Increasing connectivity through self-complementarity enables permanent porosity in a halogen-bonded organic framework

Abstract

Halogen bonding has emerged as an intuitive and programmable handle for constructing ordered, low-density molecular solids. However, its ability to support permanent porosity has not been realized. Here, we report a self-complementary strategy that surpasses this long-standing limitation, delivering the first rigorously characterized permanently porous halogen-bonded organic framework (XOF). A threefold-symmetric, 2-iodooxazole-terminated tecton spontaneously assembles into a low-density, crystalline network that remains intact upon complete solvent removal. Permanent porosity is confirmed by N₂ gas adsorption–desorption measurements using at 77 K, and the porous topology was monitored via X-ray diffraction. This framework is sustained by π-stacked tectons linked through one-dimensional helical chains of C–I⋯N halogen bonding, yielding full three-dimensional connectivity. Subtle torsional disorder within these chains can be resolved crystallographically, providing rare insight into molecular-level disorder in highly ordered porous frameworks. For comparison, study of an analogous hydrogen-bonded framework composed of a point-modified tecton found rapid structural reorganization upon solvent exchange, supporting more robust intermolecular connectivity in the halogen-bonded system. This work defines a new upper bound for halogen bonding in materials design, establishing XOFs as a distinct permanently porous materials platform.