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)degrees for (1) and 13.4 (3)degrees 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 center dot center dot center dot N and O-H center dot center dot center dot O hydrogen bonds link the molecules, forming chains along [10 (1) over bar]. The chains are linked via C-H center dot center dot center dot O hydrogen bonds, forming undulating sheets parallel to the ac plane. In the crystal of (2), molecules are linked by weak C-H center dot center dot center dot Cl hydrogen bonds, forming chains along the [204] direction. The chains are linked along the a-axis direction by pi-pi interactions [inter-centroid distance = 3.779 (4) angstrom]. 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).