Abstract
The title pyridazinone derivative, C 20 H 18 N 2 O 3 , is not planar. The phenyl ring and the pyridazine ring are inclined to each other by 10.55 (12) , whereas the 4-methylbenzyl ring is nearly orthogonal to the pyridazine ring, with a dihedral angle of 72.97 (10) . In the crystal, molecules are linked by pairs of O-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (14) ring motif. The dimers are linked by C-HÁ Á ÁO hydrogen bonds, generating ribbons propagating along the c-axis direction. The intermolecular interactions were additionally investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots. They revealed that the most significant contributions to the crystal packing are from HÁ Á ÁH (48.4%), HÁ Á ÁO/OÁ Á ÁH (21.8%) and HÁ Á ÁC/CÁ Á ÁH (20.4%) contacts. Molecular orbital calculations providing electron-density plots of HOMO and LUMO molecular orbitals and molecular electrostatic potentials (MEP) were also computed, both with the DFT/B3LYP/6-311 G++(d,p) basis set.

The title pyridazinone derivative, C 20 H 18 N 2 O 3 , is not planar. The phenyl ring and the pyridazine ring are inclined to each other by 10.55 (12) , whereas the 4-methylbenzyl ring is nearly orthogonal to the pyridazine ring, with a dihedral angle of 72.97 (10) . In the crystal, molecules are linked by pairs of O-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (14) ring motif. The dimers are linked by C-HÁ Á ÁO hydrogen bonds, generating ribbons propagating along the c-axis direction. The intermolecular interactions were additionally investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots. They revealed that the most significant contributions to the crystal packing are from HÁ Á ÁH (48.4%), HÁ Á ÁO/OÁ Á ÁH (21.8%) and HÁ Á ÁC/CÁ Á ÁH (20.4%) contacts. Molecular orbital calculations providing electron-density plots of HOMO and LUMO molecular orbitals and molecular electrostatic potentials (MEP) were also computed, both with the DFT/B3LYP/6-311 G++(d,p) basis set.
Chemical context
Pyridazinone derivatives are important biologically active heterocyclic compounds (Dubey et al., 2015; Akhtar et al., 2016) , which have been the subject of many studies because of their widespread biological activities, such as inflammatory (Barberot et al., 2018) , antibacterial (El-Hashash et al., 2014) , antidepressant (Boukharsa et al., 2016) , antihypertensive (Demirayak et al., 2004) , anti-HIV (Li et al., 2013) , anticonvulsant (Partap et al., 2018) , and their use as herbicidal agents (Asif, 2013) . In addition, it has been shown that pyridazinones are good corrosion inhibitors (Chetouani et al., 2003) and that they can be used as organic extractants of certain metal ions in the aqueous phase . ISSN 2056-9890 In a continuation of our investigations of the molecular structures and Hirshfeld surfaces of new pyridazinone derivatives (Daoui et al., 2019a,b) , we report herein on the synthesis and crystal and molecular structures of the title compound, 2-[5-(4-methylbenzyl)-6-oxo-3-phenyl-1,6-dihydropyridazin-1-yl]acetic acid, as well as the analysis of the Hirshfeld surfaces.
Structural commentary
The molecule structure of the title compound is shown in Fig. 1 . The phenyl (C1-C6) and pyridazine (C7-C10/N1/N2) rings are twisted relative to each other, making a dihedral angle of 10.55 (12) . The 4-methylbenzl ring (C14-C19) is inclined to the pyridazine ring by 72.97 (10) . Atoms C9 and C10 of the pyridazine ring show the largest deviations from planarity (r.m.s. deviation = 0.0075 Å ) in positive and negative directions [C10 = 0.0127 (11) Å and C9 = À0.0090 (11) Å ]. The O3 C10 bond length of the pyridazinone carbonyl function is 1.2433 (19) Å and the N1-N2 bond length in the pyridazine ring is 1.3516 (19) Å , both in accordance with values reported for related pyridazinones Xu et al., 2005) .
Supramolecular features
In the crystal, molecules are linked by pairs of O-HÁ Á ÁO hydrogen bonds, forming inversion dimers with an R 2 2 (14) ring motif (Table 1 and Fig. 2 ). The dimers are linked by C-HÁ Á ÁO hydrogen bonds, forming ribbons that extend along the c-axis direction ( Table 1 and Fig. 2 ). There are no other significant intermolecular interactions present. Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1; Ày þ 2; Àz; (ii) x; y; z þ 1.
Database survey

Figure 2
A view along the a axis of the crystal packing of the title compound. The O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds (see Table 1 ) are shown as dashed lines. For clarity, only H atoms H2 and H3 (grey balls) have been included.
Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.
Figure 1
viz. ethyl {5-[(3-chlorophenyl)methyl]-6-oxo-3-phenylpyridazin-1(6H)-yl}acetate (FODQUN; El Kalai et al., 2019a) and ethyl 3-methyl-6-oxo-5-[3-(trifluoromethyl)phenyl]-1,6-dihydro-1-pyridazineacetate (QANVOR; Xu et al., 2005) .
Figure 1
In FODQUN, the phenyl ring and the pyridazine ring are inclined to each other by 17.41 (13) , whereas the 3-chlorophenyl ring is nearly orthogonal to the pyridazine ring with a dihedral angle of 88.19 (13) . In the crystal, C-HÁ Á ÁO hydrogen bonds generate inversion dimers with an R 2 2 (10) ring motif. The dimers are linked by further C-HÁ Á ÁO hydrogen bonds, enclosing R 2 2 (20) ring motifs, forming ribbons, similar to the situation in the crystal of the title compound. Weak intermolecular C-HÁ Á Á interactions andinteractions are also observed in the crystal structure.
Figure 1
In QANVOR, the phenyl and pyridazinone rings are approximately coplanar with a dihedral angle of 4.84 (14) . In the crystal, inversion-related molecules form dimers through non-classical C-HÁ Á ÁO hydrogen bonds. The dimers are linked by a number of C-HÁ Á ÁF hydrogen bonds, forming a three-dimensional structure.
Hirshfeld surface analysis
Hirshfeld surface analysis was used to quantify the intermolecular contacts of the title compounds, using the software CrystalExplorer17.5 (Turner et al., 2017) . The Hirshfeld surfaces were calculated using a standard (high) surface resolution with the three-dimensional d norm surfaces plotted over a fixed colour scale of À0.7290 (red) to 1.4764 (blue) a.u.. The Hirshfeld surfaces of the title compound were mapped over d norm , shape index and curvedness, and are shown in Fig. 3a -c.
Hirshfeld surface analysis
The overall two-dimensional fingerprint plot and those delineated into HÁ Á ÁH, HÁ Á ÁC/ CÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁN/ NÁ Á ÁH and CÁ Á ÁC contacts are illustrated in Fig. 4a -f, respectively. The HÁ Á ÁH interaction makes the largest contribution (48.4%) to the overall crystal packing. The pair of wings in the fingerprint plot delineated into HÁ Á ÁC/CÁ Á ÁH contacts, which contribute 20.4% to the Hirshfeld surface, have a nearly symmetrical distribution of points with the tips at d e + d i $2.70 Å . HÁ Á ÁO/OÁ Á ÁH contacts make a 21.8% contribution to the Hirshfeld surface. The contacts are represented by a pair of sharp spikes in the region d e + d i $1.64 Å in the fingerprint plot, Fig. 4d . The HÁ Á ÁO/OÁ Á ÁH contacts arise from intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonding ( Table 2 ). The contributions of the other contacts to the Hirshfeld surface are negligible, i.e. HÁ Á ÁN/ NÁ Á ÁH of 4.1% and CÁ Á ÁC of 4.0%.
Frontier molecular orbital analysis
The energy levels for the title compound were computed theoretically via density functional theory (DFT) using the standard B3LYP functional and 6-311 G++ (d,p) basis-set calculations (Becke, 1993) as implemented in GAUSSIAN 09 (Frisch et al., 2009) . The HOMO (highest occupied molecular orbital) acts as an electron donor and the LUMO (lowest occupied molecular orbital) as an electron acceptor. When the energy gap is small, the molecule is highly polarizable and has high chemical reactivity. The energy levels, energy gaps, hardness (), softness () and electronegativity () are given in Table 2 . The electron transition from the HOMO to the LUMO energy level is shown in Fig. 5 . The chemical hardness and softness of a molecule is a sign of its chemical stability. From the HOMO-LUMO energy gap, we can see whether or not the molecule is hard or soft. If the energy gap is large, the molecule is hard and if small the molecule is soft. Soft molecules are more polarizable than hard ones because they need less energy for excitation. Therefore, from Table 2 we conclude that the title compound can be classified as a hard material with a HOMO-LUMO energy gap of 4.3585 eV.
Molecular electrostatic potentials
Molecular electrostatic potential (MEP) displays molecular size and shape as well as positive, negative and neutral electrostatic potential regions in terms of colour grading and is useful in investigating relationships between molecular structure and physicochemical properties (Murray & Sen, 1996; Scrocco & Tomasi, 1978) . The MEP map (Fig. 6 ) was calculated at the B3LYP/6-311 G++ (d,p) level of theory. The red and blue-coloured regions indicate nucleophiles (electron rich) and electrophile regions (electron poor), respectively. The white regions indicate neutral atoms. In the title molecule, the red regions are concentrated at the carbonyl group. It possesses the most negative potential and is thus the strongest repulsion site (electrophilic attack). The blue regions indicate the strongest attraction regions, which are occupied mostly by hydrogen atoms.
Synthesis and crystallization
A suspension of ethyl 2-[5-(4-methylbenzyl)-6-oxo-3-phenylpyridazin-1(6H)-yl]acetate (3.6 mmol), and 6 N NaOH (14.4 mmol) in ethanol (50 ml) was stirred at 353 K for 4 h. The mixture was then concentrated in vacuo, diluted with cold water, and acidified with 6 N HCl. The final product was filtered off with suction and recrystallized from ethanol. Yellow prismatic crystals were obtained by slow evaporation of the solvent at room temperature.
Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 . The hydrogen atoms were fixed geometrically (O-H = 0.82 Å , C-H = 0.93-0.96 Å ) and allowed to ride on their parent atoms with U iso (H) = 1.5U eq (O, C-methyl) and 1.2U eq (C) for other H atoms. For atoms C17-C20, SIMU, DELU and ISOR commands were used (SHELXL; Sheldrick, 2015b) . Theoretical molecular electrostatic potential surface for the title compound, calculated using the DFT/B3LYP/6-311 G++ (d,p) basis set. 
Figure 5
Molecular orbital energy levels of the title compound. Hirshfeld surface analysis and DFT studies of 2-[5-(4-methylbenzyl)-6-oxo-3-phenyl-1,6-dihydropyridazin-1-yl] (Macrae et al., 2008) and PLATON (Spek, 2009 ); software used to prepare material for publication: WinGX (Farrugia, 2012) , SHELXL2018 (Sheldrick, 2015b) ,
Figure 5
PLATON (Spek, 2009 ) and publCIF (Westrip, 2010) . 
2-[5-(4-Methylbenzyl)-6-oxo-3-phenyl-1,6-dihydropyridazin-1-yl]acetic acid

Data collection
Stoe IPDS 2 diffractometer Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus Plane graphite monochromator Detector resolution: 6.67 pixels mm -1 rotation method scans where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.12 e Å −3 Δρ min = −0.14 e Å −3 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.
Data collection
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 ) (10) 0.0601 (7) 0.0214 (7) 0.0150 (6) 0.0325 (6) O3 0.0785 (8) 0.1010 (10) 0.0580 (7) 0.0288 (7) 0.0140 (6) 0.0293 (7) O1 0.0939 (10) 0.1310 (12) 0.0796 (9) 0.0267 (9) 0.0331 (8) 0.0589 (9) N2 0.0532 (8) 0.0909 (10) 0.0664 (9) 0.0154 (7) 0.0119 (7) 0.0379 (8) N1 0.0535 (8) 0.0864 (10) 0.0657 (9) 0.0138 (7) 0.0053 (7) 0.0312 (8) C8 0.0572 (9) 0.0719 (11) 

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