Ternary complexes of copper(II), nickel(II), cobalt(II)and zinc(II) with thiodiacetic acid and various secondary ligands

Abstract

The formation constants of the ternary complexes of Cu(H), Ni(II), Co(II) and Zn(II) with thiodiacetic acid (TDA) as primary ligand and imidazole (IMD), ethylenediamine (en), histidine (HST), aspartic acid (ASP), methionine (MET), phenylalanine (PHAL), tryptophan (TRP), tyrosine (TYR), oxalic acid (OXA) and sulphosalicylic acid (SSA) as secondary ligands have been determined by potentiometric method at 35 ± 0.1°C and <em>μ </em>= 0.1 <em>M </em>(KNO₃). The lower s abilities of the ternary systems as compared to those of the corresponding binary systems may be due to electrostatic repulsion between the two charged ligands. This is also in accordance with the statistical considerations.