Catalytically Active, Coulombic Metal–Organic Frameworks Assembled from Zirconium Metal–Organic Cages and Polyoxometalates

Le résumé fourni par la source

Electrostatical assembly of molecular salts from appropriately designed building blocks offers an attractive route to porous crystalline materials. However, achieving permanent porosity is challenging because Coulombic interactions between charged molecules are typically weaker and far less directional than coordination bonding atom, making construction of large, guest-accessible pore architectures particularly difficult. Here, we establish a design principle that introduces directionality into electrostatic assembly through control of cage geometry and flexibility. This strategy directs anisotropic packing of trigonal bipyramidal Zr metal–organic cages with Keggin-type polyoxometalates by simple solution mixing. Such directionality enables the formation of cage-based Coulombic metal–organic frameworks (Cage-CouMOFs) with a MOF-like topology without resorting to conventional coordinate-covalent bonding. Cage-CouMOF-2 exhibits large external channels (external to the cage) with a pore limiting diameter of 13.8 Å, and a Brunauer–Emmett–Teller surface area of 1170 m 2 g –1 ; to our knowledge, both are the largest yet reported among electrostatically assembled salts. The synthesis is scalable to gram-level without compromising porosity. Cage-CouMOF-2 exhibits good stability and is competent as a recyclable heterogeneous catalyst for dibenzothiophene oxidation. These results demonstrate that molecular-level control of electrostatic assembly can generate directional, large-pore framework architectures beyond coordination bonding.

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