3,3′-Dibenzyl-1,1′-(2,4,6-trimethyl-m-phenylenedimethylene)diimidazol-3-ium dibromide

In the title molecular salt, C31H34N4 2+·2Br−, the central benzene ring makes dihedral angles of 80.47 (12) and 82.78 (12)° with the adjacent imidazole rings. The dihedral angle between the two terminal phenyl rings is 79.16 (13)°. In the crystal, the cations and anions are linked via C—H⋯Br hydrogen bonds, forming supramolecular chains along the c axis.

In the title molecular salt, C 31 H 34 N 4 2+ Á2Br À , the central benzene ring makes dihedral angles of 80.47 (12) and 82.78 (12) with the adjacent imidazole rings. The dihedral angle between the two terminal phenyl rings is 79.16 (13) . In the crystal, the cations and anions are linked via C-HÁ Á ÁBr hydrogen bonds, forming supramolecular chains along the c axis.
In the crystal structure (Fig. 2), the cations and anions are linked together via intermolecular C-H···Br (Table 1) hydrogen bonds, forming one-dimensional supramolecular chains along the c-axis.

Experimental
A mixture of imidazole (1.0 g, 14.0 mmol) and sodium hydroxide (0.6 g, 15.0 mmol) in DMSO (20 ml) was heated to 363 K for 2 h. The mixture was cooled at room temperature then 1,3-bis(bromomethyl)mesitylene (2.0 g, 6.5 mmol) in 10 ml of DMSO was added, heated to 413 K for 1 h and poured into water (200 ml), then cooled in an ice bath. The resulting precipitate was collected by filtration, washed with water (3x10 ml), and recrystallised from methanol/water to give 1,3bis(N-imidazole-1-ylmethyl)mesitylene as an off-white solid (1.45 g, 79 %). Further, a mixture of 1,3-bis(N-imidazole-1ylmethyl)mesitylene (0.7 g, 2.5 mmol) and benzyl bromide (1.0 g, 5.8 mmol) in 30 ml of acetonitrile, was refluxed for 24 h, then cooled to room temperature and left standing overnight, giving the title compound as light brown crystals which were isolated by decantation and washed with diethyl ether (2x5 ml) and placed in a desiccator. The yield was (1.15 g, 74%).
The resulting crystals were suitable for X-ray diffraction.

Refinement
All H atoms were positioned geometrically [C-H = 0.93-0.97 Å] and were refined using a riding model, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and 1.2 for all other H atoms. The highest peak in the final difference map was found at a distance of 0.77 Å from Br1.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.