Magnetic properties of binuclear copper (II) complexes of 4-substituted pyridine N-oxides

Abstract

The research for this dissertation was undertaken to study the mechanism of the superexchange interaction which results in the antiferromagnetic behavior in many binuclear copper(II) complexes. The dichlorocopper(II) complexes of 4-substituted pyridine N-oxides comprise a series in which the electron densities on the bridging oxygen atoms undergo significant changes. The extent and nature of the dependence of the exchange interaction on oxygen atom electron density changes were evaluated. The magnetic susceptibilities in the temperature range 77° to 400°K were precisely measured in fourteen binuclear complexes of 4-substituted pyridine N-oxides. The energy of the paramagnetic triplet state above the diamagnetic ground state for these complexes was determined from these data. Correlation of this energy difference with free ligand donor properties was not completely satisfactory. In the case oi Taft's resonance polar substituent constant, sigma_R, two distinct correlation lines were obtained. This behavior could not be rationalized without postulation of significant structural variations among the complexes in the solid state. These data along with more structural information should provide means for testing hypotheses concerning the nature of the superexchange mechanism in binuclear complexes.