Increasing the efficacy of ligands is crucial to many industrial processes and products. The design of new organic reagents which might find applications in automotive lubrication and extractive metallurgy are reported. Force-field based molecular modelling has been used in chapters 2 and 3 to investigate the structure of complexes of malonic acids and benzohydroxamic acids formed on binding to iron(III) oxide surfaces for which both have shown high affinity. Models were constructed in which the ligands were docked to planes in the lepidocrocite crystal structure to simulate their interaction with steel engine surfaces. The Cambridge Structural Database has been used to elucidate the structures of polynuclear complexes of carboxylic acids to define appropriate geometries for malonate complex models. The most plausible modes of surface binding involving malonic acid were modelled to establish which would show the most favourable ligand-surface and ligand-ligand secondary bonding. Modelling of hydroxamate surface binding was guided by structural motifs observed in a mononuclear trishydroxamato iron(III) complexes in a dinuclear complex [Fe2L2(μ2L)2Br2] where LH = benzohydroxamic acid. The resulting model predicted the surface activity of a range of hydroxamic acid derivatives which have been confirmed by measurements of adsorption isotherms carried out on high surface area goethite. The structures of square planar copper(II) complexes of 3-substituted salicylaldoxime ligands which are closely related to systems used in industrial hydrometallurgical processes have been investigated (chapter 4) to ascertain whether there are correlations between the solid state structures and the relative strengths of the ligands as copper extractants. It was expected that electronegative groups would enhance hydrogen bonding between ligands, pulling them towards one another with a consequent decrease in the binding cavity presented by the donor atoms. In practice the structures were found to be influenced by interactions present in the solid state. In particular, axial interactions were found to influence the inner coordination sphere geometry and these were also investigated (chapter 5) using high pressure X-ray crystal structures. Contrary to expectation, application of pressure was found to increase axial bond lengths in order to improve molecular packing efficiency so that the cell volume could decrease.

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The static indentation hardness test has been applied to the study of the environment effects on hardness, plastic deformation, and fracture properties of silicon carbide crystals. Measurements of microhardness on the (0001) planes show that the hardness of silicon carbide is significantly lowered by water absorbed from the air. Upon annealing the crystals, at very high temperatures, the hardness is found to increase. A three-dimensional distribution of stress, beneath an indenter, has been evaluated using 'elastic equations'. The mechanics of crack initiation around the contact circle of a spherical indenter with the specimen has been analysed. The crack extension force, for a crack propagating downward from the surface of the specimen, has been evaluated. Evidence of plastic deformation by slip is provided by a number of indentations, specially those with the spherical and double-cone indenters. (1010) is the preferred slip plane.

A new technique has been developed for producing mono-crystalline foils of some alkali halides for transmission electron microscopy. The formation mechanism of the crystals has been investigated. The foils, which have two free faces have been used as electron transparent substrates to grow epitaxial films of gold, on one or both surfaces of the substrates. It has been shown that by covering the above foils with a thin layer of another alkali halide, bending contours suitable for measuring the thickness of the foils, are produced. A chamber has been designed and constructed for transporting the specimen from the preparation vacuum system into the electron microscope without exposing it to the atmosphere. The variation of pressure inside the chamber has been measured and some possible modifications have been suggested. The device has been used to study the nucleation and growth from the vapour phase of LiF, NaF, NaCl, KOI, KBj, KI and Rbl, on electron transparent substrates of mica and potassium chloride. The crystallographic and atomic orientations of the above materials with respect to atomic arrangement of the substrates have been studied. It has been shown that the alkali halides form continuous films at average thicknesses below 2.5 nm on substrates of mica and KCl. The effect of the heat treatment during and after growth of the films has been studied. The effects of atmospheric moisture on the overgrowths have been studied in detail, and it has been shown that there are some similarities between the effects of atmospheric moisture and the heat treatment on the hygroscopic alkali halides. It has been shown that when thin deposits of NaCl on the substrate of KCl are heated, diffusion or re-evaporation of the deposit does not occur randomly. The consequent possibility of the existence of periodic defect sites has been discussed. From a general consideration of the results it is concluded that (a) Chemical interactions are a dominant factor in the epitaxial growth of alkali halides on mica and KCl. (b) The alkali halides deposited from vapour consist of flat crystallites at the earliest stages of growth at room temperature.

A study of the subsolidus region of the BaO-La2O3-V 2O5 phase diagram has been carried out. Four ternary phases can be prepared, one of which has not been previously identified. The four ternary phases are a palmierite solid solution Ba3-3xLa2x V2O8, Ba2LaV3O11, BaLa10V4O26 (new phase) and Ba3La 40V12O93. Addition of BaLa10V 4O26 and the previously omitted phase La1.42V 0.58)3.58 to the ternary system has resulted n a re-determination of the complete phase diagram. A comprehensive study of the Ba3-3xLa 2xV2O8 solid solution has been carried out, employing a number of techniques including x-ray diffraction, infra-red spectroscopy, thermogravemetric analysis, impedance spectroscopy, electron paramagenetic resonance spectroscopy, inductively coupled plasma mass spectroscopy and x-ray absorption near edge structure spectroscopy. Conductivity measurements show the end-member Ba3V2O8 to be an oxide ion conductor, with the conduction mechanism being facilitated by the ease of transformation of the BaO3 layers to BaO2 and vice versa. The La-doped members show an increase in conductivity, with electrons becoming the dominant conducting species. The crystal structure of Ba2LaV 3O11 was confirmed to be isostructural with Ba2BiV 3O11. A full refinement of the structural parameters has been performed. The unit cell is primitive monoclinic, a = 12.44510(3)A, b = 7.78854(12)A, c = 11.26245(21)A and beta = 103.134(4)°, space group P21/c. Preliminary structural studies have begun on the new phase BaLa10V4O26. The x-ray powder pattern has been fully indexed and a possible monoclinic unit cell of a = 20.2939A, b = 5.886A, c = 12.6234A and beta = 118.05° is proposed. The serendipitous synthesis of a barium-deficient celsian phase, Ba0.8A11.6 Si2.4O8, is reported; the structure was solved using Patterson methods. The phase has a monoclinic unit cell with, a = 8.6090(8)A, b = 13.0858(12)A, c = 7.2047(7)A and beta = 115.418(2)°, space group C2/m.

A detailed electron microscopic study of the morphology and kinetics of crystallization of trans-1,4-polyisoprene with cis isoprene units varying from Of to 19.8 has been carried out. Two crystal structures of trans3., 4-polyisoprene (LIS and in p) were generally observed. In an unstrained film, lamellar single crystals which developed into hedrites, sheaves and spherulites of both crystal modifications were observed. The morphology attained was determined by the growth rate and the nucleation density of the crystals. Electron diffraction study suggests that the lamellar crystals have a chain-folded configuration. In a strained film, a row nucleation morphology was observed LIT and FIMP lamellar crystals were observed to nucleate from the same central 'backbones'. The row nucleation density of the lamellar crystals increases with strain. The growth habits of the lamellar crystals in, both strained and unstrained films were dependent on the film thinness, and on the proximity and the orientation of the neighbouring crystals. Models for the observed growth habits were discussed. The lamellar thickness data agrees with the kinetic theory of chain folding. The lamellar thickness of both crystal structures increases with decreasing degree of supercooling. The fold surface free energies estimated were 45.1 x 10-3 J/n2 and 60.1 x 10-3 J/m2 for the LIT and F ULF crystals of gotta percha respectively. The growth kinetics data of the lamellar crystals determined agrees with the existing theories of crystal growth. At the range of temperature from 400 to 560, the HMF crystal has a faster growth rate than the LMF crystallized at the same temperature. At the same degree of supercooling, the LMF crystal has a faster growth rate. The growth rates of both the LMF and HMF crystals decrease as the cis content on a trans polymer chain increases. With 66 cis units, the growth rate of the isomerized specimen decreased to a value of 1/6 to 1/8 of that for gutta percha (0f cis), whereas in cis-polyisoprene, the growth rate is retarded by 100 times with the inclusion of trans isoprene unit. This, difference in behaviour is discussed in terms of the possibility of including non-crystallizable units in the crystal lattice. The growth rate analysis showed the importance of determining the equilibrium melting temperature and glass transition temperature for each isomerized specimen to obtain meaningful estimates of

This thesis describes the synthesis and crystallisation of a selection of known and novel transition-metal – nitrite complexes and their detailed study using non-ambient X-ray diffraction techniques. These coordination compounds are specifically investigated for their ability to undergo nitro – nitrito linkage isomerisation in the single-crystal, with conversion between isomers achieved on either thermal- or photoactivation. The lifetime of the excited-state isomer is strongly dependent on the experimental temperature and, as such, this thesis is also concerned with time-resolved crystallographic methods. This work relies primarily on the technique of photocrystallography, a growing area of crystallographic research that has enjoyed considerable interest in recent decades. Chapter 1 reviews the seminal progress made in both time-resolved and photocrystallographic research, made possible by dramatic technological advances in the field in recent decades. Chapter 2 outlines the goals of this research project, aiming to obtain a more detailed understanding of the factors that influence the solid-state nitro – nitrito isomerisation. Chapter 3 describes the X-ray methods used in these studies, introducing both fundamental crystallographic principles and detailing the experimental procedures that are undertaken. Chapters 4 and 5 record steady-state photocrystallographic studies conducted for a series of complexes containing bulky, chelating ancillary ligands accompanying a monodentate nitrite group expected to be capable of nitro – nitrito isomerism. The response of these systems to both thermal- and photoactivation is investigated via single-crystal diffraction methods. The analysis focusses on the potential steric and electronic influences from the surrounding crystalline environment, which may have an impact on the progress of the solid-state reaction. Chapter 6 introduces photocystallographic kinetic methods to investigate the progress of nitro – nitrito conversion in real time. These studies are the first of their kind to be conducted on nitrite linkage isomer species and some novel methodology is introduced. Finally, Chapter 7 discusses pseudo-steady-state and trial time-resolved experiments conducted using the new time-resolved diffraction set-up on Beamline I19 at the Diamond Light Source. These early results indicate the power of time-resolved methods for elucidating key information on the nitro – nitrito conversion process and show promise for future experiments.