Evaluation of Concomitant Halogen and Pnictogen Bonds in Cocrystals of Imines Derived from 2-Nitrobenzaldehyde and 4-Haloaniline.

Three imines have been prepared by condensation of 2-nitrobenzaldehyde and 4-haloanilines (halo = Cl, Br, and I) with functionalities that enabled them to act as both halogen and pnictogen bond donors; however, both interactions were found to be absent in the solid state. The prepared imines were further cocrystallized with 1,3-diiodotetrafluorobenzene and 1,3,5-triiodotetrafluorobenzene as halogen bond donors. Six novel cocrystals were prepared by means of liquid-assisted mechanochemical synthesis and by crystallization from solution. All six cocrystals were of 1:1 stoichiometry and comprised a N···I halogen bond between an iodine atom of the perhalogenated halogen bond donor and the imino nitrogen atom of the imine acting as an acceptor. Additionally, in all six cocrystals, the imine molecules were interconnected by NO 2 ···NO 2 pnictogen bonding interactions. Computational analysis has shown that the NO 2 ···NO 2 exhibits bond critical point electron densities in the region (4.897-8.306) × 10 -3 e Å -3 and interaction energies of 23.6-27.7 kJ mol -1 , whereas the N···I halogen bonds generally have higher critical point electron densities ((1.795-1.937) × 10 -2 e Å -3 ), but the corresponding total interaction energies are lower (19.4-20.4 kJ mol -1 ). Statistical analysis of the appearance of NO 2 ···NO 2 contacts concomitantly with halogen or hydrogen bonds seems to indicate that there is a positive correlation between the presence of NO 2 ···NO 2 pnictogen bonding interactions and other directional interactions in crystal structures.