Divalent cobalt, nickel and copper salts reacts in situ with 2,3-butanedione and its dihydrazide to form complexes containing a 16-membered tetradentate macrocyclic ligand. The complexes derived from 2,3-butanedione and its dihydrazide may be represented as [M(C16H24N8)X-2], where M=Co-II Ni-II and Cu-II and X=Cl, Br, NO3, NCS.