Synthesis, crystal structure and spectral studies of Cu(II)/Cu(I) complexes derived from diamide bisbenzimidazole ligand

A new benzimidazole based diamide ligand-N,N'-bis(2-methylbenzimidazolyl)-2,2'-oxydiethanamide (GBOA)-has been synthesized and utilized to prepare [Cu(GBOA)Cl-2] and [Cu-I(NO3)(GBOA)]. The complex [Cu(GBOA)Cl-2] has been characterized structurally. It crystallizes in monoclinic space group P2(1)/n. The Cu(II) ion is in a slightly distorted square pyramidal coordination environment (tau = 0.167). Two trans bonded chlorine atoms, and two nitrogen atoms from two different molecules of benzimidazole ligand form the basal plane while the amide oxygen occupies the axial position of the square based pyramid. The structure of the complex is a one-dimensional, ligand-bridged polymer. Solid state X-band EPR spectrum of the complex shows a slightly broadened isotropic signal at g = 2.0. The complexes display a quasi-reversible redox wave due to the Cu(II)/Cu(I) redox couple with E-1/2 values varying as NO3- < Cl-. With respect to NHE, the E-1/2 values are quite positive when compared to other benzimidazole based complexes (Inorg. Chim. Acta 151 (1988) 55). The catechol oxidase activity of [CuCl,(GBOA)] has been examined by studying the oxidation of various catechols in oxygen saturated methanol. Kinetic studies with [CuCl2(GBOA)] and DTBC (3,5-di-tert-butylcatechol) as substrate shows the initial rate of oxidation to be dependent on first power of catalyst concentration and square-root of substrate concentration. (C) 2003 Elsevier B.V. All rights reserved.