Synthesis, crystal structure and spectroscopic properties of copper(II) complexes derived from 2-methylamino-5-pyridin-2-yl-1,3,4-oxadiazole

Two new complexes with the formulae [Cu(L)(oxalatoo)(H2O)] . H2O (1) and [Cu(L)(2)(H2O)(2)](NO3)(2) (2), where L = (C8H8N4O) = 2-methylamino-5-pyridin-2-yl-1,3,4-oxadiazole, have been synthesized and characterized. The structure of compound I contains monomeric entities in which the copper(II) ions exhibit five-coordinate square-pyramidal geometry. The oxadiazole bidentate ligand links to the metal ion through the N-pyridine and one of the N-oxadiazole atoms. Two oxygen atoms from the oxalato ligand complete the basal positions. The oxygen atom of a water molecule occupies the apical one. Solvation water molecules are also present in the lattice. The structure of compound 2 consists of monomeric distorted octahedral copper(II) species. The copper(II) ions are coordinated to both bidentate oxadiazole ligands in the equatorial plane, with the two oxygen atoms of both water molecules placed in the axial positions. Nitrate groups act as counterions. The presence of pi-pi stacking interactions interconnecting the monomeric entities in both complexes is discussed. The EPR spectra of compounds 1 and 2 show axial symmetries. (C) 2002 Elsevier Science Ltd. All rights reserved.