Rational Synthesis and Characterization of the Mixed-Metal Organometallic Polyoxometalates [Cp*MoxW6–xO18]− (x = 0, 1, 5, 6)

The reaction between the oxometallic complexes Cp*2M2O5 and Na2M′O4 (M, M′ = Mo, W) in a 1:10 molar ratio in an acidic aqueous medium constitutes a mild and selective entry into the anionic Lindqvist-type hexametallic organometallic mixed oxides [Cp*MoxW6–xO18]− [x = 6 (1), 5 (2), 1 (3), 0 (4)]. All of these compounds have been isolated as salts of nBu4N+ (a), nBu4P+ (b), and Ph4P+ (c) cations and two of them (1 and 3) also with the n-butylpyridinium (nBuPyr+, d) cation. The compounds have been characterized by elemental analyses, thermogravimetric analyses, electrospray mass spectrometry, and IR spectroscopy. The molecular identity and geometry of compounds 1c, 2a, and 2c have been confirmed by single-crystal X-ray diffraction. Density functional theory calculations on models obtained by replacing Cp* with Cp (I–IV) have provided information on the assignment of the terminal MO and bridging M–O–M vibrations.

以1:10摩尔比将氧金属配合物Cp*₂M₂O₅与Na₂M′O₄（M、M′=Mo、W）在酸性水介质中反应，可为制备阴离子型林德奎斯特型（Lindqvist-type）六金属有机金属混合氧化物[Cp*MoₓW₆–ₓO₁₈]⁻（x=6（1）、5（2）、1（3）、0（4））提供温和且选择性的途径。上述所有化合物均以四正丁基铵（nBu₄N⁺，a）、四正丁基鏻（nBu₄P⁺，b）与四苯基鏻（Ph₄P⁺，c）阳离子的盐形式分离得到，其中化合物1和3还可与正丁基吡啶（nBuPyr⁺，d）阳离子形成盐。所有化合物均通过元素分析、热重分析、电喷雾质谱法及红外光谱法完成了表征。通过单晶X射线衍射实验，确认了化合物1c、2a和2c的分子结构与几何构型。以Cp取代Cp*得到的模型（I~IV）进行密度泛函理论（Density functional theory）计算，为端基M=O键与桥连M-O-M键的振动峰归属提供了相关依据。