3,3′-[1,4-Phenylenebis(methylene)]bis(1-propylbenzimidazolium) dichloride dihydrate

The asymmetric unit of the title compound, C28H32N4 2+·2Cl−·2H2O, contains half of a 3,3′-[1,4-phenylenebis(methylene)]bis(1-propylbenzimidazolium) cation, one chloride anion and one water molecule. The complete cation is generated by a crystallographic inversion center. The central benzene ring forms a dihedral angle of 66.06 (11)° with its adjacent benzimidazolium ring system. In the crystal, the cations, anions and water molecules are linked by O—H⋯Cl, C—H⋯O and C—H⋯Cl hydrogen bonds into a three-dimensional network. The crystal packing is further stabilized by π–π interactions, with centroid–centroid distances of 3.5561 (15) and 3.6708 (15) Å.

Previously, we have reported crystal structures of ortho-xylyl linked bis--benzimidazolium salts with heptyl (Haque et al., 2011), propyl , and ethyl  substitutions. In this report, we describe the crystal structure of a para-xylyl linked bis--benzimidazolium salt with propyl substitutions.
Bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable to related structures (Haque et al., 2011Iqbal et al., 2012).

Experimental
A mixture of benzimidazole (2.95 g, 25 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 min. 1-Bromopropane (2.27 ml, 25 mmol) was added dropwise into this consistently stirred mixture with further stirring for 2 h at the same temperature. The mixture was then poured into water (400 ml) and was extracted by chloroform (5 x 20 ml). The extract was dried by magnesium sulfate and evaporated under reduced pressure to get N-ethylbenzimidazole (1) as a thick yellowish fluid. Furthermore, a mixture of 1 (1.60 g, 10 mmol) and 1,4-bis(chloromethyl)benzene (0.88 g, 5 mmol) in dioxane (30 ml) was refluxed at 100 °C for 18 h. This desired compound (2.2Cl) appeared as white precipitates in the light brown solution. The mixture was filtered and the precipitates were washed with fresh dioxane (3 × 5 ml), dried at room temperature for 24 h, and the soft lumps obtained were ground into a fine powder (2.15 g, 87%). Saturated solution of 2.2Cl in methanol (0.5 ml) was exposed to diethyl ether vapours (vapour diffusion) at room temperature overnight to get single crystals suitable for X-ray diffraction study.

Refinement
Atoms H1W1 and H2W1 were located in a difference Fourier map and refined freely. The remaining H atoms were positioned geometrically [C-H = 0.95, 0.98 or 0.99 Å] and 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 group.

Figure 1
The molecular structure of the title compound with atom labels and 50% probability displacement ellipsoids. Atoms with suffix A were generated by symmetry code -x, -y + 2, -z.  The crystal packing of the title compound. Intermolecular hydrogen bonds are shown as dashed lines. H atoms not involved in the hydrogen bonds have been omitted for clarity.  (Cosier & Glazer, 1986) operating at 100.0 (1) K. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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.