2-(1,3-Dithiol-2-ylidene)-1,3-dithiole-4-carbaldehyde

The structure of the title compound, C7H4OS4, at 100 K has orthorhombic symmetry. In the crystal, tetrathiafulvalene molecules form π-stacks along the a axis, with a stacking distance of 3.4736 (6) Å. Along the b axis, parallel stacks are interconnected with each other through a network of weak C—H⋯O hydrogen bonds and short S⋯S contacts [3.4813 (7) Å]. Additional short S⋯S contacts [3.4980 (9) Å] join parallel stacks along the c axis.

The structure of the title compound, C 7 H 4 OS 4 , at 100 K has orthorhombic symmetry. In the crystal, tetrathiafulvalene molecules form -stacks along the a axis, with a stacking distance of 3.4736 (6) Å . Along the b axis, parallel stacks are interconnected with each other through a network of weak C-HÁ Á ÁO hydrogen bonds and short SÁ Á ÁS contacts [3.4813 (7) Å ]. Additional short SÁ Á ÁS contacts [3.4980 (9) Å ] join parallel stacks along the c axis.

Comment
The title compound, commonly known as 4-formyltetrathiafulvalene, was prepared from tetrathiafulvalene (TTF) and can serve as an intermediate for the synthesis of 4-(hydroxymethyl)tetrathiafulvalene by reduction with NaBH 4 , of conjugated TTF derivatives by means of Wittig reaction (Garín et al., 1994), of TTF imines by reaction with amines, and of other functional tetrathiafulvalenes (Yamada & Sugimoto, 2004;Fabre, 2004).
The molecular structure of the title compound with atom numbering scheme is shown in Fig. 1. Bond lengths and angles may be considered normal. The molecular framework excluding the carbonyl group is essentially planar, with a maximum deviation of fitted atoms from the least-square plane, defined by the heavy atoms of the TTF backbone, of 0.042 (2) Å for C6. Atoms of the carbonyl group show more substantial out of plane deviation of 0.128 (2) Å for C1 and of 0.2393 (19) Å for O1, respectively.
Details of the packing interactions are given in the Tables. Molecules of the 4-formyltetrathiafulvalene form π-stacks along the a axis with a distance of 3.4736 (6) Å between the least-square planes defined by the S1, S2, S3, and S4 atoms (Figs. 1 &2). Parallel π-stacks are interconnected with each other along the b axis by C1-H1···O1 i and C3-H3···O1 i (symmetry code: (i) -x, y + 1/2, -z + 1/2) short contacts, which can be classified as non-classical hydrogen bonds.

Refinement
Hydrogen atoms were included at calculated positions using a riding model with aromatic and formyl C-H = 0.95. The U iso (H) values were fixed at 1.2 × U eq (C) of the parent C atom.