Crystal Facets Reactivity in Metal–Organic Frameworks

Crystal facets are intrinsically defective, chemically distinct interfaces whose reactivity critically influences the function of crystalline materials. In reticular porous systems, while internal pore chemistry has been extensively engineered, growing evidence shows that chemical transformations in complex environments increasingly occur at external crystal surfaces. In this mini review, it is highlighted how the crystal facets’ reactivity can be dictated by surface functionality, particle size, defect density, or crystal morphology. Precise control of these parameters enables deliberate exposure of crystal facets, leading to enhanced crystal surface accessibility and higher reactivity. Further focus is placed on frameworks based on hemilabile bonds, whose intermediate bond strength enables dynamic yet structurally persistent crystal surfaces. In these materials, surface‐confined reactions can initiate self‐propagating cascade processes that extend beyond the crystal surface through controlled bond exchange, lattice degradation, and release of reactive species. This behavior transcends classical surface‐limited catalysis and establishes crystal facets as active, information‐bearing interfaces. Together, these insights position crystal surface reactivity as a key design parameter for developing functional materials capable of programed cascade chemistry in catalytic and biological contexts.