Transition Metal/Lanthanide-Nitrogen Double Bonds Co-stabilized in a Carbon Cage.

Metal-nitrogen double bonds have been commonly reported for conventional metal complexes, but the coexistence of both transition metal-nitrogen and lanthanide-nitrogen double bonds bridged by nitrogen within one compound has never been reported. Herein, by encapsulating a ternary transition metal-lanthanide heteronuclear dimetallic nitride into a C fullerene cage, transition metal-nitrogen and lanthanide-nitrogen double bonds are costabilized simultaneously within the as-formed clusterfullerene TiCeN@C(12)-C, which is a representative heteronuclear dimetallic nitride clusterfullerene. Its molecular structure was unambiguously determined by single-crystal X-ray diffraction, revealing a slightly bent μ-bridged nitride cluster with short Ti-N (1.

Unexpected and divergent mechanosynthesis of furanoid-bridged fullerene dimers CO and CO.

An unexpected, divergent and efficient approach toward furanoid-bridged fullerene dimers CO and CO was established under different solvent-free ball-milling conditions by simply using pristine C as the starting material, water as the oxygen source and FeCl as the mediator. The structures of CO and CO were unambiguously established by single-crystal X-ray crystallography. A plausible reaction mechanism is proposed on the basis of control experiments.

Short Didysprosium Covalent Bond Enables High Magnetization Blocking Temperature of a Direct 4f-4f Coupled Dinuclear Single-Molecule Magnet.

Coupling two magnetic anisotropic lanthanide ions via a direct covalent bond is an effective way to realize high magnetization blocking temperature of single-molecule magnets (SMMs) by suppressing quantum tunneling of magnetization (QTM), whereas so far only single-electron lanthanide-lanthanide bonds with relatively large bond distances are stabilized in which coupling between lanthanide and the single electron dominates over weak direct 4f-4f coupling. Herein, we report for the first time synthesis of short Dy(II)-Dy(II) single bond (3.61 Å) confined inside a carbon cage in the form of an endohedral metallofullerene Dy@C.

Electrosynthesis of buckyballs with fused-ring systems from PCBM and its analogue.

[6,6]-Phenyl-C-butyric acid methyl ester (PCBM), a star molecule in the fullerene field, has found wide applications in materials science. Herein, electrosynthesis of buckyballs with fused-ring systems has been achieved through radical α-C-H functionalization of the side-chain ester for both PCBM and its analogue, [6,6]-phenyl-C-propionic acid methyl ester (PCPM), in the presence of a trace amount of oxygen. Two classes of buckyballs with fused bi- and tricyclic carbocycles have been electrochemically synthesized.

Synthesis and Characterization of U≡C Triple Bonds in Fullerene Compounds.

Despite decades of efforts, the actinide-carbon triple bond has remained an elusive target, defying synthesis in any isolable compound. Herein, we report the successful synthesis of uranium-carbon triple bonds in carbide-bridged bimetallic [U≡C-Ce] units encapsulated inside the fullerene cages of C and C. The molecular structures of UCCe@C and the nature of the U≡C triple bond were characterized through X-ray crystallography and various spectroscopic analyses, revealing very short uranium-carbon bonds of 1.

Actinide-lanthanide single electron metal-metal bond formed in mixed-valence di-metallofullerenes.

Understanding metal-metal bonding involving f-block elements has been a challenging goal in chemistry. Here we report a series of mixed-valence di-metallofullerenes, ThDy@C (2n = 72, 76, 78, and 80) and ThY@C (2n = 72 and 78), which feature single electron actinide-lanthanide metal-metal bonds, characterized by structural, spectroscopic and computational methods. Crystallographic characterization unambiguously confirmed that Th and Y or Dy are encapsulated inside variably sized fullerene carbon cages.

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@C are not photoluminescent due to its narrow optical bandgap. Herein, by entrapping an Er-cyanide cluster into various C cages to form novel Er-monometallic cyanide clusterfullerenes (CYCFs), ErCN@C (C (5), C (6), and C (9)), the photoluminescent properties of CYCFs are investigated, and obvious near-infrared (NIR) photoluminescence only is observed for ErCN@C (5)-C .

Steering Single-Electron Metal-Metal Bonds and Hyperfine Coupling between a Transition Metal-Lanthanide Heteronuclear Bimetal Confined in Carbon Cages.

Metal complexes bearing single-electron metal-metal bonds (SEMBs) exhibit unusual electronic structures evoking strong magnetic coupling, and such bonds can be stabilized in the form of dimetallofullerenes (di-EMFs) in which two metals are confined in a carbon cage. Up to now, only a few di-EMFs containing SEMBs are reported, which are all based on a high-symmetry icosahedral () C cage embedding homonuclear rare-earth bimetals, and a chemical modification of the -C cage is required to stabilize the SEMB. Herein, by introducing 3d-block transition metal titanium (Ti) along with 4f-block lanthanum (La) into the carbon cage, we synthesized the first crystallographically characterized SEMB-containing 3d-4f heteronuclear di-EMFs based on pristine fullerene cages.

U@(4)-C: A Different Cage Isomer with Reactivity Controlled by U-Sumanene Interaction.

Actinide endohedral metallofullerenes (EMFs) are a fullerene family that possess unique actinide-carbon cage host-guest molecular and electronic structures. In this work, a novel actinide EMF, U@(4)-C, was successfully synthesized and characterized, and its chemical reactivity was investigated. Crystallographic analysis shows that U@(4)-C, a new isomer of U@C, has a (4)-C cage, which has never been discovered in the form of empty or endohedral fullerenes.

Two Metastable Endohedral Metallofullerenes ScC@(39656)-C and ScC@(51383)-C: Direct-C-Insertion Products from Their Most Stable Precursors.

Endohedral metallofullerenes (EMFs) are sub-nano carbon materials with diverse applications, yet their formation mechanism, particularly for metastable isomers, remains ambiguous. The current theoretical methods focus mainly on the most stable isomers, leading to limited predictability of metastable ones due to their low stabilities and yields. Herein, we report the successful isolation and characterization of two metastable EMFs, ScC@(39656)-C and ScC@(51383)-C, which violate the isolated pentagon rule (IPR).

Effects of Solvents on Reaction Products: Synthesis of Endohedral Metallofullerene Oxazoline and Epoxide.

Herein, we performed the reactions of MN@-C (M = Sc and Lu) with the methanol (CHOH) solution of TBAOH (note that both CHO and OH are nucleophiles) in benzonitrile (PhCN) and dimethylformamide, respectively. It is found that OH ions rather than CHO ions selectively attacked the fullerene cage to form the MN@C-O intermediate. Although the fullerene cage is initially attacked by OH in both PhCN and DMF solvents, the products are quite different.

UScC and UScNC Clusters with U-C Triple Bond Character Stabilized Inside Fullerene Cages.

The chemistry of f-block metal-carbon multiple bonds is underdeveloped compared to well-established carbene complexes of the d-block transition metals. Herein, we report two new actinide-rare earth mixed metal carbides and nitrogen carbide cluster fullerenes, UScC@(6)-C and UScNC@(6)-C, which contain U-C bonds with triple bond character and were successfully synthesized and characterized by mass spectrometry, UV-vis-NIR spectroscopy, Fourier transform infrared spectroscopy, single crystal X-ray diffraction, and DFT calculations. Crystallographic studies show that the two previously unreported clusters, UScC and UScNC, are stabilized in the (6)-C carbon cage and adopt unique trifoliate configurations, in which C/NC units are almost vertically inserted into the plane defined by the U and two Sc atoms.

Correction: ThC@C Th@C: unexpected formation of triangular thorium carbide cluster inside fullerenes.

[This corrects the article DOI: 10.1039/D2SC04846A.].

A vaccine delivery system promotes strong immune responses against SARS-CoV-2 variants.

Global coronavirus disease 2019 (COVID-19) pandemics highlight the need of developing vaccines with universal and durable protection against emerging SARS-CoV-2 variants. Here we developed an extended-release vaccine delivery system (GP-diABZI-RBD), consisting the original SARS-CoV-2 WA1 strain receptor-binding domain (RBD) as the antigen and diABZI stimulator of interferon genes (STING) agonist in conjunction with yeast β-glucan particles (GP-diABZI) as the platform. GP-diABZI-RBD could activate STING pathway and inhibit SARS-CoV-2 replication.

ThC@C Th@C: unexpected formation of triangular thorium carbide cluster inside fullerenes.

Synthesis of the first thorium-containing clusterfullerenes, ThC@C (6)-C and ThC@C(5)-C, is reported. These two novel actinide fullerene compounds were characterized by mass spectrometry, single-crystal X-ray diffraction crystallography, UV-vis-NIR spectroscopy, and theoretical calculations. Crystallographic studies reveal that the encapsulated ThC clusters in both C (6)-C and C(5)-C feature a novel bonding structure with one thorium metal center connected by a C[triple bond, length as m-dash]C unit, forming an isosceles triangular configuration, which has not been hitherto observed for endohedral fullerenes or for solid phase thorium carbides.

A charged diatomic triple-bonded U≡N species trapped in C fullerene cages.

Actinide diatomic molecules are ideal models to study elusive actinide multiple bonds, but most of these diatomic molecules have so far only been studied in solid inert gas matrices. Herein, we report a charged U≡N diatomic species captured in fullerene cages and stabilized by the U-fullerene coordination interaction. Two diatomic clusterfullerenes, viz.

Monometallic Endohedral Azafullerene.

Azafullerenes derived from nitrogen substitution of carbon cage atoms render direct modifications of the cage skeleton, electronic, and physicochemical properties of fullerene. Gas-phase ionized monometallic endohedral azafullerene (MEAF) [La@CN] formed via fragmentation of a La@C monoadduct was detected in 1999, but the pristine MEAF has never been synthesized. Here, we report the synthesis, isolation, and characterization of the first pristine MEAF La@CN, tackling the two-decade challenge.

Capturing the Long-Sought Dy@(5)-C 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.

Room-temperature logic-in-memory operations in single-metallofullerene devices.

In-memory computing provides an opportunity to meet the growing demands of large data-driven applications such as machine learning, by colocating logic operations and data storage. Despite being regarded as the ultimate solution for high-density integration and low-power manipulation, the use of spin or electric dipole at the single-molecule level to realize in-memory logic functions has yet to be realized at room temperature, due to their random orientation. Here, we demonstrate logic-in-memory operations, based on single electric dipole flipping in a two-terminal single-metallofullerene (ScC@C(hept)-C) device at room temperature.

Metallofullerene single-molecule magnet DyO@(5)-C with a strong antiferromagnetic Dy⋯Dy coupling.

Dysprosium-oxide clusterfullerene DyO@(5)-C is a single-molecule magnet featuring antiferromagnetic superexchange Dy⋯Dy coupling the μ-O bridge, the strongest of its kind among {Dy} complexes with non-radical bridges.

Diversity of Metal-Fullerene Framework Structures Regulated by Metal Salts.

Taking into account the diversity of fullerene ligands and metal salts, metal-fullerene frameworks (MFFs) present a variety of structures. Currently, the structural control of MFFs mainly relies on the design and synthesis of fullerene ligands, while the influence of metal building units on the structures has been rarely studied. The present work represents a systematical investigation of fullerene-linked supramolecular architectures incorporating different metal salts.

UCN@(6)-C: An Encapsulated Triangular UCN Cluster with Ambiguous U Oxidation State [U(III) versus U(I)].

Understanding the chemical behavior of actinide elements is essential for the effective management and use of actinide materials. In this study, we report an unprecedented η (side-on) coordination of U by a cyanide in a UCN cluster, which was stabilized inside a C fullerene cage. UCN@(6)-C was successfully synthesized and fully characterized by mass spectrometry, single crystal X-ray crystallography, cyclic voltammetry, spectroscopy, and theoretical calculations.

Crystallographic Characterization of U@C (2 = 82-86): Insights about Metal-Cage Interactions for Mono-metallofullerenes.

Endohedral mono-metallofullerenes are the prototypes to understand the fundamental nature and the unique interactions between the encapsulated metals and the fullerene cages. Herein, we report the crystallographic characterizations of four new U-based mono-metallofullerenes, namely, U@(6)-C, U@(8)-C, U@(15)-C, and U@(12)-C, among which the chiral cages (8)-C and (12)-C have never been previously reported for either endohedral or empty fullerenes. Symmetrical patterns, such as indacene, sumanene, and phenalene, and charge transfer are found to determine the metal positions inside the fullerene cages.