(E)-5-[1-Hydroxy-3-(3,4,5-trimethoxyphenyl)allylidene]-1,3-dimethylpyrimidine-2,4,6-trione: crystal structure and Hirshfeld surface analysis

In the title compound, C—H⋯O hydrogen bonds and aromatic π–π stacking combine to generate a three-dimensional network. A Hirshfeld surface analysis is presented.

In the title compound, C 18 H 20 N 2 O 7 , the dihedral angle between the aromatic rings is 7.28 (7) and the almost planar conformation of the molecule is supported by an intramolecular O-HÁ Á ÁO hydrogen bond, which closes an S(6) ring. In the crystal, weak C-HÁ Á ÁO hydrogen bonds and aromaticstacking link the molecules into a three-dimensional network. A Hirshfeld surface analysis showed that the major contribution to the intermolecular interactions are van der Waals interactions (HÁ Á ÁH contacts), accounting for 48.4% of the surface.

Chemical context
Bartituric acid derivatives are of interest due to their potential biological applications (Bojarski et al., 1985;Patrick, 2009). These compounds have materials science appplications due to the properties generated by -conjugation, such as push-pull chromophores (Klikar et al., 2013;Seifert et al., 2012). The chemical structures of these derivatives show five potential metal-binding sites, which makes them versatile ligands for the construction of coordination and supramolecular compounds (Mahmudov et al., 2014), also important in organic synthesis, where they are largely used as substrates for Morita-Baylis-Hilmann and Diels-Alder reactions (Goswami & Das, 2009). Herein we report the crystal structure and Hisrshfeld surface analysis of (E)-5-[1-hydroxy-3-(3,4,5-trimethoxyphenyl)allylidene]-1,3-dimethylpyrimidine-2,4,6-trione (I), which presents potential applications in the study of the photophysical properties of different isomers for the development of supramolecular structures.

Hirshfeld surfaces analysis
The Hirshfeld surface analysis shows the potential intermolecular contacts. Convex blue regions represent hydrogendonor groups and concave red regions represent hydrogenacceptor groups (Hirshfeld, 1977;McKinnon et al., 2004). In this case, the main donor groups are the methyl groups and the acceptor groups are the O atoms. The region ofinter- The molecular structure of (I), showing 50% probability displacement ellipsoids.

Synthesis and crystallization
The title compound was prepared according to the literature procedure of Gorovoy et al. (2014). A mixture of 3,4,5-trimethoxybenzaldehyde and 5-acetyl-1,3-dimethylbarbituric acid was melted at 453 K and 2-3 drops of piperidine were added under constant stirring. After 5 min, the mixture solidified, providing a yellow powder, which was allowed to cool to room temperature. The solid residue was boiled in ethanol (20 ml) for a few minutes and the precipitate was filtered off by vacuum suction. The filtrate was left at room temperature, yielding yellow needles of the title compound after three weeks.

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.