Crystal structures and Hirshfeld surface analyses of 4-benzyl-6-phenyl-4,5-dihydropyridazin-3(2H)-one and methyl 2-[5-(2,6-dichlorobenzyl)-6-oxo-3-phenyl-1,4,5,6-tetrahydropyridazin-1-yl]acetate

In each asymmetric unit of the title compounds, one independent molecule is present. In the crystal structure of 4-benzyl-6-phenyl-4,5-dihydropyridazin-3(2H)-one, adjacent molecules are linked by a pair of N—H⋯O hydrogen bonds, forming inversion dimers with an (8) ring motif. The crystal structure of methyl 2-[5-(2,6-dichlorobenzyl)-6-oxo-3-phenyl-1,6-dihydro-pyridazin-1-yl]acetate displays intermolecular C—H⋯O interactions.


Chemical context
Pyridazines are an important family of six-membered aromatic heterocycles (Akhtar et al., 2016). The chemistry of pyridazinones has been an interesting field of research for decades and this nitrogen-containing heterocycle has become a scaffold of choice for the development of potential drug candidates (Dubey & Bhosle, 2015). Pyridazinone is an important pharmacophore possessing a wide range of biological applications (Asif, 2014). A review of the literature revealed that substituted pyridazinones have received a lot of attention in recent years because of their significant potential as antimicrobial (Sö nmez et al., 2006), antihypertensive (Siddiqui et al., 2011), antidepressant (Boukharsa et al., 2016), anti-HIV (Livermore et al., 1993) and anti-inflammatory (Barberot et al., 2018) agents.

Hirshfeld surface analysis
Hirshfield surface analyses (Spackman & Jayatilaka, 2009) were carried out using CrystalExplorer (Version 17.5; Turner et al., 2017). The Hirshfeld surfaces and their associated twodimensional fingerprint plots were used to quantify the various intermolecular interactions in the structures of the title compounds. Calculations of the molecular Hirshfeld surfaces (HS) were performed using a standard (high) surface resolution with the three-dimensional d norm surfaces mapped over a fixed colour scale of À0.6062 (red) to 1.3165 a.u. (blue) for (I) and of À0.2803 (red) to 1.5329 a.u. (blue) for (II). The red spots on the surface indicate the contacts involved in hydrogen bonding. Fig. 5(a) illustrates the intermolecular N-HÁ Á ÁO hydrogen bonding in (I), with d norm mapped on the Hirshfeld surface. Likewise, C-HÁ Á ÁO hydrogen bonding is visualized in Fig. 5(b) for compound (II). Fig. 6 shows the two-dimensional fingerprint plot of the sum of the contacts contributing to the Hirhsfeld surface of compound (I), represented in normal mode. HÁ Á ÁH contacts clearly make the most significant contribution to the Hirshfeld surface (48.2%). A significant contribution of HÁ Á ÁH interactions to the total HS (72.2%) was also reported by Ilmi et al. (2019) for a similar compound. In addition, CÁ Á ÁH/HÁ Á ÁC and OÁ Á ÁH/HÁ Á ÁO contacts contribute 29.9 and 8.9%, respectively, to the Hirshfeld surface. In particular, the OÁ Á ÁH/HÁ Á ÁO contacts indicate the presence of intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO interactions.
Similarly, Fig. 7 illustrates the two-dimensional fingerprint plot of the sum of the contacts contributing to the Hirhsfeld surface of compound (II). The HÁ Á ÁH interactions appear in the middle of the scattered points in the two-dimensional fingerprint plots, with a contribution to the overall Hirshfeld surface of 34.4% (Fig. 7b). The contributions (16.5%) from the OÁ Á ÁH/HÁ Á ÁO contacts, corresponding to the C-HÁ Á ÁO interactions, are represented by a pair of sharp spikes characteristic of such hydrogen bonding (Fig. 7d).

Synthesis and crystallization
For the preparation of compound (I), sodium hydroxide (0.5 g, 3.5 mmol) was added to a solution (0.15 g, 1 mmol) of 6-phenyl-4,5-dihydropyridazin-3(2H)-one and benzaldehyde (0.11 g, 1 mmol) in 30 ml of ethanol. The solvent was evaporated under vacuum and the residue was purified by silica-gel column chromatography using hexane/ethyl acetate (7:3 v/v). Colourless single crystals were obtained by slow evaporation at room temperature.   For the preparation of compound (II), potassium carbonate (0.50 g, 3.5 mmol) was added to a solution (0.83 g, 2.5 mmol) of 4-(2,6-dichlorobenzyl)-6-phenylpyridazin-3(2H)-one in 30 ml of tetrahydrofuran (THF). The mixture was refluxed for 1 h. After cooling, ethyl bromoacetate (0.50 g, 3 mmol) was added and the mixture was refluxed for 8 h. The solid material which formed was removed by filtration and the solvent evaporated in vacuo. The residue was purified by silica-gel column chromatography using hexane/ethyl acetate (4:6 v/v). Slow evaporation at room temperature led to colourless single crystals.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For the structure of compound (I), the N-bound H atom was located in a difference Fourier map and refined with N-H = 0.86 Å . For the refinement of structure (II), reflections with a angle greater than 28 were omitted from the refinement due to their very weak intensities. The methoxy group (O3-C20) in this compound was found to be disordered over two sets of sites and was refined with an occupancy ratio of 0.626 (11):0.374 (11) (SIMU, DELU and ISOR commands in SHELX; Sheldrick, 2015b). For both structures, the C-bound H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.97 Å and U iso (H) = 1.5U eq (C) for methyl H atoms or 1.2U eq (C) otherwise.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1 0.62706 (11) 0.40510 (10)   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.96 e Å −3 Δρ min = −0.28 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.    (7)