Halogen⋯halogen interactions in assembling β-sheets into 2D layers in the bis-(4-halo-phenylamido)alkanes and their co-crystals via inter-halogen interactions

Abstract

Halogen substituted bis(amido)alkanes were synthesized and their crystal structures were studied in terms of N–H⋯O hydrogen bonds and halogen⋯halogen interactions. The N–H⋯O hydrogen bonded β-sheets of bis-amides were shown to be assembled in to 2D layers viahalogen⋯halogen interactions. Out of 17 structures studied here 13 structures were found to form β-sheets. The iodo- and bromo derivatives consistently formed β-sheets, while chloro- and fluoro derivatives resulted in β-sheets or 2D layers. In the case of fluoro compounds, C–H⋯F hydrogen bonds are preferred compared to F⋯F contacts. Four co-crystals of inter halogen (IBr or BrCl) compounds were prepared and their crystal structures determined. These results suggest that the crystal structure of co-crystals will be isomorphous with that of parents provided that the crystal structures of the parents are also isomorphous to each other. In case of non-isomorphous parents, the resultant crystal structure of a co-crystal may resemble one of the parents or may have a new structure. The X-ray powder diffraction studies also confirm these results.