Polyoxometalate Clusters: Sub-nanometer Building Blocks for Construction of Advanced Materials

Summary Cluster-assembled materials based on polyoxometalates (POMs) process unprecedented structural tunability and polymer-like behaviors because of the sub-nanometer-sized building blocks and their non-covalent linkage. Through the whole journey in their development, exquisite POM cluster assemblies with advanced functions spring up, and the control over their nanostructures tends to be more precise and reach their nature at molecular level. In this paper, recent progress in cluster-assembled materials based on POMs is overviewed, including the assembly of covalently and non-covalently modified POM clusters as well as the co-assembly of POM clusters and inorganic entities. By surfactant encapsulation, POM clusters are compatible in various solvents, and hybrid assemblies with diverse morphologies and unique properties have been achieved. The Janus POM-POSS clusters feature intricate assemblies in mixed solvent systems, which provide instructive understanding for solution behaviors of macro-ions. Notably, the POM clusters can also intervene in the nucleation of nanocrystals, resulting in the formation of cluster-nuclei co-assembled materials with well-organized structures and wide-ranging composition compatibility. Meanwhile, the chemistry of cluster-assembled materials has not been well explored, and there are great potentials as well as challenges that lie ahead.