Crystal structure of a new monoclinic polymorph of 2,4-dihydroxybenzaldehyde 4-methylthiosemicarbazone

Abstract

The title compound, C9H11N3O2S, is a second monoclinic (P21/c) polymorph of the previously reported Cc form [Tan et al. (2008b). Acta Cryst. E64, o2224]. The molecule is non-planar, with the dihedral angle between the N3CS residue (r.m.s. deviation = 0.0816 Å) and the benzene ring being 21.36 (4)°. The conformation about the C=N bond [1.292 (2) Å] is E, the two N-bound H atoms are anti, and the inner hydroxy O-bound and outer amide N-bound H atoms form intramolecular hydrogen bonds to the imine N atom. Crucially, the H atom of the outer hydroxy group is approximately syn to the H atom of the benzene C atom connecting the two C atoms bearing the hydroxy substituents. This arrangement enables the formation of supramolecular tubes aligned along [010] and sustained by N—H...O, O—H...S and N—H...S hydrogen bonds; the tubes pack with no specific interactions between them. While the molecular structure in the Cc form is comparable, the H atom of the outer hydroxy group is approximately anti, rather than syn. This different orientation leads to the formation a three-dimensional architecture based on N—H...O and O—H...S hydrogen bonds.

Keywords

• crystal structure
• thiosemicarbazone
• polymorph
• conformation
• hydrogen bonding