Crystal structure of S-hexyl (E)-3-(2-hydroxybenzylidene)dithiocarbazate

The title compound crystallizes with four independent molecules in the asymmetric unit, which have very comparable geometries. In the crystal, molecules are connected in pairs through N—H⋯S hydrogen bonds, forming dimers.

The title compound, C 14 H 20 N 2 OS 2 [systematic name: S-hexyl (E)-2-(2-hydroxybenzylidene)hydrazine-1-carbodithioate], crystallizes with four independent molecules (A-D) in the asymmetric unit. All four molecules adopt an E conformation with respect to the C N bond of the benzylidene moiety and have an intramolecular O-HÁ Á ÁN hydrogen bond generating an S(6) ring motif. In the crystal, the A and D molecules are connected by a pair N-HÁ Á ÁS hydrogen bonds, forming a dimer with an R 2 2 (8) ring motif. In the case of molecules B and C, they are linked to themselves by pairs of N-HÁ Á ÁS hydrogen bonds, forming B-B and C-C inversion dimers with R 2 2 (8) ring motifs.

Chemical context
Bidentate Schiff bases of S-methyl or S-benzyl dithiocarbazates and their metal complexes have received considerable attention for their possible bioactivities (Chan et al., 2008;How et al., 2008;Zangrando et al., 2015;Ali et al., 2002;Chew et al., 2004;Crouse et al., 2004). As part of our ongoing structural studies of S-containing Schiff bases, we report herein on the structure of a molecule having a hexyl chain, similar to other ligands reported by our group Begum, Howlader, Miyatake et al., 2015;Howlader et al., 2015) but differing in their ability to act as tridentate ligands in metal coordination .

Structural commentary
The four independent molecules (A--D) of the title compound are shown in Figs. 1 and 2. The Schiff base exists in its thione ISSN 2056-9890 tautomeric form with the dithiocarbazate fragment adopting an E conformation with respect to the C N bond of the benzylidene moiety. The -nitrogen and the thioketo sulfur are trans located with respect to bond C8-N2 bond in molecule A (and similarly for molecules B, C and D). All non-H atoms in the molecules are almost co-planar indicating, except for the alkyl chain, electron delocalization within them. The maximum deviation from the mean plane is shown by the thioketone atoms S1, S3, S5 and S7 in the four independent molecules (r.m.s deviations of 0.086, 0.118, 0.138 and 0.183 Å , respectively). The bond lengths and angles are comparable to those reported for S-hexyl (E)-3-(4-methylbenzylidene)dithiocarbazate  and S-hexyl (E)-3-(4methoxybenzylidene)dithiocarbazate . The hexyl chain in all four molecules has an extended anti-zigzag conformation. This compound in its deprotonated imino thiolate form has been reported to act as a tridentate ligand through N-, S-and O-donors to form a binuclear copper(II) complex .

Supramolecular features
The crystal packing of the title compound (Fig. 3), indicates that the molecules are connected by pairs of N-HÁ Á ÁS hydrogen bonds (Table 1) to form A-D dimers, and B-B and C-C inversion dimers, all with R 2 2 (8) ring motifs.

Synthesis and crystallization
To an ethanolic solution of KOH ( The molecular structure of molecules A and C of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3
added and the mixture refluxed for 30 min. The mixture was filtered while hot and then the filtrate was cooled to 273 K giving a precipitate of the Schiff base product. It was recrystallized from ethanol at room temperature and dried in a vacuum desiccator over anhydrous CaCl 2 . Colourless crystals of the title compound were obtained by slow evaporation of a solution in methanol/acetonitrile (3:1) [m.p. 364 K].

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were located geometrically and treated as riding atoms: C-H = 0.95-0.99 Å with U iso (H) = 1.2U eq (C). The hydrogen atoms of NH and OH groups were located in a difference Fourier map and refined with U iso (H) = 1.2U eq (N,O).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.