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

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.