Ternary Ni(II) and Cu(II) complexes with 4,6-dimethyl-1,2,3-triazolo-[4,5-d]pyrimidin-5,7-dionato and chelating aliphatic amines as auxiliary ligands: Variability in the binding site and hydrogen-bond networks

Nickel(II) and copper(II) complexes bearing the anionic form of 4,6-dimethyl-1,2,3-triazolo-[4,5-d]pyrimidin-5,7-dione (dmax−) and one of the aliphatic amines ethylenediamine (en), 1,3-diaminopropane (dap) or 1,3-bis-(3-aminopropyl)-amine (bapa) have been synthesized and characterized. The crystal structures of Ni-en, Cu-en and Cu-bapa compounds have been solved by X-ray diffraction whereas only partial data are available for the Cu-dap compound. The binding site for the heterocycle is the triazole nitrogen atom furthest from the pyrimidine ring (N2), except for the copper(II) compound with en as auxiliary ligand, for which the bond is established through N1, this binding site being unprecedented for azaxanthine derivatives. Hydrogen atoms of amine groups and interstitial water molecules form hydrogen bonds that are involved both in the first and in the second coordination spheres. In the first, N(amine)–H links to acceptor atoms of dmax− stabilize the complexes, probably conditioning, together with the Jahn–Teller distortion, the unusual N1 link in the Cu-en compound. In the second sphere, two-dimensional networks are formed with interstitial water molecules acting as the “main glue”.

The synthesis and characterization of nickel(II) and copper(II) complexes with the anionic form of 4,6-dimethyl-1,2,3-triazolo[4,5-d]pyrimidin-5,7-dione (dmax−) and aliphatic amines are described. X-ray data show coordination of dmax− through the unusual site N1 in the Cu-ethylenediamine compound and the usual binding mode through N2 in the other. H bond interactions generate two-dimensional networks.Figure optionsDownload as PowerPoint slide