The Halogen Bonding Proclivity of the sp Sulfur Atom as a Halogen Bond Acceptor in Cocrystals of Tetrahydro-4-thiopyran-4-one and Its Derivatives.

In this work, we present a systematic study of the capability of the sp hybridized sulfur atom for halogen bonding both in a small building block, tetrahydro-4-thiopyran-4-one, and two larger ones derived from it, Schiff bases with a morpholine fragment on the other end of the molecule. These three building blocks were cocrystallized with six perhalogenated aromates: 1,4-diiodotetrafluorobenzene, 1,3,5-triiodotrifluorobenzene, 1,3-diiodotetrafluorobenzene, 1,2-diiodotetrafluorobenzene, iodopentafluorobenzene, and 1,4-dibromotetrafluorobenzene. Out of the 18 combinations, only 7 (39%) yielded cocrystals, although with a high occurrence of the targeted I···S halogen bonding motif in all cocrystals (71%), and in imine cocrystals the I···O motif (100%) as well as, surprisingly, the I···N motif (100%). The I···S halogen bonds presented in this work feature lower relative shortening values than those for other types of sulfur atoms; however, the sp sulfur atom could potentially be more specific an acceptor for halogen bonding.