Abstract: A process for preparing a cobalt (III) complex is described which comprises: (i) treating a divalent cobalt salt of formula Co.sup.II X.sub.2/n where n is the valency of an anion X, with up to 15 molar equivalents of ammonia or an amine; (ii) oxidizing the resulting amine complex; (iii) converting the oxidized complex to the corresponding carboxylate of formula ?Co.sup.III (NR.sub.3).sub.5 R.sup.1 COO!X.sub.2/n where each R, which may be the same or different, represents hydrogen or an optionally substituted hydrocarbon group and R.sup.1 represents an alkyl or alkenyl group of 1 to 18 carbon atoms, at a pH above 8.5; and optionally (iv) replacing the X ion by a different anion by a metathetical reaction.