The aqueous reaction of barium carbonate with 2-nitrobenzoic acid (2-nbaH) results in the formation of a one-dimensional coordination polymer, catena-poly[[hexa(aqua)dibarium(II)]bis[($\mu_2$-2-nitrobenzoate-O,O,O-NO₂)($\mu_2$-2-nitrobenzoate-O,O,O')]] 1. On heating at 100°C compound 1 is dehydrated to anhydrous barium bis(2-nitrobenzoate) 2. The anhydrous compound can be re-hydrated to 1 on exposure to water vapour. Compounds 1 and 2 were characterized by elemental analysis, IR and UV-Vis spectra, DSC thermograms, weight loss studies and the structure of 1 was determined. 1 and 2 can be thermally decomposed to BaCO₃ by heating at 800°C. The polymer [[Ba(H₂O)₃]₂($\mu_2$-2-nba-O,O,O-NO₂)₂ ($\mu_2$-2-nba-O,O,O')₂]$_n$ 1 crystallizes in the centrosymmetric triclinic space group P$_{\bar{i}}$ and all atoms are located in general positions. The polymeric structure is based on a dimeric unit and consists of three water molecules coordinated to a central Ba(II) and two unique 2-nitrobenzoate (2-nba) anions, one of which ($\mu_2$-2-nba-O,O,O-NO₂) functions as a tridentate ligand and is linked to a Ba(II) through the oxygen atom of the -NO₂ group and forms a monoatomic $\mu_2$-carboxylate bridge between two symmetry related Ba(II) ions with a Ba$\cdots$Ba distance of 4.5726(14) Å. The second unique 2-nba anion ($\mu_2$-2-nba-O,O,O') also functions as a tridentate ligand with the carboxylate oxygen atoms linked to a Ba(II) ion in a bidentate fashion and one of the carboxylate oxygen atoms forming a monoatomic bridge between two symmetry related Ba(II) ions resulting in a Ba$\cdots$Ba separation of 4.5406(15) Å. These differing tridentate 2-nba ligands link {Ba(H₂O)₃} units into a one-dimensional polymeric chain extending along 𝑏 axis. In the infinite chain each nine coordinated Ba(II) is bonded to three water molecules and further linked to six oxygen atoms of four different 2-nitrobenzoate anions with alternating pairs of Ba(II) ions in the chain bridged by a pair of ($\mu_2$-2-nba-O,O,O-NO₂) and ($\mu_2$-2-nba-O,O,O') ligands resulting in alternating Ba$\cdots$Ba distances of 4.5406(15) and 4.5726(14) Å across the chain.