trans-Tetraaquabis[2-(4-chlorophenoxy)acetato-κO 1]nickel(II)

In the title compound, [Ni(C8H6ClO3)2(H2O)4], the NiII ion is located on a crystallographic inversion centre and is octahedrally coordinated by two 2-(4-chlorophenoxy)acetate ligands in axial positions and by four water molecules in the equatorial plane. The acetate ligands are bound to the NiII ion in a monodentate manner through a carboxylate O atom. In the crystal, O—H⋯O hydrogen bonds link the molecules, forming a two-dimensional supramolecular network lying parallel to the ab plane.

In the title compound, [Ni(C 8 H 6 ClO 3 ) 2 (H 2 O) 4 ], the Ni II ion is located on a crystallographic inversion centre and is octahedrally coordinated by two 2-(4-chlorophenoxy)acetate ligands in axial positions and by four water molecules in the equatorial plane. The acetate ligands are bound to the Ni II ion in a monodentate manner through a carboxylate O atom. In the crystal, O-HÁ Á ÁO hydrogen bonds link the molecules, forming a two-dimensional supramolecular network lying parallel to the ab plane.
Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97. The interaction of transition metal ions with biologically active molecules such as amino acids and various organic acids is very important in biological systems (Parkin, 2004;Daniele et al., 2008). 4-chlorophenoxyacetic acid is one such acid that has been used to form various complexes with transition metals (Liwporncharoenvong & Luck, 2005;Smith et al., 1980;Wang et al., 2008). We report herein on the synthesis and crystal structure of a new nickel(II) complex involving this ligand.
In the title compound the Ni II ion is located on a crystallographic inversion centre ( In the crystal, molecules are linked via O-H···O hydrogen bonds (Table 1), resulting in the formation of a complex twodimensional supramolecular network lying parallel to the ab plane (Fig. 2).

Experimental
A solution of 4-chlorophenoxyacetic acid (40 mg, 0.2 mmol) in ethanol (3 ml) was added to a solution of Ni(CH 3 OO) 2 [15.96 mg 0.1 mmol] in water (1.5 ml) and stirred for 10 min at 303 K. Slow evaporation of the resulting solution gave green block-like crystals of the title compound suitable for X-ray analysis.

Refinement
All the H atoms were included in calculated positions and treated as riding: C-H = 0.97 Å (methylene), 0.93 Å (aromatic) and O-H = 0.86 Å, with U iso (H) = k × U eq (parent atom), where k = 1.5 for water H atoms and = 1.2 for other H atoms. In the final difference Fourier map the highest residual density peak is located near the metal atom.

trans-Tetraaquabis[2-(4-chlorophenoxy)acetato-κO 1 ]nickel(II)
Crystal data 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.