2-Methylbenzimidazolium nitrate

In the title compound, C8H9N2 +·NO3 −, intermolecular N—H⋯O hydrogen bonds join the molecules into a chain extending along the b axis.

In the title compound, C 8 H 9 N 2 + ÁNO 3 À , intermolecular N-HÁ Á ÁO hydrogen bonds join the molecules into a chain extending along the b axis.

Comment
Benzimidazole and its derivatives have found practical applications in a number of fields (Wright, 1951). This ring system is present in numerous antiparasitic, antihelmintic and anti-inflammatory drugs (El-masry et al., 2000). The complexes of transition metals with benzimidazole and related ligands have been extensively studied as models of some important biological molecules (Gümüş et al., 2003). During our search to find new benzimidazole-metal complexes 2-methylbenzimidazole nitrate was unintentionally obtained.
Herein, we report the structure of the title compound, C 8 H 9 N 3 O 3 (Fig 1). The crystal structure showed that intermolecular N-H···O hydrogen bonds link the molecules into a 1D polymeric structure (Fig. 2).

Experimental
A mixture of o-phenylenediamine(1.08 g, 10 mmol) and anhydrous sodium acetate (2.46 g, 30 mmol) were dissolved in 100 mL 5% hydrochloric acid. After stirring for 2 h under reflux, the solution was cooled to room temperature. Then the solution was treated with ammonia solution to pH 9-10 and an orange precipitate was formed. The precipitate was filtred and washed with water. 2-methylbenzimidazolium chloride was gained in 27.32% yield. The compound 2-methylbenzimidazole nitrate was obtained in 35% yield when the 2-methylbenzimidazolium chloride (0.46 g, 2.73 mmol) was reacted with Cr(NO 3 ) 3 .9H 2 O (1.01 g, 2.54 mmol) in ethanol under reflux. The crystals suitable for X-ray diffraction analysis were obtained by recrystallization from ethanol.

Refinement
All H atoms were located in difference maps. H atoms bonded to C atoms were then treated as riding atoms in geometrically idealized positions, with C-H distances of 0.93 (aromatic), 0.96 (CH3-H) and 0.86 (N-H) Å, and with U iso (H) =kU eq (C), where k is 1.5 for the methyl group and 1.2 for all the other H atoms.

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 > σ(F 2 ) is used only for calculating Rfactors(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.