Single-molecule Magnet Research Articles

Auxiliary Ligands Modulated Bis(imidazolin-2-iminato) Dysprosium Single-Molecule Magnets.

A systematic study on the magneto-structural correlation plays an essential role in improving the molecular design of single-molecule magnets (SMMs). Strong axial crystal fields on Dy(III) could help enhance the uniaxial magnetic anisotropy, increasing the relaxation barrier and magnetic blocking temperature, while transverse crystal-field interactions accelerate magnetic relaxation. The imidazolin-2-iminato ligands have been viewed as promising strong-field ligands to construct high-performance Dy(III) SMMs since the large steric hindrance and strong donating capacity make imidazolin-2-iminato ligands possibly impede weak transverse interactions at equatorial positions. Herein, we synthesize a series of bis(imidazolin-2-iminato) Dy(III) SMMs with magneto-structural correlations revealed by combined magnetic and theoretical analyses. The relaxation barriers of these complexes vary over a wide range, indicating that auxiliary ligands at equatorial positions could effectively modulate SMM performance. Additionally, we found that two parameters, the relaxation energy barrier and the Dy-N bond length, follow specific correlation patterns with the N-Dy-N angle, and these correlations exhibit precisely opposite trends. The highest Ueff can be reached when the N-Dy-N angle is approximately 121°, suggesting the greatest potential of this series of complexes.

First Encapsulation of Organometallic Single-Molecule Magnet into Single-Walled Carbon Nanotubes.

An air-sensitive DyCp3 (Cp- = cyclopentadienyl) single-molecule magnet (SMM) complex (1) was encapsulated into single-walled carbon nanotubes (SWCNTs) to construct hybrid materials that are resistant to moisture and oxygen. The hybrid materials with independent slow-magnetic-relaxing centers are expected to become a key component of the next generation of information process devices based on spintronics. The resilience to moisture and oxygen further broadens its manufacturing methods and application scenarios. Furthermore, upon encapsulation into SWCNTs, DyCp3 exhibited clear ac frequency dependence in the ac magnetic susceptibility at a zero-dc field. This indicates that the guest molecule's slow magnetic relaxation properties are preserved, which is crucial and necessary to realize SMMs-based quantum information processing, by allowing a sufficient time window for quantum gate operations. Our result exemplifies that encapsulation of air-sensitive organometallic SMMs into SWCNTs enhances their chemical stability and their magnetic relaxation time at a zero-dc magnetic field, which provides a novel method for their further applications.

Role of Electron Correlation beyond the Active Space in Achieving Quantitative Predictions of Spin-Phonon Relaxation.

Single-molecule magnets (SMMs) are promising candidates for molecular-scale data storage and processing due to their strong magnetic anisotropy and long spin relaxation times. However, as the temperature rises, interactions between electronic states and lattice vibrations accelerate spin relaxation, significantly limiting their practical applications. Recently, ab initio simulations have made it possible to advance our understanding of phonon-induced magnetic relaxation, but significant deviations from the experiments have often been observed. The description of molecules' electronic structure has been mostly based on complete active space self-consistent field (CASSCF) calculations, and the impact of electron correlation beyond the active space remains largely unexplored. In this study, we provide the first systematic investigation of spin-phonon relaxation in SMMs with post-CASSCF multiconfigurational methods, specifically CAS, followed by second-order perturbation theory and multiconfiguration pair-density functional theory. Taking Co(II)- and Dy(III)-based SMMs as case studies, we analyze how electron correlation influences spin-phonon relaxation rates across a range of temperatures by comparing theoretical predictions with experimental observations. Our findings demonstrate that post-CASSCF treatments make it possible to achieve quantitative predictions for Co(II)-based SMMs. For Dy(III)-based systems, however, accurate predictions require the consideration of additional effects, underscoring the urgent necessity of further advancing the study of the effects of electronic correlation in these complex systems.

Four-Centre, Multi-Electron Bonding in Rare-Earth Germole Sandwich Complexes.

Reduction of the germole-ligated sandwich complexes [(η5-CpGe)M(η5-Cpttt)]2 (1M, M = Y, Gd, Dy) with one or two equivalents of KC8/2.2.2-cryptand produces [(η5-CpGe)M(η5-Cpttt)2]- (2M) and [(η5-CpGe)M(η5-Cpttt)2]2- (3M), respectively, as salts of [K(2.2.2-cryptand)]+ (CpGe = [GeC4-2,5-(SiMe3)2-3,4-Me2]2-, Cpttt = 1,2,4-C5tBu3H2. X-Ray crystallography shows that the bond lengths within the central {M2Ge2} rings contract markedly with each reduction. Computational analysis reveals the presence of unusual four-centre, multi-electron {M2Ge2} bonds, with the reduction increasing the germanium-germanium and metal-germanium bond orders, whilst reducing the metal-Cpttt bond order. Analysis of 2Y by EPR spectroscopy reveals delocalization of the unpaired spin across both yttrium centres. Magnetic measurements on radical-bridged 2Gd show a large exchange coupling constant of -95 cm-1 (-2J formalism). Single-molecule magnet behaviour is found for the dysprosium-germole complexes. Complexes 1Y, 2Y and 3Y can be interconverted by one-electron oxidation or reduction reactions of 2Y, which itself can also be formed by comproportionation of 1Y and 3Y. The masked divalent reactivity of 3Y is demonstrated through one-electron reduction of 2,2'-bipyridyl to give [(η5-CpGe)Y(η5-Cpttt)(2,2'-bipy)]- (4Y) and activation of Ph2Se2 to give [(η5-CpGe)Y(η5-Cpttt)(SePh)]- (5Y).

Molecular Architecture and Single-Molecule Magnet behavior Control by Playing with Lanthanide Ionic Radii and Bulkiness Ancillary Ligands.

A library of three dinuclear complexes [Yb(hfac)3(L)]2⋅3(CH2Cl2) (1)⋅3(CH2Cl2), [Dy2(hfac)6(L)3]⋅3(CHCl3) (4)⋅3(CHCl3), [Yb(tta)3(L)]2 (6), four dinuclear enantiomers [Ln(facam)3(L)]2⋅CH2Cl2 Ln=Dy ((-)7⋅CH2Cl2, (+)7⋅CH2Cl2) and Yb ((-)8⋅CH2Cl2, (+)8⋅CH2Cl2), two tetranuclear complexes [Ln2(hfac)6(L)]2⋅(CH2Cl2)n (Ln = Yb, n =1 (2)⋅CH2Cl2; Ln = Dy, n = 0 (3)) and two pentanuclear complexes [Dy5(hfac)15(L)3]⋅2(C2H4Cl2) (5)⋅2(C2H4Cl2) and [Nd5(hfac)15(L)3]⋅2(CH2Cl2) (10)⋅2(CH2Cl2) (1,1,1,5,5,5-hexafluoroacetylacetonate (hfac-), 2-tenoyltrifluoroacetylacetonate (tta-), 3-(trifluoro-acetyl-(+/-)-camphorate (facam-) and L = [4'-(4'''-pyridyl-N-oxide)-1,2':6'1''-bis-(pyrazolyl)pyridine] ligand) were isolated and characterized by single crystal X-ray diffraction. The final molecular architectures could be controlled by playing with the ionic radii of Yb(III), Dy(III) and Nd(III) ions and steric hindrance of the β-diketonate. Natural circular dichroism (NCD) highlighted no exciton CD couplet for chiral compounds. All the compounds involving Nd(III) in both O9 and N3O6, Dy(III) in O9 and Yb(III) in both O8 and N3O6 coordination sphere present field-induced SMM while Dy(III) in O8 environment displays SMM behavior in zero applied dc field. The relaxation of the magnetization occurs mainly through a Raman process with contribution of QTM in zero field and Direct process under applied field. The relaxation time of the magnetization increases with the enhancement of the steric hindrance of the ancillary β-diketonate ligands.

A Luminescent Proton Conductor Based on Dy2 SMM.

Multifunctional materials bearing photoluminescence, single-molecule magnet (SMM) behavior, and proton conduction have been particularly attractive for various promising applications in optics, molecular spintronics, high-density data storage, and fuel cells. However, these kinds of multifunctional systems have rarely been reported. Herein, a DyIII-SMM together with luminescent and proton-conducting properties, [Dy2(1-tza)4(phen)4]∙(ClO4)2∙(H2O)2 (1, 1-tza = 2-(1H-tetrazol-1-yl)acetic, phen = 1,10-phenanthroline), was prepared and structurally characterized. Complex 1 features a dinuclear structure bridged by carboxylate oxygen atoms of the 1-tza- ligands, and its supramolecular network contains a 1D stacking channel. Complex 1 exhibits strong room-temperature DyIII characteristic emissions and SMM behaviors. In addition, complex 1 shows a moderate proton conductivity with 4.00 × 10-6 S cm-1 at 37 °C and 100% R.H. (R.H. = Relative Humidity), which may be ascribed to the 1D-extended H-bonds in the 1D stacking channel of 1.

Diatomic C2/NC Ligand Induced Conformation Variation of Trimetallic Clusters within a Carbon Cage.

Understanding the interplay between conformation and electronic properties of metal complexes at the atomic level is the key for rational design of new functional molecules. Trimetallic clusterfullerenes (TMCFs) encapsulating quinary M3C2 carbide or M3NC carbonitride clusters offer an ideal model system for elucidating conformation-electronic property correlation due to its unusual conformational versatility. Herein, we synthesize and isolate two novel lanthanide-transition metal heteronuclear TMCFs, namely, CeTi2C2@Ih(7)-C80 and CeTi2NC@Ih(7)-C80. Crystallographic studies reveal singly bonded C2/NC ligands coordinating vertically to the CeTi2 trimetallic plane within the cluster, drastically different from the bat-ray conformations reported for all homonuclear TMCFs. Such bonding characters give rise to variable electronic structures of [Ce4+(Ti2)8+(C2)6-]6+@C806- and [Ce3+(Ti2)8+(NC)5-]6+@C806-, featuring a fixed tetravalent oxidation state of Ti and tunable oxidation states of Ce (Ce4+/Ce3+), as confirmed by X-ray absorption spectroscopy and magnetic measurements in combination with theoretical studies. Furthermore, scrutinizing all reported TMCFs bearing M3C2/M3NC clusters, we find that the conformations of trimetallic carbide/carbonitride clusters are precisely dictated by the bonding nature of the diatomic C2/NC ligand so as to suffice strong coordination interactions with the encapsulated metals. Following such a general rule governing conformational variation, a very strong ligand field is achieved on Ce3+ in the presence of a singly bonded NC ligand in CeTi2NC@C80, giving rise to the first Ce-based single-molecule magnet that shows an open magnetic hysteresis at 2 K.

In-Field and Zero-Field Relaxation Dynamics of Dysprosocenium in Solution.

Most of the work in expanding the frontiers of single-molecule magnets employs the chemical design of new molecules to increase the size of the effective barrier (Ueff) or the hysteresis temperature (TH). Here we explore how perturbing the local environment affects magnetic relaxation properties by dissolving [Dy(Cpttt)2][B(C6F5)4] in two different solvents: difluorobenzene (DFB) and dichloromethane (DCM). Surprisingly, we find no significant effects in the phonon-driven Raman-I regime at higher temperatures, but we do observe that the frozen-solution environment increases the rate of quantum tunneling of the magnetization (QTM) due to an increase in the size of the avoided level crossing. We find that there is a drastic decrease in the Raman relaxation rate at low temperatures for the concentrated DCM and polycrystalline samples under the applied magnetic field where the QTM process is quenched, which is attributed to changes in the low-energy phonon spectrum and is not replicated for the other samples.

Paramagnetic Cage-Type Co(II) Complexes of Chiral Macrocycles: Enantio- and Size-Selective Binding of Guest Molecules.

Two enantiomers of the cage-type complex, [Co3LR2] and [Co3LS2] of a large hexaazatriphenolic [3 + 3] macrocyclic imine L, have been synthesized and characterized on the basis of NMR, CD, and ESI MS spectra. The X-ray crystal structures of [Co3L2] crystalline forms reveal two macrocycles of cone shape stitched together by three Co(II) ions, forming a barrel-shaped molecule with a central void. Because of the limited size of the [Co3L2] cavity and the enantiopure nature of these enantiomeric complexes, both size-selective and enantioselective binding of guest molecules are observed. In the case of chiral guests, the interaction with paramagnetic Co(II) centers leads to an effective NMR enantiodifferentiation of the signals of guest molecules, even at host:guest ratios as low as 1:200. The tight binding of prochiral guest molecules such as ethanol and isopropanol within the chiral cavity results in the splitting of enantiotopic methylene and methyl signals. The dc magnetic data for [Co3L2] are in accord with the presence of high-spin Co(II) ions, and the ac susceptibility data of this complex indicate field-induced single molecule magnet (SMM) behavior. In contrast to the reaction with Co(II), the reaction of the macrocyclic ligand H3L with Ni(II) or Cu(II) salts results in the contraction of this [3 + 3] macrocycle and the formation of complexes of a smaller [2 + 2] macrocycle.

An Ambiphilic Phosphide with Three Different Coordination Modes to Group 7-10 Metals.

Phosphide anions PX2- with electron-withdrawing substituents display ambiphilic properties. The use of P(V) thiophosphorane substituents enables the coordination of the resulting bis(thiophosphoranyl)phosphide anion (BTPP = L) to a variety of transition metals from groups 7 to 10. A series of homoleptic and heteroleptic complexes was synthesized and X-ray diffraction analysis revealed that, depending on the metal, L may adopt three coordination modes (κ3-(S, P, S); κ2-(S, S); κ2-(S, P)) supporting three distinct geometries (octahedral; tetrahedral; square planar). Complex L2Co displays Single Molecule Magnet (SMM) properties, and complex LRh(COD) (COD = 1,5-cyclooctadiene) catalyzes the hydrosilylation of terminal alkynes.

Low-spin ground state of the giant single-molecule magnets {Mn70} and {Mn84}

The single-molecule magnets {Mn70} and {Mn84} are characterized by a 14-site unit cell with S=2 spin sites arranged in a circular geometry. Experimentally, these systems exhibit a magnetic ground state with a notably low total spin Stot=5–7. Up to now, this low-spin ground state has been up difficult to describe theoretically due to the complexity of the quantum Heisenberg model for such a large system. In this paper, we fill this gap and demonstrate that the ground state of {Mn70} and {Mn84} is in fact governed by a small, finite Stot in quantitative agreement with the experiment. We employ accurate, large-scale SU(2)-symmetric density-matrix renormalization group calculations for a quantum Heisenberg model with previously published exchange parameters obtained by density-functional theory. We do not find a low-spin state for the same parameters and S=1 and thus propose that frustrated systems with S≥2 are inherently prone to weak ferromagnetic interactions. This could account for the prevalence of similar low-spin Mn-based single-molecule magnets. Finally, we compute the full magnetization curve and find wide plateaus at 10/14, 11/14, 12/14, and 13/14 of the saturation, which can be traced back to nearly independent three-site clusters with broken intercluster bonds. Published by the American Physical Society 2025

Single-molecule Magnet Properties of Silole- and Stannole-ligated Erbium Cyclo-octatetraenyl Sandwich Complexes.

The synthesis, structures and magnetic properties of an η5-silole complex and an η5-stannole complex of erbium are reported. The sandwich complex anions [(η5-CpSi)Er(η8-COT)]- and [(η5-CpSn)Er(η8-COT)]-, where CpSi is [SiC4-2,5-(SiMe3)2-3,4-Ph2]2- (1Si), CpSn is [SnC4-2,5-(SiMe3)2-3,4-Me2]2- (1Sn) and COT=cyclo-octatetraenyl, were obtained as their [K(2.2.2-cryptand)]+ salts and found to be isostructural, with remarkably similar bond lengths and angles, differing only in the lengths of the Er-E interactions (E=Si, Sn). The parallels in the molecular structures of 1Si and 1Sn are reflected in their dynamic magnetic properties, which show single-molecule magnet behaviour in zero applied field, with effective energy barriers of 115±7 and 125±3 cm-1, respectively, along with comparable magnetic relaxation times. Analysis of the two complexes using ab initio calculations reveals differences at a quantitative level, but overall similar electronic structures, with the thermally activated relaxation likely to proceed via the first-excited Kramers doublet. Comparing 1Si and 1Sn with the previously reported germanium analogue 1Ge reveals that swapping one heavier group 14 element for another in complexes of the type [(η5-CpE)Er(η8-COT)]- has a minimal impact on the SMM behaviour.

A rare case of a zero-field single-ion magnet in a cerium(III) pseudo-icosahedral complex.

The synthesis and structural characterisation of [Ln(Tp2-Fu)2]I (1-Ln; Ln = La, Ce, Pr, Nd) (Tp2-Fu = hydrotris(3-(2'-furyl)-pyrazol-1-yl)borate) have been reported as an isomorphous series adopting pseudo-icosahedral ligand field geometries. Continuous shape measurement (CShM) analyses on the crystal field environments of 1-Ln show the smallest values yet reported for complexes employing two hexadentate ligands (e.g. bis-scorpionate environments), with the smallest belonging to 1-La. Single-ion magnetism for 1-Ce, 1-Pr and 1-Nd was probed with ac magnetic susceptibility studies revealing slow magnetic relaxation for 1-Nd in applied magnetic fields and in zero-applied field for 1-Ce, which is a rare observation for Ce(III)-based single-ion magnets. The energy barrier to magnetic relaxation for 1-Ce was experimentally determined to be Ueff = 30(5) cm-1, which is comparable to that of other cerium-based single-molecule magnets in the literature, where these systems stablise the mJ = ±5/2 state and possess large energy gaps between the ground and first excited state that do not agree with the experimentally determined barrier.

Rare earth stibolyl and bismolyl sandwich complexes

The design of molecular rare earth complexes to achieve unique magnetic and bonding properties is a growing area of research with possible applications in advanced materials and molecular magnetics. Recent efforts focus on developing ligand frameworks that can enhance magnetic characteristics. Here we show the synthesis and characterization of a class of rare earth complexes, [(η5-C4R4Sb)Ln(η8-C8H8)] and [(η5-C4R4Bi)Ln(η8-C8H8)], featuring η5-coordinated stibolyl and bismolyl ligands. The ligand aromaticity and bonding situation within these complexes are investigated by quantum chemical calculations. Magnetic studies of the ErIII analogues reveal large barriers and intriguing properties, including waist-restricted hysteresis and slow relaxation of the magnetization, making them single-molecule magnets. Comparison between the experimental barrier and CASSCF-SO calculations indicates that relaxation in all systems occurs through high-energy excited states. These findings suggest that stibolyl and bismolyl ligands can be promising candidates for achieving high-energy barriers in Er-based SMMs, offering a pathway to molecular designs with enhanced magnetic properties.

Investigation on the magnetic relaxation mechanism and the magnetic coupling for a CoIII2CoIIDy single molecule magnet

Investigation on the magnetic relaxation mechanism and the magnetic coupling for a CoIII2CoIIDy single molecule magnet

Mn12 and the dawn of single-molecule magnets.

Mn12 and the dawn of single-molecule magnets.

Multimetallic Half-Sandwich Complexes of the Rare-Earth Metals.

Multimetallic half-sandwich complexes of the paramagnetic lanthanides gadolinium, terbium, dysprosium, holmium, and erbium as well as of diamagnetic yttrium are readily accessible via AlMe4/halogenido exchange reactions of Cp*Ln(AlMe4)2 with the mild halogenido transfer reagents Me3SiI and Me3GeX (Cp* = C5Me5; X = Br, Cl). Depending on the rare-earth-metal center and halogenido ion size, complexes with distinct structural motifs and nuclearities are obtained, including dimeric compounds [Cp*Ln(AlMe4)(μ2-Cl)]2 for the smaller metal centers Ln = Ho, Er, iodido-bridged tetranuclear rings [Cp*Ln(μ2-I)2]4 (Ln = Y, Tb, Dy, Ho, Er), and a heterobimetallic tetramethylaluminato-bridged gadolinium cluster [Cp*4Gd4I7(AlMe4)]2. The tetranuclear dysprosium complex [Cp*Dy(μ2-I)2]4 shows single-molecule magnet (SMM) behavior in zero applied field with an effective energy barrier of 164(10) cm-1.

Quantum magnetism of spin qubits in S = 1/2 Cu(II) systems in discrete complexes, chains, and metal-organic frameworks

In the last decade, S = 1/2 systems of Cu(II) complexes and Cu(II) ions in the solid state have been found to exhibit slow magnetic relaxations. The mechanism driving this magnetic behavior is different from that of high spin single-molecule magnets and that of bulk/nanoparticle magnets. This behavior is related to spin qubits and is considered to be a new type of quantum magnetism. This review focuses on the magnetic relaxation (τ), spin-lattice relaxation (T1), and spin-spin relaxation (T2 or Tm) of isolated Cu(II) complexes, Cu(II) 1D-chains, and Cu(II)-doped metal-organic frameworks. Although these properties have been well studied in isolated Cu(II) systems, studies on systems that exhibit magnetic interactions are still elusive. With the aim of progressing toward the entanglement of spin states and quantum computing using spin qubits, a greater number of studies on molecule-based spin qubits that exhibit magnetic interactions will be conducted and will be of increasing importance from now on.

Phononic Resonant Relaxation in Magnetic Hysteresis of Single-Molecule Magnets

Abstract Lanthanide-based single-molecule magnets can exhibit broad magnetic hysteresis which basically manifests slow magnetic relaxation in strong magnetic fields. However, the cause of numerous nontrivial hysteresis behaviors remain debated. Here, we put forward two influential mechanisms: the activation of optical-phonon-mediated direct transitions within the ground-state doublet and resonant Raman process. These discoveries, coupled with the g-factor anisotropy, can account for observed hysteresis behaviors in the regimes of fast magnetic relaxation. Our findings substantially complement the recognized mechanisms used to interpret the magnetic hysteresis of single molecule magnets.

Diminution of surface spin disorder in a ferromagnet via proximity effect of single-molecule magnets

Abstract Field-dependent resistance of a magnetic layer is often used as the basic tunable operational entity in several spintronics applications. In this work we demonstrate that the magnetoresistance (MR) of a classic ferromagnetic Ni layer can be tuned significantly by controlling the surface spin scattering of electrons, by manipulating disordered surface spins via proximity effect. This was achieved by drop casting molecules of a well-known single molecule magnet Mn 12-ac on micro-tracks of a thin (~12 nm) Ni film. We found significant changes in the width and sign of the magnetoresistance of the Ni micro-tracks. This is explained in the light of possible locking of the disordered surface spins of the Ni layer with the high spin moment of adjacent Mn 12-ac molecules, causing reduction in the surface spin scattering. As expected, the spin moments of Mn 12-ac molecules were found to effectively pin the surface spins only below the blocking temperature of Mn 12-ac. Above the blocking temperature, the Mn 12-ac molecules had no effect on the MR behavior of Ni micro-tracks. This observation offers a simple route to achieve on-demand low or high resistance states of a magnetic layer, very relevant to the field of spintronics.