A new type of CH binding site in a -bridging hexafluorosilicate ultramicroporous material that offers trace CH capture.

Hybrid ultramicroporous materials (HUMs) comprising hexafluorosilicate (SiF , SIFSIX) and their variants are promising physisorbents for trace acetylene (CH) capture and separation, where the inorganic anions serve as -bridging pillars. Herein, for the first time, we report a strategy of fluorine binding engineering in these HUMs switching the coordination mode of SIFSIX from traditional to rarely explored . The first example of a rigid HUM involving -bridging SIFSIX, SIFSIX-bidmb-Cu (bidmb = 1,4-bis(1-imidazolyl)-2,5-dimethylbenzene), is reported. The resulting self-interpenetrated network is found to be water stable and exhibits strong binding to CH but weak binding to CH and CO, affording a high of 55.7 kJ mol for CH, a high CH uptake of 1.86 mmol g at 0.01 bar and high Δ values. Breakthrough experiments comprehensively demonstrate that SIFSIX-bidmb-Cu can efficiently capture and recover CH from 50/50 or 1/99 CH/CO and CH/CH binary mixtures. single crystal X-ray diffraction (SCXRD) combined with dispersion-corrected density functional theory (DFT-D) calculations reveals that the CH binding site involves two -SiF anions in close proximity (F⋯F distance of 7.16 Å), creating a new type of molecular trap that affords six uncoordinated fluoro moieties to chelate each CH sixfold C-H⋯F hydrogen bonds. This work therefore provides a new strategy for binding site engineering with selective CH affinity to enable trace CH capture.