Anomalous halogen bonds in the crystal structures of 1,2,3-tribromo-5-nitrobenzene and 1,3-dibromo-2-iodo-5-nitrobenzene

Abstract

The title trihalogenated nitrobenzene derivatives, C6H2Br3NO2 and C6H2Br2INO2, crystallize in triclinic and monoclinic cells, respectively, with two molecules per asymmetric unit in each case. The asymmetric unit of the tribromo compound features a polarized Brδ+ ···Brδ- intermolecular halogen bond. After substitution of the Br atom in the para position with respect to the nitro group, the network of X···X halogen contacts is reorganized. Two intermolecular polarized halogen bonds are then observed, which present the uncommon polarization Brδ+···Iδ-: the more electronegative site (Br) behaves as a donor and the less electronegative site (I) as an acceptor for the charge transfer.