Keggin heteropolytungstate

In 2000, experiments were conducted that defined the stoichiometry and association of cations with polyanion units undergoing reduction in solution. Grigoriev et al. prepared a series of nine 1 1 association complexes between alkali-metal cations (M = Li+, Na+, or K+) and three representative vanadium(Y)-substituted a-Keggin heteropolytungstates, a-X"1 VW, 04(,<9 n> (X = PV, SiIV, and Al111) (Equation (9) y = 1). The medium used was acetate-buffered 2 3 (v/v) H20/Bu 0H at 60 °C which facilitated control of pH, temperature, and ionic strength.92 Three lines of evidence are consistent with the formation of 1 1 ion pairs, Equation (9). First, the potentials of the POMs... 

H) The Wi20 o ligand in Keggin heteropolytungstate anions requires the presence of two non-acidic interior hydrogen atoms for stability, in the absence of the heteroatom (metatungstate, Section 2,3. the molybdenum analogue is unknown). 

Electron Transfer to Dioxygen by Keggin Heteropolytungstate Cluster Anions... 

Electron Self-Exchange Between Keggin Heteropolytungstates... 

Reaction between the one electron reduced POM anions and O2 were then summarized. These studies demonstrated that at mildly acidic to neutral pH values in water, electron transfer from Keggin heteropolytungstates to O2 occurs by an outer-sphere mechanism. In these cases, the effect of Keggin-ion charge on rate constants for the reduction of O2 was shown to be significant, and was attributed to anion-anion repulsion within the successor-complex ion pairs formed between the negatively charged POM anions and 02 . This was followed by the discovery of a concerted proton-electron (CPET) pathway for electron transfer to O2 at lower pH values (< 1). 

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