Overview of organophosphonate covalently modified polyoxometalates: From synthesis, structural diversity to applications

The synergistic interaction between polyoxometalates (POMs) and organophosphonic acids (R–PO(OH)₂ or PO(OR)(OH), OPAs) is crucial for the design of novel hybrid materials, which aim to enhance material performance through structural regulation and functional integration. As multidentate ligands, OPAs have become key units for the covalent modification of POMs, laying the chemical foundation for constructing POMs-based hybrid materials with precise structures and tunable functionalities.

 

A team of POM scientists from Henan University in Kaifeng, China, led by Jingyang Niu, recently outlined the current state of research on organophosphonate covalently modified polyoxometalates (OCMPs) in this field. Flexible, stable, and modifiable OPAs serve as ideal organic ligands for constructing structurally diverse and functionally tunable POM-based hybrid materials. These ligands not only facilitate the controlled synthesis of various POM types, thereby enriching the library of confined POM assembly systems, but also exhibit significant application potential in fields such as photochromism, photocatalysis, magnetism, catalysis, and biotherapy.

 

The team published their review in Polyoxometalates on October 19, 2025.

 

“In this review, we systematically summarize the research progress in o OCMPs. The discussion is dedicated to the synthesis strategies, structural design, and performance characteristics of this class of organic-inorganic hybrid materials. Furthermore, we also prospect the potential future development directions of such materials in areas such as multi-component synergy, stability enhancement, and application expansion.” said Jingyang Niu, professor in the School of Chemistry and Molecular Sciences at Henan University.

 

OCMPs are formed when OPA groups undergo deprotonation and establish M–O–P covalent bonds with the metal atoms in the POM framework (where M = W, Mo, V, or Nb). Their distinctive properties, including redox activity, structural tunability, low toxicity, and high stability, endow these materials with broad applications.

 

In the field of research on OCMPs, OPAs can serve as multidentate ligands. The oxygen atoms in their phosphonate groups can form covalent bonds with the metal atoms in the POM framework through various coordination modes such as monodentate, chelating, or bridging. This coordination interaction achieves stable and robust covalent modification, laying a critical foundation for constructing structurally diverse and functionally tunable hybrid materials. Furthermore, the organic R groups in OPA molecules can be pre-designed or post-modified to introduce functional groups such as amino, carboxyl, sulfonic acid groups, or even photosensitive or catalytic moieties, thereby integrating specific functional properties into the inorganic POM skeleton. This ultimately enables the targeted design and regulation of material functionalities.

 

It is noteworthy that several critical challenges still need to be addressed in this field, requiring more research efforts to be devoted to future exploration: 1) The research on other types of POM (such as polyoxoniobates, and polyoxotantalate) remains scarce or completely unexplored. Notably, no studies have been reported to date on Ln-based organophosphonate covalently modified polyoxovanadates. 2) The traditional synthesis methods have great limitations, making it imperative to develop novel and efficient synthetic strategies/methods to further broaden the structural types of OCMPs, such as liquid diffusion methods, gas diffusion methods, and inert atmosphere synthesis techniques (e.g., vacuum line, glove bag, or glove box systems). 3) Research on OCMPs across multiple fields remains in its nascent stage, with particularly prominent gaps in catalysis and therapeutic applications—especially regarding mechanistic studies of catalysis.

 

The research team hopes that this review will advance the directional design and preparation of structurally novel and functionally tunable OCMP materials, providing a critical foundation for constructing high-performance hybrid functional material systems. Professor Jingyang Niu stated, " OCMPs are expected to demonstrate enhanced structural diversity and functional integration capabilities in the future. On the same POM skeleton, precise molecular engineering strategies can enable the synergy and regulation of multiple functions such as photochromism, photocatalysis, magnetism, catalysis, and biotherapy."

 

Other contributors include Hui Kong from the School of Huanghuai University in Zhumadian, China; and Pengtao Ma and Jingping Wang from the School of Henan University in Kaifeng, China.

 

This work was supported by the National Natural Science Foundation of China (Nos. 22171071, 22071044, 21771054, and 21571050).

 

About the Author

Dr. Jingyang Niu is a full professor in the College of Chemistry and Chemical Engineering, Henan University, China. His research interests focus on polyoxometalate chemistry and functional materials. Until now, he has published more than 400 papers in J. Am. Chem. Soc.，Angew. Chem. Inter. Edi.，Coord. Chem. Rev.，ACS Catal. Inorg. Chem. and other journals, presided over 10 national/provincial scientific research projects, owns 5 invention patents. For more information, please pay attention to his research homepage. https://ccce.henu.edu.cn/info/1553/12357.htm

 

About the Journal

Polyoxometalates (ISSN 2957-9821) is a peer-reviewed (single-blind), open-access and interdisciplinary journal, sponsored by Tsinghua University. It publishes high-quality original research and authoritative reviews that focus on cutting-edge advancements in polyoxometalates, and clusters of metals, metal oxides and chalcogenides. Expeditious peer review enabling timely publication is a key feature of Polyoxometalates. It is indexed by ESCI, Scopus (CiteScore 2024 = 14.7), Ei Compendex, CAS, and DOAJ. For details about Polyoxometalates, please visit: https://www.sciopen.com/journal/2957-9821.

---

---