Complexation Equilibria and Determination of Stability Constants of Binary and Ternary Nickel(II) Complexes with Amino Acids (Glycine, α-Alanine, β-Alanine and Proline) and Dipicolinic Acid as Ligands

TLDR: In this paper, the formation of binary and ternary nickel(II) complexes involving dipicolinic acid (H2Dipic) as the primary ligand and some selected amino acids {glycine (HGly), ⍺-alanine(H⍺)-Ala), β-alanines (Hβ-Ala) and proline (HPro)} as secondary ligands were studied at 25 °C.

Abstract: In this paper we report the formation of binary and ternary nickel(II) complexes involving dipicolinic acid (H2Dipic) as the primary ligand and some selected amino acids {glycine (HGly), ⍺-alanine (H⍺-Ala), β-alanine (Hβ-Ala) and proline (HPro)} as secondary ligands. These complexes were studied at 25 °C by means of electromotive force measurements, emf(H), using 1.0 mol⋅dm−3 NaCl as the ionic medium. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the nickel(II) cation and the acid/base reactions of the ligands whose equilibrium constants were kept fixed during the analysis. In the study of the binary nickel(II)–amino acids systems the species [NiL]+, NiL2 and [NiL3]− were observed, and in the case of the ternary nickel(II)–dipicolinic acid–amino acids systems the complexes Ni(Dipic)HL, [Ni(Dipic)L]− and [Ni(Dipic)L(OH)]2− were observed. The respective stability constants were determined, and the species distribution diagrams, as a function of pH, are briefly discussed.