Tetraaquabis[2-(4-pyridylsulfanyl)acetato-κN]nickel(II)

In the centrosymmetric title complex, [Ni(C7H6NO2S)2(H2O)4], the NiII atom, located on a centre of inversion, is coordinated by two N atoms from two 2-(4-pyridylsulfanyl)acetate ligands and four water O atoms in an octahedral geometry. In the crystal, intermolecular O—H⋯O hydrogen bonds between the coordinated water molecules and the carboxylate group of the anionic 2-(4-pyridylsulfanyl)acetate ligands link these discrete mononuclear units into a three-dimensional network.

In the centrosymmetric title complex, [Ni(C 7 H 6 NO 2 S) 2 -(H 2 O) 4 ], the Ni II atom, located on a centre of inversion, is coordinated by two N atoms from two 2-(4-pyridylsulfanyl)acetate ligands and four water O atoms in an octahedral geometry. In the crystal, intermolecular O-HÁ Á ÁO hydrogen bonds between the coordinated water molecules and the carboxylate group of the anionic 2-(4-pyridylsulfanyl)acetate ligands link these discrete mononuclear units into a threedimensional network.

Comment
Recently, functional metal complexes with polycarboxylate-based pyridine ligands have gained more and more interest due to their intriguing structures and potential applications in magnetism (Zhao et al. 2010), and luminescence (Wang et al. 2007).
Acting as one of flexible multifunctional building blocks, 2-(4-pyridylsulfanyl)acetic acid with three potential metal binding sites and various flexible connection modes (Kondo et al., 2002;Zhang et al., 2004;Qin et al., 2004) has been extensively used to construct novel metal complexes with discrete mononuclear structure or polymeric coordination framework with variable dimensionality. Herein, as the continuing investigations on the coordination chemistry of the ligand, we report the crystal structure of a tetraaquonickel(II) complex with deprotonated 2-(4-pyridylsulfanyl)acetate ligand, (I).
The molecular structure of the title mononuclear complex is show Fig.1 and selected bond lengths and angles are listed in Table 1. The Ni II atom in the mononuclear structure of I lies on an inversion centre and is in a octahedral coordination environment involving two pyridyl N atoms from two different 2-(4-pyridylsulfanyl)acetate ligand and four O donors from four water molecules. In the crystal structure, four intermolecular O-H···O hydrogen bonds between the coordinated water molecules and the carboxylate group of 2-(4-pyridylsulfanyl)acetate ligand link adjacent mononuclear structures into a three-dimensional supramolecular network ( Fig.2 and Table 2).

Experimental
A methanol solution of 2-(4-pyridylsulfanyl)acetic acid (25.3 mg, 0.1 mmol) was carefully layered onto a buffer layer of ethyl acetate (2.0 ml) in a straight glass tube, meanwhile the pH value of the top layer was carefully adjusted to 7.0 by slow addition of triethylamine. Below which an aqueous solution containing NiCl 2 .6H 2 O (23.7 mg, 0.1 mmol) was placed.

Refinement
H atoms were located in a difference map, but refined using a riding model with C aromatic -H = 0.93Å, C methylene -H = 0.97Å or O-H = 0.85Å. U(H) was set to 1.2 U eq (C) or 1.5 U eq (O). Fig. 1 as those based on F, and R-factors based on ALL data will be even larger.