The work described in this dissertation is concerned with structural aspects of the chemistry of transition metal cluster compounds, in particular with carbonyl clusters of the second and third transition series. The structures of a range of these complexes have been investigated, in the solid state, by single-crystal X-ray diffraction techniques, and in the solid and in solution, to a limited extent, by EXAFS spectroscopy. In Chapter One the basics of the single-crystal X-ray diffraction technique for determining the crystal and molecular structure of compounds in the solid state is described. The various steps of sample preparation, data collection, structure solution and refinement are discussed. Chapter Two is a review of the known structural chemistry of heterometallic cluster complexes which contain gold, or gold - phosphine units coordinated to the rest of the metal framework. The majority of complexes discussed in subsequent chapters are of this type. Simple 'electron counting' schemes which have been used to rationalise the structures of this class of compound are discussed critically. Chapter Three is divided up into five sections, each of which is concerned with a different class of heterometallic cluster containing an AuPR<SUB>3</SUB> unit as a ligand. In section 1, the structure of [Os<SUB>3</SUB>(CO)<SUB>10</SUB>(AuPPh<SUB>3</SUB>)Cl], in which the Au atom bridges an Os-Os edge of the Os<SUB>3</SUB> triangle, is described. In section 2, the structures of [HOs<SUB>3</SUB>Co(CO)<SUB>13</SUB>], [Os<SUB>3</SUB>Co(CO)<SUB>13</SUB>(AuPPh<SUB>3</SUB>)], and [HOs<SUB>3</SUB>Ru(CO)<SUB>13</SUB>(AuPEt<SUB>3</SUB>)] are described, and comment is made on the structural changes which occur when a bridging hydride ligand is replaced by a bridging AuPR<SUB>3</SUB> group. In section 3 the structures of [Os<SUB>4</SUB>(CO)<SUB>13</SUB>(AuPEt<SUB>3</SUB>)], [Os<SUB>4</SUB>(CO)<SUB>12</SUB>(AuPPh<SUB>2</SUB>Me)<SUB>2</SUB>], and [Os<SUB>4</SUB>(CO)<SUB>12</SUB>(AuAsPPh<SUB>3</SUB>)<SUB>2</SUB>] are described, and a change in geometry is noted when a CO ligand is removed from the former complex and the level of unsaturation formally increased. In section 4 the structures of [Ru<SUB>5</SUB>C(CO)<SUB>14</SUB>(AuPEt<SUB>3</SUB>)<SUB>2</SUB>] and [Os<SUB>6</SUB>(CO)<SUB>18</SUB>P(AuPPh<SUB>3</SUB>)] are discussed. Both these clusters contain an interstitial atom which modifies the structural chemistry. Section 5 contains a description of the structures of [Os<SUB>6</SUB>(CO)<SUB>16 lbrace</SUB>P(OMe)<SUB>3 rbrace</SUB> (AuPEt<SUB>4</SUB>)<SUB>2</SUB>] and [Os<SUB>6</SUB>C(CO)<SUB>20</SUB>(OMe)Au]. The Os atom framework in these clusters is contrasted with a number of hexaosmium systems which do not contain gold. The structures of two hexaosmium 'raft' clusters, [Os<SUB>6</SUB>O(CO)<SUB>18</SUB>(PPh<SUB>3</SUB>)] and [H<SUB>2</SUB>Os<SUB>6</SUB>(CO)<SUB>18</SUB>(PPh)] are described in Chapter Four. The effect of the introduction of the capping O atom and the PPh group on to the previously planar metal system is discussed, and is related to molecular orbital calculations on the systems. In Chapter Five the introduction of heavy, main group metal atoms into a transition metal cluster system is discussed, with reference to the structures of [H<SUB>3</SUB>BiRu<SUB>3</SUB>(CO)<SUB>9</SUB>], [Bi<SUB>2</SUB>Os<SUB>3</SUB>(CO)<SUB>9</SUB>], and [Bi<SUB>2</SUB>Ru<SUB>4</SUB>(CO)<SUB>12</SUB>]. Both steric and electronic effects are shown to be of importance. Finally, in Chapter Six, the technique of EXAFS spectroscopy is described. The limitations of the technique when applied to transition metal cluster systems are discussed with reference to data obtained from two pentaosmium cluster complexes.

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The work presented in this thesis involves the study of a number of non-framework species in zeolites. In particular, nickel has been selected as an interesting non-framework species to study because it may be present either as charge-balancing cations interacting with the zeolite framework oxygens, or as metallic nickel clusters or particles, both in the zeolite cavities or on the outer surfaces of the zeolite particles. Temperature-programmed reduction studies have shown the influence of factors such as zeolite structure, Si/Al ratio, nature of the cocation, preparation and dehydration conditions and various modifying treatments on the ease of reduction of the nickel cations. Transmission electron microscope studies of these reduced samples have revealed the influence of such factors on the particle sizes, particle-size distributions and the sintering of the metallic nickel particles. The location of the nickel cations in the dehydrated zeolites have been determined using x-ray powder Rietveld refinement of data collected at temperatures of 400<SUP>o</SUP>C or higher in an environmental high-temperature cell. The sample preparation conditions and various modification procedures are found to significantly influence the distribution of cations amongst the available sites in the zeolite. <i>In situ</i> reduction studies have been carried out in the high-temperature environmental cell. X-ray diffraction data collected at high temperatures during reduction allows one to follow the changes in cation locations and the growth of metallic nickel particles, and to compare reducibility of nickel in samples subjected to different modification treatments. X-ray powder Rietveld refinement of data collected from the finally reduced samples has been used to locate cations after reduction; comparison with cation locations determined in samples prior to reduction help to confirm the assignment of scattering at a particular site to a given cation, and give information on the relative ease of reduction of nickel cations in different sites. Finally, some preliminary work has been carried out on a different type of non-framework species, namely sorbed organic molecules. Some infra-red studies, heat of adsorption measurements and neutron diffraction studies of zeolite-sorbate systems are discussed.

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