Halogen Bonding in Crystal Engineering - Halogen Bonding: Fundamentals and Applications - page 116

Fig. 5 Scatterplot derived from the CSD reporting the N ··· I-C angle (deg) vs. the N ··· I

distance (A) for crystal structures containing intermolecular N

I contacts; only error-
free and non-polymeric structures containing single-bonded iodine atoms and showing
no disorder with R< 0.06 are considered. The scatterplot clearly demonstrates the high
directionality of the N

···

··· IXB

sion 5.26, October 2005) scatterplots of intermolecular N ··· I-C interactions

versus N I distances, respectively.

Clearly, short interactions are more directional then long ones. A simi-
lar trend is observed also when bromine and chlorine atoms are the XB
donor sites or when XB acceptor sites other than nitrogen and oxygen are
used [138].
When n electron donors are involved, the XB is preferentially along
the axis of the donated lone pair on D. For instance, XBs around ethers,
thioethers, and amines feature a tetrahedral arrangement with preferential
axial directions for the XBs around hexacyclic amines, and equatorial direc-
tions for hexacyclic thioethers [16, 17, 124, 139-142] (Fig. 6).

···