The quantification procedures applied to raw SIMS data were devised on the basis of a simple model for the sputtering and ionisation that occur during measurement. The model and the associated quantification procedures have long been known to be inaccurate. If SIMS is to remain a useful analysis tool in the future, the quantification procedures must be adjusted such that current features of interest are accurately measured. This thesis describes the development of a more accurate (though empirical) model for the effects of the analysis, using the convolution integral. We propose a method for the quantification of SIMS depth profiles appropriate to this model, using Maximum Entropy (MaxEnt) reconstruction. SIMS depth profile data differ significantly from previous applications of the MaxEnt method: the very high signal to background ratio of the technique has lead users to plot the results on a logarithmic axis, giving much importance to extremely small signals. The noise on SIMS depth profiles has been characterised. A number of optimisation algorithms have been developed and tested, and the performance of the MaxEnt method on SIMS data has been assessed. A novel form of the entropy, particularly suited to SIMS depth profiles, has been suggested. This form has given excellent results.

The work recorded in this thesis can be divided into three sections. The first section (chapter three) is concerned with essentially weak H-bonded anions of the type XH(02CR)-, where X- is a group 7 halide ion, and R is H, CH3, CF3 or CHC12. The IR spectrum of each of the se anions has been examined and complete assignments have been made in most cases. The relationships which exist in the series, whichare a direct result of their chemical similarities, are discussed in terms of the pKa values of the acid and base concerned. The second section (chapter four) deals with Type B hydrogen dicarboxylate salts of acetic acid and its halogenated derivatives. Their IR spectra have been examined at the temperature of liquid nitrogen and assignments have been made. The importance of low isotopic shifts is discussed and used as evidence for asymmetry in the potential energy surface of the proton. Secondary evidence from other techniques, viz. NQR, inelastic neutron scattering, Raman and Far IR spectroscopy, has been obtained which parallels and mconfirms the results from IR spectroscopy. Type A salts, which are thought to be examples of symmetric H-bonds, have been examined by the same techniques which were used for Type B salts. In particular their IR spectra have been examined and assigned for the first time. Attention is drawn to the low frequency of~OH and~OD, and to its high isotopic shift. The IR spectrum of Potassium hydrogen diaspirinate has been recorded, but not analysed in detail, and it is clear that it is similar to the much simpler IR spectrum of the Type A salts prepared in this work. The latter example represents a case where very recent and accurate neutron diffraction data is available and where it was suggested that ~OH is below l000cm. This evidence, together with work on Type A and B salts, has led to an idea of the shape of the potential energy well for the proton and deuterium in Type A salts which is based on a symmetric double minimum. A similar situation is suggested for the proposed symmetric cases of HC12-, and the differences from the HF2- system is made apparent in the text.

The objective of the work presented in this thesis is to apply advanced high-resolution solid-state NMR methods for the structural characterisation of organic crystalline systems, specifically active pharmaceutical ingredients (APIs). The determination of the crystal packing is an important stage in the development of new APIs, and solid-state magic angle spinning (MAS) NMR is well suited to complement existing techniques. Improvements in spectral resolution in recent years have led to the development of homonuclear correlation experiments capable of identifying intermolecular proximities between 1H nuclei. These experiments provide a powerful probe of the local environment of each 1H nucleus in the three-dimensional structure, and the majority of the research presented in this thesis is focussed on the development of detailed analysis methods that may be used to extract more detailed structural information from 2D solid-state NMR correlation spectra. Throughout this thesis, experimental solid-state NMR results are analysed alongside computational data, including density matrix simulations of experiments and first principles calculations of shielding tensors. The results of simulations of a 1H DQ (double-quantum) correlation experiment are compared to experiment, in order to investigate the dependence of the DQ build-up (change in peak intensity as a function of the recoupling pulse duration) on the precise nature of the dipolar coupled proton network. It is found (for a simple dipeptide) that quantitative information on the relative H{H distance may be obtained by comparison of the maximum intensity reached in the corresponding 1H DQ build-up curves. This method is then applied to pharmaceutically relevant systems. It is shown that differences between two polymorphs of an API may be identified in the 1H DQ build-up of particular peaks, and, following the analysis for the dipeptide, this difference may be ascribed to differences in specific intermolecular distances. In the study of a second API, -indomethacin, it is shown that the standard 1H DQ experiment provides insufficient resolution to identify specific DQ peaks. A recently developed 1H(DQ){13C correlation experiment is used to exploit the higher resolution in the 13C dimension, hence allowing the extraction of DQ build-up curves which may be used, in conjunction with simulations, to obtain structural data. Finally, a recently discovered polymorph of the API ibuprofen is studied using 13C CPMAS (cross polarisation) solid-state NMR. Through the use of first-principles calculations, the 13C spectra of both the well known and new polymorphs are assigned, and the conversion of an amorphous solid to the new polymorph is monitored through the use of temperature-controlled solid-state NMR experiments.

Structural aspects of three related binary oxide glass systems have been studied in detail using a combination of neutron and x-ray diffraction, empirical modelling techniques, and information from bulk property and spectroscopic measurements. The local Pb2+ environment in PbO SiO2 glasses changes only subtly with composition, having, on average 3.33 short (2:70 Å) and 1.3 long (2.70 &lt; rPbO &lt; 3:27 Å) Pb- O bonds at 35 mol% PbO, and 3.57 short and 1.3(2) long Pb-O bonds at 80 mol% PbO. Therefore, over the entire series, lead behaves as a glass network forming cation, with highly asymmetric ligand distribution and stereochemically active electron lone-pair (LP), with gradual transition toward more axially symmetric environments (cf. crystalline PbO) as the PbO content increases. Structural modelling of the highest lead content oxide glass (80 PbO < 20 SiO2) to date reveals organisation of LPs to form voids, analogous to interlayer spaces in crystalline PbO polymorphs, and channels found within other crystalline lead oxide compounds such as Pb11Si3O17. The plumbite glass network is characterised by a high degree of intermediate-range ordering, evidenced by a very narrow first sharp diffraction peak (FSDP), as well as significant edge-sharing of Pb polyhedra and high oxygen-cation coordination numbers, e.g. [OPb4], [OPb3Si]. PbOGeO2 glass formation was found as high as 75 mol% PbO using rapid twinroller quenching. Such high lead glasses are analogues of the silicates, but with a 10% enhancement in correlation length derived from the FSDP. In the low PbO region a broad maximum in Ge-O coordination number of nGeO = 4:14(3) at 26:5(5) mol% PbO was observed. This is much smaller, and at higher metal oxide content than in Na, K and Cs germanate glasses and contradicts published results [N. Umesaki et al., Physica B 213, (1995), 490]. The weakness of the effect is attributed to Pb2+ playing a predominantly network forming role, although Ge-O and Pb-O coordination numbers showed positive correlation, such that the presence of [GeO5] or [GeO6] is indicative of Pb having some ‘modifying’ character. It was argued, based on empirical models and the known crystal chemistry, that Pb may occupy sites of intermediate character, with mixed s-p LP character, rather than invoking a bimodal distribution of network forming and modifying Pb sites. Homogeneous calcium germanate glasses were obtained in the region 21 to 41 mol% CaO by rapid twin-roller quenching, with glass-in-glass phase separation occuring in the low CaO region, and crystallisation around the CaGeO3 composition. A very broad maximum of nGeO = 4:30(3) at 28:0(5) mol% CaO was observed, correlating approximately with maxima in atomic number densities and glass transition temperatures. Nonbridging oxygen (NBO) are present in all glasses, again in contrast to alkali germanates. The position of the maximum is attributed to stabilisation of vertex sharing [GeOm>4] and/or [GeO6] units by divalent Ca2+. The presence of NBOs is related to the Ca-O coordination number of 7, with higher nGeO and less NBO predicted in Sr and Ba germanate glasses, where M-O coordination is expected to be larger. In both Ca and Pb germanate systems, the equilibrium crystals have much larger nGeO than the glasses, and this implies a decrease of nGeO with liquid, supercooled liquid and glass fictive temperatures. This tentative conclusion is supported by measurements on two 40 PbO 60 GeO2 glasses with different thermal histories.

Current methods of nuclear waste disposal are not suitable for the immobilisation of novel defence-based waste due to the high halogen content resulting from pyrochemical reprocessing. The objective of this thesis was to investigate β-tricalcium phosphate (β- TCP, Ca3(PO4)2) encapsulated in a sodium aluminoborophosphate glass (NABP) matrix as a potential host for this waste using a variety of structural probes. Samples were prepared to determine the structural changes in β-TCP as components of the simulated waste streams were substituted into the material. Zn, Mg, Al, and Ga incorporation was investigated. A combination of X-ray and neutron diffraction was used to determine the changes in long-range order as a function of Zn and Mg substitution up to 13% and 25% cation substitution respectively. Both Zn and Mg substitution caused a contraction of the unit cell up to complete substitution of the Ca(5) site, at which point the contraction ceased. Under further substitution on the Ca(4) site, the a lattice parameter continued to decrease, while the c lattice parameter increased, resulting in an unchanged unit cell volume. Evidence of tricalcium trimagnesium phosphate second phase was observed for the Mg-based compositions above Ca2:8Mg0:2(PO4)2, as has been previously documented, however single phase samples were observed for all Zn-based compositions, in contrast to previous studies. 31P NMR was used to confirm this Ca(5)-Ca(4) substitution model for the Zn-based β-TCP compositions by tightly constrained simulations as a function of composition. A combination of solid-state NMR techniques were used to identify the substitution mechanism of Al and Ga in β-TCP up to the composition Ca9M(PO4)7, where M is Al or Ga respectively. The 31P and 43Ca NMR spectra were simulated as with the divalent cations mentioned above to determine the origin of each resonance in the spectra. Subsequently, 27Al-f31Pg and 71Ga-f31Pg R3-HMQC experiments were performed to explicitly identify substitution on the Ca(5) site only. Studies were also performed to model the NABP:β-TCP interface formed as a result of the encapsulation process, for both pure β-TCP and Ga-substituted β-TCP. To simulate the range of compositions expected at this interface, calcium phosphate and NABP preparations were mixed in proportions from 10 wt:% to 80 wt:% (Ga-substituted) β- TCP. 31P NMR and Raman spectroscopy showed a progressive depolymerisation of the phosphorus network, consistent with the replacement of Al3+ and Na+ with Ca2+. The Al3+ was shown to exist primarily in a 4 coordinated state, showing a tendency to exist within the phosphorus network, whereas 11B NMR showed the B to move from a 4 coordinated site in NABP to a B-rich 3 coordinated environment. Differential thermal analysis showed an increase in the temperature of the two recrystallisation events as a function of both β-TCP and Ga-substituted β-TCP. Studies of the phases present after recrystallisation of the pure β-TCP-based samples showed calcium sodium phosphate and Na Al co-substituted β-TCP for the lower and higher crystallisation temperatures with β-TCP incorporation. For the Ga-containing samples, Na Al Ga co-substituted β-TCP was observed for both crystallisation temperatures. Critically, Ga was shown to displace Al in the β-TCP phase.

Organic photovoltaics (OPVs) have huge potential for competing with current inorganic photovoltaics in the search for a reliable, renewable source of energy. It is thought that only ~10 % efficiency is necessary for commercialisation and also allows avenues towards flexible, compact, lightweight optoelectronics, with current certified efficiencies already at 12%! Although the current efficiencies have surpassed expectations in order to continue the high progress new materials need to be investigated. Through understanding current materials and utilising new donor and acceptor materials the hopes of achieving higher efficiencies are realistic. Halogenation as a method to modify current organic semiconductors materials has successfully been demonstrated with minimal change to the optical properties. Successful modification of copper phthalocyanines (CuPc) to the fluorinated F16 CuPc derivative resulted in a large change in ionisation potential allowing for its use as an acceptor. This thesis will discuss the modification of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPSEpent) via chlorination in the hopes of achieving a more efficient donor material in single heterojunction devices. Through addition of electron withdrawing groups, the molecular frontier orbitals can be tuned to allow for improved stability towards C60 in solution, larger ionisation potentials which allow for larger interface gaps when used in devices, resulting in improvements in open circuit voltage (Voc), short circuit current (Jsc) and power conversion efficiency. The second part of the thesis will concentrate on the ambipolar qualities of (sub)phthalocyanines and their use as acceptors in conjunction with both the underused acene, tetracene (Chapter 5) and the more widely studied pentacene (Chapter 6). To obtain a strong understanding of using boron subphthalocyanine chloride (SubPc), Cl6-SubPc and ClAlPc as acceptors, UV –Vis absorption, atomic force microscopy (AFM), photoluminescence (PL), photoelectron spectroscopy (PES), space charge limited current (SCLC) theory to gain charge mobilities and devices were explored.

This thesis uses density functional theory (DFT) to explore the electronic structure and reaction mechanisms of open-shell transition metal ions and clusters. The early part of the thesis (Chapters 2 and 3) is devoted to high-valent metal-oxo species, both mono- and bimetallic, while Chapter 4 describes some aspects of copper-catalysed carbon-carbon bond formation. Finally, Chapter 5 highlights the role of DFT in computing magnetic and spectroscopic properties of exchange-coupled iron clusters. Whilst the chemistry contained in the thesis is rather diverse, the underlying theme of open-shell transition metal ions is common to all chapters. Moreover, we are primarily concerned with the ways in which interactions between two or more adjacent open-shells (either two metals or a metal and a ligand radical) control structure and reactivity. After a brief introduction to relevant theoretical aspects in Chapter 1, we use Chapter 2 to establish a link between the electronic structure of the high-valent Mn(V)=O porphyrin monomer species and their ability to perform oxidation reactions. The reaction profiles for oxidation of a range of substrates depend critically on the electronic structure of the isolated oxidant. Where the electronic ground state is genuinely best described as Mn(V)=O, the interaction between oxidant and substrate is repulsive at large separations, only becoming attractive when the incoming nucleophile approaches close enough to drive an electron out of oxide p manifold. In contrast, where the ground state is better described as an oxyl radical form, Mn(IV)-O.+, the oxidation occurs in sequential one-electron steps, the first of which is barrierless. In Chapter 3, we extend these ideas to bimetallic systems, where the presence of two high-valent manganese centres allows the system to oxidise water. Specifically, we focus on two model systems which have been shown to oxidise water, a Mn-porphyrin-based system synthesised by Naruta and a Mn-based system reported by McKenzie where the ligands contain a mixture of pyridine and carboxylate donors. In both cases, we again find that the emergence of oxyl radical character is the key to the reaction chemistry. However, the radical character is ‘masked’ in the electronic ground states, either by transfer of an electron from the porphyrin ring (Naruta) or by formation of a di-μ-oxo bridge (McKenzie system). In Chapter 4 we turn our attention to copper chemistry, and the role of copper complexes in catalysing atom transfer radical additions (Kharasch additions). In this reaction, the copper cycles between Cu(I) and Cu(II) oxidation states, and the result is the formation of a new C-C bonds. This Chapter makes extensive use of hybrid QM/MM techniques to model the environment of the copper centre in the target polypyrazolylborate-copper complexes (TpxCu). Finally, in Chapter 5 we consider the electronic structure, magnetic and spectroscopic properties of a pair of exchange-coupled Fe3 clusters, [Fe3(μ3-O)(μ-4-O2N-pz)6X3]2- (where pz = pyrazolato, X = Cl, Br). Our primary goal was to establish how well broken-symmetry DFT is able to reproduce the observed Mössbauer spectroscopic parameters, which are extensively used to identify the chemical environments of iron species and, in the case of mixed-valence clusters, to establish the degree of delocalisation of the additional electrons. In recent years DFT has proved able to compute these parameters with encouraging accuracy, but it is not clear to what extent the known deficiencies in broken-symmetry wavefunctions will compromise this ability. Our work suggests that neither the isomer shift nor the quadrupole splitting are strongly influenced by the nature of the coupling between the metal ions, suggesting that broken-symmetry solutions can be used as a basis for computing these parameters in more complex clusters.

Modelling of the charge transport in different types of organic semiconductors (molecular crystals and semicrystalline polymers) is undertaken using a number of different methods. Using a polarisable force field we have determined the extent of the external reorganisation energy for hole transport in molecular crystals. We have found that this key parameter is very small for naphthalene, anthracene, tetracene, pentacene and rubrene and discussed the implications of this finding in the context of charge transport modelling. Charge trapping in organic crystals due to defect states is studied by computation of the rate of escape of a trapped charge carrier using non-adiabatic rate theory. Two cases are considered, the first is hopping between separate identical defect states and the second is hopping from a defect state into the bulk (delocalised) states. This latter process is determined as the more likely to occur for a realistic defect concentration. The necessity of the inclusion of an effective quantum mode of vibration for the accurate computation of the rate is also demonstrated. A linear scaling method based on the definition of a localised molecular orbital set is devised for the computation of the electronic structure of a conjugated polymer (poly(3-hexylthiophene) (P3HT)). Utilising a combined classical and quantum chemical approach we show that charge carriers are localised in correspondence with long-lived traps which are also present in the crystalline phase of the polymer. The regio-regularity of P3HT is shown to have little impact on the shape and tail of the density of states; we compute the 2D localised trap density as ~3.1×1013 cm-2, a value which is not found to significantly change with the regioregularity. The states in the tail of the density of states are found to be predominantly localised but energetically close to delocalised "quasi-band" states which are accessible under device operation.

The purpose of the work described in this thesis was to measure standard electrode potentials and rate constants for various systems, based around cobalt and copper centred catalysts. The intention was to increase understanding of these two different types of complexes, with the knowledge described herein aiding in catalyst and system design. Two main techniques have been used, those of UME voltammetry and SECM. The UME measurements proved technically simple and were used to provide information on redox kinetics and coupled solution reactions. Conversely, the SECM experiments were more complex to perform but allow more complicated systems to be studied. The results obtained in Chapter 3 provide further information about the properties of [Cu] ATP catalysts. Enhanced information could be obtained with better knowledge of the values ofE1I2 or F!., but the work has shown that in organic solvents even simple parameters are difficult to obtain due to complexities such as ion pairing. The theme of Chapter 4; the reaction of [CUll] with Cu o had previously been unexamined. This reaction has been characterised and provides new information of the processes involved in adding Cu o to ATP reaction mixtures. A computer simulation was applied that described the theoretical behaviour of an oxidative etching event. A good fit was obtained between experiment and theory at large values of d/a and at short times. The potentials of a number of [CuI]/[CUIl ]and [Cul]/[CUO] redox couples have been measured in order to understand the substrate potential response during the SECM etching process. The rate of reaction of a number of different [COl] with E2mB has been measured in a range of solvents, as described in Chapter 5. The solvent was seen to have a great effect on the behaviour of each system, stabilising the formation of R[Colll ], such that two reduction processes became evident where mma was the solvent. Such [Co] species are commonly used as C - C bond forming reagents and therefore knowledge of their behaviour in certain solvents is invaluable. Additionally the [Colt E2mB system may be used as an initiator/catalyst system for polymerisation reactions, either in homogeneous or emulsion solutions.

Crystalline and glassy silicates were investigated by means of 17O NMR. The dependence of the measured efg on the Si-O-Al bond angle was investigated in some crystalline aluminosilicate sodalites and kalsilite. The results show that CQ increases with increasing bond angle while 11 decreases with increasing bond angle and they both follow a similar function to that found for the Si-O-Si bond angle. The cluster calculations also confirm that the dependence of CQ and il on the Si-O-Al bond angle is similar to that of one Si-O-Si linkage. The chemical shift decreases as the bond angle increases. However this dependence does not seem to be monotonic. The structural role of Al in aluminosilicate glasses was studied by means of 17O 3Q MAS NMR in sodium aluminosilicate glasses with Si/Al= 3,1.5,1,0.7.3Q MAS NMR results showed the presence of Si-O-Si species as well as Si-O-Al species in glasses with Si/Al>1. The 3Q MAS NMR spectrum of glass with Si/A1=0.7 displayed the presence of Al-O-Al linkage as well as Si-O-Al. These results showed that as the Si/Al ratio decreases from 3 to 0.7 Si-O-Si linkage is replaced by Al-O-AI linkage as a result of addition of Al into the structure. The structural role of Sn in tin-silicate glasses was also studied mainly by means of 17O MAS NMR. The model developed from the 17O MAS NMR spectra of these glasses showed the possible coexistence of two and three coordinated oxygen atoms in the structure. Therefore some of the Sn has to be in three coordinated to oxygen for charge balancing. The 17O MAS NMR spectra of a partially crystallised sample showed three distinct sites which are assigned as Sn-O-Sn, Si-O-Sn, and Si-O-Si on the basis of their chemical shift. The CQ values obtained from the simulations of these peaks supports this assignment. The 29Si MAS NMR of the same sample showed two crystalline and a glassy peaks which are fitted to two crystalline and two glassy sites. The possible composition of this sample was calculated and found to be SiSn3O10.