A structural and computational comparison of close contacts and related intermolecular energies of interaction in the structures of 1,3-diiodo-5-nitrobenzene, 1,3-dibromo-5-nitrobenzene, and 1,3-dichloro-5-nitrobenzene.

1,3-Diiodo-5-nitrobenzene, C 6 H 3 I 2 NO 2 , and 1,3-dibromo-5-nitrobenzene, C 6 H 3 Br 2 NO 2 , crystallize in the centrosymmetric space group P2 1 /m, and are isostructural with 1,3-dichloro-5-nitrobenzene, C 6 H 3 Cl 2 NO 2 , that has been redetermined at 100 K for consistency. While the three-dimensional packing in all three structures is similar, the size of the halogen atom affects the nonbonded close contacts observed between molecules. Thus, the structure of 1,3-diiodo-5-nitrobenzene features a close Type 1 I...I contact, the structure of 1,3-dibromo-5-nitrobenzene features a self-complementary nitro-O...Br close contact, while the structure of 1,3-dichloro-5-nitrobenzene also has a self-complementary nitro-O...Cl interaction, as well as a bifurcated C-H...O(nitro) close contact. Notably, the major energetically attractive intermolecular interaction between adjacent molecules in each of the three structures corresponds to a π-stacked interaction. The self-complementary halogen...O(nitro) and C-H...O(nitro) interactions correspond to significant cohesive attraction between molecules in each structure, while the Type 1 halogen-halogen contact is weakly cohesive.