pH-metric Investigation on Mixed-Ligand Complexes of Ca(II), Mg(II) and Zn(II) with L-Dopa and 1, 10-Phenanthroline in Propylene glycol -Water Mixtures

摘要

The stability constants of ternary complexes of Ca(II), Mg(II) and Zn(II) with L-dopa as primary ligands and 1, 10-phenantbroline as a secondary ligand were determined pH-metrically. The study was conducted in varying concentrations (0-60% v/v) of propylene glycol-water mixtures and at an ionic strength of 0.16 mol L-1 using NaCl as an electrolyte at 303.0 K. Values of log X and Δ log K was discussed on the basis of statistical considerations and the nature of the species formed. The formation of various ternary species was established by modeling studies using the computer program MINIQUAD75. The formation and distribution of different species with relative concentrations of metal and ligands (M:L:X = 1.0:2.5:2.5, 1.0:2.5:5.0, 1.0:5.0:2.5) with varying pH were represented in the form of distribution diagrams. Influence of the solvent on the speciation was discussed based on the dielectric constant of the medium. The stability of the mixed ligand complexes are discussed in terms of the molecular structure of dopa and phen as well as the nature of the metal ion.