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[(mu(2)-2-nitrobenzoate-O,O,O-NO2)(mu(2)-2-nitrobenzoate-O,O,O')]] 1. On heating at 100 degrees 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 degrees 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 PT 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...Ba distance of 4.5726(14) angstrom. 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...Ba separation of 4.5406(15) angstrom. 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 center dot center dot center dot Ba distances of 4.5406(15) and 4.5726(14) angstrom across the chain.