We have synthesized [ 6 3 Cu(bbim) 2 ]( I I Bu 4 N) 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 - 4 cm - 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)()(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 [ 6 3 Cu(bbim) 2 ]( n Bu 4 N) 2 in a frozen glass.