Mecanochemical 17O Enrichment of Polyoxometalates
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Despite the fact that polyoxometalates are molecular metal oxides with structures characterised by the environments for the constituent oxygen atoms, the use of 17O NMR spectroscopy for characterization and reactivity studies is still limited by the low natural abundance of 17O (0.0037%) , which generally necessitates sample enrichment. Herein, we report the 17O isotopic enrichment of polyoxometalates using a solvent-free, mechanochemical approach involving ball milling with 17O-enriched water. This method was applied to four representative molybdates and tungstates with Lindqvist and Keggin type, structures. Time-dependent 17O NMR analysis revealed that mechanochemical exchange is significantly faster and more efficient than conventional solution-phase enrichment, particularly for the molybdates. The impact of the milling conditions was also evaluated, showing that there is minimal loss of 17O-enriched water due to the heat generated during the milling process. Overall, this work demonstrates that mechanochemistry provides a cost-effective and scalable strategy for 17O labeling while offering valuable atomic-level insight into POM reactivity. To gain further insight into the 17O exchange mechanism, we combined DFT calculations on a Mo6 fragment with classical molecular dynamics simulations, showing that a metal-centered, water-assisted pathway is operative under ball milling conditions, while poor preorganization of water around the POM rationalizes the low exchange efficiency in acetonitrile solution.
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DOI: 10.19061/iochem-bd-2-87
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Manuscript title: Mecanochemical 17O Enrichment of Polyoxometalates
