Nickel(II) complexing with glycylglycine and acid-base equilibria of the ligand in aqueous ethanol solvents

Abstract

The protonation and dissociation constants of glycylglycine and the stability constants of its complexes with nickel(II) in aqueous ethanol of a variable composition with the ethanol mole fraction ranging from 0.00 to 0.55 are determined potentiometrically at a 0.1 M (NaClO4) ionic strength and temperature of 298 K. The stability of nickel(II) complexes of glycylglycine is found to grow with an increase in ethanol concentration in a solution. The solvation contributions of reagents into the displacement of complexing equilibria are analyzed. The change in the stability of nickel(II) glycylglycinate complexes is explained by the weakening of ligand solvation in aqueous ethanol.