Pore-Space-Partitioned Cage-Based Ionic Co(II) Framework for Selective Adsorption and Atmospheric Pressure Recyclable Cycloaddition of CO2

The advancement of multifunctional metal-organic frameworks (MOFs) incorporating task-specific sites holds significant potential for carbon footprint reduction. We report the synthesis of a thermochemically robust and microporous, charged Co(II)-organic framework, assembled from a -NH2-functionalized dicarboxylate ligand, a triazine core containing a tris-pyridyl linker, and an in situ generated [Co3(μ3-O)(COO)6N3]2- secondary building unit. Interestingly, C3-symmetric linkers partition the larger channels into trigonal-bipyramidal-shaped smaller cages. The activated MOF demonstrates substantial CO2 adsorption with moderate framework-gas interaction and also divulges minor CO2 loss during multiple capture-release cycles. The presence of diverse polar sites benefits the material, exhibiting selective CO2 adsorption over N2 and CH4 with a 23% enhancement in CO2/N2 selectivity upon increasing the temperature from 273 to 298 K. This anionic framework acts as a solvent-free CO2 cycloaddition catalyst that works effectively under atmospheric pressure with appreciable reusability, wide substrate tolerance, and pore-partition-governed size selectivity. The pendent -NH2 sites facilitate epoxide activation through hydrogen-bonding interactions, complemented by the π-electron-deficient triazine core moiety. In addition to computational studies, the crucial roles of pore-affixed functionalities in CO2 fixation are corroborated by diverse control experiments, including substrate-mediated fluorescence modulation, which rationalizes the reaction mechanism. This study provides valuable insights into the modulation of the microenvironment in cage-based MOFs for effective adsorption, separation, and catalytic fixation of CO2.