Infinite building blocks for directed self-assembly of a supramolecular polyoxometalate–cyclodextrin framework for multifunctional oxidative catalysis

Abstract

The utility of infinite building blocks (IBBs) has encouraged the facile construction of porous organic–inorganic hybrid materials such as metal–organic frameworks. However, this strategy remains less explored for building functional supramolecular frameworks that are assembled by weak supramolecular interactions. Here, we report the self-assembly of a supramolecular polyoxometalate–cyclodextrin (POM–CD) framework directed by IBBs of ({MnV₁₂Ce₆}{PW₁₀V₂}₂)_∞ for multifunctional oxidative catalysis. The IBBs exhibit an infinite 1D rod shape embedded by {MnV₁₂} and {PW₁₀V₂} POM clusters which specifically interact with the outer walls of α-CD because of a weak chaotropic effect and size-mismatch. This has allowed the ordered packing of α-CD between adjacent IBBs via hydrogen bonding and van der Waals contacts, leading to a porous framework containing interconnected channels along two dimensions, with the largest opening up to 12 × 17 Å. The incorporation of catalytically active POM clusters on the porous channels enables the high performance of the POM–CD framework towards selective oxidation of sulfides to sulfoxides. Moreover, cross-linking the POM–CD framework with hexamethylene diisocyanate afforded a more stable porous framework that can be used as an authentically heterogeneous catalyst for not only sulfoxidation but also oxidative cleavage of styrenes under harsher conditions. The robust cross-linked framework can preserve its structural integrity after cycling 5 times with little loss of catalytic performance. This work may pave the way for the rational design of porous organic–inorganic hybrid materials with customized functionalities based on the IBB strategy.