Endo vs Exo Bowl: Complexation of Xanthone by Pyrogallol[4]arenes

Cocrystal systems containing pyrogallol[4]arene, xanthone, and solvent molecules are examined and discussed. Three types of pyrogallol[4]arenes are cocrystallized with xanthone in isopropanol, acetonitrile, dimethyl sulfoxide, and a mixture of isopropanol and methanol. It is found that the solvent controls complexation of the xanthone molecule, whereas pyrogallol[4]arene tail length affects cocrystal packing. With a single-solvent system, the xanthone molecule is outside (exo) of the bowl of the pyrogallol[4]arene, but with a two-solvent system, the xanthone molecule is inside (endo) of the bowl of the pyrogallol[4]arene.