Kinetics of hydrolysis of di-µ-hydroxo-bis[nitrilotriacetatocobaltate(III)] to diaqua(nitrilotriacetato)cobalt(III), and some reactions of the latter with non-metallic substrates in aqueous solution

Abstract

The kinetic behaviour of di-µ-hydroxo-bis[nitrilotriacetatocobaltate(III)] on hydrolysis in acid solution gives evidence for two isomeric forms of different reactivity. The product, diaqua(nitrilotriacetato)cobalt(III), is reduced to cobalt(II) by hydrazine. hydroquinone, hydroxylamine. iodide, and thiosulphate in acidic solutions. With thiocyanate, replacement of ligand water occurs, and with nitrite, ligand water substitution occurs at pH 4.5, and reduction of cobalt(III) occurs at pH 5.6. Similarities in the rate constants for these reactions suggest that the formation of an inner-sphere complex with the substrate is rate determining. Sulphite also reduces the cobalt(III) complex, but here decomposition of a rapidly formed sulphitocobalt(III) inner-sphere complex appears to be the slow step.