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

The title trihalogenated nitro­benzene derivatives, C(6)H(2)Br(3)NO(2) and C(6)H(2)Br(2)INO(2), 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 Br(δ+)⋯Br(δ-) 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 Br(δ+)⋯I(δ-): the more electronegative site (Br) behaves as a donor and the less electronegative site (I) as an acceptor for the charge transfer.