title: Crystal structure of a new monoclinic polymorph of 2,4-di-hydroxy-benzaldehyde 4-methyl-thio-semi-carbazone.
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 mol-ecule 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 hy-droxy O-bound and outer amide N-bound H atoms form intra-molecular hydrogen bonds to the imine N atom. Crucially, the H atom of the outer hy-droxy group is approximately syn to the H atom of the benzene C atom connecting the two C atoms bearing the hy-droxy substituents. This arrangement enables the formation of supra-molecular 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 inter-actions between them. While the mol-ecular structure in the Cc form is comparable, the H atom of the outer hy-droxy 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.
authors.affiliation: Bangladesh Petroleum Exploration and Production Co. Ltd (BAPEX), 4 Karwan Bazar, BAPEX Bhabon, Dhaka 1215, Bangladesh.
authors.forename: M A
authors.initials: MA
authors.lastname: Salam
authors.affiliation: Department of Chemistry, College of Science, University of Basrah, Basra 61004, Iraq.
authors.forename: Mouayed A
authors.initials: MA
authors.lastname: Hussein
authors.affiliation: Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia.
authors.forename: Edward R T
authors.initials: ER
authors.lastname: Tiekink
keywords: conformation; crystal structure; hydrogen bonding; polymorph; thio­semicarbazone