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Polyoxometalate (POM)-based materials are increasingly finding applications in energy storage/conversion and catalysis. While 17O NMR spectroscopy provides an apparently ideal method for monitoring POM structure and reactivity, its use remains rather limited because of the low natural abundance of 17O (0.0037%). Convenient 17O isotopic enrichment with efficient use of the expensive sources of 17O is therefore crucial, and we report here 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. An evaluation of the impact of the milling conditions showed that the heat generated during the milling process resulted in minimal loss of 17O-enriched water. 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 explains the low exchange efficiency in acetonitrile solution.

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Please use this identifier to cite or link to this collection: DOI: 10.19061/iochem-bd-2-87

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Manuscript title: Mecanochemical 17O Enrichment of Polyoxometalates