Efficient Capture of Trace Acetylene by an Ultramicroporous Metal–Organic Framework with Purine Binding Sites

Efficient separation of acetylene (C₂H₂) from its byproducts, especially CO₂, is difficult because of their similar physicochemical properties, including molecular dimensions and boiling point. Herein, we demonstrate trace C₂H₂ removal from C₂H₂/CO₂ mixtures enabled by a new ultramicroporous metal–organic framework (MOF) adsorbent, IPM-101, which features an optimal pore size of 4 Å (close to the kinetic diameter of C₂H₂, 3.3 Å) and one-dimensional channels lined by Lewis basic purine groups. Single-component gas adsorption isotherms revealed a clear affinity toward C₂H₂ versus CO₂ at low pressures with a substantial C₂H₂ uptake of 0.9 mmol g^–1 at 3000 ppm and 298 K. Dynamic column breakthrough experiments revealed separation of C₂H₂ from 1:1 and 1:99 v/v C₂H₂/CO₂ mixtures. IPM-101 exhibits one of the highest dynamic separation selectivity (α_AC) values yet reported, 22.5 for 1:1 C₂H₂/CO₂. Computational simulations indicated that the purine moiety was key to the strong C₂H₂ selectivity thanks to C₂H₂ selective N···HC≡CH interactions.