Host–Guest Complexation of Perethylated Pillar5arene with Alkanes in the Crystal State

Activated perethylated pillar5arene crystals show an unexpected alkane-shape- and -length-selective gate-opening behavior. Activated crystals were obtained upon removing solvents from perethylated pillar5arene crystals by heating. The activated crystals could quantitatively take up n-alkanes with carbon chains containing more than five carbon atoms as a consequence of their gate-opening pressure. As the chain length of the n-alkanes increased, the gate pressure decreased. A transformation into a herringbone structure was induced when n-hexane was used as a guest. By contrast, cyclic and branched alkanes were not taken up and could not induce a crystal transformation because they were too large to fit in the cavities of the pillar5arene. Alkane-shape-selective molecular recognition of pillar5arenes in the solution state was translated into the vapor/crystal state.