5,6-Dimethylpyrazine-2,3-dicarboxylic acid

The asymmetric unit of the title compound, C8H8N2O4, consists of one complete molecule and a second molecule generated by the application of twofold axis. The mean planes of the two carboxyl groups attached to the pyrazine ring at neighboring positions are twisted by 10.8 (1) and 87.9 (1)° in the complete molecule and 43.0 (1)° in the symmetry-generated molecule. The crystal packing features O—H⋯N hydrogen bonds, which link the molecules into layers along [101].

The asymmetric unit of the title compound, C 8 H 8 N 2 O 4 , consists of one complete molecule and a second molecule generated by the application of twofold axis. The mean planes of the two carboxyl groups attached to the pyrazine ring at neighboring positions are twisted by 10.8 (1) and 87.9 (1) in the complete molecule and 43.0 (1) in the symmetrygenerated molecule. The crystal packing features O-HÁ Á ÁN hydrogen bonds, which link the molecules into layers along [101].
The author thanks the Jilin Business and Technology College for financial support. Similarly, the crystal structure of the title compound containing one water molecule in the unit cell has also been reported (Vishweshwar et al., 2001;Vishweshwar et al., 2004), In view of the importance of compounds containing this ligand we report herin the crystal structure of the title compound, (I).
The asymmetric unit of the title compound, C 8 H 8 N 2 O 4 , consists of one molecule and a second complete molecule generated by the application of a centre of inversion ( Fig. 1). For each molecule, the mean planes of the two carboxyl groups attached to the pyrazine ring at neighboring positionsare twisted by 10.8 (1)° and 87.9 (3)°. Crystal packing is stabilized by O-H···N hydrogen bonds which link the molecules into layers along [101] (Fig. 2).

Experimental
The compound was synthesized by a reported reaction (Tsuda & Fujishima, 1981) and crystallized by a solvent-thermal reaction as follows: 196.16 mg (1 mmol) C 8 H 8 N 2 O 4 and 10 mlN, N-dimethylformamide (DMF) was added to a 20 ml Teflon vessel. The vessel was sealed and placed inside a stainless steel autoclave, which was kept at 130°C for 72 h. Crystals suitable for single-crystal analysis were formed upon standing.

Refinement
H atoms bonded to O atom were located in a Fourier difference map and refined with distance restraints of O-H = 0.820 Å, and with U iso (H) = 1.5Ueq(O). The remaining H atoms were positioned geometrically and refined using the riding model, with C-H = 0.960 Å and with U iso (H) = 1.5 times U eq (C). Fig. 1. Molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.