The semi-empirical PM3 method is used to simulate the infrared spectra of the title compounds. It has been restrained that benzidine has a planar structure belonging to the symmetry point group D-2h in the complexes. It is found that the simulated IR spectra are consistent with the proposed structures derived from the FTIR and Raman spectra. The band assignments on the basis of the three-dimensional dynamic image of the vibrations corresponding to each normal mode have also been given. Coordination effects on internal modes of benzidine, particularly on the NH2 group vibrations are in close agreement with the observed results. (C) 2003 Elsevier B.V. All rights reserved.