Noncontinuum solvent effects upon the intrinsic free-energy barrier for electron-transfer reactions

Joseph T Hupp, Michael J. Weaver

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Abstract

A phenomenological electrochemical approach is outlined by which "noncontinuum" contributions to the outer-shell intrinsic barrier to electron transfer, ΔG*os, resulting from specific reactant-solvent interactions can be estimated from the measured dependence of the formal potential upon the molecular and structural properties of the solvent. A simplified derivation, based on electrochemical half-reactions, of the conventional dielectric continuum expression is given in order to clarify the physical origins of the outer-shell intrinsic barrier and to identify likely additional noncontinuum components. Numerical calculations for ammine and other redox couples involving specific ligand-solvent interactions indicate that the noncontinuum contributions to ΔG*os for both homogeneous and electrochemical exchange reactions can be surprisingly small (typically ≲1-2 kcal mol-1) even when the thermodynamics of ion solvation are in severe disagreement with the dielectric continuum (Born) predictions. An additional noncontinuum component associated with vibrational distortions of outer-shell solvent may be significant for multicharged aquo complexes and other reactants engaging in strong ligand-solvent hydrogen bonding.

Original languageEnglish
Pages (from-to)1601-1608
Number of pages8
JournalJournal of Physical Chemistry
Volume89
Issue number9
Publication statusPublished - 1985

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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