Polymorphism of 2-(5-benzyl-6-oxo-3-phenyl-1,6-dihydropyridazin-1-yl)acetic acid with two monoclinic modifications: crystal structures and Hirshfeld surface analyses

The molecules of the two title polymorphs mainly differ in the orientation of the carboxylic OH group that results in different packing features.

Two polymorphs of the title compound, C 19 H 16 N 2 O 3 , were obtained from ethanolic (polymorph I) and methanolic solutions (polymorph II), respectively. Both polymorphs crystallize in the monoclinic system with four formula units per cell and a complete molecule in the asymmetric unit. The main difference between the molecules of (I) and (II) is the reversed position of the hydroxy group of the carboxylic function. All other conformational features are found to be similar in the two molecules. The different orientation of the OH group results in different hydrogen-bonding schemes in the crystal structures of (I) and (II). Whereas in (I) intermolecular O-HÁ Á ÁO hydrogen bonds with the pyridazinone carbonyl O atom as acceptor generate chains with a C(7) motif extending parallel to the b-axis direction, in the crystal of (II) pairs of inversionrelated O-HÁ Á ÁO hydrogen bonds with an R 2 2 (8) ring motif between two carboxylic functions are found. The intermolecular interactions in both crystal structures were analysed using Hirshfeld surface analysis and two-dimensional fingerprint plots.

Structural commentary
The title compound is dimorphic with two monoclinic polymorphs. The molecular structure of polymorph (I) is shown in Fig. 1 and that of polymorph (II) in Fig. 2. The differences in the conformations of the two molecules is shown in the structural overlap drawing (Fig. 3). The main difference between (I) and (II) pertains to the OH function of the carboxyl group, which is reversed in the two molecules. All other conformational features are quite similar in the molecules of the two polymorphs. In (I), the phenyl ring (C1-C6) and the pyridazine ring (N1/N2/C10-C7) are nearly co-planar, making a dihedral angle of 5.92 (2) whereas the phenyl ring of the benzyl group (C14-C19) is perpendicular to the pyridazine ring, with a dihedral angle of 89.91 (1) (Fig. 1). In (II), the corresponding values are 15.44 (2) and 89.13 (1) , respectively. In the molecule of (I), the carboxyl group has a C12-O2 bond length of 1.277 (2) Å between the C atom and the OH function, and the C12 O3 bond length of the carbonyl group is 1.187 (2)   The molecular structure of (II) with displacement ellipsoids drawn at the 30% probability level.

Figure 1
The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level.

Figure 3
Structural overlap of molecules (I) and (II). bond lengths of the two carboxylic groups can be attributed to their different roles in intermolecular hydrogen bonding (see below). In both molecules, weak intramolecular hydrogen bonds [C-HÁ Á ÁN for (I) and C-HÁ Á ÁO for (II); Figs. 1 and 2, Tables 1 and 2] stabilize the molecular conformation.

Figure 4
The crystal packing of (I). The O-HÁ Á ÁO hydrogen bonds are shown as blue dotteded lines, andcontacts are represented by green dotted lines. For clarity, only H atoms involved in hydrogen bonding (white sticks) were included.

Figure 5
The crystal packing of (II), with O-HÁ Á ÁO and C-HÁ Á ÁO interactions shown as blue and black dotted lines, respectively.

Hirshfeld surface analysis
Hirshfeld surface analysis was applied to quantify the intermolecular contacts in (I) and (II), using CrystalExplorer17.5   (a) The Hirshfeld surface of (I) mapped over d norm , and plotted in the range À0.7266 (red) to 1.4843 (blue) a.u.; (b) the Hirshfeld surface mapped over shape-index; (c) the Hirshfeld surface mapped over curvedness.

Synthesis and crystallization
A suspension of ethyl 2-(5-benzyl-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 by suction filtration and recrystallized from ethanol or methanol. Single crystals of (I) were obtained by slow evaporation of an ethanolic solution at room temperature, and single crystals of (II) were obtained by slow evaporation of a methanolic solution at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The atom labelling for molecules of (I) and (II) is identical. In the refinement of (I), SIMU, DELU and ISOR commands were used for atoms C12 and O3. For both structures, hydrogen atoms of the carboxylic group were located in a difference-Fourier map and were refined with a fixed O-H distance of 0.82 Å and with U iso (H) = 1.5U eq (O). All other hydrogen atoms were placed in calculated positions, with C-H = 0.93-0.96 Å and allowed to ride on their parent atoms with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other H atoms.
Acta Cryst. (2020). E76, 432-437 research communications      where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.35 e Å −3 Δρ min = −0.34 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.