Harnessing Halogen Bonds in Porous Molecular Crystals for Efficient SF₆/N₂ Separation

Halogen bonding offers a directional and tunable noncovalent interaction that remains underexplored in the design of porous molecular materials. Here, we report FPMC-1-β, a porous molecular crystal that uniquely integrates permanent porosity, high thermal stability, solution processability, and halogen bonding capability. Upon desolvation, FPMC-1-α undergoes a structural transformation into the denser FPMC-1-β phase, featuring distorted 1D channels lined with exposed σ-holes on bromine atoms. This architecture enables selective halogen bond-mediated interactions with fluorinated gases. FPMC-1-β exhibits a sulfur hexafluoride (SF₆)/N₂ selectivity of 178.6 at 298 K and 1 bar-setting a new record among all reported porous molecular crystals and soluble porous materials. Combined experimental and computational studies reveal that the high selectivity arises from strong F⋯Br halogen bonding with SF₆, in contrast to the weak, nonspecific interactions observed for N₂.