6,7-Difluoro-1,2,3,4-tetrahydroquinoxaline-5,8-dicarbonitrile

In the title compound, C10H6F2N4, the Car—N bonds are slightly shortened with respect to a standard aniline C—N bond [1.3580 (16) and 1.3618 (16) versus 1.39 Å], thus indicating some π–π conjgation with the electron-acceptor CN groups. The molecule, except for two C atom of the ethylene bridge, is nearly planar, the largest deviation of the other non-H atoms from the mean plane being 0.309 (2) Å. The N—C—C—N torsion angle involving the ethylene bridge is 50.23 (18)°. In the crystal, molecules are connected by pairs of N—H⋯N hydrogen bonds into chains along [21-1].

In the title compound, C 10 H 6 F 2 N 4 , the C ar -N bonds are slightly shortened with respect to a standard aniline C-N bond [1.3580 (16) and 1.3618 (16) versus 1.39 Å ], thus indicating someconjgation with the electron-acceptor CN groups. The molecule, except for two C atom of the ethylene bridge, is nearly planar, the largest deviation of the other non-H atoms from the mean plane being 0.309 (2) Å . The N-C-C-N torsion angle involving the ethylene bridge is 50.23 (18) . In the crystal, molecules are connected by pairs of N-HÁ Á ÁN hydrogen bonds into chains along [211].
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: YK2078). As important organic intermediates, tetrafluoroterephthalonitrile and its hydrolyzed product tetrafluoroterephthalic acid can be used to prepare pesticide tefluthrin (Meazza et al., 2007;Orthaber et al., 2010). The S N Ar reaction of tetrafluoroterephthalonitrile with ethylenediamine under ultrasound irradiation yields 6,7-difluoro-1,2,3,4-tetrahydroquinoxaline-5,8-dicarbonitrile [C 10 H 6 F 2 N 4 , compound (I)] as the main product. While the crystal structure of compound (I) was suspiciously unknown. Herein, we report the crystal structure of (I) for comparison and reference purposes.
Compound (I) crystallizes in triclinic P1 space group. A perspective view of the title compound (I) is shown in Fig. 1.
The bond lengths and angles are within normal ranges. In the molecule, two nitrile groups are nearly coplanar with the central benzene plane. Within the tetrahydroquinoxaline ring, the torsion angle N3-C10-C9-N4 is -50.23 (18)°.
Hydrogen-bonding interactions between the imino groups and cyano groups give rise to cyclic system of two N-H···N bonds between two adjacent molecules with the graph-set motif R 2 2 (12) (Etter, 1990). Due to the chemical symmetry of the molecule itself, such hydrogen-bonding interactions link the molecules to form a one-dimensional (1-D) tape structure (Fig. 2).

Experimental
Compound (I) was synthesized by the ultrasound reaction of tetrafluoroterephthalonitrile and ethylenediamine at room temperature in the presence of sulfur and assisted by ultrasound irradiation. The title compound was purified through column chromatography with ethyl acetate/petroleum ether as the eluent. Qualified crystalline samples were obtained through slow evaporation from the EtOH solution of (I).

Refinement
All H atoms were positioned geometrically (C-H = 0.97 Å, N-H = 0.86 Å) and included in the refinement in the ridingmodel approximation, with U iso (H) = 1.2U eq (C,N). program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2005); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).   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 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.