Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

James H. Espenson

Abstract

The cation (H[subscript]2O)[subscript]5CrO[subscript]2[superscript]2+ has a considerable lifetime in aqueous solution in the absence of Cr[superscript]2+. One pathway for decomposition consists of bond homolysis, CrO[subscript]2[superscript]2+ → Cr[superscript]2+ + O[subscript]2. The resulting Cr[superscript]2+ then reacts very rapidly with CrO[subscript]2[superscript]2+. A second pathway, yielding HCrO[subscript]4[superscript]-, proceeds by a bimolecular reaction between two CrO[subscript]2[superscript]2+ ions. The data do not require a description of CrO[subscript]2[superscript]2+ as other than a superoxochromium(III) ion;The oxidation-reduction reactions of the superoxochromium(III) ion have been examined with several well-known one electron reducing agents, Ru(NH[subscript]3)[subscript]6[superscript]2+, Co(sep)[superscript]2+, and V(OH[subscript]2)[subscript]6[superscript]2+. The results are consistent with outer-sphere mechanisms. Studies were also carried out with several mild reducing agents with labile coordination positions, Fe(OH[subscript]2)[subscript]6[superscript]2+, Co((14) aneN[subscript]4)(OH[subscript]2)[subscript]2[superscript]2+, and Co((15) aneN[subscript]4)(OH[subscript]2)[subscript]2[superscript]2+. The results are consistent with inner-sphere mechanisms characterized by the formation of a binuclear intermediate and subsequent decomposition of this intermediate;The cobalt(II) macrocycle L[subscript]2Co(dmgBF[subscript]2)[subscript]2 has been characterized by crystallography (L = CH[subscript]3OH) and by spectroscopic UV/vis, EPR, electrochemical, and magnetic methods as well as elemental analysis for L = H[subscript]2O. In aqueous perchloric acid the diaquo complex is reversibly oxidized to (H[subscript]2O)[subscript]2Co(dmgBF[subscript]2)[subscript]2[superscript]+ by Fe[superscript]3+. The equilibrium constant was determined for this reaction yielding the reduction potential for the Co(III)/Co(II) couple. The prominent inverse-(H[superscript]+) component suggests an inner-sphere reaction between (H[subscript]2O)[subscript]2FeOH[superscript]2+ and the Co(II) complex. A detailed analysis of the mechanism interpreted on that basis is presented; it suggests that intramolecular electron transfer within a binuclear intermediate is the rate limiting step;The characterization, kinetics, and mechanisms of the reactions of (H[subscript]2O)[subscript]2Co(dmgBF[subscript]2)[subscript]2 with various oxidants were studied in aqueous solution. The reaction of (H[subscript]2O)[subscript]2Co(dmgBF[subscript]2)[subscript]2 with hydrogen peroxide follows a 1:1 reaction stoichiometry ((H[subscript]2O)[subscript]2Co(dmgBf[subscript]2)[subscript]2:H[subscript]2O[subscript]2). This reaction has a complex mechanism which includes the oxidation of the Co(II) metal center as a first stage. The reaction of (H[subscript]2O)[subscript]2Co(dmgBF[subscript]2)[subscript]2 with t-BuOOH follows a 2:1 reaction stoichiometry ((H[subscript]2O)[subscript]2Co(dmgBF[subscript]2)[subscript]2:t-BuOOH). The mechanism for this reaction includes the formation of (H[subscript]2O)[subscript]2Co(dmgBF[subscript]2)[subscript]2[superscript]+ and CH[subscript]3Co(dmgBF[subscript]2)[subscript]2(H[subscript]2O). ftn[superscript] aDOE Report IS-T-1297. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

DOI

https://doi.org/10.31274/rtd-180813-12845

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Mark Erick Brynildson

Language

en

Proquest ID

AAI8805049

File Format

application/pdf

File Size

230 pages

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