Tetraaquabis(2-{[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]sulfanyl}acetato)cobalt(II) monohydrate

In the title compound, [Co(C9H6N3O3S)2(H2O)4]·H2O, the two 2-{[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]sulfanyl}acetate ligands are monodentate. One coordinates the metal atom via the pyridyl N atom whereas the other coordinates via the carboxylate O atom. The CoII atom adopts a slightly distorted octahedral coordination geometry with four O atoms of the coordinated water molecules located in the equatorial plane and the N and O atoms of the two POA ligands in axial positions. In the crystal, the components are connected through O—H⋯O and O—H⋯N hydrogen bonds into a three-dimensional framework.

In the title compound, [Co(C 9 H 6 N 3 O 3 S) 2 (H 2 O) 4 ]ÁH 2 O, the two 2-{[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]sulfanyl}acetate ligands are monodentate. One coordinates the metal atom via the pyridyl N atom whereas the other coordinates via the carboxylate O atom. The Co II atom adopts a slightly distorted octahedral coordination geometry with four O atoms of the coordinated water molecules located in the equatorial plane and the N and O atoms of the two POA ligands in axial positions. In the crystal, the components are connected through O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds into a three-dimensional framework.

Comment
Recently, pyridyl-containing 1,3,4-oxadiazole-2-thiones have been systematically explored as promising bridging ligands in coordination chemistry (Du et al., 2006;Tripathi et al., 2007). Our contribution to these studies is synthesis of the mul- As shown in Fig. 1 (I) is a mononuclear complex. The asymmetric unit consists of the complex molecule and one water of crystallization. In (I) the Co II center is ligated by four O atoms from four water molecules located in the equatorial plane, and two monodentate POA anions. One POA anion coordinates the metal center via the pyridyl N atom whereas the other via the carboxylate O atom. The Co II ion is in a slightly distorted octahedral coordination environement with the in-plane and axial-trans angles being 175.09 (15), 177.66 (14) and 178.54 (13)°, and the bond distances Co-O and Co-N ranging from 2.074 (4) to 2.164 (4) Å.
In (I) the hydrogen-bonding interactions result in a 3D supramolecular network as shown in Fig. 2. The 3D hydrogenbonded network is stabilized through the intermolecular π···π interactions with a center-to-center distance of pyridyl groups being 3.662 Å and a center-to-center distance of oxadiazole groups being 3.375 Å, respectively. There are complicated hydrogen-bonding system in (I): each coordination water molecule forms two O-H···O hydrogen bonds while every uncoordinated carboxyl group of POA in one monomer adopts bridging and chelating coordination modes to links with two other monomers through the formed three O-H···O hydrogen bonds, and especially the lattice water O11 acting as a tetrahedral hydrogen-bonding connector binds with four monomers (1) through three O···O hydrogen bonds and one O···N hydrogen bond. In this way monomers of (I) are linked into the 3D supramolecular architecture.
Pale yellow precipitate was filtered. After recrystallized from alcohol/water (2:1), the obtained pure product was 2.76 g. The title compound (1), was prepared according to the following process. A mixture of NaPOA (51.8 mg, 0.2 mmol), CoCl 2 .6H 2 O (23.8 mg, 0.1 mmol) and deionized water (20 ml) was stirred for 30 minutes and then filtered. The filtrate was allowed to evaporate at room temperature for a week, and then red block crystals were obtain in 57% yield. Selected

Refinement
The H atoms of water molecules were located from difference Fourier maps and refined with restraints imposed on O-H and H···H distances and with U iso (H) = 1.5U eq (O). The remaining hydrogen atom positions were generated geometrically.
All H atoms were allowed to ride on their parent atoms with U iso (H) = 1.5U eq (C). Fig. 1. ORTEP diagram of of the title compound with 30% probability ellipsoids for all nonhydrogen atoms.  (1).

Figures
Crystal data [Co(C 9

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 > 2sigma(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.