Synthesis, molecular structure and reactivity of a new dicopper(II) benzimidazole complex with non-identical copper(II) sites

• Published in: Polyhedron Vol. 15; no. 13; pp. 2179 - 2185
• Main Authors: Holz, Richard C., Gobena, Feben T.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.1996
• ISSN: 0277-5387
• DOI: 10.1016/0277-5387(95)00501-3

The dinucleating ligand ethylene glycol-bis(β-aminoethyl ether) N,N,N′N′-tetrakis[2-(1-ethylbenzimidazoyl)] (EGTB-Et, 1) has been synthesized in good yield by the condensation of 1,2-diaminobenzene with ethylene glycol-bis(β-aminoethyl ether) N,N,N′,N′-tetraacetic acid. This ligand was used to synthesize the dinuclear Cu II diacetonitrile complex [Cu 2(EGTB-Et)(CH 3CN) 2](ClO 4) 4·2CH 3CN ( 2). The X-ray structure shows two distinct square pyramidal Cu II centres with each Cu II ion bound by two benzimidazole nitrogen atoms, one amine nitrogen atom, an ether oxygen atom and one acetinitrile nitrogen atom. The Cu--Cu separation is 5.809A˚. Spectral titration of 2 with sodium acetate or sodium cyanide results in new complexes with terminal acetate or cyano groups. X-band EPR spectra of a powdered sample and an acetonitrile solution of 2 show isotropic signals with g = 2.10 and 2.14, respectively. The gDM s = 2 transition at g ∼ 4.5 expected for magnetically coupled Cu II ions is not observed for either the powder or acetonitrile solution samples of 2. Based on the EPR spectra, the room-temperature magnetic moment (μ effCu= 2.16BM) and the X-ray structure, no orbital overlap between the magnetic d x 2 - y 2 orbital of Cu(2) and the magnetic d x 2 - y 2 orbital of Cu(1) occurs requiring the two Cu II centres to be uncoupled. Therefore, 2 is a dinuclear Cu II complex with non-interacting Cu II centres in non-identical sites.