Solvent, ligand, and ionic charge effects on reaction entropies for simple transition-metal redox couples

Joseph T Hupp, Michael J. Weaver

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The dependence of the reaction entropies, ΔS°rc, for simple M(III/II) redox couples (M = Ru, Fe Os, Cr) upon the nature of the ligands and the solvent is examined with a view toward correlating ΔS°rc with simple physical parameters. For couples containing ammine, ethylenediamine, polypyridine, cyclopentadiene, or pseudohalide ligands, ΔS°rc in a given solvent is found to correlate well with (Zox 2 - Zred 2), where Zox and Zred are the charge numbers of the oxidized and reduced forms, and with 1/r, where r is the effective radius of the redox couple. This suggests that specific ligand-solute interactions do not provide a predominant contribution to ΔS°rc for these systems, although this effect is probably important for aquo redox couples in water. The dependence of ΔS°rc upon the solvent correlates reasonably well with the solvent "acceptor number" and other solvent polarity parameters. This is rationalized in terms of a contribution to ΔS°rc arising from disruption of the surrounding solvent structure by the charged solute. The predictive as well as interpretative virtues of such semiempirical correlations of reaction entropies are pointed out.

Original languageEnglish
Pages (from-to)3639-3644
Number of pages6
JournalInorganic Chemistry
Issue number22
Publication statusPublished - 1984


ASJC Scopus subject areas

  • Inorganic Chemistry

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