Ligand Fluorination Tailors Electronic Structure in 2D Ag₁₈ Cluster-Based MOF for Enhanced Knoevenagel Condensation

Atomically defined silver nanoclusters are ideal building blocks for functional materials, yet their macroscopic assembly into stable and functionally tunable frameworks remains challenging. Metal organic frameworks (MOFs) offer a promising way to integrate such clusters into ordered architectures. Herein, two structurally and functionally comparable 2D silver cluster-based MOFs (Ag₁₈BDC and Ag₁₈FBDC) were constructed via a ligand fluorination strategy, employing the [(CrO₄)@Ag₁₈(tBuC≡C)₁₂] cluster as the node and 1,4-benzenedicarboxylate (BDC) along with its fluorinated 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylate (FBDC) as the linkers. Both materials exhibit excellent chemical and thermal stabilities. Ag₁₈FBDC outperforms Ag₁₈BDC in Knoevenagel condensation across various aromatic aldehydes, owing to its stronger Lewis acidity that enhances carbonyl electrophilicity and facilitates nucleophilic attack. X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) calculations, and N-methylacridone (NMA) fluorescence probing consistently confirm that the electron-withdrawing effect of fluorine reduces electron density at the Ag core and strengthens its Lewis acidity, providing electronic-level insight into the superior catalytic performance of Ag₁₈FBDC. This work expands the range of cluster nodes for MOF assembly and demonstrates how ligand fluorination strategies can tailor electronic structures to design better heterogeneous catalysts.