Date of Award

11-16-1998

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

David T. Pierce

Abstract

This Ph.D. research focused on improvement in the understanding of structurally perturbed electron transfer (ET) events. This broad category of ET was divided into the two categories of concerted and sequential mechanisms. Investigations of the concerted mechanism focused on the electrochemical behavior of six redox couples: (Cr(III/II)TCTA($\rm\sp{0/-},\ \lbrack Mn(II/III)TCTA\rbrack\sp{-/0}$, (Mn(III/IV)TCTA) $\sp{\rm 0/+$, (Fe(II/III)TCTA) $\sp{\rm 0/-}$, (Co(II/III)TCTA) $\sp{\rm -/0}$, and (Ni(II/III)TCTA) $\sp{\rm /-}$ (where TCTA is 1,4,7-triazacyclononane N,N$\rm\sp\prime,N\sp{\prime\prime}$ triacetate). After synthesis of TCTA and the Cr(III), Mn(II), Mn(III), Fe(II), Fe(III), Co(III) Ni(II) and Ni(III) TCTA complexes, each complex was characterized by UV-vis-near IR, FTIR, magnetic susceptibility and Molar Conductance. Electrochemical characterization of each couple in aqueous media was performed. The ET rate constants were determined for (Mn(II/III)TCTA) $\sp{\rm -/0}$, (Fe(II/III)TCTA) $\sp{\rm 0/-}$, and (Ni(II/III)TCTA) $\sp{\rm 0/-}$ utilizing both cyclic voltammeter and scanning electrochemical microscopy in water and mixed water/acetonitrile solvents. Correlation's of ET events in aqueous media with conventional Marcus-Hush ET theory were excellent for two couples ((Mn(II/III)TCTA) $\sp{\rm -/0}$, and (Fe(II/III)TCTA) $\sp{\rm O/-})$ when double layer corrections could be adequately performed. Asymmetric solvation was examined and it was conclusively shown that a very small change in the 3-dimensional structure of a molecule can induce profound changes in the solvation sphere. It was also demonstrated that double layer effects at a Pt electrode may not correlate with those observed at an Hg$\sp\circ$ electrode.Studies of the sequential ET mechanism relied upon six complexes of (Ni(II)TETA) (where TETA is 1,4,8,11-tetraazacyclotetradecane N,N$\rm\sp\prime, N\sp{\prime\prime},N\sp{\prime\prime\prime}$-tetraacetate). Four new species were synthesized: N$\rm\sb2{\bf O}\sb4$-(Ni(II)TETA), $\rm {\bf N}\sb4{\bf O}(H\sb4{\bf O}$)-trans-I- (Ni(II)TETA), $\rm {\bf N}\sb2{\bf O}\sb2$-(H$\sb2$O) $\sb2$ (Ni(II)H$\sb2$TETA) and N$\rm\sb3{\bf O}\sb3$- (Ni(II)HTETA) in addition to the two previously known, $\rm {\bf N}\sb4{\bf O}\sb2$- (NiH$\sb2$(II)TETA) and $\rm {\bf N}\sb4{\bf O}\sb2$-cis-V- (Ni(II)H$\sb2$TETA. Structural characterization and solution reactivity and electrochemical characterization followed. The electrochemical behavior of $\rm {\bf N}\sb2{\bf O}\sb4$- (Ni(II)TETA) and $\rm {\bf N}\sb4{\bf O}\sb2$- (NiH$\sb2$(II)TETA) showed a simple quasi-reversible one electron transfer process. Three oxidatively induced isomerization reactions were shown to occur: $\rm {\bf N}\sb4{\bf O}(H\sb2{\bf O}$)-trans-I- (Ni(II)TETA) to $\rm {\bf N}\sb2{\bf O}\sb4$- (Ni(II)TETA), $\rm {\bf N}\sb3{\bf O}\sb3$- (Ni(II)HTETA) to $\rm {\bf N}\sb2{\bf O}\sb4$- (Ni(II)TETA) and $\rm {\bf N}\sb4{\bf O}\sb2$-cis-V- (Ni(II)H$\sb2$TETA to $\rm {\bf N}\sb4{\bf O}\sb2$- (Ni(II)H$\sb2$TETA), although each had associated with the isomerization reaction the competing reaction of water hydrolysis.

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