Giant Five-Shell Polyoxometalate Cages and the Single-Cluster-Based Nanowire Superstructures

The preparation of polyoxometalate molecular cages has always been a long-term and challenging pursuit. In this work, we have successfully prepared two unprecedented giant heterogeneous POM-based purely inorganic molecular cages with Oh symmetry, which contain the aggregation of M6 (M = Ni, Co)-substituted trilacunary {PW9} and Mn-bridged {W4}. Sodium ions are used as templates to fill the cages. The polyanions of cages can be represented as {Na6(MnO6)12(W4O4)12[MnO4(OH2)]6(PW9Ni6O49H15)8} and {Na6(MnO6)12(W4O4)12[MnO4(OH2)]6(PW9Co6O49H15)8}. The entire structure can also be considered as a five-shell Na6@Mn12@{W4}12@Mn6@{PW9M6}8 arrangement. The electrostatic effects of sodium ions within the cages enhance the stability of the structures, allowing them to maintain a monodisperse and stable state in aqueous solutions. Interestingly, the cages assemble into nanowires through electrostatic contact with the cationic CTA+ ligand, demonstrating its flexible assembly capability at the single-cluster level. This giant POM inorganic molecular cage holds significant potential for application in the preparation of functional nanomaterials.