A polymorph of 2,4-dinitro-phenyl-hydrazine.

The crystal structure of a previously unreported polymorph (form II) of 2,4-dinitro-phenyl-hydrazine (DNPH), C6H6N4O4, was determined at 90†K. The first polymorph (form I) is described in the monoclinic space group P21/c [Okabe et al. (1993 ▶). Acta Cryst. C49, 1678-1680; Wardell et al. (2006 ▶). Acta Cryst. C62, o318-320], whereas form II is in the monoclinic space group Cc. The mol-ecular structures in forms I and II are closely similar, with the nitro groups at the 2- and 4-positions being almost coplanar with the benzene ring [dihedral angles of 3.54†(1) and 3.38†(1)°, respectively in II]. However, their packing arrangements are completely different. Form I exhibits a herringbone packing motif, whereas form II displays a coplanar chain structure. Each chain in form II is connected to adjacent chains by the inter-molecular inter-action between hydrazine NH2 and 2-nitro groups, forming a sheet normal to (101). The sheet is stabilized by N-H⋯π inter-actions.