Synthesis, Molecular Structure and Reactivity of a New Dicopper(II) Benzimidazole Complex with Non-Identical Copper(II) Sites
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 CuII diacetonitrile complex [Cu2(EGTB-Et)(CH3CN)2](ClO4)4·2CH3CN (2). The X-ray structure shows two distinct square pyramidal CuII centres with each CuII 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 △Ms = 2 transition at g ∼ 4.5 expected for magnetically coupled CuII ions is not observed for either the powder or acetonitrile solution samples of 2. Based on the EPR spectra, the room-temperature magnetic moment (μeffCu= 2.16BM) and the X-ray structure, no orbital overlap between the magneticdx2-y2 orbital of Cu(2) and the magneticdx2-y2 orbital of Cu(1) occurs requiring the two CuII centres to be uncoupled. Therefore, 2 is a dinuclear CuII complex with non-interacting CuII centres in non-identical sites.