INFLUENCE OF PROPYLENE GLYCOL ON CHEMICAL SPECIATION OF TERNARY COMPLEXES OF BI- AND TRI-DENTATE LIGANDS WITH SOME ESSENTIAL METAL IONS

Equilibria of complexation of Co(II), Ni(II) and Cu(II) ions with L-aspartic acid and ethylenediamine were investigated pH metrically in 0.0–60.0% v/v propylene glycol-water mixtures maintaining an ionic strength of 0.16 mol L-1 at 303.0±0.1 K. Stability constants of ternary complexes were calculated and various models were refined with MINIQUAD75. The best fit chemical models were selected based on statistical parameters and residual analysis. The species detected were MLXH, MLX and ML2X for Co(II), Ni(II) and Cu(II). The appropriateness of experimental conditions was verified by introducing errors intentionally in the concentrations of ingredients. The stabilities of the complexes followed the Irving-Williams order, i.e., Co(II) < Ni(II) < < Cu(II).