(2Z)-3-Hydroxy-1-(pyridin-2-yl)-3-(pyridin-3-yl)prop-2-en-1-one: crystal structure and Hirshfeld surface analysis

The title molecule, featuring an intramolecular O—H⋯O hydrogen bond, is non-planar as seen in the dihedral angle between the pyridyl rings of 7.45 (7)°. In the crystal, supramolecular chains are formed via π(pyridin-2-yl)–π(pyridin-3-yl) interactions.


Chemical context
The -diketonates of virtually all metals are known (Lamprey, 1960) because of the stability of the resulting six-membered metallocycle formed from bidentate coordination through the two oxygen atoms and the ability of the ligand to be accommodated within the common octahedral, tetrahedral and square-pyramidal coordination geometries. There has been an interest over the last few years to introduce extra donor functionality such as nitrile and pyridyl to this class of ligand to generate heterometallic complexes and novel coordination networks. Dipyridyl -diketonates, for example, have been used to synthesize mixed-metal-organic frameworks. Burrows and co-workers employed di(pyridin-4-yl)propane-1,3-dione to prepare the corresponding Al III and Ga III octahedral building blocks for network structures linked by Ag I ions (Burrows et al., 2010). Carlucci and co-workers used the same ligand to make Fe III metalloligands that were again joined by coordination to Ag I ions. The type of the resulting two-or three-dimensional coordination polymer depended on the nature of the counter-ion to silver (Carlucci et al., 2011). By comparison, the di(pyridin-2-yl)propane-1,3-dione ligand, which also has extra donor functionality available for coordination, is sterically hindered to allow network formation. Tan and co-workers prepared the Cd II and Cu II complexes from this ligand and did indeed observe chelation through the 2,2 0nitrogen atoms (Tan et al., 2012). However, they did not observe solid-state network formation from bridging oxygen-atom, 2 -Cl or 3 -Cl donors in the Cd II complexes; the Cu II complex was a tetranuclear oligomer linked via bridging water and acetate counter-ions (Tan et al., 2012). Less work has been performed with the unsymmetrical pyridyl -diketonates. Zhang and co-workers have made the Fe III salt of 3-(pyridin-4yl)-2,4-pentanedione as well as the mixed-MOF with AgNO 3 in a two-dimensional honeycomb structure while at higher Ag I concentrations, a one-dimensional ladder motif was formed (Zhang et al., 2008). This ligand and the symmetrical 4,4 0 -and 3,3 0 -variants have been treated with hydrazine to give the corresponding pyrazoles that were used to prepare strongly photoluminescent Cu I coordination polymers (Zhan et al., 2011).
All of the mentioned dipyridyl ligands can be conveniently prepared by the Claisen condensation of an acetylpyridine with a pyridine carboxylic ester. The title compound, (I), has not previously been reported, but was prepared in this way from 2-acetylpyridine and ethyl nicotinate, and crystals suitable for X-ray crystallography were obtained by recrystallization from a mixture of dichloromethane and hexane. Herein, the crystal structure analysis of (I) is described along with a detailed investigation of the molecular packing by a Hirshfeld surface analysis.
the C-C bonds in the rings confirm their assignment. The central C 3 O 2 residual in (I), Fig. 1, is essentially planar with the r.m.s. deviation of the five atoms being 0.0095 Å . The syn arrangement of the oxygen atoms enables the formation of an intramolecular hydroxy-O-HÁ Á ÁO(carbonyl) hydrogen bond, Table 1. The dihedral angles formed between the central plane and the N1-and N2-pyridinyl rings are 8.91 (7) and 15.88 (6) , respectively, indicating twists in the molecule. The dihedral angle between the pyridyl rings is 7.45 (7) . The conformation about the C2 C3 [1.3931 (17) Å ] is Z, and, to a first approximation, the N1 and N2 atoms lie to the same side of the molecule.

Supramolecular features
The molecular packing in the crystal is dominated byinteractions formed between the N1-and N2-pyridinyl rings of translationally related molecules [Cg(N1-pyridinyl)Á Á ÁCg(N2pyridinyl) = 3.7662 (9) Å , angle of inclination = 7.45 (6)  The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level. Table 1 Hydrogen-bond geometry (Å , ). (14) 160 ( A view of the Hirshfeld surface mapped over electrostatic potential for (I). The red and blue regions represent negative and positive electrostatic potentials, respectively.

Figure 4
Two views of the Hirshfeld surface mapped over d norm for (I): the brightred spots at (a) C5 and (b) C10 indicate their involvement in short intermolecular CÁ Á ÁC contacts.

Figure 5
The two-dimensional fingerprint plots for (I): (a) all interactions, and From the Hirshfeld surface mapped over electrostatic potential, Fig. 3, the negative potentials around the oxygen atoms of the hydroxy and carbonyl groups as well as about the nitrogen atoms of pyridyl rings prevent their participation in intermolecular interactions in the crystal of (I) due to the electrostatic repulsion that would eventuate. The presence of a short intermolecular CÁ Á ÁC contact between the C5 and C10 atoms [C5Á Á ÁC10 = 3.313 (2) Å ; symmetry code: À1 + x, y, z], which fall within thecontacts between pyridyl rings (Fig. 2a), is viewed as bright-red spots near these atoms on the Hirshfeld surface mapped over d norm , Fig. 4.
The overall 2D fingerprint plot, Fig. 5a, and those delineated into HÁ Á ÁH, CÁ Á ÁC, OÁ Á ÁH/HÁ Á ÁO, CÁ Á ÁH/HÁ Á ÁC and NÁ Á ÁH/HÁ Á ÁN contacts are illustrated in Fig. 5b-f, respectively; their relative contributions to the surface are quantified in Table 2. The interatomic HÁ Á ÁH contacts (McKinnon et al., 2007) appear as the scattered points over the greater part of the plot shown in Fig. 5b, with a single peak at (d e , d i ) less than the van der Waals separation corresponding to a short H13Á Á ÁH13 contact of 2.33 Å (symmetry code: 1 À x, Ày, Àz). The short interatomic C5Á Á ÁC10 contact andstacking interactions appear as an arrow-like distribution of points with the tip at d e + d i $ 3.3 Å (Fig. 5c). The presence ofstacking interactions between the pyridyl rings is also apparent from the appearance of red and blue triangle pairs on the Hirshfeld surface mapped with shape-index property identified with arrows in the image of Fig. 6, and in the flat region on the Hirshfeld surface mapped over curvedness in Fig. 7.
The two-dimensional fingerprint plots delineated into OÁ Á ÁH/HÁ Á ÁO, CÁ Á ÁH/HÁ Á ÁC and NÁ Á ÁH/HÁ Á ÁN interactions exhibit their usual characteristic features in their respective plots; Fig. 4d-f. However, the points are distributed at (d e , d i ) distances greater than their respective van der Waals separations. This is consistent with the repulsion between the atoms having electrostatic negative potential dominating the molecular packing, hence the lack of specific intermolecular interactions between supramolecular chains.  Table 3 Dihedral angle ( ) data for (I)-(III). Notes: (a) Groom et al. (2016); (b) isolated as a 1:1 co-crystal with benzoic acid.

Figure 6
A view of the Hirshfeld surface mapped with shape-index property for (I). The red and blue triangles identified with arrows indicatestacking interactions.

Figure 7
A view of the Hirshfeld surface mapped over curvedness for (I). The flat regions highlight the involvement of rings in thestacking interactions.

Figure 8
Overlay diagram of molecules of (I) (red image), (II) (green) and (III) (blue). The molecules have been overlapped so that the central fivemembered rings are coincident.

Synthesis and crystallization
2-Acetylpyridine (3.0562 g, 25.2 mmol) was added to a suspension of NaH (60% dispersion in mineral oil, 2.0058 g, 50.0 mmol) in anhydrous THF (10 ml) at room temperature with stirring. Ethyl nicotinate (7.5675g, 50.1 mmol) in anhydrous THF (10ml) was added dropwise to the mixture over 3 min. The yellow mixture was refluxed under a nitrogen atmosphere for 1.3 h and then quenched with ice-water (50 ml). Glacial acetic acid was added to adjust the pH to 6-7.

(2Z)-3-Hydroxy-1-(pyridin-2-yl)-3-(pyridin-3-yl)prop-2-en-1-one
Crystal data 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.