Two Metastable Endohedral Metallofullerenes Sc2C2@C1(39656)-C82 and Sc2C2@C1(51383)-C84: Direct-C2-Insertion Products from Their Most Stable Precursors

The formation mechanism of metal cluster fullerenes Sc3N@Cn: force field development and molecular dynamics simulations

Metal cluster fullerenes are a class of molecular nanomaterials with complex structures and novel properties. An in-depth study of their formation mechanism is a key topic for developing new high-yield synthesis methods and promoting the practical application of such molecular nanomaterials. To elucidate the formation mechanism of Sc3N@Cn, a representative sub-class of metal cluster fullerenes, this study developed a ReaxFF force field parameter set CNSc.ff using a single parameter optimization method and conducted systematic molecular dynamics simulations on a C-N-Sc mixed system using the newly developed force field parameter set. The results show that atomic nitrogen has strong attraction to both C and Sc atoms, and it plays a key role in the formation of Sc3N@Cn; the formation of Sc3N@Cn includes carbon cluster growth, Sc-based cluster growth and their encapsulation; temperature, carbon density, and atomic ratio all affect the relative yield of Sc3N@Cn; and the final products are a mixture of amorphous carbon, fullerenes, metallofullerenes, and metal cluster fullerenes. This study rationalizes the phenomena observed in the synthesis experiments and provides insights for the development of selective and high-yield synthesis methods for metal cluster fullerenes.

Precision Chemistry of Metallofullerenes and Graphene: Recent Advances

Precision chemistry of synthetic carbon allotropes including fullerene and graphene, characterized by a well-controlled and spatially resolved addends bonding, has received widespread attention owing to its capability to tailor their physicochemical properties for high-end applications. In the context of fullerene, particularly endohedral metallofullerenes (EMFs), precision chemistry emphasizes the regioselective binding of a specific number of moieties to the fullerene cage. In the case of graphene, precision chemistry focuses on achieving precise patterning and tailored modifications. Inspired by their intriguing advantages, the precision chemistry of these two members has witnessed rapid advancements. While existing reviews have outlined advancements in the precision chemistry of EMFs and graphene, this review uniquely concentrates on the most recent progress. Finally, the prospects in this field, with a special focus on the potential for creating functional materials through strategically patterned binding of fullerene and graphene networks are envisioned.

Thirty Years of Hide-and-Seek: Capturing Abundant but Elusive MIII@C3v(8)-C82 Isomer, and the Study of Magnetic Anisotropy Induced in Dy3+ Ion by the Fullerene π-Ligand

Our knowledge about endohedral metallofullerenes (EMFs) is restricted to the structures with sufficient kinetic stability to be extracted from the arc-discharge soot and processed by chromatographic and structural techniques. For the most abundant rare-earth monometallofullerene MIII@C82, experimental studies repeatedly demonstrated C2v(9) and Cs(6) carbon cage isomers, while computations predicted equal stability of the "missing" C3v(8) isomer. Here we report that this isomer is indeed formed but has not been recovered from soot using standard protocols. Using a combination of redox extraction and subsequent benzylation and trifluoromethylation with single-crystal XRD analysis of CF3 adduct, we prove that Dy@C3v(8)-C82 is one of the most abundantly produced metallofullerenes, which was not identified in earlier studies because of the low kinetic stability. Further, using the Dy@C3v(8)-C82(CF3) and Dy@C3v(8)-C82(CH2Ph) monoadducts for the case study, we analyzed the role of metal-fullerene bonding on the single-ion magnetic anisotropy of Dy in EMFs. The multitechnique approach, combining ab initio calculations, EPR spectroscopy, and SQUID magnetometry, demonstrated that coordination of the Dy ion to the fullerene cage induces moderate, nonaxial, and very fluid magnetic anisotropy, which strongly varies with small alterations in the Dy-fullerene coordination geometry. As a result, Dy@C3v(8)-C82(CH2Ph) is a weak field-induced single-molecule magnet (SMM), whose signatures of magnetic relaxation are detectable only below 3 K. Our results demonstrate that metal-cage interactions should have a detrimental effect on the SMM performance of EMFs. At the same time, the strong variability of the magnetic anisotropy with metal position suggests tunability and offers strategies for future progress.

The formation mechanism of Sc-based metallofullerenes: a molecular dynamics simulation study

The practical applications of endohedral metallofullerenes (EMFs) are mainly constrained by their low yields. Understanding the formation mechanisms is therefore crucial for developing methods for high-yield and selective synthesis. To address this, a novel force-field parameter set, "CSc.ff", was created using a single-parameter search optimization method, then molecular dynamics simulations of various systems with a carbon-to-scandium atomic ratio of 12.5 were carried out. The simulations were run under a constant atomic number, volume, and energy (NVE) ensemble. The influence of the working gas, helium, as well as temperature gradients on the formation process was examined. Our simulations reveal that the cage growth patterns of Sc-based EMFs (Sc-EMFs) closely resemble those of hollow fullerenes, evolving from free carbon atoms to chains, rings, and, ultimately, to cage-shaped clusters. Importantly, the Sc-EMFs formed in the simulation frequently exhibit structural defects or under-coordinated carbon atoms. Scandium atoms, whether at the periphery or on the surface of these cages, can be incorporated into the cages, forming Sc-EMFs. Helium was found to not only promote the formation of carbon cages but also facilitate the encapsulation of scandium atoms, playing a crucial role in the formation of cluster fullerenes. Moreover, cooling effectively inhibits the uncontrollable growth of the carbon cage and is essential for forming stable, appropriate-sized cages. This study enhances our understanding of the formation of Sc-EMFs and provides valuable insights for developing more efficient synthetic methods.

Stabilizing a non-IPR C2(13333)-C74 cage with Lu2C2/Lu2O: the importance of encaged non-metallic elements

A difference in encaged non-metallic element (i.e., C2versus O) leads to a clear change of intramolecular interactions and shifts in redox potentials of Lu2C2@C2(13333)-C74 and Lu2O@C2(13333)-C74, as a result of their distinct molecular orbital energy levels. Different from these two endoherals whose HOMOs are located on the cage, experimentally absent Lu2@C2(13333)-C74 possesses a HOMO predominantly delocalized on the internal Lu-Lu bond, accompanied by a much smaller HOMO-LUMO gap, suggesting that the presence of a non-metallic unit broadens the electrochemical gaps and consequently improves the kinetic stability. These findings shed light on the role of non-metallic moieties in clusterfullerenes, providing valuable insights into the stability and properties of metallofullerenes.