Form III of 2,2',4,4',6,6'-hexanitroazobenzene (HNAB-III).

The crystal structure of form III of the title compound, HNAB [systematic name: bis(2,4,6-trinitrophenyl)diazene], C12H4N8O12, has finally been solved as a pseudo-merohedral twin (monoclinic space group P2(1), rather than the orthorhombic space group C222(1) suggested by diffraction symmetry) using a dual space recycling method. The significant differences in the room-temperature densities of the three crystalline forms allow examination of molecular differences due to packing arrangements. An interesting relationship with the stilbene analog, HNS, is discussed.