Supramolecular Entanglement in a Hydrogen-Bonded Organic Framework Enables Flexible-Robust Porosity for Highly Efficient Purification of Natural Gas.

The development of porous materials with flexible-robust characteristics shows some unique advantages to target high performance for gas separation, but remains a daunting challenge to achieve so far. Herein, we report a carboxyl-based hydrogen-bonded organic framework (ZJU-HOF-8a) with flexible-robust porosity for efficient purification of natural gas. ZJU-HOF-8a features a four-fold interpenetrated structure with dia topology, wherein abundant supramolecular entanglements are formed between the adjacent subnetworks through weak intermolecular hydrogen bonds. This structural configuration could not only stabilize the whole framework to establish the permanent porosity, but also enable the framework to show some flexibility due to its weak intermolecular interactions (so-called flexible-robust framework). The flexible-robust porosity of ZJU-HOF-8a was exclusively confirmed by gas sorption isotherms and single-crystal X-ray diffraction studies, showing that the flexible pore pockets can be opened by CH and n-CH molecules rather by CH and CH. This leads to notably higher CH and n-CH uptakes with enhanced selectivities than CH over CH under ambient conditions, affording one of the highest n-CH/CH selectivities. The gas-loaded single-crystal structures coupled with theoretical simulations reveal that the loading of n-CH can induce an obvious framework expansion along with pore pocket opening to improve n-CH uptake and selectivity, while not for CH adsorption. This work suggests an effective strategy of designing flexible-robust HOFs for improving gas separation properties.