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.