A strictly dinuclear MnIII-GdIII complex: synthesis and magnetic properties
Résumé
A strictly heterodinuclear MnIII-Gd complex was prepared from a tripodal ligand and characterized by positive fast-atom bombardment mass spectrometry, which evidenced replacement of a nitrato counterion by a monoethylcarbonato anion. Variable-temperature direct current and alternating current studies confirm that the MnIII-Gd magnetic interaction is antiferromagnetic. Fitting of the magnetic susceptibility data yields an extremely weak interaction parameter JMnGd equal to -0.04 cm-1, along with a weak axial zero-field splitting parameter DMn = 0.1 cm-1. This result confirms that a change in the manganese oxidation state, from MnII to MnIII, corresponds to a radical transformation of the magnetic behavior of Mn-Gd, from a ferromagnetic to an antiferromagnetic interaction. In accordance with the magnetic behavior of CoII-Gd complexes previously studied (high-spin and low-spin CoII ions), the observed magnetic behavior change may be explained by the difference in the electronic occupancy of the Mn 3d x 2-y 2 orbital, which is singly occupied for MnII and vacant for MnIII.