Single-Electron Lanthanide-Lanthanide Bonds Inside Fullerenes toward Robust Redox-Active Molecular Magnets

Attaining record-high magnetic exchange, magnetic anisotropy and blocking barriers in dilanthanofullerenes

While the blocking barrier (U eff) and blocking temperature (T B) for "Dysprocenium" SIMs have been increased beyond liquid N2 temperature, device fabrication of these molecules remains a challenge as low-coordinate Ln3+ complexes are very unstable. Encapsulating the lanthanide ion inside a cage such as a fullerene (called endohedral metallofullerene or EMF) opens up a new avenue leading to several Ln@EMF SMMs. The ab initio CASSCF calculations play a pivotal role in identifying target metal ions and suitable cages in this area. Encouraged by our earlier prediction on Ln2@C79N, which was verified by experiments, here we have undertaken a search to enhance the exchange coupling in this class of molecules beyond the highest reported value. Using DFT and ab initio calculations, we have studied a series of Gd2@C2n (30 ≤ 2n ≤ 80), where an antiferromagnetic J Gd⋯Gd of -43 cm-1 was found for a stable Gd2@C38-D 3h cage. This extremely large and exceptionally rare 4f⋯4f interaction results from a direct overlap of 4f orbitals due to the confinement effect. In larger cages such as Gd2@C60 and Gd2@C80, the formation of two centre-one-electron (2c-1e-) Gd-Gd bonds is perceived. This results in a radical formation in the fullerene cage leading to its instability. To avoid this, we have studied heterofullerenes where one of the carbon atoms is replaced by a nitrogen atom. Specifically, we have studied Ln2@C59N and Ln2@C79N, where strong delocalisation of the electron yields a mixed valence-like behaviour. This suggests a double-exchange (B) is operational, and CASSCF calculations yield a B value of 434.8 cm-1 and resultant J Gd-rad of 869.5 cm-1 for the Gd2@C59N complex. These parameters are found to be two times larger than the world-record J reported for Gd2@C79N. Further ab initio calculations reveal an unprecedented U cal of 1183 and 1501 cm-1 for Dy2@C59N and Tb2@C59N, respectively. Thus, this study offers strong exchange coupling as criteria for new generation SMMs as the existing idea of enhancing the blocking barrier via crystal field modulation has reached its saturation point.

Electrophilic Trifluoromethylation of Dimetallofullerene Anions en Route to Air-Stable Single-Molecule Magnets with High Blocking Temperature of Magnetization

Lanthanide dimetallofullerenes with single-electron M-M bonds are an important class of single molecular magnets and qubit candidates, but stabilization of their unique electronic and spin structure in the form of a neutral molecule requires functionalization of the fullerene cage with a single radical group. The lack of selectivity of the currently available procedure results in a complicated and tedious separation process. Here we demonstrate that electrophilic trifluoromethylation of a mixture of metallofullerene anions with Umemoto reagent II is highly selective toward M₂@C₈₀^- (M = Tb, Y) anions, yielding M₂@C₈₀(CF₃) monoadducts as the main reaction product. Single-crystal X-ray diffraction study proved attachment of the CF₃ group to the pentagon/hexagon/hexagon junction and revealed that positions of metal atoms inside the fullerene cage in the cocrystal with NiOEP are strongly related to the position of the porphyrin moieties. Magnetic characterization of Tb₂@C₈₀(CF₃) showed that it is a robust single-molecule magnet with broad magnetic hysteresis, 100 s blocking temperature of 25 K, and the relaxation barrier of 801(4) K, corresponding to the flipping of the Tb magnetic moment in the strongly ferromagnetically coupled [Tb³⁺-e-Tb³⁺] spin system.

Radical-Bridged Ln4 Metallocene Complexes with Strong Magnetic Coupling and a Large Coercive Field

Inducing magnetic coupling between 4f elements is an ongoing challenge. To overcome this formidable difficulty, we incorporate highly delocalized tetrazinyl radicals, which strongly couple with f-block metallocenes to form discrete tetranuclear complexes. Synthesis, structure, and magnetic properties of two tetranuclear [(Cp*₂ Ln)₄ (tz^. )₄ ]⋅3(C₆ H₆ ) (Cp*=pentamethylcyclopentadienyl; tz=1,2,4,5-tetrazine; Ln=Dy, Gd) complexes are reported. An in-depth examination of their magnetic properties through magnetic susceptibility measurements as well as computational studies support a highly sought-after radical-induced "giant-spin" model. Strong exchange interactions between the Ln^III ions and tz^. radicals lead to a strong magnet-like behaviour in this molecular magnet with a large coercive field of 30 kOe.

Molecular structures and magnetic properties of endohedral metallofullerenes

Endohedral metallofullerenes have fascinating core-shell structures, with metal atoms or metal clusters encaged in fullerene cages, and they display various chemical, optical and magnetic properties derived from different types of fullerene cages and metal moieties. Fullerene cages can act as carriers to stabilize unusual cluster moieties. Many bizarre species that are hard to produce via synthetic methods survive well under the protection of a fullerene cage, making metallofullerenes ideal platforms for generating new clusters and bonds. Fullerene cages can also be carriers to hold active unpaired electrons. Some metallofullerenes possess electron spin and show intriguing magnetic properties, making them applicable for use in quantum computing, high density information storage and magnetoreception systems. The exploration of new metallofullerenes is still ongoing, while function-oriented studies are also promoted for the future application of metallofullerenes. Herein, we highlight the recent progress in the synthesis, electron spin characteristics and magnetic properties of metallofullerenes. Discussions and an outlook on the future development of metallofullerenes are also stated.

Temperature-dependent dynamics of endohedral fullerene Sc2@C80(CH2Ph) studied by EPR spectroscopy

Endohedral fullerenes are promising materials for the quantum information and quantum processing due to the unique properties of the electron-nuclear spin system well isolated from the environment inside the fullerene cage. The endofullerene Sc₂@C₈₀(CH₂Ph) features a strong hyperfine interaction between one electron spin 1/2 localized at the Sc₂ dimer and two equivalent ⁴⁵Sc nuclear spins 7/2, which yields 64 well resolved EPR transitions. We report a comprehensive analysis of the temperature dependence of the EPR spectrum of Sc₂@C₈₀(CH₂Ph) dissolved in d-toluene measured in a wide temperature range above and below the melting point. The nature of the electron spin coherence phase memory is investigated. The properties of all resonance lines in a liquid phase were treated within the model of the free rotational diffusion. Both, analytical expressions and numerical examination provide an excellent agreement between the experimental and simulated spectra. A detailed study of the experimental data confirms the assumption of the independent motions of the fullerene cage and the Sc₂ core. The data obtained show three regimes of molecular motion detected at different temperatures: the free rotation of both the fullerene cage and its bi-metal core, the motion of the core in the frozen fullerene cage, and, finally, a state with a fixed structure of both parts of the metallofullerene molecules. The data analysis reveals a significant nuclear quadrupole interaction playing an important role for the mixing of the different nuclear spin multiplets.

Metallofullerene photoswitches driven by photoinduced fullerene-to-metal electron transfer

We report on the discovery and detailed exploration of the unconventional photo-switching mechanism in metallofullerenes, in which the energy of the photon absorbed by the carbon cage π-system is transformed to mechanical motion of the endohedral cluster accompanied by accumulation of spin density on the metal atoms. Comprehensive photophysical and electron paramagnetic resonance (EPR) studies augmented by theoretical modelling are performed to address the phenomenon of the light-induced photo-switching and triplet state spin dynamics in a series of Y _x Sc_3-x N@C₈₀ (x = 0-3) nitride clusterfullerenes. Variable temperature and time-resolved photoluminescence studies revealed a strong dependence of their photophysical properties on the number of Sc atoms in the cluster. All molecules in the series exhibit temperature-dependent luminescence assigned to the near-infrared thermally-activated delayed fluorescence (TADF) and phosphorescence. The emission wavelengths and Stokes shift increase systematically with the number of Sc atoms in the endohedral cluster, whereas the triplet state lifetime and S₁-T₁ gap decrease in this row. For Sc₃N@C₈₀, we also applied photoelectron spectroscopy to obtain the triplet state energy as well as the electron affinity. Spin distribution and dynamics in the triplet states are then studied by light-induced pulsed EPR and ENDOR spectroscopies. The spin-lattice relaxation times and triplet state lifetimes are determined from the temporal evolution of the electron spin echo after the laser pulse. Well resolved ENDOR spectra of triplets with a rich structure caused by the hyperfine and quadrupolar interactions with ¹⁴N, ⁴⁵Sc, and ⁸⁹Y nuclear spins are obtained. The systematic increase of the metal contribution to the triplet spin density from Y₃N to Sc₃N found in the ENDOR study points to a substantial fullerene-to-metal charge transfer in the excited state. These experimental results are rationalized with the help of ground-state and time-dependent DFT calculations, which revealed a substantial variation of the endohedral cluster position in the photoexcited states driven by the predisposition of Sc atoms to maximize their spin population.

Spectroscopic Investigation of a Metal-Metal-Bonded Fe6 Single-Molecule Magnet with an Isolated S = 19/2 Giant-Spin Ground State

The metal-metal-bonded molecule [Bu₄N][(^HL)₂Fe₆(dmf)₂] (Fe₆) was previously shown to possess a thermally isolated spin S = ¹⁹/₂ ground state and found to exhibit slow magnetization relaxation below a blocking temperature of ∼5 K [J. Am. Chem. Soc. 2015, 137, 13949-13956]. Here, we present a comprehensive spectroscopic investigation of this unique single-molecule magnet (SMM), combining ultrawideband field-swept high-field electron paramagnetic resonance (EPR) with frequency-domain Fourier-transform terahertz EPR to accurately quantify the spin Hamiltonian parameters of Fe₆. Of particular importance is the near absence of a 4th-order axial zero-field splitting term, which is known to arise because of quantum mechanical mixing of spin states on account of the relatively weak spin-spin (superexchange) interactions in traditional polynuclear SMMs such as the celebrated Mn₁₂-acetate. The combined high-resolution measurements on both powder samples and an oriented single crystal provide a quantitative measure of the isolated nature of the spin ground state in the Fe₆ molecule, as well as additional microscopic insights into factors that govern the quantum tunneling of its magnetization. This work suggests strategies for improving the performance of polynuclear SMMs featuring direct metal-metal bonds and strong ferromagnetic spin-spin (exchange) interactions.

Stabilizing a three-center single-electron metal-metal bond in a fullerene cage

Trimetallic carbide clusterfullerenes (TCCFs) encapsulating a quinary M3C2 cluster represent a special family of endohedral fullerenes with an open-shell electronic configuration. Herein, a novel TCCF based on a medium-sized rare earth metal, dysprosium (Dy), is synthesized for the first time. The molecular structure of Dy3C2@I h(7)-C80 determined by single crystal X-ray diffraction shows that the encapsulated Dy3C2 cluster adopts a bat ray configuration, in which the acetylide unit C2 is elevated above the Dy3 plane by ∼1.66 Å, while Dy-Dy distances are ∼3.4 Å. DFT computational analysis of the electronic structure reveals that the endohedral cluster has an unusual formal charge distribution of (Dy3)8+(C2)2-@C80 6- and features an unprecedented three-center single-electron Dy-Dy-Dy bond, which has never been reported for lanthanide compounds. Moreover, this electronic structure is different from that of the analogous Sc3C2@I h(7)-C80 with a (Sc3)9+(C2)3-@C80 6- charge distribution and no metal-metal bonding.

Magnetic Hysteresis at 10 K in Single Molecule Magnet Self-Assembled on Gold

Tremendous progress in the development of single molecule magnets (SMMs) raises the question of their device integration. On this route, understanding the properties of low-dimensional assemblies of SMMs, in particular in contact with electrodes, is a necessary but difficult step. Here, it is shown that fullerene SMM self-assembled on metal substrate from solution retains magnetic hysteresis up to 10 K. Fullerene-SMM DySc2N@C80 and Dy2ScN@C80 are derivatized to introduce a thioacetate group, which is used to graft SMMs on gold. Magnetic properties of grafted SMMs are studied by X-ray magnetic circular dichroism and compared to the films of nonderivatized fullerenes prepared by sublimation. In self-assembled films, the magnetic moments of the Dy ions are preferentially aligned parallel to the surface, which is different from the disordered orientation of endohedral clusters in nonfunctionalized fullerenes. Whereas chemical derivatization reduces the blocking temperature of magnetization and narrows the hysteresis of Dy2ScN@C80, for DySc2N@C80 equally broad hysteresis is observed as in the fullerene multilayer. Magnetic bistability in the DySc2N@C80 grafted on gold is sustained up to 10 K. This study demonstrates that self-assembly of fullerene-SMM derivatives offers a facile solution-based procedure for the preparation of functional magnetic sub-monolayers with excellent SMM performance.

The anisotropy of the internal magnetic field on the central ion is capable of imposing great impact on the quantum tunneling of magnetization of Kramers single-ion magnets

In this work, a theoretical method, taking into account the anisotropy of the internal magnetic field (B[combining right harpoon above]int), is proposed to predict the rate of quantum tunneling of magnetization (QTM), i.e., τQTM-1, for Kramers single-ion magnets (SIMs). Direct comparison to both experimental and previous theoretical results of three typical Kramers SIMs indicates the necessity of the inclusion of the anisotropy of B[combining right harpoon above]int for accurate description of QTM. The predictions of the method here are consistent with the theory proposed by Prokof'ev and Stamp (PS). For Kramers SIMs of high magnetic axiality, the QTM rates, predicted by the method here, are almost linearly proportional to the results by the PS method. The dependence of τQTM-1 on various parameters is analyzed for model systems. The averaged magnitude of B[combining right harpoon above]int (Bave) and principal g value of the axial direction (gZ) are the parameters on which τQTM-1 is linearly dependent. The ones on which τQTM-1 is quadratically dependent are gXY, i.e., the principal g value of the transversal direction, and xaniso characterizing the anisotropy of B[combining right harpoon above]int. Compared to Bave and gZ, gXY and xaniso provide a higher order of dependence for QTM. Therefore regulation of the SMM property via introduction of desired values of gXY and xaniso ought to be a strategy more efficient than the one via Bave and gZ. Being different from the one via gXY, the strategy via xaniso to regulate the QTM has been rarely touched upon according to our best knowledge. However, this strategy could also lead to significant improvement since it is the same as gXY in the aspect of the dependence of τQTM-1.

Predicting the new carbon nanocages, fullerynes: a DFT study

In this study, based on density functional theory, we propose a new branch of pseudo-fullerenes which contain triple bonds with sp hybridization. We call these new nanostructures fullerynes, according to IUPAC. We present four samples with the chemical formula of C4nHn, and the structures derived from fulleranes. We compare the structural and electronic properties of these structures with those of two common fullerenes and fulleranes systems. The calculated electron affinities of the sampled fullerynes are negative, and much smaller than those of fullerenes, so they should be chemically more stable than fullerenes. Although fulleranes also exhibit higher chemical stability than fullerynes, but pentagon or hexagon of the fullerane structures cannot pass ions and molecules. Applications of fullerynes can be included in the storage of ions and gases at the nanoscale. On the other hand, they can also be used as cathode/anode electrodes in lithium-ion batteries.

Significant Roles of a Particularly Stable Two-Center Two-Electron Lu-Lu σ Bond in Lu2@C86: Electronic Structure of Lu and Radius of Lu2

There is still dispute over the stability of endohedral metallofullerenes (EMFs) M₂C_2n, and recently, multiform lutetium-based dimetallofullerenes have been dropped in experiments. The thermodynamic stabilities of Lu₂C₈₆ EMFs are revealed by density functional theory (DFT) in conjunction with statistical thermodynamic analyses. Inevitably, besides the experimentally reported Lu₂@C_2v(63751)-C₈₆, Lu₂@C_s(63750)-C₈₆, and Lu₂@C_s(63757)-C₈₆, other three metal carbide clusterfullerenes, Lu₂C₂@D_2d(51591)-C₈₄, Lu₂C₂@C₁(51383)-C₈₄, and Lu₂C₂@C_s(id207430)-C₈₄, rather than Lu₂@C₈₆ are first characterized as thermodynamically stable isomers of Lu₂C₈₆. Specially, the C_s(id207430)-C₈₄ is a newly non-classical fullerene containing one heptagon, which is stabilized via encaging Lu₂C₂. Another interesting phenomenon is that the outer fullerene cages of thermodynamically stable Lu₂C_82-88 molecules are geometrically connected through C₂ addition/loss and Stone-Wales (SW) transformation, suggesting a special relationship between thermodynamic stabilities and geometries of Lu₂C_82-88 EMFs. Furthermore, the electronic configurations of (Lu₂)⁴⁺@C₈₆^4- and (Lu₂C₂)⁴⁺@C₈₄^4- were confirmed. A significantly stable two-center two-electron (2c-2e) Lu-Lu σ single bond is formed in Lu₂@C₈₆. By comparing M-M bonds in M₂@C_2v(63751)-C₈₆ (M = Sc, Y, La, and Lu), two significant factors, the valence atomic orbital (ns) of metal atoms and radius of M²⁺, are found to determine the stability of the M-M bond in the C_2v(63751)-C₈₆. Additionally, the simulated UV-vis-NIR spectra of thermodynamically stable Lu₂C₈₆ isomers were simulated, which further disclose their electronic features.

Magnetic investigation in di- and tetranuclear lanthanide complexes

Dinuclear and tetranuclear dysprosium-based complexes have been constructed by using a crab-like hydrazone ligand, with the former acting as a typical single-molecule magnet and the later showing diamagnetic ground state.

Rotation of fullerene molecules in the crystal lattice of fullerene/porphyrin: C60 and Sc3N@C80

The temperature driven rotation of the encapsulated Sc₃N cluster in a C₈₀ fullerene cage was unraveled by variable temperature X-ray diffraction, which is significantly different from its analogues (Ho₂LuN/Lu₃N).

Valence electrons in lanthanide-based single-atom magnets: a paradigm shift in 4f-magnetism modeling and design

Impact of valence electrons on the magnetic properties of lanthanide-based monatomic magnetic systems on surfaces and in molecules. And FV-magnetism - as a crucial bit in the further understanding and design of a new generation of atomic magnets.

Metal-encapsulation induces a highly regioselective Bingel-Hirsch reaction of the labile Y@Cs(6)-C82

The chemical properties of a prototypical labile mono-EMF, Y@Cs(6)-C82, have been systematically disclosed for the first time via a Bingel-Hirsch reaction. Three mono-adduct isomers, namely, 2a, 2b and 2c out of 44 possibilities for the Y@Cs(6)-C82 cage have been readily isolated, demonstrating surprisingly high regioselectivity. Crystallographic results of 2b unambiguously confirm its molecular structure with a singly bonded bromomalonate group attached onto the Cs(6)-C82 cage. Further computational results rationalize that the high regioselectivity is a consequence of the localization of high spin density and large frontier molecular orbital distribution on the corresponding carbon atoms stemming from the encapsulation of an yttrium atom into the low-symmetry Cs(6)-C82 cage with three-electron transfer from the metal to the cage.

Unusually large hyperfine structure of the electron spin levels in an endohedral dimetallofullerene and its spin coherent properties

We report the synthesis, ESR spectroscopic and spin coherent properties of the dimetallofullerene Sc2@C80(CH2Ph). The single-electron metal-metal bond of the Sc2 dimer inside the fullerene's cage is stabilized with the electron spin density being fully localized at the metal bond. This results in an extraordinary strong hyperfine interaction of the electron spin with the 45Sc nuclear spins with a coupling constant a = 18.2 mT (∼510 MHz) and yields a fully resolved hyperfine-split ESR spectrum comprising 64 lines. The splitting is present even at low temperatures where the molecular dynamics are completely frozen. The large extent and the robustness of the hyperfine-split spectra enable us to identify and control the well-defined transitions between specific electron-nuclear quantum states. This made it possible to demonstrate in our pulse ESR study the remarkable spin coherent dynamics of Sc2@C80(CH2Ph), such as the generation of arbitrary superpositions of the spin states in a nutation experiment and the spin dephasing times above 10 μs at temperatures T < 80 K reaching the value of 17 μs at T ≤ 20 K. These observations suggest Sc2@C80(CH2Ph) as an interesting qubit candidate and motivate further synthetic efforts to obtain fullerene-based systems with superior spin properties.

Magnetic hysteresis and strong ferromagnetic coupling of sulfur-bridged Dy ions in clusterfullerene Dy2S@C82

Two isomers of metallofullerene Dy₂S@C₈₂ with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature. Analysis of the level crossing events for different orientations of a magnetic field showed that even in powder samples, the hysteresis steps caused by quantum tunneling of magnetization can provide precise information on the strength of intramolecular Dy⋯Dy inter-actions. A comparison of different methods to determine the energy difference between ferromagnetic and antiferromagnetic states showed that sub-Kelvin hysteresis gives the most robust and reliable values. The ground state in Dy₂S@C₈₂ has ferromagnetic coupling of Dy magnetic moments, whereas the state with antiferromagnetic coupling in C _s and C _3v cage isomers is 10.7 and 5.1 cm^-1 higher, respectively. The value for the C _s isomer is among the highest found in metallofullerenes and is considerably larger than that reported in non-fullerene dinuclear molecular magnets. Magnetization relaxation times measured in zero magnetic field at sub-Kelvin temperatures tend to level off near 900 and 3200 s in C _s and C _3v isomers. These times correspond to the quantum tunneling relaxation mechanism, in which the whole magnetic moment of the Dy₂S@C₈₂ molecule flips at once as a single entity.

New Horizons in Chemical Functionalization of Endohedral Metallofullerenes

This overview explains some new aspects of chemical functionalization of endohedral metallofullerenes (EMFs) that have been unveiled in recent years. After differences in chemical reactivity between EMFs and the corresponding empty fullerenes are discussed, cage-opening reactions of EMFs are examined. Then, the selective bisfunctionalization of EMFs is explained. Finally, single-bonding derivatization of EMFs is addressed. The diversity and applicability of the chemical functionalization of endohedral metallofullerenes are presented to readers worldwide.

Fulvalene as a platform for the synthesis of a dimetallic dysprosocenium single-molecule magnet

The dinucleating fulvalenyl ligand [1,1',3,3'-(C5 t Bu2H2)2]2- (Fvtttt) was used to synthesize the dimetallic dysprosocenium cation [{Dy(η5-Cp*)}2(μ-BH4)(η5:η5-Fvtttt)]+ (3) as the salt of [B(C6F5)4]- (Cp* = C5Me5). Compound [3][B(C6F5)4] was obtained using a method in which the double half-sandwich complex [{Dy(BH4)2(THF)}2(Fvtttt)] (1) was reacted with KCp* to give the double metallocene [{Dy(Cp*)(μ-BH4)}2(Fvtttt)] (2), followed by removal of a bridging borohydride ligand upon addition of [(Et3Si)2(μ-H)][B(C6F5)4]. The dimetallic fulvalenyl complexes 1-3 give rise to single-molecule magnet (SMM) behaviour in zero applied field, with the effective energy barriers of 154(15) cm-1, 252(4) cm-1 and 384(18) cm-1, respectively, revealing a significant improvement in performance across the series. The magnetic properties are interpreted with the aid of ab initio calculations, which show substantial increases in the axiality of the crystal field from 1 to 2 to 3 as a consequence of the increasingly dominant role of the Fvtttt and Cp* ligands, with the barrier height and hysteresis properties being attenuated by the equatorial borohydride ligands. The experimental and theoretical results described in this study furnish a blueprint for the design and synthesis of poly-cationic dysprosocenium SMMs with properties that may surpass those of benchmark systems.

Dy2@C79N: a new member of dimetalloazafullerenes with strong single molecular magnetism

Enhancing the exchange interaction between magnetic ions is a long-term target in molecular magnetism. Endohedral metallofullerenes (EMFs) provide a possibility for achieving such a goal by imprisoning multiple magnetic centers inside the confined inner space of a fullerene cage. Here, we report a new member of dimetallic azafullerene Dy2@C79N via crystallographic determination for the first time. Magnetic studies indicate that the strong ferromagnetic coupling between lanthanide ions and unpaired electrons enables Dy2@C79N to be a favorable SMM with large energy barrier of U = 669 K and observable hysteresis loops below 24 K.

Shape-adaptive single-molecule magnetism and hysteresis up to 14 K in oxide clusterfullerenes Dy2O@C72 and Dy2O@C74 with fused pentagon pairs and flexible Dy-(μ2-O)-Dy angle

Dysprosium oxide clusterfullerenes Dy2O@Cs(10528)-C72 and Dy2O@C2(13333)-C74 are synthesized and characterized by single-crystal X-ray diffraction. Carbon cages of both molecules feature two adjacent pentagon pairs. These pentalene units determine positions of endohedral Dy ions hence the shape of the Dy2O cluster, which is bent in Dy2O@C72 but linear in Dy2O@C74. Both compounds show slow relaxation of magnetization and magnetic hysteresis. Nearly complete cancelation of ferromagnetic dipolar and antiferromagnetic exchange Dy…Dy interactions leads to unusual magnetic properties. Dy2O@C74 exhibits zero-field quantum tunneling of magnetization and magnetic hysteresis up to 14 K, the highest temperature among Dy-clusterfullerenes.

Substrate-Independent Magnetic Bistability in Monolayers of the Single-Molecule Magnet Dy2 ScN@C80 on Metals and Insulators

Magnetic hysteresis is demonstrated for monolayers of the single-molecule magnet (SMM) Dy2 ScN@C80 deposited on Au(111), Ag(100), and MgO|Ag(100) surfaces by vacuum sublimation. The topography and electronic structure of Dy2 ScN@C80 adsorbed on Au(111) were studied by STM. X-ray magnetic CD studies show that the Dy2 ScN@C80 monolayers exhibit similarly broad magnetic hysteresis independent on the substrate used, but the orientation of the Dy2 ScN cluster depends strongly on the surface. DFT calculations show that the extent of the electronic interaction of the fullerene molecules with the surface is increasing dramatically from MgO to Au(111) and Ag(100). However, the charge redistribution at the fullerene-surface interface is fully absorbed by the carbon cage, leaving the state of the endohedral cluster intact. This Faraday cage effect of the fullerene preserves the magnetic bistability of fullerene-SMMs on conducting substrates and facilitates their application in molecular spintronics.

Endohedral Metallofullerenes: New Structures and Unseen Phenomena

Endohedral metallofullerenes (EMFs), namely fullerenes with metallic species encapsulated inside, represent an ideal platform to investigate metal-metal or metal-carbon interactions at the sub-nanometer scale by means of single-crystal X-ray diffraction (XRD) crystallography. Herein, recent progress in the identification of new structures and unprecedented properties are discussed according to the categories of monometallofullerenes, dimetallofullerenes, carbide clusterfullerenes, and nitride clusterfullerenes. In particular, the dimerization and the cage-isomer dependent oxidation state of the inner metal atom are summarized in terms of pristine monometallofullerenes. Metal-metal bonds involving lanthanide-lanthanides or actinide-actinides are discussed based on both experimental and theoretical studies. The cluster-cage matching and/or mutual selections, as well as the rarely seen M=C double bonds, are discovered in M₂ C₂ @C_2n , U₂ C@C₈₀ , M₂ TiC@C₈₀ , and Ti₃ C₃ @C₈₀ . Subsequently, the geometries of different M₃ N clusters in various cages are discussed, revealing size-matching between the internal M₃ N cluster and the outer cage induced by the planarity of the cluster. Finally, an outlook regarding the future developments of the molecular structures and applications of EMFs is presented.

Single-Molecule Magnets DyM2 N@C80 and Dy2 MN@C80 (M=Sc, Lu): The Impact of Diamagnetic Metals on Dy3+ Magnetic Anisotropy, Dy⋅⋅⋅Dy Coupling, and Mixing of Molecular and Lattice Vibrations

The substitution of scandium in fullerene single-molecule magnets (SMMs) DySc2 N@C80 and Dy2 ScN@C80 by lutetium has been studied to explore the influence of the diamagnetic metal on the SMM performance of dysprosium nitride clusterfullerenes. The use of lutetium led to an improved SMM performance of DyLu2 N@C80 , which shows a higher blocking temperature of magnetization (TB =9.5 K), longer relaxation times, and broader hysteresis than DySc2 N@C80 (TB =6.9 K). At the same time, Dy2 LuN@C80 was found to have a similar blocking temperature of magnetization to Dy2 ScN@C80 (TB =8 K), but substantially different interactions between the magnetic moments of the dysprosium ions in the Dy2 MN clusters. Surprisingly, although the intramolecular dipolar interactions in Dy2 LuN@C80 and Dy2 ScN@C80 are of similar strength, the exchange interactions in Dy2 LuN@C80 are close to zero. Analysis of the low-frequency molecular and lattice vibrations showed strong mixing of the lattice modes and endohedral cluster librations in k-space. This mixing simplifies the spin-lattice relaxation by conserving the momentum during the spin flip and helping to distribute the moment and energy further into the lattice.

Structurally modulated single-ion magnets of mononuclear β-diketone dysprosium(iii) complexes

Four perturbed eight-coordinated mononuclear β-diketone based Dy(iii) SIMs with distinct hydrogen bond interactions and electron delocalization are noteworthily modulated by the aromatic groups of auxiliary ligands.

Physical stimulus and chemical modulations of bistable molecular magnetic materials

In this Feature Article, we summarize the recent progress made in modulating the multifaceted magnetic behaviour of single-molecule magnets (SMMs) and spin-crossover (SCO) materials based on chemical modifications and external stimuli.