crystal structures of 3,5-bis[(e)-3-hydroxybenzylidene]-1-methylpiperidin-4-one and 3,5-bis[(e)-2-chlorobenzylidene]-1-methylpiperidin-4-one

The title compounds, C20H19NO3, (1), and C20H17Cl2NO, (2), are the 3-hydroxybenzylidene and 2-chlorobenzylidene derivatives, respectively, of curcumin [systematic name: (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione]. The dihedral angles between the benzene rings in each compound are 21.07 (6)° for (1) and 13.4 (3)° for (2). In both compounds, the piperidinone rings adopt a sofa confirmation and the methyl group attached to the N atom is in an equatorial position. In the crystal of (1), two pairs of O—H...N and O—H...O hydrogen bonds link the molecules, forming chains along [10-1]. The chains are linked via C—H...O hydrogen bonds, forming undulating sheets parallel to the ac plane. In the crystal of (2), molecules are linked by weak C—H...Cl hydrogen bonds, forming chains along the [204] direction. The chains are linked along the a-axis direction by π–π interactions [inter-centroid distance = 3.779 (4) Å]. For compound (2), the crystal studied was a non-merohedral twin with the refined ratio of the twin components being 0.116 (6):0.886 (6).