1-Benzyl-3-methylimidazolium bromide

The molecular structure of the title compound, (BenzMIm)Br (BenzMIm=1-benzyl-3-methylimidazolium), consists of separated bromide anions and 1-benzyl-3-methylimidazolium cations connected via short C—H⋯Br contacts.

The title compound, (BenzMIm)Br (BenzMIm=1-benzyl-3-methylimidazolium), C 11 H 13 N 2 + ÁBr À , was obtained as single crystals directly from a pure and liquid sample of the compound over several weeks. The molecular structure of (BenzMIm)Br consists of separated bromide anions and 1-benzyl-3-methylimidazolium cations connected via short C-HÁ Á ÁBr contacts. The compound exhibits a relatively low melting point (m.p. = 72 C) and is a supercooled, highly viscous transparent liquid at ambient conditions. The title compound crystallizes with two unique ion pairs in the asymmetric unit of the orthorhombic unit cell.

Structure description
For the last 20 years, ionic liquids as salts with low melting points have attracted great interest because of their unique properties and applications. These properties include, for instance, large liquid ranges, broad electrochemical windows as well as low vapor pressures (Hallett & Welton, 2011;Welton, 1999). The title compound, which is a useful starting material in our ongoing efforts to investigate metal-containing ionic liquids (Peppel et al., 2010;Peppel et al., 2017;Peppel et al., 2019) was obtained as single crystals over a period of several weeks directly from its pure, highly viscous and supercooled liquid. 1-Benzyl-3-methylimidazolium bromide expands the range of known single-crystal X-ray structures of ionic liquids of the general formula (BenzMIm)X (X = Cl, PF 6 (Ji et al., 2010; Hillesheim & Scipione, 2014) with a third example (X = Br). It can be seen from Fig. 1 that the (BenzMIm)Br is characterized by discrete 1-benzyl-3-methylimidazolium cations and bromide anions. The shortest C-HÁ Á ÁBr contacts equal 2.740 Å (sum of van der Waals radii for H and Br: 3.0 Å ). All bond lengths and angles within the cation are in expected ranges (Leclercq et al., 2009). The two symmetry-independent molecular units mainly differ by the angle between the phenyl and the imidazolium ring which is 84.02 (7) in one of the cations and to 80.47 (7) in the other. The title compound data reports crystallizes with two unique ion pairs in the asymmetric unit of the orthorhombic unit cell.

Synthesis and crystallization
The title compound, (BenzMIm)Br, was obtained in high purity as a transparent, supercooled, highly viscous liquid in multi-gram scale from N-methylimidazole and benzyl bromide in ethyl acetate solution under ambient conditions. Benzyl bromide (15.0 g, 87.7 mmol) was added in one portion to a vigorously stirred solution of N-methylimidazole (5.0 g, 60.9 mmol) in 100 ml ethyl acetate at room temperature. The clear solution became turbid after a few minutes and was stirred at room temperature overnight. Afterwards, the product was washed several times with portions of ethyl acetate and dried in vacuo (T = 90 C, p = 20 mbar, yield: 13.1 g, 85%).
Analytic data for (

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.