Multimetal multiligand complexes. Part-11. Equilibrium study on the formation and stability of mixed-metal, mixed-ligand complexes of cobalt-, nickel-, copper- and zinc(II) with aspartate and benzimidazole in aqueous solution

Potentiornctric study of ternary and quaternary mixtures consisting of M^2+ ions (M = M^1, M^2 = Co, Ni, Cu and Zn), aspartate (A^2-) and benzimidazole (B) as ligands provides evidence of formation of homo- and heterobinuclear complexes : M2(A)2B, M2(A)2(BH), M^1 M^2(A)2B and M^1M^2(A)2(B-H) involving bridging bidentate coordination by the Ni and Ns atoms of benzimidazole to two metal ions. (N1H) deprotonation of bidentate coordinated bridging benzimidazole ligand in the binuclear complexes at pH >6 is evident from spectral measurements. (N1H) deprotonation constants are found to be higher with complexes of higher stability constants.