Comparative study of the electrochemical and pulse-radiolytic oxidation of the complexes of nickel(II) and copper(II) containing 1,4,8,11-tetra-azacyclotetradecane

Abstract

Electrochemical and pulse-radiolytic oxidation of [Ni(cyclam)]²⁺ and [Cu(cyclam)]²⁺(cyclam = 1,4,8,11-tetra-azacyclotetradecane) have been studied in aqueous acidic perchlorate and sulphate media. As with other nickel macrocyclic systems, [Ni(cyclam)]²⁺ is oxidized to Ni^III, the stability of which is enhanced by sulphate complexation. In contrast, [Cu(cyclam)]³⁺ is much less stable than the nickel analogue and does not form a stable sulphate complex. Electrochemical oxidation of [Cu(cyclam)]²⁺ at pH 1.6 is a multistep process which is catalysed by sulphate ion. The mechanism appears to involve the transfer of four electrons resulting in a copper(II) macrocyclic diene complex.