Modeling of coordination equilibria of polynuclear cobalt(II) ethylenediaminetetraacetates formation in aqueous solutions of aminoethanoic acid

Coordination equilibria in ternary systems containing cobalt(II) salt, ethylediaminetetraacetic (EDTA) and aminoethanoic (glycine) acids were investigated by absorption spectrophotometry at various molar ratios of reagents and at a wide pH- range. Mathematical treatment of obtained data allowed to evaluate the existence of a variety of complex species in solutions and to choose those which were sufficient to describe the experimental results. It was determined the stoichiometry (Co(II):glycine:EDTA) of polynuclear mixed-ligand complexes (2:2:1, 2:4:1, 3:6:1, 4:8:1), their pH-ranges of existence and stability constants and also their possible structures were suggested.