Mixed dysprosium-lanthanide nitride clusterfullerenes DyM2N@C80-Ih and Dy2MN@C80-Ih (M = Gd, Er, Tm, and Lu): synthesis, molecular structure, and quantum motion of the endohedral nitrogen atom

Covalency versus magnetic axiality in Nd molecular magnets: Nd-photoluminescence, strong ligand-field, and unprecedented nephelauxetic effect in fullerenes NdM2N@C80 (M = Sc, Lu, Y)

Nd-based nitride clusterfullerenes NdM2N@C80 with rare-earth metals of different sizes (M = Sc, Y, Lu) were synthesized to elucidate the influence of the cluster composition, shape and internal strain on the structural and magnetic properties. Single crystal X-ray diffraction revealed a very short Nd-N bond length in NdSc2N@C80. For Lu and Y analogs, the further shortening of the Nd-N bond and pyramidalization of the NdM2N cluster are predicted by DFT calculations as a result of the increased cluster size and a strain caused by the limited size of the fullerene cage. The short distance between Nd and nitride ions leads to a very large ligand-field splitting of Nd3+ of 1100-1200 cm-1, while the variation of the NdM2N cluster composition and concomitant internal strain results in the noticeable modulation of the splitting, which could be directly assessed from the well-resolved fine structure in the Nd-based photoluminescence spectra of NdM2N@C80 clusterfullerenes. Photoluminescence measurements also revealed an unprecedentedly strong nephelauxetic effect, pointing to a high degree of covalency. The latter appears detrimental to the magnetic axiality despite the strong ligand field. As a result, the ground magnetic state has considerable transversal components of the pseudospin g-tensor, and the slow magnetic relaxation of NdSc2N@C80 could be observed by AC magnetometry only in the presence of a magnetic field. A combination of the well-resolved magneto-optical states and slow relaxation of magnetization suggests that Nd clusterfullerenes can be useful building blocks for magneto-photonic quantum technologies.

Single-Molecule Magnet with Thermally Activated Delayed Fluorescence Based on a Metallofullerene Integrated by Dysprosium and Yttrium Ions

It is vital to construct luminescent single-molecule magnets (SMMs) and explore their applications in quantum computing technique and magneto-luminescence devices. In this work, we report a luminescent single-molecule magnet with thermally activated delayed fluorescence (TADF) based on metallofullerene DyY₂N@C₈₀. DyY₂N@C₈₀ was constructed by integrating dysprosium and yttrium ions into a fullerene cage. Magnetic results suggest that DyY₂N@C₈₀ exhibits magnetic hysteresis loops below 8 K originating from the Dy³⁺ ion. Moreover, DyY₂N@C₈₀ exhibits TADF originating from the Y³⁺-coordinated carbon cage, whose luminescence peak positions and peak intensities can be obviously influenced by Dy³⁺. Furthermore, a supramolecular complex of DyY₂N@C₈₀ and [12]Cycloparaphenylene ([12]CPP) was then prepared to construct a single-molecule magnet with multiwavelength luminescence. The effects of host-guest interaction on photoluminescence properties of DyY₂N@C₈₀ were disclosed. Theoretical calculations were also employed to illustrate the structures of DyY₂N@C₈₀ and DyY₂N@C₈₀⊂[12]CPP.

Capturing the Missing Carbon Cage Isomer of C84 via Mutual Stabilization of a Triangular Monometallic Cyanide Cluster

Monometallic cyanide clusterfullerenes (CYCFs) represent a unique branch of endohedral clusterfullerenes with merely one metal atom encapsulated, offering a model system for elucidating structure-property correlation, while up to now only C₈₂ and C₇₆ cages have been isolated for the pristine CYCFs. C₈₄ is one of the most abundant fullerenes and has 24 isomers obeying the isolated pentagon rule (IPR), among which 14 isomers have been already isolated, whereas the C_2v(17)-C₈₄ isomer has lower relative energy than several isolated isomers but never been found for empty and endohedral fullerenes. Herein, four novel C₈₄-based pristine CYCFs with variable encapsulated metals and isomeric cages, including MCN@C₂(13)-C₈₄ (M = Y, Dy, Tb) and DyCN@C_2v(17)-C₈₄, have been synthesized and isolated, fulfilling the first identification of the missing C_2v(17)-C₈₄ isomer, which can be interconverted from the C₂(13)-C₈₄ isomer through two steps of Stone-Wales transformation. The molecular structures of these four C₈₄-based CYCFs are determined unambiguously by single-crystal X-ray diffraction. Surprisingly, although the ionic radii of Y³⁺, Dy³⁺, and Tb³⁺ differ slightly by only 0.01 Å, such a subtle difference leads to an obvious change in the metal-cage interactions, as inferred from the distance between the metal atom and the nearest hexagon center of the C₂(13)-C₈₄ cage. On the other hand, upon altering the isomeric cage from DyCN@C₂(13)-C₈₄ to DyCN@C_2v(17)-C₈₄, the Dy-cage distance changes as well, indicating the interplay between the encapsulated DyCN cluster and the outer cage. Therefore, we demonstrate that the metal-cage interactions within CYCFs can be steered via both internal and external routes.

High blocking temperatures for DyScS endohedral fullerene single-molecule magnets

Dy-based single-molecule magnets (SMMs) are of great interest due to their ability to exhibit very large thermal barriers to relaxation and therefore high blocking temperatures. One interesting line of investigation is Dy-encapsulating endohedral clusterfullerenes, in which a carbon cage protects magnetic Dy3+ ions against decoherence by environmental noise and allows for the stabilization of bonding and magnetic interactions that would be difficult to achieve in other molecular architectures. Recent studies of such materials have focused on clusters with two Dy atoms, since ferromagnetic exchange between Dy atoms is known to reduce the rate of magnetic relaxation via quantum tunneling. Here, two new dysprosium-containing mixed-metallic sulfide clusterfullerenes, DyScS@C s(6)-C82 and DyScS@C 3v(8)-C82, have been successfully synthesized, isolated and characterized by mass spectrometry, Vis-NIR, cyclic voltammetry, single crystal X-ray diffractometry, and magnetic measurements. Crystallographic analyses show that the conformation of the encapsulated cluster inside the fullerene cages is notably different than in the Dy2X@C s(6)-C82 and Dy2X@C 3v(8)-C82 (X = S, O) analogues. Remarkably, both isomers of DyScS@C82 show open magnetic hysteresis and slow magnetic relaxation, even at zero field. Their magnetic blocking temperatures are around 7.3 K, which are among the highest values reported for clusterfullerene SMMs. The SMM properties of DyScS@C82 far outperform those of the dilanthanide analogues Dy2S@C82, in contrast to the trend observed for carbide and nitride Dy clusterfullerenes.

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.

A luminescent single-molecule magnet of dimetallofullerene with cage-dependent properties

It is important to explore luminescent single-molecule magnets (SMMs) to promote their application in high-density data storage. Herein, we report two dimetallofullerenes of DyEr@C₈₂ isomers, which exhibit cage-dependent single-molecule magnet behavior and photoluminescence properties. DyEr@C₈₂ isomers were characterized with a C_s and C_3v cage symmetry by UV-vis-NIR spectroscopy and single-crystal X-ray diffraction analysis. Magnetic results revealed that DyEr@C_3v-C₈₂ displays SMM behavior below 3 K, whereas DyEr@C_s-C₈₂ is a paramagnet. In addition, photoluminescence (PL) was also observed for both of these two isomers, whose peak patterns are different. Theoretical calculations revealed the presence of a one-electron-two-center Dy-Er bond in these two isomers, and different electronic structures of DyEr@C_s-C₈₂ and DyEr@C_3v-C₈₂, which agrees well with the experimental results. These results show that dimetallofullerenes are promising magneto-luminescent materials with varied properties.

Molecular spinning top: visualizing the dynamics of M3N@C80 with variable temperature single crystal X-ray diffraction

Variable temperature X-ray diffraction studies on two single crystals containing M3N@C80, i.e., Ho2LuN@C80·NiOEP·2(C6H6) and Lu3N@C80·NiOEP·2(C6H6), (NiOEP = Nickel octaethylporphyrin) unravelled the temperature dependent rotation of the M3N cluster and C80 cage on the static NiOEP molecule.