Solvent-dependent supramolecular self-assembly of boron cage pillared metal–organic frameworks for selective gas separation

Abstract

A novel family of microporous boron cage pillared supramolecular metal–organic frameworks BSF-n (n = 4–8) were synthesized with the self-assembly behavior controlled by solvents. Their porous structures of formula [CuB₁₂H₁₂(L)₂]_n (L = 4,4′-azopyridine for BSF-4 and BSF-5; L = 1,2-bis(4-pyridyl)acetylene for BSF-6; L = 1,4-di(pyridine-4-yl)benzene for BSF-7; L = 4,4′-dipyridine for BSF-8) were all characterised by single crystal diffraction analysis. The use of ethylene glycol leads to non-interpenetrated structures while methanol/water solution affords interpenetrated frameworks. Gas adsorption experiments indicated that interpenetrated BSF-4 has the potential for highly selective separation of C₂H₂/C₂H₄ and C₂H₂/CO₂ mixtures.