A nonconventional host-guest cubic assembly based on γ-cyclodextrin and a Keggin-type polyoxometalate

Supramolecular self-assembly allows components to organize themselves into regular patterns by using non-covalent interactions to find the lowest-energy configuration. However, self-assembling organic and inorganic building blocks together into an ordered framework remains a challenge due to the difficulties in rationally interfacing two dissimilar materials. Herein, we report on the host-guest ensemble of polyoxometalates (POMs) using cyclodextrins (CDs) as the trapping agent to form POM@gamma-CD entities. Two unprecedented super cubic isostructures, Co/Cu-PW12O40-gamma-CD, were obtained. The self-assembly has been observed both in solution (MS, 1D NMR and 2D DOSY) and in the solid state. Single-crystal X-ray diffraction reveals that in a unit cell, the inner (POM@gamma-CD)(12) cube is encapsulated by the outer (POM@gamma-CD)(24) cube. Besides, due to the rather large spherical voids, two (POM@gamma-CD)(24) cubes are interspersed together. Preliminary investigations of the redox properties of the [PW12O40](3-) encapsulated in the gamma-cyclodextrins indicate that the redox properties of the trianion are largely retained, yet an additional electrochemical stabilization is observed. The adduct reported here opens the door to a new generation of hybrid materials with tuned structures and customized functionalities.