Crystal structure and magnetic characterization of a building block for quasi one-dimensional heterobimetallic polymeric complexes bridged by 2,2′-bibenzimidazolate ligands

We have synthesized [63Cu(bbim)2] (nBu4N)2(1)by 2,2′-bibenzimidazolate ligands (bbim) with multi-proton donor property as a building block of models for quasi one-dimensional heterobimetallic polymeric complexes with dπ-pπ interaction. The study of the molecular and electronic structures of 1 and the non-deprotonated form of 1, in terms of crystal structure analysis and magnetic characterization by single-crystal ESR spectroscopy, has been carried out. The angular dependence of the Cu(II) hyperfine ESR spectra of 1 showed that the parallel orientation (B0 //c axis) gave both the maximum copper hyperfine splitting (84 × 10−4cm−1) and the maximum anisotropic g value (g // =2.218). The substantially isotropic behavior of the g value (g⊥=2.05) was obtained in the perpendicular orientation. The findings show that the copper(II) ion is bound at the site of a tetragonally distorted tetrahedral field, being in accord with the molecular structure of the donor site with the distorted tetrahedral symmetry as obtained by the X-ray crystal analysis. The results from the ESR measurements of 1 indicate that the ground-state electronic configuration for the copper(II) ion is (z2)(2)…(yz)(yz)(xy)¦ in terms of d-orbitals. Superhyperfine structures due to the nitrogen atoms of bbim2− dianion were detected in the g⊥ region of the ESR spectrum of [63Cu(bbim)2](nBu4N)2 in a frozen glass.