Isomorphism and pseudosymmetry in 2,6-dichloro- and 2,6-dibromobenzonitrile

The title compounds are isomorphous, with two half-molecules in the asymmet ric unit of a monoclinic unit cell in the space group C2/m. For the chloro compound: a = 18.0525 (8), b = 20.7374 (10), c = 3.8334 (2) Angstrom, beta = 101.143 (1)degrees; for the bromo compound: a = 18.2269 (15), b = 21.349 (2), c = 3.9663 (3) Angstrom, beta = 101.446 (2)degrees. The dominant inter molecular interactions are between halogen atoms rather than between haloge n and nitrile, as is the case in the corresponding 2,4,6-trihalobenzonitril es. The molecules pack into layers with a fourfold pseudosymmetry. The pseu dosymmetry appears to be the consequence of halogen-halogen intermolecular interactions.