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 O_h 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.