Abstract
The transformation of three types of polyoxovanadates, {(n-C4H9)4N}3[H3V10O28], {(n-C4H9)4N}4[V12O32] and {(n-C4H9)4N}3[V13O34] have been investigated according to the rational chemical equations, and the best transformation conditions were reported. By the reaction of [H3V10O28]3− with 0.33 equivalents of {(n-C4H9)4N}OH in acetonitrile at 80 °C, [V12O32]4− was formed with 92% yield. The reaction in nitroethane with 0.69 equivalents of p-toluenesulfonic acid gave [V13O34]3− with 91% yield. The 51V NMR observation of each reaction suggests the complete transformations of [H3V10O28]3− to [V12O32]4− and to [V13O34]3− proceeded without the formation of any byproducts and it provides the reliable synthetic route. Decavanadates were produced by the hydrolysis of [V12O32]4− or [V13O34]3−. While the direct transformation of [V13O34]3− to [V12O32]4− partly proceeded, the reverse one could not be observed. For the thioanisole oxidation, [V13O34]3− showed the highest activity of the three.
Highlights
Polyoxometalates have been attracting much attention in broad fields such as catalyst chemistry, magnetochemistry, and pharmaceutical chemistry [1,2,3]
All solvents were purchased from Wako Pure Chemical Industries (Osaka, Japan) and used as received. p-Toluenesulfonic acid monohydrate (TsOH) and 40% tetra-n-butylammonium hydroxide aqueous solution were purchased from Wako Pure Chemical Industries and Sigma-Aldrich (Tokyo, Japan) and used after the dilution to 0.1 M solution with acetone
The quantitative conversions among deca, dodeca- and tridecavanadates were established by monitoring through 51V NMR to determine the optimized transformation conditions
Summary
Polyoxometalates have been attracting much attention in broad fields such as catalyst chemistry, magnetochemistry, and pharmaceutical chemistry [1,2,3]. Units have been synthesized [6,7,8,9,10,11,12,13,14,15,16,17,18,19] Since the properties such as redox and optics of polyoxovanadates depend on the anion structures, it is crucially important to control those cluster frameworks [14,19]. Cronin’s group synthesized the manganese-substituted polyoxovanadate with the same anion structure of [V13O34]3− [25]. As like synthesis of Cronin’s cluster from the related manganese-containing polyoxovanadate, the control of the structure transformation is important. We report on the structure transformation among [H3V10O28]3−, [V12O32]4− and [V13O34]3−, including the improved synthesis of {(n-C4H9)4N}3[V13O34]. Oxidation of thioanisole using these polyoxovanadates is discussed
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