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

Abstract

We have synthesized [ 63Cu(bbim) 2] ( nBu 4N) 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 ( B 0 // 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 (z 2)( 2)…(yz)( yz)(xy)¦ in terms of d-orbitals. Superhyperfine structures due to the nitrogen atoms of bbim 2− dianion were detected in the g ⊥ region of the ESR spectrum of [ 63Cu(bbim) 2]( nBu 4N) 2 in a frozen glass.