Effect of vanadium valence state on the solution chemistry and the stability of vanadium substituted polyoxometalates

Abstract

The reactions of lacunary Keggin-type silicotungstates ({SiW_12−x}, x = 1–3) with vanadyl sulfate (V^IVOSO₄) as the tetravalent vanadium source were monitored in real-time by ESI-MS in conjunction with DPV. Different phenomena from the pentavalent vanadium counterpart (NaV^VO₃) were found: the substitution products are unexpectedly stable whereas spontaneous transformations from mono- into di- and eventually tri-vanadium substituted products ({SiW₁₁V} → {SiW₁₀V₂} → {SiW₉V₃}) were observed when the substituted vanadium is of +5 valence state. DFT calculations were utilized to interpret the intrinsic structural reasons for distinctive stability of the vanadium-substituted POMs with different valences and with different substitution degrees. The effect of the vanadium valence states on the solution chemistry and stability of the substituted POMs were thereby unraveled.