Beyond Solution Chemistry: Mechanochemistry Enables Clustered Defects in Metal-Organic Frameworks

Defects in metal-organic frameworks (MOFs) have attracted significant attention in recent years due to the unique properties arising from missing linkers and/or metal nodes. In this work, we introduce mechanochemistry as a de novo synthetic strategy for incorporating extrinsic defects into MOFs by employing symmetry-reduced or defective ligands. By systematically comparing defective MOFs prepared via mechanochemical and conventional solvothermal methods, we demonstrate that mechanochemical synthesis not only enables precise incorporation of defective ligands due to its rapid reaction but also promotes their spatial aggregation, leading to the formation of locally missing domains within the lattice. These clustered defects, in turn, generate observable hierarchical porosity, a capability that surpasses that of traditional solution-based approaches. This work presents a unique example of cluster defects in MOF, analogous to the Koch-Cohen cluster observed in nonstoichiometric iron oxides, yet arising from the uneven distribution of defective ligands in the solid state─a phenomenon not previously observed in MOF chemistry.