Reactions of the Schiff base ligand derived from 4-acetyl-5,6-diphenyl-3(2H)-pyridazinone and ethyl-enediamine with Ni(II) and Co(II) using different metal salts; NO3, AcO, ClO4 and Cl yielded binary metal complexes. Mixed-ligand complexes were synthesized by using extra ligands including 8-hydroxyquinoline or glycine as nitrogen, oxygen-donors; 1,10-phenanthroline or 2-aminopyridine as nitrogen, nitrogen-donors. Elemental and thermal analyses, spectroscopic techniques (IR, electronic and mass), conductivity and magnetic susceptibility measurements were utilized to characterize the structures of the complexes. Electronic spectra and magnetic moment measurements showed that all complexes are octahedral and tetrahedral. In addition, activation energies of thermal degradation were calculated by means of Coats-Redfern equations. The activation energies were also used to evaluate kinetic and thermodynamic parameter of the metal complexes including Ea, Delta H, Delta S and Delta G. The XRD patterns for the ligand and its metal complexes indicate crystalline nature with nano particle sizes. The biological activity of the chelating agent and its metal complexes was conducted towards S. aureus and B. subtilis as Gram-+ve bacteria, S. typhimurium and E. coli as Grame-ve bacteria, C. albicans (yeast) and A. fumigatus (fungus). The chelating agent and some Ni(II) and Co(II) complexes showed antitumor activity towards HepG2 cell line. (C) 2020 Elsevier B.V. All rights reserved.