2-(Furan-2-yl)-1,3-bis(furan-2-ylmethyl)-1H-benzimidazol-3-ium chloride monohydrate

The title hydrated salt, C21H17N2O3 +·Cl−·H2O, exhibits disorder in one of the furan rings. The major and minor components have a refined occupancy ratio of 0.844 (19):0.156 (19). The structure displays intermolecular hydrogen bonding involving the water molecule and the chloride anion. Close intermolecular C—H⋯Cl and C—H⋯(furan ring) interactions complete the hydrogen bonding.

The title hydrated salt, C 21 H 17 N 2 O 3 + ÁCl À ÁH 2 O, exhibits disorder in one of the furan rings. The major and minor components have a refined occupancy ratio of 0. 844 (19):0.156 (19). The structure displays intermolecular hydrogen bonding involving the water molecule and the chloride anion. Close intermolecular C-HÁ Á ÁCl and C-HÁ Á Á(furan ring) interactions complete the hydrogen bonding.
A perspective view of the benzimidazolium cation of the title compound is shown in Figure 1  The H12A···Cl1 distance is 2.77 Å with C12···Cl1 = 3.627 (2) Å. Also, there is a weak C-H···aromatic interaction involving H15 and the furan ring containing O3. The closest approach is with O3 with H15···O3 = 2.63 Å. H15 is 2.602 (3) Å from the furan mean plane. These interactions result in chains of molecules parallel to the (0 0 1) plane as shown in Figure 3.

Experimental
A single-crystal of the title compound was obtained during the attempted crystallization of 2-(2-furanyl)-1-(furanylmethyl)-1H-benzimidazole prepared via the aluminium trichloride catalyzed reaction of 1,2-diaminobenzene and furan-2-carbaldehyde in refluxing dichloromethane. The product was isolated by column chromatography on silica gel using an eluant that varied from 1:2 ethylacetate:hexanes to pure ethyl acetate.
The crystal used for the diffraction study was obtained by vapor diffusion of heptane into a methanol solution of the chromatographed product. Based on 1 H NMR spectroscopy, the title compound makes up less than 5% of the bulk product.

Refinement
All hydrogen atoms were observed in difference fourier maps. The H atoms were refined using a riding model with a C-H distance of 0.99 Å for the methylene carbon atoms and 0.95 Å for the phenyl and furan carbon atoms. All C-H hydrogen atom thermal parameters were set using the approximation U iso = 1.2U eq . supplementary materials The water oxygen atom was refined anisotropically. During the course of the refinement, SHELXL suggested that the oxygen atom of the water could be split into two atoms. However, attempts to refine the water assuming disorder result in no improvement in the GOF or the R values. The O-H distances were contrained to ~0.84 Å using DFIX and the H-O -H angles were restrained to ~104° using a DANG value of 1.34 Å between corresponding H atoms. The O-H hydrogen atom thermal parameters were set using the approximation U iso = 1.2U eq .
During the later stages of refinement, elongated thermal ellipsoids were noted for one of the furan rings. A disorder model was developed in which the minor component of the furan ring was modeled using the metrics of the major components as a guide. The pivot atom (C8) was assumed to have full occupancy and so was not included in the disorder model. The minor four-atom components (O1′, C9′, C10′ and C11′) were constrained to planarity using FLAT.
Corresponding bond distances of the minor component and major component were set equal using SADI and corresponding thermal parameters were held the same using EADP. All atoms were refined anisotropically with hydrogen atoms in calculated positions using a riding model. With these constraints, the site occupancy of the major component refined to 0.84 (2). Based on this model, the angle between the mean planes of the major and minor components of the disordered furan ring is 22.
(2)°. Improvement in the usual indicators occurred with the introduction of the disorder model. The S improved from 1.06 to 1.04. The R decreased from 0.046 to 0.045 and wR decreased from 0.132 to 0.129. However, an unusually large residual peak (0.61 e -/Å 3 ) that is 1.00 Å from a hydrogen atom exists. The hydrogen atom in question (H12A) is involved in a close interaction with the chloride ion (2.78 Å). The next largest residual peak is 0.37 e -/Å 3 and it is located 1.29 Å from H15, which is involved in a weak C-H···aromatic ring hydrogen bonding interaction (the closest approach is to O3 at 2.63 Å). program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XSHELL (Bruker, 2004) and Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).   View of the unit cell showing the hydrogen bonding network. Only the major component of the disordered furan is shown. Ellipsoids are drawn at the 25% probability level.

Figure 3
Close intermolecular C-H···Cl and C-H···O(furan) interactions resulting in a chain structure.

Special details
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (