catena-Poly[[diiodidomercury(II)]-μ2-2-aminopyrazine-κ2 N 1:N 4]

In the crystal of the title polymeric compound, [HgI2(C4H5N3)]n, the HgII cation is located on a twofold rotation axis and is coordinated by two I− anions and two 2-aminopyrazine ligands in a distorted HgI2N2 tetrahedral geometry. In the crystal, the 2-aminopyrazine ligand is equally disordered over two positions about an inversion center, and bridges the HgII cations with pyrazine N atoms to form a polymeric chain running along the c axis. In the polymeric chain, the amino groups link to the coordinated I− anions via intermolecular N—H⋯I hydrogen bonds.

In the crystal of the title polymeric compound, [HgI 2 (C 4 H 5 N 3 )] n , the Hg II cation is located on a twofold rotation axis and is coordinated by two I À anions and two 2-aminopyrazine ligands in a distorted HgI 2 N 2 tetrahedral geometry. In the crystal, the 2-aminopyrazine ligand is equally disordered over two positions about an inversion center, and bridges the Hg II cations with pyrazine N atoms to form a polymeric chain running along the c axis. In the polymeric chain, the amino groups link to the coordinated I À anions via intermolecular N-HÁ Á ÁI hydrogen bonds.
The asymmetric unit of the title compound, (Fig. 1), contains one half molecule. The Hg II atom is four-coordinated in a distorted tetrahedral configuration by two N atoms from two 2-aminopyrazine and two I atoms. The Hgd-I and Hg-N bond lengths angles are collected in Table 1.
Intermolecular N-H···I hydrogen bonds (Table 2) seem to be effective in the stabilization of the polymeric structure ( Fig. 2).

Experimental
For the preparation of the title compound, a solution of 2-aminopyrazine (0.15 g, 1.50 mmol) in methanol (10 ml) was added to a solution of HgI 2 (0.55 g, 1.50 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 needle crystals of the title compound were isolated (yield 0.63 g, 76.4%).

Refinement
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). In the crystal, the 2-aminopyrazine ring is equqlly disordered over two positions about an inversion center.

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: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 2.67 e Å −3 Δρ min = −2.69 e Å −3 Extinction correction: SHELXTL (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.015 (2) 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.  (7) 0.0154 (5)