5,6-Di-2-thienyl-2,3-dihydropyrazine

In the title compound, C12H10N2S2, which was synthesized by the reaction of 2,2′-thenil and ethylenediamine, the dihedral angle between the two thiophene rings is 66.33 (9)°. In the crystal structure, intermolecular C—H⋯N hydrogen bonds link the molecules into infinite chains along the b axis and weak C—H⋯π interactions may further stabilize the structure.

In the title compound, C 12 H 10 N 2 S 2 , which was synthesized by the reaction of 2,2 0 -thenil and ethylenediamine, the dihedral angle between the two thiophene rings is 66.33 (9) . In the crystal structure, intermolecular C-HÁ Á ÁN hydrogen bonds link the molecules into infinite chains along the b axis and weak C-HÁ Á Á interactions may further stabilize the structure.
Cg2 is the centroid of the S2/C9-C12 ring. Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 Thienyl-based guests have shown preferential inclusion into the host by keeping thienyl ring S atoms pointed away from the face of growing crystals, possibly to avoid unfavorable electrostatic interactions between sulfur lone pairs coplanar with the thiophene ring and molecules already incorporated into the growing crystal face (Shimon et al., 1993). The structural studies on thenoins (Crundwell et al., 2002a,b) and thenils , and other thiophene-containing molecules such as 2,5-diphenyl-3,4-dithien-3-ylcyclopentadien-1-one (Linehan et al., 2003) and 4-bromo-2-thiophenecarboxaldehyde (Stacy et al., 2003) have been reported in the literature. In continuation of this area of study, the crystal structure of the title compound, (I), is reported here.
In the molecule of the title compound ( Fig. 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges.
The dihedral angle between the two thiophene rings S1/C1-C4 and S2/C9-C12 is 66.33 (9)°. In the crystal structure, intermolecular C-H···N hydrogen bonds (Table 1) link the molecules (Fig. 2) into infinite chains along the b axis, in which they may be effective in the stabilization of the structure. The crystal structure is further stabilized by C-H···π interactions (Table 1), involving the S2/C9-C12 (centroid Cg2) ring.
The resulting solution was then cooled to room temperature. After a few days of slow evaporation of the solvent, brown plates of (I) were obtained.

Refinement
All H atoms were positioned geometrically (C-H = 0.93 or 0.97 Å) and were refined using a riding model, with U iso (H) = 1.2 or 1.5U eq (C). In the absence of significant anomalous scattering effects, 1899 Friedel pairs were merged. Fig. 1. The asymmetric unit of (I) with displacement ellipsoids drawn at the 50% probability level.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(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.