We have synthesized [Cu-63(bbim)(2)]((Bu4N)-Bu-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 dp-pp 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 parallel to c axis) gave both the maximum copper hyperfine splitting (84 X 10(4) cm(-1)) and the maximum anisotropic g value (g(parallel to) = 2.218). 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. Superhyperfine structures due to the nitrogen atoms of bbim(2-) dianion were detected in the g(perpendicular to) region of the ESR spectrum of[Cu-63(bbim)(2)]((Bu4N)-Bu-n)(2) in a frozen glass.