Different classical hydrogen-bonding patterns in three salicylaldoxime derivatives, 2-HO-4-XC6H3C=NOH (X = Me, OH and MeO)

Abstract

The crystal structures of three salicyaldoxime compounds, namely 2-hydroxy-4-methylbenzaldehyde oxime, C8H9NO2, 1, 2,4-dihydroxybenzaldehyde oxime, C7H7NO3, 2, and 2-hydroxy-4-methoxybenzaldehyde oxime, C8H9NO3, 3, are discussed. In each compound, the hydroxyl groups are essentially coplanar with their attached phenyl group. The interplanar angles between the C=N—O moieties of the oxime unit and their attached phenyl rings are 0.08 (9), 1.08 (15) and 6.65 (15)° in 1, 2 and 3, respectively. In all three molecules, the 2-hydroxy group forms an intramolecular O—H...N(oxime) hydrogen bond. In compound (1), intermolecular O—H(oxime)...O(hydroxyl) hydrogen bonds generate R 2 2(14) dimers, related by inversion centres. In compound 2, intermolecular O—H(oxime)...O(4-hydroxy) hydrogen bonds generate C9 chains along the b-axis direction, while O—H(4-hydroxyl)...O(2-hydroxyl) interactions form zigzag C6 spiral chains along the c-axis direction, generated by a screw axis at 1, y, 1/4: the combination of the two chains provides a bimolecular sheet running parallel to the b axis, which lies between 0–1/2 c and 1/2–1 c. In compound 3, similar C9 chains, along the b-axis direction are generated by O—H(oxime)...O(4-methoxy) hydrogen bonds. Further weaker, C—H...π (in 1), π–π (in 2) and both C—H...π and π–π interactions (in 3) further cement the three-dimensional structures. Hirshfeld surface and fingerprint analyses are discussed.