(2,2′-Bipyridine-6,6′-dicarboxylato-κ3 N,N′,O 6)(6′-carboxy-2,2′-bipyridine-6-carboxylato-κ3 N,N′,O 6)cobalt(III)

The CoIII atom in the title compound, [Co(C12H6N2O4)(C12H7N2O4)], is six-coordinated in a distorted octahedral geometry by four N atoms and two O atoms of the chelating 2,2′-bipyridine-6,6′-dicarboxylate and 6′-carboxy-2,2′-bipyridine-6-carboxylate ligands. Intermolecular O—H⋯O hydrogen bonds and face-to-face π-stacking interactions [centroid–centroid distance = 3.6352 (16) Å] between inversion-related pyridine rings link adjacent mononuclear units into a two-dimensional supramolecular structure, and several intermolecular C—H⋯O interactions are also observed.


Related literature
For the structure of a Co II compound with pyridine-2,6dicarboxylate and 4,4 0 -bipyridine, see: Ghosh et al. (2005). For the structures and thermal properties of five Ln III (Ln is a lanthanide) compounds with the title ligand, see: Wang et al.
In the title compound, the Co III center is six-coordinated in a distorted octahedral geometry by four N atoms and two O atoms of two chelating ligands L and HL (H 2 L= 2,2′-bipyridine-6,6′-dicarboxylic acid) (Fig. 1). Support for the assignment of a +3 oxidation state to Co comes from the Co-N and Co-O bond distances [1.8546 (19) Table 1].

Experimental
The title compound was obtained by the reaction of the mixture of Co(NO 3 ) 2 .6H 2 O, and 2,2′-dipyridine-6,6′-dicarboxylic acid in a molar ratio of 1:0.8 and 8 ml of water under hydrothermal conditions (at 393 K for 4 days and cooled to room temperature with a 2 K h -1 rate). The brown block crystals were washed by water (Yield: 30%).

Figure 1
The structure of the title compound with 50% probability displacement ellipsoids.

Figure 2
The two-dimensional layer structure of the title compound via hydrogen bonds and face-to-face π-stacking interactions.

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.