Novel mononuclear [Cu(HPnAO)H2O]ClO4 (2), homodinuclear [Cu(PnAO)Cu(phen)(H2O)(2)](ClO4)(2) (3), homotrinuclear [Cu-3(PnAO)(2)(H2O)(2)](ClO4)(2) (4) and heterodinuclear [Cu(PnAO)Mn(phen)(2)(H2O)](ClO4)(2) (5) complexes have been prepared from 3,3'-(1,3-propanediyldiimine)bis-(3-methyl-2-butanone)dioxime (H(2)PnAO) and characterized by elemental analyses, magnetic moments, i.r., u.v.-vis., and by mass spectral studies. The geometry of the metal chelates is discussed with the help of magnetic and spectroscopic measurements. I.r. spectra show that the ligand acts in a tetradentate manner and coordinates through the (C=N) and (N-H) groups. The elemental analyses, stoichiometry and the spectroscopic data of the complexes indicate that the copper(II) ions are coordinated by the ligand dianion. The heterodinuclear complex (5) displays in vitro ability to scavenge superoxide radicals produced by the xanthine-xanthine oxidase (XXO) system, using nitroblue tetrazolium as an indicator. The complex also supports aerobic growth of Escherichia coli (sodA(-) sodB(-)) in vivo in minimal media, indicating that complex (5) is a speculative potent SOD-mimic.