6,6′-Diethoxy-2,2′-[propane-1,3-diyldioxybis(nitrilomethylidyne)]diphenol

The complete molecule of the title compound, C21H26N2O6, is generated by a crystallographic twofold axis and adopts a trans configuration with respect to the azomethine group. The two benzene rings are almost perpendicular to one another, making a dihedral angle of 89.53 (3)°. In the molecular structure, pairs of intramolecular O—H⋯N hydrogen bonds generate two six-membered rings. The crystal structure is further stabilized by intermolecular C—H⋯O hydrogen bonds, which link four adjacent molecules into a network structure.

The complete molecule of the title compound, C 21 H 26 N 2 O 6 , is generated by a crystallographic twofold axis and adopts a trans configuration with respect to the azomethine group. The two benzene rings are almost perpendicular to one another, making a dihedral angle of 89.53 (3) . In the molecular structure, pairs of intramolecular O-HÁ Á ÁN hydrogen bonds generate two six-membered rings. The crystal structure is further stabilized by intermolecular C-HÁ Á ÁO hydrogen bonds, which link four adjacent molecules into a network structure.

Comment
Salicylaldehyde and its derivatives are an important class of compounds which can be used in a variety of studies such as organic synthesis, catalysis, drug design, the spice industry and the life sciences (Dong et al., 2007a;Dong & Duan, 2008). In the past few decades, continuing attention has been drawn to derivatives of the salicylaldehyde and their metal complexes for the investigation of luminescent properties which could be finely tuned by different substituent groups bonded to the phenolic ring (Dong et al., 2008). In this paper, we report synthesis and X-ray structure of 6,6'-diethoxy-2,2'-[(1,3propylene)dioxybis(nitrilomethylidyne)]diphenol, (I).

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.

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