2-Trifluoromethyl-1H-benzimidazol-3-ium nitrate

Ihe title salt, C8H6F3N2 +·NO3 −, the F atoms of the triflouromethyl group are disordered over two sets of sites in a 0.58 (2):0.42 (2) ratio. In the crystal, N—H⋯O hydrogen bonds link the cations and anions into chains running parallel to the b axis. There is π–π stacking between symmetry-related benzene rings with a centroid-centroid distance of 3.949 (3) Å. The crystal studied was a non-merohedral twin, with a 19% minor component.

Ihe title salt, C 8 H 6 F 3 N 2 + ÁNO 3 À , the F atoms of the triflouromethyl group are disordered over two sets of sites in a 0.58 (2):0.42 (2) ratio. In the crystal, N-HÁ Á ÁO hydrogen bonds link the cations and anions into chains running parallel to the b axis. There isstacking between symmetry-related benzene rings with a centroid-centroid distance of 3.949 (3) Å . The crystal studied was a non-merohedral twin, with a 19% minor component.

Ming-Liang Liu Comment
Recently much attention has been devoted to crystals containing organic ions and inorganic ions due to the possibility of tuning their special structural features and their potential ferroelectrics properties (Fu et al., 2011;Zhang et al., 2010.). In our laboratory, the title compound (I) has been synthesized to investigate its potential ferroelectric propeties. However, it was found that the dielectric constant of the compound as a function of temperature indicated that the permittivity is basically temperature-independent (ε = C/(T-T 0 )), suggesting that this compound is not ferroelectric or there may be no distinct phase transition occurring within the measured temperature range (below the melting point).
The asymmetric unit that consists of one 2-trifluoromethyl-1H-benzimidazole cation and nitrate anionwhich are linked by N2-H2A···O1 hydrogen bond. Figure 1. The N3-H3A···O2 hydrogen bond links the the asymmetric units together into chains which run parallel to the b-axis. (Fig 2). There is π···π stacking between the six-membered rings at (x,y,z) and (1-x,1-y,-z) with a centroid to centroid distance of 3.949 (3)Å, perpendicular distance between the planes of 3.514 (2)Å and a slippage of 1.802Å. The triflouromethyl group is disordered. Experimental 0.144 g (1 mmol) of 2-trifluoromethyl-1H-benzimidazol was firstly dissolved in 30 ml of ethanol, to which 0.063 g (1 mmol) of nitric acid was added forming a solution at the ambient temperature. Single crystals suitable for X-ray structure analysis were obtained by the slow evaporation of the above solution after 3 days in air.

Refinement
H atoms were placed in calculated positions (N-H = 0.89 Å; C-H = 0.93Å for Csp 2 atoms and C-H = 0.96Å and 0.97Å for Csp 3 atoms), assigned fixed U iso values [U iso = 1.2Ueq(Csp 2 ) and 1.5Ueq(Csp 3 ,N)] and allowed to ride. The trifluoromethyl group is modelled as being disordered over two sites with refined site occupancies of 0.58 and 0.42 respectively. The crystal was twinned. A .hkl file suitable for twin refinement was created using the TwinRotMat option in PLATON (Spek, 2009), and refined using the HKLF 5 option in SHELXL (Sheldrick,2008), giving a final BASF value of 0.19. Thus the ratio of the twin components was 0.81/0.19.   View of the cation/anion chain running parallel to the b axis. Minor component F atoms and H atoms not involved in the hydrogen bonding are omitted for clarity. Atoms labelled with a *(star) are at (x,-1+y,z) and those labelled with a #(hash) are at (x,1+y,z). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.23 e Å −3 Δρ min = −0.27 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (