2,2′-Sulfonyldipyrazine 4-oxide

In the title compound, C8H6N4O3S, the dihedral angle between the pyrazine rings is 85.04 (1)°. In the crystal, molecules are arranged along the a axis and are linked by C—H⋯N hydrogen bonds and pyrazine–pyrazine π–π interactions [centroid–centroid distance = 3.800 (1) Å, forming an infinite chain array. The chains are connected by C—H⋯O(oxide) hydrogen bonds into layers lying parallel to the ab plane. Along the c axis, the layers are stacked and linked through C—H⋯O(sulfonyl) interactions, forming a three-dimensional network.

In the title compound, C 8 H 6 N 4 O 3 S, the dihedral angle between the pyrazine rings is 85.04 (1) . In the crystal, molecules are arranged along the a axis and are linked by C-HÁ Á ÁN hydrogen bonds and pyrazine-pyrazineinteractions [centroid-centroid distance = 3.800 (1) Å , forming an infinite chain array. The chains are connected by C-HÁ Á ÁO(oxide) hydrogen bonds into layers lying parallel to the ab plane. Along the c axis, the layers are stacked and linked through C-HÁ Á ÁO(sulfonyl) interactions, forming a three-dimensional network.
In the title compound, the value of the C1(sp 2 )-S1-C5(sp 2 ) angle is 103.92 (1)° with two attached pyrazinyl rings exhibiting a dihedral angle of 85.04 (1)°, as shown in Fig. 1. The angular-shaped molecules are arranged along the a axis.

Experimental
The title compound was obtained as a serendipitous byproduct as the 2,2′-dipyrazine sulfide (0.022 g, 0.1 mmol) was dissolved in a mixture of methanol 2 ml and acetonitrile 2 ml to react with Mn(ClO 4 ) 2 .6H 2 O (0.036 g, 0.1 mmol) with constantly stirring at room temperature. After three hours, the clear solution was filtrated and kept in air for about one week to yield colourless block crystals (7 mg, 29% yield). We got the the title compound as a matter of the oxidability by perchlorate acid from Mn(ClO 4 ) 2 .6H 2 O.

Refinement
All hydrogen positions were calculated after each cycle of refinement using a riding model with C-H = 0.93 Å and U iso (H) = 1.2U eq (C). The highest peak (0.8 e.Å -3 ) in the difference Fourier map is located at 1.1 Å from atom N4. The refinement of a model including one H atom at this position led to lower R 1 and wR 2 values but it is chemically meaningless since there is no counter ion in the crystal structure. A positional disorder of the oxo O atom (partially on atoms O4 and O2) is surely the best solution but in this case too many restraints had to be used in the final refinements to get an acceptable model (with an site-occupancy ratio greater than 0.9:0.1).

Figure 1
The atom-numbering scheme of the title complex. Displacement ellipsoids are drawn at the 35% probability level and H atoms are shown as sticks of arbitrary radii.

Figure 2
The hydrogen-bonding (C-H···N) and π···π stacking interactions between parallel chains along the a axis, which are respectively shown as thin red-dashed lines and thick blue-dashed lines (symmetry codes: i = -x + 2, -y + 1, -z + 1; ii = x + 1, y, z).  Three-dimensional structure of the title molecule viewed down the a direction. The red dashed lines represent hydrogenbonding interactions. 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 > 2sigma(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.