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

Abstract

The 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 <i>p</i>H-metric measurements at 37°C and <i>l </i>= 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 <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-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/<img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-histidine(B) systems. it binds the metal in a bidentate manner.