catena-Poly[[[diaquacobalt(II)]-μ-(3,5-dinitro-2-oxidobenzoato)-κ3 O 1,O 2:O 1′-[tetraaquacobalt(II)]-μ-(3,5-dinitro-2-oxidobenzoato)-κ3 O 1:O 1′,O 2] dihydrate]

In polymeric title compound, {[Co2(C7H2N2O7)2(H2O)6]·2H2O}n, obtained from the reaction of 3,5-dinitrosalicylic acid with cobalt(II) acetate, both CoII atoms are located on inversion centres and exhibit a distorted octahedral coordination geometry. The coordination sphere about one CoII atom comprises four O-atom donors from two bidentate chelate (Ophenolate and Ocarboxyl) and bridging dianionic ligands and two water molecules [Co—O range = 2.0249 (11)–2.1386 (14) Å], while that about the second CoII atom has four water molecules and two bridging carboxylate O-donor atoms [Co—O range = 2.0690 (14)–2.1364 (11) Å]. The coordinated water molecules as well as the water molecules of solvation give O—H⋯O water–water and water–carboxyl hydrogen-bonding interactions in the three-dimensional framework structure.

In polymeric title compound, {[Co 2 (C 7 H 2 N 2 O 7 ) 2 (H 2 O) 6 ]Á-2H 2 O} n , obtained from the reaction of 3,5-dinitrosalicylic acid with cobalt(II) acetate, both Co II atoms are located on inversion centres and exhibit a distorted octahedral coordination geometry. The coordination sphere about one Co II atom comprises four O-atom donors from two bidentate chelate (O phenolate and O carboxyl ) and bridging dianionic ligands and two water molecules [Co-O range = 2.0249 (11)-2.1386 (14) Å ], while that about the second Co II atom has four water molecules and two bridging carboxylate O-donor atoms [Co-O range = 2.0690 (14)-2.1364 (11) Å ]. The coordinated water molecules as well as the water molecules of solvation give O-HÁ Á ÁO water-water and water-carboxyl hydrogen-bonding interactions in the three-dimensional framework structure.

Related literature
For the structures of similar hydrated complexes of Co II , see: Deng et al. (2008); Sobolev et al. (2003); Tahir et al. (1996Tahir et al. ( , 1997. For the structure of a mixed-ligand Co II complex with 3,5-dinitrosalicylic acid and the structures of the acid and its salts, see: Zhong et al. (2009);Kumar et al. (1999);Smith et al. (2003Smith et al. ( , 2007.
In the structure (Fig. 1 which extend along the b cell direction (Fig. 2). The coordinated water molecules as well as the water molecule of solvation (O4W) give both water-water and inter-chain O-H···O carboxyl, nitro hydrogen-bonding associations (Table 1), giving an overall three-dimensional framework structure.

Experimental
The title compound was synthesized by heating together under reflux for 10 minutes, 1 mmol of cobalt(II) acetate and 2 mmol of 3,5-dinitrosalicylic acid in 50 ml of 50% ethanol-water. After concentration to ca 30 ml, partial room temperature evaporation of the hot-filtered solution gave large well formed red block crystals of (I).

Refinement
Hydrogen atoms potentially involved in hydrogen-bonding interactions were located by difference methods and their positional and isotropic displacement parameters were refined. Other H atoms were included in the refinement in calculated positions with C-H = 0.93 Å and allowed to ride, with U iso (H) = 1.2U eq (C).