Synthesis, characterization and supramolecular analysis for (E)-3-(pyridin-4-yl)acrylic acid

In the title compound, the pyridine ring is fused to acrylic acid, forming an almost planar structure with an E-configuration about the double bond. In the crystal, O—H⋯N and C—H⋯O interactions together with π–π stacking interactions lead to the formation of the three-dimensional structure.


Chemical context
Cinnamic acid and its derivatives have been used in several applications related to medicinal chemistry (Deng et al., 2023), organic synthesis (Chen et al., 2020), and coordination chemistry (Zhou et al., 2016).Cinnamic acids are reactive molecules due to possessing an unsaturated carbonyl moiety, which can be considered a Michael acceptor and benzene ring.Both make it possible to modify them, resulting in synthetic cinnamic acid derivatives with a broad range of biological properties, including antibacterial (Ruwizhi & Aderibigbe, 2020) antituberculosis (Teixeira et al., 2020), antimalarial (Fonte et al., 2023), antidiabetic (Adisakwattana, 2017;Feng et al., 2022), anticancer (Feng et al., 2022), antifungal (Liu et al., 2024), Alzheimer's treatment (Drakontaeidi & Pontiki, 2024), antioxidant (Nouni et al., 2023), and cosmetic (Gunia- Krzyz ˙ak et al., 2018).Among the various types of cinnamic acids documented, 4-pyridylacrylic acid (4-Hpya) is considered a highly valuable ligand because of several structural characteristics that make it suitable for the construction of coordination compounds.These characteristics include multiple coordination sites, which enable the formation of higher-dimensional structures, and versatile coordination modes to form different structures (Khalfaoui et al., 2021).On the other hand, its capacity to function as both a hydrogenbond donor and acceptor facilitates the creation of intricate hydrogen-bonded networks (Jiao et al., 2007;Zhu et al., 2005).

Structural commentary
The title compound crystallizes in space group P1 with one molecule per asymmetric unit (Fig. 1).The pyridinic ring is fused to acrylic acid, forming an almost planar structure with an E-configuration about the double bond, with a C8-C4-C3-C2 torsion angle of À 6.1 (2) � .
A Hirshfeld surface analysis was performed to confirm, visualise and quantify the supramolecular interactions present in title compound.The Hirshfeld surface mapped over d norm and 2D fingerprint plots (Spackman & Jayatilaka, 2009) were generated using Crystal Explorer 17 (Spackman, et al., 2021).Fig. 3 shows the strongest interactions as red spots.These are associated with the donor and acceptor atoms, in this case for the O-H� � �N interaction.The weakest interactions, associated with the C-H� � �O contacts, are shown as white areas.
These interactions were quantified through the fingerprint plots, indicating that the most abundant contacts are associated with H� � �H interactions (36.2%) while O� � �H/H� � �O, N� � �H/H� � �N and C� � �H/H� � �C interactions represent 27.8%, 8.7% and 10.7%, respectively.These results show that crystal packing is governed mainly by dispersion and electrostatic interactions.

Figure 3
Hirshfeld surface and fingerprint plot analysis for the title compound.

Synthesis and crystallization
The synthesis of (E)-3-(pyridin-4-yl)acrylic acid compound was performed following the procedure reported by Kudelko et al. (2015) for the synthesis of 3-(pyridyl)acrylic acids (Fig. 4).In a 25 mL flat-bottomed flask, 728 mg of malonic acid (0.335 mmol) and 300 mg of 4-pyridincarboxyaldehyde (0.33 5 mmol) were mixed with 2 ml of pyridine.The reaction mixture was refluxed under constant stirring for 3 h.The reaction synthesis was ice-cooled, and then drops of 37% HCl were added until precipitate formation was observed.The obtained solid was separated by filtration and washed with acetone.The solid product was recrystallized by slow water evaporation, giving a colourless crystalline powder and small prismatic crystals in 97.9% yield.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.The O-bound hydrogen atom (H1) was found in electron density maps and freely refined.C-bound hydrogen atoms were positioned geometrically and refined using a riding model [C-H = 0.93 A ˚, U iso (H) = 1.2U eq (C)].

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
Figure 1

Figure 2
Figure 2 Supramolecular interactions in the title compound.(a) O-H� � �N interactions forming chains, (b) two chains joined by C-H� � �O interactions and (c) �-� stacking interactions between the pyridine rings and the acrylic group.