Structural effects of halogen bonding in iodochalcones.

The structures of three iodochalcones, functionalized with fluorine or a nitro group, have been investigated to explore the impact of different molecular electrostatic distributions on the halogen bonding within each crystal structure. The strongly withdrawing nitro group presented a switch of the halogen bond from a lateral to a linear motif. Surprisingly, this appears to be influenced by a net positive shift in charge distribution around the lateral edges of the σ-hole, making the lateral I...I bonding motif less preferable. A channel of amphoteric I...I type II halogen bonds is observed for a chalcone molecule, which was not previously reported in chalcones, alongside an example of the common synthon involving extended linear chains of I...O2N donor-acceptor halogen bonds. This work shows that halogenated chalcones may be an interesting target for developing halogen bonding as a significant tool within crystal engineering, a thus far underexplored area for this common structural motif.