Pyrazine-2(1H)-thione

In the crystal, the molecules are linked by N—H⋯N and C—H⋯S hydrogen bonds.

Molecular Hirshfeld surface (Spackman & Jayatilaka, 2009) and fingerprint plots (Spackman & McKinnon, 2002), were generated with Crystal Explorer 3.1 (Wolff et al., 2012) using the automatic procedures implemented in the program. The surfaces are mapped with a normalized contact distance (d norm ), with values ranging from À0.58 to 1.05 a.u. Graphical representations of the Hirshfeld fingerprint plots for selected types of intermolecular interactions are presented in Fig. 4. The C-HÁ Á ÁS and N-HÁ Á ÁN hydrogen bonds make major contribution to the overall Hirshfeld surface with 36.8% and 13.8% contributions, respectively. In addition, HÁ Á ÁH (24.8%) and HÁ Á ÁC (11.7%) contacts make a significant contribution to the crystal packing.

Figure 2
The molecular structure of pyrazine-2(1H)-thione, showing the atomlabelling scheme and displacement ellipsoids at the 50% probability level. structure of this compound and its oxidised form were not found.

Synthesis and crystallization
Crystals suitable for X-ray measurements were obtained from commercially available reagents (Aldrich Chemical Co.) which were used without further purification. 0.5 mmol of 2-mercaptopyrazine (II) was mixed with 0.5 mmol of isonicotinic acid N-oxide (III) and dissolved in ethanol (4 ml).
The obtained solution was kept at room temperature. Crystals (yellow plates) for X-ray diffraction were obtained after slow evaporation of the solvent within 2 weeks.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.19 e Å −3 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. Hydrogen atoms of aromatic rings were introduced in calculated positions with idealized geometry and constrained using a rigid body model with isotropic displacement parameters equal to 1.2 the equivalent displacement parameters of the parent atoms. The H atom of the NH group was located in a difference Fourier map and freely refined.