Activation Volumes for Peroxodisulphate Oxidation of Low-spin Iron(II) Complexes in Aqueous Salt Solutions

Abstract

Activation volumes are reported for peroxodisulphate oxidation of the four complexes of the Fe2+-2,2′-bipyridyl-cyanide sequence, viz. [Fe(bipy)3]2+, [Fe(bipy)2(CN)2], [Fe(bipy)(CN)4]2- and [Fe(CN)6]4- (abbr. bipy for 2,2′-bipyridyl), in aqueous solutions of a selection of nitrate, sulphate, and perchlorate salts of Li+, Na+, K+, and Mg2+ containing up to 6 mol dm-3 of added salt. The dependences of activation volumes on the nature and concentration of the added salt, and on the nature of the iron(II) complex, are established and discussed. Ancillary information relevant to hydration of the substrate complexes in the initial state for peroxodisulphate oxidation has been obtained from solvatochromism (halochromism) of [Fe(bipy)2(CN)2] and of [Fe(bipy)(CN)4]2-, and from the solubility of [Fe(bipy)2(CN)2], in some of the electrolyte solutions used in the high pressure kinetic studies.