Quantitative and Qualitative Photoelectrochemical Studies on the 18-Molybdodisulfate Anion [S2Mo18O62]4-

Abstract

The heteropoly anion clusters [SzMoigOea]4-and [S2Moi8062]5may be photochemically activated to generate extremely powerful oxidants. Quantitative photoelectrochemical measurements using laser excitation at 325 nm of acetonitrile solutions of [S2M018O62]4containing the electron donors (ED), toluene and tetrahydrofuran, with hydrodynamic voltammetric monitoring at a platinum channel electrode are consistent with the following CECE mechanism: S2Mo,8062]4" + 2e" (E); ED+ (fast) --products. Photochemical oxidation of other electron donors such as methanol, [BPI14]-, ferrocene, and Cr(CO)s (arene) also occurs to generate [S2Moi8062]5-and [S2Moi8062]6-but not the more highly reduced [S2M0180e2]7-and [S2Moi8C>62]8-anions. It is concluded on the basis of these studies that [S2Moi8062]4-is a potentially valuable photooxidant in the synthetic sense, since it may be readily synthesised in large quantities from inexpensive materials.

Photophysics of Ion Clusters Formed between [Ru(bpy)3]2+ and the Polyoxotungstate Anion [S2W18O62]4-

“…where subscripts Ru, W, and RuW refer to [Ru(bpy) 3 the stability constant can be calculated from the ratio of the intercept:slope. This plot shows a graph that is initially linear and whose slope increases after the cation:anion ratio is less than 4.1:1.…”

“…[Ru(bpy) 3 ] 2+ in particular is deemed to be a suitable candidate due to its strong absorption in the visible region and its well-characterized photophysical properties. Recently, we demonstrated that [Ru(bpy) 3 4 In the present paper, we report the electronic and photophysical properties of the equivalent adducts formed in acetonitrile with the tungstate analogue [S 2 W 18 O 62 ] 4-. Again, strong electronic communication between the ions appears to be a feature of these ion clusters, but in contrast to the polymolybdate system, a relatively long-lived luminescent charge-transfer component is detected.…”

“…With increasing addition of salt, the luminescence intensity of the solution increased until it maximized at 0.167 mol dm -3 LiClO 4 . At this concentration, the luminescence intensity was indistinguishable from that of free [Ru(bpy) 3 Scheme 1 provides a model for the formation of 1:1 and 2:1 ion clusters under the conditions employed in the steady state luminescence: The luminescence data were fitted to the Stern-Volmer model (eq 1, Figure 3):…”

Polyoxo Anions: Synthesis and Structure

“…425,426 Earlier electrochemical investigations had shown that reductions can proceed beyond the two-electron stage; a recent example is the behavior of [S 2 Mo 18 O 62 ] 4À which, like other molybdates, can be reduced by up to six electrons. 141,[427][428][429][430] Density functional theory calculations have been reported for Keggin anions treated as clathrates of XO 4 nÀ in a neutral M 12 O 36 shell; these provide satisfactory explanations for the relative stabilities of the a-and b-structures (see Table 8) and for the first reduction steps of 2, 2, and 2 electrons. 109,431 Several structure determinations of heteropoly blues have now been reported but, as expected, none can unambiguously locate the reduced metal centers.…”

“…The products of reaction of organophosphonyl and organosilyl precursors with a variety of lacunary anions lead to a class of organic-inorganic hybrids, Table 28, that have been used for grafting into polymer matrices and the incorporation of magnetic nanoparticles. 428 …”