Antiferromagnetism in transition-metal complexes. Part VI. Low-lying excited states of dinuclear copper(II) complexes with bridging multidentate Schiff's base groups and some related compounds

Abstract

Variable-temperature magnetic susceptibility data for a number of multidentate Schiff's-base complexes of copper(II) and related molecules are reinterpreted on a model which allows for the thermal population of excited states other than those predicted by the vector-coupling model. The mechanism of superexchange through the oxygen bridges is discussed and its magnitude is found to increase sensibly through the series quadridentate Schiff's base < terdentate Schiff's base < bidentate Schiff's base < aromatic N-oxide. This is also the reverse order of the overall, nephelauxetic effect of the ligands upon the metal d-orbitals, so that the additional direct interaction is of similar magnitude for the terdentate Schiff's base series as for copper carboxylates.