Synthesis of water-soluble dinuclear metal complexes [metal = cobalt(II) and nickel(II)] and their behavior in solution

Two dinuclear metal complexes, [Co2(bhmp)(MeCO2)2]ClO4 · 2H2O (1) and [Ni2(bhmp)(MeCO2)2]ClO4 · 2H2O (2), were synthesized with a dinucleating ligand, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [H(bhmp)]. Both complexes were easily soluble in water as well as in DMF. Electronic spectra for both complexes were measured in both solvents and analyzed using the angular overlap model (AOM). From the electronic spectra and molar conductance, both complexes were determined to exist as [M2(bhmp)(MeCO2)2]+ (M = CoII or NiII) in DMF, dissociating perchlorate ions. On the other hand, in water, it was concluded that the acetate ions were partially dissociated and each complex existed as a mixture of some dissociated species, such as [M2(bhmp)(MeCO2)(H2O)2]2+ and [M2(bhmp)(H2O)4]3+ (M = CoII or NiII). Such dissociation was also confirmed by precipitation of the dissociated species when NaBPh4 was added into an aqueous solution of the nickel complex.