Cobalt Polyoxometalate Co4V2W18O6810–: A Critical Investigation of Its Synthesis, Purity, and Observed 51V Quadrupolar NMR

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• 作者：Scott J. Folkman ; Joel T. Kirner ; Richard G. Finke
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：June 6, 2016
• 年：2016
• 卷：55
• 期：11
• 页码：5343-5355
• 全文大小：505K
• 年卷期：0
• ISSN：1520-510X

文摘

The vanadium-containing cobalt polyoxometalate (Co-POM) Co₄V₂W₁₈O₆₈^10– (hereafter Co₄V₂W₁₈) has been reported to be a stable, homogeneous water-oxidation catalyst, one with a claimed record turnover frequency that is also reportedly 200-fold faster than its phosphorus congener, Co₄P₂W₁₈O₆₈^10–. The claimed superior water-oxidation catalysis activity of the vanadium congener, Co₄V₂W₁₈, rests squarely on the reported synthesis of Co₄V₂W₁₈, its purity, and its stability in both the solid-state and in solution. Attempts to repeat the preparation of Co₄V₂W₁₈ by either of two literature syntheses, along with the other studies reported herein, led to the discovery of multiple, convoluted problems in the prior literature of Co₄V₂W_18. The three most serious of those problems proved to be the prior misunderstanding of the quadrupolar (herein ⁵¹V) NMR peak widths in complexes that also contain paramagnetic metals such as Co(II), the incorrect assignment of a –506.8 ppm ⁵¹V NMR to Co₄V₂W₁₈, and then the use of that –506.8 peak to argue for the stability of Co₄V₂W₁₈ in solution. The results are reported in a somewhat historical, “story” fashion en route to elucidating and fully supporting the 11 insights and take-home messages listed in the Summary and Conclusions section.