Fluorine-Decorated {Tb2}-Organic Framework for Efficiently Catalyzing the Chemical Fixation of CO2 and Knoevenagel Condensation

Lanthanide–organic frameworks (LnOFs), as a category of catalytic materials in organic reactions, have attracted great attention due to the strong Lewis acidity of Ln³⁺ ions originating from their high-coordination properties. Herein, spindle-like [Tb₂(CO₂)₁₀(DMF)₂] clusters (defined as {Tb₂}) and fluorine-functionalized tetratopic F–H₄PTTA ligands are unified into a robust nanocage-containing framework of {[(CH₃)₂NH₂][Tb(FPTTA)(DMF)](DMF)₂(H₂O)}_n (NUC-160, F–H₄PTTA = 2′,3′-difluoro-[p-terphenyl]-3,3″,5,5′′-tetracarboxylic acid). In NUC-160, eight {Tb₂} clusters and six PTTA^4– organic modules are shaped into a nanocage-like void with a diameter of 11.3 × 12.8 Ų. After thermal activation, plentiful Lewis acidic Tb³⁺ sites and basic sites of −F groups are uniformly dispersed in the confined microspace of the NUC-160a host framework. NUC-160a demonstrates superior catalytic activity in the coupling reaction between CO₂ and epoxides under mild conditions, attributed to its integrated basic–acidic bifunctional sites that synergistically activate both reactants. The material further exhibits efficient catalytic performance in Knoevenagel condensation reactions, where the open metal sites selectively activate aldehydes, and the fluorine (–F) groups facilitate malononitrile activation through distinct mechanistic pathways. In the two organic reactions, the ability of the NUC-160a catalyst to be recycled more than five times and to achieve a conversion rate of over 95% for reactants proves its suitability as a catalyst for industrial use.