Temperature-Variant CO₂ Separation in Entangled Metal-Organic Framework with Carboxamide Functionality-Fueled Atmospheric-Pressure Cycloaddition and Size-Exclusive Tandem Knoevenagel Condensation

The pressing need to lower atmospheric carbon dioxide (CO2) concentration has captivated global focus on point-source capture and transformation of this greenhouse gas to chemicals. Purpose-driven pore-functionality engineering in metal–organic frameworks (MOFs) can lead to high-temperature and humid-condition adsorption and efficient cycloaddition of CO2 and further assist in achieving unconventional methodologies for sustainable tandem catalysis. Herein, we develop a [Zn2(COO)4N4] building unit-containing chemo-robust framework with carboxamide functionality, free oxygen atoms, and π-electron-rich moieties affixed to one-dimensional channels. This 3-fold entangled MOF exhibits strong framework–gas interactions and unveils variable-temperature CO2 adsorption with recurrent capture–release cycles even under 75% relative humidity. Interestingly, the CO2/N2 selectivity shows a remarkable 82% increase with an increase in the temperature from 273 K (79) to 313 K (143), which overpowers several porous adsorbents and validates potential of this MOF in flue gas separation. This microporous MOF catalyzes solvent-free and recyclable CO2 cycloaddition with various epoxides under atmospheric pressure. In contrast to the classical Lewis acid-mediated reaction, controlled experiments, including performance comparison of a urea functionality-truncated isostructural framework corroborate the unique two-point hydrogen bonding-mediated cycloaddition pathway. The suitably oriented carboxamide moiety within the MOF channels further acts as a hydrogen bond donor (HBD) site in the tandem deacetalization–Knoevenagel condensation reaction with >99% conversion under solvent-less mild conditions in 4 h. The cooperative role of acid–base dual sites in substrate activation is comprehensively supported by studies using external additives, fluoro-titration-derived interactions, and comparison with an unfunctionalized framework. To the best of our knowledge, in this one-pot reaction, acetals having larger molecular dimensions exhibit poor formation of α,β-unsaturated dicyanides, and demonstrate pore-fitting-mediated size-exclusive catalysis.