1,3-Dithian-2-one azine

In an asymmetric unit of the title compound, C8H12N2S4, there are two crystallographically independent half molecules lying on inversion centers. One of the molecules is disordered over two positions with relative occupancies of 82.0 (2) and 18.0 (2) for the major and minor components. In the crystal structure, molecules are linked into a three-dimensional framework via intermolecular C—H⋯N hydrogen-bonding interactions.

In an asymmetric unit of the title compound, C 8 H 12 N 2 S 4 , there are two crystallographically independent half molecules lying on inversion centers. One of the molecules is disordered over two positions with relative occupancies of 82.0 (2) and 18.0 (2) for the major and minor components. In the crystal structure, molecules are linked into a three-dimensional framework via intermolecular C-HÁ Á ÁN hydrogen-bonding interactions.
In the title compound, there are two crystallographically independent half molecules in the asymmetric unit, which lie on centres of symmetry; referred as molecules A and B. The atoms of the molecule B are disordered over two positions with relative occupancies of 82.0 (2) and 18.0 (2) for the major and minor components, respectively. All the dithian rings adopt twist-boat conformations (Boeyens, 1978). The atoms S1/S2/C1/C3/N1 in molecule A lie in a plane and the atoms C2 and C4 lie above and below this plane. Similarly, atoms S3/S4/C5/C7/N2 in molecule B also lie in a plane and the atoms C6 and C8 lie above and below the plane. The molecular dimensions in the two molecules are similar with the corresponding molecular dimensions reported in similar structures from our previous work (Yang et al.., 2007;; Liu, Liu, Dai et al., (2008).
In the crystal structure the molecules are joined into a zig-zag chain by C8-H8B···N1 inter-molecular hydrogen-bond ( Fig. 2, Tab. 1). At the same time C2-H2B···N2 inter-molecular hydrogen-bonds form another zig-zag chain along the molecular long axis and vertically the first chain. Both of them generate a sheet with edge-fused R 4 4 (22) rings in graph set notation (Bernstein et al., 1995) in the ab-plane. Besides these chains, there are two more zig-zag chains, formed by C6-H6B···N1 and C4-H4B···N2 inter-molecular hydrogen-bonds which make up the adjacent sheet into a three dimensional frame work along the c axis (Fig. 3).

Experimental
The title compound was prepared according to the reference method (Mayer & Schaefer, 1964;Xu et al., 2005) and crystallized from a mixture of ethanol and petroleum ether (1:8).

Refinement
The atoms of the molecule B are disordered over two positions with relative occupancies of 82.0 (2) and 18.0 (2) for the major and minor components, respectively; their anisotropic dispalcement parameters were constrained to be equal. Restraints were applied to bond distances in the disordered molecule B in reference to the molecule A. All H atoms were placed at ideal positions and allowed to ride on the parent C atoms, with C-H = 0.97 and U iso (H) values of 1.2U eq (C).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.