Environmental effects on the rate of electron transfer in mixed-valence molecules
Lowery, Michael Dean
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Permalink
https://hdl.handle.net/2142/19121
Description
Title
Environmental effects on the rate of electron transfer in mixed-valence molecules
Author(s)
Lowery, Michael Dean
Issue Date
1989
Doctoral Committee Chair(s)
Hendrickson, David N.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Language
eng
Abstract
Recently, it has become evident that the environment both in the solid state and in solution about a mixed-valence complex can have a pronounced effect on the rate of intramolecular electron transfer. For 1$\sp\prime$,1$\sp{\prime\prime\prime}$-dimethylbiferrocenium triiodide hemi(iodine) it was found that the environment imposed by the I$\sb{8\sp-}$ anion was nearly symmetric (space group C2), and variable temperature $\sp{57}$Fe Mossbauer spectroscopy showed that the complex changed from a valence trapped to a valence detrapped description abruptly at $\sim$325 K. This behavior is similar to that found in 1$\sp\prime$,1$\sp{\prime\prime\prime}$-diethyl(-d$\sb3$)biferrocenium triiodide (where the ethyl group has been deuterium labeled) which detraps at $\sim$275 K on the $\sp{57}$Fe Mossbauer timescale. $\sp2$H NMR spectroscopy showed that the ethyl group undergoes rapid C$\sb3$ rotation, but the $\sp2$H NMR spectrum did not change appreciably as the complex changes from valence trapped to detrapped. The ethyl group does not appear to be directly involved in the valence detrapping process. Variable temperature $\sp2$H NMR spectroscopy has also been used to probe the environment about the Creutz-Taube ion, ((ND$\sb3$)$\sb5$Ru(pyz)Ru(ND$\sb3$)$\sb5$) Cl$\sb5$5D$\sb2$O. It was found that the hydrate water structure changed dramatically from rapid nearly isotropic motion at room temperature to hindered motion below 200 K. It was postulated that the decrease in the solvate water dynamics could result in an asymmetry in the environment about the Creutz-Taube ion and possibly result in partial valence trapping at low temperature. Lastly, the solution intervalence transfer (IT) spectra for a series of mixed-valence complexes was examined. From pressure induced freezing studies it was found that classical Marcus theory does not appear to be applicable to these systems. Also, a pronounced concentration dependence was observed for the IT band characteristics. It was shown that these effects resulted from the formation of ion aggregates in solution. With the formation of ion aggregates in solution (which perturbs the environment about the mixed-valence cation), the applicability of the Marcus, Hush, and PKS methods of analysis of electron transfer parameters from the IT band characteristics is questioned.
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