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.