Several
synthetic techniques are available for the preparation
of halogen-bonded adducts, including traditional solvent-evaporation
methods and mechanochemistry. With the intention of reducing solvent
usage and experimental times, we establish cosublimation as a synthetic
technique for preparing halogen-bonded cocrystals, focusing on the
C–I···N motif involving nitrogen-containing
heterocycles. We selected four common halogen-bond donors (I2, 1,4-diiodobenzene, 1,4-diiodotetrafluorobenzene, 1,3,5-trifluoro-2,4,6-triiodobenzene)
and four halogen-bond acceptors (2,3,5,6-tetramethylpyrazine, 1,4-diazabicyclo[2.2.2]octane,
2,2′-bipyridyl, 1-adamantanecarbonitrile), by virtue of their
range in volatility, and explored all 16 combinations via the following
methods: solvent evaporation, overnight cosublimation in a sealed
glass tube using a two-zone furnace, and expedited cosublimation in
a vacuum sublimation apparatus. We show that the raw crystals obtained
from overnight cosublimation are of suitable quality for single-crystal
X-ray diffraction, resulting in five new crystal structures, two of
which are, currently, unobtainable through other methods. Of these
new structures, the first halogen bond to the nitrile group of 1-adamantanecarbonitrile
is reported, resulting in the formation of a supramolecular rotor
in a spinning top configuration as evidenced by 13C and 15N solid-state NMR spectroscopy. Strikingly, the cosublimation
approach overcomes an anticooperative halogen-bonding effect to produce
fully saturated cocrystals of the tritopic halogen bond donor 1,3,5-trifluoro-2,4,6-triiodobenzene
with 1,4-diazabicyclo[2.2.2]octane. Finally, we show that cosublimation
can be used to rapidly prepare and purify bulk samples using a vacuum
sublimation apparatus, enabling the scalable preparation of halogen-bonded
cocrystals within 10 to 30 min using common laboratory equipment.
The methods described here enable a broad exploration of the polymorphic
landscape and may be extended to the facile preparation of other classes
of cocrystals.