Abstract
The majority of 51V NMR studies on V(V) complexes have been reported in water, which currently limits the usefulness of 51V NMR in identifying V(V) species in non-aqueous solvents. In this report, the 51V NMR spectra have been obtained for vanadate and peroxovanadate complexes that exist at pH ≤ 7 in solutions containing 2–90% water in acetonitrile. Millimolar vanadate and peroxovanadate solutions in acetonitrile containing as little as 2% water were prepared by diluting a conc. aq. solution of vanadate (Bu 4N + salt) with acetonitrile. As with simple oxovanadate oligomers and peroxovanadate complexes in aqueous solutions, the species present in acetonitrile solution are a function of vanadium, acid and peroxide concentrations. The 51V resonances for several species can be assigned by correlating changes in chemical shifts as a function of water concentration. Species definitively characterized include VO 2 +, H x VO 4 x−3 , HV 2O 7 3−, V 4O 12 4−, V 5O 15 5−, V 10O 28 6−, VO(O 2) +, VO(O 2) 2 − and V 2O 2(O 2) 3. While the chemical shift for every assigned species moves downfield as water concentration is decreased, the magnitude of the downfield shift is highly dependent on the vanadium species. The assignments provided herein from the foundation for establishing the reactivity patterns for peroxovanadate in non-aqueous media.
Published Version
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