catena-Poly[[[aqua(pyrazine-2-carboxamide-κ2 N 1,O)zinc]-μ-pyrazine-2-carboxamide-κ3 N 1,O:N 4] dinitrate]

In the crystal of the title compound, {[Zn(C5H5N3O)2(H2O)](NO3)2}n, the ZnII cation is N,O-chelated by two pyrazine-2-carboxamide (PCA) ligands and is further coordinated by one water molecule and by one pyrazine-N atom from an adjacent PCA ligand in a distorted ZnN3O3 octahedral geometry. One of the two independent PCA ligands bridges two ZnII cations, forming a zigzag polymeric chain running along the c axis. In the crystal, the NO3 − anions link to the chain via O—H⋯O and N—H⋯O hydrogen bonding. Weak intermolecular C—H⋯O interactions also occur.

In the crystal of the title compound, {[Zn(C 5 H 5 N 3 O) 2 (H 2 O)]-(NO 3 ) 2 } n , the Zn II cation is N,O-chelated by two pyrazine-2carboxamide (PCA) ligands and is further coordinated by one water molecule and by one pyrazine-N atom from an adjacent PCA ligand in a distorted ZnN 3 O 3 octahedral geometry. One of the two independent PCA ligands bridges two Zn II cations, forming a zigzag polymeric chain running along the c axis. In the crystal, the NO 3 À anions link to the chain via O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonding. Weak intermolecular C-HÁ Á ÁO interactions also occur.
The asymmetric unit of the title compound, (Fig. 1), contains one Zn II cation, two pyrazine-2-carboxamide ligands, one water molecule and two NO 3counter-ions. The Zn II atom is six-coordinated in a distorted octahedral configuration by two N and two O atoms from two pyrazine-2-carboxamide ligands and one O atom from one water molecule. The sixth coordination site is occupied by N atom from one bridging pyrazine-2-carboxamide ligand. The Zn-O and Zn-N bond lengths and angles are collected in Table 1. In the crystal structure, intra and intermolecular O-H···O, N-H···O 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 Zn(NO 3 ) 2 .4H 2 O (0.26 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 block crystals of the title compound were isolated (yield 0.36 g, 79.3%).

Refinement
Water H atoms were located in a difference Fourier map and refined isotropically. Other 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 (N,C).   Unit-cell packing diagram for title molecule. Hydrogen bonds are shown as dashed lines.  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.