Two homometal–organic coordination polymers, [Ba(C7H3NO5)2(H2O)4Ba(H2O)3]n(2H2O)n and [[Cu(C7H2- NO5)(C5H6N2)2]2Cu(C5H6N2)2(H2O)2]n(6H2O)n, have been synthesized and characterized by X-ray single-crystal diffraction. In the barium compound (the first example of chelidamic acid introduced into the alkaline earth metal organic framework), two independent barium ions are coordinated by water and chelidamic acid molecules in monocapped and bicapped square anti-prismatic geometries. The two independent chelidamic acid molecules bridge several alkaline earth metal ions assembling a layered metal organic structure. In the copper compound, chelidamic acid shows its versatility as a ligand since it bridges three copper ions, with the carboxylate O atoms, the hydroxyl O atom, and the pyridine N atom coordinating the 3D metal ions. 4-Aminopyridine and water as ligands complete the coordinating sphere of the two independent Cu ions in distorted octahedral geometries. The equilibrium constants for the chelidamic acid- 4-aminopyridine proton transfer system and the stoichiometry and stability of complexation of this system with Cu(II) and Ba(II) ions in aqueous solution were investigated by potentiometric pH titration method. The stoichiometry of some complex species in solution was found to be similar to the cited crystalline metal ion complexes.
