5,12-Dimethylpyrazino[1,2-a:4,5-a′]dibenzimidazole-5,12-diium dichloride dihydrate

The title hydrated salt, C18H18N4 2+·2Cl−·2H2O, sits about an inversion centre, such that the asymmetric unit contains one half-molecule. In the crystal, hydrogen bonds occur between the water molecules and chloride anions, and there is π–π stacking of the benzene and imidazole rings of inversion-related pairs of molecules, with a centroid–centroid distance of 3.704 (17) Å.

The title hydrated salt, C 18 H 18 N 4 2+ Á2Cl À Á2H 2 O, sits about an inversion centre, such that the asymmetric unit contains one half-molecule. In the crystal, hydrogen bonds occur between the water molecules and chloride anions, and there isstacking of the benzene and imidazole rings of inversionrelated pairs of molecules, with a centroid-centroid distance of 3.704 (17) Å .
In addition to their biological activity, there are numerous other studies, including coordination and corrosion inhibitor abilities of benzimidazoles. Bis-benzimidazoles are also strong chelating agents (Sun et al., 2010). Some of these derivatives are used as photographic materials and dyes. As part of our ongoing investigation of benzimidazole derivatives, the title compound was synthesized and its crystal structure is reported herein.

Experimental
N-methylbenzene-1,2-diamine (2.5 mol), 2-chloroacetic acid (3 mmol), polyphosphoric acid (10 ml) and silica gel (1 g) were mixed and introduced in an open Erlenmeyer flask. The reaction mixture was irradiated in a domestic microwave oven for 3 min. After cooling to room temperature, methanol was added (20 ml) and the reaction mixture filtered. The filtrate was evaporated to dryness and subjected to column chromatography (10% hexane/ethyl acetate) to give green needle-like crystals of the title compound.

Refinement
All H atoms attached to C atoms were generated in idealized positions and constrained to ride on their parent atoms, with C-H = 0.96 Å (methyl) and 0.93 Å (aromatic) with U iso (H) = 1.2U eq (C, aromatic) and U iso (H) = 1.5U eq (C, methyl). H atoms of water molecules were located in a difference Fourier map and refined with 1,2 and 1,3 distance restraints of 0.85 (2) Å and 1.39 (2) Å.

Computing details
Data collection: APEX2 (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008   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.