Crystal structure of 2-{[(E)-(4-anilinophenyl)iminiumyl]methyl}-5-(diethylamino)phenolate

The title compound, C23H25N3O, crystallized with one single molecule in the asymmetric unit and present in the zwitterionic form. In the crystal, molecules are connected by N—H⋯O hydrogen bonds generating –A–B–A–B– zigzag chains extending along [010]. The chains are linked via C—H⋯π interactions and π–π interactions [with a centroid–centroid distance of 3.444 (3) Å)] between the benzene ring and the imino group of symmetry-related molecules, forming slabs lying parallel to (100).


Chemical context
Our research interest focuses on study of Schiff bases derived from 4-diethylamino-2-hydroxybenzaldehyde. It is well known that Schiff bases of salicylaldehyde derivative may exhibit thermochromism or photochromism, depending on the planarity or non-planarity of the molecule, respectively (Cohen & Schmidt, 1964;Amimoto & Kawato, 2005). Schiff bases often exhibit various biological activities and in many cases have been shown to possess antibacterial, anticancer, anti-inflammatory and antitoxic properties (Lozier et al., 1975). They are used as anion sensors (Dalapati et al., 2011), as non-linear optical compounds (Sun et al., 2012) and as versatile polynuclear ligands for multinuclear magnetic exchange clusters (Moroz et al., 2012). Schiff bases have also been used to prepare metal complexes (Faizi & Sen, 2014;Faizi & Hussain, 2014;Penkova et al., 2010). We report herein on the crystal structure of the title compound synthesized by the condensation reaction of 4-diethylamino-2-hydroxybenzaldehyde and N-phenyl-p-phenylenediamine.
The conformation of the molecule is determined by the orientation of the terminal aminophenyl ring (C18-C23) with respect to the central benzene ring (C12-C17); the dihedral angle between them is 54.21 (14) . The two outer aromatic rings (C18-C23 and C1-C6) are inclined to one another by 74.54 (14) . The C-N, C N and C-C bond lengths are normal and close to the values observed in related structures (Sliva et al., 1997;Petrusenko et al., 1997;Fritsky et al., 2006).

Database survey
There The molecular structure of the title compound, showing the atom labelling and the intramolecular N-HÁ Á ÁO hydrogen bond as a dashed line (see Table 1 for details). Displacement ellipsoids are drawn at the 40% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view of the one-dimensional -A-B-A-B-zigzag hydrogen-bonded chain extending along the b axis. Hydrogen bonds are shown as dashed lines; see Table 1 for details.

Figure 3
A view along the c axis of the crystal packing of the title compound. The hydrogen bonds, C-HÁ Á Á interactions andinteractions between the benzene ring and the imino group are shown as dashed lines (see Table 1 for details; for the latter interactions, the atoms involved are shown).

Synthesis and crystallization
100 mg (1 mmol) of N-phenyl-p-phenylenediamine was dissolved in 10 ml of absolute ethanol. To this solution, 85 mg (1 mmol) of 4-diethylamino-2-hydroxybenzaldehyde in 5 ml of absolute ethanol was dropwisely added under stirring. This mixture was stirred for 10 min, two drops of glacial acetic acid were then added and the mixture was further refluxed for 2 h. The resulting yellow precipitate was recovered by filtration, washed several times with a small portions of EtOH and then with diethyl ether to give 150 mg (88%) of 5-diethylamino-2- Crystals of the title compound suitable for X-ray analysis were obtained within three days by slow evaporation of the DMF solvent.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The N-H and H atoms were located in a difference Fourier map. Their positional and isotropic thermal parameters were included in further stages of the refinement. All C-bound H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.97 Å and with U iso (H) = 1.2-1.5U eq (C). Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenberg & Putz, 2006) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

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 > 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.