catena-Poly[[diaquanickel(II)]-bis(μ-2-{[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]sulfanyl}acetato)]

In the title compound, [Ni(C9H6N3O3S)2(H2O)2]n, the NiII atom, located on an inversion center, is ligated in an octahedral geometry by two carboxylate O atoms from two 2-{[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]sulfanyl}acetate (L) ligands and two O atoms from water molecules in the equatorial plane, and two pyridine N atoms from other two L ligands at the apical sites. Two L ligands bridge pairs of metal atoms in an antiparallel manner, forming centrosymmetric dinuclear quasi-rectangular units which are linked into infinite double-stranded chains parallel to [100]. O—H⋯O hydrogen bonds between the coordinating water molecules and the carboxylate groups of the L ligand as well as interchain S⋯N interactions [2.726 (2)–3.363 (2) Å] lead to the formation of a layer structure parallel to (001).

In the title compound, [Ni(C 9 H 6 N 3 O 3 S) 2 (H 2 O) 2 ] n , the Ni II atom, located on an inversion center, is ligated in an octahedral geometry by two carboxylate O atoms from two 2-{[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]sulfanyl}acetate (L) ligands and two O atoms from water molecules in the equatorial plane, and two pyridine N atoms from other two L ligands at the apical sites. Two L ligands bridge pairs of metal atoms in an antiparallel manner, forming centrosymmetric dinuclear quasi-rectangular units which are linked into infinite double-stranded chains parallel to [100]. O-HÁ Á ÁO hydrogen bonds between the coordinating water molecules and the carboxylate groups of the L ligand as well as interchain SÁ Á ÁN interactions [2.726 (2)-3.363 (2) Å ] lead to the formation of a layer structure parallel to (001).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: ZJ2075).
In (1) the Ni II center is located at the inversion center ligated by two carboxylato O atoms from two deprotonated L and two O atoms from water molecules in the equatorial plane, and two pyridyl N atoms from other two deprotonated L at the apical sites. Thus the Ni II ion is in a six-coordinated octahedral coordination geometry (Fig. 1). The bond distances of Ni -O and Ni-N range from 2.070 (2) to 2.116 (2) Å, while O-Ni-N angles range from 85.90 (7) to 94.10 (7) °, indicating a slight distortion from an ideal octahedron.
Complex (1) displays an extended infinite double-strand chain structure constructed of dinuclear quasi-rectangle units (Fig. 2). The dinuclear quasi-rectangle units are centrosymmetric and formed by two L anions antiparallelly bridging two metal centers in monodentate modes with two nickel atoms and two methylene carbon atoms of the L at the corners and the diagonal Ni···Ni distances of 11.886 (2) Å. As for L, the pyridyl group and the acetate group deviate from the center ring of oxadiazole-2-thione group, with the dihedral angels being 36.0 (7) and 88.5 (7) °, respectively. Notably, the conformation of L is apt to the dinuclear quasi-rectangle which is further stabilized by CH···π stacking interactions between antiparallel the pyridyl-1,3,4-oxadiazol groups of the L in the same rectangle unit with the distances of H pyridyl to centroid of oxadiazol group being 3.320 (2) Å and 3.353 (2) Å. The chains of complex (1) are connected by O-H···O hydrogen bonds between the coordinated water molecules (as donors) and the carboxylate groups of L (as acceptors), leading to the formation of a two-dimensional network structure (Fig. 2, Table 3). Additionally, the interchain weak interactions between S and N of the oxadiazole-2-thione groups of L stabilize the layer structure (the distances of S···N being in a range of 2.726 (2) to 3.363 (2) Å).
The filtrate was allowed to evaporate at room temperature for three days, and then green needle crystals were obtain in

Refinement
The H atoms of water were located from difference Fourier maps and included in the final refinement by using geometrical restrains, while the other hydrogen atom positions were generated geometrically and these H atoms were allowed to ride on their parent atoms.

Figure 1
Coordination environment of the nickel atom in (1). Displacement ellipsoids are drawn at the 30% probability level.

catena-Poly[[diaquanickel(II)]-bis(µ-2-{[5-(pyridin-4-yl)-1,3,4oxadiazol-2-yl]sulfanyl}acetato)]
Crystal data [Ni(C 9  Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.