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, C(20)H(19)NO(3), (1), and C(20)H(17)Cl(2)NO, (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).