Energy transfer between Reineckate ion (donor) and hexacyanochromate(III) ion (acceptor) has been studied through quenching of donor phosphorescence (lifetime and intensity) and sensitization of acceptor phosphorescence. Results from all measurements fit the expected Stern-Volmer relationship with a quenching constant kQH = 7.2 x 10⁵ M⁻¹ sec⁻¹ at -65°C. The pre-exponential factor and activation energy of kQH are 6.6 x 10¹º M⁻¹ sec⁻¹ and 4.8 Kcal/mol respectively. The constant, kQH’ is attributed entirely to an energy transfer rather than a quenching process. The electronic states directly involved are the ²Eg (and/or² T₁g) states of both donor and acceptor. Energy transfer is a diffusion-controlled (collisional) process. Hexacyanochromate(III) ion is itself quenched in the presence of Reineckate ion. The quenching constant, k'QH, which may be attributed to back energy transfer from acceptor to donor, has a pre-exponential factor of 2 x 10¹² M⁻¹ sec⁻¹ and an activation energy of 7.6 Kcal/mol. In the same system, quenching of photoaquation has also been studied at -65°C. The photoaquation quantum yield of Reineckate ion is 1.02 x 10⁻². It is reduced in the presence of hexacyanochromate(III) ion, but not as much as the phosphorescence of Reineckate ion is reduced. The limiting unquenchable part, ϕ∞chem, occurs via the ⁴T₂g state, while the quenchable part must occur through the ²Eg state as an intermediate. The actual path for the quenchable part proposed is back intersystem crossing from the ²Eg to the ⁴T₂g state, which then undergoes aquation. The primary processes of ²Eg state molecules have been investigated through the temperature dependence of phosphorescence lifetimes of some Cr(III) complexes. All the available evidence supports the idea of the thermally activated back intersystem crossing. According to this mechanism, the origins of the ⁴T₂g states of Cr (III)complexes reached by crossing are far lower in energy than has been expected. Assuming the occurrence of back intersystem crossing, the application of energy transfer to the determination of intersystem crossing quantum yield, ϕisc’ has been demonstrated. The values of ϕisc for Reineckate and hexacyanochromate (III) ions are estimated to be 0.52 and 0.35, respectively. The variation of ϕisc with temperature for these Cr(III) complexes has also been measured, which suggests that in general, internal conversion has a strong temperature dependence. From the rise of phosphorescence with time after pulse excitation, a new parameter, Tx, has been obtained which represents population of the phosphorescing state and is believed to be the lifetime of the ⁴T₂g (or less likely ²T₁g) state. Efforts have been made to confirm and identify this parameter. Studies of ϒx have been carried out as a function of temperature. Mechanisms based on different tentative assignments of ϒx are proposed and their implications examined. All primary processes, except the intrinsic radiative transitions, seem to consist of at least two components, which take different pathways and are different functions of temperature. / Science, Faculty of / Chemistry, Department of / Graduate

Although the organo hydride derivatives of boron and aluminum are well characterized, little work has been reported on the corresponding gallium systems. The present study was initiated to determine the relative stabilities and reactivity of organo gallium hydride derivatives as compared with the stabilities and reactions of the corresponding compounds of boron and aluminum. Various preparative routes to this new class of gallium compounds have been investigated. These include the use of organo-mercury, organo-lithium and lithium hydride derivatives in reactions with gallium hydride and gallium alkyl compounds and their halogen substituted derivatives: Me₃NGaH₃ + HgR₂ → Me₃NGaH₂R + 1/2Hg + 1/2H₂ Me₃NGaH₂Cl + LiR → Me₃NGaH₂R + LiCl Me₃NGaR₂Cl + LiH → Me₃NGaHR₂ + LiCl A fourth preparative method involves disproportionation reactions between gallium hydride compounds and organo gallium compounds to yield the mixed organo hydride derivatives. Alkyl-hydride disproportionation reactions were also examined using organo and hydride derivatives of different Group IIIB elements in order to obtain a better understanding of the exchange process. Both infrared and proton NMR spectroscopy have been used extensively in following the progress of these reactions and in the characterization of the products. / Science, Faculty of / Chemistry, Department of / Graduate

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In Chapter One, the sodium salt of tris (2-oxo-1-t-butylimidazolyl) hydroborate, [To^But]Na, as an [O_3] donor ligand has been prepared. The yield for this reaction was low because there is a significant amount of side product in which the double bond of the oxoimidazole starting material is reduced. Treatment of sodium borohydride with bezannulated oxoimidazole at high temperature leads to the generation of the sodium salt of tris (2-oxo-1-R-methylbenimidazolyl) hydroborate in high yield, [To^RBenz]Na. These ligands have been prepared with different alkyl substituents, methyl, t-butyl and adamantyl, to achieve the desired steric environment. Furthermore, these benzannulated ligand have been used to synthesize a series [To^RBenz]Tl complexes, which exist as a discrete mononuclear complexes in the solid state. Finally, [To^RBenz]Tl complexes are more pyramidal than the sulfur counterpart, [Tm^RBenz]Tl, but less pyramidal than those in the tris (pyrazolyl)hydroborato counterpart, [Tp^R,R]]Tl. In Chapter Two, the properties of [To^R] ligands have been evaluated versus related L_2X ligands. [To^R] ligands are substantially more sterically demanding than the corresponding [Tm^R] sulfur donor ligand and related [O_3] donor ligands. However, electronically, the [To^R] ligands exhibit weaker electron donating properties than other L_2X type ligands. Finally, the coordination chemistry of [To^R] ligands with various metal compounds has been briefly investigated. The synthesis of a new class of bidentate ligands has been detailed in Chapter Three. Namely the bis(2-oxo-1-t-butylimidazolyl)hydroborato and bis (2-oxo-1-alkylbenzimidazolyl)hydroborato, [Bo^But] and [Bo^RBenz], have been synthesized via the reaction of MBH_4 with two equivalents of the respective 2-imidazolone. Chelation of [Bo^But] and [Bo^MeBenz] to a metal center results in a flexible 8-membered ring that is capable of adopting a "boat-like" conformation that allows for secondary M—H—B interactions. Chapter Four describes the synthesis of [Bo^RBenz]_2Zr(CH_2Ph)_2and [To^RBenz]Zr(CH_2Ph)_3 with different alkyl substituents. Treatment of [To^ButBenz]Zr(CH_2Ph)_3 with ([PhNHMe_2][B{C_6F_5}_4]) in a coordinating solvent, Et_2O, generates {[To^ButBenz]Zr(CH2Ph)_2(OEt_2)}{B(C_6F_5)_4} which exhibit a very low activity for ethylene polymerization. However, a coordinatively unsaturated cationic zirconium alkyl complex was obtained by the treatment of ([PhNHMe_2][B{C_6F_5}_4]) with [To^ButBenz]Zr(CH_2Ph)_3 or [To^AdBenz]Zr(CH_2Ph)_3 which generate [To^ButBenz]Zr(CH_2Ph)_2[B(C_6F_5)_4 or [To^AdBenz]Zr(CH_2Ph)_2[B(C_6F_5)_4], respectively. Moderate activity for ethylene polymerization was obtained for t-butyl while high activity was obtained for the adamantyl derivatives. Finally, Chapter Five describes the synthesis of new oxygen-rich ligands, namely tris (2-pyridonyl)methane, [Tpom^R]H. They are obtained via the reaction of 2-pyridones with CHX_3 and K_2CO_3 in the presence of [Bu^n _4N]Br, followed by acid-catalyzed isomerization with camphorsulfonic acid. These compounds provide access to a new class of L_3X alkyl ligands that feature oxygen donors and are capable of forming metallacarbatranes, as exemplified by [Κ^4-Tpom^But]ZnOC6H4Bu^t. In addition, the [Tpom^But] ligand also allows isolation of a monovalent thallium alkyl compound, [Tpom^But]Tl, in which the Tl—C bond is long and has little covalent character.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Washington. / Bibliography: l. 157-163.

Thesis (MSc)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.