| Summary: | The heteropoly anion clusters [S2Mo18O62]4- and [S2MO18O62]5- may be photochemically activated to generate extremely powerful oxidants. Quantitative photoelectrochernical measurements using laser excitation at 325 nm of acetonitrile solutions of [S2Mo18O62]4- containing the electron donors (ED), toluene and tetrahydrofuran, with hydrodynamic voltammetric monitoring at a platinum channel electrode are consistent with the following CECE mechanism: [S2Mo18O62]4- + ED (k1(hv)) → [S2Mo18O62]5- + ED+ (C); [S2Mo18O62]5- ⇄ [S2Mo18O62]4- + e- (E); [S2MO18O62]5- +ED (k2(hv)) → [S2Mo18O62]6- + ED+ (C); [S2Mo18O62]6- ⇄ [S2Mo18O62]4- + 2e- (E); ED+ (fast) → products. Photochemical oxidation of other electron donors such as methanol, [BPh4]-, ferrocene, and Cr(CO)3 (arene) also occurs to generate [S2Mo18O62]5- and [S2MO18O62]6- but not the more highly reduced [S2MO18O62]7- and [S2Mo18O62]8- anions. It is concluded on the basis of these studies that [S2Mo18O62]4- is a potentially valuable photooxidant in the synthetic sense, since it may be readily synthesised in large quantities from inexpensive materials. © 1995 American Chemical Society.
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