2-Methyl-5-nitro-1H-benzimidazol-6-amine dihydrate

The title benzimidazole molecule, C8H8N4O2·2H2O, is planar with a maximum deviation of 0.079 (2) Å (for one of the O atoms in the nitro group). It crystallized as a dihydrate and intermolecular O—H⋯O and N—H⋯O hydrogen bonds link the uncoordinated water molecules, and the nitro and amine groups, respectively. In the crystal, N—H⋯O, O—H⋯N, O—H⋯O and C—H⋯O hydrogen bonds link the molecules to form a three-dimensional network. A π–π contact between the benzene rings, [centroid–centroid distance = 3.588 (1) Å] may further stabilize the crystal structure.


Comment
Benzimidazole derivatives are privileged structures in pharmaceutical chemistry because of their biological activities and clinical applications. They exhibit antitumor, anthelmintic, antibacterial, virucidal and fungucidal properties (Refaat, 2010;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.

Experimental
For the preparation of the title compound, a solution of Na 2 S.9H 2 O (35.0 g) and S (9.0 g) in warm water (150 ml) was added slowly to a solution of 2-methyl-5,6-dinitro-1H-benzimidazole (30.0 g) in water (150 ml,) and the mixture was warmed at 333-343 K for 20 min. After the reaction was completed, the mixture was filtered, acidified with dilute HCl and heated until termination of H 2 S and SO 2 formation. After cooling, the reaction mixture was treated with dilute ammonium hydroxide.
The precipitate was filtered and crystallized from ethanol to give red rod-shaped crystals of the the title compound (m.p.

563-565 K).
supplementary materials sup-2 Refinement Atoms H4 (of the NH group), H21 and H22 (of the NH 2 group), H31, H32, H41 and H42 (of the water molecules) were located in a difference Fourier map and were 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. Fig. 1. The molecular structure of the title compound, with the crystallographic labelling scheme and displacement ellipsoids drawn at the 50% probability level. The O-H···O and N-H···O hydrogen bonds are shown as dashed lines (see Table 1 for details).  Table 1 for details).

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.