Effect of nickel(II) ternary complex formation on the coordination behaviour of glycylglycine in aqueous solution

576-579The stability constants of parent complexes of the ligands glycylglycine and glycinamide(A) with Ni(Il). and of the ternary complexes formed with Iigands imidazole, histamine and L-histidine(B) have been determined by the pH-metric measurements at 37°C and l = 0.15 mol dm- 3 (NaCIO4). It has been found that the ligands A form NiABH, NiAB, and NiAH-1 B mixed ligand complexes with histamine and -histidine(B) Iigands. while with imidazole(B) ligand the saturated NiA B2 and unsaturated NiAB species have been found to be present. The mode of coordination of ligands A and B in the NiABH and NiAB/NiAB2 ternary species is similar to their binding in their respective binary species. Though amide deprotonated glycylglycine is tridentate in its NiAH-1 species, in the NiAH -1B ternary species in the Ni(II)-glycylglycine(A)-histamine/-histidine(B) systems. it binds the metal in a bidentate manner