2-Hydroxymethyl-1,3-dimethyl-1H-benzimidazol-3-ium iodide

In the cation of the title compound, C10H13N2O+·I−, all non-H atoms, with the exception of the O atom, are essentially coplanar, with a maximum deviation of 0.04 (1) Å. In the crystal, the cations and anions are arranged in layers parallel to (100). The cations are connected to the anions via an O—H⋯I hydrogen bond and there are significant π–π stacking interactions between cation layers, with centroid–centroid distances in the range 3.606 (5)–3.630 (5) Å. A weak intramolecular C—H⋯O hydrogen bond is also observed. The crystal studied was an inversion twin with refined components of 0.52 (5) and 0.48 (5).


Comment
Benzimidazole, is isosteric with indole and purine nuclei, which are present in a number of fundamental cellular components and bioactive compounds. This structural similarity means the benzimidazole molecule is endowed with a variety of interesting biological properties (Kucukguzel, et al., 2001;Islam et al., 1991;Tonelli et al., 2010). Some of these compounds are marketed as antifungal, (Preston, 1974), antihelmintic, (Hazelton et al., 1995). Furthermore, benzimidazole derivatives can be also used as epoxy resin curing agents, catalysts, and metallic surface treatment agents (Li et al., 2003;Abboud et al., 2006). In previous work, we have reported the synthesis and structure determination of some new heterocyclic compounds bearing an imidazole unit (Bahnous et al., 2012;Zama et al., 2013;Chelghoum et al., 2011). Herein, we describe the synthesis and the structure determination of 1,3-dimethyl-2-hydroxymethylbenzimidazolium iodide (I) resulting from the quaternization reaction of 1-methyl-2-hydroxymethylbenzimidazole with methyl iodide.
The molecular structure of (I) is shown in Fig. 1. The asymmetric unit contains a 1,3-dimethyl-2-hydroxymethylbenzimidazolium cation and an iodide anion. All non-H atoms in the cation, with the exception of the O atom, are essentially co-planar with a maximum deviation of 0.04 (1)Å for N1. In the crystal, the cations and anions are arranged in layers parallel to (100) (Fig. 2). The cations are hydrogen bonded to the anions via an O-H···I hydrogen bond and there are significant π-π stacking interactions between cation layers with centroid-centroid distances in the range 3.606 (5) -3.630 (5)Å.

Experimental
To a solution of 1-methyl-2-hydroxymethylbenzimidazole derivatives (10 mmol) in 20 ml of acetonitrile, was added 30 mmol of methyl iodide. The reaction mixture was refluxed. When the reaction was over (TLC), the solvent volume was reduced and the crude product was then filtered off and washed with cold acetonitrile. Suitable crystals for X-ray analysis were obtained by slow evaporation of a water solution of (I).

Refinement
Approximate positions for all H atoms were first obtained from the difference electron density map. However, the H atoms were ultimately placed in idealized positions and treated as riding. The applied constraints were as follows: C aryl -H aryl = 0.93 Å; C methylene -H methylene = 0.97 Å; C methyl -H methyl = 0.96 Å and C hydroxy -H hydroxy = 0.82 Å. The idealized methyl group was allowed to rotate about the C-C bond during the refinement by application of the command AFIX 137 in SHELXL97 (Sheldrick, 2008). U iso (H methyl or H hydroxy ) = 1.5U eq (C methyl or O hydroxy ) or U iso (H aryl or H methylene ) = 1.2 U eq (C aryl or C methylene ). The crystal used is an inversion twin with refined components 0.52 (5)  program(s) used to solve structure: SIR2002 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg & Berndt, 2001); software used to prepare material for publication: WinGX (Farrugia, 2012) and CRYSCAL (T. Roisnel, local program).

Figure 1
The molecular structure of (I) with displacement ellipsoids drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radius. Hydrogen bonds are shown as dashed lines.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 1.34 e Å −3 Δρ min = −0.72 e Å −3 Absolute structure: Flack (1983), 1518 Friedel pairs Absolute structure parameter: 0.48 (5) 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 O1