1,4-Bis(benzimidazol-2-yl)benzene dimethylformamide disolvate

The aromatic molecule of the title compound, C20H14N4·2C3H7NO, occupies a special position on an inversion center. The benzimidazole unit (planar to within 0.008 Å) forms a dihedral angle of 9.1 (2)° with the central benzene ring. The benzimidazole H atom participates in a hydrogen bond with the dimethylformamide solvent molecule, thus giving rise to the title 1:2 aggregate. These aggregates are further linked in the crystal structure by aromatic π–π stacking interactions [centroid–centroid distance = 6.356 (2) Å].

The aromatic molecule of the title compound, C 20 H 14 N 4 Á-2C 3 H 7 NO, occupies a special position on an inversion center. The benzimidazole unit (planar to within 0.008 Å ) forms a dihedral angle of 9.1 (2) with the central benzene ring. The benzimidazole H atom participates in a hydrogen bond with the dimethylformamide solvent molecule, thus giving rise to the title 1:2 aggregate. These aggregates are further linked in the crystal structure by aromaticstacking interactions [centroid-centroid distance = 6.356 (2) Å ].
The 1,4-bis(2-benzimidazolyl)benzene molecule occupies a special position on the inversion center, and benzimidazole moiety (planar within 0.0078 Å) forms dihedral angle of 9.1 (2)° with the plane of the central benzene ring (Fig. 1). This shows that 1,4-(2-benzimidazolyl)benzene molecule in the structure of the title compound deviates from planarity to a much lesser degree than in the unsolvated structure, wherein the corresponding dihedral angle is equal to 31.0° (Bei et al., 2000;Dudd et al., 2003).

Experimental
The title compound was synthesized by refluxing terephthalaldehyde (0.53 g, 4 mmol) and benzene-1,2-diamine (0.86 g, 8 mmol) in absolute methanol (50 ml) for 8 h. After cooling to room temperature, the yellow solid thus formed was isolated and dried under vacuum (1.13 g, yield 80 %). Single crystals suitable for X-ray structure analysis were obtained by the slow evaporation of a dimethylformamide solution in air.

Figures
Fig . 1. The structure of 1,4-bis(2-benzimidazolyl)benzene and dimethylformamide molecules in the crystal of the title compound, showing the atomic numbering scheme and 30% probability displacement ellipsoids. Unlabelled atoms are related to the labelled atoms by the (1 -x, -y, 1 -z) symmetry transformation.

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.