Dinuclear copper(II), nickel(II) and mixed valence CuII-CuI complexes: influence of donor groups on redox behaviour of dicopper complexes

Abstract

Dinuclear copper(II) and nickel(II) complexes of hexadentate Schiff base ligands derived from 2,6-diformyl-4-methylphenol, 1,3-diaminopropane with various ortho and/or para substituted anilines have been synthesized and investigated for their magnetic and electrochemical properties. The dinuclear copper(II) complexes exhibit strong antiferromagnetic interactions between the metal centres (μeff/copper atom = 0.98–1.10 μB). For the nickel(II) complexes the interaction is weak (μeff/nickel atom = 2.83–3.02 μB). These complexes undergo sequential one-electron transfers at two different potentials. The first electron-reduction potential (E1) shifts to more negative values for copper(II) complexes having potential donor groups at the ortho position of the phenylazomethine ring. This has been attributed to the weak bonding interaction of these groups with the central metal ion. Analogous mononuclear copper(II) complexes with donor groups such as OMe, OEt and SMe are shown to give irreversible CV peaks. Mixed-valence CuIICuI complexes of analogous para substituted anilines have been synthesized by chemical methods and the unpaired electron is found to be localized on one of the coppers.