The Effect of Ligand Structure on Spectral Characteristics and Kinetics of Redox Reactions of Copper(II) and Copper(III) Complexes with Macrocyclic Ligands Containing amide Groups

Spectral characteristics of macrocyclic copper(II) and copper(III) complexes with 13- and 14-membered tetraaza ligands containing two amine and two deprotonated amide groups (CuL) have been studied. It was shown that, unlike copper(II) complexes, the spectral properties of copper(III) compounds are more sensitive to such ligand structure parameters as ring size and the presence of benzyl substituents. Rate constants and activation parameters for oxidation of CuIIL by peroxodisulfate and decomposition reactions of CuIIIL in aqueous solutions at pH 5 were also measured. Activation parameters were shown to be dependent on ligand structure and the tendencies of their changes are opposite in these two types of reactions. Decomposition of copper(III) compounds proceeds probably through protonation of the amide group in acidic media and through deprotonation of amine group in alkaline media. The copper(III) complex with a benzyl-substituted 13-membered ligand was found to be most kinetically stable among all compounds studied. Possible reaction mechanisms are discussed.