Crystal structure and Hirshfeld surface analysis of 1-[(E)-2-(5-chloro-2-hydroxyphenyl)hydrazin-1-ylidene]naphthalen-2(1H)-one

The molecular structure of the newly synthesized dye (E)-1-[2-(5-chloro-2-hydroxyphenyl)hydrazinylidene]naphthalen-2(1H)-one was determined by X-ray diffraction at 173 K. The asymmetric unit of the title contains two crystallographically independent molecules, which adopt an s-trans conformation.


Structural commentary
The asymmetric unit of title compound contains two crystallographically independent molecules (A and B) in which the N1A-N2A, N1B-N2B, C8A-O1A and C8B-O1B bond lengths are 1.307 (5), 1.307 (5), 1.262 (7) and 1.271 (7) Å , respectively, which indicates that the dye compound has crystallized in its neutral hydrazo tautomeric form (Fig. 1); this is common when there is a OH group in the ortho-position corresponding to the azo group. Bond lengths and angles are within normal ranges and are comparable to those observed in related structures (Bougueria et al., 2014;Chetioui et al., 2013a). The conformational differences between molecules A and B are highlighted in an overlay diagram shown in Fig. 2. The naphthol and phenol rings attached to the hydrazo group are almost coplanar, subtending a dihedral angle of 13.11 (2) in molecule A and 10.35 (2) in molecule B, indicating significant electron delocalization within the molecules. The molecular structures of A and B are each stabilized by two intramolecular N-HÁ Á ÁO hydrogen bonds with S(6) and S(5) motifs and involving the hydrogen atoms from the hydrazo groups (Table 1, Fig. 1).

Supramolecular features
In the crystal, the presence of hydroxyl groups leads indeed to the formation of intermolecular O-HÁ Á ÁO hydrogen bonds, generating infinite zigzag chains along the c-axis direction ( Overlay image of the two molecules in the asymmetric unit of the title compound. Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
View of the two independent molecules of the title compound, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. Intramolecular hydrogen bonds are shown as dashed lines.

Figure 3
A partial packing diagram of the title compound showing a zigzag chain formation along the c axis.
observed, despite the presence of aromatic rings in the molecules.

Analysis of the Hirshfeld surfaces
A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was undertaken using CrystalExplorer17 (Turner et al., 2017) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were generated. The Hirshfeld (HS) surfaces of the title compound mapped over d norm are given in Fig. 4. The normalized contact distance, d norm , varies from red to blue to white depending on the contact distances relative the sum of the van der Waals radius The intense red spots labelled 1 and 2 are related to the presence of O-HÁ Á ÁO hydrogen bonds in the crystal structure. Weak contacts are highlighted by red circles. More significant contacts and their percentage contributions to the Hirshfeld surface are given in

Figure 4
Hirshfeld surface mapped over d norm for the title compound in the range À0.728 to +1.258 arbitrary units.

Synthesis and crystallization
The title compound was synthesized according to a reported method (Wang et al., 2003). A solution of hydrochloric acid (12 mmol, in 6 mL of water) was added to 2-amino-4-chlorophenol (12 mmol) at 273 K. Sodium nitrite solution (24 mmol, in 8 mL of water) was added dropwise to the cooled mixture and stirred for 20 min. To the formed diazonium chloride was added dropwise an aqueous solution of 2-naphthol (12 mmol in 100 mL of water) containing hydroxide sodium (16 mL). The produced mixture was allowed to stir for 1 h at 278 K. The resulting red precipitate was filtered and washed with water several times. The crude azo dye was recrystallized from hot ethanol giving a pure azo dye in a good yield (80.0%). Single crystals suitable for X-ray analysis, were obtained by dissolving the compound in a minimum amount of THF/H 2 O (1/1 v/ v) at room temperature. To confirm the formula of the compound, an elementary analysis was carried out: calculated for C 16 H 11 N 2 OCl, C 64.33%, N 9.38%, H 3.71%, found C 64.41%, N 8.45%, H 3.70%. The IR spectra (KBr pellet) were recorded using a Shimadzu FTIR 8000 series Fourier transform spectrometer in the range 4000 to 400 cm À1 . IR (cm À1 ):

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydrogen atoms of hydroxyl and hydrazo groups were localized in a difference-Fourier map and refined with O-H = 0.84 (1) Å and N-H = 0.88 (1) Å , respectively, and with U iso (H) set to 1.5U eq (O) or 1.2U eq (N). The other hydrogen atoms were placed in calculated positions with C-H = 0.93 Å and refined using a riding model with fixed isotropic displacement parameters [U iso (H) = 1.2U eq (C)].  program(s) used to solve structure: SHELXT2018/3 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 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. Refined as a 2-component twin.