Efficient Separation of cis- and trans-1,2-Dichloroethene Isomers by Adaptive Biphen[3]arene Crystals

Reported here is the highly efficient separation of industrially important cis- and trans-1,2-dichloroethene (cis-DCE and trans-DCE) isomers by activated crystalline 2,2 ',4,4 '-tetramethoxyl biphen[3]arene (MeBP3) materials, MeBP3 alpha. MeBP3 can be synthesized in excellent yield (99 %), and a cyclic pentamer is also obtained when using 1,2-dichloroethane as the solvent. The structure of MeBP3 in the CH3CN@MeBP3 crystal displays a triangle-shape topology, forming 1D channels through window-to-window packing. Desolvated crystalline MeBP3 materials, MeBP3 alpha, preferentially adsorb cis-DCE vapors over its trans isomer. MeBP3 alpha is able to separate cis-DCE from a 50:50 (v/v) cis/trans-isomer mixture, yielding cis-DCE with a purity of 96.4 % in a single adsorption cycle. Single-crystal structures and powder X-ray diffraction patterns indicate that the uptake of cis-DCE triggers a solid-state structural transformation of MeBP3, suggesting the adaptivity of MeBP3 alpha materials during the sorption process. Moreover, the separation can be performed over multiple cycles without loss of separation selectivity and capacity.