An inorganic–organic hybrid Eu–W-implanted tartrate-connected selenotungstate tetramer {[Eu₄(H₂O)₁₂W₆O₁₂(tar)₂][B-α-SeW₉O₃₃]₄}¹⁶⁻ (1a, H₄tar = tartaric acid) was successfully obtained by introducing the flexible multidentate tartrate ligand into the Se-templated lacunary polyoxometalate (POM) and lanthanide (Ln) system. Within 1a, two identical penta-nuclear Eu₂W₃-cluster-encapsulated dimeric units {[Eu₂(H₂O)₆W₃O₆][B-α-SeW₉O₃₃]₂}⁴⁻ are arranged in an ''open C-shaped'' configuration, interconnected by double tetra-dentate tar⁴⁻ linkers. Moreover, 1a demonstrates notable stability and intense photoluminescence (PL) emission in an aqueous environment. This emission proves effective in discriminating the toxic chemical pollutant o-nitrophenol (o-NP) from its isomers m-nitrophenol (m-NP) and p-nitrophenol (p-NP), achieving highly selective and sensitive discrimination of o-NP with a low detection limit of 0.73 μM. The practical applicability of probe 1a was demonstrated in lake water, exhibiting suitable recoveries. The PL sensing mechanism involving static quenching and competitive absorption was elucidated finally. This accomplishment sets the groundwork for the deliberate synthesis of novel organic ligands and Ln-functionalized POM hybrids. Furthermore, it propels the exploration of POM materials for the recognition of environmental pollutants.

Polyoxometalate-based metal–organic frameworks (PMOFs) as extended solids assembled from metal-oxide cluster units and metal–organic groups have drawn wide research attention in recent years due to the unique advantages of containing both polyoxometalate (POM) and metal–organic framework (MOF) units, which allow their multifunctional applications in catalysis, sensing, and energy storage. In this review, the recent progress on the syntheses, structural diversity, and potential applications of PMOFs are summarized. In terms of structure, two categories of PMOFs, POM@MOFs and POM–MOFs, are discussed. POM@MOFs are PMOFs in which the POM units are not coordinated to the MOF, whereas POM–MOFs are PMOFs in which the POM units are coordinated to the MOF. In terms of properties, some selected investigations on the application of PMOFs in catalysis, dye adsorption and degradation, chemical sensing and energy storage are covered. To conclude, a personal outlook and viewpoints on this field are presented. It is expected that this review will inspire researchers and provide helpful tips for the future rational design of function-oriented PMOFs.