Solution Equilibria and Stabilities of Binary and Ternary Systems of Nickel(II) Complexes with Dipicolinic Acid and the Amino Acids (Histidine, Cysteine, Aspartic and Glutamic Acids)

TLDR: In this paper, the formation constants of the resulting mixed ligand complexes have been determined at 25 °C and ionic strength 1.0 millimol·dm−3 NaCl.

Abstract: Solution equilibria in the binary systems of Ni(II)–amino acid {aspartic acid (H2asp), glutamic acid (H2glu), cysteine (H2cys) and histidine (Hhis)} and in the ternary systems of Ni(II)–dipicolinic acid (H2dipic)–amino acid {aspartic acid (H2asp), glutamic acid (H2glu), cysteine (H2cys) and histidine (Hhis)} have been studied pH-potentiometrically. The formation constants of the resulting mixed ligand complexes have been determined at 25 °C and ionic strength 1.0 mol·dm−3 NaCl. In the Ni(II)–H2asp system the data indicated the formation of the [NiHL]+, NiL and [NiL2]2− complexes. For the Ni(II)–H2glu system, the formation of the species NiL and [NiL2]2− are indicated. In the Ni(II)–H2cys system the complexes [NiHL]+, NiL and [NiHL2]− were detected, while in the Ni(II)–Hhis system the species [NiH2L]3+ [NiHL]2+, NiL+, [Ni(HL)2]2+, [NiHL2]+ and NiL2 were detected. In the ternary system Ni(II)–H2dipic–H2asp, the species Ni(dipic)(H2L), [Ni(dipic)(HL)]−, [Ni(dipic)(L)]2− and [Ni(dipic)(L)(OH)]3− were detected. In the Ni(II)–H2dipic–H2glu system, the species Ni(dipic)(H2L), [Ni(dipic)(HL)]−, [Ni(dipic)(L)]2− and [Ni(dipic)(L)(OH)]3− were detected. In the Ni(II)–H2dipic–H2cys system, the species Ni(dipic)(H2L), [Ni(dipic)(HL)]− and [Ni(dipic)(L)]2− were detected. Finally, in the Ni(II)–H2dipic–Hhis system, the species [Ni(dipic)(L)]− and [Ni(dipic)(L)(OH)]2− were detected. Species distribution diagrams as a function of pH are briefly discussed.