Two novel barium(ii) 2D coordination polymers, {[Ba(µ-H2O)(H2O)2(µ-pyzdc)]}n (1) and {[Ba(H2O)2(µ-Hpyzdc)(Hpyzdc)]⋅2H2O}n (2) (pyzdcH2 = 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.
