Lanthanides in molecular magnetism: old tools in a new field

Abstract

In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure-property relationships in these systems.

Synthesis, Structural, and Magnetic Characterization of a Mixed 3d/4f 12-Metallacrown-4 Family of Complexes

“…To be more descriptive, the angle between the four-fold axis and the Ln-O bond direction, θ, corresponds to compression or elongation along the tetragonal axis, depending on its value. The magic value for perfect square-antiprismatic (SAP) geometry is θ = 54.74°, while smaller angles correspond to elongation and wider ones lead to compression [38][39][40]. In complex 2, the average value of θ was found to be 56.15°, indicating axial compression.…”

Direct measurement of dysprosium(III)˙˙˙dysprosium(III) interactions in a single-molecule magnet

“…The SMM behaviour observed for Ln complexes is due to the large magnetic anisotropy of the individual ions, caused by strong spin-orbit coupling and the crystal field (CF) effects due to the ligand environment 13,14 . Other interactions, for example intermolecular effects, often favour efficient quantum tunnelling of magnetization at zero external field, and this factor can mean little magnetic hysteresis is seen even in compounds with very large U eff 13 .…”

“…Other interactions, for example intermolecular effects, often favour efficient quantum tunnelling of magnetization at zero external field, and this factor can mean little magnetic hysteresis is seen even in compounds with very large U eff 13 . When considering polymetallic Ln complexes, the situation becomes even more complicated.…”

An electrostatic model for the determination of magnetic anisotropy in dysprosium complexes

“…The Complete Active Space Self Consistent Field (CASSCF) method can accurately predict the magnetic properties of lanthanide complexes 13,14 , and calculations of this type have become an indispensable tool for the explanation of increasingly interesting magnetic phenomena 6,[15][16][17] . These calculations are especially useful in cases of low symmetry, where previous methods have provided intractable, over parameterized problems 18,19 . Although CASSCF ab initio calculations are extremely versatile and implicitly include all effects required to elucidate the magnetic properties, the results offer little in the way of chemically intuitive explanations and to obtain reliable results requires considerable intervention by expert theorists equipped with access to powerful computational resources.…”