Recent advances in mono-lacunary Keggin-type polyoxometalate-based crystalline materials: From synthetic strategies, diverse structures to functional applications

The mono-lacunary Keggin-type polyoxometalate (MLKP)-based crystalline materials are of significant interest due to their remarkable structural characteristics and functionalities. MLKPs are the basic building units in this class of crystalline materials, which can be modified to achieve significant chemical tuning. Remarkably, the existence of vacant sites could enhance the coordination reactivity of MLKPs, allowing them to coordinate with various metal ions and organic ligands, thereby demonstrating the prospects of MLKPs in manufacturing different structures and applications. This review focuses on MLKP-based crystalline materials featuring isolated, onedimensional (1D) chains, two-dimensional (2D) layer and three-dimensional (3D) framework structures, and examines their optical, electrical, magnetic and catalytic properties. The objective of this review is to establish a comprehensive understanding of MLKP-based materials and provide insights in the development of more novel MLKPs materials.