Syntheses, Structures, and Properties of Five Coordination Compounds Based N-Heterocyclic Ligands

Abstract

Five coordination compounds based on 2,6-dihydroxypyrimidine-4-carboxylic acid (H3pymca), Ni2(Hpymca)2(bipy)(H2O)6?2H2O (1), Co2(Hpymca)2(bipy)(H2O)6?2H2O (2), Ni(Hpymca)(pya)(H2O)2 (3), Zn(Hpymca)(pyrapyri)(H2O)?H2O (4), and [Ba(H2pymca)2]n (5) (bipy = 4,4'-bipyridine, pya = pyridine-2-aldoxime, pyrapyri = 2-(1H-pyrazol-3-yl)pyridine) have been synthesized by hydrothermal methods and structurally characterized. The structure analyses showed that compounds 1 and 2 are isostructural with triclinic, P-1 space group, where the bipy molecule bridges with two metal ions, and Hpymca2- anions serve as bidentate-terminated ligands around the metal ions through carboxylate and pyrimidine groups. For compounds 3 and 4, the Hpymca2- ligands and N-heterocyclic auxiliary molecules bind to the central metal atoms in the chelating coordination modes to form the mononuclear structures. For compound 5, Ba ions and H2pymca- anions are self-assembled to construct a 3D network with a column-layered structure through coordination interactions. In addition, compounds 1?4 are further expanded into 3D and 2D supramolecular structures by hydrogen bonding, respectively. Compounds 1?5 indicated the characteristic fluorescence emissions of the H3pymca ligand, which were observed at 415 nm, 437 nm, 436 nm, 445 nm, and 475 nm, respectively.. KEYWORDS :Coordination compound, Pyridine-2-aldoxime, 2,6-Dihydoxypyrimidine-4-carboxylic acid, 2-(1H-pyrazol- 3-yl)pyridine, 4,4'-Bipyridine.