Synthesis, structural, magnetic and electrochemical studies of antiferromagnetically coupled symmetric oxamidate-bridged binuclear copper(II) complexes

Abstract

The new binuclear copper(II) complexes Cu2L1-3 and [Cu2L4,5](ClO4)2 were synthesized by reaction of the monomeric cis-N,N′-bis(3-aminopropyl)oxamidatocopper(II) complex [Cu(oxpn)] with acetylacetone, benzoylacetone, salicyl-aldehyde, 2-pyridinecarboxaldehyde and diacetyl monoxime in the presence of copper(II) acetate or perchlorate owing to the trans isomerisation of the cis-oxamidato complex. The crystal structure of Cu2L1 consists of centrosymmetric binuclear copper(II) ions which are bridged by an oxamidato group in the trans conformation with a copper-copper distance of 5.121 Å. Each copper(II) ion occupies an inner site of the N2O2 donor with a distorted square-planar environment. Electrochemical studies showed that two quasireversible one-electron reduction waves are obtained in the cathodic region (Epc1 = -0.48 to -1.02 V, E pc2 = -1.08 to -1.34 V). The conproportionation constants Kcon for the mixed-valence CuICuII complexes have been determined electrochemically. Room-temperature magnetic-moment studies of binuclear copper(II) complexes reveal the presence of a strong antiferromagnetic interaction (μeff = 1.14-1.24 μB) which is also observed from the broad spectra with g = 2.1. A variable-temperature magnetic-susceptibility study of the complexes 1 and 4 gives J values of -510 cm-1 and -497 cm-1 respectively. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.