Influence of the Amide Groups in the CO₂/N₂ Selectivity of a Series of Isoreticular, Interpenetrated Metal-Organic Frameworks

Here we report the use of a pillaring strategy for the design and synthesis of three novel amide-functionalized metal-organic frameworks (MOFs), TMUs-22/-23/-24, isoreticular to the recently reported imine-functionalized TMU-6 and TMU-21 MOFs. An extensive study of their CO₂ sorption properties and selectivity for CO₂ over N₂, from single gas sorption isotherms to breakthrough measurements, revealed that not only the incorporation of amide groups but also their accessibility is crucial to obtain enhanced CO₂ sorption and CO₂/N₂ selectivity. Therefore, the MOF with more accessible amide groups (TMU-24) shows a CO₂/N₂ selectivity value of ca. 10 (as revealed by breakthrough experiments), which is ca. 500% and 700% of the selectivity values observed for the other amide-containing (TMU-22 and TMU-23) and imine-containing (TMU-6 and TMU-21) MOFs.