Dichloridobis(pyrazine-2-carboxamide-κN 4)zinc(II)

In the crystal of the title compound, [ZnCl2(C5H5N3O)2], the molecule has m symmetry, with the ZnII cation and Cl− anions located on the mirror plane. The ZnII cation is coordinated by two Cl− anions and two pyrazine-2-carboxamide ligands in a distorted ZnCl2N2 tetrahedral geometry. The two pyrazine rings are nearly perpendicular to each other [dihedral angle = 86.61 (10)°]. Intermolecular N—H⋯O and N—H⋯N hydrogen bonds and weak C—H⋯O interactions stabilize the crystal packing.

In the crystal of the title compound, [ZnCl 2 (C 5 H 5 N 3 O) 2 ], the molecule has m symmetry, with the Zn II cation and Cl À anions located on the mirror plane. The Zn II cation is coordinated by two Cl À anions and two pyrazine-2-carboxamide ligands in a distorted ZnCl 2 N 2 tetrahedral geometry. The two pyrazine rings are nearly perpendicular to each other [dihedral angle = 86.61 (10) ]. Intermolecular N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds and weak C-HÁ Á ÁO interactions stabilize the crystal packing.
Here, we report the synthesis and structure of the title compound.
The asymmetric unit of the title compound, (Fig. 1), contains one Zn II atom, two Cl 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 Cl atoms. The Zn-Cl and Zn-N bond lengths and angles are collected in Table 1. In the crystal structure, intermolecular N-H···O, N-H···N and C-H···O hydrogen bonds (Table 2, Fig. 2) may stabilize the structure.

Experimental
A solution of pyrazine-2-carboxamide (0.25 g, 2.0 mmol) in methanol (10 ml) was added to a solution of ZnCl 2 (0.13 g, 1.0 mmol) in methanol (10 ml) and the resulting colorless solution was stirred for 15 min at room temperature. This solution was left to evaporate slowly at room temperature. After one week, colorless plate crystals of the title compound were isolated (yield 0.30 g, 78.4%).

Refinement
All 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).

Computing details
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008    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.