Magnetic, catalytic, EPR and electrochemical studies on binuclear copper(II) complexes derived from 3,4-disubstituted phenol

Abstract

New symmetrical compartmental binucleating ligands 2,6-bis[N-(2-dimethylaminoethyl)-N-methyl)aminomethyl]-3,4-dimethylphenol [HL1] and 2,6-bis[N-(2-diethylaminoethyl)-N-ethyl)aminomethyl]-3,4-dimethylphenol [HL2], and their copper(II) complexes [Cu2L1–2(X)]ClO4, (X = NO2 -, OAc- and OH-) have been prepared. Spectral, catalytic, magnetic, EPR and electrochemical studies have been carried out. A catecholase activity study indicates that only HL1 complexes have efficient catalytic activity due to a less sterically hindered methyl group and enhanced planarity (larger-2J values) with respect to the oxidation of 3,5-di-t-butylcatechol to the corresponding quinone. Variable temperature magnetic susceptibility studies of the complexes show antiferromagnetic interaction between the copper atoms. X-band EPR signals could not be observed for polycrystalline samples both at room temperatures and liquid nitrogen, consistent with two antiferrromagnetically coupled copper centres in the solid state. EPR spectral studies in methanol solvent show well-defined four hyperfine signals at room temperature due to decomposition of the dimer into monomers. This however is not seen in frozen methanol glass, may be owing to restructuring of the monomers into dimers due to an increase in viscosity of the solvent. Electrochemical studies revealed chemically irreversible behaviour due to chemical or/and stereochemical changes subsequent to electron transfer.