Exceptionally Stable and 20-Connected Lanthanide Metal–Organic Frameworks for Selective CO2 Capture and Conversion at Atmospheric Pressure

Highly thermal and chemically stable, 20-connected lanthanide metal–organic frameworks (MOFs) [{Ln­(BTB)­(H2O)}­·H2O] n (where Ln = Sm (MOF1)/Gd (MOF2), BTB = 1,3,5-tris (4-carboxy phenyl) benzene) have been synthesized solvothermally and characterized by single-crystal X-ray diffraction analysis and other physicochemical methods. MOF1 and 2 are isostructural and feature three-dimensional honeycomb-like structure with large one-dimensional hexagonal channels of dimension ∼10.20 × 10.11 Å2. Gas uptake studies of the samples revealed selective adsorption properties of MOF1 for CO2 over other (N2, Ar, and H2) gases. The activated samples of the MOF1/2 act as efficient recyclable catalysts for heterogeneous cycloaddition of CO2 with styrene oxide, resulting in cyclic carbonate with high yield and selectivity. Interestingly, the pore size-dependent catalytic conversion of epoxides has been observed, suggesting the potential utility of MOF1 as a promising heterogeneous catalyst for cycloaddition of carbon dioxide. Furthermore, the MOF1 catalyst can be easily recycled for several cycles without significant loss of catalytic activity as well as structural rigidity. MOF1 and 2 represent rare examples of 20-c lanthanide MOFs exhibiting selective capture and efficient cycloaddition of CO2 with epoxides at mild conditions.