Hexaaquamagnesium(II) bis{[2-(1-phenyl-1H-tetrazol-5-yl)sulfanyl]acetate}

The asymmetric unit of the title compound, [Mg(H2O)6](C9H7N4O2S)2, contains one-half of a [Mg(H2O)6]2+ cation ( symmetry) and one uncoordinated 2-[(1-phenyl-1H-tetrazol-5-yl)sulfanyl]acetate anion. The MgII cation is coordinated by six water molecules, exhibiting a slightly distorted octahedral coordination. A two-dimensional network parallel to (001) is formed via extensive hydrogen-bonding interactions involving the water molecules as donors and the tetrazole N and carboxylate O atoms of the anion as acceptors. The shortest distance between two adjacent parallel benzene rings is 3.315 (2) Å. The dihedral angle between the benzene ring and the tetrazole ring is 40.98 (2)°.

The asymmetric unit of the title compound, [Mg(H 2 O) 6 ]-(C 9 H 7 N 4 O 2 S) 2 , contains one-half of a [Mg(H 2 O) 6 ] 2+ cation (1 symmetry) and one uncoordinated 2-[(1-phenyl-1H-tetrazol-5-yl)sulfanyl]acetate anion. The Mg II cation is coordinated by six water molecules, exhibiting a slightly distorted octahedral coordination. A two-dimensional network parallel to (001) is formed via extensive hydrogen-bonding interactions involving the water molecules as donors and the tetrazole N and carboxylate O atoms of the anion as acceptors. The shortest distance between two adjacent parallel benzene rings is 3.315 (2) Å . The dihedral angle between the benzene ring and the tetrazole ring is 40.98 (2) .

Comment
The design and synthesis of supramolecular complexes with a high-nuclearity and N-containing carboxylate ligands, especially tetrazole-containing ligands, has been a rapidly growing area of research due to their fascinating structures and interesting physical properties (He et al., 2005). Several transition metal and rare earths metal complexes with similar ligand systems were reported (Yang et al., 2008).
We are interested in the solid-state coordination chemistry of ligands derived from 2-(1-phenyl-1H-tetrazol-5ylthio)acetic acid (HPsta). In order to understand the behavior of alkali earth metals with the HPsta ligand, we prepared the title compound, [Mg(H 2 O) 6 ](Psta) 2 , (I), the synthesis and structure of which are reported here.
As shown in Fig. 1, the asymmetric unit of (I) consists of one-half of a [Mg(H 2 O) 6 ] 2+ cation (site symmetry 1) and an uncoordinated 2-(1-phenyl-1H-tetrazol-5-ylthio)acetate monoanion. The Mg II atom is coordinated by six water molecules in a slightly distorted octahedral coordination. The corresponding Mg-O distances (  (Zhang et al., 2006;Zhou et al., 2008). The dihedral angle between the benzene ring and the tetrazole ring is 40.98 (2) °. In the crystal structure, the two Psta groups are involved in a number of intermolecular hydrogen bonds (Table 2) involving the O and N atoms as acceptors and the coordinated water molecules as donor groups ( Fig. 2; Table 2), leading to a layer structure extending parallel to (001). In addition, π-π stacking is observed with a shortest distance between two adjacent parallel benzene rings of 3.315 (2) Å.

Experimental
The ligand 2-(1-phenyl-1H-tetrazol-5-ylthio)acetic acid (HPsta) was synthesized according to the literature method (D'Amico et al., 1957). To prepare the title complex, the ligand HPsta (0.4 mmol,0.0944 g) was dissolved in methanol (6 ml) at 348 K and an aqueous solution (4 ml) containing MgCO 3 (0.0336 g, 0.4 mmol) was added. The resulting solution was stirred at 348 K for 4 h, then cooled to room temperature and filtered. Colorless, prismatic crystals suitable for X-ray diffraction were obtained by slow evaporation over several days, with a yield of 61%. Elemental analysis, found (

Refinement
Water H atoms were located in a difference Fourier map and refined freely. All other H atoms were placed in their calculated positions and refined as riding with U iso (H) = 1.2U eq (C).

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq