Recent Developments in CoIII 2LnIII 2 Single-Molecule Magnets

Abstract

In this work we review the Co2 IIILn2 III family of compounds reported up to date that shows SMM features. The vast majority of them show a butterfly arrangement with LnIII ions placed at the body positions. The number of DyIII examples constitutes the majority, probably because of the intrinsic properties of this lanthanide ion regarding SMMs characteristics. Butterfly complexes have a SAP geometry around LnIII ions with a variety of distortion degrees. However, when looking at the key Ueff parameter trend through this family of complexes, it becomes clear that a pure geometrical consideration is not enough to explain it. Ab initio based calculations provide evidence of highly anisotropic mJ ground states for complexes where LnIII = DyIII, pointing to exclusively mJ = 15/2 ground Kramers doublets. These calculations also agree with the thermally activated relaxation involving the first excited state and, in some examples where multiple relaxation pathways are observed, higher excited states. A few examples prove that Raman and/or direct mechanisms cannot be discarded a priori. Only two examples of isostructural LnIII families of the same Co2 IIILn2 III complex can be found.