SPECTROPHOTOMETRIC AND ESR EVIDENCE FOR VANADIUM(IV) DEFEROXAMINE COMPLEXES

Complexes of vanadium(IV), vanadyl, are reported to be formed with the trihydroxamic acid deferoxamine (H3DF+). One complex exhibits a reddish-violet color, with a major absorbance peak at 386 nm and a smaller peak at 520 nm. This complex is potentially useful for the microdetermination of vanadyl. The apparent molar absorptivity is 3.91 mM-1 cm-1, and the complex obeys Beer's law in the concentration range of 0.6-63 ppm. Electron spin resonance studies indicate the formation of two vanadyl complexes that are 1:1 in vanadyl and deferoxamine, but have two or three bound hydroxamate groups. ESR and spectrophotometric evidence indicate that the red, low pH form, involves an octahedral vanadium (4+) ion coordinated by three hydroxamate ligands. One of these hydroxamates is displaced by an oxygen at pH > 2.8 according to the following equilibria: VO2+ + H3DF+ double-line-arrow-pointing-to-left-and-right V(IV)(DF)2+ + H3O+, V(IV)(DF)2+ + H2O double-line-arrow-pointing-to-left-and-right VO(HDF)+ + H+, where pk2 = 2.8.