Chaotropic Effect as an Assembly Motif to Construct Supramolecular Cyclodextrin-Polyoxometalate-Based Frameworks

摘要

In aqueous solution, low-charged polyoxometalates (POMs) exhibit remarkable self-assembly properties with nonionic organic matter that have been recently used to develop groundbreaking advances in host-guest chemistry, as well as in soft matter science. Herein, we exploit the affinity between a chaotropic POM and native cyclodextrins (alpha-, beta-, and gamma-CD) to enhance the structural and functional diversity of cyclodextrin-based open frameworks. First, we reveal that the Anderson-Evans type polyoxometalate [Al-Mo6O18(OH)(6)](3-) represents an efficient inorganic scaffold to design open hybrid frameworks built from infinite cyclodextrin channels connected through the disk-shaped POM. A single-crystal X-ray analysis demonstrates that the resulting supramolecular architectures contain large cavities (up to 2 nm) where the topologies are dictated by the rotational symmetry of the organic macrocycle, generating honeycomb (bnn net) and checkerboard-like (pcu net) networks for alpha-CD (C-6) and gamma-CD (C-8), respectively. On the other hand, the use of beta-CD, a macrocycle with C7 ideal symmetry, led to a distorted-checkerboard-like network. The cyclodextrin-based frameworks built from an Anderson-Evans type POM are easily functionalizable using the molecular recognition properties of the macrocycle building units. As a proof of concept, we successfully isolated a series of compartmentalized functional frameworks by the entrapment of polyiodides or superchaotropic redox-active polyanions within the macrocyclic host matrix. This set of results paves the way for designing multifunctional supramolecular frameworks whose pore dimensions are controlled by the size of inorganic entities.