Microporous 2D indium metal–organic frameworks for selective CO2 capture and their application in the catalytic CO2-cycloaddition of epoxides

Abstract

Four new 2D indium metal–organic frameworks (MOFs) (Me₂NH₂)[In(SBA)₂] (1), (Me₂NH₂)[In(SBA)(BDC)] (2), (Me₂NH₂)[In(SBA)(BDC-NH₂)] (3), and (NH₄)₃[In₃Cl₂(BPDC)₅] (4), (H₂SBA = 4,4′-sulfonyldibenzoic acid; H₂BDC = 1,4-benzenedicarboxylic acid; H₂BDC-NH₂ = 2-amino-1,4-benzenedicarboxylic acid; H₂BPDC = 4,4′-biphenyldicarboxylic acid) have been synthesized under solvothermal reaction conditions for compounds 1 to 3 and the DES (deep eutectic solvent) reaction has been attempted for compound 4. The structure of these MOFs has been determined by using single crystal X-ray diffraction study and all of theses four 2D monolayer framework with porous properties. The N₂ gas sorption measurements indicated that Brunauer–Emmer–Teller (BET) and Langmuir surface areas of compound 1 are 207 and 301 m² g⁻¹, respectively, which is probably the first one having substantial gas uptake properties in the entire 2D In-MOF family to date. Furthermore, these new indium MOFs on the addition of n-Bu₄NBr were active for the cycloaddition of CO₂ and propylene oxide, generating propylene carbonates in high conversions under mild conditions. Particularly, the most active MOF 4 was found to efficiently couple CO₂ with a series of terminal epoxides to give the corresponding cyclic organic carbonates with high selectivities.