Stability and Electronic Properties of Mixed Rare-Earth Tri-Metallofullerenes YxDy3-x@C80 (x = 1 or 2).

Tri-metallofullerenes, specifically M3@C80 where M denotes rare-earth metal elements, are molecules that possess intriguing magnetic properties. Typically, only one metal element is involved in a given tri-metallofullerene molecule. However, mixed tri-metallofullerenes, denoted as M1xM23-x@C80 (x = 1 or 2, M1 and M2 denote different metal elements), have not been previously discovered. The investigation of such mixed tri-metallofullerenes is of interest due to the potential introduction of distinct properties resulting from the interaction between different metal atoms. This paper presents the preparation and theoretical analysis of mixed rare-earth tri-metallofullerenes, specifically YxDy3-x@C80 (x = 1 or 2). Through chemical oxidation of the arc-discharge produced soot, the formation of tri-metallofullerene cations, namely Y2Dy@C80+ and YDy2@C80+, has been observed. Density functional theory (DFT) calculations have revealed that the tri-metallofullerenes YxDy3-x@C80 (x = 1 or 2) exhibit a low oxidation potential, significantly lower than other fullerenes such as C60 and C70. This low oxidation potential can be attributed to the relatively high energy level of a singly occupied orbital. Additionally, the oxidized species demonstrate a large HOMO-LUMO gap similar to that of YxDy3-xN@C80, underscoring their high chemical stability. Theoretical investigations have uncovered the presence of a three-center two-electron metal-metal bond at the center of Y2DY@C80+ and YDy2@C80+. This unique multi-center bond assists in alleviating the electrostatic repulsion between the metal ions, thereby contributing to the overall stability of the cations. These mixed rare-earth tri-metallofullerenes hold promise as potential candidates for single-molecule magnets.

Bandgap Engineering of Erbium-Metallofullerenes toward Switchable Photoluminescence.

Encapsulating photoluminescent lanthanide ions like erbium (Er) into fullerene cages affords photoluminescent endohedral metallofullerenes (EMFs). Few reported photoluminescent Er-EMFs are all based on encapsulation of multiple (two to three) metal atoms, whereas mono-Er-EMFs exemplified by Er@C82 are not photoluminescent due to its narrow optical bandgap. Herein, by entrapping an Er-cyanide cluster into various C82 cages to form novel Er-monometallic cyanide clusterfullerenes (CYCFs), ErCN@C82 (C2 (5), Cs (6), and C2 v (9)), the photoluminescent properties of CYCFs are investigated, and obvious near-infrared (NIR) photoluminescence only is observed for ErCN@C2 (5)-C82 . Combined with a comparative photoluminescence study of three medium-bandgap di-Er-EMFs, including Er2 @Cs (6)-C82 , Er2 O@Cs (6)-C82 , and Er2 C2 @Cs (6)-C82 , this study proposes that the optical bandgap can be used as a simple criterion for switching the photoluminescence of Er-EMFs, and the bandgap threshold is determined to be between 0.83 and 0.74 eV. Furthermore, the photoluminescent patterns of these three di-Er-EMFs differ dramatically. It is found that the location of the Er atom within the same Cs (6)-C82 cage is almost fixed and independent on the endo-unit; thus the previous statement on the key role of metal position in photoluminescence of di-Er-EMFs seems erroneous, and the geometric configuration of the endo-unit, especially the bridging mode of two Er ions, is decisive instead.

Effects of Aqueous Dispersions of C60, C70, and Gd@C82 Fullerenes on DNA Oxidative Damage/Repair and Apoptosis in Human Embryonic Lung Fibroblasts.

Fullerenes and metallofullerenes play an active role in homeostasis of reactive oxygen species and may cause oxidative damage to cells. As pristine fullerenes are a basis for derivatization, studying oxidative DNA damage/repair and apoptosis is important in terms of genotoxicity and cytotoxicity for their biomedical application. Aqueous dispersions of C60, C70, and Gd@C82 (5 nM and 1.5 µM) were cultured with human fetal lung fibroblasts for 1, 3, 24, and 72 h. Oxidative DNA damage/repair was assessed through concentration of 8-oxodG, double-strand breaks, and activation of BRCA1. Activity of apoptosis was assessed through the BCL2/BAX ratio. All three fullerenes caused oxidative modification of DNA at the early stages; C60 caused the most long-term damage, Gd@C82 caused the most short-term damage, and C70 caused "wave-like" dynamics. The dynamics of DNA repair correlated with the dynamics of oxidative damage, but Gd@C82 caused more prolonged activation of the repair system than C60 or C70. The oxidative toxicity of Gd@C82, is minor and the oxidative toxicity of C60 is mild and short-term, in contrast to C70. In relation to the studied effects, the fullerenes can be arranged in a safety row of Gd@C82 > C60 > C70.

Capturing the Long-Sought Dy@C2v(5)-C80 via Benzyl Radical Stabilization.

Endohedral metallofullerenes (EMFs) are one type of intriguing metal/carbon hybrid molecule with the molecule configuration of sphere cavity-encapsulating metal ions/metal clusters due to their unique physicochemical properties and corresponding application in the fields of biological materials, single molecule magnet materials and energy conversion materials. Although the EMF family is growing, and versatile EMFs have been successfully synthesized and confirmed using crystal structures, some expected EMF members have not been observed using the conventional fullerene separation and purify strategy. These missing EMFs raise an interesting scientific issue as to whether this is due to the difficulty in separating them from the in situ formed carbon soot. Herein, we successfully captured a long-sought dysprosium-based EMF bearing a C2v(5)-C80 cage (Dy@C2v(5)-C80) in the form of Dy@C2v(5)-C80(CH2Ph)(Ph = -C6H5) from carbon soot containing versatile EMFs using simple benzyl radical functionalization and unambiguously confirmed the molecule structure using single crystal X-ray diffraction characterization. Meanwhile, the crystal structure of Dy@C2v(5)-C80(CH2Ph) showed that a single benzyl group was grafted onto the (5,6,6)-carbon, suggesting the open-shell electronic configuration of Dy@C2v(5)-C80. The theoretical calculations unveiled that the benzyl radical addition enables the modulation of the electronic configuration of Dy@C2v(5)-C80 and the corresponding stabilization of Dy@C2v(5)-C80 in conventional organic solvents. This facile stabilization strategy via benzyl radical addition exhibits the considerable capability to capture these missing EMFs, with the benefit of enriching the endohedral fullerene family.

Stabilities, Geometries, Electronic Structures, and Conversion Rules of Carbide Cluster Metallofullerenes.

Since the discovery of the first carbide cluster metallofullerene (CCMF) Sc2 C2 @C84 in 2001, CCMFs have attracted great concerns with variable structures and fascinating characteristics. To date, there are hundreds of studies on CCMFs. Crystallography studies on CCMFs are carried out by single-crystal X-ray diffraction. Theoretical calculations can also be used to study CCMFs in detail without being limited by low experimental yields. This review analyzes the stability of CCMFs reported previously, and indicates that the C2 unit contributes a lot to their stability. At the same time, the relationship between the structures of inner carbide cluster and cage size is systematically discussed, and the four-electron transfer always occurs. Furthermore, the possible transformation rule between di-EMFs and CCMFs is indicated. Finally, an outlook regarding the future developments and applications of CCMFs is presented.

Amine Functionalized Trimetallic Nitride Endohedral Fullerenes: A Class of Nanoparticle to Tackle Low Back/Leg Pain.

Low back pain is the most common health problem with a prevalence of over 80% worldwide and an estimated annual cost of $100 billion in the United States. Intervertebral disc degeneration accounts for a major cause of low back pain. However, there is still a lack of safe and effective treatment to tackle this devastating condition. In this study, we synthesized four functionalized trimetallic nitride endohedral metallofullerenes (carboxyl-f-Sc3N@C80, carboxyl-f-Gd3N@C80, amino-f-Sc3N@C80, and amino-f-Gd3N@C80) and characterized them with X-ray photoelectron spectroscopy, matrix-assisted laser desorption/ionization-time of flight mass spectrometry, and UV-vis. Via electron paramagnetic resonance, all four metallofullerene derivatives possessed dose-dependent radical scavenging capabilities (hydroxyl radicals and superoxide anions), with the most promising radical scavenging properties shown in the amine functionalized C80 metallofullerenes. Both amino-f-Sc3N@C80 and amino-f-Gd3N@C80 at 1 µM significantly reduced lipopolysaccharide induced reactive oxygen species production and mRNA expressions of pro-inflammatory mediators (inos, tnf-α, il-1, and cox-2) in macrophages without apparent cytotoxicity through regulating activity of p38 MAPK, p65, and nuclear translocation of NF-κB. Furthermore, in an established mouse model of lumbar radiculopathy, amino-f-Sc3N@C80 and amino-f-Gd3N@C80 effectively alleviated ipsilateral mechanical hyperalgesia for up to 2 weeks. In dorsal root ganglia explant culture, we also showed that amino-f-Sc3N@C80 and amino-f-Gd3N@C80 ameliorated TNF-α elicited neuroinflammation. In summary, we presented results for a potent radical scavenging, anti-inflammatory and analgesic nanoparticle, amino-functionalized eighty-carbon metallofullerenes in vitro and in vivo. Our study provides important assets for developing pleiotropic treatment strategies to tackle the inflammation, a significant pathological hallmark in the intervertebral disc degeneration and associated pain.

Imaging the Single-Electron Ln-Ln Bonding Orbital in a Dimetallofullerene Molecular Magnet.

Chemically robust single-molecule magnets (SMMs) with sufficiently high blocking temperatures TB are among the key building blocks for the realization of molecular spintronic or quantum computing devices. Such device applications require access to the magnetic system of a SMM molecule by means of electronic transport, which primarily depends on the interaction of magnetic orbitals with the electronic states of the metallic electrodes. Scanning tunneling microscopy in combination with ab initio calculations allows to directly address the unoccupied component of the single-electron molecular orbital that mediates the ferromagnetic exchange coupling between two 4f ions within a lanthanide endohedral dimetallofullerene deposited on a graphene surface. The single-electron metal-metal bond provides a direct access to the molecule's magnetic system in the transport experiments, paving the way for investigation and controlled manipulation of the spin system of individual dimetallofullerene SMMs, essential for molecular spintronics.

Octapalladium Strings Trap C60 and C70 Fullerenes Affording Metal-Chain-Wired Bucky Balls.

Reactions of Pd8 strings supported by meso-Ph2 PCH2 P(Ph)CH2 P(Ph)CH2 PPh2 (meso-dpmppm) ligands, [Pd8 (meso-dpmppm)4 (L)2 ]4+ (L=CH3 CN (1), XylNC (2)) with C60 resulted in the exclusive formation of unprecedented metal-chain-wired C60 bucky balls, [{Pd4 (meso-dpmppm)2 (L)}2 (C60 )]4+ (L=CH3 CN (11), XylNC (12)), in which a C60 fullerene is trapped in the central Pd-Pd junction, as unambiguously established by spectroscopic, X-ray crystallographic, and theoretical techniques. The similar reaction of Pd8 strings supported by rac-dpmppm, [Pd8 (rac-dpmppm)4 (CH3 CN)2 ]4+ (3) also afforded a racemic mixture of [{Pd4 ((R*,R*)-dpmppm)2 (CH3 CN)}2 (C60 )]4+ (13) without scrambling the Pd4 fragments with (R,R)- and (S,S)-dpmppm ligands. Consequently, those of enantiopure chiral Pd8 strings, [Pd8 ((R*,R*)-dpmppm)4 (CH3 CN)2 ]4+ , certainly afforded chiral bucky balls of [{Pd4 ((R*,R*)-dpmppm)2 (CH3 CN)}2 (C60 )]4+ (13RR and 13SS ), that exhibit mirror-image circular dichroism spectra. The reactions of 1 and 2 were also applied for trapping a C70 fullerene to give 2 : 1 adducts of [{Pd4 (meso-dpmppm)2 (L)}2 (C70 )]4+ (L=CH3 CN (21), XylNC (22)). These results provide useful information for creating a platform to develop dimensionally and chirality controlled metal-carbon nanocomposite materials.

Effects of Aqueous Dispersions of C60, C70 and Gd@C82 Fullerenes on Genes Involved in Oxidative Stress and Anti-Inflammatory Pathways.

BACKGROUND: Fullerenes and metallofullerenes can be considered promising nanopharmaceuticals themselves and as a basis for chemical modification. As reactive oxygen species homeostasis plays a vital role in cells, the study of their effect on genes involved in oxidative stress and anti-inflammatory responses are of particular importance. METHODS: Human fetal lung fibroblasts were incubated with aqueous dispersions of C60, C70, and Gd@C82 in concentrations of 5 nM and 1.5 µM for 1, 3, 24, and 72 h. Cell viability, intracellular ROS, NOX4, NFκB, PRAR-γ, NRF2, heme oxygenase 1, and NAD(P)H quinone dehydrogenase 1 expression have been studied. RESULTS & CONCLUSION: The aqueous dispersions of C60, C70, and Gd@C82 fullerenes are active participants in reactive oxygen species (ROS) homeostasis. Low and high concentrations of aqueous fullerene dispersions (AFD) have similar effects. C70 was the most inert substance, C60 was the most active substance. All AFDs have both "prooxidant" and "antioxidant" effects but with a different balance. Gd@C82 was a substance with more pronounced antioxidant and anti-inflammatory properties, while C70 had more pronounced "prooxidant" properties.

Vibrational spectra of La@C60 and Ce@C60 endohedral fullerenes: Influence of spin state multiplicity.

Endohedral fullerenes with paramagnetic encapsulated atoms are new magnetic materials of interest for numerous applications from medicine to quantum computers. An important phenomenon with endohedral fullerenes is the appearance of new vibrational frequencies not associated with empty fullerenes. The vibrational spectra of the lanthanide endohedral fullerenes La@C60 and Ce@C60 in various spin states are calculated using the density functional method. Most of the spectral lines lie in the 300-1600 cm-1range, and their intensities change dramatically depending on the molecule's symmetry and spin state, which are determined by the encapsulated lanthanide atom. The average frequency shift of the carbon cage vibrations caused by spin transition is only 5 cm-1. The calculated frequencies of the coupled "metal-carbon cage" vibrations of the lanthanide endohedral fullerenes La@C60 and Ce@C60 in various spin states lie in the 10-170 cm-1range. The computational results for both the frequencies and intensities of the metal-cage modes depend considerably on the spin state. The changes in these vibrational modes are due to the changes in the molecular symmetry and the metal-carbon bond lengths. Such dependence can be used as a basis for controlling the spin state of metallofullerenes by measuring the vibration frequencies in the far-infrared zone, which could be important for nanoelectronics and quantum informatics.

Redox Modulation of the Reactivity and Regioselectivity in Diels-Alder Reaction of Metallofullerene La@C82 with Cyclopentadiene.

Modulation of the reactivity of metallofullerenes is critical for production of metallofullerene derivatives with desired properties and functionalities. In this study, we investigate the effects of reduction and oxidation on the reactivity and regioselectivity in Diels-Alder reaction of metallofullerene La@C82 by means of density functional theory calculations. Because of the enhanced electron-deficiency characteristic upon oxidation, the oxidized metallofullerene exhibits higher thermodynamic and kinetic reactivity as compared with neutral La@C82 . The regioselectivity in the reaction of La@C82 with cylcopentadiene is remarkably changed after oxidation of the metallofullerene, which is explained in terms of the changes in the geometrical structure and the electronic structure of the metallofullerene. Quantitative analysis based on the activation-strain model demonstrates that the low activation energy barrier for the reaction of the cation La@C82 + with cyclopentadiene originates from small strain energy and large interaction energy between the reactants. Energy decomposition analysis on the transition states of the reactions reveals that the exchange-repulsion interaction energy is one of the critical factors that determine the kinetic reactivity of the metallofullerene. This study not only provides new theoretical insights on how to modulate the reactivity of metallofullerenes, but also offers guideline for future experimental synthesis of new metallofullerene derivatives.

Activation of the Unreactive Bond in C70 Fullerene toward Diels-Alder Reaction by Encapsulation of a Lithium Atom.

Diels-Alder cycloaddition reaction is useful for generation of covalent derivatives of fullerenes. Diels-Alder reactions of C70 and dienes usually take place at the carbon-carbon bond that has a short bond length in C70 , while the bonds with long lengths are generally unreactive. In this paper, we investigated the reactivities of Li+ @C70 and Li@C70 toward Diels-Alder reactions with cyclohexadiene by means of density functional theory calculations. We found that the thermodynamic and kinetic reactivities of the fullerene cage are changed significantly after the encapsulation of the lithium ion or atom. The encapsulated lithium ion causes a remarkable decrease of the activation barrier for the cycloaddition reaction, which can be ascribed to the enhanced orbital interaction between cyclohexadiene and the fullerene cage. The unreactive bond with a long length in C70 is activated efficiently after the encapsulation of the lithium atom. According to the activation-strain model analysis, the improved reactivity of the long bond is associated with the small deformation energy and large interaction energy of the reactants. Unlike conventional Diels-Alder reactions that proceed through concerted mechanism, the reaction of Li@C70 and cyclohexadiene undergoes an unusual stepwise mechanism because of the open-shell electronic structure of Li@C70 .

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 @C2n , 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.

Preferential Formation of Mono-Metallofullerenes Governed by the Encapsulation Energy of the Metal Elements: A Case Study on Eu@C2n (2n=74-84) Revealing a General Rule.

Encapsulating one to three metal atoms or a metallic cluster inside fullerene cages affords endohedral metallofullerenes (EMFs) classified as mono-, di-, tri-, and cluster-EMFs, respectively. Although the coexistence of various EMF species in soot is common for rare-earth metals, we herein report that europium tends to prefer the formation of mono-EMFs. Mass spectroscopy reveals that mono-EMFs (Eu@C2n ) prevail in the Eu-containing soot. Theoretical calculations demonstrate that the encapsulation energy of the endohedral metal accounts for the selective formation of mono-EMFs and rationalize similar observations for EMFs containing other metals like Ca, Sr, Ba, or Yb. Consistently, all isolated Eu-EMFs are mono-EMFs, including Eu@D3h (1)-C74 , Eu@C2v (19138)-C76 , Eu@C2v (3)-C78 , Eu@C2v (3)-C80 , and Eu@D3d (19)-C84 , which are identified by crystallography. Remarkably, Eu@C2v (19138)-C76 represents the first Eu-containing EMF with a cage that violates the isolated-pentagon-rule, and Eu@C2v (3)-C78 is the first C78 -based EMF stabilized by merely one metal atom.

Crystallographic and Theoretical Investigations of Er2 @C2 n (2 n=82, 84, 86): Indication of Distance-Dependent Metal-Metal Bonding Nature.

Successful isolation and characterization of a series of Er-based dimetallofullerenes present valuable insights into the realm of metal-metal bonding. These species are crystallographically identified as Er2 @Cs (6)-C82 , Er2 @C3v (8)-C82 , Er2 @C1 (12)-C84 , and Er2 @C2v (9)-C86 , in which the structure of the C1 (12)-C84 cage is unambiguously characterized for the first time by single-crystal X-ray diffraction. Interestingly, natural bond orbital analysis demonstrates that the two Er atoms in Er2 @Cs (6)-C82 , Er2 @C3v (8)-C82 , and Er2 @C2v (9)-C86 form a two-electron-two-center Er-Er bond. However, for Er2 @C1 (12)-C84 , with the longest Er⋅⋅⋅Er distance, a one-electron-two-center Er-Er bond may exist. Thus, the difference in the Er⋅⋅⋅Er separation indicates distinct metal bonding natures, suggesting a distance-dependent bonding behavior for the internal dimetallic cluster. Additionally, electrochemical studies suggest that Er2 @C82-86 are good electron donors instead of electron acceptors. Hence, this finding initiates a connection between metal-metal bonding chemistry and fullerene chemistry.

Functional Metallofullerene Materials and Their Applications in Nanomedicine, Magnetics, and Electronics.

Endohedral metallofullerenes exhibit combined properties from carbon cages as well as internal metal moieties and have great potential in a wide range of applications as molecule materials. Along with the breakthrough of mass production of metallofullerenes, their applied research has been greatly developed with more and more new functions and practical applications. For gadolinium metallofullerenes, their water-soluble derivatives have been demonstrated with antitumor activity and unprecedented tumor vascular-targeting therapy. Metallofullerene water-soluble derivatives also can be applied to treat reactive oxygen species (ROS)-induced diseases due to their high antioxidative activity. For magnetic metallofullerenes, the internal electron spin and metal species bring about spin sensitivity, molecular magnets, and spin quantum qubits, which have many promising applications. Metallofullerenes are significant candidates for fabricating useful electronic devices because of their various electronic structures. This Review provides a summary of the metallofullerene studies reported recently, in the fields of tumor inhibition, tumor vascular-targeting therapies, antioxidative activity, spin probes, single-molecule magnets, spin qubits, and electronic devices. This is not an exhaustive summary and there are many other important study results regarding metallofullerenes. All of this research has revealed the irreplaceable role of metallofullerene materials.

Modular Covalent Graphene Functionalization with C60 and the Endohedral Fullerene Sc3 N@C80 : A Facile Entry to Synthetic-Carbon-Allotrope Hybrids.

Two novel graphene-fullerene hybrid structures, containing C60 and endohedral Sc3 N@C80 bound to graphene, instead of the formerly used graphene oxide, were efficiently synthesized via a reductive activation/exfoliation approach starting from pristine graphite. The structures of these multifunctional hybrid systems were unambiguously characterized by statistical Raman spectroscopy, TG-MS, TG-GC-MS, and LD-TOF mass spectroscopy, confirming the covalent bonding of the respective C60 /Sc3 N@C80 moieties to the pristine graphene. Furthermore, assisted by temperature-dependent Raman spectroscopy studies the corresponding defunctionalization processes were also investigated. Finally, the formation of a carbon allotrope hybrid material on the basis of C60 /Sc3 N@C80 moieties coupled to graphene could be visualized by HRTEM.

In Situ Atomic-Level Studies of Gd Atom Release and Migration on Graphene from a Metallofullerene Precursor.

We show how gadolinium (Gd)-based metallofullerene (Gd3N@C80) molecules can be used to create single adatoms and nanoclusters on a graphene surface. An in situ heating holder within an aberration-corrected scanning transmission electron microscope is used to track the adhesion of endohedral metallofullerenes (MFs) to the surface of graphene, followed by Gd metal ejection and diffusion across the surface. Heating to 900 °C is used to promote adatom migration and metal nanocluster formation, enabling direct imaging of the assembly of nanoclusters of Gd. We show that hydrogen can be used to reduce the temperature of MF fragmentation and metal ejection, enabling Gd nanocluster formation on graphene surfaces at temperatures as low as 300 °C. The process of MF fragmentation and metal ejection is captured in situ and reveals that after metal release, the C80 cage opens further and fuses with the surface monolayer carbon glass on graphene, creating a highly stable carbon layer for further Gd adatom adhesion. Small voids and defects (∼1 nm) in the surface carbon glass act as trapping sites for Gd atoms, leading to atomic self-assembly of 2D monolayer Gd clusters. These results show that MFs can adhere to graphene surfaces at temperatures well above their bulk sublimation point, indicating that the surface bound MFs have strong adhesion to dangling bonds on graphene surfaces. The ability to create dispersed single Gd adatoms and Gd nanoclusters on graphene may have impact in spintronics and magnetism.

Isolation and Crystallographic Characterization of Lu3 N@C2n (2n=80-88): Cage Selection by Cluster Size.

The small Sc3 N cluster has only been found in such small cages as C2n (2n=68, 78, 80, 82), whereas the large M3 N (M=Y, Gd, Tb, Tm) clusters choose those larger cages C2n (2n=82-88). Herein, concrete experimental evidence is presented to establish the size effect of the internal metallic cluster on selecting the outer cage of endohedral metallofullerenes (EMFs) by using a medium-sized metal, lutetium, which possesses an ionic radius between Sc and Gd. A series of lutetium-containing EMFs have been obtained and their structures are unambiguously determined as Lu3 N@Ih (7)-C80 , Lu3 N@D5h (6)-C80 , Lu3 N@C2v (9)-C82 , Lu3 N@Cs (51365)-C84 , Lu3 N@D3 (17)-C86 , and Lu3 N@D2 (35)-C88 by single-crystal X-ray diffraction crystallography. It was confirmed that the encaged Lu3 N cluster always adopts a planar geometry in Lu3 N@C80-88 isomers to ensure substantial metal-cage/metal-nitrogen interactions. As a result, the Lu3 N cluster selects the C2v (9)-C82 cage, which also encapsulates Sc3 N, instead of the Cs (39663)-C82 cage which is more suitable for M3 N (M=Y, Gd, Tb, Tm). However, different from Sc3 N, Lu3 N can also template the C84-88 cages which are absent for Sc3 N-containing EMFs, confirming clearly the size effect of the internal cluster on selecting the outer cage.