Crystal packing: An examination of the packing of molecules approximately isosteric with 4,5-dichlorophthalic anhydride

The crystal structures of five 5,6-disubstituted benzofurazan 1-oxides are presented and compared with five previously reported structures: three polymorphs of 5,6-dichlorobenzofurazan 1-oxide plus 4,5-dichloro- and 4,5-dibromophthalic anhydride. All but one of these compounds pack with similar two-dimensional layers. The benzofurazan oxides all show disorder about a crystallographic twofold or pseudo-twofold axis. In addition, six complexes of phthalic anhydride and benzofurazan oxides are reported. With the packing in the complexes principally directed by the π complexing, the disorder, invariably found in the uncomplexed benzofurazan oxides, is diminished, and, in two cases, eliminated.