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]_<i>n</i> (where Ln = Sm (MOF<b>1</b>)/Gd (MOF<b>2</b>), 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. MOF<b>1</b> and <b>2</b> are isostructural and feature three-dimensional honeycomb-like structure with large one-dimensional hexagonal channels of dimension ∼10.20 × 10.11 Ų. Gas uptake studies of the samples revealed selective adsorption properties of MOF<b>1</b> for CO₂ over other (N₂, Ar, and H₂) gases. The activated samples of the MOF<b>1/2</b> 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 MOF<b>1</b> as a promising heterogeneous catalyst for cycloaddition of carbon dioxide. Furthermore, the MOF<b>1</b> catalyst can be easily recycled for several cycles without significant loss of catalytic activity as well as structural rigidity. MOF<b>1</b> and <b>2</b> represent rare examples of 20-c lanthanide MOFs exhibiting selective capture and efficient cycloaddition of CO₂ with epoxides at mild conditions