2-(3-Chloro-1,2-dihydropyrazin-2-ylidene)malononitrile

In the crystal structure of the title compound, C7H3ClN4, neighbouring molecules are linked via pairs of N—H⋯N hydrogen bonds into inversion dimers, thereby forming an R 2 2(12) ring motif. With respective average deviations from planarity of 0.009 (1) and 0.006 (1) Å, the pyrazine skeleton and the malononitrile fragment are oriented at an angle of 6.0 (1)° with respect to each other. The mean planes of the pyrazine ring lie either parallel or are inclined at an angle of 68.5 (1)° in the crystal structure.

In the crystal structure of the title compound, C 7 H 3 ClN 4 , neighbouring molecules are linked via pairs of N-HÁ Á ÁN hydrogen bonds into inversion dimers, thereby forming an R 2 2 (12) ring motif. With respective average deviations from planarity of 0.009 (1) and 0.006 (1) Å , the pyrazine skeleton and the malononitrile fragment are oriented at an angle of 6.0 (1) with respect to each other. The mean planes of the pyrazine ring lie either parallel or are inclined at an angle of 68.5 (1) in the crystal structure.
In the molecule of the title compound ( Fig. 1) the bond lengths and angles characterizing the geometry of the pyrazines skeleton are typical for this group compounds (Vishweshwar et al., 2000;Wardell et al., 2006). With respective average deviations from planarity of 0.009 (1) and 0.006 (1) Å, the pyrazine skeleton and malononitrile fragment are oriented at an angle 6.0 (1)° to each other. The mean planes of the pyrazine skeleton lie either parallel or are inclined at an angle of 68.5 (1)°i n the lattice. One of the nitrile fragment (delineated by C7, C8 and N9 atoms) is nearly in the plane of the heterocyclic ring (the angle between the mean planes of the pyrazine skeleton and nitrile fragment is equal 178.4 (2)°) while the other (involving C7, C10 and N11 atoms) is out of plane the pyrazine skeleton (the angle between the mean planes of the pyrazine skeleton and nitrile fragment is equal 172.8 (2)°).
In the crystal structure, neighbouring molecules are linked through N-H···N hydrogen bond forming R 2 2 (12) ring motif (Table 1 and Fig. 2). The interactions demonstrated were found by PLATON (Spek, 2009).
Experimental 2-[3-Chloropyrazin-2(1H)-ylidene)malononitrile was obtained by the aromatic nucleophilic substitution of chlorine in 2,3dichloropyrazine with malononitrile Foks, 1981 and1982). A mixture of 2,3-dichloropyrazine, malononitrile and potassium carbonate was dissolved in DMSO. The mixture was stirred for 4 h in 333 K to give an orange solution. After cooling the reaction mixture to room temperature, water was added. Then mixture was acidified with hydrochloric acid.
Single crystals suitable for X-ray analysis were grown in methanol solution [m.p. = 436 K].

Refinement
All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C) and N-H = 0.86 Å and U iso (H) = 1.2U eq (N). Fig. 1. The molecular structure of the title compound showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 25% probability level and H atoms are shown as small spheres of arbitrary radius.

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 > σ(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.