A one-dimensional barium(II) coordination polymer with a coordinated nitro group of 2-nitrobenzoate

Abstract

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[(μ 2-2-nitrobenzoate-O,O,O-NO2)(μ 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(μ 2-2-nba-O,O,O-NO2)2 (μ 2-2-nba-O,O,O′)2] n 1 crystallizes in the centrosymmetric triclinic space group Pī 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 (μ 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 μ 2-carboxylate bridge between two symmetry related Ba(II) ions with a Ba···Ba distance of 4·5726(14) Å. The second unique 2-nba anion (μ 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···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 (μ 2-2-nba-O,O,O-NO2) and (μ 2-2-nba-O,O,O′) ligands resulting in alternating Ba···Ba distances of 4·5406(15) and 4·5726(14) Å across the chain.