Crystal structure and Hirshfeld surface analysis of ethyl 2-({5-acetyl-3-cyano-6-methyl-4-[(E)-2-phenylethenyl]pyridin-2-yl}sulfanyl)acetate

The styryl and ester substituents are displaced to opposite sides of the plane through the pyridine ring while the acetyl group is rotated well out of that plane. In the crystal, inversion-related C—H⋯O hydrogen bonds form chains extending parallel to the a-axis direction, which pack with partial intercalation of the styryl and ester substituents.


Chemical context
Numerous pyridine-containing natural products and synthetic organic compounds with various biophysio-and pharmacological activities have been reported (Gibson et al., 2007;Vidaillac et al., 2007). These scaffolds are also of widespread interest in supramolecular and coordination chemistry, as well as for materials science (Balasubramanian & Keay, 1996). The above findings promoted us to study the crystal structure of the title compound, C 21 H 20 N 2 O 3 S.

Structural commentary
The styryl substituent and the ester group are displaced to opposite sides of the plane of the pyridine ring (Fig. 1). The dihedral angle between the mean planes of the phenyl (C8-C13) and pyridine (N1/C1-C5) rings is 27.86 (3) . The C1-C2-C14-C15 torsion angle of 68.1 (2) indicates that the ISSN 2056-9890 acetyl group is rotated well out of the plane of the pyridine ring, while the N1-C4-S1-C18 torsion angle of À5. 66 (12) shows that the link to the ester group is nearly coplanar with the pyridine ring.

Supramolecular features
In the crystal, inversion dimers are formed by intermolecular C15-H15AÁ Á ÁO2 hydrogen bonds between a methyl H atom of the acetyl group and the carbonyl O atom of the ester function. These dimers are further linked by inversion-related C18-H18BÁ Á ÁO1 hydrogen bonds between a methylene H atom and the carbonyl O atom of the acetyl group (Table 1) to form ribbons of molecules extending parallel to the a-axis direction (Fig. 2). The chains pack with a partial intercalation of the styryl and ester substituents (Fig. 3).

Figure 2
A portion of one hydrogen-bonded chain in a view along the c-axis direction. C-HÁ Á ÁO hydrogen bonds are depicted by dashed lines.

Figure 3
Packing of the molecules in the title compound in a view along the b-axis direction. C-HÁ Á ÁO hydrogen bonds are depicted by dashed lines.
The title molecule with labelling scheme and displacement ellipsoids at the 50% probability level.

Figure 4
A view of the three-dimensional Hirshfeld surface for the title compound, plotted over d norm in the range À0.1607 to +1.3888 a.u. units is depicted in Fig. 4, where the red regions indicate apparent hydrogen bonds in this structure. The intensities of the red areas are greater for C15-H15AÁ Á ÁO2 and C18-H18BÁ Á ÁO1, indicating the strongest interactions as compared to other red spots on the Hirshfeld surface; Table 2 lists corresponding close intermolecular contacts. The two-dimensional fingerprint plots (Fig. 5) reveal that the largest contributions are from HÁ Á ÁH (43.6%; Fig. 5b

Database survey
A search of the Cambridge Structural Database (version 5.42, update 1, Feb 2021; Groom et al., 2016) for related structures with the 2-sulfanylpyridine-3-carbonitrile moiety of the title compound gave the following matches: ethyl 4-methyl-2phenyl-6-thioxo-1,6-dihydro-5-pyrimidinecarboxylate monohydrate (DEWCIS; Cunha et al., 2007), ethyl 4-(5-ethoxycarbonyl-6-methyl-2-phenyl-4-pyrimidinyldisulfanyl)-6-methyl-2-phenyl-5-pyrimidinecarboxylate (DEWCAK; Cunha et al., 2007), Compound DEWCIS crystallizes in the space group P2 1 /c with one molecule in the asymmetric unit. N-HÁ Á ÁO, O-HÁ Á ÁN and O-HÁ Á ÁS interactions involving the water molecules, as well asstacking interactions between the molecules along the b axis contribute to the formation of layers parallel to the bc plane. The stability of the molecular packing is achieved by van der Waals interactions between these layers. Compound DEWCAK crystallizes in the space group P1 with one molecule in the asymmetric unit. In the crystal structure of DEWCAK, there are no classical hydrogen bonds. The molecular packing is stabilized by C-HÁ Á Á interactions andstacking interactions. Compound NILKOL crystallizes in the space group P1 with one molecule in the asymmetric unit, whereas compounds NILKUR and NILLAY crystallize in the space group P2 1 /c with two and one molecules, respectively, in their asymmetric units. The conformation of each molecule is best defined by the dihedral angles formed between the pyrimidine ring and the planes of the two aryl substituents attached at the 2-and 4-positions. The only structural difference between the three compounds is the substituent at the 5-position of the pyrimidine ring, but they present significantly different features in their hydrogenbonding interactions. NILKOL displays a chain structure whereby the chains are further extended into a two-dimensional network. In NILKUR and NILLAY, the hydrogenbonded chains have no further aggregation.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-bound H atoms were refined freely, while the H atoms of the C16 methyl group were placed geometrically (C-H = 0.98 Å ) and refined as riding atoms with U iso (H) = 1.5U eq (C).  publCIF (Westrip, 2010).

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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. Independent refinement of the hydrogen atoms attached to C16 led to an unreasonable geometry so these were included as riding contributions (C-H = 0.98 Å) with an AFIX 137 instruction.