A third polymorph of 1,4-bis(1H-benzimidazol-2-yl)benzene

The title compound, C20H14N4, is a new polymorph of the previously reported structures, which were orthorhombic, space group Pbca [Bei et al. (2000). Acta Cryst. C56, 718–719] and monoclinic, space group P21/c [Dudd et al. (2003). Green Chem. 5, 187–192]. The asymmetric unit consists of two independent molecules in which the dihedral angels between the central benzene ring and the outer benzimidazole ring systems are 16.81 (10) and 14.23 (10)° in one molecule and 26.09 (10) and 37.29 (10)° in the other. In the crystal, molecules are linked by N—H⋯N and C—H⋯N hydrogen bonds into a tape running along the c-axis direction.


Related literature
H atoms treated by a mixture of independent and constrained refinement Á max = 0.21 e Å À3 Á min = À0.21 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). Financial support by the key discipline project of Hunan Province is gratefully acknowledged.
Supporting information for this paper is available from the IUCr electronic archives (Reference: IS5361).

Comment
Benzimidazole and their derivatives have been widely researched for their potential applications in medicinal chemistry, biochemistry and material chemistry. 1,4-bis(benzimidazol-2-yl)benzene has been synthesized with many methods in different groups. Zhuang have synthesized 1,4-bis(benzimidazol-2-yl)benzene with microwave method (Zhuang et al., 2011). Zhao have synthesized it using phosphoric acid as a catalyst (Zhao et al., 2012) instead of polyphosphoric acid which are commonly used in synthesis of benzimidazole (Alcalde et al., 1992). Its crystal structure has been determined by Bei et al. (2000) and Dudd et al. (2003). Recently, its crystal structures with solvent molecules DMF or methanol have also been reported (Wu & Hu, 2009;Su et al., 2011). Here, we report a new crystal structure of 1,4-bis(benzimidazol-2yl)benzene.

Experimental
1,4-Bis(benzimidazol-2-yl)benzene was synthesized according to literature method (Alcalde et al., 1992;Zhao et al., 2012) and single crystals suitable for X-ray diffraction were obtained by slow evaporation of DMF solution at room temperature.

Refinement
N-bound H atoms were located in a difference Fourier map and were refined with bond-length restraints of N-H = 0.86 (2) Å. C-bound H atoms were positioned geometrically and treated as riding atoms with C-H = 0.93 Å, and with U iso (H) = 1.2U eq (C). Rigid-bond restraints (DELU) were applied for atoms C11 and C14.  An ORTEP drawing for the asymmetric unit of the title compound with displacement ellipsoids drawn at the 30% probability level.

Figure 2
A packing diagram of the title compound viewed along c direction. The hydrogen bonds are highlighted by dashed lines.

Special details
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 )
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