An intriguing N-oxide-functionalized 3D flexible microporous MOF exhibiting highly selectivity for CO2 with a gate effect

The axial chiral ligand 2,2′-bipyridyl-3,3′-dicarboxylic acid-1,1′-dioxide (H2bdd) has been employed to synthesize a 3D flexible microporous metal-organic framework (MOF), {[Cu2(bdd)2(bpa)2(H2O)2]·6.5H2O}n (1) (bpa=1,2-bis(4-pyridyl)ethane), which contains an N-oxide open donor site. A gas adsorption test shows that complex 1′ (dehydrated 1) has a high adsorption selectivity for CO2 rather than N2 and H2. In particular, its CO2 adsorption isotherms exhibit an uncommon gate effect adsorption. The CO2 adsorption enthalpies were calculated from the adsorption isotherm. Compared to a flexible framework with respiration, 1′ displays a low energy consumption for sorbent regeneration, indicating the potential application of complex 1 in gas separation.