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.
|Number of pages||6|
|Publication status||Published - 1984|
ASJC Scopus subject areas
- Inorganic Chemistry