4-(1H-Benzimidazol-2-ylmethoxy)-3-methoxybenzaldehyde tetrahydrate

In the title compound, C16H14N2O3·4H2O, the dihedral angle between the mean planes of the benzimidazole ring system and benzene ring is 2.9 (1)°. The aldehyde group is disordered over two sets of sites with refined occupancies of 0.559 (4) and 0.441 (4). In the crystal, extensive intermolecular O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds in concert with weak π–π stacking interactions [centroid–centroid distances = 3.6104 (9), 3.6288 (9) and 3.9167 (10) Å] create a three-dimensional network.

The molecular structure of the title compound is shown in Fig. 1. In (I) the dihedral angle between the mean planes of the benzimidazole ring system and benzene ring is 2.9 (1)°. The aldehyde group is disordered over two sets of sites corresponding to a rotation of approximately 180° about the C12-C16 bond with refined occupancies of 0.441 (4) and 0.559 (4). Bond distances are in normal ranges (Allen et al., 1987). Extensive O-H···O, O-H···N and N-H···O hydrogen bonds (Table 1) in concert with weak π-π stacking interactions (Table 2) create a 3-D network (Fig. 2).
The reaction mixture was cooled to room temperature and poured into crushed ice. The solid products that separated out were filtered off and recrystallized in ethanol. Single crystals were grown from ethanol by the slow evaporation method which yielded the tetrahydrate of the product (m.p.: 381-382 K) with an yield of 46%.

Refinement
The N-H atom was located in a difference Fourier map and refined isotropically with DFIX = 0.86Å. The O-H atoms were also located in differnce Fourier maps and refined isotropically with DFIX = 0.84Å and DANG = 1.35Å. DFIX and DANG commands are in the SHELXL (Sheldrick, 2008) software. The C and O atoms on the aldehyde group were refined as disordered over two sets of sites for C16/C16A and O3/O3A [occupancy ratio 0.441 (4):0.559 (4)]. All of the remaining H atoms were placed in calculated positions and refined using a riding-model approximation with C-H lengths of 0.95Å (CH), 0.99Å (CH 2 ) or 0.98Å (CH 3 ). The isotropic displacement parameters for these atoms were set to 1.19-1.21 (CH, CH 2 ) or 1.50 (CH 3 ) times U eq of the parent atom. Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 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.