Crystal structure of (E)-4-hydroxy-6-methyl-3-{1-[2-(4-nitrophenyl)hydrazinylidene]ethyl}-2H-pyran-2-one

(E)-4-Hydroxy-6-methyl-3-{1-[2-(4-nitrophenyl)hydrazinylidene]ethyl}-2-H-pyran-2-one has been synthesized and characterized by single-crystal X-ray diffraction and by using FT–IR, 1H and 13C NMR and UV–Vis spectroscopic techniques.


Chemical context
For the last several decades, Schiff bases have remained an important and popular area of research for the scientific community due to their simple synthesis, versatility and extensive range of applications (Cozzi, 2004;Chen et al., 2008). A number of carbonyl compounds and amines have been utilized for the synthesis of Schiff bases (Zheng et al., 2009;Hussain et al., 2014). However, there are only a few reports where dehydroacetic acid (DHA) has been used for the preparation of Schiff bases for various applications (Liu et al., 1991;Luo et al., 1995). In some cases, DHA-based Schiff bases are used for the synthesis of metal complexes, leading to their utilization in various biomedical applications due to their antifungal, antibacterial, antimalarial and anticancer activities (Chan & Wong, 1995;Erkkila et al., 1999;Ganjali et al., 2007;Gupta & Sutar, 2008). In general, the compounds are formed via a condensation product of hydrazine and the respective aldehyde or ketone in a 1:1 molar ratio. Structurally, a Schiff base (also known as an imine or azomethine) is a nitrogen analogue of an aldehyde or ketone in which the carbonyl group (C O) has been replaced by an imine or azomethine group.
The reaction between p-nitrophenylhydrazine and dehydroacetic acid (DHA) in a 1:1 molar ratio in distilled ethanol afforded the title compound within 4 h. We report herein on its characterization by FT-IR, 1 H and 13 C NMR and UV-Vis spectroscopic and single-crystal X-ray diffraction techniques.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The dihedral angle between the pyran (O2/C9-C13) and benzene (C1-C6) rings is 12.9 (1) . The approximate planarity of the entire molecule maybe influenced by an intramolecular O1-H1Á Á ÁN3 hydrogen bond, which forms an S(6) ring.

Supramolecular features
The crystal packing features strong N2-H2Á Á ÁO3 i hydrogen bonds between the NH group and the O carbonyl atom of the DHA moiety of symmetry-related molecules, creating infinite chains along [101] (see Table 1 for symmetry code). This O carbonyl atom is also weakly hydrogen bonded to a symmetryrelated hydrogen atom (C5-H5Á Á ÁO3 i ), forming a bifurcated N-H,C-HÁ Á ÁO hydrogen bond (Fig. 2). In a similar fashion, the O2 atom of the pyran ring forms a weak hydrogen bond to the methyl hydrogen of an adjacent molecule (C7-H7AÁ Á ÁO2 i ). The chains are arranged in a herringbone pattern in the three-dimensional structure (Fig. 3).

Hirshfeld surface analysis
The Hirshfeld surface was mapped with d norm to visualize the intermolecular interactions and 2-D fingerprint plots were generated using Crystal Explorer (Wolff et al., 2012) (Fig. 4).

Spectroscopic and TG analysis
The FT-IR spectrum of the title compound shows a characteristic peak at 1687 cm À1 which has been consigned for The molecular structure of the title compound, showing the atom-naming scheme. The displacement ellipsoids are shown at the 50% probability level.

Figure 2
A chain parallel to [101] formed by the intermolecular hydrogen bonding (dashed lines) between the N-H group and carbonyl O atom of the DHA moiety. Weak C-HÁ Á ÁO hydrogen bonds are also shown as dashed lines.

Figure 3
The crystal packing showing the herringbone arrangement of HMNP, viewed along the a axis. C-bound H atoms have been omitted for clarity. Hydrogen bonds are shown as dashed lines. Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) x À 1 2 ; Ày þ 1 2 ; z À 1 2 .
C=N , whereas the broad signal at 3280 cm À1 ( O-H ) indicates the presence of a phenolic group. The 1 H NMR spectrum display a singlet at 15.23 ppm, which clearly indicates the dominance of the enol form of the title compound over the keto form. The absorption spectra for HMNP was recorded in C 2 H 5 OH, and max was observed at 394 nm, which is ascribed to the !* or n!* transition of the C O or C N group. To probe the thermal stability of HMNP, thermogravimetric analysis (TGA) was undertaken and it was found that HMNP is stable to 513 K.

Synthesis and crystallization
Materials and methods: p-Nitrophenylhydrazine and dehydroacetic acid were of analytical grade and purchased from Spectrochem and Merck (India), respectively, and used as received. However, analytical grade solvents were purified wherever necessary as per as the standard literature method (Perrin et al., 1980). The FT-IR spectra were recorded with a Perkin-Elmer FTIR-2000 spectrometer. The NMR spectroscopic measurements were carried out with a JEOL AL-400 MHz spectrometer. The thermogravimetric analysis (TGA) measurement was performed on an SDT Q600 (V20.9 Build 20) instrument (Artisan Technology Group, Champaign, IL) under N 2 atmosphere with a heating rate of 10 K min À1 . The absorbance spectrum was recorded on a JASCO V-530 UV/vis Spectrophotometer.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The NH and OH hydrogen atoms were located in a difference-Fourier map and freely refined. The C-bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.93-0.96 Å , O-H= 0.82 Å with U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (C methyl ). The crystal studied was a non-merohedral twin with the refined ratio of the twin components being 0.3720 (19): 0.6280 (19) using twin matrix (10 0) (0 1 0)  program(s) used to solve structure: SHELXS2013 (Sheldrick 2008); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015); molecular graphics: X-SEED (Barbour 2001); software used to prepare material for publication: publCIF (Westrip 2010).

(E)-4-Hydroxy-6-methyl-3-{1-[2-(4-nitrophenyl)hydrazin-1-ylidene]ethyl}-2H-pyran-2-one
Crystal data 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.