Design of a new inclusion host: 3,7-diphenylbicyclo[3.3.0]octane-endo-3,endo-7-diol

Abstract

3,7-Diphenylbicyclo[3.3.0]octane-endo-3,endo-7-diol 2 was identified as a very simple achiral molecule that was likely to pack with difficulty in the solid state just by itself. Such substances are expected to be susceptible to inclusion of a second type of molecule in their crystals in order to achieve lower energy through more efficient packing. In accord with this prediction, four different crystal forms have been prepared and their structures determined using X-ray crystallography: the solvent-free (apohost) structure, two lattice inclusion compounds (2)₂·(benzene) and (2)·(o-xylene), and the hydrogen bonded cocrystalline material (2)·(methanol). Further evidence of the packing difficulties of 2 was obtained. Three of the four crystal forms contain two crystallographically independent diol molecules, and two of these structures also contain independent guests. Further, the adopted apohost structure forces the achiral molecule 2 to crystallise in a chiral space group. These results show that simple, but awkward, molecules likely to exhibit inclusion behaviour can be identified successfully and predictions made.