The solution chemistry and reactivity of lacunary Keggin silicotungstates monitored in real-time by a combination of mass spectrometry and electrochemistry

The solution chemistry of a series of mono-, di- and trilacunary Keggin silicotungstates was investigated by electrospray ionization mass spectrometry (ESI-MS) and general electrospray features especially for lacunary POMs are summarized. The reactions of vanadium incorporation into the lacunary structures were successfully monitored in real-time by a combination of ESI-MS and differential pulse voltammetry (DPV). It was found that all the reactions took place instantaneously and that a subtle speciation change occurred at prolonged reaction times for the pair of reactants, monovacant silicotungstate and sodium metavanadate, suggesting a conversion of mono- to divanadium substituted derivatives. This was shown to result from a solution process, not an ESI-induced reaction, by DPV measurements. The relative stabilities of the V-substituted products were assessed in both solution and gas phases.