Synthesis and magnetic properties of copper(II) complexes derived from dihydrazones

A series of new acyldihydrazones, H2Ln, obtained by condensation of ethylpyruvate with oxalic, malonic, succinic, glutaric and adipic dihydrazides, undergoes quantitative hydrolysis of the -2C(O) OC2H5 group via reactions with copper( II) acetate in alcoholic medium. Dicopper( II) complexes of the general formula [Cu-2(L-/n) center dot H2O] center dot xH(2)O have been isolated, where L-'n refers to the quadruply deprotonated pyruvic acid dihydrazone ligand and n refers to the number of carbon atoms of the aliphatic spacer between the two acylhydrazone units. The isolated complexes were characterized by elemental analyses, infrared spectra, mass spectra, as well as variable temperature magnetic susceptibility measurements. Magnetic susceptibility measurements in the 4.2 - 298 K range indicate significant antiferromagnetic coupling between copper( II) centers and suggest association of the coordinated copper( II) units Cu(ONO) via oxazine oxygen bridges. This leads to a polymeric structure where the dimeric units are connected together with aliphatic spacer. From the best fit values of the mole fraction of paramagnetic uncoupled copper( II) centers (rho), the degree of association in these polynuclear copper( II) complexes has been estimated.