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A Spectroscopic Study of Uranium(IV) Solution Chemistry.

Oulabi, Mawieh. (1989) A Spectroscopic Study of Uranium(IV) Solution Chemistry. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

Uranium(IV) forms nine-coordinate complexes with some β-diketones and a monodentate substrate, e.g., U(TTA)4.pyridine. This thesis describes the formation of the nine-coordinate complexes in non aqueous solvents using 25 different substrates S (where S may have nitrogen or oxygen donor atoms or both) and thenoyltrifluoroacetonate (TTA) as the β-diketone. Both electronic and 1H nmr spectroscopy are used to investigate the systems. It has been shown that the the equilibrium constant (K) for the reaction in non-aqueous solvents U(TTA)4 + S ↔ U(TTA)4.S can be measured by a u.v./visible spectrophotometric method (benzene solvent) with good reliability. The value of log10K is shown (i) to decrease with decrease in the basicity of the substrate S and (ii) to decrease with increased steric hindrance at the substrate donor atom. In suitable circumstances both nitrogen and oxygen donor substrates gave relatively high values of K. It was shown that U(TTA)4 is eight-coordinate in benzene but nine-coordinate in acetone. 1H nmr spectra of the substrates in the presence of U(TTA)4 were little broadened and shifted by what is thought to be a pseudocontact shift mechanism. The values of the shifts obtained at various S concentrations clearly demonstrate which substrate atom is coordinated to uranium(IV). For example, with substrate such as 4-aminoantipyrine the carboxyl oxygen atom rather than the amino group nitrogen atom is coordinated. There was no evidence that a ligand S could coordinate in a bidentate fashion and U(TTA)4.S appears to be always nine-coordinate. In addition, the 1H nmr data were used to find K and AB (the bound chemical shift) for some substrates. The values of K were less reliable than those found from electronic spectroscopy, for a given substrate each independent hydrogen atom has an individual value of ΔB and ratios of them were used to illustrate the relative importance of contact and pseudocontact shifts but with inconclusive results. However, these ratios clearly confirm that the correct coordinating donor atom had been found. Experiments in acetone and benzene show in general that K is greater for a given substrate in benzene. The value of K for S=H2O was found in acetone and (surprisingly) appears to have a smaller value in benzene. Preliminary experiments on the oxidation of uranium(IV) in non-aqueous solvents were performed in order to find the ideal conditions for spectroscopic experiments. Rapid manipulation of the reactants in air was shown to be a suitable method rather than the use of nitrogen lines and boxes which have little advantage and are time-consuming.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Oulabi, Mawieh.
Date : 1989
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 1989.
Depositing User : EPrints Services
Date Deposited : 06 May 2020 14:23
Last Modified : 06 May 2020 14:29
URI: http://epubs.surrey.ac.uk/id/eprint/856166

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