A polymorph of 2,4-dinitrophenyl-hydrazine

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)degrees, 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 center dot center dot center dot pi interactions.