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Optimized Separation of Acetylene from Carbon Dioxide and Ethylene in a Microporous Material

Lin, Rui-Biao, Li, Libo, Wu, Hui, Arman, Hadi, Li, Bin, Lin, Rong-Guang, Zhou, Wei, Chen, Banglin
Journal of the American Chemical Society 2017 v.139 no.23 pp. 8022-8028
acetylene, carbon dioxide, coordination polymers, crystal structure, ethylene, hydrogen bonding, ligands, molecular models, molecular weight, neutrons, porous media, shrinkage, sieving, sorption isotherms, zinc
Selective separation of acetylene (C₂H₂) from carbon dioxide (CO₂) or ethylene (C₂H₄) needs specific porous materials whose pores can realize sieving effects while pore surfaces can differentiate their recognitions for these molecules of similar molecular sizes and physical properties. We report a microporous material [Zn(dps)₂(SiF₆)] (UTSA-300, dps = 4,4′-dipyridylsulfide) with two-dimensional channels of about 3.3 Å, well-matched for the molecular sizes of C₂H₂. After activation, the network was transformed to its closed-pore phase, UTSA-300a, with dispersed 0D cavities, accompanied by conformation change of the pyridyl ligand and rotation of SiF₆²– pillars. Strong C–H···F and π–π stacking interactions are found in closed-pore UTSA-300a, resulting in shrinkage of the structure. Interestingly, UTSA-300a takes up quite a large amounts of acetylene (76.4 cm³ g–¹), while showing complete C₂H₄ and CO₂ exclusion from C₂H₂ under ambient conditions. Neutron powder diffraction and molecular modeling studies clearly reveal that a C₂H₂ molecule primarily binds to two hexafluorosilicate F atoms in a head-on orientation, breaking the original intranetwork hydrogen bond and subsequently expanding to open-pore structure. Crystal structures, gas sorption isotherms, molecular modeling, experimental breakthrough experiment, and selectivity calculation comprehensively demonstrated this unique metal–organic framework material for highly selective C₂H₂/CO₂ and C₂H₂/C₂H₄ separation.