Halogen-C2H2 Binding in Ultramicroporous Metal-Organic Frameworks (MOFs) for Benchmark C2H2/CO2 Separation Selectivity

Acetylene (C2H2) 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 CO2 and C2H4. In the case of CO2, the respective physicochemical properties are so similar that traditional physisorbents, such as zeolites, silica, and activated carbons cannot differentiate well between CO2 and C2H2. Herein, we report that a family of three isostructural, ultramicroporous (<7 angstrom) diamondoid metal-organic frameworks, [Cu(TMBP)X] (TMBP=3,3 ',5,5 '-tetramethyl-4,4 '-bipyrazole), TCuX (X=Cl, Br, I), offer new benchmark C2H2/CO2 separation selectivity at ambient temperature and pressure. We attribute this performance to a new type of strong binding site for C2H2. Specifically, halogen...HC interactions coupled with other noncovalent in a tight binding site is C2H2 specific versus CO2. 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.