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 CO 2 sorption properties and selectivity for CO 2 over N 2, 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 CO 2 sorption and CO 2 /N 2 selectivity. Therefore, the MOF with more accessible amide groups ( TMU-24 ) shows a CO 2 /N 2 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.