1-[2-(Pyrazin-2-ylsulfanyl)ethyl]pyrazine-2(1H)-thione

The title multifunctional twisted organic ligand, C10H10N4S2, contains a short C=S bond [1.671 (2) Å]. The dihedral angle between the two pyrazine rings is 39.83 (6)°. In the crystal, intermolecular C—H⋯N and C—H⋯S hydrogen bonds result in the formation of a supramolecular network.

The title multifunctional twisted organic ligand, C 10 H 10 N 4 S 2 , contains a short C S bond [1.671 (2) Å ]. The dihedral angle between the two pyrazine rings is 39.83 (6) . In the crystal, intermolecular C-HÁ Á ÁN and C-HÁ Á ÁS hydrogen bonds result in the formation of a supramolecular network.

Related literature
The assembly of molecular units in predefined arrangements is a key goal in the synthesis of crystal structures by design, see: Zheng et al. (2003). For bond lengths and angles in the ligand, see: Etter et al. (1992). For a description of the Cambridge Structural Database, see: Allen (2002). For versatile ligands, see: Devel et al. (2003).

Comment
In the synthesis of crystal structures by design, the assembly of molecular units in predefined arrangements is a key goal (Zheng et al., 2003). Pyrazine-2-thiol is a versatile ligand which may adopt a variety of bonding modes in its coordination compounds. We originally attempted to synthesize complexes featuring Co metal chains by reaction of the Co(II) ion with pyrazine-2-thiol ligand. Unfortunately, we obtained only the title ligand, and we report herein its crystal structure. In I ( Fig.   1), the ligand bond lengths and angles are within normal ranges (Etter et al., 1992). The C=S bond length was compared with the mean C-S and C=S bond lengths retrieved from a search of thiol and thione crystal structures from the CSD (Allen, 2002). X-ray data from I give a C=S bond length of 1.671 (2) Å, which is shorter than the value of 1.698 (2) Å for 2-thiopyridone and indicates a C=S rather than C-S bond. In the crystal structure, intermolecular C-H···N and C-H···S hydrogen bonds (Table 1 and Fig. 2) result in the formation of a supramolecular network structure.

Experimental
For the preparation of (I), a solution of CoCl 2 .6H 2 O (47.9 mg, 0.2 mmol) in 5 ml distilled water was added dropwise to a solution of pyrazine-2-thiol (250 mg, 2 mmol) and 1,2-dibromoethane (0.09 ml, 1 mmol) in 15 ml sodium ethoxide/ethanol solution. The resulting solution was stirred at 352 K for 3 h, then cooled to room temperature and filtered. A yellow-block crystal suitable for X-ray diffraction were obtained by slow evaporation after several days.

Refinement
H atoms were positioned geometrically, with C-H = 0.93 and 0.97 Å for aromatic and methyl H atoms, and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C)