Dual impact of water on stability of metal-organic frameworks

The widespread application of metal-organic frameworks (MOFs) is hindered by their hydrolytic instability in aqueous and humid environments. To overcome this bottleneck, herein, we evaluate four representative MOFs-MOF-303 (highly stable), MIL-127(Fe) (stable), HKUST-1 (moderately unstable), and UMCM-1 (unstable) - using periodic and fragment-based density functional theory. By distinguishing the water adsorption, condensation, and hydrolysis pathways, we identify the structural and chemical factors that govern stability. Our results reveal the dual impact of water: it can destabilize frameworks by facilitating metal-ligand bond cleavage and improving ligand-ligand interactions of detached linkers, as in UMCM-1 and HKUST-1, but can also enhance stability by forming extended hydrogen-bond networks with polar ligands, as observed in MOF-303. This cooperative water-ligand interaction shields metal-oxygen bonds and prevents pore collapse, challenging the prevailing view that hydrophobicity is key to promoting stability. These insights clarify contradictory experimental reports and establish general design principles, highlighting that water is both a threat and a stabilizer depending on the framework's connectivity and ligand chemistry.