4-Bromo-2-(5-bromothiophen-2-yl)-1-[(5-bromothiophen-2-yl)methyl]-5,6-dimethyl-1H-benzimidazole

The title compound, C18H13Br3N2S2, was obtained via the reaction of N-bromosuccinamide with 5,6-dimethyl-2-(thiophen-2-yl)-1-[(thiophen-2-yl)methyl]-1H-benzimidazole. The compound exhibits rotational disorder of the 5-bromothiophen-2-yl substituent with a refined major:minor occupancy ratio of 0.876 (7):0.124 (7). The 5-bromothiophen-2-yl mean plane is canted to the benzimidazole plane by 20.0 (4) and 21 (4)° in the major and minor components, respectively. In the crystal, weak C—H⋯N interactions link the molecules into infinite C(7) chains along the 21 axes.

Compound I crystallizes with one molecule in the asymmetric unit. A perspective view of the molecule with the atomlabeling scheme is shown in figure 1. The benzimidazole ring system is essentially planar. The largest deviation from planarity is 0.017 (6) Å for C5. The 2-(5-bromothiophen-2-yl) plane is canted 20.0 (4) o and 21 (4) o to the benzimidazole plane in the major and minor disorder components, respectively.
The extended structure exhibits chains along the 2 1 screw axes formed by weak intermolecular C-H···N hydrogen bonds ( Table 1) involving one of the 5-bromothiophen-2-ylmethyl hydrogen atoms (H14) and the unsubstitued benzimidazole nitrogen atom (N2). The result is infinite C(7) chains. Figure
Based on a comparison of a 1 H NMR spectrum of the product mixture and simulated spectra of mono-, di-and tribrominated products, the reaction product mixture is approximately 50% tri-brominated species. Single crystals of the tri-

Refinement
During the later stages of refinement, it became obvious that the molecule exhibited rotational disorder about the 5bromothiophen-2-yl substituent. The disorder was successfully modeled using the metrics of the major component to define the minor component. Similarity restraints were used for the bond distances using SAME and anisotropic displacement parameters of the minor component atoms were constrained to those of the major component using EADP.
The structure converged with a refined major:minor occupancy ratio of 0.876 (7):0.124 (7). All hydrogen atoms were observed in difference Fourier fourier maps. The H atoms were refined using a riding model with a C-H distance of 0.99 Å for the methylene carbon atoms, 0.98 Å for the methyl carbon atoms and 0.95 Å for the phenyl and thiophene carbon atoms. The methyl C-H hydrogen atom isotropic displacement parameters were set using the approximation U iso (H) = 1.5U eq (C). All other C-H hydrogen atom isotropic displacement parameters were set using the approximation U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of the title compound with anisotropic displacement parameters of nonhydrogen atoms drawn at the 50% probability level. Only the major contributor to the disordered bromothiophene substituent is shown.  A packing diagram emphasizing the weak C-H···N hydrogen bonds that link molecules along the 2 1 screw axes. All hydrogen atoms except H14 have been omitted for clarity. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.87 e Å −3 Δρ min = −1.90 e Å −3

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 )
x y z U iso */U eq Occ. (