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Host–guest complexation has been mainly investigated in solution, and it is unclear how guest molecules access the assembled structures of host and dynamics of guest molecules in the crystal state. In this study, we studied the uptake, release, and molecular dynamics of n‐hexane vapor in the crystal state of pillar[5]arenes bearing different substituents. Pillar[5]arene bearing 10 ethyl groups yielded a crystal structure of herringbone‐type 1:1 complexes with n‐hexane, whereas pillar[5]arene with 10 allyl groups formed 1:1 complexes featuring a one‐dimensional (1D) channel structure. For pillar[5]arene bearing 10 benzyl groups, one molecule of n‐hexane was located in the cavity of pillar[5]arene, and another n‐hexane molecule was located outside of the cavity between two pillar[5]arenes. The substituent‐dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n‐hexane guest. The substituent effects were not observed in host–guest chemistry in solution, and these features are unique for the crystal state host–guest chemistry of pillar[5]arenes. Gasses in crystals: The uptake, release, and molecular dynamics of n‐hexane vapor in the crystal state of pillar[5]arenes bearing different substituents was studied (see figure). The substituent‐dependent differences in molecular arrangement influenced the uptake, release, and molecular dynamics of the n‐hexane guest. [ABSTRACT FROM AUTHOR]

Activated perethylated pillar[5]arene crystals show an unexpected alkane-shape- and -length-selective gate-opening behavior. Activated crystals were obtained upon removing solvents from perethylated pillar[5]arene 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 pillar[5]arene. Alkane-shape-selective molecular recognition of pillar[5]arenes in the solution state was translated into the vapor/crystal state. [ABSTRACT FROM AUTHOR]

Host–guest complexation has been mainly investigated in solution; therefore, revealing crystal‐state host–guest complexation is a challenging task. This work reports the unique features of crystal‐state host–guest complexation; that is, how guest molecules access the host assembled structures and the dynamics of guest molecules encapsulated in crystals. More information can be found in the Full Paper by T. Ogoshi et al. on page 2497. [ABSTRACT FROM AUTHOR]