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

Abstract

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 M 6 (M = Ni, Co)-substituted trilacunary {PW 9 } and Mn-bridged {W 4 }. Sodium ions are used as templates to fill the cages. The polyanions of cages can be represented as {Na 6 (MnO 6 ) 12 (W 4 O 4 ) 12 [MnO 4 (OH 2 )] 6 (PW 9 Ni 6 O 49 H 15 ) 8 } and {Na 6 (MnO 6 ) 12 (W 4 O 4 ) 12 [MnO 4 (OH 2 )] 6 (PW 9 Co 6 O 49 H 15 ) 8 }. The entire structure can also be considered as a five-shell Na 6 @Mn 12 @{W 4 } 12 @Mn 6 @{PW 9 M 6 } 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.