3,3′-[1,2-Phenylenebis(methylene)]bis(1-heptylbenzimidazolium) dibromide monohydrate

In the title salt, C36H48N4 2+·2Br−·H2O, the central benzene ring makes dihedral angles of 84.77 (9) and 69.92 (7)° with the adjacent imidazole rings. In the crystal, one of the heptyl groups is disordered over two sets of sites with an occupancy ratio of 0.474 (5):0.526 (5). In the crystal, the cations, anions and water molecules are connected via intermolecular O—H⋯Br, C—H⋯Br and C—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title salt, C 36 H 48 N 4 2+ Á2Br À ÁH 2 O, the central benzene ring makes dihedral angles of 84.77 (9) and 69.92 (7) with the adjacent imidazole rings. In the crystal, one of the heptyl groups is disordered over two sets of sites with an occupancy ratio of 0.474 (5):0.526 (5). In the crystal, the cations, anions and water molecules are connected via intermolecular O-HÁ Á ÁBr, C-HÁ Á ÁBr and C-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Experimental
A mixture of benzimidazole (2.36 g, 20 mmol) and finely ground potassium hydroxide (2.36 g, 30 mmol) in 30 ml of DMSO was stirred at room temperature (27-28 °C) for 30 minutes. 1-bromoheptane (3.14 ml, 20 mmol) was added drop-wise in this consistently stirred mixture with further stirring for 2 h at the same temperature, poured into water (300 ml) and was extracted by chloroform (5 × 20 ml). The extract was dried by magnesium sulphate and evaporated under reduced pressure to afford N-heptylbenzimidazole (1) as a thick yellowish fluid (3.87 g, 89.6%). Furthermore, a mixture of 1 (2.16 g, 10 mmol) and 1,2-bis(bromomethyl)benzene (1.32 g, 5 mmol) in dioxane (30 ml) was refluxed at 90 °C for 12 h. Desired compound (2.2Br) appeared as beige-colored precipitates in dark brown solution. The mixture was filtered and precipitates were washed by fresh dioxane (3 × 5 ml), dried at room temperature for 24 h, and soft lumps so obtained were ground to fine powder (1.72 g, 49.4%). Hot (saturated) solution of 2.2Br in deuterated DMSO (0.5 ml) was cooled to room temperature in NMR tube overnight to get single (prismatic) crystals suitable for X-ray diffraction study.

Refinement
Atoms H1W1 and H1W2 were located in a difference Fourier map and refined freely [O-H = 0.79 (3)-0.84 (2) Å]. The remaining H atoms were positioned geometrically (C-H = 0.95-0.99 Å) and were refined using a riding model, with U iso (H) = 1.2 or 1.5U eq (C). A rotating group model was applied to the methyl groups. One of the heptyl group is disordered supplementary materials sup-2 over two sets of sites, with an occupancy ratio of 0.474 (5):0.526 (5). SAME restraints were applied in the refinement of the disordered components. In addition, the thermal ellipsoids of C32/C32X and C28/C29 were restrained to be equal. Fig. 1. The asymmetric unit of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. H atoms have been omitted for clarity.

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.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )