Synthesis, chemical characterization, X-ray crystal structure and magneticproperties of oxalato-bridged copper(II) binuclear complexes with 2,2 '-bipyridine and diethylenetriamine as peripheral ligands

Two new mu-oxalato binuclear copper(II) complexes, [{Cu(NO3)(H2O)(bipy)}(2) (ox)] (1) and [{Cu(dien)}(2)(ox)](NO3)(2) (2), with ox = oxalate, dien = di ethylenetriamine and bipy = 2,2'-bipyridine, have been synthesized and thei r crystal and molecular structures have been determined by single-crystal X -ray diffraction methods. The crystal structure of 1 consists of centrosymm etric neutral dimers where the copper atoms lie in a strongly elongated oct ahedral environment, surrounded by two nitrogen atoms of a bipy molecule an d two oxygen atoms of the bridging oxalato group in the equatorial plane an d oxygen atoms of water molecules and nitrate ions in the axial positions. Crystal structure of 2 is made up of non-coordinated nitrate anions and asy mmetric binuclear cations in which copper atoms are in a distorted square-p yramidal coordination with three atoms of a diethylenetriamine ligand and a n oxygen atom of the asymmetrically coordinated oxalato bridge building the basal plane and the other oxygen atom of the oxalato ligand filling the ap ical position. Both compounds have been also characterized by Fourier trans form infrared (FT-IR) and electron spin resonance (ESR) spectroscopies, the rmal analysis and variable temperature magnetic susceptibility measurements . The two compounds exhibit antiferromagnetic exchange with a singlet-tripl et separation of -382 and -6.5 cm(-1) for 1 and 2, respectively. Magnetic a nd ESR results are discussed with respect to the crystal structure of the c ompounds. (C) 1999 Elsevier Science Ltd. All rights reserved.