A Dysprosium Metallocene Single‐Molecule Magnet Functioning at the Axial Limit

Abstraction of a chloride ligand from the dysprosium metallocene [(Cp^ttt)₂DyCl] ( 1_Dy Cp^ttt=1,2,4‐tri(tert ‐butyl)cyclopentadienide) by the triethylsilylium cation produces the first base‐free rare‐earth metallocenium cation [(Cp^ttt)₂Dy]⁺ ( 2_Dy ) as a salt of the non‐coordinating [B(C₆F₅)₄]⁻ anion. Magnetic measurements reveal that [ 2_Dy ][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 2_Dy 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 M_J value, with no significant mixing even in the higher doublets.     

“Isolated” DyO+ Embedded in a Ceramic Apatite Matrix Featuring Single‐Molecule Magnet Behavior with a High Energy Barrier for Magnetization Relaxation

Meeting the challenges of Moore's Law, predicting ambitious miniaturization rates of integrated circuits, requires to go beyond the traditional top‐down approaches, and to employ synthetic chemistry methods, to use bottom‐up techniques. During the recent decades, it has been shown that open‐shell coordination compounds may exhibit intramolecular spontaneous magnetization, thus offering promising prospects for storage and processing of digital information. Against this background we regarded it rewarding to implement similar magnetic centers into a ceramic material, which would provide better long‐term mechanical and chemical durability. Here we present new robust inorganic compounds containing separate DyO⁺ ions in an apatite matrix, which behave like single‐molecule magnets. The materials exhibit a blocking temperature of 11 K and an energy barrier for spin reversal of a thousand inverse centimeters which is among the highest values ever achieved.     

161Dy Time‐Domain Synchrotron Mössbauer Spectroscopy for Investigating Single‐Molecule Magnets Incorporating Dy Ions

Time‐domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of ¹⁶¹Dy has been used to investigate the magnetic properties of a Dy^III‐based single‐molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy₃PO)₂(H₂O)₅]Br₃?2 (Cy₃PO)?2 H₂O?2 EtOH is with B₀=582.3(5) T significantly larger than that of the free‐ion Dy^III with a ⁶H_15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the Dy^III ion. This study demonstrates that ¹⁶¹Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy‐containing compounds.     

Hyperfine‐Interaction‐Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single‐Ion Magnet

An extremely rare non‐Kramers holmium(III) single‐ion magnet (SIM) is reported to be stabilized in the pentagonal‐bipyramidal geometry by a phosphine oxide with a high energy barrier of 237(4) cm⁻¹. The suppression of the quantum tunneling of magnetization (QTM) at zero field and the hyperfine structures originating from field‐induced QTMs can be observed even from the field‐dependent alternating‐current magnetic susceptibility in addition to single‐crystal hysteresis loops. These dramatic dynamics were attributed to the combination of the favorable crystal‐field environment and the hyperfine interactions arising from ¹⁶⁵Ho (I =7/2) with a natural abundance of 100 %.     

Insight into D6h Symmetry: Targeting Strong Axiality in Stable Dysprosium(III) Hexagonal Bipyramidal Single‐Ion Magnets

Following a novel synthetic strategy where the strong uniaxial ligand field generated by the Ph₃SiO^? (Ph₃SiO^?=anion of triphenylsilanol) and the 2,4‐di‐^tBu‐PhO^? (2,4‐di‐^tBu‐PhO^?=anion of 2,4‐di‐tertbutylphenol) ligands combined with the weak equatorial field of the ligand L^N6 , leads to [Dy^III(L^N6)(2,4‐di‐^tBu‐PhO)₂](PF₆) ( 1 ), [Dy^III(L^N6)(Ph₃SiO)₂](PF₆) ( 2 ) and [Dy^III(L^N6)(Ph₃SiO)₂](BPh₄) ( 3 ) hexagonal bipyramidal dysprosium(III) single‐molecule magnets (SMMs) with high anisotropy barriers of U_eff=973 K for 1 , U_eff=1080 K for 2 and U_eff=1124 K for 3 under zero applied dc field. Ab initio calculations predict that the dominant magnetization reversal barrier of these complexes expands up to the 3rd Kramers doublet, thus revealing for the first time the exceptional uniaxial magnetic anisotropy that even the six equatorial donor atoms fail to negate, opening up the possibility to other higher‐order symmetry SMMs.     

Quantum Monte Carlo Simulations and High‐Field Magnetization Studies of Antiferromagnetic Interactions in a Giant Hetero‐Spin Ring

Chromium lanthanide heterometallic wheel complexes {Cr₈Ln₈} (Ln=Gd, Dy and Y) with alternating metal centres are presented. Quantum Monte Carlo simulations reveal antiferromagnetic exchange‐coupling constants with an average of 2.1 K within the {Cr₈Gd₈} wheel, which leads to a large ground spin state (S _T=16) that is confirmed by magnetization studies up to 20 Tesla. The {Cr₈Dy₈} wheel is a single‐molecule magnet.     

Mononuclear Clusterfullerene Single‐Molecule Magnet Containing Strained Fused‐Pentagons Stabilized by a Nearly Linear Metal Cyanide Cluster

Fused‐pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non‐IPR clusterfullerenes multiple (two or three) metals are required to stabilize the strained fused‐pentagons, making it difficult to access the single‐atom properties. Herein, we report the syntheses and isolations of novel non‐IPR mononuclear clusterfullerenes MNC@C₇₆ (M=Tb, Y), in which one pair of strained fused‐pentagon is stabilized by a mononuclear cluster. The molecular structures of MNC@C₇₆ (M=Tb, Y) were determined unambiguously by single‐crystal X‐ray diffraction, featuring a non‐IPR C _2v (19138)‐C₇₆ cage entrapping a nearly linear MNC cluster, which is remarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR‐obeying C₈₂ cages. The TbNC@C₇₆ molecule is found to be a field‐induced single‐molecule magnet (SMM).