6,6′-Diethoxy-2,2′-[2,2-dimethylpropane-1,3-diylbis(nitrilomethylidyne)]diphenol

In the crystal structure, the title Schiff base compound, C23H30N2O4, exhibits crystallographic twofold rotation symmetry. The imino group is coplanar with the aromatic ring with an N—C—C—C torsion angle of -179.72 (9)°. An intramolecular O—H⋯N hydrogen bond forms a six-membered ring, producing an S(6) ring motif. The dihedral angle between symmetry related benzene rings is 28.05 (5)°. The ethoxy group makes a C—O—C—C torsion angle of −7.20 (16)° with the benzene ring. The crystal structure is stabilized by intermolecular C—H⋯π interactions.

In the crystal structure, the title Schiff base compound, C 23 H 30 N 2 O 4 , exhibits crystallographic twofold rotation symmetry. The imino group is coplanar with the aromatic ring with an N-C-C-C torsion angle of -179.72 (9) . An intramolecular O-HÁ Á ÁN hydrogen bond forms a sixmembered ring, producing an S(6) ring motif. The dihedral angle between symmetry related benzene rings is 28.05 (5) . The ethoxy group makes a C-O-C-C torsion angle of À7.20 (16) with the benzene ring. The crystal structure is stabilized by intermolecular C-HÁ Á Á interactions.

Comment
The condensation of primary amines with carbonyl compounds yields Schiff base (Casellato & Vigato, 1977) that are still now regarded as one of the most potential group of chelators for facile preparations of metallo-organic hybrid materials.
In the past two decades, the synthesis, structure and properties of Schiff base complexes have stimulated much interest for their noteworthy contributions in single molecule-based magnetism, materials science, catalysis of many reactions like carbonylation, hydroformylation, reduction, oxidation, epoxidation and hydrolysis, etc (Pal et al., 2005;Reglinski et al., 2004;Hou et al., 2001;Ren et al., 2002). This is due to the fact that Schiff bases offer opportunities for inducing substrate chirality, tuning the metal-centered electronic factor and enhancing the solubility and stability of either homogeneous or heterogeneous catalysts. Only a relatively small number of free Schiff base ligands have been characterized (Calligaris & Randaccio, 1987). As an extension of our work on the structural characterization of Schiff base compounds, the title compound, is reported here.
The molecule of the title compound, (Fig. 1), has a crystallographic twofold rotation symmetry. The atom C9 lies across a crystallographic twofold rotation symmetry. An intramolecular O-H···N hydrogen bond forms a six-membered ring, producing a S(6) ring motif (Bernstein et al. 1995). The dihedral angle between the symmetry related benzene rings is 28.05 (5)°. The ethoxy group makes a torsion angle (C11-O2-C2-C3) of -7.20 (16)° with the benzene ring. The N atom is in close proximity to the H atom of the methylene group of the diamine segment, with H8B-N1 distance of 2.70 Å. The crystal structure is stabilized by intermolecular C-H···π interactions [Cg1 is the centroid of the C1-C6 benzene ring] (Table 1).

Experimental
The synthetic method has been described earlier (Reglinski et al., 2004), except that 3-ethoxysalicylaldehyde was used.
Single crystals suitable for X-ray diffraction were obtained by evaporation of an methanol solution at room temperature.   Fig. 1. The molecular structure of the title compound with atom labels and 50% probability ellipsoids for non-H atoms. The suffix A corresponds to symmetry code (-x + 1, y, -z + 1/2).  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.