Heterometallic YbCo–Organic Framework for Efficiently Catalyzing Cycloaddition of CO₂ with Epoxides and Knoevenagel Condensation

Due to the excellent catalytic performance of Co-MOFs and Ln-MOFs on the chemical fixation of CO2, the self-assembly of microporous heterometallic compounds with the aid of designed functional ligands is carried out in our group. Herein, the solvothermal self-assembly of Co2+, Yb3+, and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H5BDCP) generated a rarely reported {CoYb}n-chain-based framework of {[CoYb(BDCP)(H2O)]·3DMF·3H2O}n (NUC-70) with quasi-nanoporous channels (aperture ca. 11.4 Å) shaped by six rows of {CoYb(CO2)5(H2O)}n nodes. To the best of our knowledge, this is a rare 3d-4f heterometallic chain of {CoYb(CO2)5(H2O)}n with a staggered arrangement of Co2+ and Yb3+. After removing the associated water molecules, NUC-70a possesses the excellent characteristics of a large specific surface area, unsaturated open metal sites of Co2+ and Yb3+ as Lewis acid sites, and high heat/water-resistant physicochemical properties. Catalytic experiments showed that NUC-70a possessed a high catalytic activity on the cycloaddition reactions of epoxides with CO2 under mild conditions. Furthermore, the experiments performed confirmed that the Knoevenagel condensation reactions of aldehydes and malononitrile could be efficiently catalyzed by NUC-70a. This work illustrates that characteristic ligand design plays a key role in the self-assembly of MOFs with specific functions.