1-Butyl-3-ethyl-1H-benzimidazol-3-ium tetrafluoroborate

In the title salt, C13H19N2 +·BF4 −, an ionic liquid, the butyl and ethyl substituents bonded to the N atoms of the imidazole ring [r.m.s. deviation = 0.019 (1) Å] adopt equatorial positions. The crystal structure exhibits slipped π–π interactions between the imidazole and benzene rings of neighbouring molecules [centroid–centroid distance = 3.529 (2) Å]. In the tetrafluoroborate anion, the B and F atoms are disordered over two sets of sites with site-occupancy factors of 0.813 (7) and 0.187 (7).

In the title salt, C 13 H 19 N 2 + ÁBF 4 À , an ionic liquid, the butyl and ethyl substituents bonded to the N atoms of the imidazole ring [r.m.s. deviation = 0.019 (1) Å ] adopt equatorial positions. The crystal structure exhibits slippedinteractions between the imidazole and benzene rings of neighbouring molecules [centroid-centroid distance = 3.529 (2) Å ]. In the tetrafluoroborate anion, the B and F atoms are disordered over two sets of sites with site-occupancy factors of 0.813 (7) and 0.187 (7).
DRS would like to thank the Keene State College Chemistry Department Alumni Fund for supporting his work. JPJ acknowledges the NSF-MRI program (grant No. CHE1039027) for funds to purchase the X-ray diffractometer.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LX2260).
supplementary materials Acta Cryst. (2012). E68, o2862 [doi:10.1107/S1600536812037476] 1-Butyl-3-ethyl-1H-benzimidazol-3-ium tetrafluoroborate Denise M. Junge, Derek R. Scadova, James A. Golen and Jerry P. Jasinski Comment Due to their unique properties, ionic liquids have emerged as environmentally friendly alternatives for volatile organic solvents (Zhao et al., 2002). In particular, imidazolium-based ionic liquids have been used as solvents and catalysts for a wide variety of chemical processes (Welton, 1999;Hallett et al., 2011). Benzimidazole can be viewed as a homologue of imidazole and, therefore, similar properties and applications as seen with the imidazolium-based ionic liquids is expected (Costache et al., 2007;Chen et al., 2008). In continuation of our work with ionic liquids, we report herein the crystal structure of the title compound.
In the title molecule ( Fig. 1), imidazole ring is essentially planar, with a mean deviation of 0.019 (1) Å from the leastsquares plane defined by the five constituent atoms. In the tetrafluoroborate group, the B and F atoms are disordered over two positions with site-occupancy factors, from refinement of 0.813 (7) (part A) and 0.187 (7) (part B). The butyl and ethyl substituents bonded to the nitrogen atoms with the mean plane of the imidazole ring adopt equatorial positions.
Bond lengths are in normal ranges (Allen et al., 1987).
The reaction mixture was then extracted with dichloromethane (4 x 5 ml) and dried over Na 2 SO 4 . The dichloromethane was removed solvent by rotary evaporation, and dried under vacuum to yield the title product (m.p.: 354 -356 K).

Refinement
The B and F atoms in the tetrafluoroborate anion are disordered over two sets of site with an occupancy ratio: 0.813 (7):0.187 (7) and with all B-F distances fixed at 1.36 (2) 1.20 (CH), 1.20 (CH 2 or 1.50 (CH 3 ) times U eq of the parent atom.

Figure 1
The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as small spheres of arbitrary radius. The B and F atoms of the tetrafluoroborate group are disordered over two positions with refined site-occupancy factors of 0.813 (7) (part A) and 0.187 (7) (part B).  A view of the π-π interactions (dotted lines) in the crystal structure of the title compound. (Cg1 and Cg2 are the centroids of the N1/C1/N2/C7/C2 imidazole ring and the C2-C7 benzene ring, respectively; Symmetry code: 1-x, 1-y, 1-z).
Disordered tetrafluoroborate group and all H atoms were omitted for clarity.

1-Butyl-3-ethyl-1H-benzimidazol-3-ium tetrafluoroborate
Crystal data C 13 H 19 N 2 + ·BF 4 − M r = 290.11 Monoclinic, P2 1 /n Hall symbol: -P 2yn a = 11.0043 (13) Å b = 12.0372 (9) Å c = 11.3693 (10) Å β = 99.312 (9)  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.46 e Å −3 Δρ min = −0.25 e Å −3 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 > 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 Occ. (