1-Phenyl-2-[4-(trifluoromethyl)phenyl]-1H-benzimidazole

In the title molecule, C20H13F3N2, the benzimidazole unit is close to being planar [maximum deviation = 0.012 (1) Å] and forms dihedral angles of 31.43 (7) and 61.45 (9)° with the 4-(trifluoromethyl)phenyl and 1-phenyl rings, respectively; the dihedral angle between these rings is 60.94 (10)°. In the crystal, C—H⋯F hydrogen bonds link the molecules into chains along the c-axis direction. The CF3 group is rotationally disordered with an occupancy ratio of 0.557 (8):0.443 (8) for the F atoms.


Related literature
36 restraints H-atom parameters constrained Á max = 0.15 e Å À3 Á min = À0.14 e Å À3 Table 1 Hydrogen-bond geometry (Å , ). The imidazole ring can be easily accommodated with functional groups which allows the covalent incorporation of the NLO chromophores into polyimides leading to NLO side chain polymers (Bu et al., 1996).
The NLO property of benzimidazole and its thermal stability in guest host systems have drawn our attention towards this chromophore (Cross et al., 1995).
The asymmetric unit contains the title compound C 20 H 13 F 3 N 2 in the space group P-1. The benzimidazole ring system in the molecule N1/N2/C8-C14 is essentially planar with maximum deviations of 0.012 (1) for N1. In the molecules the benzimidazole ring N1/N2/C8-C14 makes dihedral angles of 61.45 (9)° and 31.43 (7)° respectively with the phenyl ring C15-C20 and the trifluoromethyl substituted phenyl ring C2-C7.

Experimental
To pure N-phenyl-o-phenylenediamine(17 mmol,3.128 g) in ethanol (10 ml) was added 4-(trifluoromethyl)-benzaldehyde (17 mmol, 2.38 ml) and ammonium acetate (3 g) were added while the temperature was maintained at 80°C. The reaction mixture was refluxed for 48 h and the reaction completion was monitored by TLC and finally it was extracted with dichloromethane. The separated solid was purified by column chromatography using petroleum ether as the eluent. Yield: 2.87 g (50%). Single crystals were grown in ethanol as solvent within a period of one week.

Refinement
All the hydrogen atoms were geometrically fixed and allowed to ride on their parent atoms with C-H = 0.93 -0.96 Å, and U iso = 1.5 eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms.
The disordered trifluoromethyl was modelled with restrained bonds and angles based on the average values found for the non-disordered trifluoromethyl group with initial positions being derived from a difference map. In the final stages of refinement the group was refined as a riding and rotating group as for a methyl group.

Figure 1
The molecular structure and labelling scheme for (I) with displacement ellipsoids for non-H atoms are drawn at the 30% probability level (major component only).

Figure 2
A packing diagram for (I) is drawn. Dashed lines indicate the intermolecular hydrogen bonding interactions.

1-Phenyl-2-[4-(trifluoromethyl)phenyl]-1H-benzimidazole
Crystal data C 20 H 13 F 3 N 2 M r = 338.32 Triclinic, P1 Hall symbol: -P 1 a = 8.7179 (4) Å b = 9.6796 (5) Å c = 11.3612 (6) Å α = 67.654 (2) where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.15 e Å −3 Δρ min = −0.14 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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. (