Halogen Bonding in Crystal Engineering - Halogen Bonding: Fundamentals and Applications - page 117

Fig. 6 XBs around ethers, thioethers and amines feature a tetrahedral arrangement with
preferential axial directions for the XBs around hexacyclic amines ( A , co-crystal be-
tween 1,4-dimethylpiperazine and 1,2-diiodotetrafluoroethane) and ethers ( B , co-crystal
between 1,4-dioxane and tetraiodoethene), and equatorial directions for hexacyclic
thioethers ( C , co-crystal between 1,4-dithiane and iodoform)

X-C interactions, the C - X moiety is roughly coplanar with
the pyridine and the two C-N

In pyridine ···

Xanglesareapproximately120 ◦ [129, 143,
144]. The same holds for other nitrogen heteroaromatics (e.g. pyrazine,
quinoline, etc.) [145-147]. A carbonyl group pins the donors after a trigonal
planar geometry and works either as a mono- [148, 149] or bidentate XB ac-
ceptor [150]. Sulfoxides behave similarly [151, 152] and imines form XB along
the expected axis of the lone pair [153].

···

3
Halogen-Bonded Supramolecular Architectures

After considering the atomic and molecular characteristics determining the
properties of the XB given by a halocarbon and its partner, let's focus on the
potential of this interaction in relating the geometries of the starting modules
with the geometries of the supramolecular architectures that the halocarbon
anditspartnergiveriseto.Theattentionwillbefocussedonsomeprototype
topologies in order to show the XB effectiveness in bridging molecular and
supramolecular topologies and to formulate some basic concepts in XB-based
molecular tectonics. The key starting points are the remarkable strength and
the particularly high directionality (both on the donor and on the acceptor