Halogen–C<sub>2</sub>H<sub>2</sub> Binding in Ultramicroporous Metal–Organic Frameworks (MOFs) for Benchmark C<sub>2</sub>H<sub>2</sub>/CO<sub>2</sub> Separation Selectivity
Soumya Mukherjee, Yonghe He, Douglas Franz, Shi‐Qiang Wang, Wan‐Ru Xian, Andrey A. Bezrukov, Brian Space, Zhengtao Xu, Jun He, Michael J. Zaworotko
Abstract
Abstract Acetylene (C 2 H 2 ) capture is a step in a number of industrial processes, but it comes with a high‐energy footprint. Although physisorbents have the potential to reduce this energy footprint, they are handicapped by generally poor selectivity versus other relevant gases, such as CO 2 and C 2 H 4 . In the case of CO 2 , the respective physicochemical properties are so similar that traditional physisorbents, such as zeolites, silica, and activated carbons cannot differentiate well between CO 2 and C 2 H 2 . Herein, we report that a family of three isostructural, ultramicroporous (<7 Å) diamondoid metal–organic frameworks, [Cu(TMBP)X] (TMBP=3,3′,5,5′‐tetramethyl‐4,4′‐bipyrazole), TCuX (X=Cl, Br, I), offer new benchmark C 2 H 2 /CO 2 separation selectivity at ambient temperature and pressure. We attribute this performance to a new type of strong binding site for C 2 H 2 . Specifically, halogen ⋅⋅⋅ HC interactions coupled with other noncovalent in a tight binding site is C 2 H 2 specific versus CO 2 . The binding site is distinct from those found in previous benchmark sorbents, which are based on open metal sites or electrostatic interactions enabled by inorganic fluoro or oxo anions.