1-(4-Bromobenzyl)-2-(4-bromophenyl)-1H-benzimidazole

There are two molecules in the asymmetric unit of the title compound, C20H14Br2N2. In the first, the dihedral angles between the mean plane of the benzimidazole group and those of the 4-bromobenzyl and 4-chlorophenyl groups are 50.72 (17) and 71.29 (16)°, respectively, while the corresponding angles in the second molecule are 42.09 (16) and 89.05 (17)°. The 4-bromobenzyl and 4-bromophenyl groups make an angle of 68.1 (2) and 85.1 (21)° with each other in the two molecules. In the crystal, weak C—H⋯N and C—H⋯Br hydrogen bonds link the molecules along the c-axis direction. Br⋯Br interactions [3.5733 (9)Å] are also observed.


Comment
Organic ligands containing multiple heterocyclic rings are very useful tools in the self-assembly of metallosupramolecular compounds (Steel, 1990). Functionalized benzimidazoles represent an important class of Ncontaining heterocyclic compounds and have received considerable attention in recent times because their derivatives bear versatile pharmacological properties (Bhattacharya & Chaudhuri, 2008) based on their presence in both clinical medicines (Horton et al., 2003) and compounds of broad biological functions (Boiani et al., 2005). They are important intermediates in many organic reactions (Bai et al., 2001;Hasegawa et al., 1999), and act as ligands to transition metals for modelling biological systems (Bouwman et al., 1990;Pujar et al., 1988). Herein, we report the synthesis and crystal structure of a new benzimidazole derivative 1-(4-bromobenzyl)-2-(4-bromophenyl)-1H-benzimidazole ( Fig. 1)·In the title compound C 20 H 14 N 2 Br 2 , there are two molecules in the asymmetric unit. The dihedral angles between the least-squares plane of the benzimidazole group and those of the 4-bromobenzyl and 4-chlorophenyl groups are 50.72 (17); 42.09 (16) and 71.29 (16);89.05 (17) respectively. The 4-bromobenzyl and 4-bromophenyl groups make an angle of 68.1 (2); 85.1 (2) (1) with each other. Weak intramolecular hydrogen bonds of C-H···N and Br···Br interactions are observed.

Experimental
1.0 mmol 4-bromobenzaldehyde and 2 ml water were located in a round bottom flask, and 0.5 mmol benzene-1, 2-diamine was then added. Finally, 0.5 mmol TMSCl was injected to the mixture. The reaction was stirred at room temperature for 5 h to form homogeneous suspension. The suspension was then filtered and the residue was washed with 10 ml water to give product. The crude product was recrystallized with ethanol.

Refinement
All H atoms were placed in calculated positions with C(sp3)-H = 0.97 and C(sp2)-H = 0.93 \%A, and torsion angles were refined. In the absence of significant anomalous scattering effects, Friedel pairs were averaged.

Figure 1
A view of the asymmetric unit of the title compoud with atomic numbering scheme. Displacement ellipsoids were drawn at the 30% probability level. [Symmetry codes: (i) x, y, z; (ii) -x, -y, -z].

1-(4-Bromobenzyl)-2-(4-bromophenyl)-1H-benzimidazole
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.