Formation of heteropolynuclear cobalt(II) and nickel(II) complexonates with EDTA and 2-aminopropanoic acid

Coordination equilibria in the Co(II)–Ni(II)–2-aminopropanoic acid (HAla)–EDTA system have been studied spectrophotometrically at different molar ratios of the reagents in a wide pH range. It has been found that, when metal ions are in excess with respect to EDTA at pH 5–9, polyheteronuclear complexonates [(CoAla)Edta(NiAla)]2–, [(CoAla2)Edta(NiAla2)]4–, [(NiAla2)Edta(CoAla2)2]4–, [(CoAla2)Edta(NiAla2)2]4–, and [(NiAla2)2Edta(CoAla2)2]4– form in a solution. The equilibrium constants of formation of these complexes and their overall stability constants have been calculated. Possible structures of the polynuclear complexonates are discussed.