Solvent-Mediated Structural Tuning of Eu-MOFs for the N -Formylation of Amines with CO ₂

The controllable synthesis of metal–organic frameworks (MOFs) with tailored structures and functionalities remains a key focus in materials chemistry, with solvent engineering serving as a powerful strategy for structural regulation. Herein, four europium-based MOFs (Eu-MOFs) derived from 2,5-dihydroxyterephthalic acid (H 2 DHTA) were solvothermally synthesized by varying the H 2 O/CH 3 CN solvent ratio ([Eu(DHTA) 1.5 (H 2 O) 3 ]·H 2 O 1; [Eu 2 (DHTA) 3 (H 2 O) 6 ]·2H 2 O 2; [Eu 2 (DHTA) 3 (H 2 O) 4 ] 3; and [Eu 2 (DHTA) 3 (H 2 O) 4 ]·H 2 O 4 ). Single-crystal X-ray diffraction analyses demonstrate that the solvent composition precisely regulates the crystal structures of Eu-MOFs, including framework dimensionality, metal nuclearity, dihedral angles, and interligand angles, through hydrogen-bonding interactions and competitive coordination effects. Notably, compound 3 exhibits excellent catalytic activity toward the CO 2 -based N -formylation of amines at room temperature, affording high conversion for a wide range of amine substrates. In situ DRIFTS measurements further clarify the catalytic mechanism. This work not only systematically explores the solvent effect on the structural tuning of Eu-MOFs but also provides a highly efficient catalyst for the green conversion of CO 2, demonstrating promising potential in sustainable catalysis and energy-related applications.