Ning Chen

Actinide–carbon multiple bonds are synthetically challenging to access, primarily due to high bond polarization and poor energetic matching between metal and ligand orbitals. This challenge is especially pronounced for thorium, such that thorium–carbon multiple bonds are exceptionally rare. Herein, we report the synthesis of a novel actinide endohedral fullerene, UCTh@D3h(5)-C78, which encapsulates a unique heterobimetallic actinide carbide cluster. Single-crystal X-ray diffraction analysis reveals a carbon-bridged U–C–Th cluster stabilized within a D3h(5)-C78 cage, featuring remarkably short U–C and Th–C distances of 1.962(8) Å and 2.121(8) Å, respectively. Quantum chemical studies further indicate that the U–C bond possesses a rare triple-bond character, while the Th–C bond can be described as a partial triple bond─a bonding mode previously unreported for thorium. This work uncovers a unique bonding motif involving multiple bonds for both uranium and thorium, most notably a rare Th–C interaction with triple-bond character. These findings provide important perspectives toward the design and synthesis of compounds containing thorium-based triple bonds.

Zirconium-based endohedral metallofullerenes (EMFs) were first detected in the gas phase in 1992, but their bulk synthesis has remained elusive over the past three decades. Herein, we present the first successful synthesis of Zr-based EMFs, addressing this longstanding challenge in fullerene chemistry. By utilizing an optimized synthesis strategy with zirconium carbide as the metal source, we obtained three Zr-based carbide clusterfullerenes, namely, Zr₂C₂@D_3h(5)-C₇₈, Zr₂C₂@I_h(7)-C₈₀, and Zr₃C₂@I_h(7)-C₈₀. Single-crystal X-ray diffraction analyses revealed that the Zr₂C₂ clusters adopt a planar rhombic configuration bridged by a (C≡C)^2- unit, while the Zr₃C₂ cluster exhibits a rare trifoliate geometry with a bridging (C-C)^6- unit. The coordination modes in these Zr-based clusters are different from those observed in conventional organozirconium complexes, highlighting the unique coordination environments within fullerene cages. Combined experimental and theoretical studies further reveal the electronic structures of the Zr-based EMFs as (Zr₂C₂)⁶⁺@(C_2n)^6- (2n = 78, 80) and (Zr₃C₂)⁶⁺@(I_h(7)-C₈₀)^6-. This breakthrough in the synthesis of Zr-based EMFs not only offers new insights into the mechanisms of arc-discharge reaction and the formation of EMFs but also provides a substantial guideline for the encapsulation of new elements into fullerene cages, establishing a foundation for the design and synthesis of novel EMFs.

Actinidofullerenes constitute a family of fullerenes that exhibit different metal–cage interactions, electronic structures, and properties compared to lanthanidofullerenes. In this study, we investigate the reactivity of mono-uranofullerene U@C2v(9)-C82 under the Bingel–Hirsch reaction and observe significantly higher regioselectivity, along with other differences in the reaction products, compared to La@C2v(9)-C82. Two products are obtained: a cycloadduct, which is the most abundant and has been characterized by x-ray crystallography, and a minor regioisomer that is most likely a single-bond product. Density functional theory calculations can explain the experimental structure and the formation of the two products and indicate that uranium is formally U(III) in both of them. The most abundant cycloadduct is formed under kinetic control, as found for other Bingel–Hirsch adducts, whereas the single-bond product is formed after oxidation of the anionic intermediate of the conventional Bingel–Hirsch reaction. This work is a new example of the unique reactivity and chemical properties of actinidofullerenes, which arise from their distinctive actinide–fullerene interactions.

Pt‐group metal single‐atom catalysts (SACs) with a large single‐atom areal density are highly desirable for efficient electrocatalysis but remain challenging to synthesize. Herein, a facile vacuum direct current arc discharge (DCAD) strategy is reported for the rapid and scalable synthesis of Pt SACs with an unprecedented areal density of 10.6 atoms nm ⁻² (3.82 wt.% Pt loading) firmly anchored on CoNi nanoalloy and confined by carbon nanotubes (CoNiPt _SA @G). Notably, due to the strong electron trapping effect between Pt SA and CoNi substrates, CoNiPt _SA @G retains its structural integrity at 1000 °C, demonstrating an outstanding thermal stability despite the ultra‐high areal density. Moreover, the DCAD strategy is universal, which can be applied to other metals such as Iridium. It is also scalable, with a demonstrated gram‐scale yield achieved within 0.5 h. The resulting CoNiPt _SA @G catalyst exhibits exceptional hydrogen evolution reaction performance, achieving an overpotential of 23 mV at 10 mA cm ⁻² , a mass activity over 5 times higher than that of 20 wt.% Pt/C catalyst and high stability during the 120 h test. This work provides a groundbreaking pathway for the large‐scale production of high single‐atom areal density, thermally robust SACs, advancing their practical applications in clean energy technologies.

Metal–ligand multiple bonds are ubiquitous in coordination and organometallic chemistry. In contrast, lanthanide–carbon multiple bonds are difficult to form. The isolation of complexes containing lanthanide–carbon double bonds with terminal methyl carbene (=CH₂) and lanthanide–carbon triple bonds remains challenging. Here we present the synthesis of a lanthanide–carbon triple bond contained inside an endohedral fullerene cage. More specifically, we report a cerium–carbide [Ce≡CSc₂] cluster encapsulated inside a C₈₀ fullerene cage. The molecular structure of Ce≡CSc₂@C₈₀ and the nature of the Ce≡C triple bond are studied through X-ray crystallography, spectroscopic analyses and quantum chemical calculations. Our data reveal a very short Ce≡C distance of 1.969(7) Å. Chemical bonding analysis suggests that the formation of the Ce≡C bond primarily arises from the stronger bonding affinity between carbon and cerium compared with scandium inside the encapsulated cluster. The fullerene cage plays a crucial role in stabilizing and protecting this trimetallic carbide cluster featuring a Ce≡C triple bond.

Two open-shell paramagnetic mono-metallofullerenes, M@C₂(10612)-C₇₂ (M = Ce, Gd), have been successfully synthesized and isolated in their pristine form.

An unprecedented double-butterfly Ti₃C₃ cluster with a rare Ti–C coordination mode was stabilized inside a C₈₂ cage, forming a novel tri-metal carbide clusterfullerene, Ti₃C₃@C_2v(9)-C₈₂.

A novel monometallic nitride cluster fullerene, UN@C ₈₄ , with a UN triple bond located on the C ₂ axis.

A thorium-carbon double bond that corresponds to the sum of theoretical covalent double bond radii has long been sought after in the study of actinide-ligand multiple bonding as a synthetic target. However, the stabilization of this chemical bond remains a great challenge to date, in part because of a relatively poor energetic matching between 5f-/6d- orbitals of thorium and the 2s-/2p- frontier orbitals of carbon. Herein, we report the successful synthesis of a thorium-carbon double bond in a carbon-bridged actinide-transition metal cluster, i.e., [Th═C═Ti], encapsulated inside a fullerene cage of C₈₂. ThCTi@C_s(6)-C₈₂ was successfully synthesized by a modified arc discharging method and characterized by mass spectrometry, single-crystal X-ray crystallography, various spectroscopy, and theoretical calculations. X-ray crystallographic analysis reveals a bent μ₂-bridged carbide cluster with a Th-C distance of 2.123(18) Å, which is the shortest reported to date in an isolable compound and is comparable to the sum of the covalent Th═C double bond radii (2.10 Å). In addition, Th═C═Ti takes an unexpected nonlinear configuration with a bond angle of 133.0(10)°. The combined experimental and theoretical investigation further revealed the bonding nature of Th═C, which is polarized toward the bridged carbon but has a notably higher covalency than the Th-C bonds reported previously for organometallic compounds. Moreover, pronounced cage-to-metal donation appears to be stabilizing the encapsulated Th═C═Ti cluster. This work offers a deeper understanding of the bonding behavior of thorium and features the unique ability of fullerene cages to stabilize bonding motifs containing different types of metal-ligand multiple bonds.

Endohedral fullerenes are known for their exceptional ability to host metal clusters that contain unique bonding motifs. In this study, we report a facile strategy to synthesize a new family of clusterfullerenes, fluoride clusterfullerenes (FCFs). This work demonstrates that actinides and rare earth metals as well as alkaline earth metals can be encapsulated within a variety of fullerene cages, and these fullerenes can be obtained in their pristine form without additional functionalization methods. Notably, Th₂F@I_h(7)-C₈₀ and CaScF@C_s(6)-C₈₂ were isolated and their molecular structures and magnetic properties were characterized by X-ray single-crystal diffraction and multiple spectroscopic techniques as well as DFT calculations. These findings reveal that the unique internal addition of a single fluorine atom significantly alters the metal-metal bonding interactions of Th-Th and Ca-Sc. While Th₂@I_h(7)-C₈₀ hosts a σ² Th-Th bond, an unprecedented actinide-actinide (Th-Th) single electron metal-metal bond is formed inside Th₂F@I_h(7)-C₈₀ upon the internal addition of fluoride. Similarly, while a Ca-Sc single electron bond exists in CaSc@C_s(6)-C₈₂, which exhibits excellent molecular qubit properties, the addition of fluoride transforms the compound into a singlet. The present study not only highlights the successful synthesis of a novel family of FCFs, which will likely be an extensive family, it also shows that fluorine doping can induce novel metal-metal bonding motifs leading to potentially intriguing magnetic properties.