A second monoclinic polymorph of N-(2,4-dinitrophenyl)-2,4-dinitroaniline

The title compound, C12H7N5O8, was previously described in space group P21/n with Z = 4 [Wu et al. (2007 ▶). Acta Cryst. E63, o4194]. The current monoclinic P21/c polymorph was obtained from a mixed solution of dichloromethane and hexane. The dihedral angle between the benzene rings is 44.16 (5)°, smaller than in the previously reported polymorph [56.3 (2)°]. As a result of the steric hinderance of the nitro groups, hydrogen bonding is limited intramolecularly. The dihedral angles between the phenyl rings and their attached nitro groups are 18.97 (6) and 17.71 (5)° at the 2-position, and 18.52 (6) and 32.41 (6)° at the 4-position.

The title compound, C 12 H 7 N 5 O 8 , was previously described in space group P2 1 /n with Z = 4 [Wu et al. (2007). Acta Cryst. E63,o4194]. The current monoclinic P2 1 /c polymorph was obtained from a mixed solution of dichloromethane and hexane. The dihedral angle between the benzene rings is 44.16 (5) , smaller than in the previously reported polymorph [56.3 (2) ]. As a result of the steric hinderance of the nitro groups, hydrogen bonding is limited intramolecularly. The dihedral angles between the phenyl rings and their attached nitro groups are 18.97 (6) and 17.71 (5) at the 2-position, and 18.52 (6) and 32.41 (6) at the 4-position.
P2 1 /c polymorph was obtained by recrystallization from a mixed solution of dichloromethane and hexane.
The bond lengths and angles of the current molecule were almost similar to those of the reported one. However the significant difference was recognized at the dihedral angle between the two benzene rings. Although the angle of the reported molecule was 56.3 (2)°, that of the current molecule was 44.16 (5)°. Owing to the relatively small dihedral angle, the intramolecular distances between the N-bound H atom and the O atoms of the nitro groups at 2-position became close (Table 1). Because of the steric hinderance of the nitro groups, hydrogen-bondings are limited within the molecule.

Experimental
Preparation of the title compound was carried out according to the reported procedure (Elliot & Smith, 2000). Single crystals with sufficient quality for X-ray crystallographical analysis were prepared by recrystallization from a mixed solution of dichloromethane and hexane.

Refinement
The C-bound H atoms were placed at ideal positions and were refined as riding on their parent C atoms. U iso (H) values of the H atoms were set at 1.2U eq (parent atom). The N-bound H atom was obtained from a difference Fourier map and was refined isotropically with the restriction of N-H range between 0.807 Å and 0.847 Å.

Figure 1
The asymmetric unit of the title compound with atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres.

N-(2,4-Dinitrophenyl)-2,4-dinitroaniline
Special details Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).