Enhanced C₂H₂/CO₂ Separation in a Microporous Hydrogen-Bonded Organic Framework Bearing Phenyl Cyanide-Based Electronegative Channels

Separating acetylene (C 2 H 2 ) from carbon dioxide (CO 2 ) is challenging due to the similarities in their kinetic diameters and physical properties. Common methods, such as size sieving and binding affinity in hydrogen-bonded organic frameworks (HOFs), have been applied to address this issue. Here, we report on an HOF, KUF-5, which utilizes electronegative pore environments to selectively enhance C 2 H 2 affinity over CO 2 . KUF-5 features a three-dimensional structure with a pore size of 5.38 Å and exhibits an S-shaped isotherm, achieving a record-high C 2 H 2 /CO 2 uptake ratio of 4.8 at 273 K and 1 bar, showing a rare S-shaped curve for C 2 H 2 . Single-crystal X-ray diffraction analysis reveals a cyanide-based electronegative pore environment within KUF-5 that promotes multiple N···H–C hydrogen bonds and π–π interactions with C 2 H 2 molecules. Dispersion-corrected Density Functional Theory calculations indicate that the C 2 H 2 binding energy in KUF-5 is higher than that of CO 2 . Additionally, exposure tests under harsh conditions confirm the chemical stability of KUF-5, underscoring its robustness and potential for practical applications in C 2 H 2 /CO 2 separation.