Importance of Packing Coefficients of Host Cavities in the Isomerization of Open Host Frameworks: Guest-Size-Dependent Isomerization in Cholic Acid Inclusion Crystals with Monosubstituted Benzenes

Abstract

The crystal structures of inclusion compounds of cholic acid (CA) with 28 monosubstituted benzenes have been systematically investigated. All of the crystals belong to the monoclinic space group P21 and have bilayer structures with one-dimensional molecular channels that can include guest compounds. They are classified into four types of host frameworks that depend on the conformations and stacking modes of the host compound. The host frameworks and the host–guest ratios depend primarily on the molecular volumes of the guest compounds. The packing coefficient of the host cavity (PCcavity), which is the volume ratio of the guest compound to the host cavity, is used to clarify the relationship between the guest volume and isomerization of the host frameworks. The value of PCcavity for stable inclusion compounds lies in the range of 55–70 %. Compounds out of this range induce isomerization of the host frameworks. The packing coefficients of other host–guest compounds, in which the guest components are included in the host cavities through steric dimensions and van der Waals forces, are also in this range. These results indicate that PCcavity is a useful parameter correlation for guest recognition and isomerization of the host frameworks. Packing coefficients of host cavities (PCcavity) play an important role in guest recognition and in the isomerization of host frameworks. This isomerization depends on the guest components in crystalline inclusion compounds (see scheme). Moreover, PCcavity of lattice inclusion compounds are intermediate between those of crystalline materials and liquids. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2001/f2555_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.