Chemical speciation studies of binary complexes of malonic acid with some essential biologically important metal ions in 1, 2-propanediol-water mixtures

Belete Yilma Hirpaye1 Mekonen

Abstract

Chemical speciation of Co(II), Ni(II), Cu(II) and Zn(II) complexes of malonic acid in 0.0-60.0% v/v 1, 2- propanediol-water mixtures maintaining an ionic strength of 0.16 M at 303±0.1 K has been studied pH metrically. The predominant complexes formed are ML, ML2, ML2H and ML2H2 for Co(II) and Cu(II) and ML2, ML2H and ML2H2 for Ni(II) and Zn(II). Models containing different numbers of species were refined by using the computer program MINIQUAD75. Selection of the best-fit chemical models was arrived at based on statistical parameters. The trend in variation of complex stability constants with change in the dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces. Distributions of species, formation equilibria and effect of influential parameters on the stability constants have been presented. Possible structures of the various species present in solution are also indicated on the basis of the analysis of the pH metric data.