Di-μ-aqua-bis[aqua(2,2′-bipyridine)(4-nitrobenzoato)cobalt(II)] bis(4-nitrobenzoate)

The title compound consists of a centrosymmetric bimetallic complex charge-balanced by free 4-nitrobenzoate anions. Each CoII ion exhibits a distorted cis-CoN2O4 octahedral coordination environment. In the crystal, the dications and anions are linked by O—H⋯O and C—H⋯O hydrogen bonds.


data reports
[Co 2 (H 2 O) 2 (C 10 H 8 N 2 ) 2 (C 7 H 4 NO 4 ) 2 ( 2 -H 2 O) 2 ] 2+ , the other half being generated by inversion symmetry (Fig. 1). The crystallographic inversion centre is situated at the midpoint of the line connecting the Co II atoms in the dimer. A chargebalancing 4-nitrobenzoate ion completes the structure.
In the centrosymmetric dimer, each Co II ion exhibits a distorted octahedral environment and is bonded to a terminal aqua ligand, a monodentate 4-nitrobenzoate ligand disposed cis to the terminal aqua ligand and a bidentate 2,2 0 -bipyridine molecule. A pair of cis-aqua ligands bridges the metal centres and completes the hexa-coordination around the metal ions resulting in a CoÁ Á ÁCo(1 -x, 1 -y, 1 -z) separation of 3.326 (2) Å . It is interesting to note that in three of the four known dinuclear cobalt compounds (Singh et al., 2007;Yang et al., 2011;Wang & Qi, 2014), the 4-nitrobenzoate anion functions as a monodentate ligand as in the title compound. One example each of a dinuclear (Jung et al., 2009) and a tetranuclear cobalt compound (Dimitrou et al., 2001) is known where the 4-nitrobenzoate ion functions as a symmetric bridging ligand.
The geometric parameters of 1 are in their normal ranges and are in agreement with reported data (Srinivasan et al., 2020). The Co-O w (w = water) bonds [2.0743 (10) and 2.1617 (9) Å ] are elongated as compared to the Co-O c (c = carboxylate) distance, which is the shortest at 2.0494 (9) Å . The cis-O-Co-O and N-Co-N bond angles range between 77.97 (4) and 100.02 (4) , while the trans bond angles deviate from ideal values, indicating a distortion of the {CoN 2 O 4 } octahedron.

Figure 2
The hydrogen-bonding scheme around the 4-nitrobenzoate anion showing the O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds as dashed lines. For symmetry codes see Table 1.

Figure 3
Environment of the anion, showing its hydrogen bonds to four symmetrically related dications via O-HÁ Á ÁO and C-HÁ Á ÁO bonds.

Figure 4
The hydrogen-bonding scheme around the dication showing its linking with eight anions and two cations via O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds.

Figure 1
The dinuclear dication in 1 with displacement ellipsoids drawn at the 50% probability level. Intramolecular hydrogen bonds are shown as broken lines [Symmetry code: total of four O-HÁ Á ÁO and five C-HÁ Á ÁO hydrogen bonds (Table 1). Each free 4-nitrobenzoate anion is linked with four symmetry-related dications with the aid of two O-HÁ Á ÁO hydrogen bonds and four C-HÁ Á ÁO hydrogen bonds (Figs. 2 and 3). Each of the dinuclear dicobalt dicationic species is linked with two symmetry-related dications and eight symmetry-generated anions (Fig. 4), resulting in a threedimensional supramolecular network.

Synthesis and crystallization
Crystals of 2 (0.0292 g, 0.05 mmol) were taken in DMSO (3 ml) to obtain a purple solution. 2,2 0 -Bipyridine (0.0078 g, 0.05 mmol) was dissolved in DMSO (3 ml) in a separate beaker and then was added dropwise to the cobalt solution with continuous swirling. The pale-orange solution thus obtained was left undisturbed at room temperature. After to days, dark-orange blocks of 1 started forming in the solution, which were isolated by filtration and air dried. Yield 60%.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 0.36 e Å −3 Δρ min = −0.31 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.