Spectroscopic Characterization of L-ascorbic Acid-induced Reduction of Vanadium(V) Dipicolinates: Formation of Vanadium(III) and Vanadium(IV) Complexes from Vanadium(V) Dipicolinate Derivatives

• A novel vanadium(V) complex was structurally characterized by X-ray crystallography.
• A reaction with L-ascorbic acid and vanadium(V) complexes produced vanadium(III) and vanadium(IV) species.
• All vanadium(III) species were identified by HFEPR spectroscopy for the very first time.
• All vanadium(IV) species were identified by X-band EPR spectroscopy.

A Br-substituted dioxidovanadate dipicolinate complex was prepared and structurally characterized by X-ray crystallography. The counter ion in the solid state is the ammonium cation in a monoclinic crystal cell with, P2(1)/c. The X-ray structure is similar to the structure generated from the analogous nitro substituted dipicolinate ligand. When exploring reactions of this and other dipicolinate-containing compounds with L-ascorbic acid, both vanadium(IV) and vanadium(III) species were formed under acidic conditions; then identified by conventional (X-band) and high-frequency and -field electron paramagnetic resonance (EPR) spectroscopy. A reaction with half an equivalent of L-ascorbic acid led to the formation of vanadium(IV) species, and addition of substituents (X = H, Cl, Br, OH, and NH2) in the para position of dipicolinic acid did not have a major effect on the vanadium(IV) species formed. In a reaction with excess L-ascorbic acid and vanadium(V)dipic-X complexes (where X = H, Cl, Br, OH, and NH2), vanadium(III) species were observed, thus proving that vanadium(III) species can be formed under acidic conditions resembling those in biological systems.

The crystal structure of NH4[VO2(dipic-Br)] was solved. X- band EPR and HFEPR spectra were acquired for vanadium(IV) and vanadium(III) species, respectively, which were produced after the reaction between vanadium(V) complexes (with dipicolinic acid and its analogues as ligands) and L-ascorbic acid in aqueous acidic media.Figure optionsDownload as PowerPoint slide