catena-Poly[[bis(pyrazine-2-carboxamide-κN 4)mercury(II)]-di-μ-bromido]

In the crystal structure of the title compound, [HgBr2(C5H5N3O)2]n, the HgII cation is located on an inversion center and is coordinated by two N atoms from the pyrazine rings and four bridging Br− anions in a distorted octahedral geometry. The Br− anions bridge the HgII cations with significantly different Hg—Br bond distances of 2.4775 (8) and 3.1122 (8) Å, forming polymeric chains running along the a axis. Intermolecular N—H⋯O and N—H⋯N hydrogen bonds are effective in the stabilization of the crystal structure.

In the crystal structure of the title compound, [HgBr 2 -(C 5 H 5 N 3 O) 2 ] n , the Hg II cation is located on an inversion center and is coordinated by two N atoms from the pyrazine rings and four bridging Br À anions in a distorted octahedral geometry. The Br À anions bridge the Hg II cations with significantly different Hg-Br bond distances of 2.4775 (8) and 3.1122 (8) Å , forming polymeric chains running along the a axis. Intermolecular N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds are effective in the stabilization of the crystal structure.

Comment
A large variety of pyridine and pyrazine amide ligands have been synthesized for investigating their metal-binding properties (Sasan et al., 2008;Khavasi et al., 2009;Petro & Mukherjee, 1999;Sigh & Mukherjee, 2005). The coordination chemistry of parazineamides is rich. Examples of coordination via the pyrazine N atoms, the carbonyl O atoms and the amide N atoms of the ligand in a non-, mono-, or bis-deprotonated form are known (Hausmann & Brooker, 2004;Cati & Stoeckli-Evans, 2004;Miyazaki et al., 2007) and metal complexes of the ligands have been used extensively to mimic the properties of biologically active systems. Here we synthesized the title compound, (I), and report here its crystal structure.
The asymmetric unit of the title compound, (I), contains one half-molecule (Fig. 1). The Hg II atom is six-coordinated in a distorted octahedral configuration by two N atoms from pyrazine amides and four bridging Br atoms. The bridging function of bromo atoms leads to a one-dimensional chain structure. The Hg-Br and Hg-N bond lengths and angles (Table 1) are within normal ranges. In the crystal structure (Fig. 2), intermolecular N-H···O and N-H···N hydrogen bonds (Table 2) result in the formation of a supramolecular structure, in which they may be effective in the stabilization of the structure.

Experimental
For the preparation of the title compound, a solution of pyrazineamide (0.246 g, 2.0 mmol) in methanol (10 ml) was added to a solution of HgBr 2 (0.360 g, 1.0 mmol) in methanol (5 ml) at room temperature. The suitable crystals for X-ray analysis were obtained by slow evaporation from methanolic solution after one week (yield 0.500 g, 82.5%).

Refinement
All of the H atoms were positioned geometrically with C-H = 0.93 and N-H = 0.86 Å and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C,N). The largest peak and deepest hole are near to the Hg1 atom (0.90 and 0.79 Å, respectively). Fig. 1. The molecular structure with the atom-numbering scheme. Displacement ellipsoids are drawn at 30% probability level.