C-H⋯X hydrogen-bonded organic frameworks: assembly, structural characteristics and emerging applications

Hydrogen-bonded organic frameworks (HOFs) have emerged as a promising class of crystalline porous materials. Conventional HOFs assembled through O/N-H⋯O/N hydrogen bonds have been extensively studied because these strong and directional interactions have long been considered crucial for structural stability and functionality. This has left HOFs assembled primarily through weaker C-H⋯X (X = O, N, S, F, etc.) non-conventional hydrogen bonds relatively underexplored despite their rapid development over the past decade. Notably, the reduced directionality and flexible geometrical tolerance of C-H⋯X interactions can give rise to diverse framework architectures, adaptive porosity, stimulus-responsive behavior, and, in selected systems, flexible-robust characteristics. However, understanding of the principles governing their assembly, structural regulation, and structure-function relationships remains fragmented. In this Review, we summarize recent advances in C-H⋯X hydrogen-bonded organic frameworks (C-H⋯X HOFs), covering their supramolecular assembly, structural characteristics, regulation strategies, and emerging applications. Current challenges and future opportunities for the development of C-H⋯X HOFs are also discussed. We anticipate that this Review will provide useful insights into the design and development of non-covalent porous materials constructed from weak yet cooperative intermolecular interactions.