Polyoxometalate condensation and transformation mediated by adaptive coordination-assembled molecular flasks.

Here we report polyoxometalate (POM) condensation or transformation reactions mediated by adaptive coordination-assembled molecular flasks. Addition of NaSiO to the (MoO)⊂1·(NO) complex containing Lindquist-type clusters as guests leads to the formation of a new (SiMoO)⊂2·(NO) host-guest complex, where the generated Keggin-type cluster served as a trigger for the host transformation from cage 1 to isomeric bowl 2. Conversion from 1 to 2 driven by the condensation was found to be 27.5-fold faster than the direct templation with independently prepared SiMoO . As a comparison, cage 1 was noticed to bind only one WO cluster in its cavity, and the formation of (WO)⊂2·(NO) as the main product and (SiWO)⊂2·(NO) as the minor host-guest complex was observed when it was used for the above condensation reaction, highlighting the crucial role of encapsulation in cavity-confined POM transformations. The reaction processes and the final structure of all the new host-guest complexes have been investigated by NMR, ESI-TOF-MS and SCXRD. Our findings not only showcase a unique example of inorganic-reaction-driven responsive supramolecular system, but also provide a new approach for the preparation of functional POMs⊂cage composite materials.