Crystal structure of benzimidazolium salicylate

In the anion of the title molecular salt, C7H7N2 +·C7H5O3 − (systematic name: 1H-benzimidazol-3-ium 2-hydroxybenzoate), there is an intramolecular O—H⋯O hydrogen bond that generates an S(6) ring motif. The CO2 group makes a dihedral angle of 5.33 (15)° with its attached ring. In the crystal, the dihedral angle between the benzimidazolium ring and the anion benzene ring is 75.88 (5)°. Two cations bridge two anions via two pairs of N—H⋯O hydrogen bonds, enclosing an R 4 4(16) ring motif, forming a four-membered centrosymmetric arrangement. These units are linked via C—H⋯O hydrogen bonds, forming chains propagating along the b-axis direction. The chains are linked by C—H⋯π and π–π interactions [inter-centroid distances = 3.4156 (7) and 3.8196 (8) Å], forming a three-dimensional structure.


S1. Structural commentary
Benzimidazoles and their derivatives have diverse biological and clinical applications (Narasimhan et al., 2012).
The molecular structure of the title salt is illustrated in Fig. 1. The geometric parameters are comparable with those reported for similar structures (Ennajih et al., 2010;Haque et al., 2012;Mani et al., 2015). The molecular structure of the anion is stabilized by an intramolecular O-H···O hydrogen bond which generates an S(6) ring motif (Table 1 and Fig. 1).

S2. Synthesis and crystallization
Benzimidazole (6 g) and salicylic acid (7.002 g) were dissolved in an equimolar ratio in methanol and stirred well for ca 6 h. The saturated solution was filtered and allowed to evaporate slowly at room temperature. Colourless block-shaped crystals of the title compound were obtained within seven days.

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydroxyl H atom was located in a difference Fourier map and refined with a distance restraint: O-H = 0.82 (1) Å with U iso (H) = 1.5U eq (O).
The NH and C-bound H atoms were positioned geometrically and refined using a riding model:

Figure 1
The molecular structure of the title salt, with atom labelling. The displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The crystal packing of the title molecular salt, viewed along the b axis. The N-H···O and C-H···O hydrogen bonds are shown as dashed lines (see Table 1). H atoms not involved in these interactions have been omitted for clarity.

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.