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

Separating acetylene (C₂H₂) from carbon dioxide (CO₂) 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 C₂H₂ affinity over CO₂. 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 C₂H₂/CO₂ uptake ratio of 4.8 at 273 K and 1 bar, showing a rare S-shaped curve for C₂H₂. 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 C₂H₂ molecules. Dispersion-corrected Density Functional Theory calculations indicate that the C₂H₂ binding energy in KUF-5 is higher than that of CO₂. Additionally, exposure tests under harsh conditions confirm the chemical stability of KUF-5, underscoring its robustness and potential for practical applications in C₂H₂/CO₂ separation.