PRESSURE-DEPENDENCE OF THE ELECTRODE-POTENTIALS OF SOME IRON(III II),COBALT(III/II), AND NI(III/II) COUPLES IN AQUEOUS-SOLUTION - ESTIMATION OF THE REACTION VOLUMES FOR M(III)/M(II) COUPLES/

Pressure dependence of the electrode potentials for various M3+/(2+) c ouples (M = Fe, Co, and Ni with o-phenanthroline, bipyridine, terpyrid ine, 1,4,7-triazacyclononane, and 1,4,7-trithiacyclononane) was measur ed by cyclic voltammetry in aqueous solution vs. a Ag/AgCl reference e lectrode. The reaction Volume of the Ag/AgCl reference electrode was e stimated from the change in the partial molar volumes of Fe-aq(3+/2+) and Co(terpyidine)(2)(3+/2+) couples, and the volumes for the formatio n of M2+ from M3+ were determined. The electrostrictive component for the change in the oxidation state for the M3+/2+ couple was calculated on the basis of the Drude-Nernst equation and by the mean spherical a pproximation (MSA). The isolated volumes for the formation of M2+ from M3+ were compared with the values predicted by theory.