Synthesis and chemical characterization of CuII, NiII and ZnII complexes of 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole ligands

The synthesis and structural characterization of NiII, CuII and ZnII complexes of two chelating 1,2,4-oxadiazole ligands, namely 3,5-bis(2′-pyridyl)-1,2,4-oxadiazole (bipyOXA) and 3-(2′-pyridyl)5-(phenyl)-1,2,4-oxadiazole (pyOXA), is here reported. The formed hexacoordinated metal complexes are [M(bipyOXA)2(H2O)2](ClO4)2 and [M(pyOXA)2(ClO4)2], respectively (M = Ni, Cu, Zn). X-ray crystallography, 1H and 13C NMR spectroscopy and C, N, H elemental analysis data concord in attributing them an octahedral coordination geometry. The two coordinated pyOXA ligands assume a trans coplanar disposition, while the two bipyOXA ligands are not. The latter result is a possible consequence of the formation of H-bonds between the coordinated water molecules and the nitrogen atom of the pyridine in position 5 of the oxadiazole ring. The expected splitting of the d metal orbitals in an octahedral ligand field explains the observed paramagnetism of the d8 and d9 electron configuration of the nickel(II) and copper(II) complexes, respectively, as determined by the broadening of their NMR spectra.

The reaction of copper(II), nickel(II) and zinc(II) with a 3-(2’-pyridyl)-1,2,4-oxadiazole ligand, substituted in 5 by phenyl or by 2-pyridyl, is described and the structure of the coordination complexes obtained characterized by NMR and X-ray crystallography.Figure optionsDownload as PowerPoint slideHighlights
► Hexacoordinated NiII, CuII and ZnII complexes of two 1,2,4-oxadiazole ligands.
► Structure elucidation by X-ray crystallography and NMR spectroscopy.
► Coordination chemistry explains the paramagnetism of the octahedral NiII complexes.