A stable Co(II)-based metal-organic framework with dual-functional pyrazolate-carboxylate ligand: Construction and CO2 selective adsorption and fixation

By taking the functional advantages of both pyrazolate and carboxylate ligands, a unique dual-functional pyrazolate-carboxylate ligand acid, 4-(3,6-di(pyrazol-4-yl)-9-carbazol-9-yl)benzoic acid (H₃PCBA) was designed and synthesized. Using it, a new Co(II)-based metal-organic framework (MOF), Co₃(PCBA)₂(H₂O)₂ (BUT-75) has been constructed. It revealed a (3,6)-connected net based on the 6-connected linear trinuclear metal node, and showed good chemical stability in a wide pH range from 3 to 12 at room temperature, as well as in boiling water. Due to the presence of rich exposed Co(II) sites in pores, BUT-75 presented high selective CO₂ adsorption capacity over N₂ at 298 K. Simultaneously, it demonstrated fine catalytic performance for the cycloaddition of CO₂ with epoxides into cyclic carbonates under ambient conditions. This work has not only enriched the MOF community through integrating diverse functionalities into one ligand but also contributed a versatile platform for CO₂ fixation, thereby pushing MOF chemistry forward by stability enhancement and application expansion.