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

Abstract

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.