Metatungstate salts α-[R4N]5H[H2W12O40] (R = Pr or Bu) were produced by phase transfer methods. Two one-electron reduction processes (E1/2
â1100, â1590 mV versus AgâAgCl (saturated KCl in MeCN)) are seen for [Bu4N]5H[H2W12O40] in MeCN (Bu4NClO4, 0.1 M) solution. They convert into a single two-electron process in MeCNâwater (95â¶5 v/v) upon the addition of acid. Controlled potential electrolysis in aqueous HCl at the two electron potentials resulted in isolation of the six-electron reduced salt [NH4]4H8[H2W12O40] in which one of the oxidised WVI3 trinuclear caps of metatungstate is reduced to a WIV3 trinuclear cap. [Bu4N]3H9[H2W12O40] and related salts were generated by phase transfer. The anion [H2WIV3(OH2)3}WVI9O34(OH)3]3â is obtained by dissolving [Bu4N]3H9[H2W12O40] in dry CD3CN. The distribution of the eleven protons present in this anion is mapped by 1H and 183W NMR, allowing assessment of the structural changes which accompany reduction. Cs point symmetry is observed and imposed by the association of the three surface hydroxyl protons with the reduced WIV3 trinuclear cap and one of the oxidised WVI3 trinuclear caps. Three WOW links appear to be converted into longer W(OH)W links to accommodate the significant shortening (â0.7 Ã
) in Wââ¯âW separation anticipated to occur upon reduction.
偏
钨酸盐 \(\alpha\)-[R4N]5H[H2W12O40] (R = Pr 或 Bu) 通过相转移方法制备。在 MeCN (Bu4NClO4, 0.1 M) 溶液中,[Bu4N]5H[H2W12O40] 显示出两个单电子还原过程 (E1/2 ≈ -1100, -1590 mV vs Ag-AgCl (饱和 KCl in MeCN))。当加入酸后,在 MeCN-
水 (95:5 v/v) 中转变为单一的双电子过程。在
水溶液 HCl 中进行双电子电位控制电解,最终分离出六电子还
原盐 [NH4]4H8[H2W12O40],其中偏
钨酸盐的一个氧化态为 WVI3 的三核盖被还原为 WIV3 的三核盖。[Bu4N]3H9[H2W12O40] 及相关盐通过相转移生成。将 [Bu4N]3H9[H2W12O40] 溶解在干燥的 CD3CN 中得到阴离子 [H2WIV3(OH2)3}WVI9O34(OH)3]3-。通过 1H 和 183W NMR 映射出该阴离子中的十一个质子的分布,从而评估伴随还原发生的结构变化。观察到并施加了 Cs 点对称性,这是由于三个表面羟基质子与还原的 WIV3 三核盖和一个氧化态为 WVI3 的三核盖的关联。三个 WOW 键似乎转变为更长的 W(OH)W 键,以适应预期在还原过程中发生的显著缩短 (≈0.7 Å) 的 W-W 分离。