Synthesis, Characterization, and Modeling of Magnetic Properties of a Hexanuclear Amino Alcohol-Supported {CoII2CoIII2DyIII2} Pivalate Cluster

A heterometallic hexanuclear mixed-valence Co–Dy cluster [Co4Dy2(OH)2­(O2CCMe3)8­(HO2CCMe3)2­(teaH)2(N3)2]·2­(EtOH) (1) has been prepared from the reaction of dinuclear Co­(II) pivalate with triethanolamine and azide ligands and characterized by elemental analysis, IR spectroscopy, and X-ray crystallography. The metal atoms in the {CoII2CoIII2DyIII2} cluster core are bridged by two μ3-hydroxy groups, two azide N3– anions, six pivalate residues, and two doubly deprotonated teaH2– ligands. A theoretical model has been developed to explain the magnetic behavior of 1. The model takes into account the crystal fields acting on the DyIII ions and the anti- and ferromagnetic exchange interactions in the pairs Co–Dy and Co–Co, respectively. The Stark structure for the DyIII ions is calculated with due account of the covalence effects within the frames of the exchange charge model of the crystal field. It is demonstrated that at low temperatures the magnetic properties of the cluster are determined by the interaction of the ground state Kramers doublet of the CoII ion with those Stark levels of the DyIII ions, for which the energies are smaller than the spin–orbital coupling parameter. At higher temperatures, the population of the CoII ion multiplets with the angular momentum values 3/2 and 5/2 leads to the increase of the magnetic susceptibility. The observed temperature dependence of the χMT product and field dependence of the magnetization are satisfactorily explained within the framework of the suggested model.