Crystal structure of ethyl 2-(2-{(1E)-[(E)-2-(2-hydroxybenzylidene)hydrazin-1-ylidene]methyl}phenoxy)acetate

In the title compound, C18H18N2O4, the planes of the benzene rings are twisted with respect to each other at 27.25 (7)°. The molecule displays an extended conformation with an intramolecular O—H⋯N hydrogen bond. In the crystal, weak C—H⋯O interactions link the molecules, forming supramolecular chains running along the b-axis direction.


Related literature
For a similar structure, see: Mague et al. (2015). For background to related Schiff base ligands and their biological activity, see: Adsule et al. (2006); Karthikeyan et al. (2006); Amimoto & Kawato (2005); Cohen & Schmidt (1964 Table 1 Hydrogen-bond geometry (Å , ).  et al., 2006;Karthikeyan et al., 2006). They also may exhibit thermochromism or photochromism depending on the planarity or nonplanarity, respectively, of the molecule (Amimoto & Kawato, 2005;Cohen & Schmidt, 1964). As part of our research efforts in the area of schiff base ligands we report in this study the synthesis and crystal structure determination of the title compound.
The title molecule is in an extended conformation with the phenyl rings C1-C6 and C9-C14, respectively, making dihedral angles of 7.4 (1)° and 19.8 (1)° with the mean plane of the central C7, N1, N2, C8 unit. The bond lengths and bond angles of the title molecule are normal and are comparable to those reported for a similar structure (Mague et al., 2015).
The former angle is smaller as a result of the intramolecular O1-H1a···N1 hydrogen bond (Table 1). The packing consists of chains of molecules formed by weak C15-H15B···O3 interactions running parallel to the b axis with adjacent pairs of chains associated via C15-H15a···O4 interactions across centers of symmetry ( Fig. 2 and Table 1).

S2. Experimental
A mixture of 0.01 mol of 2-hydroxybenzohydrazide and 0.01 mol of ethyl 2-(2-formylphenoxy)acetate in 20 ml of ethanol was heated under reflux for 2 h. The solid product which precipitated from the hot solution was collected by filtration and dried under vacuum. Colourless crystals sufficient for X-ray diffraction were obtained by recrystallization from an ethanol solution. m.p. 428 K, yield 92%.

S3. Refinement
H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.99 Å) and refined in riding mode while hydroxyl-O atom was located in a difference Fourier map and refined by riding in its as-found relative position to oxygen atom. U iso (H) = 1.5U eq (C) for methyl H toms and 1.2U eq (C,O) for the others. Perspective view of the title molecule with 50% probability ellipsoids and showing the atom labeling scheme and the intramolecular O-H···N hydrogen bond.

Figure 2
Packing viewed down the b axis showing C-H···O interactions as black dotted lines.  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 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. H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.99 Å) while that attached to oxygen was placed in a location derived from a difference map and its parameters adjusted to give O-H = 0.84 Å. All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms.