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)

Solution equilibria in the binary systems of Ni(II)-amino acid {aspartic acid (H(2)asp), glutamic acid (H(2)glu), cysteine (H(2)cys) and histidine (Hhis)} and in the ternary systems of Ni(II)-dipicolinic acid (H(2)dipic)-amino acid {aspartic acid (H(2)asp), glutamic acid (H(2)glu), cysteine (H(2)cys) and histidine (Hhis)} have been studied pH-potentiometrically. The formation constants of the resulting mixed ligand complexes have been determined at 25 A degrees C and ionic strength 1.0 mol center dot dm(-3) NaCl. In the Ni(II)-H(2)asp system the data indicated the formation of the [NiHL](+), NiL and [NiL2](2-) complexes. For the Ni(II)-H(2)glu system, the formation of the species NiL and [NiL2](2-) are indicated. In the Ni(II)-H(2)cys 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)-H(2)dipic-H(2)asp, the species Ni(dipic)(H2L), [Ni(dipic)(HL)](-), [Ni(dipic)(L)](2-) and [Ni(dipic)(L)(OH)](3-) were detected. In the Ni(II)-H(2)dipic-H(2)glu 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)-H(2)dipic-H(2)cys system, the species Ni(dipic)(H2L), [Ni(dipic)(HL)](-) and [Ni(dipic)(L)](2-) were detected. Finally, in the Ni(II)-H(2)dipic-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.