[U(Tp^Me2)₂(bipy)]⁺: A Cationic Uranium(III) Complex with Single-Molecule-Magnet Behavior

Abstract

The addition of 2,2'-bipyridine to [U(Tp(Me2))(2)I] (1) results in the displacement of the iodide and the formation of the cationic uranium(III) complex [U(Tp(Me2))(2)(bipy)]I (2). This compound was isolated as a dark-green solid in good yield and characterized by IR and NMR spectroscopies, and its molecular structure was determined by single-crystal X-ray diffraction. Studies of its magnetic properties revealed a frequency dependence of magnetization with a blocking temperature of 4.5 K and, at lower temperatures, a slow relaxation of magnetization with an energy barrier of 18.2 cm(-1), characteristic of single-molecule-magnet behavior.

Radical ligand-containing single-molecule magnets

“…This uranium complex displays slow magnetic relaxation under zero dc field with an U eff = 19.8 cm −1 (U eff = 22.6 cm −1 , 0.05 T) [366]. The spin relaxation barrier measured at zero field is slightly higher than that of the complex containing the non-radical bipyridyl ligand [345]. The U III complex bearing the hexadentate ligand (1,4,7-tris(3-adamantyl-5-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclonane) (( Ad ArO) 3 tacn) was shown to reduce CO 2 by one electron to form the U IV radical complex (( Ad ArO) 3 tacn)U IV (CO 2 −• ) (42; Fig.…”

“…Additionally, in contrast to lanthanides, actinides provide a wide range of accessible oxidation states [320]. However, only a few actinide complexes have been shown to exhibit slow magnetic relaxation, with nearly all of these being uranium complexes [343][344][345][346][347][348][349][350][351]. Nevertheless, despite the difficulties associated with handling of the more radioactive transuranic elements, neptunium and plutonium-based singlemolecule magnets have also been reported [352][353][354].…”

Molecular single-ion magnets based on lanthanides and actinides: Design considerations and new advances in the context of quantum technologies

“…In contrast, the energy gaps in 2 are much smaller and as such the relaxation becomes much faster [41,93] [94]. A follow-up study used molecular circular dichroism to probe hysteretic behaviour and found the neutral complex [Pc2Tb] 0 (30) to have a well-defined hysteresis loop marked by coercivity. In contrast, compounds 31 and 32 only showed a butterfly-shaped hysteresis (Fig.…”

“…Single-ion magnets (SIMs) are simply a subclass of SMMs wherein the electronic spin term originates from a single magnetic centre [7,8]. In SIMs, the ion bearing the spin is most commonly a transition metal [9][10][11][12][13], lanthanoid [14][15][16][17][18][19][20][21][22], or actinoid [23][24][25][26][27][28][29][30]. The term SIM is somewhat of a misnomer: all SIMs are molecular in nature since the ligand field is a vital prerequisite for their slow relaxation.…”

Field-induced single-ion magnetic behaviour in a highly luminescent Er3+ complex

“…At 1.6 K a clear opening of the magnetic hysteresis is observed as one moves away from zero field, revealing strong field dependence. The absence of coercivity can be due to an efficient quantum tunnelling of the magnetization occurring at zero field, probably caused by low symmetry components of the crystal field, as it was already observed in other mononuclear lanthanide [17,18,28] and uranium [29,30] compounds with SMM behaviour. At this temperature and up to 10 T, magnetization approaches a value of 7.9 μB, still far from the expected saturation value for a free Er 3+ ion.…”