¹⁷O NMR spectroscopy in polyoxometalate chemistry: advances, challenges, and applications in structure and catalysis

¹⁷O Nuclear Magnetic Resonance (NMR) spectroscopy has become an increasingly valuable technique for investigating the structure, dynamics, and reactivity of polyoxometalates (POMs), a diverse class of metal-oxygen clusters with broad applications in catalysis, energy storage, and materials science. The oxygen framework of POMs plays a very important role in dictating their physical and chemical properties, making direct probing of oxygen environments essential. However, the quadrupolar nature and low natural abundance (0.037%) of ¹⁷O nuclei impose significant experimental challenges, including low sensitivity and broad line shapes. Recent methodological breakthroughs such as the development of ultra-high-field NMR instrumentation, the use of magic angle spinning (MAS) to minimize anisotropic broadening, and the implementation of dynamic nuclear polarisation (DNP) to boost signal intensity have greatly enhanced the resolution and feasibility of ¹⁷O NMR studies. These advances now enable the differentiation of terminal, bridging, and internal oxygen sites, offering unique insights into structural isomerism, substitution effects, and protonation states in various POM archetypes including Lindqvist, Keggin, and Dawson structures. Beyond structural assignments, ¹⁷O NMR has provided mechanistic understanding of catalytic processes by tracking oxygen participation in redox transformations and proton-coupled electron transfer. When integrated with computational approaches such as density functional theory (DFT) and artificial intelligence (AI), ¹⁷O NMR delivers predictive power for interpreting chemical shifts, quadrupolar parameters, and dynamic behaviour. This review consolidates recent progress, highlights case studies, and underscores the emerging role of ¹⁷O NMR as a cornerstone for advancing POM chemistry at the interface of structural science, catalysis, and theoretical modeling.