Multitopic acid modulation unlocks a new dimensionality in defect-engineered MOFs.

Defect engineering is a powerful strategy to tailor the physicochemical properties of metal-organic frameworks (MOFs). Among various approaches, modulation synthesis - typically employing monotopic modulators - has emerged as the most widely used method to introduce structural defects. However, conventional modulation strategies aiming for high defect densities typically rely on using large quantities of monocarboxylic acids and/or strong acidity. Herein, we introduce a third dimension to modulate the defects of MOFs by employing multitopic carboxylic acids as modulators, wherein the topicity of the modulator exceeds that of the pristine linker. Using UiO-66 as a model system, multitopic modulators with varying topic numbers and carboxylate positions significantly influence defect incorporation. In particular, ortho-substituted acids and higher-topic modulators efficiently generate higher defect densities at much lower dosages without relying on harsh acidic conditions. Catalytic epoxide ring-opening studies demonstrate that defect engineering enhances activity by creating accessible active sites. This establishes multitopic modulation as a tunable strategy for controlling MOF structure-function relationships.