An orthorhombic polymorph of 1-benzyl-1H-benzimidazole

The title compound, C14H12N2, in contrast to the previously reported monoclinic polymorph [Lei et al. (2009 ▶). Acta Cryst. E65, o2613], crystallizes in the orthorhombic crystal system. The dihedral angle between the imidazole ring system and the phenyl ring is 76.78 (16)°. Weak C—H⋯N and C—H⋯π interactions are observed in the crystal structure.

The structure reported here is an orthorhombic form polymorph of the title compound, (C 14 H 12 N 2 ), which has been characterized previously in a monoclinic form (Lei & Zhou, 2009). The bond lengths and angles are closely similar to those previously described . The dihedral angle between the imidazole ring and the benzyl ring is 76.78 (16)°, indicated that those two rings are not mutually perpendicular. In the crystal structure, molecules are linked via weak intermolecular C-H···N interactions, forming a chain along the b-axis direction. The structure is further stabilized by C-H···π contacts involving both of the aromatic rings. This arrangement is similar to that observed in the monoclinic polymorph.

Experimental
The title compound was obtained by reacting benzimidazole (1.18 g, 0.01 mol) with benzyl chloride (1.25 g, 0.01 mol) and potassium carbonate (1.38 g, 0.01 mol) in acetone (50 ml). The reaction mixture was refluxed for 10 h. After removal of the solvents, the residue was dispersed in water to obtain an oil layer. Then the oil was dissolved in hot ethanol/water (2:1) and colourless blocks of (I) arose.

Refinement
The absolute sturcture of (I) is indeterminate in the present refinement. The methylene H atoms were freely refined. The other H atoms were positioned geometrically (C-H = 0.93Å) and refined as riding with Uiso(H) = 1.2Ueq(C). Fig. 1. The asymmetric unit of (I), showing 50% probability displacement ellipsoids.  supplementary materials sup-3

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.