Dibromidobis(pyrazine-2-carboxamide-κN 4)zinc

The title complex, [ZnBr2(C5H5N3O)2], shows crystallographic mirror symmetry with the Zn atom and the two bromine ligands located on the mirror plane. The Zn atom is four-coordinated in a distorted tetrahedral fashion by two N atoms from two pyrazine-2-carboxamide ligands and two Br atoms. Only one of the amino H atoms is involved in an N—H⋯O hydrogen bond. The crystal packing is further stabilized by weak N—H⋯N and C—H⋯O interactions.

The title complex, [ZnBr 2 (C 5 H 5 N 3 O) 2 ], shows crystallographic mirror symmetry with the Zn atom and the two bromine ligands located on the mirror plane. The Zn atom is four-coordinated in a distorted tetrahedral fashion by two N atoms from two pyrazine-2-carboxamide ligands and two Br atoms. Only one of the amino H atoms is involved in an N-HÁ Á ÁO hydrogen bond. The crystal packing is further stabilized by weak N-HÁ Á ÁN and C-HÁ Á ÁO interactions.
The asymmetric unit of the title compound, (Fig. 1), contains one Zn II atom, two Br atoms and one pyrazine-2carboxamide ligand. The Zn II atom is four-coordinated in a distorted tetrahedral configuration by two N atoms from two pyrazine-2-carboxamide ligands and two terminal Br atoms.
Only one of the amino H atoms is involved in a N-H···O hydrogen bond. The crystal packing is further stabilized by weak N-H···N and C-H···O interactions.

Experimental
A solution of pyrazine-2-carboxamide (0.25 g, 2.0 mmol) in methanol (10 ml) was added to a solution of ZnBr 2 (0.23 g, 1.0 mmol) in methanol (10 ml) and the resulting colourless solution was stirred for 15 min at room temperature. This solution was left to evaporate slowly at room temperature. After one week, colourless block shaped crystals of the title compound were isolated (yield 0.38 g, 80.6%).

Refinement
All H atoms were positioned geometrically, with C-H = 0.93 Å and N-H = 0.86 Å and constrained to ride on their parent atoms, with U iso (H)=1.2U eq (C,N).

Computing details
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 0.77 e Å −3 Δρ min = −1.19 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.