Supramolecular Halogen-Bonded Organic Frameworks (XOFs): From Structural Construction to Functional Applications

Supramolecular halogen-bonded organic frameworks (XOFs) have emerged as a distinct class of crystalline material in which halogen bonding, rather than covalent or coordination chemistry, defines the framework. Two types of XOFs have developed. Classical XOFs are assembled from electroneutral R-X···D contacts; their single-point character biases assembly toward chains, sheets, and three-dimensional networks. Cationic XOFs exploit halonium ions, whose vacant p orbital bridges two Lewis bases in a three-center, four-electron [N···X···N]⁺ motif. The halogen scope has widened from iodine-(I) through bromine-(I) to chlorine-(I), a species otherwise observable only transiently at cryogenic temperatures. This review surveys both families with respect to structural classification, synthetic strategyfrom cocrystallization to silver-halogen exchange, and dynamic ligand exchangeand functional application, including gas adsorption and separation, iodine capture, photocatalysis, luminescent and vapochromic sensing, and biomedicine. Halogen bonding offers an assembly logic tunable through halogen identity, counterion, and ligand that has no direct analogue in coordination or covalent chemistry.