Formation of endohedral metallofullerene (EMF) ions of MnC2m+ (M = La, Y, n ≤ 6, 50 ≤ 2m ≤ 194) in the laser ablation process with graphene as precursor

Dual Stabilization of a Tri-Metallofullerene Radical Er3@C80: Exohedral Derivatization and Endohedral Three-Center Bonding

The enclosed space within fullerene molecules, capable of trapping metal clusters, offers an opportunity to investigate the behavior of metal atoms in a highly confined sub-nanometer environment. However, the studies on trimetallofullerenes M3@C80 have been very limited due to their difficult obtainability. In this paper, we present a new method for obtaining a tri-metallofullerene Er3@C80 through exohedral modification of the fullerene cage. Our findings reveal that Er3@C80 exhibits a radical character and can react with the dichlorobenzene radical to generate a stable derivative Er3@C80PhCl2. Theoretical calculations demonstrate the presence of a three-center two-electron metal-metal bond in the center of the fullerene cage. This bond serves to counterbalance the Coulomb repulsion between the Er ions. Consequently, both exohedral derivatization and endohedral three-center bonding contribute to the substantial stability of Er3@C80PhCl2. Furthermore, molecular dynamics simulations indicate that the Er3 cluster within the molecule possesses a rigid triangle structure. The availability of M3@C80 derivatives opens avenues for future investigations into interactions among metal atoms, such as magnetic coupling, within fullerene cages.

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.

Ln3@C80+ (Ln = lanthanide): a new class of stable metallofullerene cations with multicenter metal-metal bonding in sub-nanometer confined space

Among the large number of members in the metallofullerene family, the nitride clusterfullerene M3N@C80 (M = trivalent metal) is a special one with unordinary high stability. It is generally thought...

Open-shell nature of non-IPR fullerene С40: isomers 29 (C2) and 40 (Td)

It is well-known that the small non-IPR fullerenes C_n (n < 60) are highly unstable and that is why they cannot be obtained as empty cages. However, they become stable as exohedral or endohedral derivatives. In this report, the molecular structures of non-IPR isomers 29 (C₂) and 40 (T_d) of fullerene C₄₀ are investigated using a semiempirical approach developed earlier for higher fullerenes. Quantum-chemical calculations (DFT) show that isomers 29 (C₂) and 40 (T_d) have open-shell structures. The distributions of single, double, and delocalized π-bonds in the isomer molecules in question are presented for the first time as well as their molecular formulas. It is found unusual for higher fullerenes chain of π-bonds passing through some cycles. Identified features in the structures of small fullerene molecules can be predictive of the ability to their synthesis as derivatives and will assist in their structure determination.

Generation of sodium halide endohedral metallofullerenes in the gas phase

RATIONALE

Recent theoretical calculations show that ionic bond encapsulated endohedral metallofullerenes (EMFs) have great potential in the application of molecular electronic components. However, experimental study of these species is very limited, due to the difficulty in their generation. Thus, it is important to study the possibility and optimized conditions of these species generated in the gas phase.

METHODS

Mixtures of graphene and metal halides (MX), where M = Na, K; and X = Cl, Br, I, were used as the precursors for the experiments. Mass spectra were obtained in positive ion mode by laser irradiation of these mixtures of graphene and metal halides using a 7.0 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer equipped with a 355 nm YAG laser.

RESULTS

EMF ions of NaCl@C+ 2n (2n = 120-244), NaBr@C+ 2n (2n = 110-240), and NaI@C+ 2n (2n = 116-198) were observed in the laser ablation mass spectra. However, the encapsulated ion could not be replaced by Li or K in these experiments, indicating that the effects of the metal cation on the EMFs are larger than those of halide anions.

CONCLUSIONS

Ionic bond encapsulated EMF ions of NaX@C+ 2n (X = Cl, Br and I, 110 ≤ 2n ≤ 244) were generated by laser ablation of the mixture of graphene and sodium halides, but no species containing lithium or potassium were observed. This work opens the possibilities of using laser ablation for the synthesis of large-sized salt-encaged EMFs. Further study of the mechanism for these processes is important for the generation of the missing species.

A systematic study on the generation of multimetallic lanthanide fullerene ions by laser ablation mass spectrometry

RATIONALE

Laser ablation masss spectromety has been previously proved to be a powerful tool for studying endohedro metallofullerene (EMF) ions. Our previous study showed the possiblity of forming multi-metallofullerene ions containg more than six metal atoms for La, Y and Lu. Thus, it is important to conduct a systematic study on the generation of multi-metallofullerenes and their distribuitons for all lanthanide elements.

METHODS

Experiments were performed on a 7.0 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Laser ablation mass spectra were obtained by laser irradiation on mixtures of graphene and MCl₃ on a stainless steel plate, applying a 355 nm Nd:YAG laser with a typical energy of 2.5 mJ/pulse. Reaction test experiments were performed by introducing O₂ into the FTICR cell with a pulse valve.

RESULTS

Multi-metallofullerene ions Ce2-4C2m+, Pr2-4C2m+, Gd2-4C2m+, Nd3C2m+, Dy2-3C2m+, Tb2-7C2m+, Ho2-6C2m+ were observed in the mass spectra. For the metals Sm and Eu, no multi-metallofullerene ion was observed. No reaction with O₂ was observed in the reaction experiments, verifying that these species had endohedral structures. For the observed series of multi-metallofullerene ions, tri-metallofullerene ions dominated their mass spectra. The results were further compared with previously generated EMF ions for La, Er, Tm, Yb and Lu.

CONCLUSIONS

Endohedral lanthanide metallofullerene ions were generated by laser ablation of graphene and the corresponding metal salts MCl₃ (M = Ce, Pr, Nd, Gd, Tb, Dy and Ho) and studied with a FTICR mass spectrometer. Typically, multi-metallofullerene ions of TbnC2m+2≤n≤780≤2m≤176 and Ho6C2m+2≤n≤674≤2m≤162 were observed. The results show that the formation of multi-EMF ions containing lanthanides that have +3 and + 4 oxidation states is easier than those containing +2 oxidation states in the process of laser ablation.