), every fourth lead atom has an acetone Chapter 2 Literature Survey 92 molecule replacing an iodide atom. The oxygen atom now bridges two lead atoms in the same way the iodide atom would (See Figure 2.53) (Krautscheid et al, 1996). Figure 2.53: The 1-D chains of [(Na3(OCMe2)12)Pb4I11(OCMe2)]3-, which has face-sharing involving three I atoms or alternately, two I atoms and one O atom from an acetone solvent molecule. The 1-D inorganic motif need not necessarily consist of only one chain. There is a reported structure of a compound that has two parallel chains of trans face-sharing octahedra, similar to the ones described above, which are then joined by additional Pb atoms so that they themselves undergo face-sharing again. These linkages are spaced apart regularly as shown in Figure 2.54 below. The molecular formula then becomes [(Ph4P)2Pb5I12] (Krautscheid et al, 1996) (CSD ref. code: TOPZAZ). Chapter 2 Literature Survey 93 Figure 2.54: The twin 1-D chain of face-sharing PbI6 octahedra. There is no reported case of purely cis-related face-sharing octahedral chains. However, the compound [(Me3N(CH2)6NMe3)PbI3]2 (CSD ref. code: XEPDEB) contains trans face-shared octahedra and cis face-shared octahedra in the same chain linked along the crystallographic a- axis in the manner [cis-trans-cis-trans-cis-trans] as shown in Figure 2.55 below (Krautscheid et al, 2001). Chapter 2 Literature Survey 94 Figure 2.55: The 1-D chain of [(Me3N(CH2)6NMe3)PbI3]2. The face-shared octahedra are alternatively cis and trans related. 2.11.1.4 Motifs based on edge-sharing As in the corner-sharing and face-sharing one dimensional chains, the edges that are shared between adjacent metal halide units can be purely trans, cis or a combination of both. To the best of my knowledge, only two cases of trans edge-sharing exist for lead(II) iodide, where square pyramidal PbI5 units are connected to form infinite 1-D chains with the counterion either tetrahedral (Pr4N)+ (CSD ref. Code: GIYREL01) or octahedral Mg(dmf)62+ (CSD ref. Code: GOGNAR) (Krautscheid and Vielsack, 1999). The bridging Pb-I bond distances cover a larger range with the former counterion, 3.1017(9) ? to 3.4553(9) ?, compared to the more symmetrical bond length range of 3.1836(5) ? to 3.2407(6) ? when the latter, bulkier counterion is included in the hybrid structure (Krautscheid and Vielsack, 1998). Chapter 2 Literature Survey 95 Figure 2.56: The 1-D chain of the hybrid [(Pr4N)PbI3]. A similar compound that has purely edge-sharing chains is (4-(CH3)C5H3NH)CdBr3 (CSD ref. code: POPHED). The geometry of the cadmium(II) bromide is tetragonal pyramidal. The authors, Ishihara et al (2006), feel that the pentagonal coordination of the metal halide moiety, instead of octahedral, is due to the hydrogen bond between the basic 4-methyl-pyridinium and the bromine at the top of the pyramid (See Figure 2.57). Chapter 2 Literature Survey 96 Figure 2.57: The 1-D chain of the hybrid [(4-(CH3)C5H3NH)CdBr3], which has a single hydrogen bond between the anionic chain and the organic cation. The other metal that exhibits trans edge-sharing is mercury. Here, the 1-D chain has alternating octahedral and tetrahedral mercury(II) chloride units (Salah et al, 1983b) (Figure 2.58). The counterion is (CH3)3NH+ and hydrogen bonds via the single hydrogen to the chlorides (CSD ref. code: CEGMOQ). Figure 2.58: The 1-D chain of the hybrid [((CH3)3NH)HgCl3]. Chapter 2 Literature Survey 97 2.11.2 Motifs based upon combinations of edge- and face-sharing This 1-D motif based on edge- and face-sharing octahedra, has been observed most often with lead(II) iodide. The motif can be described by the shorthand notation (fme)n for m adjacent face- sharing octahedra , f, connected by octahedra sharing an edge, denoted e. Structures with m = 3 have been synthesized based on lead iodide with the counterions (C13H7O2(CH2)2NH3)+ (Maxcy et al, 2003) (CSD Ref. code.: WADMAQ), (Me3N-C3H6-NMe3)2+ (Krautscheid and Vielsack, 1997) (CSD Ref. code.: TIDVUX) and (H3NCH2CH(CH3)CH2CH2CH2NH3)2+ (Corradi et al, 1999) (CSD Ref. code.: CAJZIW) and for tin iodide octahedra (Lode and Krautscheid, 2001) (CSD Ref. code: RAJNAR) octahedra with the counter ion containing a tertiary ammonium group (Me2HN-(CH2)2-NMe2H)2+. The case with m = 1, [((PhCH2)4P)Pb3I8] (CSD Ref. code.: XEPDAX) has PbI6 octahedra that share a face with PbI5 square pyramids, which in turn share an edge (Krautscheid et al, 2001). 2.11.3 One-dimensional "Ribbon" type motifs Connecting many 1-D chains of either corner-, edge- or face-sharing octahedra together gives 1- D motifs with a certain width, resembling polymeric "ribbons". The most common inorganic ribbon motif has extended chains of trans edge-sharing octahedra, which are connected to each other again via cis related edges. This inorganic motif is based on strips of the CdI2-type structure along the <100> direction (Pohl et al, 1987) (See Fig. 2.59). The simplest case has two chains connected, as shown in Figure 2.60 below, to form 1-D extended double-chains. Chapter 2 Literature Survey 98 Figure 2.59: A single layer cutout of the CdI2-Structure type. The octahedra in light grey show the twin anionic chains seen in lead iodide inorganic-organic hybrids. Figure 2.60: The packing diagram of [(C10H7CH2NH3)PbI3] is shown on the left together with the hydrogen bonds in dashed lines. On the right is an illustration of the anionic twin chains of edge-sharing PbI6 octahedra (Papavassiliou et al, 1999b; CSD ref. code: COTVUC). The width of the 1-D ribbon can vary. The compound [(Pr3N-C2H4-NPr3)Pb6I14(dmf)2] ? 4 DMF (CSD ref. code: GEQGOY) has three parallel rows of lead atoms, octahedral PbI6 in the centre and in the two outer rows of Pb atoms, all the Pb atoms are coordinated to five bridging iodides, as well as in an alternating fashion, a single dmf and a single iodide ligand in the terminal position in the manner [PbI6-PbI5dmf-PbI6-PbI5dmf] (Krautscheid et al, 1998). The dmf molecule Chapter 2 Literature Survey 99 is a solvent molecule that gets incorporated into the anionic inorganic chain. This happens again in the closely related compound [(Ph4P)4Pb15I34(dmf)6] (Krautscheid et al, 1996) (CSD ref. code: TOPZED), which also has iodide and dmf molecules coordinated to lead. The anionic chain has the same middle row of PbI6 octahedra as the structure above but the sequence of the two outer lead rows is [PbI6-PbI5dmf-PbI5dmf-PbI6]. There is another motif of polymeric ribbons of edge-sharing octahedra that can be regarded as different band-shaped sections of the CdI2 structure (Pohl et al, 1986). The two compounds are [(Ph4P)Sb3I10] (Pohl et al, 1987) (CSD ref. code: GANSET) and [((Me2N)3C3)Sb3I10] (Pohl et al, 1986) (CSD ref. code: FAFGUO) and their polymeric anionic structures are shown in Figure 2.61. Figure 2.61: The anionic polymeric chains of [(Ph4P)Sb3I10] (a) and [((Me2N)3C3)Sb3I10] (b) shown schematically (light grey octahedra) as cutouts of the layer structure of CdI2 (dark grey octahedra). Just as individual edge-sharing chains can interconnect to form 1-D ribbons that are several octahedra wide, so do corner-sharing chains. This inorganic motif is closely related to the layered perovskite-type type motif, as shown in Figure 2.62 below, were a single row of trans corner- sharing chains is absent at regular intervals. The motif was first seen in a paper in 1999 and the authors claim it was then a heretofore never before seen structural archetype and coined the term "polymeric inorganic ribbons" (Corradi et al, 1999). The formula for the compound is [(H3N(CH2)3NH3)2Pb1.5Br7].H20 (CSD ref. code: CAKDIB). The authors contend that it is the water of hydration that prevents the formation of the 2-D layered perovskite-type motif as it is uncoordinated and replaces the missing row of octahedra. It does however hydrogen bond to the Chapter 2 Literature Survey 100 bromides between the ribbons in the crystallographic b direction and hence forms pseudo 2-D layers (See Figure 2.63). The diammonium cation hydrogen bonds to adjacent layers in the crystallographic a direction, similar to the layered perovskites. Figure 2.62: The cut-out of the layered perovskite-type inorganic motif that gives rise to the 1-D inorganic ribbons, shown as light grey octahedra. Every fourth row is missing, shown as dark grey octahedra. Chapter 2 Literature Survey 101 Figure 2.63: Two inorganic ribbons, connected by hydrogen bond interactions between the terminal bromides and the oxygen molecules between them. Finally, it is possible to have ribbons of double chains that have three or two types of sharing within the ribbon. For example, [(Na(dmf)3)4Pb6I16] has [Pb6I16]4- (CSD ref. code: XEPDIF) has building blocks consisting of a 2 x 3 array of three face-sharing and two edge-sharing PbI6 octahedra (Krautscheid et al, 2001) (Figure 2.64). Adjacent units are linked by four common I atoms. This inorganic motif can also be described as double chains of the (f3e)n motif described previously. [(CH3SC(NH2)2)(HSC(NH2)2)SnBr4] (CSD ref. code: IGECAY) has double chains of two edge-sharing octahedra which are corner connected to each other (Raptopoulou et al, 2002) (Figure 2.65). Figure 2.64: Twin anionic chains of face- and edge-sharing lead(II) iodide. Chapter 2 Literature Survey 102 Figure 2.65: Twin anionic chains of edge- and corner-sharing Sn(II) bromide. The compound [(PrN(C2H4)3NPr)Pb2I6] (CSD ref. code: XEPDUR) combines face-, edge- and corner-sharing in twin anionic chains (Krautscheid et al, 2001) (Figure 2.67). Figure 2.67: Twin anionic chains of lead(II) iodide, that has the three types of sharing in one structure. 2.12: Zero-dimensional inorganic motifs Isolated compounds are classified as those that have no 1-D or 2-D inorganic motif. The isolated compounds can exist as either isolated, individual metal halide units or be isolated clusters consisting of several connected metal halide units. Hydrogen bonding interactions between the organic and inorganic moieties can form 1-D or even 2-D hydrogen bonded networks and those are included in this section. Chapter 2 Literature Survey 103 Only three inorganic-organic hybrids have been found with isolated octahedra. The organic cations all contain primary ammonium groups and an extensive hydrogen bonded network exists. Even though the compound [(H3N-C6H4-C6H4-NH3)2PbCl6] (Bourne and Mangombo, 2004) (CSD ref. code: HAJTIW) has no extended 1-D or 2-D lead(II) chloride inorganic motif, it has alternating inorganic and organic layers that are connected via hydrogen bonds to form a chain of hydrogen bonded interactions along the a-axis. Along the b-axis, adjacent isolated octahedra are bridged by the ammonium groups on both sides of the organic cation so that a 2-D system of hdrogen bonds results (See Figure 2.68). A secondary interaction occurs between the rings on one end of the benzidine molecules as they are parallel to each other with a separation of 3.7 ? between them. The use of the same ammonium cation but exchanging the lead atom for copper, gives the layered perovskite. Figure 2.68: Alternating organic and inorganic layers bridged by hydrogen bonds in [(H3N- C6H4-C6H4-NH3)2PbCl6]. The other case of isolated lead chloride octahedra is seen with the cation 2-chloro-ethylamine, Cl- C2H4-NH3+, which contains isolated chloride anions (Geselle and Fuess, 1995) (CSD ref. code: Chapter 2 Literature Survey 104 HIBTIV). The three individual units are linked via hydrogen bonds to form a 1-D "ribbon" along the crystallographic b-axis (See Figure 2.69). Figure 2.69: Incomplete part of the unit cell of [(Cl-C2H4-NH3)6PbCl6]?2Cl, showing only a single ribbon of the hydrogen bonded interactions between the alternating PbCl6 octahedra and the cations. The only reported case of lead(II) iodide forming isolated octahedra is the compound [(CH3NH3)4PbI6]?2H2O (Vincent et al, 1987) (CSD ref. code: FOLLIB). The occurrence of this compound is important as it was prepared from the same solution that produced crystals of the hybrid with a 3-D perovskite structure, CH3NH3PbI3, discussed in the layered perovskite section 2.2.4.1 above. The crystals were prepared by adding drop wise aqueous Pb(NO3)2 to an aqueous solution of CH3NH3I. When the temperature at which this was carried out was above 40?C, the product was black coloured CH3NH3PbI3. Below this temperature, the product was yellow [(CH3NH3)4PbI6]?2H2O, which has a 0-D structure. Furthermore, if one takes the solution containing the black precipitate and cools it down, a conversion to the yellow precipitate occurs spontaneously. The asymmetric unit of the isolated case contains PbI64- ions, two CH3NH3+ cations and a single water molecule. Each iodide ligand acts as an acceptor atom for two hydrogen bonded interactions and each water molecule is hydrogen bonded to the two cations to Chapter 2 Literature Survey 105 form centrosymmetric pairs. Overall, the authors contend that a 3-D network of hydrogen bonds exist in the packing of the hybrid, shown in Figure 2.70. Figure 2.70: Two views of a filled unit cell of [(CH3NH3)4PbI6]?2H2O. The cif file did not contain any hydrogen atom coordinates so the interactions are shown as dashed lines between the various acceptor and donor atoms. Four-coordinate lead(II) iodide is seen only in the isolated structures (Figure 2.71). The coordination geometry of these anions can be regarded as incomplete octahedra. [(Ph4P)2Pb2I6] (CSD ref. code: GOGNEV) (Krautscheid and Vielsack, 1999) has [Pb2I6]2- clusters connected by sharing a single edge. The individual lead atoms have only four iodide ligands, arranged in a pseudo-octahedral coordination, as two of the octahedral positions are not occupied. The angle between cis ligands are in the range 85.22(2)? to 97.69(2)?. Single, isolated [PbI4]2- four- coordinate pseudo-octahedra are seen in only two hybrids, both with quaternary ammonium cations, [(Bu3N-(CH2)3-NBu3)PbI4] (Krautscheid and Vielsack, 1999) (CSD ref. code: GOGNIZ) and [(Pr4N)2PbI4] (Geselle and Fuess, 1997) (CSD ref. code: GIYRIP). Chapter 2 Literature Survey 106 Figure 2.71: The anions and cations of [(Ph4P)2Pb2I6] (left), [(Pr4N)2PbI4] (middle) and [(Bu3N- (CH2)3-NBu3)PbI4] (right) that contain tetra-coordinated lead atoms. Larger lead(II) iodide clusters have also been reported, which consist of purely edge-sharing PbI6 octahedra, as in [(Bu4N)8Pb18I44] (Krautscheid and Vielsack, 1995) (CSD ref. code: ZETLIT). The [Pb18I44]8- anion is shown in Figure 2.72 below and has alternating Pb and I layers stacked on top of each other. Figure 2.72: The cluster anion [Pb18I44]8-. Chapter 2 Literature Survey 107 2.13: Summary and Conclusion The field of inorganic-organic hybrids exhibits a large range of inorganic motifs, from 3-D to 0- D. The 2-D layered perovskite-type motif has a rich literature of phase transitions when using alkylammonium chains and various optical and electronic properties for a variety of organic ammonium cations. Review articles that have touched on these phenomena include: Templating and structural engineering in organic-inorganic perovskites (Mitzi, 2001); Synthesis, Structure, and Properties of Organic-Inorganic Perovskites and Related Materials (Mitzi, 1999a), Organic- Inorganic Layer Compounds: Physical Properties and Chemical Reactions (Day, 1985) and Crystal Structures of Three New Copper(II) Halide Layered Perovskites: Structural, Crystallographic, and Magnetic Correlations (Willett et al, 1988). However, little SC-XRD work has been done on the phase transitions of the layered perovskite-type hybrids [(CnH2n+1NH3)2PbI4] (n = 4 - 18) and one of the objectives of this work is to determine the nature of the structural changes and compare them to the previously investigated phase transitions. A second objective is to investigate the changes in the crystal structures of the lead(II) halide inorganic-organic hybrids as a function of cation and halide identity, in other words, other possible structural motifs. Chapter 2 Literature Survey 108 Chapter 3 Experimental Methods 109 Chapter 3 Experimental Methods 3.1 Synthesis The major obstacles to overcome in preparing crystals suitable for characterization via SCX-RD of these inorganic-organic hybrids with a layered perovskite-type motif all relate to the different solubilities of the inorganic metal halide and the organic amine components. The synthesis of the layered perovskite-type hybrids with either a monoamine or diamine is given by the following reaction schemes: PbX2 + 2R-NH2 + 2HX ? (R-NH3)2PbX4 PbX2 + H2N-R-NH2 + 2HX ? (H3N-R-NH3)PbX4 Generally, the ratio of metal halide to monoamine to acid halide is 1 to 2 to 2. Generally, the two most successful techniques for growing crystals are solution growth (SG) and slow cooling (SC) (Arend et al, 1978). All compounds used were obtained commercially and used without further purification. Detailed information on the experimental preparation can be found in the chapters to follow. 3.1.1 Slow cooling Within this project, this technique proved to be the most successful in overcoming the differing solubility issue. The metal halide and amine are weighed out into a glass sample vial and 5 to 10 ml of the required acid halide is added. Generally, a precipitate would form that would not dissolve at room temperature even after being submersed in an ultrasound bath. The vial is then heated in an oil bath that is controlled by a programmable temperature controller (Fig. 3.1). The oil bath is heated to between 80 and 100?C, and then held constant at that temperature until all the precipitate dissolves (usually between 1 hr and 24 hrs). The sample vial is then sealed with its polytop lid and the height of the vial in the oil bath adjusted such that the vial is only immersed Chapter 3 Experimental Methods 110 up to the level of the solution inside the vial. This is to allow the vapour to condense in the upper half of the vial. Figure 3.1: The basic experimental setup used to grow crystals of the inorganic-organic hybrids. After the precipitate dissolves, the oil bath is cooled at a rate of 2?C/hr. Well-formed crystals generally appear during the cooling process (See Figure 3.2). Chapter 3 Experimental Methods 111 Figure 3.2: The pictures show the important stages of the slow cooling technique. An orange precipitate of the layered perovskite-type hybrid [(C8H17NH3)2PbI4] at room temperature slowly dissolves as the temperature of the solution increases to 100?C and then becomes a clear solution after a few hours. As the cooling takes place, orange plate-like crystals grow first at the surface of the solution and then at the bottom. Chapter 3 Experimental Methods 112 3.1.2 Slow evaporation If the precipitate does not dissolve after 24 hrs at an elevated temperature, then adding a suitable solvent to the vial until dissolution occurs is preferred. The procedure is then to use less of the acid halide, of the order of 1 to 2 ml as the acid halide dissolves the metal halide easily. The resulting precipitate then needs to be dissolved and a choice of solvents is available. These include methanol, ethanol, acetone, acetonitrile, DMF, water and ethyl acetate. The latter has been particularly useful in dissolving the long chain alkylammonium hybrids. The sample vial is left open to the atmosphere in a fume hood and crystals grow by the evaporation of the given solvent. 3.1.3 List of compounds prepared with corresponding chapter reference in this thesis Section 4.2 Chapter 3 Experimental Methods 113 Section 4.3 Section 4.4 Chapter 3 Experimental Methods 114 Section 4.5 Chapter 3 Experimental Methods 115 Section 4.6 Chapter 3 Experimental Methods 116 Section 4.7 Section 5.2 Chapter 3 Experimental Methods 117 Section 5.3 Section 5.4 Chapter 3 Experimental Methods 118 Chapter 6 Chapter 3 Experimental Methods 119 3.2 X-ray Diffraction Once crystals have been obtained and harvested, they are glued onto a thin glass fibre with 10 minute epoxy under a microscope (Figure 3.3). 3.2.1 Instruments used Redundant sets of diffraction data were collected on a Siemens SMART 1K Single Crystal Diffractometer (Figure 3.3). All the intensity data were collected initially at room temperature and then at -100?C to improve the quality of the data. The crystals were often plate-like and would fracture if they were cooled too rapidly. This is especially true of the layered perovskite- like hybrids with long alkylammonium chains, as they would fracture easily when cooled. To investigate the phase transitions of the layered perovskite-type hybrids with alkylammonium chains, the crystals had to be both cooled and heated simultaneously. A newer model of the SMART system, the Bruker APEX II, was fitted with an Oxford CRYOSTREAM 700 that is designed for operation in the temperature range of -150?C to 120?C (Figure 3.3). Chapter 3 Experimental Methods 120 Figure 3.3: The CCD instruments used. (a) Siemens SMART 1K with Kryoflex. (b) The Bruker APEX II with an Oxford Cryostream. (c) Close-up picture of the APEX II showing the centering video camera, CCD detector plate, collimator and heating tube. 3.2.2 Face-indexed absorption corrections A major problem encountered in SC-XRD with "heavy atoms" is absorption of the X-ray beams by the crystal, thereby reducing the intensity of the incoming and diffracted beam. The drop off in intensity of the diffracted beam I is given by I = I0e-??(?/?)? where I0 is the intensity of the incident beam, ? the thickness of the absorber and (?/?)? the mass absorption coefficient of the material (Stout and Jensen, 1989). The mass absorption coefficient is dependent on the wavelength used. Hence, the bigger the crystal and the greater the absorption Chapter 3 Experimental Methods 121 coefficient of the material, the greater the drop-off in intensity. A secondary problem is that the pathlengths of the incident and diffracted beam can vary considerably depending on the particular reflection and the shape of the crystal. For weakly absorbing crystals, such as those of purely organic molecules, that have a uniform size, the effect is not great and semi-empirical methods such as SADABS (Siemens, 1996) can address the problem satisfactorily. However, heavy atoms, such as lead and iodine, have large mass absorption coefficients, and semi-empirical methods proved inadequate. Analytical methods are used in these instances, which require the exact shape of the crystals. This is done by indexing the faces of the crystals and measuring the distances between the faces (Figure 3.4). Once the shape is known, programs such as XPREP2 (Bruker, 2003) can calculate the path lengths of the incident and diffracted beams through the crystal and correct for the decrease in intensity. For materials with a ? > 2 mm-1 (EUHEDRAL, http://www.crystal.chem.uu.nl/distr/euhedral/index.html), this is the recommended method. The range in ? for the inorganic-organic hybrids studied varied from 14.4 mm-1 to 21.7 mm-1. Furthermore, the shapes of the crystals studied in this project were often plate-like, with the thickness of the plates no more than 0.01 mm and the width in excess of 0.30 mm. Hence, depending on if the crystal is face-on or edge-on to the incident beam, large discrepancies in the diffracted intensities has to be corrected for. Chapter 3 Experimental Methods 122 Figure 3.4: Typical crystal shape of hybrid with the layered perovskite-type motif. 3.3 Thermal Analysis Differential Scanning Calorimetry was used to determine the transition temperatures of the phase transitions and their enthalpies. The device used was a Mettler Toledo 822e calorimeter, which was fitted with a cold finger to increase its range from -50?C to 400?C and further allows for controlled heating and cooling scans. This was sufficient to monitor all the phase transitions of the layered perovskite-type hybrids. 3.4 Elemental analysis Elemental analysis of all the compound was performed by the Institute of Soil, Climate and Weather (Pretoria, South Africa). The instrument used was a Carlo Erba Instruments, model NA 1500, Nitrogen/Carbon/Sulphur Analyser. The instrument was modified to do CHN elemental analyses as well (Philpott, 2002). Chapter 3 Experimental Methods 123 3.5 Hot Stage Microscopy The thermochromic phase transitions of the alkylammonium hybrids displayed colour changes and were easily observed by heating up the crystals to be determined on a hot plate under a microscope (Figure 3.5). Figure 3.5: Locally modified Koffler Hot Stage. Chapter 3 Experimental Methods 124 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 125 125 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 4.1 Introduction In this chapter I present the structures of 54 inorganic-organic hybrids that did not display any phase transitions. The essence of this chapter deals with the structural trends observed in the structure of the inorganic-organic hybrid as a function of the cation identity and the halide identity. Six separate investigations were carried out on various systems. Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 126 126 4.2 Synthesis and crystal structures of inorganic-organic hybrids incorporating an aromatic amine with a chiral functional group Journal: CrystEngComm Date Submitted: 17 May 2006 Reference Code of Submitted Article: B606987H Date Accepted: 7 July 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). CrystEngComm, 8, 686-695. Brief Synopsis In this paper, eight inorganic-organic hybrids were made using the metal lead and the halides chloride, bromide and iodide. The counter cations were the R, S and racemic forms of 1- phenethylammonium. The objective was to observe the inorganic motif obtained for various inorganic-organic hybrids. The work discussed in this paper was featured on the cover of the journal Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 127 127 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 128 128 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 129 129 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 130 130 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 131 131 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 132 132 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 133 133 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 134 134 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 135 135 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 136 136 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 137 137 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 138 138 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 139 139 4.3 Inorganic-organic hybrids incorporating a chiral cyclic ammonium cation Journal: CrystEngComm Date Submitted: Pending, before 30 April 2007 Reference Code of submitted article: Date Accepted: Final Reference: Brief Synopsis In this paper, eight inorganic-organic hybrids were made using the metal lead and the halides chloride, bromide and iodide. The counter cations were R, S and racemic forms of 1- cyclohexylethylammonium. This is a similar study to the one discussed in Chapter 4.2. Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 140 140 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 141 141 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 142 142 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 143 143 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 144 144 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 145 145 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 146 146 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 147 147 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 148 148 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 149 149 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 150 150 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 151 151 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 152 152 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 153 153 4.4 Inorganic-organic hybrid materials incorporating primary cyclic ammonium cations: The lead iodide series Journal: CrystEngComm Date Submitted: 17 May 2006 Reference Code of Submitted Article: B618196A Date Accepted: 19 December 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). CrystEngComm, 9, 236-244. Brief Synopsis In this paper, six hybrids were made using the metal lead and the halide iodide. The counter cations were six cyclic hydrocarbons with increasing ring size. The effect of the ring size on the inorganic motif was analyzed. Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 154 154 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 155 155 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 156 156 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 157 157 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 158 158 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 159 159 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 160 160 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 161 161 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 162 162 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 163 163 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 164 164 4.5 Inorganic-organic hybrid materials combining primary cyclic ammonium cations with bromoplumbate and chloroplumbate anions Journal: CrystEngComm Date Submitted: Pending, before 30 April 2007 Reference Code of Submitted Article: Date Accepted: Final Reference: Brief Synopsis This paper, presenting the structures of 12 inorganic-organic hybrids, is a continuation of the work started in Chapter 4.4. In this paper, the same metal and counter cations are used as in Chapter 4.4 but using the halides bromide and chloride instead. This paper discusses the trends observed in the bromide and chloride series and then summarizes the results together with the iodide series. Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 165 165 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 166 166 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 167 167 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 168 168 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 169 169 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 170 170 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 171 171 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 172 172 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 173 173 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 174 174 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 175 175 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 176 176 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 177 177 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 178 178 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 179 179 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 180 180 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 181 181 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 182 182 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 183 183 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 184 184 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 185 185 4.6 Effect of heteroatoms in the layered perovskite-type system [(XCnH2nNH3)2PbI4], n = 2, 3, 4, 5, 6; X = OH, Br and I; and [(H3NC2H4S2C2H4NH3)PbI4]. Journal: CrystEngComm Date Submitted: Pending, before 30 April 2007 Reference Code of submitted article: Date Accepted: Final Reference: Brief Synopsis In this paper, ten inorganic-organic hybrids were made, nine of which have the layered perovskite-type motif. The objective was to observe how the inorganic layered perovskite-type motif changes by changing the identity of the heteroatoms and the length of the alkylammonium chain within the hybrid structure. Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 186 186 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 187 187 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 188 188 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 189 189 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 190 190 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 191 191 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 192 192 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 193 193 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 194 194 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 195 195 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 196 196 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 197 197 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 198 198 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 199 199 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 200 200 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 201 201 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 202 202 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 203 203 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 204 204 4.7 Inorganic-organic hybrids incorporating diammonium cations Journal: CrystEngComm Date Submitted: Pending, before 30 April 2007 Reference Code of Submitted Article: Date Accepted: Final Reference: Brief Synopsis In this paper, nine inorganic-organic hybrids were made using the metal lead and the halides iodide and bromide. The counter cations were different alkyldiammonium chains. Some structural trends are discussed. Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 205 205 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 206 206 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 207 207 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 208 208 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 209 209 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 210 210 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 211 211 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 212 212 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 213 213 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 214 214 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 215 215 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 216 216 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 217 217 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 218 218 Chapter 4 Structural Motifs of Inorganic-Organic Hybrids 219 219 Chapter 5 Phase Transitions of Inorganic-Organic Layered Perovskite-type Hybrids 220 220 Chapter 5 Phase Transitions of Inorganic-Organic Layered Perovskite-type Hybrids 5.1 Introduction In this chapter I present the SC-XRD structures of 11 inorganic-organic hybrids that have the layered perovskite-type motif. The counter cations are simple alkylammonium chains with chain lengths from 4 carbon atoms to 18. All of the compounds display phase transitions. The essence of this chapter deals with the SC-XRD structures of the different phases and from this information, discussing the structural changes that undergo at the phase transitions. Chapter 5 Phase Transitions of Inorganic-Organic Layered Perovskite-type Hybrids 221 221 5.2 Synthesis, characterization and phase transitions in the inorganic-organic layered hybrids [(CnH2n+1NH3)2PbI4], n = 4, 5 and 6 Journal: Acta Crystallographica B, Structural Science Date Submitted: 23 February 2007 Reference Code of Submitted Article: BS5044 Date Accepted: Final Reference: Brief Synopsis In this paper, the phase transitions of the inorganic-organic layered perovskite-type hybrids [CnH2n+1NH3)2PbI4] (n = 4, 5 and 6) are presented. The techniques used were SC-XRD, DSC and Hot Stage Microscopy (HSM). Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 222 222 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 223 223 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 224 224 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 225 225 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 226 226 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 227 227 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 228 228 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 229 229 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 230 230 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 231 231 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 232 232 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 233 233 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 234 234 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 235 235 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 236 236 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 237 237 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 238 238 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 239 239 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 240 240 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 241 241 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 242 242 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 243 243 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 244 244 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 245 245 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 246 246 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 247 247 5.3 Synthesis, Characterisation and Phase Transitions of the inorganic-organic layered hybrids [(CnH2n+1NH3)2PbI4], n = 7, 8, 9 and 10 Journal: Crystal Growth and Design Date Submitted: Pending, before 30 April 2007 Reference Code of submitted article: Date Accepted: Final Reference: Brief Synopsis In this paper, the phase transitions of the inorganic-organic layered perovskite-type hybrids [CnH2n+1NH3)2PbI4] (n = 7, 8, 9 and 10) are presented. The techniques used were SC-XRD, DSC and Hot Stage Microscopy (HSM). Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 248 248 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 249 249 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 250 250 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 251 251 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 252 252 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 253 253 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 254 254 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 255 255 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 256 256 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 257 257 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 258 258 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 259 259 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 260 260 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 261 261 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 262 262 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 263 263 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 264 264 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 265 265 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 266 266 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 267 267 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 268 268 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 269 269 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 270 270 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 271 271 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 272 272 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 273 273 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 274 274 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 275 275 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 276 276 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 277 277 Chapter 5.4 Structural transitions of the inorganic-organic layered perovskite-type hybrids [(CnH2n+1NH3)2PbI4]; n = 12, 14, 16, 18 Journal: Dalton Transactions Date Submitted: Pending, before 30 April 2007 Reference Code of submitted article: Date Accepted: Final Reference: Brief Synopsis In this paper, the phase transitions of the inorganic-organic layered perovskite-type hybrids [CnH2n+1NH3)2PbI4] (n = 12, 14, 16 and 18) are presented. The techniques used were SC-XRD, DSC and Hot Stage Microscopy (HSM). Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 278 278 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 279 279 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 280 280 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 281 281 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 282 282 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 283 283 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 284 284 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 285 285 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 286 286 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 287 287 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 288 288 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 289 289 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 290 290 Chapter 5 Phase Transitions of Layered Perovskite-type Hybrids 291 291 Chapter 6 Miscellaneous Structures and Motifs 292 292 Chapter 6 Miscellaneous Structures and Motifs 293 293 Chapter 6 Miscellaneous Structures and Motifs 6.1 Introduction In this chapter I present the structures of 11 inorganic-organic hybrids that did not display any phase transitions. Chapter 4 consisted of the systematic studies of structural trends in the inorganic-organic hybrids. Those structures that did not fit together with the studies done in Chapter 4, except for those given in section 6.2 and 6.3 below, were published on their own in either Acta Crystallographica C or Acta Crystallographica E and these published articles are presented here. Chapter 6 Miscellaneous Structures and Motifs 294 294 Chapter 6 Miscellaneous Structures and Motifs 295 295 6.2 Bis[(S)-?-phenethylammonium] tribromoplumbate(II) Journal: Acta Crystallographica Section E, Structure Reports Online Date Submitted: 25 April 2003 Reference Code of Submitted Article: NA6231 Date Accepted: 19 May 2003 Final Reference: Billing, D.G., Lemmerer, A. (2003). Acta Cryst. E59, m381-m383. Brief Synopsis The inorganic-organic hybrid bis[(S)-?-phenethylammonium] tribromoplumbate(II) has 1-D chains of face-sharing PbBr6 octahedra. This compound is part of the structural study reported in Section 4.2. Chapter 6 Miscellaneous Structures and Motifs 296 296 Chapter 6 Miscellaneous Structures and Motifs 297 297 Chapter 6 Miscellaneous Structures and Motifs 298 298 Chapter 6 Miscellaneous Structures and Motifs 299 299 6.3 Bis(pentane-1,5-diammonium) decaiodotriplumbate(II) Journal: Acta Crystallographica Section C, Crystal Structure Communications Date Submitted: 9 March 2004 Reference Code of Submitted Article: FG1746 Date Accepted: 30 March 2004 Final Reference: Billing, D.G., Lemmerer, A. (2004). Acta Cryst. C60, m224-m226. Brief Synopsis The inorganic-organic hybrid bis(pentane-1,5-diammonium) decaiodotriplumbate(II) has 1-D chains of edge- and face-sharing PbI6 octahedra. This compound is part of the structural study reported in Section 4.7. Chapter 6 Miscellaneous Structures and Motifs 300 300 Chapter 6 Miscellaneous Structures and Motifs 301 301 Chapter 6 Miscellaneous Structures and Motifs 302 302 Chapter 6 Miscellaneous Structures and Motifs 303 303 6.4 p-phenylenediammonium tetraiodozincate(II) dihydrate Journal: Acta Crystallographica Section E, Structure Reports Online Date Submitted: 9 March 2006 Reference Code of Submitted Article: BT2029 Date Accepted: 10 March 2006 Final Reference: Lemmerer, A., Billing, D.G. (2006). Acta Cryst. E62, m779-m781. Brief Synopsis The inorganic-organic hybrid p-phenylenediammonium tetraiodozincate(II) dihydrate has isolated ZnI4 tetrahedra. This compound was part of preliminary work where as many different divalent metals with halide ligands where crystallized out with ammonium cations. Chapter 6 Miscellaneous Structures and Motifs 304 304 Chapter 6 Miscellaneous Structures and Motifs 305 305 Chapter 6 Miscellaneous Structures and Motifs 306 306 Chapter 6 Miscellaneous Structures and Motifs 307 307 6.5 1-Naphthylammonium triiodoplumbate(II) Journal: Acta Crystallographica Section E, Structure Reports Online Date Submitted: 24 March 2006 Reference Code of submitted article: BT2043 Date Accepted: 27 March 2006 Final Reference: Lemmerer, A., Billing, D.G. (2006). Acta Cryst. E62, m904-m906. Brief Synopsis The inorganic-organic hybrid (1-Naphthylammonium) triiodoplumbate(II) has 1-D chains of face-sharing PbI6 octahedra. Chapter 6 Miscellaneous Structures and Motifs 308 308 Chapter 6 Miscellaneous Structures and Motifs 309 309 Chapter 6 Miscellaneous Structures and Motifs 310 310 Chapter 6 Miscellaneous Structures and Motifs 311 311 6.6 catena-Poly[tetrakis(3-phenylpropylammonium) [iodoplumbate(II)-tri-?-iodo- plumbate(II)-tri-?-iodo-plumbate(II)-di-?-iodo]] Journal: Acta Crystallographica Section C, Crystal Structure Communications Date Submitted: 7 March 2006 Reference Code of Submitted Article: FG3008 Date Accepted: 10 March 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). Acta Cryst. C62, m174-m176 Brief Synopsis The inorganic-organic hybrid tetrakis(3-phenylpropylammonium) decaiodotriplumbate(II) has a 2-D net-type inorganic layer, built up from corner- and face-sharing PbI6 octahedra. Chapter 6 Miscellaneous Structures and Motifs 312 312 Chapter 6 Miscellaneous Structures and Motifs 313 313 Chapter 6 Miscellaneous Structures and Motifs 314 314 Chapter 6 Miscellaneous Structures and Motifs 315 315 6.7 Bis(propane-1,2-diammonium) hexaiodoplumbate(II) trihydrate Journal: Acta Crystallographica Section E, Structure Reports Online Date Submitted: 12 April 2006 Reference Code of Submitted Article: BT2054 Date Accepted: 18 April 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). Acta Cryst. E62, m1103-m1105. Brief Synopsis The inorganic-organic hybrid bis(propane-1,2-diammonium) hexaiodoplumbate(II) trihydrate has 0-D motif of isolated PbI6 octahedra. Chapter 6 Miscellaneous Structures and Motifs 316 316 Chapter 6 Miscellaneous Structures and Motifs 317 317 Chapter 6 Miscellaneous Structures and Motifs 318 318 Chapter 6 Miscellaneous Structures and Motifs 319 319 6.8 Octakis(3-propylammonium) octadecaiodopentaplumbate(II): a new layered structure based on layered perovskites Journal: Acta Crystallographica Section C, Crystal Structure Communications Date Submitted: 31 March 2006 Reference Code of Submitted Article: FG3016 Date Accepted: 20 April 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). Acta Cryst. C62, m238-m240. Brief Synopsis The inorganic-organic hybrid octakis(3-propylammonium) octadecaiodopentaplumbate(II) has a 2-D net-type inorganic layer motif that has not been observed before. The net-type layer is built up from corner- and face-sharing PbI6 octahedra. Chapter 6 Miscellaneous Structures and Motifs 320 320 Chapter 6 Miscellaneous Structures and Motifs 321 321 Chapter 6 Miscellaneous Structures and Motifs 322 322 Chapter 6 Miscellaneous Structures and Motifs 323 323 6.9 catena-Poly[bis(tert-butylammonium) [plumbate(II)-tri-?-iodo] iodide dihydrate] Journal: Acta Crystallographica Section C, Crystal Structure Communications Date Submitted: 24 April 2006 Reference Code of Submitted Article: GD3019 Date Accepted: 2 May 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). Acta Cryst. C62, m264-m266. Brief Synopsis The inorganic-organic hybrid bis(tert-butylammonium) triiodoplumbate(II) iodide dihydrate has 1-D chains of face-sharing PbI6 octahedra. This compound appeared on the cover of the June issue of Acta Crystallographica C. Chapter 6 Miscellaneous Structures and Motifs 324 324 Chapter 6 Miscellaneous Structures and Motifs 325 325 Chapter 6 Miscellaneous Structures and Motifs 326 326 Chapter 6 Miscellaneous Structures and Motifs 327 327 Chapter 6 Miscellaneous Structures and Motifs 328 328 6.10 Poly[bis[2-(1-cyclohexenyl)ethylammonium] di-?-iodo-diodoplumbate(II)] Journal: Acta Crystallographica Section C, Crystal Structure Communications Date Submitted: 20 March 2006 Reference Code of submitted article: TR3004 Date Accepted: 18 April 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). Acta Cryst. C62, m269-m271. Brief Synopsis The inorganic-organic hybrid bis(2-(1-cyclohexenyl)ethylammonium) tetraiodoplumbate(II) has a layered perovskite-type motif. Chapter 6 Miscellaneous Structures and Motifs 329 329 Chapter 6 Miscellaneous Structures and Motifs 330 330 Chapter 6 Miscellaneous Structures and Motifs 331 331 Chapter 6 Miscellaneous Structures and Motifs 332 332 6.11 Two packing motifs based upon chains of edge-sharing PbI6 octahedra Journal: Acta Crystallographica Section C, Crystal Structure Communications Date Submitted: 18 August 2006 Reference Code of Submitted Article: AV3041 Date Accepted: 27 September 2006 Final Reference: Billing, D.G., Lemmerer, A. (2006). Acta Cryst. C62, m597-m601. Brief Synopsis The inorganic-organic hybrids bis(p-phenylenediammonium)tetraiodoplumbate(II) and bis(3,5- dimethylanilinium)tetraiodoplumbate(II) have 1-D chains of edge-sharing PbI6 octahedra. These two compounds were the only inorganic-organic hybrids found in this work with that motif. Chapter 6 Miscellaneous Structures and Motifs 333 333 Chapter 6 Miscellaneous Structures and Motifs 334 334 Chapter 6 Miscellaneous Structures and Motifs 335 335 Chapter 6 Miscellaneous Structures and Motifs 336 336 Chapter 6 Miscellaneous Structures and Motifs 337 337 Chapter 6 Miscellaneous Structures and Motifs 338 338 Chapter 7 Conclusion 339 339 Chapter 7 Conclusion 7.1 Concluding remarks The synthesis and SC-XRD structures of 76 inorganic-organic lead(II) halide hybrids are described in this thesis. A diversity of inorganic motifs has been encountered, as listed in Table 8.1. Of the 76 hybrids, 47 hybrids have the layered perovskite-type motif with different organic ammonium countercations from alkyl chains to aromatics to various saturated hydrocarbons. All the layered perovskite-type hybrids with alkyl ammonium chains displayed reversible phase transitions as a function on temperature, as discussed in Chapter 5. The layered perovskite-type hybrids without alkyl chains displayed structural trends of the inorganic layers that depend on the size of the organic ammonium group and the identity of the halide atom, as discussed in Chapter 6. A simple way of describing the structural changes the inorganic layers and the ammonium cations undergo during the phase changes and the structural trends is using the acute and obtuse description of the position of the ammonium cations relative to the layers and the equilateral and right-angled description of the hydrogen bonding. These two descriptors are new and first reported in this thesis. Chapter 7 Conclusion 340 340 Table 7.1: Summary of the inorganic motifs of the 76 inorganic-organic hybrids that were made in this thesis. 2-D 1-D 0-D Section layered perovskite- type Other motif face- sharing edge- sharing corner- sharing Ribbon edge + corner 4.1 2 4 2 4.2 4 2 2 4.3 4 1 1 4.4 8 1 1 2 4.5 9 1 4.6 7 1 1 1 5.1 3 5.2 4 5.3 4 6.1-10 1 2 3 2 1 2 7.2 Future Work All the work reported here focused on the metal lead. A logical extension would be to repeat the study using the metal tin. Preliminary work done on the compound [(C6H13NH3)2SnI4] shows a phase transition below room temperature, somewhere between -30 and -40?C. This phase transition is similar as the phase transition from phase IV to phase III reported for [(C6H13NH3)2PbI4] in this thesis. Figure 8.1 shows how the inorganic layers change from a staggered arrangement at -30?C to an eclipsed arrangement at -55?C. The hexylammonium cation does not change its position relative to the layers (acute). 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