2,2′-(4-{[(E)-4-Methoxybenzylidene]amino}phenylimino)diethanol

In the title compound, C18H22N2O3, the dihedral angle between the aromatic rings is 3.9 (2)°. Both H atoms of the hydroxy groups are involved in intermolecular O—H⋯O hydrogen bonding. In the crystal structure, this hydrogen bonding assembles molecules into chains of 21 symmetry extending parallel to the b axis. The almost planar (within 0.09 and 0.06 Å) 4-CH3O–C6H4–CH=N–C6H4– groups are oriented outwards the twofold screw axis.

In the title compound, C 18 H 22 N 2 O 3 , the dihedral angle between the aromatic rings is 3.9 (2) . Both H atoms of the hydroxy groups are involved in intermolecular O-HÁ Á ÁO hydrogen bonding. In the crystal structure, this hydrogen bonding assembles molecules into chains of 2 1 symmetry extending parallel to the b axis. The almost planar (within 0.09 and 0.06 Å ) 4-CH 3 O-C 6 H 4 -CH N-C 6 H 4 -groups are oriented outwards the twofold screw axis.

Related literature
For practical interest in Shiff bases of general type p-R 0 -C 6 H 4 -CH=N-C 6 H 4 -R 00 -p in various areas, see: von Kö nig et al.   Table 1 Hydrogen-bond geometry (Å , ).

Comment
Shiff bases of the general type p-R'-C 6 H 4 -CH=N-C 6 H 4 -R"-p are well-known compounds that find practical application in various areas [photography (for instance, see von König et al., 1982), medicinal and pharmaceutical chemistry (for instance, see Haldavanekar et al., 2009;Ferlin et al., 2004;Lewis et al., 2009)]. Recently, we were interested in preparation of a series  Table]. In (I), molecules along with their equivalents generated by a 2 1 screw axis form a one-dimensional infinite chain stretched along the b-axis. Organic moieties are oriented outwards the corresponding screw axis (see Fig. 2). These one-dimensional assemblies do not interact with their equivalent neighbours by any hydrogen bonds and are just stacked one by another. This results in an evident flattening of the entire CH 3 O-C 6 H 4 C(H)=NC 6 H 4 moieties for the inter-chain repulsion diminishing. Crystal lattice packing of (I) differs markedly from that of (II) (Liu et al., 2010)). Reduction of the nitro-group was carried out as described by Lewis et al. (2009). Schiff-base preparation was done by a modification of the procedure reported by von König et al. (1982).

Refinement
All non-H atoms were refined anisotropically. H atoms except of H7 and OH were treated as riding atoms with distances of C-H = 0.96 (CH 3 ), 0.97 (CH 2 ), 0.93 Å (C Ar H), and U iso (H) = 1.5 U eq (C), 1.2 U eq (C), and 1.2 U eq (C), respectively. Atoms H7 and OH hydrogen atoms were found from difference Fourier syntheses and refined isotropically. Despite the fact that an achiral compound (I) crystallizes in a chiral space group P2 1 , neither the absolute structure determination nor approval of the inversion twinning was possible due to evident reasons (Mo-Kα radiation with no atoms heavier than oxygen) and the refinement for (I) was preformed with the Friedel opposites merged (MERG 3 instruction). Fig. 1. Asymmetric unit of (I) showing the labelling scheme and thermal ellipsoids at the 50% probability level. Fig. 2. View of a 2 1 -symmetrical chain assembled by molecules of (I) via hydrogen bonds. Hydrogen atoms except of the OH ones are omitted for clarity. Labelling is provided only for atoms involved in H-bonding. H-bonds are depicted as dashed lines. 2-fold screw axis is depicted as a long-dash line.

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.
supplementary materials sup-4 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 > 2σ(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 )