Stability constants of the ternary nickel(II) complexes with salicylic acid and selected amino acids

In this work, we present the study of the ternary Nickel(II) complexes with salicylic acid and the amino acids: aspartic acid (H2Asp, H2L), glutamic acid (H2Glu, H2L), cysteine (H2Cys, H2L) and histidine (HHis, HL) formed in aqueous solution at 25 °C and 1.0 mol·dm− 3 NaCl as the ionic medium. The analysis of the potentiometric data by means of the computational least-squares program LETAGROP, indicate the formation of the ternary complexes [Ni(Sal)H2L]2 − n, [Ni(Sal)HL]1 − n, [Ni(Sal)L]− n, [Ni(Sal)L(OH)]−(1 + n). Where n = 1 for histidine and 2 for the other amino acids. The relative stability of the ternary complexes compared to the binary ones were evaluated considering the values of ∆ log K, log X and % R.S. Species distribution diagrams as a function of pH were briefly discussed.