Search

Single-ion anisotropy is vital for the observation of Single-Molecule Magnet (SMM) properties (i.e., a slow dynamics of the magnetization) in lanthanide-based systems. In the case of europium, the occurrence of this phenomenon has been inhibited by the spin and orbital quantum numbers that give way to J = 0 in the trivalent state and the half-filled population of the 4f orbitals in the divalent state. Herein, by optimizing the local crystal field of a quasi-linear bis(silylamido) Eu II complex, the [Eu II (N{SiMePh 2 } 2 ) 2 ] SMM is described, providing an example of a europium complex exhibiting slow relaxation of its magnetization. This behavior is dominated by a thermally activated (Orbach-like) mechanism, with an effective energy barrier of approximately 8 K, determined by bulk magnetometry and electron paramagnetic resonance. Ab initio calculations confirm second-order spin-orbit coupling effects lead to non-negligible axial magnetic anisotropy, splitting the ground state multiplet into four Kramers doublets, thereby allowing for the observation of an Orbach-like relaxation at low temperatures., (© 2024. The Author(s).)

The best-performing single-molecule magnets (SMMs) have historically relied on pseudoaxial ligands delocalized across several coordinated atoms. This coordination environment has been found to elicit strong magnetic anisotropy, but lanthanide-based SMMs with low coordination numbers have remained synthetically elusive species. Here we report a cationic 4f complex bearing only two bis-silylamide ligands, Yb(III)[{N(SiMePh 2 ) 2 } 2 ][Al{OC(CF 3 ) 3 } 4 ], which exhibits slow relaxation of its magnetization. The combination of the bulky silylamide ligands and weakly coordinating [Al{OC(CF 3 ) 3 } 4 ] - anion provides a sterically hindered environment that suitably stabilizes the pseudotrigonal geometry necessary to elicit strong ground-state magnetic anisotropy. The resolution of the m J states by luminescence spectroscopy is supported by ab initio calculations, which show a large ground-state splitting of approximately 1,850 cm -1 . These results provide a facile route to access a bis-silylamido Yb(III) complex, and further underline the desirability of axially coordinated ligands with well-localized charges for high-performing SMMs., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)