6,6'-Dieth-oxy-2,2'-[4,5-dimethyl-o-phenyl-enebis(nitrilo-methyl-idyne)]diphenol-ethanol-water (1/1/1).

The title bis-Schiff base compound, C(26)H(28)N(2)O(4)·C(2)H(6)O·H(2)O, crystallizes as an ethanol and water solvate. Strong intra-molecular O-H⋯N hydrogen bonds generate S(6) ring motifs. The water H atoms form bifurcated O-H⋯(O,O) inter-molecular hydrogen bonds with the O atoms of the hydroxyl and eth-oxy groups with R(1) (2)(5) ring motifs, which may, in part, influence the mol-ecular configuration. The dihedral angles between the central benzene ring and the two outer benzene rings of the Schiff base mol-ecule are 5.64 (8) and 44.78 (9)°. The crystal structure is further stabilized by inter-molecular C-H⋯O and π-π inter-actions [centroid-centroid distances = 3.6139 (11)-3.7993 (11) Å].


Comment
Schiff bases have received much attention because of their potential applications with some of these compounds exhibiting various pharmacological activities, such as anticancer (Dao et al., 2000), anti-HIV (Sriram et al., 2006), antibacterial and antifungal (Karthikeyan et al., 2006 properties. Although numerous transition-metal complexes of Schiff bases have been structurally characterized (Granovski et al., 1993), relatively few free Schiff bases have been similarly characterized.
N-substituted salicylaldimines show photochromism and thermochromism in the solid state. These effects are produced by intramolecular proton transfer associated with a change in the π-electron configuration (Hadjioudis et al. 1987). In addition, some of them may be used as analytical reagents for the determination of trace elements (Eltayeb & Ahmed, 2005a,b) such as nickel in some natural food products (Fakhari et al., 2005) or biologically important species (Shahrokhian et al., 2000). As part of a general study of tetradenate and bidentate Schiff bases (Fun, Kargar & Kia 2008;Fun, Kia & Kargar 2008), we determined the structure of the title compound.

Experimental
The title compound was synthesized by adding 3-ethoxy-salicylaldehyde (4 mmol) to a solution of 4,5-dimethyl-o-phenylenediamine (2 mmol) in ethanol (20 ml). The mixture was refluxed with stirring for half an hour. The resultant yellow solution was filtered. Yellow single crystals of the title compound suitable for X-ray structure determination were recrystallized from ethanol by slow evaporation of the solvents at room temperature over several days.

Refinement
H atoms of the hydroxy groups of the Schiff base and ethanol were positioned by a freely rotating O-H bond, see Table   1. The hydrogen of the water molecule were located from the difference Fourier map and refined freely. The remaining H atoms were positioned geometrically and refined as a riding model approximation. A rotating group model was used for the methyl groups.   Glazer, 1986) operating at 100.0 (1) K.
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 > 2sigma(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.