Both mefenamic acid (MA) and tolfenamic acid (TA) are polymorphic with three and five forms respectively. MA and TA are structurally similar molecules that differ in the replacement of a methyl on MA with a chloro group on TA. This thesis uses a joint computational and experimental approach to investigate the polymorphism of MA and TA and explores differences in the packings upon chloro-methyl replacement. To compliment an earlier crystal structure prediction (CSP) study on TA, the crystal energy landscape of MA was computed. Analysis showed there were a number of predicted structures that were competitive in energy with the known forms of MA. Isostructural relationships between MA and TA that were identified from the observed polymorphs and the predicted forms from the CSP studies were investigated in a range of templating experiments. The isostructural, not isomorphous, relationship between MA I and TA IV was explored and a solid solution series, isomorphous with MA form I, was obtained from ethanol and characterised by low temperature single crystal X-ray diffraction (SCXRD). Seeding an ethanol solution of TA with MA form I seeds nucleated a new polymorph of TA (VI) that was characterised by SCXRD and was isomorphous with MA form I. A second new form of TA (VII) was discovered, and identified by powder X-ray diffraction, when exploring the sublimation of TA onto a copper surface. Thermal analysis showed that TA VII transformed to TA I upon heating. Using a similar sublimation procedure, it was observed that if MA was sublimed onto copper, form I was obtained, yet if MA was sublimed onto glass, form II was obtained. The CSP methodology was tested by participation in the CCDC blind test and was successful in predicting the observed crystal structure of the cocrystal XXV as the global minimum.

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Acoustic transducers operate using polycrystalline lead zirconate titanate (PZT) since the 1950s’. Recently, relaxor-lead titanate (relaxor-PT) single crystals have been developed and exhibit up to 650% higher piezoelectric charge coefficient and up to 50% higher electromechanical coupling factor, compared with PZT. Transducers built with relaxor-PT crystals show increased bandwidth, lower power consumption and increased sensitivity. Despite the significant advantages over PZT, a growth method for relaxor-PT single crystals that is both economical and able to produce homogeneous, highly dense crystals is yet to be found. Furthermore, one of the most important relaxor-PT solid solution is Mn modified Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3- PbTiO3 due to its thermal stability and low electrical and mechanical losses compared with other relaxor-PT solid solutions. However, the behaviour of Mn in this compound is not fully understood and control of properties, such as the mechanical quality factor, is difficult. The aim of this study was to compare Bridgman and Solid State techniques for growth of single crystalline Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3. Subsequent to this, several Mn modified compositions were designed and investigated to determine the mechanisms by which mechanical and electrical losses are lowered upon Mn incorporation. Bridgman experiments have shown that a 20 mm ø x 60 mm length and highly dense single crystal can be obtained, with (011) the natural growth direction. Seeded Bridgman was also investigated as a method of controlling the orientation of the grown crystal, but was proven challenging due to nucleation of several crystallites. Solid State experiments, which involve attaching a single crystal seed to a polycrystalline matrix and promoting boundary migration of the seed into the matrix, showed that crystal growth is encouraged when a Pb-based interlayer exists in between the seed and matrix. An epitaxially deposited, uniform thin film as interlayer was found particularly beneficial. More research is needed to determine conditions for growth of a single crystal of useful size by Solid State. Analysis of several relaxorPT compositions modified with the same amount of Mn revealed that alterations of the relaxor-PT formulation affects behaviour of the multi-valent Mn which in turn in- fluences electromechanical properties. These findings are of use to the industrial and scientific communities. Crystal growth results indicate Bridgman as suitable method if growth of crystals is desired in a short time frame, whilst Solid State results provide the basis of a new approach for growing relaxor-PT crystals. The study of Mn modified compositions provides new insights into the role of Mn substitution for manipulating the electrical and mechanical properties of complex, relaxor-PT solid solutions.

Crystallographic disorder is common in the solid state but it is rarely investigated explicitly despite having a fundamental impact on the solid-state structure of a material. In this work, nuclear magnetic resonance (NMR) crystallography methods are utilised to achieve a detailed understanding of the structure and dynamics of solid organic systems containing disorder. Several new cocrystal systems are studied, each containing a topical drug molecule (caffeine, naproxen or furosemide) and each serving to demonstrate how NMR crystallography can be applied to a variety of structural questions. Hydrogen bonding motifs are identified using single crystal X-ray diffraction experiments, where possible, and are subsequently verified by solid-state NMR. Alternative hydrogen bonding models are ruled out by comparison of experimental solid-state NMR data with density functional theory calculated shieldings, and proton transfer can be investigated by monitoring the energy of the system with respect to proton position. In a particularly challenging case, 2D solid-state NMR experiments go some way to identify the hydrogen bonds in a system that cannot be crystallised. Dynamic disorder of fragments and solvent molecules are characterised by variable temperature solid-state NMR, including analysis of relaxation times to establish energy barriers and rates of motion. A mechanism of motion is also proposed for dynamic acetone molecules in a new cocrystal solvate, which is supported by good agreement between experimental and simulated 2H static NMR line shapes. Finally, the current limit of NMR crystallography is identified with respect to the reproducibility of calculated NMR parameters following geometry optimisation. It is shown that the geometry optimisation protocol does not affect standard NMR crystallography investigations pertaining to atom assignment, but it is significant for cases where very subtle structural features are probed, such as NMR linewidths. Overall, NMR crystallography investigations allow a deeper understanding of solid materials to be achieved than would be possible with any single technique and this work highlights the applicability of such methods to complex materials containing disorder.

This work has two principal sections. The first section is a study of the hydrogen bonding in a series of urea inclusion compounds, utilising neutron diffraction methods and a novel technique for growing neutron diffraction-suitable single crystals. The second section focusses on high pressure crystallography as a technique for exploring polymorphic landscapes, of a series of acid-base co-crystals, and the well-known active pharmaceutical ingredient 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY). Single crystal neutron structures at several temperatures have been determined for -phase urea inclusion compounds containing hexadecane, 1,6-dibromohexane and 2,7-octanedione guests. The neutron structure of the ‘partial channel’ co-crystal of urea and DMF is also reported. This includes an in-depth discussion and analysis of the structure and bonding of this urea series, in particular, how the guest compound affects the symmetry and hydrogen bonding of the host urea network. Additionally, the challenge of obtaining crystals suitable for neutron diffraction is addressed and a new heating/cooling device to aid crystallisation is presented. Pyridine and formic acid have been crystallised at differing ratios by both cryo-crystallisation and compression in a diamond anvil cell. Mixtures of the liquids in 1:1, 1:2 and 1:4 ratios all crystallise at high pressure, while only the 1:1 and 1:4 compositions were crystallised by in situ low temperature capillary crystallisation. The 1:2 structure crystallised by high pressure is a previously unknown co-crystal of pyridine - formic acid. For the 1:4 mixture, a new polymorph has been identified at a pressure of 14.2 kbar with a distinctly different structure and bonding pattern to that of the previously reported low temperature form. Five new co-crystals of 2,6-dimethylpyridine (DMP) with formic acid (FA) were crystallised by application of pressure in a diamond anvil cell and by in situ cryo-crystallisation. Mixtures in ratios 1:1, 1:2 and 1:3 of DMP: FA have been crystallised via both methods. Both the 1:2 and 1:3 co-crystals exhibit high pressure/low temperature polymorphism. ROY has been crystallised from acetone solution using a diamond anvil cell. The needle-like form obtained, named ONP shows similarities with the ORP, ON and Y forms, determined by Raman spectroscopy. The ONP crystals were recovered from the pressure cell by freezing with liquid nitrogen. Synchrotron X-ray data were collected on the sample, although no structure solution and refinement was possible. The unit cell of the ONP shows a crystallographic relationship to the ORP form.

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General crystallographic investigations have been carried out on the complexes of dihalogeno-(N,N,N',N'-tetramethylethylenediamine) M(II) ((TMED)MX2), where M = Zn, Cd or Hg and X = C1, Br or I. All except TMEDZnI2 crystallize in the space group P21/c. TMEDZnI2 crystallizes in space group C2/c. Three complexes viz. TMEDZnC12, TMEDCdBr2 and TMEDZnI2 were chosen for detailed crystallographic investigations. The crystal and molecular structure of all three have been determined. The crystals of TMEDZnC12 belong to the monoclinic system: P21/c, a = 7.716(3), b = 13.335(9), c = 11.545(5)A, beta = 105.59(6)° and Z = 4. The structure was solved by Fourier methods and refined by full-matrix least squares to a final R (conventional) of 6.7%. Anisotropic thermal parameters were evaluated for the non-hydrogen atoms but the hydrogen atoms were assigned the isotropic thermal parameters of the carbon atom to which they were bonded. The geometry around the zinc atom is distorted tetrahedral, with the Zn - C1 and Zn - N average bond lengths of 2.207(4) and 2.08(1)A respectively. TMEDCdBr2 crystallizes in the monoclinic system: P21/c, a = 7.532(2), b = 10.689(6), c = 14.674(7)A, beta = 91.91(7)° and Z = 4. The structure was solved by Fourier methods and refined by full-matrix least squares to a final R 6.1%. Each cadmium atom is octahedrally co-ordinated by two pairs of bromine atoms, giving average Cd - Br bond lengths of 2.753(2) and 2.844(2)A and a pair of nitrogen atoms in the cis configuration with an average Cd - N bond length of 2.46(1)A. The average Br - Cd - Br and N - Cd - Br angles are 88.1 and 90.6° respectively. The bromine atoms provide bridges to the metal atoms and form a structure consisting of infinite chains with the chain direction approximately parallel to the x-axis The crystals of TMEDZnI2 are monoclinic: C2/c, a = 13.118(8), b = 7.811(5), c = 13.566(8)A, beta = 111.39(4)° and Z - 4. The zinc and the nitrogen atoms have tetrahedral configurations. The molecule possesses crystallographic two-fold symmetry, the diad axis passing through the C - C bond of the TMED-ring. The mercury and zinc complexes have tetrahedral geometry in general and the cadmium complexes have octahedral geometry.

X-ray line broadening techniques were used to investigate the deformation characteristics of various hard materials. A detailed comparison of the Warren-Averbach, variance and integral breadth methods of analysing a broadened X-ray diffraction peak showed that they give comparable results. The effect of temperature on the deformation characteristics of materials with different types of chemical bonding was investigated. Ionic and covalent bonds are extreme examples of the same type of bond, and in materials with these bond types it was found that the amount of covalency in the bond governed the microplastic behaviour. The behaviour of the transition metal carbides was less predictable on account of their complicated mixture of metallic, ionic and covalent bonding. Studies on tungsten carbide powders showed that considerable deformation was induced by ball milling. The deformation could be relieved by annealing. Deformation stacking faults, involving slip on the basal plane, were observed. Studies on the worn surfaces of sintered blocks and single crystals revealed plastic deformation that extended to a depth of several microns below the surface. Hafnium carbide showed a marked anisotropic behaviour when deformed. The deformation could be annealed out by recovery and recrystallisation processes as in metals. The hafnium carbide lattice was found to be remarkably stable at high temperatures compared with other transition metal carbides. Studies on the polymorphic refractory oxide, zirconia, showed that tetragonal zirconia was formed from monoclinic zirconia when the particle size was made sufficiently small by ball milling. The transformation normally occurs above 1000°C. Calculations showed that tetragonal zirconia formed by milling, or by thermal decomposition, is stable at room temperatures mainly because of its small particle size and resultant high free surface energy.