Environmental effects on the rate of electron transfer in mixed-valence molecules

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Lowery, Michael Dean

Contributors dc:contributor

• Hendrickson, David N.

• Chemistry, Inorganic

Statement dc:rights

• Copyright 1989 Lowery, Michael Dean

Language dc:language

eng

Identifier

AAI9010943
(UMI)AAI9010943

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/19121