5-Nitro-1,3-bis(prop-2-ynyl)-1H-1,3-benzimidazol-2(3H)-one

The title compound, C13H9N3O3, crystallizes with two identical but differently oriented molecules in the asymmetric unit, the dihedral angle between the fused-ring systems of the two molecules being 64.39 (7)°. The two prop-2-ynyl chains are located on opposite sides of the molecule and are nearly perpendicular to the fused ring plane, as indicated by the C—N—C—C torsion angles in the range 106.0 (3)–113.4 (3)°. In the crystal, the two molecules are linked through C—H⋯O hydrogen bonds into dimers, which are subsequently linked by further C—H⋯O interactions, building a three-dimensional network.

The title compound, C 13 H 9 N 3 O 3 , crystallizes with two identical but differently oriented molecules in the asymmetric unit, the dihedral angle between the fused-ring systems of the two molecules being 64.39 (7) . The two prop-2-ynyl chains are located on opposite sides of the molecule and are nearly perpendicular to the fused ring plane, as indicated by the C-N-C-C torsion angles in the range 106.0 (3)-113.4 (3) . In the crystal, the two molecules are linked through C-HÁ Á ÁO hydrogen bonds into dimers, which are subsequently linked by further C-HÁ Á ÁO interactions, building a three-dimensional network.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: KJ2228).

Essassi and Lahcen El Ammari Comment
Benzimidazoles are very useful intermediates/subunits for the development of molecules of pharmaceutical or biological interest. Benzimidazole and its derivatives are an important class of bioactive molecules in the field of drugs and pharmaceuticals. Benzimidazole derivatives have found applications in diverse therapeutic areas including anti-ulcers, anti-hypertensive, anti-viral, anti-fungal, anti-cancers, (Horton et al., 2003;Kim et al., 1996;Roth et al., 1997). The difference between the two independent molecules lies in the crystallographic environment of each in addition to their orientations in the crystal. Indeed, in molecule I (C1 to C13), carbon C5 is involved in a C5-H5···O6 intermolecular hydrogen bond while in molecule II (C14 to C26) the corresponding carbon (C18 ) is not engaged in such a bond. In the crystal, the two molecules are linked through C8-H8A···O4 and C21-H21B···O1 hydrogen bonds in order to form dimers, which are linked together by the other C-H···O hydrogen bonds to build a three-dimensional network as shown in Fig.2 and Table 2.

Refinement
All H atoms could be located in a difference Fourier map. However, they were placed in calculated positions with C-H = 0.93 Å (aromatic), N-H = 0.86 and C-H = 0.97 Å (methylene) and refined as riding on their parent atoms with U iso (H) = 1.2 U eq (C, N).
In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined and thus 2580 Friedel pairs were merged.

Figure 1
The molecular structure of the title compound with 50% probability displacement ellipsoids (molecule I, left; molecule II, right).  Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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 O1 0.07911 (10