A polymorph of 2,4-dinitro­phenyl­hydrazine

The crystal structure of a previously unreported polymorph (form II) of 2,4-dinitro­phenyl­hydrazine (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 mol­ecular 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 inter­molecular inter­action between hydrazine NH₂ and 2-nitro groups, forming a sheet normal to (101). The sheet is stabilized by N—H...π inter­actions.