Some reactions of di-µ-hydroxo-bis{dioxalatocobaltate(III)} in aqueous solution

Abstract

The kinetics of hydrolysis of di-µ-hydroxo-bis{dioxalatocobaltate(III)} to give dioxalatodiaquocobaltate(III) have been studied in aqueous solutions in the pH range 3·5–4·6. Under these conditions, cobalt(II) is the final product, but is formed by the decomposition of the dioxalatodiaquocobaltate(III), not directly from the dinuclear complex. The accelerating effect of increasing the carboxylate buffer concentration at constant pH is interpreted by postulating replacement by the carboxylate of the ligand water in the singly bridged dinuclear intermediate of the hydrolysis.

The slow reduction of di-µ-hydroxo-bis{dioxalatocobaltate(III)} by tin(II) at pH 4·5 in dilute sodium chloride solution does not markedly induce the reduction of trioxalatocobaltate(III). This observation shows that no free tin(III) is produced as an intermediate. Nevertheless, the rate of the reaction suggests that the reaction involves two consecutive electron transfers from tin to the cobalt complex, the first electron transfer determining the rate of the overall reaction.