A Low‐Symmetry Dysprosium Metallocene Single‐Molecule Magnet with a High Anisotropy Barrier

Abstract

The single‐molecule magnet (SMM) properties of the isocarbonyl‐ligated dysprosium metallocene [Cp*2Dy{μ‐(OC)2FeCp}]2 (1Dy), which contains a rhombus‐shaped Dy2Fe2 core, are described. Combining a strong axial [Cp*]− ligand field with a weak equatorial field consisting of the isocarbonyl ligands leads to an anisotropy barrier of 662 cm−1 in zero applied field. The dominant thermal relaxation pathways in 1Dy involves at least the fourth‐excited Kramers doublet, thus demonstrating that prominent SMM behavior can be observed for dysprosium in low‐symmetry environments.

Cyclopentadienyl Ligands in Lanthanide Single-Molecule Magnets: One Ring To Rule Them All?

“…This observation is consistent with the properties of the dimetallic SMMs 9 and 10, in which the Having established that two cyclopentadienyl ligands provide Dy 3+ with a strongly axial coordination environment, and that equatorial ligands limit Ueff whilst being highly detrimental to the hysteresis, the next logical step was to propose [Cp2Dy] + itself as an SMM. 32 In agreement with Scheme 1, [(Cp ttt )2DyCl] showed no clear maxima in the ''() plots, and only very narrow hysteresis loops even at 1.8 K. In stark contrast, the ''() data for 15…”

“…Here, ab-initio theoretical studies were invaluable in demonstrating that the magnetic ground state of Dy 3+ in compounds of the type [Cp2Ln(-X)]n is typically a Kramers doublet with significant MJ = ±15/2 character; the main magnetic axis in this ground doublet is oriented towards the two cyclopentadienyl ligands in every case studied. 19,[24][25][26][27][28][29][30][31][32][33] Hence, an axial direction can be defined according to Scheme 1, with the dominant crystal field being provided by the cyclopentadienyl ligands (see also Figures 1 and 2). The equatorial coordination sites comprises the ligands X, whose presence diminish the axiality, meaning that the SMM properties vary to an extent that depends on the -bridging ligand.…”

Lanthanide(III) Hexanuclear Circular Helicates: Slow Magnetic Relaxation, Toroidal Arrangement of Magnetic Moments, and Magnetocaloric Effects

“…21 Thus the isotropic Gd III ions with S = 7/2 are the main candidates in the construction of polynuclear clusters with significant MCEs. 22 Following this, some remarkable results in lanthanide-based polynuclear systems have been achieved: a number of complexes including Dy 2 , 23 Dy 5 , 24 Dy 4 K 2 25 and Ho 5 24 which exhibit some of the largest anisotropy barriers have been described in the literature. Especially Dy 4 K 2 25 displays the highest energy barrier of 842 K in polynuclear SMMs.…”

Structure and Magnetization Dynamics of Dy−Fe and Dy−Ru Bonded Complexes

“…If species such as [FeCp(CO) 2 ] À are to be used, the LnÀTM bond has to outcompete the oxophilicity of the Ln ion, which would favor the formation of Ln isocarbonyl complexes.S imilarly,t he steric bulk of the Ln-supporting ligand has to be minimized to avoid the formation of isocarbonyl species.F or example,t he steric bulk around the Dy 3+ ion in its bis(pentamethylcyclopentadienyl) complexes favors the formation of isocarbonyl complexes over the formation of DyÀFe bonds in reactions between Cp* 2 Dy(PhBPh 3 )and [FeCp(CO) 2 ] À . [10] As such, we can formulate two prerequisites for the formation of Ln À TM bonds:1 )The Ln ions need to be sterically accessible,a nd 2) the metal-centered charge needs to be localized on the TM fragment in such away as to favor LnÀTM over LnÀOCÀTM bonding.W ei dentified the structurally rigid yet not overly sterically demanding ligand PyCp 2 2À (PyCp 2 2À = [2,6-(CH 2 C 5 H 3 ) 2 C 5 H 3 N] 2À ) [11] as ap otential ligand platform for the generation of Ln À TM bonded species.T he triflatebridged dinuclear Dy 3+ complex shown in Scheme 1d issociates readily in thf solution into its corresponding monomers, [11c] which can be reacted with stoichiometric amounts of K[FeCp(CO) 2 ]orK[RuCp(CO) 2 ]toyield crystalline material of PyCp 2 Dy-FeCp(CO) 2 (1)a nd PyCp 2 Dy-RuCp(CO) 2 (2), respectively.…”

“…[10] As such, we can formulate two prerequisites for the formation of Ln À TM bonds:1 )The Ln ions need to be sterically accessible,a nd 2) the metal-centered charge needs to be localized on the TM fragment in such away as to favor LnÀTM over LnÀOCÀTM bonding.W ei dentified the structurally rigid yet not overly sterically demanding ligand PyCp 2 2À (PyCp 2 2À = [2,6-(CH 2 C 5 H 3 ) 2 C 5 H 3 N] 2À ) [11] as ap otential ligand platform for the generation of Ln À TM bonded species.T he triflatebridged dinuclear Dy 3+ complex shown in Scheme 1d issociates readily in thf solution into its corresponding monomers, [11c] which can be reacted with stoichiometric amounts of K[FeCp(CO) 2 ]orK[RuCp(CO) 2 ]toyield crystalline material of PyCp 2 Dy-FeCp(CO) 2 (1)a nd PyCp 2 Dy-RuCp(CO) 2 (2), respectively. If species such as [FeCp(CO) 2 ] À are to be used, the LnÀTM bond has to outcompete the oxophilicity of the Ln ion, which would favor the formation of Ln isocarbonyl complexes.S imilarly,t he steric bulk of the Ln-supporting ligand has to be minimized to avoid the formation of isocarbonyl species.F or example,t he steric bulk around the Dy 3+ ion in its bis(pentamethylcyclopentadienyl) complexes favors the formation of isocarbonyl complexes over the formation of DyÀFe bonds in reactions between Cp* 2 Dy(PhBPh 3 )and [FeCp(CO) 2 ] À .…”