Copper(II), Nickel(II), Zinc(II), and Molybdenum(VI) Complexes of Desferrioxamine B in Aqueous Solution

Based on pH-metric, spectrophotometric, and EPR measurements, stability constants and bonding modes are reported for the complexes formed in aqueous solutions of the copper(II)-, nickel(II)-, zinc(II)-, and molybdenum(VI)-desferrioxamine B (DFA) systems. Besides the totally deprotonated species, several protonated mononuclear complexes were found in the copper(II)-, nickel(II)-, and zinc(II)-DFA systems, and also the dinuclear species [Cu2AH]2+. All three hydroxamate groups are able to coordinate to nickel(II) and zinc(II), but only two of them to the copper(II). Molybdenum(VI) yields only one complex species, [MoO2(H2DFA)]+. This species, which exists below pH 7, involves two hydroxamate groups coordinated to the metal ion. DFA completely prevents the formation of polyoxomolybdates below pH 7, but MoO42- and free DFA exist above this pH.