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

The title mol­ecule, C(13)H(4)O(2)S(5), 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.