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

In the title hydrated molecular salt, C38H52N4 2+·2Br−·H2O, the central benzene ring of the dication makes dihedral angles of 89.47 (13) and 72.69 (12)° with the pendant benzimidazol-3-ium rings. The conformations of the octyl side chains are completely different. In the crystal, the components are linked by O—H⋯Br, C—H⋯Br and C—H⋯O hydrogen bonds into a two-dimensional network lying parallel to the ac plane. Aromatic π–π stacking interactions are also observed [shortest centroid-to-centroid separation = 3.5047 (16) Å].

In the title hydrated molecular salt, C 38 H 52 N 4 2+ Á2Br À ÁH 2 O, the central benzene ring of the dication makes dihedral angles of 89.47 (13) and 72.69 (12) with the pendant benzimidazol-3ium rings. The conformations of the octyl side chains are completely different. In the crystal, the components are linked by O-HÁ Á ÁBr, C-HÁ Á ÁBr and C-HÁ Á ÁO hydrogen bonds into a two-dimensional network lying parallel to the ac plane. Aromaticstacking interactions are also observed [shortest centroid-to-centroid separation = 3.5047 (16) Å ].

Experimental
A mixture of benzimidazole (5.90 g, 50 mmol) and finely ground potassium hydroxide (4.50 g, 80 mmol) in 50 ml of DMSO was stirred at room temperature (27-28 °C) for 30 min. 1-Bromoctane (8.70 ml, 50 mmol) was added drop-wise into this consistently stirred mixture with further stirring for 2 h at the same temperature. The mixture was then poured into water (700 ml) and was extracted by chloroform (5 × 30 ml). The extract was dried by filtering through five plies of Whatman filter papers. This process was repeated twice to collect crystal a clear solution which was evaporated under reduced pressure to get N-octylbenzimidazole (1) as a thick yellowish fluid. Furthermore, a mixture of 1 (4.04 g, 20 mmol) and 1,2-bis(bromomethyl)benzene (2.64 g, 10 mmol) in 1,4-dioxane (50 ml) was refluxed at 100 °C for 18 h. After cooling the reaction mixture to room temperature, the desired compound (2.2Br) appeared as white crystalline powder.
The salt was filtered and washed by fresh 1,4-dioxane (3 × 5 ml), dried at room temperature for 24 h. The product was collected as white crystalline powder (7.42 g, 97.76%). Saturated solution of 2.2Br in methanol (0.5 ml) was exposed to diethyl ether vapours (vapour diffusion) at room temperature to get colourless blocks of (I). Single crystals were also obtained by slow evaporation of saturated solution of 2.2Br in MeOH/CH 3 CN (70:30) and by evaporating saturated solution of title compound in d 6 -DMSO at room temperature.

Refinement
The H atoms of the water molecule were located in a difference with U iso (H) = 1.2 or 1.5U eq (C). A rotating group model was applied to the methyl groups.

Figure 1
The molecular structure of the title compound, showing 30% probability displacement ellipsoids.  The crystal packing of the title compound. Those H atoms not involved in the intermolecular interactions (dashed lines) have been omitted for clarity.