Heteropolynuclear cobalt(II) and nickel(II) ethylenediaminetetraacetates in aqueous solutions of aminoethanoic acid

Complexation in the Co(II)‒Ni(II)‒aminoethanoic acid (HGly)‒EDTA (H4Edta) system was studied at different molar ratios of components by absorption spectrophotometry. The mathematical modeling of A = f(pH) curves was used to establish that bi-, tri-, and tetranuclear heteroligand complexes like [(CoGly)Edta(NiGly)]2‒, [(CoGly2)Edta(NiGly2)]4‒, [(CoGly2)Edta(NiGly2)2]4‒, [(CoGly2)2Edta(NiGly2)]4‒, and [(CoGly2)2Edta(NiGly2)2]4‒, whose accumulation fraction attained 80‒100% at optimal pH values, were formed depending on the ratio of reagents and the acidity of a medium. The formation equilibrium and total stability constants of these complexes were calculated, and a hypothesis about their structure was made.