The unifying objective of this work is the study of model systems that will assist in the development of new metal catalysts capable of converting carbon monoxide and hydrogen (syngas) into organic oxygenates at mild temperature and pressure. The selective catalytic transformation of carbon monoxide and hydrogen to liquid fuels and chemical feedstocks represents a major "Grand Challenge" of catalysis science. A core objective is the study of a macrocycle that is related to a porphyrin ligand in order to circumvent some of the disadvantages of utilizing porphyrins in catalysis. The rhodium complex of the macrocycle dibenzotetramethylaza[14]annulene ([(tmtaa)Rh]2]) was reacted with a series of small molecules relevant to CO reduction and hydrogenation. Several complexes were formed that demonstrated the ability to partially reduce and hydrogenate carbon monoxide, including the dirhodium ketone (Rh-C(O)-Rh) and an example of a thermodynamically favorable metal formyl complex ((tmtaa)Rh-C(O)H). An important feature of this work is the measurement of thermodynamic data to provide experimental benchmarks for obtaining key species in CO reduction and hydrogenation. A thorough study of the (tmtaa)Rh system will help in identifying structural features that assist or hinder CO hydrogenation. All reactions are monitored by 1H NMR which permits determination of solution thermodynamics from equilibrium constants obtained by NMR peak integrations. DFT calculations have supplemented experimental results by providing estimates to compare with the experimentally determined thermodynamic data. These computations also provide insight into the structures and thermodynamics of species that cannot be observed directly such as short lived intermediates and thermodynamically unfavorable products. Heterobimetallic complexes of (tmtaa)Rh* with a second metal radical have been utilized to attempt to convert CO to organic products. Reactivity with CO and H2 has been accomplished, with most of these metal systems providing (tmtaa)Rh-C(O)H and M-H as final products. These systems are now ideally set up for catalysis in which M-H can deliver hydrogen to reduce and hydrogenate the rhodium formyl unit. Performing these reactions at high pressures of CO/H2 or with a more sterically hindered analog of tmtaa may provide the conditions necessary for catalysis. Reactivity, thermodynamic and computational studies have been used to analyze and compare bond energies in this current work with previous studies accomplished in the Wayland group. These comparisons permit further understanding into the factors that control bond strength, guiding future studies and allowing tuning of bond strengths based on choice of conditions for a catalytic process. This research has resulted in a more complete understanding of the factors that control the favorability of various intermediates in CO reduction and hydrogenation and the application of these results can be used to guide the next generation of metal ligand systems that will yield organic oxygenates at mild conditions. / Chemistry

<p>Series of rare-earth intermetallic compounds were synthesized and studied.</p> <p>The Gd₄Ge_3-<em>x</em><em>Pn_x</em> (<em>Pn</em> = P, Sb, Bi; <em>x</em> = 0.5 - 3) series of compounds were synthesized to explore the stability of the non-existent Gd₄Ge₃ binary through partial <em>Pn</em> substitutions to increase valence electron concentrations. Electronic band structure calculations were performed to elucidate the relationships between the hypothetical "Gd₄Ge₃" and Gd₅Ge₄ binaries. All Gd₄Ge_3-<em>x</em><em>Pn_x</em> phases order ferromagnetically with relatively high Curie temperatures of 234 to 356 K.</p> <p>The Gd₅Ge_4-<em>x</em>P<em>_x</em> phases were synthesized to explore the effects of both atomic size and valence electron concentration differences between Ge and P atoms. Partial substitution of P for Ge atoms occur on the interslab site, which causes the interslab distances to increase. In Gd₅Ge_4-<em>x</em>P<em>_x</em>, only a small amount of P substitution (<em>x</em> = 0.25) is required to induce ferromagnetic ordering. The appearance of a Griffiths phase is also discussed.</p> <p>The temperature dependence of the different <em>RE</em>₂Fe₁₇ (<em>RE</em> = Gd - Ho) phases was tracked by reciprocal space images generated from single crystal X-ray diffraction.</p> <p>GdCo₄B was synthesized by arcmelting and tri-arc techniques to confirm the presence of magnetostriction. Single crystal and powder X-ray diffraction, dilatometer and magnetic measurements were done.</p> / Master of Science (MSc)

No description available.

A detailed programme of research is presented to design, build and operate a high resolution h?hz5000 curved crystal Johann-type x-ray spectrometer for the waveband below 13A. The spectrometer is used to observe line emission features from different laboratory x-ray sources. Characteristics of the Johann geometry are described with emphasis given to the properties of sensitivity, dispersion, resolving power and waveband. The tolerance of the instrumental parameters is defined for successful high spectral resolution operation. The key feature of the spectrometer is the unique crystal bending device which can generate a high quality cylindrical curvature of radius R=150?5000mm. The crystal focusing alignment and testing procedures are evaluated. Choice of crystals suitable for the observation programme is discussed together with analysis techniques for interpretation of the x-ray spectral line profiles. The instrument is optimised for time-integrated and time-resolved ion temperature measurements of UKAELA DITE Tokamak at the Culham Fusion Laboratory. X-ray line emission results from medium Z He-like and H-like impurity ions are presented for different plasma conditions. Density sensitive He-like and Li-like Aluminium ion satellite emission features are studied for intense transient laser produced plasmas at the Central Laser Facility, SERC Rutherford Appleton Laboratory. The peak plasma electron density of 0.1 time solid density is estimated from these line intensity ratios and is in good agreement with Stark line width measurements. X-ray emission from beam-foil interactions is observed on the Folded Tandem accelerator of the Nuclear Physics Department, Oxford University. The proposed improvement in the intrinsic spectral line broadening due to the accelerator is investigated by high resolution axial beam measurements of the He-like Silicon and H-like Neon n=2 transitions. The Lyman-a intensity ?-ratio and wavelength separation ?hFS is studied for the fine-structure of Hydrogenic Neon, Magnesium, Aluminium and Silicon. The fine-structure separation is compared with the Dirac theory and other experimental data, while the possible mechanisms giving rise to the non-statistical value of the ?-ratio are analysed.

A simplified description is given of the operation of a multiwire proportional chamber (MWPC) in the soft X-ray imaging application. Expressions are developed to allow the calculation of the distribution of induced charge on the cathodes of an MWPC. With extensions to permit direct comparison, the calculations are subjected to detailed experimental verification. A generalised, approximate formulation of the distribution with one independent parameter is described. The prediction of cathode system position response using the theoretical distributions is demonstrated. The available MWPC position readout methods are reviewed, and where possible their differential non-linearity is measured experimentally. A new position-sensitive cathode of good linearity and spatial resolution is presented. The effect of the wires of an MWPC on its imaging performance is briefly considered. An attempt is made to assess the contribution to MWPC spatial resolution of the range of the electrons produced initially by an X-ray absorption event in argon-methane mixtures. In conclusion, the important causes of MWPC imaging imperfection are noted and classified.

Alkali-metal diuranates (VI) and dineptunates (VI) have been prepared by controlled thermal decomposition of well-characterised alkali-metal uranyl (VI) and neptunyl (VI) triacetates having the desired stoicheiometricalkali-metal to actinide ratio. The compounds in the series MI2MVI207 (MI = Na - Cs incl., MVI = U or Np) have been obtained in this way. This preparative method failed to provide further evidence for the existence of the controversial ternary oxide, Li2U207. Isolation of the analogous neptunium complex, Li2Np207, was not achieved. Enthalpies of formation have been derived from the enthalpies of solution in 1 mol dm-3HC1 and auxiliary thermodynamic data. The values for Na2U207 and Cs2U207 are in good agreement with those assessed by Cordfunke and O'Hare and thus confirm the reliability of the method of preparation of such mixed oxides, as compared to the 'classical' methods which involve heating an actinide oxide with an alkali-metal binary oxide, nitrate or carbonate. The values for K2U207 and Rb2U207 are previously unreported. Confirmation of an earlier assessment of the enthalpy of formation of Na2Np207 and preliminary values for the enthalpies of formation of K2Np207, Rb2Np207 and Cs2Np207 have been obtained.

The general theme of this thesis is the effect of solvents on the initial state and transition state contributions. This has involved kinetic and thermodynamic measurements. The kinetics were examined for a variety of inorganic reactions with the aim of investigating rate laws, products of reaction (where possible) and suitability for an initial state-transition state analysis. The following reactions were followed:- (a) 2,2'- Bipyridyltetracarbonylmolybdenum (0) and various related compounds with cyanide and other nucleophiles; (b) manganese and rhenium carbonyl halides with cyanide and amino-acids; (c) potassium tetrachloroplatinate (II) with cyanide; (d) hexadentate Schiff base complexes of iron(II) with cyanide and with hydroxide. An extension of mercury (II) catalysis was carried out in the examination of solvent effects on such catalysis, and on the hydrolysis reaction, of the pharmaceutical fenclorac (?-3-dichloro-4-cyclohexyl-benzeneacetic acid). The thermodynamics and solubility measurements have enabled the calculation of Gibbs free energies of transfer. This has been done for potassium cyanide in non-aqueous and in mixed aqueous media, also for potassium tetrachloroplatinate (II) and 2,2'-bipyridyltetracarbonyl-molybdenum (0) in limited ranges of solvents and solvent mixtures. From this [special character omitted](non electrolytes), directly, and (ions), using standard extrathermodynamic assumptions, may be obtained to get data on the initial state. These together with the kinetic data permit an initial state - transition state dissection of solvent effects on reactivity. Such an analysis was successfully carried out for 2,2'-bipyridyltetracarbonylmolybdenum (0) and potassium tetrachloro-platinate(II). In connection with the reaction of the iron(II)-hexadentate Schiff base complex with cyanide and hydroxide, it was necessary to carry out an X-ray structure determination to be certain the central moiety of the hexadentate ligand was in the form -NHCH2CH2-NH rather than the diimine form -N=CH CH=N-.

Solvation trends of ternary iron(II)-cyanide-diimine complexes in binary aqueous media are examined using spectroscopic and thermodynamic techniques. The observed trends are discussed in terms of the solvent-solute interactions present, and how the relative importance of these interactions varies with the technique and the complex. Crystallographic data for two of these structures are reported and show the effect of the solvate molecules on the structure. Pressure effects on MLCT frequencies are investigated, and the correlation between piezochromic and solvatochromic effects for mono- and binuclear iron(II) and iron(III)-diimine complexes is shown. Pressure and solvent modification of the rate of oxidation of a series of iron(II)-diimine complexes are interpreted and discussed in terms of the solvation changes that occur upon transition state formation. Complementary partial molar volume data for these complexes are also reported, and combined to form a volume profile for one reactant pair. The structure of a binuclear iron(II)-diimine complex is examined in the solid state and in solution. Solvation trends in binary aqueous media are reported for this binuclear cation, and comparisons are made with mononuclear iron(II) and cobalt(III), and with binuclear cobalt(III) complexes. Kinetics of base hydrolysis of several binuclear iron(II)-diimine complexes are discussed in terms of the structural differences between these complexes. The effects of added organic cosolvents on the rate constants for one of these binuclear complexes is also reported. Spectroscopic evidence for a ligand substituted intermediate is found. The structure of such intermediates is discussed with respect to existing data for mononuclear iron(II)-diimine complexes. Finally, a preliminary chemical and electrochemical redox investigation is made on the most suitable binuclear iron(II)-diimine complex in light of the base hydrolysis reactivity patterns established.

The reaction between WF6 and C6F5NH2 is found to proceed via iminolysis. 19F NMR analysis of acetonitrile (MeCN) solutions show the product to be a mixture containing [C6F5NH3]+[WF5(NC6F5)]-, [C6F5NH3]+[W2F9(NC6F5)2]-, [C6F5NH3]+F- and the unique mixed imido-, oxo-species [O=WF4-F-WF4(NC6F5)] - formed from traces of oxyfluoride impurities. The 19F nmr spectrum of a trifluoroacetic acid (TFA) solution showed the presence of the dimeric anion salt and fluorination products. An X-ray crystallographic study of a single crystal of [C6F5NH3]+[W2F9(NC6F5)2]-, grown from TFA, revealed the compound to adopt a triclinic (space group P1)structure, with two formula units in the unit cell, each with a slightly differing geometry about the bridging fluorine atom. The reaction of Me3SiNCO with MF6 (M= Mo,W) was examined. The products are assigned as MF5NCO3 from IR spectra recorded. The reaction between MoF6 and (Me3Si)2NH results in the formation of MoF4NH. Addition of MeCN to MoF4NH produces a 1:1 adduct, MoF4NH.MeCN. Analysis of the IR spectra of the two compounds indicates that MoF4NH adopts a cis-fluorine bridged chain structure, and MoF4NH.MeCN adopts a pseudo-octahedral (C4), monomeric stucture in the solid state. WOF4 reacts with Me3SiNCO to form WOF3NCO, identified from its mass spectrum. The hexafluorides MF6 (M= Mo,Re), when allowed to react with tetrakis-tri-methylsilylhydrazine (TTSH) undergo reduction to the pentafluoride in approximately 80% yield. Tungsten hexafluoride is believed to react with TTSH to form the diazene compound, WF4N-MWF4.

The reaction between Fe(phen)32+ and Nu (Nu = OH-, CN-) in aqueous methanol mixtures was analysed, in terms of H into initial state-transition state contributions. The racemisation of the (-) Fe(phen)32+ cation in aqueous DMSO and aqueous methanol mixtures was analysed, in terms of G, into initial state-transition state contributions. Fe(mppm)32+ was resolved, and the kinetics of racemisation were investigated. Fe(5NO2 phen)32+ was resolved and found to racemise very quickly at 25�C. Ru(5NO2 phen)32+ was resolved, and showed no tendency to racemise at 25�C. Attempts to resolve Fe(btz)32+ and Ru(btz)32+ were unsuccessful. The reactions between Fe(btz)32+ and R (R = OH-, H+, Hg2+, Cd2+, S2,O82-, phen, bipy) are reported. The stability constants of Fe(btz)32+, Agbtz+, Cdbtz2+ and Hgbtz2+ were measured. The solvatochromism of Mo(CO)4 btz, Mo(CO)4 bipym, PNA, DMIA, Fe(btz)2 (CN)2 are reported. The solvatochromism of Mo(CO)4 btz, PNA and DMIA were analysed into ground state-excited state contributions. The structure of Mo(C0)4 btz is described. The solvolysis of Mo(CO)4 btz was analysed in terms of initial state-transition state contributions. The reactions between Mo(CO)4 btz and Q (Q = Hg2+, HgC12, PtC142-, In3+, Cd2+, MeI, PtC12, PPh3, P(OPh)3, Mo(CO)4 (pip)2) are reported. The reactions between Mo(CO)4 (pip)2. and R (R = btz, dt, (btz + bipy), PtC12btz) are reported. The preparation of PtC12btz is described.