Modular assembly of polyoxometalate clusters at the sub-1 nm scale

Atomic-level manufacturing enables the bottom-up fabrication of nanomaterials with tailored structures and properties. Clusters with atomic precise structures can be used as superatom building blocks to construct superstructures with exceptional properties beyond their individual properties. However, the programmable and large-scale synthesis of cluster assemblies remains challenging. This protocol describes the detailed experimental procedures for the modular assembly of polyoxometalate (POM) clusters into subnanomaterials by programmable interactions under simple and mild conditions. In this approach different types of POM clusters (0.7-1.8 nm in size) are coated with quaternary ammonium or oleylamine ligands using either two-phase or solvothermal methods. The assembly process depends on the interactions between atom clusters, ligands and the reaction matrix, all of which can be modified to generate a library of subnanometer superstructures. The four intercluster connection modes are metal cation-induced coordinative connection, anion bridged covalent connection, synergistic noncovalent interaction and cluster-nucleus co-assembly. A library that includes single-cluster nanowires, clusterphenes and nanosheets with single-cluster thicknesses, can be prepared within 3-12 h. Owing to their ultrahigh surface atom ratio and electron delocalization, the resulting subnanometer POM assemblies with rich structural and compositional diversity exhibit excellent properties and application potential in terms of mechanics, catalysis and chirality. This procedure is suitable for users with prior expertise in the synthesis of inorganic and cluster-based nanomaterials.