Two Different Barium(II) 2D Coordination Polymers Constructed with Pyrazine-2,3-Dicarboxylate: Synthesis, Crystal Structures, and Thermal Decomposition to Barium(II) Carbonate Nanoparticles

Two novel barium(II) 2D coordination polymers, {[Ba(mu-H2O)(H2O)(2)(m-pyzdc)]}(n) (1) and {[Ba(H2O)(2)(mu-Hpyzdc) (Hpyzdc)]center dot 2H(2)O}(n) (2) (pyzdcH(2) = pyrazine-2,3-dicarboxylic acid), were prepared by reaction of barium(II) chloride dihydrate and pyrazine-2,3-dicarboxylic acid under similar experimental conditions (slightly different pH values) and characterised by elemental analysis, IR spectroscopy, and thermogravimetric analysis/differential thermal analysis methods. Their crystal structures were determined by single-crystal X-ray structure analysis and it was revealed that the barium(II) ion has a distorted bicapped square antiprismatic coordination geometry in 1 and a distorted tricapped trigonal prismatic geometry in 2, composed of water molecules, carboxylate O, and pyrazine N atoms in both cases. The polymers 1 and 2 have different connectivity, as the pyrazine-2,3-dicarboxylate ion acts as multidentate bridging ligand in both 1 and 2, but also as an N,O'-bidentate terminal ligand in 2. There are terminal coordinated water molecules in both 1 and 2, but bridging water molecules are present only in 1 and water molecules of crystallisation only in 2. BaCO3 nanoparticles were formed by thermal decomposition of 1 in the presence of polyethylene glycol, and their structure and morphology were studied by powder X-ray diffraction and scanning electron microscopy. According to the powder X-ray diffraction pattern, BaCO3 was formed with an orthorhombic witherite structure.