No description available.

The work in this thesis is mainly concerned with the discussion of effect of solvation on the reaction kinetics of inorganic complexes. Rate constants for chemical reactions in various aqueous cosolvent systems have been measured and analysed. Crystal structure of several Fe (II) complexes are analysed from crystallographic data for possible structural parameters which might have effect on solvation. Solubility data, for a range of inorganic salts containing simple and complex ions, are reported for aqueous solutions and for solutions in aqueous cosolvent mixtures. Transfer chemical potentials for single ions in aqueous i-PrOH and t-BuOH solvent mixtures are determined using solubility data for salts in conjunction with TATB, tetraphenylarsonium tetraphenylboranate, assumption and are compared with those in corresponding aqueous methanol, ethanol and acetone solvent mixtures. Kinetic data are reported for reaction between [Fe (gmi)3]²+ and hydroxide ions at atmospheric and elevated pressures in above binary aqueous mixtures. Initial state and transition state analysis of reactivity trends for hydroxide attack on other Fe (II) diimine complexes in aqueous methanol solvent mixtures are reported. Dependence of visible absorption spectra on solvent has been examined for a number of Fe (II) and Fe (III) mixed ligand complexes. Preliminary redox study of the of Fe (II) and Fe (III) complexes is also reported.

A series of cyclometalated gold(III) complexes with N-heterocyclic carbine (NHC) or alkynyl as auxiliary ligand were synthesized and characterized. Complexes [AuIII(R1 –C^N^C)(NHC)](OTf) and [AuIII(C^N^C)(C≡CR2)] (HC^N^CH = 2,6-di(naphthalene-2-yl)pyridine; R1 = H or 4-methoxyphenyl; R2 =aryl) are emissive in solution at room temperature with quantum yields in the range of 0.65–11.4% and lifetimes ranging from 98 to 506 s. [AuIII(4-(4-OMePh)–C^N^C)(NHC)](OTf) showed prominent photochemical properties. This complex effectively catalyses photo-induced oxidation of secondary amines (to the corresponding imines) and -functionalization of tertiary amines in good to excellent yields; it also acts as a photosensitizer for hydrogen generation in a water/acetonitrile mixture, producing more than 350 turnovers of hydrogen after 4 hours of irradiation. Palladium(II) meso-tetrakis(pentafluorophenyl)porphyrin was found to be an efficient and robust catalyst for the photo-induced oxidative C–H bond functionalization reactions. Several kinds of -functionalized tertiary amines were obtained in good to excellent yields by irradiating a mixture of palladium(II) catalyst, corresponding tertiary amine and nucleophile under aerobic conditions. The nucleophiles for these reactions include cyanide, nitromethane, dimethyl malonate, diethyl phosphite and acetone. Two examples of novel intramolecularly cyclized amines were also described. Comparison of the UV-vis absorption spectra before and after reaction indicated that the palladium catalyst was highly robust. The practical potential of this catalyst was shown by the success in reactions at a low catalyst loading and on a large scale. The palladium(II) catalyst could also sensitize photo-induced oxidation of sulfide to sulfoxide and photo-induced hydrogen production in a water/acetonitrile mixture with up to 240 turnovers. [FeIII(L-N4Me2)Cl2][FeCl4] (L-N4Me2 = N,N’-dimethyl-2,11-diaza[3,3] (2,6)pyridinophane) was demonstrated to be an active catalyst for water oxidation. When cerium ammonium nitrate (CAN) was used as the oxidant, the iron(III) catalyst oxidized water to oxygen with up to 93 turnovers after 30 minutes in 0.1 M nitric acid, whereas changing the oxidant to sodium periodate (NaIO4) resulted in only 44 turnovers of oxygen after 30 minutes. The mechanism of the reaction was explored by high resolution electrospray ionization mass spectrometry (ESI-MS), 18O labeling, UV-vis absorption spectroscopy, kinetic plots and DFT calculations. In the case of using CAN, an FeIV-oxo species was detected by ESI-MS and UV-vis absorption spectroscopy. The rate of oxygen evolution was found to be linearly dependent on both concentrations of catalyst and oxidant. 18O labeling studies confirmed that the origin of oxo ligands was from water and was irrespective of the choice of oxidant. This reaction was proposed to involve a coupling between an FeIV-oxo species and a hydroxocerium(IV) radical. In the case of using NaIO4, an FeV-dioxo species was detected by ESI-MS as a major species, and a small amount of FeIV-oxo species was detected by UV-vis absorption spectroscopy. As the rate of oxygen evolution was found to be linearly dependent on the concentration of catalyst only, the reaction was proposed to involve a cis-FeV-dioxo species. DFT calculations showed that the cis-FeV-dioxo species was capable of oxidizing water to oxygen through the formation of an [FeIII(L-N4Me2)(OO?)(OH)]+ intermediate. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Not available / text

Full X-ray structure analyses ot sixteen .etal cluster compounds of nuclearity 3 to 11 have been carried out to investigate to what extent the attached surface ligands govern the structure in the solid state and how this relates to the chemistry of the cluster in solution. The structure of the tetranuclear cluster [AgRu,(CO),(CzBut)(PPh,)] has completed a series of related clusters [MRu,(CO),(CzBut)(PPh,)] [M a Cu, Ag or Au]. This is only the second example of a complete series of Group IB cluster analogues and confirms earlier evidence that the bonds fro. gold are different in character to those trom silver and copper. The structures of the copper clusters [Cu,Ru.(~,-H),(CO)'Z{P(C6H'1)'}Z] and [Cu,Ru.(~,-H)Z (CO)tZ {P(CHMel ) l} l ] compared to the reported structure [Cu,Ru"(~J-H)z(CO)tZ(PPhl)l] indicate that the 'bulk' of the organophosphine groups is a major factor in determining the type of metal geometry adopted by this type of compound in the solid state. Comparison of the structural results obtained for the hexanuclear clusters [M,Ru,,(CO).,(PPh,),] [M a Cu or Ag] to those reported for the hydrido analogues [MlRu.(~,-H)z(CO)'l(PPh')l] have shown that small changes in the surface ligand set can have marked effects on the metal geometry in the solid state, providing further evidence that the energy differences between the various structural types are small for heteronuclear clusters containing Group IB metal atoms. The X-ray structure analyses of [AulRu.(~-H)(~,-H)(CO)ll{~-Ph,PCH=CHPPhz}] and [Au,Ru,,(~-H)(CO),,{~-PhzPCH,PPhz}(PPhJ)] have enabled the correlation of earlier structural data of related hexanuclear and heptanuclear mixed-metal clusters to account tor the marked differences between the structures of gold-ruthenium clusters with monodentate organophosphines, -compared to those with bidentate phosphine ligands. The X-ray structures ot the isomers [Os,Hz(CCHOEt)(CO).l and [Os.H,(HCCOEt) (CO),] provide a rare exaaple of cluster isomers differing only in the nature of the organo ligands. The structures of the high nuclearity hydrido clusters [Os.HZ(CO)'7- P(OMe),]' [Os7HZ (CO)u], and [Os7HZ (CO)..{MeCaCMe}] have shown nove1 metal fraaeworks, supporting previous observations that when hydrido ligands are present, osmium cluster geo.etries can often be unpredictable in the solid state. The structural characterisation of the large hydrido cluster monoanions [HsOs,o(CO),.]- and [HOs"C(CO)Z7]- have provided evidence for the presence of intersU Ual hydrido ligands. Comparison of these results to those reported for related compounds supports the view that in some cases. interstitial ligands become important in preventing surface ligand. overcrowding.

1. The invasion of Betula spp. (B.pendula and B.pubescens) triggers a phase transition between lowland heath and scrub vegetation states. Transition to scrub is currently the most serious threat to the conservation of UK lowland heath; it has been found to correlate with soil phosphorus sorption capacity (PSC) at the landscape scale. 2. It was hypothesised that Betula invasion of Lowland heath was limited by numerous factors that may be subdivided into safe-site and seed limitation and that phosphorus availability was a key axis in the determination of a Betula safe-site. 3. An implicit assumption of earlier research was that PSC affected the P available to invading plants. An approach combining observation, statistical modelling and experimentation found that PSC affected the retention and availability of phosphorus in heathland soils. Synthesis of these findings with the published literature suggests that the direct effect of PSC on P-availability is small compared to indirect effects on organic matter (SOM) accumulation and vegetation cycling. 4. These findings allowed the hypothesis that P-availability affects the likelihood of invasion to be tested within an experimental framework. P-availability, seed rain and disturbance were experimentally manipulated in a multifactorial field experiment on a wet heath ecosystem in a stable, uninvaded heath area. Betula seedling densities and numerous covariates were also measured. It was assumed throughout this research that Betula seedling densities were indicative of the likelihood of heath-scrub transition. 5. Analysis of deviance found that all three treatments had significant effects on Betula seedling densities with seed availability proving to be the single greatest limitation at the site. Conversion of the experimental treatment factors into a continuous form allowed for a more detailed description of the phase transitional area within the site. The most significant descriptors of seedling densities were seed-rain, various plant neighbour variables and P-availability. 6. Replication of this experiment with fewer treatment levels and replicates at two additional sites found that the identity of the factors controlling Betula seedling densities was broadly similar, (e.g. vegetation and seed availability factors played a role at all sites) but that their relative contributions to within-site heterogeneity varied widely. 7. A single statistical model was fitted to data collected from three experimental sites. The model, which explained 59.8% of the deviance in seedling densities, describes Betula colonisation as a function of biomass density, necromass density, vegetation height, seed bank density, phosphorus availability, and to a lesser extent, soil water content. The form of the fitted relationships was complex with numerous interaction and polynomial terms. If the model is applicable to a wider range of conditions then it may be concluded that it is heathlands close to seed sources and in the degenerate state, and possibly those subjected to severe bums, that are the most likely to shift to the Betula scrub state. At larger scales these conditions are probably most common in low management intensity, high phosphorus sorption capacity (PSC) regions. 8. Validification of the combined-site model was attempted using data that was equivalent to that used in the fitting of the model and which was collected over two 5ha grids of 130 sampling points and covering a wider range of heathland environments. Low predicted and actual seedling densities prevented formal testing of the models accuracy but predictions were qualitatively accurate, despite extrapolation. 9. Exploration of spatial heterogeneity in the determinant factors using the aforementioned spatial grid data, was achieved with geostatistics. This revealed that seed bank densities and edaphic factors displayed small-scale patchiness of around 50m while vegetation factors possessed longer ranging autocorrelation resulting in single across-site gradients. The proportion of spatially structured variance in the variables, within the studied range (17.6-150m), was low for many factors. The pattern of these factors is discussed with reference to the exclusion of Betula colonists and management recommendations are proposed. 10. It is concluded that the combined-site model provides a coarse but fairly accurate definition of the phase-transitional area between lowland heath and Betula scrub ecosystem states and that the determinant factors are at larger scales governed by landscape-scale processes (e.g. soil (PSC), climate and management regimes). These factors may explain regional differences in the scale and extent of scrub transition.

Not available / text

Not available / text

No description available.