Diaquabis(benzoato-κO)bis[4,4,5,5-tetramethyl-2-(pyridin-4-yl-κN)imidazoline-1-oxyl 3-oxide]cobalt(II)

The title compound, [Co(C7H5O2)2(C12H16N3O2)2(H2O)2], was obtained from a conventional solvent evaporation method. The complex molecule is centrosymmetric, so pairs of equivalent ligands lie trans to each other in a slightly distorted octahedral CoN2O4 geometry. The CoII ion is coordinated by the pyridine N atoms from NITpPy ligands [NITpPy is 4,4,5,5-tetramethyl-2-(pyridin-4-yl)imidazoline-1-oxyl 3-oxide), water O atoms and two monodentate benzoate O atoms. The complex molecules are connected by O—H⋯O hydrogen bonds between water molecules and benzoate ligands, forming chains parallel to [100]. π–π stacking interactions between the benzoate ligands with centroid–centroid distances of 3.752 (2) Å connect the chains into layers parallel to (10-1).

The title compound, [Co(C 7 H 5 O 2 ) 2 (C 12 H 16 N 3 O 2 ) 2 (H 2 O) 2 ], was obtained from a conventional solvent evaporation method. The complex molecule is centrosymmetric, so pairs of equivalent ligands lie trans to each other in a slightly distorted octahedral CoN 2 O 4 geometry. The Co II ion is coordinated by the pyridine N atoms from NITpPy ligands [NITpPy is 4,4,5,imidazoline-1oxyl 3-oxide), water O atoms and two monodentate benzoate O atoms. The complex molecules are connected by O-HÁ Á ÁO hydrogen bonds between water molecules and benzoate ligands, forming chains parallel to [100].stacking interactions between the benzoate ligands with centroidcentroid distances of 3.752 (2) Å connect the chains into layers parallel to (101).
The title compound is isotypic with the analogous Mn II (Fettouhi et al., 1999) and Ni II structures (Zhao et al., 2003). It is a centrosymmetric monoculear compound (Fig. 1). The Co II ion is located on a crystallographic center of inversion and adopts a slightly distorted octahedral coordination environment defined by two pyridine N atoms from the NITpPy  Table 2). Furthermore, π-π stacking interactions among the benzoate aromatic rings with a Cg···Cg distance of 3.752 (2) Å connect neighbouring chains into a layered structure parallel to (101) (Fig. 3).

Experimental
The title compound was prepared by dropwise adding a methanol solution (15 ml) of cobalt(II) benzoate (0.0067 g, 0.2 mmol) to a solution of NITpPy (0.0468 g, 0.2 mmol) in dichloromethane (10 ml). The mixture was then stirred for 0.5 h and filtered. The clear blue filtrate was kept in the dark and was slowly evaporated at room temperature. A few weeks later, dark-blue crystals suitable for X-ray analysis were obtained.

Refinement
The H atoms of aromatic ring and methyl groups were generated geometrically and were included in the refinement in the riding model approximationwith d(C-H) = 0.93 Å, U iso = 1.2 U eq (C) and d(C-H) = 0.96 Å, U iso = 1.5 U eq (C), respectively. The H atoms of water molecules were located in difference Fourier maps and were constrained with d(O-

Figure 1
The molecular structure of the title complex with the atom-numbering scheme (symmetry code: A -x + 1, -y, -z + 1).
Ellipsoids were drawn at the 30% probability level.  The chain structure formed by O-H···O hydrogen bonds (dotted lines).

Figure 3
The packing of the title compound.

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.

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