Halogen...halogen interactions in pressure-frozen ortho- and meta-dichlorobenzene isomers

Isomers 1,2-dichlorobenzene (o-DCB) and 1,3-dichlorobenzene (m-DCB) were high-pressure frozen in-situ in a Merrill-Bassett diamond-anvil cell and their structures determined at room temperature and at 0.18 (5) GPa for o-DCB, and 0.17 (5) GPa for m-DCB by single-crystal X-ray diffraction. The patterns of halogen...halogen intermolecular interactions in these structures can be considered to be the main cohesive forces responsible for the molecular arrangements in these crystals. The molecular packing of dichlorobenzene isomers, including three polymorphs of 1,4-dichlorobenzene (p-DCB), have been compared and relations between their molecular symmetry, packing arrangements, intermolecular interactions and melting points discussed. The topology of the crystal packing in dichlorobenzene isomers results from the interplay of the molecular shape, steric hindrances and intermolecular interactions. The non-planar arrangement of the dichlorobenzene molecules in the crystal structures can be justified by the distributions of the electrostatic potential on molecular surfaces, which determines electrostatic intermolecular interactions.