Thiophene-2-carbaldehyde azine

The asymmetric unit of the title compound, C10H8N2S2, is composed of two independent half-molecules, each residing on a center of symmetry. In the crystal, weak C—H⋯π interactions join the two symmetry-independent molecules together into interlinked chains parallel to [011]. The crystal structure was refined as a two-component pseudo-merohedral twin using the twin law 001 0-10 100. The refined domain fractions are 0.516 (3) and 0.484 (3).

The asymmetric unit of the title compound, C 10 H 8 N 2 S 2 , is composed of two independent half-molecules, each residing on a center of symmetry. In the crystal, weak C-HÁ Á Á interactions join the two symmetry-independent molecules together into interlinked chains parallel to [011]. The crystal structure was refined as a two-component pseudo-merohedral twin using the twin law 001 010 100. The refined domain fractions are 0.516 (3) and 0.484 (3).

Comment
The title compound was a side product in the attempted reduction of a nitro-substituted benzimidazole derivative but was subsequently rationally synthesized as outlined in the experimental section.
A view of the unit cell is shown in Figure 2. Weak C-H···π interactions between the symmetry independent molecules result in chains parallel to [011]. The C1-H1···C8 and C1-H1···C9 intermolecular distances are 2.77 and 2.85 Å, respectively. There is a short intermolecular distance of C8-H8···C4 (2.77 Å). Experimental 0.126 ml (4.05 mmol) of hydrazine hydrate in 1 ml of ethanol was slowly added to 0.82 ml (0.98 g, 8.8 mmol) of 2-thiophene carboxaldehyde in 35 ml of ethanol at room temperature with stirring. The reaction was refluxed for 4 h and monitored by TLC. The reaction mixture was cooled to 0°C and the product was obtained by vacuum filtration. 0.32 g obtained (33% yield). R f = 0.88 (EtOAc/EtOH, 2:1 (v/v) on silica gel Single crystals suitable for X-ray diffraction were obtained by slow evaporation of an ethanol/ethylacetate solution.

Refinement
The autosolve routine of the APEXII software (Bruker, 2010) chose an orthorhombic, C-centered cell, but no suitable space group could be found. Subsequently, the structure was solved in P2 1 /n and refined to R 1 = 0.17 and S = 3.27.
Refinement as a pseudo-merohedral twin with the twin law 001 0-10 100 resulted in a dramatic improvement in the model. The domain fractions refined to 0.516 (3) and 0.484 (3).
The H atoms were refined using a riding model with a C-H distance of 0.95 Å and the thermal parameters were set using the approximation U iso = 1.2U eq (C).

Figure 1
Perspective view of the title compound showing the atom-labeling scheme used for the two half molecules in the asymmetric unit. Displacement ellipsoids of the nonhydrogen atoms are drawn at the 50% probability level.   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.61 e Å −3 Δρ min = −0.28 e Å −3

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.