Alkane Shape‐ and Size‐Recognized Selective Vapor Sorption in “Channel‐Like” Crystals Based on Thiacalixarene Assemblies

Alkanes composed of C−C and C−H show a low electric polarization, and therefore, there is only very weak interaction between alkanes and adsorbents. Thus, it is difficult to separate a specific alkane from a mixture of alkanes by adsorption. Here, two activated “channel‐like” crystals generated from brominated thiacalix[4]arene propyl ethers, which adopt 1,3‐alternate and partial cone conformations, recognize specific alkane vapors depending on alkane‐shape and ‐size, sorting in three‐type alkane guests such as linear, branched, and cyclic alkanes. Two activated crystals, which are prepared by removal of solvent upon heating under reduced pressure, incorporate branched and/or cyclic alkane vapors by a unique “gate‐opening” mechanism via a crystal transformation in the process. Linear alkane vapors do not trigger gate opening and are not taken up by the activated crystals. The shape and size molecular‐recognition properties of the activated crystals promises considerable usefulness for the separation of linear, branched, and cyclic alkanes. Two activated crystals obtained from two channel‐like crystals based on two thiacalix[4]arene conformational isomers showed selective vapor adsorption for branched and/or cyclic alkanes and effectively took up vaporous branched and/or cyclic alkanes with gate‐opening pressure. In contrast, no sorption of linear alkane vapors by the two activated crystals was observed.