Di-μ-aqua-bis{triaqua[5-(1-oxopyridin-4-yl)tetrazol-1-ido]sodium}

In the title compound, [Na2(C6H4N5O)2(H2O)8], the NaI atom is in a distorted octahedral environment defined by six O atoms, one from the 5-(1-oxopyridin-4-yl)tetrazolide anion and five from water molecules. Two water molecules act as bridging ligands, resulting in the formation of dimeric units organized around inversion centers. In the organic anion, the pyridine and tetrazole rings are nearly coplanar, forming a dihedral angle of 4.62 (1)°. The dimeric units and organic anions are connected by O—H⋯O and O—H⋯N hydrogen bonds, leading to the formation of a three-dimensional network.

In the title compound, [Na 2 (C 6 H 4 N 5 O) 2 (H 2 O) 8 ], the Na I atom is in a distorted octahedral environment defined by six O atoms, one from the 5-(1-oxopyridin-4-yl)tetrazolide anion and five from water molecules. Two water molecules act as bridging ligands, resulting in the formation of dimeric units organized around inversion centers. In the organic anion, the pyridine and tetrazole rings are nearly coplanar, forming a dihedral angle of 4.62 (1) . The dimeric units and organic anions are connected by O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds, leading to the formation of a three-dimensional network.

Comment
Tetrazole compounds attracted more attention as phase transition dielectric materials for its application in micro-electronics, memory storage. With the purpose of obtaining phase transition crystals of tetrazol-pyridine compounds, its interaction with various metal ions has been studied and a series of new materials have been elaborated with this organic molecule (Zhao et al., 2008;Fu et al., 2007;. In this paper, we describe the crystal structure of the title compound, tetraaquabis[5-(1-oxopyridin-4-yl)tetrazol-1-ide]sodium(I).
In the title compound, the asymmetric unit is composed of one organic anion, four H 2 O molecules and one Na + cation.
The Na I center, with slightly distorted octahedral geometry, is surrounded by six oxygen atoms. Two water molecules act as abridging ligand, resulting in the formation of dimeric unit ( Fig. 1) organized around inversion center. In the organic anion, the tetrazole N atoms are deprotonated. The pyridine and tetrazole rings are nearly coplanar and only twisted from each other by a dihedral angle of 4.62 (1)°. The geometric parameters of the tetrazole rings are comparable to those in related molecules (Zhao et al., 2008;Fu et al., 2009).
In crystal structure, the intermolecular hydrogen bonds are formed by all H atoms of the water molecules with tetrazole  (Table 1 and Fig.2).

Experimental
A mixture of 4-(1H-tetrazol-5-yl)pyridine 1-oxide (0.4 mmol) and NaOH (0.4 mmol), ethanol (1 ml) and a few drops of water sealed in a glass tube was maintained at 373 K. Colorless needle crystals suitable for X-ray analysis were obtained after 3 days.
While the permittivity measurement shows that there is no phase transition within the temperature range (from 100 K to 400 K), and the permittivity is 8.4 at 1 MHz at room temperature.

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.93 Å (aromatic) with U iso (H) = 1.2U eq (C). H atoms of water molecule were located in difference Fourier maps and included in the subsequent refinement using restraints (O-H= 0.85 (1)Å and H···H= 1.40 (2)Å) with U iso (H) = 1.5U eq (O). In the last cycles of refinement, they were treated as iding on their parent O atoms.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.