Crystal structure of 4,5-dinitro-1H-imidazole

The title compound, C3H2N4O4, forms crystals with two molecules in the asymmetric unit which are conformationally similar. With the exception of the O atoms of the nitro groups, the molecules are essentially planar. In the crystal, adjacent molecules are associated by N—H⋯N hydrogen bonds involving the imidazole N—H donors and N-atom acceptors of the unsaturated nitrogen of neighboring rings, forming layers parallel to (010).


S1. Comment
In addition to more mundane uses as pharmaceuticals (Windaus & Vogt, 1907), imidazoles make quality backbones for energetic materials (Epishina et al., 1967) because of their nitrogen content. The dinitro-bearing title compound, C 3 H 2 N 4 O 4 , is of interest because of its better oxygen balance (Cooper, 1996), contributing to its effectiveness as an explosive. To better understand the nature of explosive sensitivity as it relates to intermolecular forces, the title compound ( Fig. 1) was of interest for comparison with other imidazoles previously studied (Parrish et al., 2015;Windler et al., 2015).
In the title compound, the two independent molecules (A, defined by C1-N3 and B, defined by C4-N7) in the asymmetric unit ( In the crystal, intermolecular N-H···N hydrogen bonding interactions N3-H···N7 and N8-H···N4 between the A and B molecules (Table 1), generate layered structures lying roughly parallel to (010) (Fig. 2).

S2. Experimental
Caution! The title compound is an explosive and should only be handled with appropriate safety equipment in small quantities by an experienced explosive handler.
The title compound was prepared by literature methods (Novikov et al., 1970). Crystals were obtained by slow evaporation of a concentrated solution in ethyl acetate.

S3. Refinement
All hydrogen atoms was located in a difference-Fourier and the positional parameters were fully refined, with U iso (H) set invariant at 0.08.

Figure 1
The molecular structure of the title compound with atom labeling. Ellipsoids are drawn at the 50% probability level and the hydrogen atoms are drawn as spheres of arbitrary size.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.