2,3-Dimethyl-1H-imidazol-3-ium chloride

The title compound crystallizes in an orthorhombic unit cell with a single cation–anion pair in the asymmetric unit. Hydrogen bonding appears to be the dominant intermolecular force between the individual ions, forming extended networks.

The title salt, C 5 H 9 N 2 + ÁCl À , exhibits multiple hydrogen-bonding interactions between the cationic imidazole moiety and the chloride anion. The protonated aromatic nitrogen moiety displays the shortest hydrogen-bonding interactions while weaker hydrogen bonding is observed between the aromatic H atoms and the chloride anion. The crystal studied was refined as a two-component inversion twin with a twin ratio of 0.71 (5) to 0.29 (5).

Structure description
The title structure, 2,3-dimethyl-1H-imidazol-3-ium chloride (Fig. 1), crystallizes in the P2 1 2 1 2 1 orthorhombic space group with a single cation-anion pair in the asymmetric unit. The acidic hydrogen, H1, exhibits a strong hydrogen bond to the chloride anion with a distance of 2.122 (19) Å . Longer hydrogen bonds between the chloride anion and H atoms on both methyl groups on the imidazolium ring as well as to the aromatic H atoms on adjacent cations form the dominant intermolecular interactions in the overall network (see Table 1). The positioning of the cations, likely to facilitate hydrogen bonding, also precludes any possible long-distanceinteractions given the canted angles of the rings with respect to each other (see Fig. 2).

Synthesis and crystallization
1,2-Dimethylimidazole (0.2568 g, 2.662 mmol) and trityl chloride (0.7439 g, 2.668 mmol) were dissolved in separate 50 mL beakers with toluene. The reactants were then combined in a single-necked 100 mL round-bottom flask equipped with a magnetic stir bar and left to stir for 2 d at room temperature. The solvent was removed under vacuum leaving a white solid residue. This solid was washed twice with tetrahydrofuran and data reports recovered via vacuum filtration. Crystals were grown at room temperature by vapor diffusion with acetonitrile as the solvent and tetrahydrofuran as the anti-solvent. Colorless crystals of the hydrolyzed byproduct (2,3-dimethyl-1H-imidazol-3-ium chloride) were observed within one week.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The crystal studied was refined as a two-component inversion twin with a twin ratio of 0.71 (5) to 0.29 (5).    (13) 138.0 (14)

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