Dihalobenzene Shape Sorting by Nonporous Adaptive Crystals of Perbromoethylated Pillararenes.

The separation of dihalobenzene isomers, such as dichlorobenzene isomers and difluorobenzene isomers, has a high practical value in both synthetic chemistry and industrial production. Herein we provide a simple to operate and energy-efficient adsorptive separation method using nonporous adaptive crystals of perbromoethylated pillar[5]arene (BrP5) and pillar[6]arene (BrP6). BrP6 crystals show a preference towards the ortho isomer of dichlorobenzene in isomer mixtures, but cannot discriminate difluorobenzene isomers. Single-crystal structures reveal that this selectivity is derived from the stability of the new host-guest crystal structure of BrP6 after uptake of the preferred guest and the binding strength of the host-guest interactions. Furthermore, because of the reversible transition between guest-free and guest-loaded structures, BrP6 crystals are recyclable.