2-(2-Benzyloxyphenyl)-1H-benzimidazole

The asymmetric unit of the title compound, C20H16N2O, contains two molecules. The dihedral angles between the benzimidazole ring systems and the attached benzene rings are 10.6 (5) and 13.7 (5)°. The conformers are linked by bifurcated three-centre hydrogen bonds, forming chains along the diagonal of the a b plane. The packing is further stabilized by π–π and C—H⋯π interactions.

The asymmetric unit of the title compound, C 20 H 16 N 2 O, contains two molecules. The dihedral angles between the benzimidazole ring systems and the attached benzene rings are 10.6 (5) and 13.7 (5) . The conformers are linked by bifurcated three-centre hydrogen bonds, forming chains along the diagonal of the ab plane. The packing is further stabilized byand C-HÁ Á Á interactions.
Data collection: SMART (Bruker, 2000); cell refinement: SAINT-Plus NT (Bruker, 2001); data reduction: SAINT-Plus NT; program(s) used to solve structure: SHELXTL-NT (Sheldrick, 2008); program(s) used to refine structure: SHELXTL-NT; molecular graphics: SHELXTL-NT; software used to prepare material for publication: PLATON (Spek, 2003). (Lehn, 1990). Recently, we have reported the synthesis of a small library of 2-arylbenzimidazole compounds that show spasmolytic and relaxant activity (Moreno-Diaz et al., 2006;Navarrete-Vázquez et al., 2006;Estrada-Soto et al., 2006). In order to extend our research on the relationship between the structure of benzimidazole derivatives and their pharmacological activity we have determined the crystal structure of (I).
The asymmetric unit of (I) contains two conformers (Ia, Ib) ( Fig. 1). Bond lengths between equivalent non-H atoms of each conformer are similar, with differences less than 3 s.u. The dihedral angles between the benzimidazole ring systems and the 2-benzyloxyphenyl substituents in Ia and Ib are 10.6 (5) and 13.7 (5)°, respectively. Both molecules display bifurcated N-H···N and N-H···O hydrogen bonds, Table 1 (Desiraju & Steiner, 1999). These hydrogen bonds interconnect molecules into chains running between the a and b axes (Fig. 2). Packing is further stabilized by C-H···π interactions involving the methylene H atoms on C14 of molecule Ia with the C27N4C26C21N3 benzimidazole ring (centroid Cg1) and the C28-C33 benzene ring (centroid Cg4) of two adjacent molecules of Ib (Fig. 3, Table 1). In the crystal packing there are also π-π interactions between adjacent molecules Ia and Ib, with a distance between the centroids of the C15-C20 (Cg3) and C28-C33 (Cg2) benzene rings of 3.859 (2) Å (Fig. 3, Table 1). In conclusion, this crystal structure illustrates four types of cooperative intra and intermolecular interactions: offset π-π stacking and C-H···π interactions as well as classical N-H···N and N-H···O hydrogen bonds.

Experimental
The title compound, (I), was synthesized according to the method of Moreno-Diaz et al. (2006). Single crystals of (I) were obtained from methanol with yield 2.07 g, 75%.

Refinement
Aromatic and methylene H atoms were positioned geometrically, were constrained to the riding-model approximation [C-H aryl = 0.93 Å, U iso (H aryl ) = 1.2U eq (C aryl ); C-H methylene = 0.97 Å, a U iso (H methylene ) = 1.5 U eq (C methylene )]. Atoms H1 and H3A, which are involved in hydrogen-bonding interactions, were located in a difference Fourier map and refined freely with isotropic displacement parameters. In the absence of significant anomalous dispersion effects, Friedel pairs were averaged. Fig. 1. The asymmetric unit of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.    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.