Crystal structure and Hirshfeld surface analysis of (Z)-2-amino-4-(2,6-dichlorophenyl)-5-(1-hydroxyethylidene)-6-oxo-1-phenyl-1,4,5,6-tetrahydropyridine-3-carbonitrile

The molecular conformation of the title compound is stabilized by an intramolecular O—H⋯O hydrogen bond, forming an S(6) ring motif. Intermolecular N—H⋯N and C—H⋯N hydrogen bonds, as well as N—H⋯π and C—H⋯π interactions create a three-dimensional network in the crystal.


Chemical context
The development of effective methods for the construction of small-sized molecules bearing a nitrogen heterocycle is a very important proposition in organic synthesis and catalysis (Abdel-Hafiz et al., 2012;Gurbanov et al., 2018;Zubkov et al., 2018). As members of this family, pyridine derivatives play a key role in flavor chemistry, crystal engineering, and the development of biologically active compounds (Adams & De Kimpe, 2006;Mahmoudi et al., 2019;Mamedov et al., 2020). The pyridine core is a key bioactive fragment of diverse natural products (niacin, pyridoxine, nicotine, NADP + ) and series of derivatives constitute promising drugs in medicinal chemistry (Mohsin & Ahmad, 2018).

Figure 1
The molecular structure of the title compound showing the atomnumbering scheme and displacement ellipsoids at the 50% probability level.

Table 2
Interatomic contacts of the title compound (Å ).
The Hirshfeld surfaces were calculated and the twodimensional fingerprint plots generated using Crystal Explorer 17.5 (Turner et al., 2017). The use of various hues and intensities to represent short and long contacts, as well as the relative intensity of the connections, allows Hirshfeld surfaces to depict intermolecular interactions. Fig. 4 shows the threedimensional Hirshfeld surfaces of the title compound plotted over d norm (normalized contact distance) in the range of À0.4290 to 1.5192 a.u. The red patches that appear around N2 are caused by the intermolecular N3-H3AÁ Á ÁN2 and C16-H16Á Á ÁN2 interactions, which are important in the packing of the title molecule. Bright red dots near N2 and amine hydrogen atoms H3A and H3B highlight their functions as hydrogen-bonding acceptors and donors, respectively; these also appear as blue and red areas on the Hirshfeld surface mapped over electrostatic potential (Spackman et al., 2008) in Fig. 5, corresponding to positive and negative potentials. Positive electrostatic potential (hydrogen-bond donors) is shown in blue, whereas negative electrostatic potential is indicated in red (hydrogen-bond acceptors).

Figure 5
View of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.0500 to 0.0500 a.u. using the STO-3 G basis set at the Hartree-Fock level of theory. Hydrogen-bond donors and acceptors are shown as blue and red regions, respectively, around the atoms, corresponding to positive and negative potentials.  ClÁ Á ÁCl, OÁ Á ÁC/CÁ Á ÁO and NÁ Á ÁN contacts contribute less than 2.1% to Hirshfeld surface mapping and have little directional influence on molecular packing (Table 3).
In both the related salts, JEBRAM (space group: P1) and JEBREQ (space group: P1) , the N atom in the 1-position of the pyrimidine ring is protonated. In JEBRAM, the protonated N atom and the amino group of the pyrimidinium cation interact with the carboxylate group of the anion through N-HÁ Á ÁO hydrogen bonds, forming a heterosynthon with an R 2 2 (8) ring motif. In the hydrated salt JEBREQ, the presence of the water molecule prevents the formation of the familiar R 2 2 (8) ring motif. Instead, an expanded ring [i.e. R 3 2 (8)] is formed involving the sulfonate group, the pyrimidinium cation and the water molecule. Both salts form a supramolecular homosynthon [R 2 2 (8) ring motif] through N-HÁ Á ÁN hydrogen bonds. The molecular structures are further stabilized bystacking, and C OÁ Á Á, C-HÁ Á ÁO and C-HÁ Á ÁCl interactions. None of these are found in the crystal packing of the title compound. It appears that the protonation state of the pyrimidine ring influences the intermolecular interactions within the crystal lattices to a substantial extent.

Synthesis and crystallization
The title compound was synthesized using our previously reported procedure (Maharramov et al., 2018), and colorless prisms were obtained upon recrystallization from its methanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The positional parameters of the H atoms of the hydroxy and amine groups were determined from difference electron-density maps and were refined freely [O2-H2 = 0.86 (4) Å , N3-H3A = 0.86 (4) Å and N3-H3B = 0.88 (4)    refined using a riding model with U iso (H) set to either 1.2U eq (N) for the NH 2 group or 1.5U eq (O) for the OH group. The C-bound H atoms were positioned geometrically (C-H = 0.95-1.00 Å ) and allowed to ride on their parent atoms, with U iso (H) = 1.5U eq (C) for the methyl group and U iso (H) = 1.2U eq (C) for aromatic and methine H atoms.