Crystal structure, Hirshfeld surface analysis and DFT studies of 6-[(E)-2-(thiophen-2-yl)ethenyl]-4,5-dihydropyridazin-3(2H)-one

In the crystal, the molecules are linked by N—H⋯O and C—H⋯O interactions, forming a three-dimensional network. The theoretical geometrical parameters are in good agreement with XRD results.

In the title compound, C 10 H 10 N 2 OS, the five atoms of the thiophene ring are essentially coplanar (r.m.s. deviation = 0.0037 Å ) and the pyridazine ring is nonplanar. In the crystal, pairs of N-HÁ Á ÁO hydrogen bonds link the molecules into dimers with an R 2 2 (8) ring motif. The dimers are linked by C-HÁ Á ÁO interactions, forming layers parallel to the bc plane. The theoretical geometric parameters are in good agreement with XRD results. The intermolecular interactions were investigated using a Hirshfeld surface analysis and twodimensional fingerprint plots. The Hirshfeld surface analysis of the title compound suggests that the most significant contributions to the crystal packing are by HÁ Á ÁH (39.7%), CÁ Á ÁH/HÁ Á ÁC (17.3%) and OÁ Á ÁH/HÁ Á ÁO (16.8%) contacts.

Chemical context
Pyridazinone derivatives have been tested for their chemical and biological properties and achieved an increased interest in recent years (Akhtar et al., 2016). The pyridazinone moiety is known as a 'wonder nucleus' as it can form diverse derivatives with many types of pharmacological activities such as antidepressant (Boukharsa et al., 2016), anti-HIV (Livermore et al., 1993, anti-inflammatory (Barberot et al., 2018), anticonvulsant (Partap et al., 2018), antihistaminic (Tao et al. 2012) and glucan synthase inhibition (Zhou et al., 2011) as well as acting as herbicidal agents (Asif, 2013). We report the synthesis and the crystal and molecular structure of the title compound ( Fig. 1), as well as an analysis of its Hirshfeld surface and DFT studies.

Structural commentary
Selected geometrical parameters are given in Table 1. The five atoms of the thiophene ring are essentially coplanar (r.m.s. ISSN 2056-9890 deviation = 0.0037 Å ) while the pyridazine ring is non-planar with atom C2 furthest from the mean molecular plane at a distance of 0.610 (5) Å .

Supramolecular features
In the crystal, the molecules are connected pairwise through N-HÁ Á ÁO hydrogen bonds (Table 2), forming dimers with an R 2 2 (8) graph set motif. The dimers are linked by C-HÁ Á ÁO hydrogen bonds, forming layers parallel to the bc plane (Fig. 2). A packing diagram is shown in Fig. 2.

Figure 1
Molecular structure of the title compound showing the atom labelling and displacement ellipsoids drawn at the 50% probability level.

Figure 3
The Hirshfeld surfaces of the title compound mapped over d norm , shapeindex and curvedness. scale of À0.532 (red) to 1.345 (blue) a.u. The pale-red spots symbolize short contacts and negative d norm values on the surface correspond to the N-HÁ Á ÁO and C-HÁ Á ÁO interactions ( Table 2). The overall fingerprint plot and those delineated into HÁ Á ÁH, HÁ Á ÁC/ CÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, NÁ Á ÁH/ HÁ Á ÁN and NÁ Á ÁÁC/CÁ Á ÁÁN contacts are shown in Fig. 4 along with their relative contributions to the Hirshfeld surface. The largest contribution is from HÁ Á ÁH interactions (40.0%). The shape-index map of the title complex was generated in the range À1 to 1 Å , with the convex blue regions indicating hydrogen-donor groups and the concave red regions hydrogen-acceptor groups. The curvedness map, generated in the range À4 to 0.4 Å , shows large regions of green which denote a relatively flat surface area (planar), while the blue regions denote areas of curvature.
A view of the molecular electrostatic potential, in the range À 0.084 to 0.084 a.u. generated by the DFT method using the 6-31G(d,p) basis set is shown in Fig. 5. Here the N-HÁ Á ÁO hydrogen-bond donors and acceptors are shown as blue and red areas around the atoms related with positive (hydrogenbond donors) and negative (hydrogen-bond acceptors) electrostatic potentials, respectively.
The theoretical calculations were performed using GAUS-SIAN03 (Frisch et al., 2004). The initial geometry was taken from the X-ray coordinates and this geometry was optimized using the DFT/B3LYP (Becke, 1993) method with LANL2DZ as the basis set. The theoretical geometrical parameters are in good agreement with XRD results (Table 1).

Frontier molecular orbitals
The highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) are known as frontier molecular orbitals (FMOs). The FMOs play an important role in the optical and electric properties. The frontier orbital gap can indicate the chemical reactivity and the kinetic stability of the molecule. If the energy gap is small then the molecule is highly polarizable and has high chemical reactivity. A molecule with a small frontier orbital gap is generally associated with a high chemical reactivity, low kinetic stability and is termed a soft molecule. Two-dimensional fingerprint plots for the title compound, with a d norm view and the relative contributions of the atom pairs to the Hirshfeld surface.

Figure 5
A view of the molecular electrostatic potential for the title compound in the range À0.084 to 0.084 a.u. generated by DFT using the 6-31G(d,p) basis set.

Figure 6
The electron distribution of the HOMO and LUMO energy gaps of the title compound.

Figure 7
The total electron density three-dimensional surface mapped for the compound with the electrostatic potential calculated at the B3LYP/6-31G(d,p) level. compound indicates the chemical reactivity is strong and the kinetic stability is weak. A map of the electron density is shown in Fig. 7.

Synthesis and crystallization
To a solution of 4-oxo-6-(thiophen-2-yl)hex-5-enoic acid (0.21 g, 1 mmol) in 20 mL of ethanol, it was added an equimolar amount of hydrazine hydrate. The mixture was maintained under reflux for 4h, until TLC indicated the end of the reaction. The reaction mixture was poured into cold water, and the precipitate formed was filtered out, washed with ethanol and recrystallized from ethanol. Slow evaporation at room temperature led to formation of single crystals.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atoms were fixed geometrically and treated as riding, the C-bound H atoms were placed in idealized positions and refined as riding: C-H = 0.93 Å for methylene U iso (H) = 1.5U eq (C) and C-H = 0.97 Å for the other C atoms with U iso (H) = 1.2U eq (C). The NH H atom was located in a difference-Fourier map and freely refined.

6-[(E)-2-(Thiophen-2-yl)ethenyl]-4,5-dihydropyridazin-3(2H)-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.