Hexaaquamagnesium dibromide 5-(pyridinium-3-yl)tetrazol-1-ide

In the title compound, [Mg(H2O)6]Br2·2C6H5N5, the MgII atom, lying on an inversion center, is coordinated by six water molecules in a distorted octahedral geometry. The pyridine and tetrazole rings in the 5-(pyridinium-3-yl)tetrazol-1-ide zwitterion are nearly coplanar, twisted from each other by a dihedral angle of 5.70 (1)°. The zwitterions, Br anions and complex cations are connected by O—H⋯Br, O—H⋯N and N—H⋯Br hydrogen bonds, leading to the formation of a three-dimensional network.

In the title compound, [Mg(H 2 O) 6 ]Br 2 Á2C 6 H 5 N 5 , the Mg II atom, lying on an inversion center, is coordinated by six water molecules in a distorted octahedral geometry. The pyridine and tetrazole rings in the 5-(pyridinium-3-yl)tetrazol-1-ide zwitterion are nearly coplanar, twisted from each other by a dihedral angle of 5.70 (1) . The zwitterions, Br anions and complex cations are connected by O-HÁ Á ÁBr, O-HÁ Á ÁN and N-HÁ Á ÁBr hydrogen bonds, leading to the formation of a three-dimensional network.

Comment
Tetrazole compounds have attracted more attention as phase transition dielectric materials for its applications in micro-electronics, memory storage. With the purpose of obtaining phase transition crystals of 3-(1H-tetrazol-5-yl)pyridine compounds, its interaction with various metal ions has been studied and a series of new materials have been elaborated with this organic molecule (Fu et al., 2007Zhao et al., 2008). In this paper, we describe the crystal structure of the title compound.
The asymmetric unit of the title compound ( Fig. 1) is composed of one zwitterionic organic molecule, half [Mg(H 2 O) 6 ] 2+ cation and one Br anion. In the zwitterionic organic molecule, the pyridine N atom is protonated. The pyridine and tetrazole rings are nearly coplanar and only twisted from each other by a dihedral angle of 5.70 (1)°. The geometric parameters of the tetrazole ring are comparable to those in related molecules (Fu et al., 2009;Zhao et al., 2008).
In the crystal structure, the intermolecular hydrogen bonds are formed by all H atoms of the water molecules and pyridine N atoms with the tetrazole N atoms or Br anions. The complex cations [Mg(H 2 O) 6 ] 2+ and Br anions are linked in the crystal through O-H···Br hydrogen bonds into an infinite cation-anion sheet parallel to (0 0 1). The two-dimensional sheets are linked by organic molecules through O-H···N and N-H···Br hydrogen bonds into a three-dimensional network (Table 1 and Fig. 2).

Experimental
MgBr 2 .6H 2 O (2 mmol) and 3-(1H-tetrazol-5-yl)pyridine (0.528 g, 2 mmol) were dissolved in 70% methanol aqueous solution, and then 2 ml HBr was added. Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of the solution at room temperature after two weeks. The crystals were colourless, block, and of average size 0.2×0.3×0.4 mm.
The permittivity measurement shows that there is no phase transition within temperature range from 100 to 400 K, and the permittivity is 9.1 at 1 MHz at room temperature.

Refinement
H atoms attached to C and N atoms were positioned geometrically and treated as riding, with C-H = 0.93 and N-H = 0.86 Å and with U iso (H) = 1.2U eq (C, N). H atoms of water molecules were located in a difference Fourier map and refined using a riding model, with U iso (H) = 1.5U eq (O).