/pdf/lanthanide-single-molecule-magnets-efv9mucvem.pdf

Lanthanide single-molecule magnets.

Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(CpiPr5)Dy(Cp*)]+ (CpiPr5 = penta-iso-propylcyclopentadienyl, Cp* = pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of Ueff = 1,541 cm–1 is also measured. The magnetic blocking temperature of TB = 80 K for this cation overcomes an essential barrier towards the development of nanomagnet devices that function at practical temperatures.

Magnetic hysteresis up to 80 kelvin in a dysprosium metallocene single-molecule magnet

Single-molecule magnets (SMMs) with a large spin reversal barrier have been recognized to exhibit slow magnetic relaxation that can lead to a magnetic hysteresis loop. Synthesis of highly stable SMMs with both large energy barriers and significantly slow relaxation times is challenging. Here, we report two highly stable and neutral Dy(III) classical coordination compounds with pentagonal bipyramidal local geometry that exhibit SMM behavior. Weak intermolecular interactions in the undiluted single crystals are first observed for mononuclear lanthanide SMMs by micro-SQUID measurements. The investigation of magnetic relaxation reveals the thermally activated quantum tunneling of magnetization through the third excited Kramers doublet, owing to the increased axial magnetic anisotropy and weaker transverse magnetic anisotropy. As a result, pronounced magnetic hysteresis loops up to 14 K are observed, and the effective energy barrier (Ueff = 1025 K) for relaxation of magnetization reached a breakthrough among the SMMs.

A Stable Pentagonal Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K.

ion of a chloride ligand from the dysprosium metallocene [(Cpttt)2DyCl] (1Dy Cpttt=1,2,4-tri(tert-butyl)cyclopentadienide) by the triethylsilylium cation produces the first base-free rare-earth metallocenium cation [(Cpttt)2Dy]+ (2Dy) as a salt of the non-coordinating [B(C6F5)4]− anion. Magnetic measurements reveal that [2Dy][B(C6F5)4] is an SMM with a record anisotropy barrier up to 1277 cm−1 (1837 K) in zero field and a record magnetic blocking temperature of 60 K, including hysteresis with coercivity. The exceptional magnetic axiality of 2Dy is further highlighted by computational studies, which reveal this system to be the first lanthanide SMM in which all low-lying Kramers doublets correspond to a well-defined MJ value, with no significant mixing even in the higher doublets.

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A Dysprosium Metallocene Single-Molecule Magnet Functioning at the Axial Limit.

Toward promising candidates of quantum information processing, the rapid development of lanthanide-based single-molecule magnets (Ln-SMMs) highlights design strategies in consideration of the local symmetry of lanthanide ions. In this review, crystal-field theory is employed to demonstrate the electronic structures according to the semiquantitative electrostatic model. Then, specific symmetry elements are analysed for the elimination of transverse crystal fields and quantum tunnelling of magnetization (QTM). In this way, high-performance Ln-SMMs can be designed to enable extremely slow relaxation of magnetization, namely magnetic blocking; however, their practical magnetic characterization becomes increasingly challenging. Therefore, we will attempt to interpret the experimental behaviours and clarify some issues in detail. Finally, representative Ln-SMMs with specific local symmetries are summarized in combination with the discussion on the symmetry strategies, and some of the underlying questions are put forward.

Symmetry strategies for high performance lanthanide-based single-molecule magnets

Lanthanide Single-Molecule Magnets

Single-Molecule Magnetism in Tetrametallic Terbium and Dysprosium Thiolate Cages

Lithiation of hydrothermally synthesized Li1–xFex(OH)Fe1–ySe turns on high-temperature superconductivity when iron ions are displaced from the hydroxide layers by reductive lithiation to fill the vacancies in the iron selenide layers. Further lithiation results in reductive iron extrusion from the hydroxide layers, which turns off superconductivity again as the stoichiometric composition Li(OH)FeSe is approached. The results demonstrate the twin requirements of stoichiometric FeSe layers and reduction of Fe below the +2 oxidation state as found in several iron selenide superconductors.

http://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.6b01734

The Parent Li(OH)FeSe Phase of Lithium Iron Hydroxide Selenide Superconductors.

The reactions of the heteroleptic lithium amide [Li3(μ-hmds)2(μ,μ-hpp)] (1), where [hmds]− = hexamethyldisilazide and [hpp]− = hexahydropyrimidopyrimidide, with MnCl2, CoCl2 or ZnBr2 result in the formation of the separated ion-pairs [MLi7(μ8-O)(μ,μ-hpp)6]+[A]−, which each consist of a {MLi7} oxo-centred cube structural motif (M = Mn 2, Co 4, Zn 5), with each face of the cube being bridged by an [hpp]− ligand. In the case of M = Mn and Co, the counter ion, [A]−, is the pentagonal anionic inverse crown [{Li(μ-hmds)}5(μ5-Cl)]− (3), whereas the reaction with M = Zn produces the known tris-amido zincate [Zn(hmds)3]− counter anion.

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Daniel N. Woodruff

Papers

Lanthanide single-molecule magnets.

Lanthanide Single-Molecule Magnets

Single-Molecule Magnetism in Tetrametallic Terbium and Dysprosium Thiolate Cages

The Parent Li(OH)FeSe Phase of Lithium Iron Hydroxide Selenide Superconductors.

Synthesis and structure of cationic guanidinate-bridged bimetallic {Li7M} cubes (M = Mn, Co, Zn) with inverse crown counter anions