Crystal structure of benzyl (E)-2-(3,4-dimethoxybenzylidene)hydrazine-1-carbodithioate

In the crystal of the title compound, which crystallized with two independent molecules (A and B) in the asymmetric unit, the A and B molecules are linked via pairs of N—H⋯S hydrogen bonds, forming dimers with an (8) ring motif. The dimers are linked via pairs of C—H⋯O hydrogen bonds and C—H⋯π interactions, forming ribbons propagating along [100].

The title compound, C 17 H 18 N 2 O 2 S 2 , synthesized via a condensation reaction between S-benzyl dithiocarbazate and 3,4-dimethoxybenzaldehyde, crystallized with two independent molecules (A and B) in the asymmetric unit. Both molecules have an L-shape but differ in the orientation of the benzyl ring with respect to the 3,4-dimethoxybenzylidine ring, this dihedral angle is 65.59 (8) in molecule A and 73.10 (8) in molecule B. In the crystal, the A and B molecules are linked via pairs of N-HÁ Á ÁS hydrogen bonds, forming dimers with an R 2

Chemical context
Schiff bases have been proven to possess a variety of biological activities, and this has led to extensive studies on this group of compounds with particular emphasis on those derived from dithiocarbazates. Dithiocarbazate-derived Schiff bases have generally been found to exhibit interesting cytotoxic and antimicrobial activities. One of the most investigated dithiocarbazates has been S-benzyldithiocarbazate (SBDTC) whose derivatives have shown promising biological activities (Break et al., 2013). Therefore, as part of our research which is aimed at developing anticancer and antimicrobial drugs, we have synthesized a novel Schiff base via the condensation reaction of SBDTC and 3,4-dimethoxybenzaldehyde. We report herein on the synthesis and crystal structure of the title compound.

Structural commentary
The title compound, Fig. 1, crystallized with two independent molecules (A and B) in the asymmetric unit. Both molecules have an l-shape but differ in the orientation of the benzyl ring with respect to the 3,4-dimethoxybenzylidine ring, this dihedral angle being 65.59 (8) in molecule A and 73.10 (8) in molecule B (Fig. 2).
The C-N and N(H)-C bond lengths (C1-N1 and N2-C9 in A, and C21-N21 and N22-C29 in B) are 1.331 (2) and 1.282 (2) Å , respectively, in molecule A, and 1.336 (2) and 1.280 (2) Å , respectively, in molecule B. The shorter length of the C-N bond suggests the existence of a double bond which belongs to the imine group. Similarly, the shorter C-S bond length [C1-S1 = 1.681 (2) Å in A, and C21-S21 = 1.677 (2) Å in B] relative to that of [C1-S2 = 1.749 (2) Å in A, and C21-S22 = 1.749 (2) Å in B] suggests that the former possesses double-bond character, indicating that the molecule exists in its thione form in the solid state. The functional group identities proposed from these bond lengths are further supported by data obtained from the IR analysis reported below. Furthermore, the bond distances in the title compound are similar to those found for other carbodithioate-derived Schiff bases (Break et al.;2013;Khoo et al., 2014).
Both molecules (A and B) crystallizes in the conformer in which the two aromatic rings of the compound are cis with respect to each other across the C N bonds, while the thione sulfur atom is trans with respect to the same bond.

Supramolecular features
In the crystal, the A and B molecules are linked by pairs of N-HÁ Á ÁS hydrogen bonds, forming dimers with an R 2 2 (8) ring motif (Table 1 and Fig. 3). The dimers are linked via pairs of C-HÁ Á ÁO hydrogen bonds, giving inversion dimers of dimers. These units are linked by C-HÁ Á Á interactions, forming ribbons propagating in the [100] direction ( Fig. 3 and Table 1).   A view of the molecular structure of the two independent molecules (A and B) of the title compound, showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. N-HÁ Á ÁS hydrogen bonds are shown as dashed lines (see Table 1 for details). Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view of the molecular overlay (Mercury; Macrae et al., 2008) of the two independent molecules (A blue and B red) of the title compound.

Figure 3
A view approximately along the b axis of the crystal structure of the title compound. The hydrogen bonds and C-HÁ Á Á interactions are shown as dashed lines (see Table 1 for details; for clarity only the H atoms involved in these interactions are shown).

Synthesis and crystallization
1.98 g (0.01 mol) of S-benzyldithiocarbazate in 30 ml of absolute ethanol was added to an equimolar quantity of 3,4dimethoxybenzaldehyde in 10 ml of absolute ethanol, followed by the addition of 2-4 drops of concentrated H 2 SO 4 . The mixture was heated over a steam bath for 15 min and a precipitate started to form. The Schiff base which precipitated was filtered, washed with cold ethanol and dried in vacuo over silica gel, giving a white yellowish product. Yellow crystals of the title compound, suitable for X-ray analysis, were obtained

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were all located in a difference Fourier map, but those attached to carbon atoms were repositioned geometrically. The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-0.98 Å , N-H in the range 0.86-0.89 Å ), with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other H atoms.