2-(Pyridin-4-yl)-1H-benzimidazole

The title compound, C12H9N3, is an unhydrated analogue of the previously reported trihydrate. The molecule is essentially planar, with a 3.62 (11)° angle between the pyridine and benzimidazole planes. In the crystal, N—H⋯N hydrogen bonds result in chains of molecules parallel to [010], which are additionally linked by weak π–π stacking interactions [centroid–centroid distance = 3.7469 (17) Å], resulting in extended sheets of molecules parallel to (103).

The title compound, C 12 H 9 N 3 , is an unhydrated analogue of the previously reported trihydrate. The molecule is essentially planar, with a 3.62 (11) angle between the pyridine and benzimidazole planes. In the crystal, N-HÁ Á ÁN hydrogen bonds result in chains of molecules parallel to [010], which are additionally linked by weakstacking interactions [centroid-centroid distance = 3.7469 (17) Å ], resulting in extended sheets of molecules parallel to (103).
Hydrogen-bonding interactions involving the benzimidazole N-H and the pyridine result in chains of molecules parallel to [0 1 0]. Figure 2 shows a packing diagram with the hydrogen-bonded chains displayed. The trihydrate (Huang et al., 2004) hydrogen-bonding network is much more extensive, involving the three waters of hydration, the benzimidazole amine group and the pyridine. As seen in figure 2, pairs of molecules related by an inversion center exhibit π stacking. The spacing between the mean planes formed by the molecules is 3.43 Å. The shortest internuclear separation between related molecules is 3.460 (2) Å (N2···C7).

Experimental
The title compound was prepared by stirring 0.373 g (3.45 mmole) o-phenylenediamine, 0.67 ml (7.1 mmole) 4-pyridinecarboxaldehyde, and 0.75 g NH 4 Cl in 25 ml CHCl 3 for 5 days at room temperature. After removal of the solvent, the crude product mixture was extracted with water and ethylacetate and the solvent was removed from the organic phase.
The resulting solid was passed through a short silica column using a 30:70 mixture of hexanes: ethyl acetate, yielding 0.442 g of solid that contained two components based on TLC analysis was obtained. The mixture was passed through a second silica column using 90:10 ethyl acetate: ethanol. The first component isolated was the title compound (0.380 g,

Refinement
All hydrogen atoms were observed in difference Fourier maps. The H atoms bonded to carbon were refined using a riding model with C-H = 0.95 Å and U iso = 1.2U eq (C). The coordinates and isotropic thermal parameters of the amine H atom were refined without constraints.

Special details
Experimental. The H atoms bonded to carbon were refined using a riding model with C-H = 0.95 Å and U iso = 1.2U eq (C). The coordinates and isotropic thermal parameters of the amine H atom were refined freely. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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 N1 0.4979 (