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

摘要

The reactions of lacunary Keggin-type silicotungstates ({SiW12-x}, x-1-3) with vanadyl sulfate ((VOSO4)-O-IV) as the tetravalent vanadium source were monitored in real-time by ESI-MS in conjunction with DPV. Different phenomena from the pentavalent vanadium counterpart ((NaVO3)-O-V) were found: the substitution products are unexpectedly stable whereas spontaneous transformations from mono-into di-and eventually trivanadium 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.