Single-molecule magnets (SMMs) based on lanthanide are currently widely studied because of their potential contribution in high-density information storage, quantum computing or spintronics. Until now, trivalent lanthanides lead the race thanks to the large magnetic anisotropy coming from the 4f electrons. This makes them suitable for designing complexes with long magnetic relaxation time, which is sought after to produce a performing magnet. Even if numerous SMMs are designed with this idea, all the factors influencing the magnetic relaxation time are not yet understood, and other strategies may yet be discovered.
This work, lead in collaboration with the Institut Polytechnique Paris and the Université Paris-Saclay, highlights the first divalent thulium sandwich complex behaving as a SMM in absence of an external magnetic field. This means that trivalent lanthanide might not be the only way to obtain SMMs.
Divalent lanthanide organometallics are well-known highly reducing compounds usually used for single electron transfer reactivity and small molecule activation. Thus, their very reactive nature prevented for many years the study of their physical properties. But in this study, divalent complexes were synthesized, crystallized and analyzed at low temperature, making them stable enough to work with. Magnetic measurements on these divalent sandwich complexes with different environments were performed and indicate that small structural modifications drastically influence the magnetic relaxation. Indeed, two identical charged complexes were prepared and crystalized with different counter-ions. One of the compounds formed polymeric chains, making it comparatively more stable, but it is not a magnet, while the other one did not polymerize but shown a slow relaxation process in absence of magnetic field and behaves as a genuine magnet. Furthermore, when isolated from its congeners in a diamagnetic isomorphic matrix the Tm(II) magnet is more performant. This unusual behavior paves the way to new possibilities for this exotic chemistry.
Jules Moutet, Jules Schleinitz, Léo La Droitte, Maxime Tricoire, Fabrice Pointillart, Frédéric Gendron, Thomas Simler, Carine Clavaguéra, Boris Le Guennic, Olivier Cador*, Grégory Nocton*
Bis-Cyclooctatetraenyl Thulium(II): Highly Reducing LanthanideSandwich Single-Molecule Magnets
Angew. Chem. Int. Ed. 2021, 60, 2–7 (not final page numbers)
Published February 11, 2020