Giant Polyoxoniobate-Based Inorganic Molecular Tweezers: Metal Recognitions, Ion-Exchange Interactions and Mechanism...

This work reports the interesting and unique cation-exchange behaviors of the first indium-bridged purely inorganic 3D framework based on high-nuclearity polyoxoniobates as building units. Each nanoscale polyoxoniobate features a fascinating near-icosahedral core-shell structure with six pairs of unique inorganic "molecular tweezers" that have changeable openings for binding different metal cations via ion-exchanges and exhibit unusual selective metal-uptake behaviors. Further, the material has high chemical stability so that can undergo single-crystal-to-single-crystal metal-exchange processes to produce a dozen new crystals with high crystallinity. Based on these crystals and time-dependent metal-exchange experiments, we can visually reveal the detailed metal-exchange interactions and mechanisms of the material at the atomic precision level. This work demonstrates a rare systematic and atomic-level study on the ion-exchange properties of nanoclusters, which is of significance for the exploration of cluster-based ion-exchange materials that are still to be developed.