3,3′-Bithiophene

The title compound, C8H6S2, is disordered [occupancy ratio = 0.839 (2):0.161 (2)] and sits across a centre of symmetry. In the crystal, the molecules are linked by a weak C—H⋯π interaction.

The title compound, C 8 H 6 S 2 , is disordered [occupancy ratio = 0.839 (2):0.161 (2)] and sits across a centre of symmetry. In the crystal, the molecules are linked by a weak C-HÁ Á Á interaction.

Related literature
For a discussion of the disorder in this compound, see: Visser et al. (1968). For thiophene C-S bond distances, see: Allen et al. (1987).  Table 1 Hydrogen-bond geometry (Å , ).

LRG thanks the Fundaçã o para o Ensino e Cultura
Fernando Pessoa for support.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: OM2327).

Comment
The disorder in the title compound was discussed briefly by Visser et al. (1968). However, this paper gives no coordinates and the structure determination was at room temperature. This is a low temerature determination. A view of the major, 0.839 (2), site occupancy, and minor, 0.161 (2), site occupancy, components are shown in Fig. 1. There is a weak C-H···π interaction, C2-H2···Cg(thiophene) (0.5-x, y, z-0.5) in which H2···Cg is 2.86Å and C2···Cg is 3.6039 (17) Å. The angle at H2 ia 136° for the major component. The C2···Cg2 distance for the minor component is 3.607 (5) Å. The H2···Cg distance and angle at H2 are the same.

Experimental
The compound was obtained commercially and re-crystallised from dichloromethane.

Refinement
H atoms were treated as riding atoms with C-H(aromatic), 0.95Å. The S atom was disordered by rotation of 180° around the bond connecting the 2 thiophene rings. The C-S distances were restrained the average value quoted in Allen, et al., 1987 using tight restraints. Specifically, the C2-C5a and C4-C5 bonds were restrained in SHELXL97 refinements using DFIX 1.380 0.001 and the C5-S1, C2-S1, C4-S1A and C5A-S1A bonds were restrained using DFIX 1.72 0.001. The anisotropic thermal parameters for atom C5A (minor component) were constrained to be the same as those those of atom C5 (major component) using the EADP instruction. Fig. 1. A view of the title compound with our numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. The molecule sits across the centre-of-symmetry at (0.5,0.5,0.5). The bonds in the minor component are marked as dotted lines.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.