Abstract Two cobalt and two Nickel complexes of bis[ N-(2,6-diisopropylphenyl)imino]acenaphthene ( Pr-BIAN) ligand, have been synthesized. These complexes, namely [Co(Pr-BIAN)Cl 2] 1, [Co(OAc) 2 (Pr-BIAN) 2](ClO 4) 2, [Ni(Pr-BIAN)(NO 3) 2] 3 and [Ni(Pr-BIAN)2](ClO 4) 2 4, were characterized by elemental analyses, molar conductance, spectral (IR, UV–Visible and NMR) and magnetic moment measurements. In these complexes the geometries about the metal center are significantly different. While for complexes 2 and 3 an octahedral structure is proposed, in complex 4, square-planar coordination with an almost perfect planar arrangement of two Pr-BIAN ligands around the nickel center is suggested. In 1, two imine nitrogen atoms of Pr-BIAN and two chloride atoms are coordinating in a tetrahedral fashion around the cobalt center. Molecular mechanics (MM+) and semiempirical molecular orbital calculations have been performed for the most biologically active complex 1 and its free ligand Pr-BIAN and compared with inactive ligand bis[ N-( p-tolylphenyl)imino]acenaphthene 6, to get insight into their molecular structures and to learn more about their stable molecular conformations.