Mixed-Ligand Complex Formation Equilibria of Nickel(II) with Salicylic Acid and Some Amino Acids in 1.0 M NaCl at 25 oC

Abstract

ABSTRACT In an effort to get information on the stability constants of the mixed ligand complexes formed between Nickel(II) – Salicylate (Sal2-, L2-) and the amino acids Serine (Ser), Threonine (Thr), Methionine (Met), Phenylalanine (Phe), Glycine (Gly), Proline (Pro), α-Alanine (α-Ala), β-Alanine (β-Ala), Leucine (Leu), Isoleucine (Iso), Valine (Val) and Tryptophan (Trp), all potential bidentate ligands- the speciation of the complexes was studied by potentiometric titrations in aqueous solution at 25°C and 1.0 mol dm−3 NaCl for different ligand to metal molar ratios. A computer-assisted analysis of the potentiometric titration data within the 2–11 pH range allowed us to estimate the equilibrium constants for ternary systems. Several different complexes were separately considered during the analysis, and evidence was found for the presence of Ni(Sal)HL, [Ni(Sal)L]−, [Ni(Sal)L(OH)]2-, [Ni(Sal)L2]2- and [Ni(Sal)2L]3- species. Species distribution diagrams as a function of pH are briefly discussed.