Nickel and cobalt complexes of 15,15-disubstituted 1,4,7,10,13-pentaazacyclohexadecane-14,16-dione ligands

► Novel Co(III) and Ni(II) complexes of pentaazamacrocyclic ligands were synthesized. ► Six X-ray structures, EA, MS, UV, IR and CV were used for characterization. ► The ligands can adopt a N3 or N5 coordination mode to the metal centers. ► The switch between these modes was caused by ligand substitution and solvent effects.