Crystal structure of 1,3-bis(4-methylbenzyl)-1H-1,3-benzimidazol-3-ium bromide monohydrate

In the title hydrated symetrically substituted 1,3-bis(4-methylbenzyl)benzimidazolium salt, C23H23N2 +·Br−·H2O, the dihedral angles between the benzimidazole ring system (r.m.s. deviation = 0.003 Å) and the pendant benzene rings are 73.18 (16) and 77.52 (16)°. Both benzene rings lie to the same side of the benzimidazole ring system, giving the cation an overall U-shape. In the crystal, the cation is linked to the water molecule by a short C—H⋯O hydrogen bond and the water molecule forms O—H⋯Br hydrogen bonds. Together, these interactions lead to [010] chains. The packing is consolidated by C—H⋯Br hydrogen bonds and aromatic π–π stacking interactions [centroid–centroid distances = 3.5401 (17) and 3.8815 (18) Å], generating a three-dimensional network.


S1. Comment
N-heterocyclic carbenes (NHCs), on which many studies have been conducted over the past 40 years, have been frequently used as ligands in organometallic and coordination chemistry (Arduengo et al., 1991;Akkoç & Gök, 2013;Akkoç et al. 2014;Berding et al., 2009;Gök et al., 2014). These ligands have such properties as being strong-donors, weak-acceptors, of low toxicity, easily-synthesized and able to control the steric and electronic effects of substituents on the nitrogen atom, and being more stable against air and moisture compared to phosphine types.
In the title compound ( Fig. 1), the benzene rings (C9-C14 and C17-C22) which form a dihedral angle of 75.4 (2)° make dihedral angles of 73.18 (16) and 77.52 (16)° with respect to the central benzimidazole ring system (N1/N2/C1-C7). All bond lengths and bond angles in Table 1 are in normal range, and they are in a good agreement with those found in related compounds Akkurt et al., 2012).

S2. Experimental
To a solution of benzimidazole and potassium hidroxide in ethyl alcohol, 4-methylbenzyl bromide was added slowly. This mixture was refluxed at 18 h. Then, it was filtered and was dried under vacuum. 4-Methylbenzyl bromide (1.0 mmol) was added slowly to a solution of the obtained N-4-methylbenzylbenzimidazole (1.0 mmol) in DMF (4 ml) at room temperature and the resulting mixture was heated up to 353 K for 12 h. Diethyl ether (15 ml) was added to obtain a crystalline solid which was filtered off. The solid was washed with diethyl ether (2x15 ml) and dried under vacuum. The crude product was recrystallized from ethyl alcohol/diethyl ether at room temperature to yield colourless blocks.

S3. Refinement
The H atoms H1W and H2W of the water molecule were located in a difference View of the hydrogen bonding and molecular packing of the title compound along a axis. Only H atoms involved in H bonding are shown.

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 on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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