Adsorption in Reversed Order of C₂ Hydrocarbons on an Ultramicroporous Fluorinated Metal-Organic Framework

Metal-organic frameworks have been widely studied in the separation of C₂ hydrocarbons, which usually preferentially bind unsaturated hydrocarbons with the order of acetylene (C₂ H₂ )>ethylene (C₂ H₄ )>ethane (C₂ H₆ ). Herein, we report an ultramicroporous fluorinated metal-organic framework Zn-FBA (H₂ FBA=4,4'-(hexafluoroisopropylidene)bis(benzoic acid)), shows a reversed adsorption order characteristic for C₂ hydrocarbons, that the uptake for C₂ hydrocarbons of the framework and the binding affinity between the guest molecule and the framework follows the order C₂ H₆ >C₂ H₄ >C₂ H₂ . Density-functional theory calculations confirm that the completely reversed adsorption order behavior is attributed to the close van der Waals interactions and multiple cooperative C-H⋅⋅⋅F hydrogen bonds between the framework and C₂ H₆ . Moreover, Zn-FBA exhibits a high selectivity of about 2.9 for C₂ H₆ over C₂ H₄ at 298 K and 1 bar. The experimental breakthrough studies show that the high-purity C₂ H₄ can be obtained from C₂ H₆ and C₂ H₄ mixtures in one step.