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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Studies of the dissociation and energetics of gaseous ions

King, S.-J. January 2008 (has links)
Dissociations of C2F62+, SiCl42+, C2H22+, CC > 22+ and H2O2+. Estimates of the dication precursor state energies for forming ion pairs are derived, and are shown to be in good agreement with existing experimental and theoretical data. The measurements presented in this thesis include the first estimates of the electronic state energies of the C2F62+ and SiCU2+ dications. A breakdown scheme for C2H22+ is derived, which in combination with the relative PICS for ion pair formation, yields branching ratios for primary two-body charge separating dissociation. Comparison of this scheme with recent theoretical calculations suggests that below 75 eV, C2H22+ dissociates predominantly on the ground triplet potential energy surface (3 g). By contrast, the dissociations of the C2F62+ dication are postulated to be predominantly impulsive in nature, for which fast-sequential decay mechanisms are proposed for forming ion pairs.

Fluorine derivatives of antimony and some transition metals

Hewitt, Alan John January 1976 (has links)
Incomplete fluorination of antimony metal in a flow system produces SbF5 and a mixture of yellow and white high melting solids. Vacuum sublimation of the mixture at -140 produces a white crystalline solid which consists of a mixture of Sb11F43 and SbF3, whereas sublimation at >240 yields a compound con-taining the [Sb2F11]- anion. The ruthenium carbonyl fluorides, (Ru(C0)3F2)4 and Ru(CO)3F3 have been prepared in high yield by the room temperatur fluorination of Ru3(CO)12 in 1,1,2-trichlorotrifluoroethane or anhydrous hydrogen fluoride as solvents, and (Ru(CO)3F2.RuF5)2 by the high temperature fluorination of Ru3(CO)12 with XeF2 and by carbonylation of RuF5 with carbon monoxide. Infrared spectroscopy, magnetic susceptibility and electron spin resonance spectroscopy have shown that Ru(CO)3F3 is monomeric but that the structure of (Ru(CO)3F2.RuF5)2 is closely related to that of (Ru(CO)3F2)4 and (RuF5)4, which have been previously character-ized by single crystal X-ray diffraction as fluorine-bridged tetramars. The reaction of one mole of Os3(CO)12 with greater than or equal to three moles of XeF2 yields the osmium carbonyl fluoride, (Os(CO)3F2)4, whereas reaction with XeF6 yields products which have not fully been characterized. The rhenium carbonyl fluoride, Re(CO)5F, has been prepared by the reaction of Re(CO)5Cl with anhydrous hydrogen fluoride.

Kinetic and thermochemical studies of rhenium-halogen compounds

Cartwright, S. J. January 1975 (has links)
This thesis is concerned with aspects of the solution kinetics and thermochemistry of several binary and complex halides of rhenium. The standard enthalpies of formation of potassium hexachlororhenate(IV), potassium hexabromorhenate(IV), ?-rhenium tetrachloride, rhenium tetrabromide and rhenium oxide tetrachloride have been determined as -1333.1 +/- 5.5, -1036.0 +/- 10.3, -360.7 +/- 15.1, -303.0 +/- 17.2 and -600.1 +/- 16.6 kJ mol-1, respectively. Hence, the Lewis acidities, ?H2X-, of ?-rhenium tetrachloride and rhenium tetrabromide have been estimated as -7.1 and +135.4 kJ mol-1, respectively. ?H2X- is the enthalpy change for the reaction, ReX4 (c) + 2X- (g)?ReX62- (g) The solution enthalpies of the sparingly soluble caesium hexachlororhenate(IV) and caesium hexabromorhenate(IV) have been determined as +88 and +96 kJ mol-1, respectively. Hence, the single-ion hydration enthalpies of the gaseous hexachlororhenate (IV) and hexabromorhenate(IV) anions have been estimated as -846 and -784 kJ mol-1, respectively, and have been compared with estimates for other polyatomic anions. Attempts have been made to correlate the solubility of caesium exachlororhenate(IV) in mixed aqueous solvents with empirical solvent parameters and to estimate transfer parameters for the hexachlororhenate(IV) anion. Metal-ion (Hg2+, Tl3+, Cd2+ and In3+) catalysed aquations of hexachlororhenate(IV) and hexabromorhenate(IV) in acid aqueous solutions have been investigated. A rate law, rate constants and activation parameters have been determined and have been compared with data for similar systems. The possible connection between the effectiveness of the catalysts and the stability constants of their monohalo- complexes has been discussed. The reactions of rhenium pentacarbonyl iodide, bromide and chloride with cyanide ion in methanol-water mixtures all follow a two step consecutive pattern, with the formation of a common product, [Re (CO)4(CN)2]-. Rate laws, rate constants and activation parameters have been determined. The Gibbs free energy of transfer of rhenium pentacarbonyl iodide, from 50 vol.% to 70 vol.% methanol-water, has been estimated as -3.3 kj mol-1. The reactivity trend for the Re(CO)5I/CN- reaction upon change of solvent medium has been discussed in terms of transfer parameters.

Controlled crystallisation of calcium phosphate and calcium carbonate via bio-inspired approaches : additives and confinement

Cantaert, Bram January 2013 (has links)
This thesis describes the investigation of the two bio-inspired approaches, confinement and additives, to manipulate the crystallization of calcium carbonate and calcium phosphate. The first experimental chapter deals with the investigation of calcium phosphate rods grown in confined environments in the absence and presence of polyaspartic acid. Although similar results were obtained in the absence and presence of the additive, growing calcium phosphate in confinement allowed formation of polycrystalline rods with an orientation comparable to bone. This demonstrated that confinement may play a more significant role in bone formation than previously anticipated. The second chapter deals with the effect of positively charged additives on the crystallisation of CaCO3. Although neglected before in literature, this chapter demonstrates that positively charged additives have a profound effect on the crystallisation of CaCO3 changing the morphology to films and fibers. This morphology change was linked to a phase separation process, forming hydrated amorphous droplets of calcium carbonate by a carbonate-polymer interaction, which had the tendency to coalesce and form films. Fiber formation was attributed to oriented attachment of anisotropic particles due to unequal distribution of charge. In the third chapter, based on bone, the mineralisation of collagen by CaCO3 was investigated. By formation of a highly hydrated liquid-like amorphous phase of CaCO3, it was possible to infiltrate the nanoscale gaps of collagen. After crystallisation, nanocrystals of calcite and vaterite were formed, 5 nm thick, but randomly oriented, demonstrating collagen templates the shape but not the orientation of the crystals. In a final chapter hollow rods of CaCO3 were formed by templating them inside membrane pores. The influence of time, pore size, additives and surface chemistry was investigated. Most hollow rods were formed at early timescales which filled up at later times. By changing the surface chemistry, the amount of hollow rods increased significantly in the 200 nm pores

Mechanisms of formation of pseudocalixarene Schiff base macrocycles investigated by ESI-MS

Kulmaczewski, Rafal January 2011 (has links)
Starting from 4-substituted phenols, three dialdehydes were synthesised as Schiff base pseudocalixarene macrocyclic precursors. Two of the dialdehydes, 2,2'methylene-bis- [(6-hydroxymethyl)-4-methylphenol] and 2,2'-methylene-bis-[(6-hydroxymethyl)-4- phenylphenol] were structurally characterised. For the phenyl substituted compound condensation with 1,3-diaminopropan-2-ol, with transition metal ions as template, was investigated and a series of dinuclear complexes was synthesised and characterised by IR, FAB-MS and elemental analysis. The analytical data implied that the complexes have the same saddle shape conformation controlled by hydrogen bonds resulting from mono-deprotonation of the methylendiphenol units as was observed in previous work. A range of TM2M trinuclear complexes [TM = Cu(II), Ni(II) and M = Li(I), Na(I), Mg(II), Ca(II)] of (2+2) macrocycles was synthesised and characterised by IR, MS (FAB, ESI) and elemental analysis. Additionally [Cu2Ca(2+2)(NO3)2](MeOH)2 was characterised by X-ray crystallography. An ESI-MS was used to follow condensation reactions between 2,2'-methylene-bis-[(6- hydroxymethyl)-4-tert-butylphenol] and 1,3-diaminopropan-2-ol in solution with various templates. It was found that, when a transition metal is used alone, the reaction produces only the (2+2) macrocycle. Cu(II) produced equilibrium mixtures containing dicopper(II) and tricopper(II) species but Ni(II) and Zn(II) yielded only dinuclear complexes. When transition metal ions were used in combination with group 1 or group 2 metal ions, the size of the macrocycle and nuclearity of the complex depended on the synthetic route and nature of alkali or alkaline earth metal. Among the products identified in the ESI-MS spectra were trinuclear complexes of the (2+2) macrocycle, pentanuclear sandwich complexes of two (2+2) macrocycles, tetranuclear (3+3) complexes, pentanuclear (4+4) and hexanuclear (6+6) species. One of the routes resulted in formation of [BaCu4(4+4)]2+ ion via a [BaCu4(dialdehyde)4]2+ cluster which was established to be a double template process where both metals are necessary for formation of the macrocycle. The central Ba(II) ion holds the dialdehydes together and the Cu(II) ion orients the carbonyl groups for Schiff base condensation.

Computational studies of molecular actinide and lanthanide complexes

Ingram, K. I. M. January 2007 (has links)
This thesis reports computational DFT studies of three families of complexes (see below). Before presenting the results from these studies, the first chapter introduces the lanthanides and actinides and investigates their similarities and differences through a discussion of selected compounds of each of the series of metals. The second chapter introduces the electronic structure methods that were used in this research and mentions some of the relevant computational utilities. Chapter 3 discusses DFT studies of mixed water/hydroxide uranyl systems, U02(H20)a-:r- OH)x (2-x)+ for x = 0 -> 5 with a = 5, and some a = 3, 4. The reasons for the observed lengthening, and resultant weakening, of U-Oy/ as x increases are investigated. These studies show that this lengthening appears to be predominantly due to a reduction in ionic character stemming from charge build up on the U centre, and not from hydroxide / Oyi competition for U 6d, as has been previously suggested. Time-Dependent DFT is used in chapter 4 to simulate the electronic spectra of U02(NCN)2 and U02(NPN)2 in order to investigate why these complexes are coloured red rather than the normally observed green/yellow of uranyl systems. This chapter involves some preliminary benchmarking calculations on three other uranyl complexes, U02Cl2(TBP)2 , UC>2Cl2(THF)2 , U02(NC>3)2(TBP)2 , as there is as yet no literature suggesting suitable exchange potentials and/or basis sets for TD-DFT calculations on actinides. The conclusion was reached that the unusual colour of the nitrogen donor complexes is due to a small HOMO-LUMO gap resulting from the relatively low energy nitrogen based ligand MOs compared with usual uranyl ligands such as O and CI. Chapter 5 systematically investigates M(N(EPR.2)2)3 , M = Ln (Ln = La, Ce, Pr, Pm, Eu), An (An = U, Np, Pu, Am, Cm) E = O, S, Se, Te R = H to investigate the ligands' suitability for extraction of An(III) from Ln(III), and also to test the suitability of La and U as models for Eu and Am/Cm respectively. The results lead me to conclude that chalcogen donor ligands are extremely promising for successful separation of Cm from Am and Eu, but good separation factors of Am from Eu seem unlikely. Furthermore I conclude that La and U are not suitable models for Eu and Am/Cm as the 2+ capability of Eu seems present in with S, Se, Te U shows considerable covalency in M-E with the heavier chalcogens and there is no evidence of covalency in any Am-E or Cm-E.

The chemistry of isocyanide complexes of iridium (I) and iridium (III)

Bedford, Wendy Margaret January 1976 (has links)
No description available.

Tunable stimulated electronic Raman scattering in alkali metal vapours

Cotter, D. January 1976 (has links)
No description available.

Synthesis of multifunctional ensembles for asymmetric catalysis and chiral recognition : investigation of palladium-trost ligand complexes

Racys, Daugirdas January 2014 (has links)
The palladium complex 1, bearing the Trost 'Standard' Ligandi (TSL) 2 is an efficient and highly selective catalyst used to facilitate asymmetric allylic alkylation. Earlier research conducted by Lloyd Jones and co-workers suggested that the selectivity of the catalyst 1 monomeric species may arise via ligand-accelerated catalysis pathway. TSL 2 has a degree of flexibility that is crucial for the selectivity, but also responsible for the rapid equilibrium of the Pd-TSL monomers 1 with the low selectivity and diminished activity oligomers (I)n. The oligomers (I)n are known to be the dominant catalyst 1 species at higher concentrations responsible for effects observed and are memory in allylic alkylation catalytic cycle. The aim of this work was to further develop the understanding of the aggregated catalyst (I)n. n 1 {(1 )4}n Small-angle neutron scattering (SANS) revealed that Pd-TSL oligomers (I-BArF)n readily aggregate to form cylinders in common organic solvents. According to molecular mechanics modelling at MM3 theory level the architecture is the most consistent with linear stacks of cyclic disc-shaped tetramers {(I-BArF)4}n. In low polarity solvents the rods can grow up to ~200 A long and may contain between 10 to 14 tetramer discs (1)4, sandwiched with bulky BArF anion layers. In polar organic media the solvation is more effective and shorter (30 A) stacks were detected by SANS. Molecular dynamics simulations also supported these observations. Finally, the kinetic SANS experiments showed that the architecture remains effectively unchanged during the catalytic cycle. 1< ~ 200A >1 16-20 A 31p NMR measurements, however, indicated that the highest concentration of monomer 1 with only trace amounts of oligomer {(I)4}n is accessible in very dilute dichloromethane solution of < 4 mM. In contrast, high dielectric constant solvents favour almost complete oligomerisation. Further experiments focused on the structure of {(I-BArF)4}n racemic mixtures. SANS measurements required the complementary perdeuterated complex [Dd-I-BArF. An enantiopure, deuterium labelled [Dd-I-BArF pseudo-enantiomer was prepared by a new divergent synthetic route of 8 steps in the longest linear branch and employing simple commercially available starting materials. SANS data analysis indicated that [Dd-I-BArF formed shorter cylinders than I-BArF. However, the measurements were not sensitive enough to resolve the exact composition of pseudo-racemic mixtures [DoID47I-I-BArF.

Optical properties of transition metal dichaleogenides and their intercalation complexes

Beal, Alan Robert January 1973 (has links)
No description available.

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