2-Sulfanylidene-1,3-dithiolo[4,5-b]naphtho[2,3-e][1,4]dithiine-5,10-dione

The title molecule, C13H4O2S5, is folded by 47.83 (6)° along the S⋯S vector of the [1,4]dithiine six-membered ring, with the naphthoquinone and [1,3]dithiole-2-thione moieties being nearly planar [largest deviations from least-squares planes = 0.028 (2) and 0.016 (1) Å, respectively]. This boat conformation is close to that observed in the analogous compound [Mendez-Rojas et al. (2001). J. Chem. Crystallogr. 31, 17–28] including a 2-oxo group [folding angle: 42.3 (1)° at 213 (2) K]. Both compounds are indeed isomorphous, and the small difference in the folding angle probably results from the involvement of the thioxo group of the title compound in intermolecular S⋯S contacts [3.5761 (13) Å]. In the crystal structure, molecules are stacked in the [100] direction, with dithiole rings making π–π interactions. In a stack, alternating short and long separations are observed between the centroids of dithiole rings, 3.5254 (17) and 4.7010 (18) Å.

Financial support from CONACyT-48038-R and VIPE-UDLA are gratefully acknowledged. The development of new types of π-electron donors and acceptors with high polarizability continues to be an attractive topic in material sciences. Such compounds are not only interesting as candidates for single-component conductors, but also because they have low excitation energies and promising applications as NLO materials and near-IR absorbing dyes.
Sulfur-based heterocycles are good candidates for building such materials, and donors like TTF and BEDT-TTF became emblematic systems in the 70's, after they allowed to synthesize molecular metals and superconductor materials (Wudl, 1984;Jérome, 2007).
The title compound belongs to the 1,4-dithiine derivatives, which have a particular conformational flexibility, because the energy barrier between the planar and boat conformations is very low (Hayakawa et al., 1982). Ab initio computations showed for example that for 1,4-dithiine, the C 2v (boat) → D 2h (planar) conformational interconversion requires less than 3 kcal/mol (see Table II and Fig. 4 in Kao et al., 1985). A fine tuning of the geometry and electron distribution may thus be expected by varying the substituents of this heterocycle. For example, electron withdrawing groups seem to stabilize the unfolded conformer (Brisse et al., 2000).
The title molecule is isomorphous with the 2-oxo analogue (Mendez-Rojas et al., 2001). However, it is interesting to note that both the molecular and the crystal structures present significantly different metrics for the 2-thioxo and the 2-oxo compounds. In the latter, the folding angle is 42.3 (1)°, and the separations in the dithiole stacks parallel to [100] are 3.566 and 4.345 Å. Despite of the clear dimerization along the stacks for both compounds, the title molecule seems to be more prone to Peierls instability, compared to its 2-oxo analogue.

Refinement
The four aromatic H atoms of the naphthoquinone were placed in idealized positions and refined with C-H bond lengths fixed to 0.93 Å and isotropic displacement parameters fixed to 1.2 times the equivalent displacement of the carrier C atom. Fig. 1. The structure of the title compound, with displacement ellipsoids for non-H atoms at the 30% probability level.