Combining Mixed-Linker Design and Selective Etching for Precise Control of Defect Type and Distribution in...

Mixed-linker strategies combined with selective etching enable precisely introduce defects into metal-organic frameworks (MOFs). However, random linker distributions in most mixed-linker systems limit control over the type and spatial arrangement of defects. Here, a unique MOF, Zr₆(BDC)₃(Fum)₃, featuring crystallographically ordered terephthalic acid (BDC) and fumaric acid (Fum) linkers, is designed as a model to study ordered defect generation. Due to the distinct chemical stability between aromatic and alkenyl linkers, both thermal etching and ozonolysis are employed to selectively remove Fum linkers. While direct thermal treatment caused partial framework collapse, although ozone oxidation is impossible to completely remove Fum, it provides a milder pathway that preserved crystallinity. Combined ozonolysis-thermal treatment strategy enabled the gradual removal of Fum linkers, generating controllable missing-linker defects. Catalytic evaluation using the ring-opening of styrene oxide reveals a volcano-type correlation between defect density and activity: the conversion rate increased with defect number up to approximately two missing linkers per cluster, beyond which framework degradation led to reduced catalytic performance. This work demonstrates an effective strategy for constructing ordered single-type defects in MOFs and highlights the fundamental limitation of defect tolerance in the UiO-type framework.