Due to the wide range of applications of band-gap engineering in optoelectronics and photocatalysis, the rational design of polyoxometalate (POM) frameworks is highly desired. Here, we have successfully synthesized a series of mixed addenda (Mo and W) sandwich POMs by systematically varying pH, concentrations of salts, and counterions in Weakley-type sandwich POMs by incorporating Mo into the framework of tetrasubstituted sandwich POMs. Crystallographic analysis reveals the centrosymmetric structure; with variation in the Mo to W ratio, Mo preferentially binds to μ₂ oxygen connected to transition metals in the sandwich position. UV–visible spectroscopy, electrochemical, and theoretical modeling rationalize the band-gap modulations. Theoretical studies and cyclic voltammograms indicate that during the reduction, the incoming electrons preferentially go to substituted transition metals followed by Mo. Flat band potential calculated from the Mott–Schottky enables tuning of the electronic properties of composites based on these sandwich POMs. Moreover, the dioxygen binding and activation studies of these polyoxometalates have been highlighted.

中文翻译：

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夹心多金属氧酸盐中混合附加物对带隙和氧化还原性质的调节

由于带隙工程在光电子学和光催化领域的广泛应用，人们非常需要合理设计多金属氧酸盐（POM）框架。在这里，我们通过系统地改变 Weakley 型夹心 POM 中的 pH 值、盐浓度和抗衡离子，将 Mo 纳入四取代夹心 POM 的框架中，成功合成了一系列混合附加物（Mo 和 W）夹心 POM。晶体学分析揭示了中心对称结构；随着Mo与W比率的变化，Mo优先与连接到夹心位置的过渡金属的μ _{2氧结合。}紫外可见光谱、电化学和理论模型使带隙调制合理化。理论研究和循环伏安图表明，在还原过程中，进入的电子优先进入取代的过渡金属，然后是 Mo。根据莫特-肖特基计算得出的平带电势能够调整基于这些夹层 POM 的复合材料的电子性能。此外，这些多金属氧酸盐的分子氧结合和活化研究也受到了重视。