2-Methyl-5,6-dinitrobenzimidazolium chloride

In the title compound, C8H7N4O4 +·Cl−, the cation possesses twofold symmetry, with the twofold axis bisecting the 2-methyl-5,6-dinitrobenzimidazolium cation. The methyl H atoms are disordered about this twofold axis and were assigned equal half-occupancies. The chloride anion also lies on a twofold axis. In the crystal, N—H⋯Cl and C—H⋯O hydrogen bonds link the ions to form a three-dimensional network.

In the title compound, C 8 H 7 N 4 O 4 + ÁCl À , the cation possesses twofold symmetry, with the twofold axis bisecting the 2methyl-5,6-dinitrobenzimidazolium cation. The methyl H atoms are disordered about this twofold axis and were assigned equal half-occupancies. The chloride anion also lies on a twofold axis. In the crystal, N-HÁ Á ÁCl and C-HÁ Á ÁO hydrogen bonds link the ions to form a three-dimensional network.
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 1999 Laryea et al., 2010;Horton et al., 2003;Spasov et al., 1999;Soula & Luu-Duc, 1986). In addition to their biological activities, a review of the literature reveals that there are numerous studies including the coordination and corrosion inhibitor abilities of benzimidazoles (Kuznetsov & Kazansky, 2008;Subramanyam & Mayanna, 1985). Some of these derivatives, particularly nitro derivatives, are used as photographic materials in photography and on the other hand, the development of the chemistry of the benzimidazole dyes has been remarkable (Hoffmann et al., 2011;Alamgir et al., 2007). As a part of our ongoing investigations of benzimidazole derivatives, the title compound was synthesized and its crystal structure is reported herein.
The asymmetric unit of the title compound, (Fig. 1), contains one half of each component. It consists of an imidazole ring with the one CH 3 and two NO 2 groups bonded at positions 2, 5 and 6, respectively, and one chloride anion. Both the 2-methyl-5,6-dinitrobenzimidazolium moiety and the chloride anion lie on twofold axes. The methyl H atoms are disordered about the twofold axis with equal half occupancies.
In the crystal of the title compound N-H···Cl hydrogen bonds link the cations to form zigzag chains propagating in [001].
There are also C-H···O hydrogen bonds linking these chains to form a three-dimensional network (Table 1 and Fig. 2).

Experimental
For the preparation of the title compound a solution of 2-methyl-5-nitro-benzimidazole (3.0 g) in sulphuric acid (3.0 ml) was treated with nitric acid (6.0 ml) and refluxed for 3 h, then poured onto ice. The precipitate was filtered off and washed with cold water. Hydrogen chloride was passed into a suspension of the crude dinitro product in warm water. After cooling, the precipitate was filtered and crystallized from ethanol to give yellow block-like crystals of the the title compound (m.p.

Refinement
Atom H2A (for the NH group) was located in a difference Fourier map and was freely refined. The C-bound H-atoms were positioned geometrically with C-H = 0.93 and 0.96 Å, for aromatic and methyl H-atoms, respectively, and constrained to ride on their parent atoms, with U iso (H) = k × U eq (C), where k = 1.5 for methyl H-atoms and k = 1.2 for all other H-atoms.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound with the displacement ellipsoids drawn at the 50% probability level. The N-H···Cl hydrogen bond is shown as a dashed line.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (