Ionic association equilibria in the dimethyl sulphoxide solutions of Mn(CF 3COO) 2, Co(CF 3COO) 2 and Ni(CF 3COO) 2

Abstract

The molar conductivity curves have been determined for Mn(CFR 3COO) 2, Co(CF 3COO) 2 and Ni(CF 3COO) 2 in dimethyl sulphoxide at 25°C. The first step association constants are derived. Auxiliary measurements of the visible absorption spectra and the nmr chemical shifts of the solvent protons indicate lack of coordination 1 1 Throughout this paper the term “coordination” will be used to denote formation of an inner-sphere complex, usually of the type MXL − n ( M, X and L denoting the metal cation, the anion and the solvent molecule, respectively). The other type of ionic association, leaving the first coordination sphere of the cation essentially unchanged will be referred to as outer sphere association. of the anion in the solutions of Ni(CF 3COO) 2. On the other hand, bidentate coordination of the anion, taking place to a small extent in addition to the outer-sphere association, is inferred for Co(CF 3COO) 2. On the assumption that the outer-sphere association constants are approximately the same for the three metal trifluoroacetates, the highest extent of the inner-sphere association is inferred for Mn(CF 3COO) 2.