Carbon Cage Research Articles

Preparation and crystal structure of D2d-C84(23)Cl24 chlorofullerene

Chlorofullerene D2d-C84(23)Cl24 was prepared by chlorination of D2d-C84(23) with VCl4 or SbCl5 at 320–350 °C. An X-ray crystallographic study with the use of synchrotron radiation revealed the addition pattern of 24 Cl atoms stabilized by the formation of isolated C=C bonds and benzenoid rings on the carbon cage.

Cage-C22 and Cage-C28: Two novel superhard orthorhombic carbon allotropes

In this work, two novel three-dimensional Cage carbon allotropes with all-sp3 and mixed sp2-sp3 hybridized networks, namely, Cage-C22 and Cage-C28 are theoretically predicted by the analysis executed using based on the density functional theory. Cage carbon superhard crystals possess Pmmm (47) symmetry (space group no. 25) which are orthorhombic crystals. The electronic properties, mechanical properties (hardness, elastic anisotropy, elastic modulus, and directional dependence of Young's modulus in GPa), and structural properties for both the carbon phases are systematically investigated and analyzed. The calculated phonon dispersions and elastic coefficients Cij show that Cage carbon allotropes are dynamically and mechanically stable at ambient conditions (0 GPa). To study the mechanical properties of these structures, the (Young's, shear, bulk) modulus were obtained by using the Voigt-Reuss-Hill approximation. The ratios of Emax/Emin as significant ratios of mechanical anisotropy in Young's modulus are greater than that of diamond (1.10) which means that Cage structures show elastic anisotropy. Furthermore, the electronic properties of these two new structures show that Cage-C22 crystal is a direct semiconductor and its gap energy is about 1.5 eV at Z point, while Cage-C28 is a metal because it has zero band gap between valence bands (VB) and conduction bands (CB). The calculated X-ray spectrum patterns show noncrystalline behavior which is derived from its structural complexity, and bond angles and bond lengths are also effective in this matter. The calculated results indicate that these two 3D superhard structures have the required potential for the use of cathode materials in capacitors, electrical and mechanical applications.

Engineering of single atomic Fe-N4 sites on hollow carbon cages to achieve highly reversible MoS2 anodes for Li-ion batteries

Although the single atom electrocatalysts have been demonstrated as efficient catalysts for promoting Li2S/Na2S formation and decomposition in Li-S/Na-S batteries, the functional morphological and structural engineering capable of exposing more active sites is regarded as an essential factor to further enhance the catalytic activity. Here, we have synthesized a single atomically dispersed Fe sites embedded within hollow nitrogen doped carbon cages (Fe-N-HCN) using Fe3O4 spheres as an oxidant and sacrificial template, which is used as a high-efficiency catalyst for boosting the reversible capacity of MoS2 anode in lithium-ion batteries (LIBs). As expected, the electrochemical reaction of MoS2/Fe-N-HCN anode exhibits higher reversibility than pure MoS2 electrodes. Moreover, density functional theory is also employed to reveal that Fe-N-HCN can be effectively adsorbed and catalyze the rapid decomposition of Li2S. The hollow carbon cage structure can facilitate the exposure of the active Fe-N4 sites and favor the mass transfer during the electrochemical reactions, thus the synergistic effect of the Fe-N4 site and the hollow carbon cage structure together improve the catalytic activity for the conversion reaction of MoS2 anode.

Endometallofullerenes in the Gas Phase: Progress and Prospect

This review describes the progress of the gas-phase study of endometallofullerenes (EMFs) by mass spectrometry and theoretical calculation over the past 15 years. The attention herein focuses on the gas-phase syntheses, reactions, and generation mechanisms of some novel EMF ions, along with their structures and properties. The highlighted new species include EMFs with small-size carbon cages of C2n (n < 60), multiple metal atoms (Mx@C2n, x ≥ 3), late transition metals, and encaged ionic bonds. Furthermore, the gas-phase experimental and calculational supports for top-down or bottom-up models are summarized and discussed. These gas-phase results not only provide experimental evidence for the existence of related novel EMF species and possible synthesis methods for them, but they also provide new insights about chemical bonds in restricted space. In addition, the opportunities and further development directions faced by gas-phase EMF study are anticipated.

Hydrodeoxygenation of furfural to 2-methylfuran over Cu-Co confined by hollow carbon cage catalyst enhanced by optimized charge transfer and alloy structure

Hydrodeoxygenation of furfural over non-noble metal catalyst is an effective route to synthesis 2-methylfuran, but the reaction is often hampered by the low activity and selectivity of the catalyst. Herein, a bimetallic catalyst with CuCo alloy encapsulated in a hollow nitrogen-doped carbon cages (CuCo/NC) are fabricated by using ZIF-67 as a sacrificial template, which exhibited superior catalytic performance and a full conversion of furfural with a 95.7 % selectivity towards 2-methylfuran was achieved at an under relatively mild reaction conditions (150 ℃, 1.5 MPa H2 and 4.0 h). The characterizations and density functional theory calculations clearly evidenced that the introduced Cu species acts as a switch to regulate the activity and selectivity of the catalyst via two aspects. On the one hand, the Cu species perturb the Co electronic structure leading to adsorption configuration of furfural change from flat to vertical on the catalyst surface, which successfully hindered the hydrogenation of furan ring, resulting high selectivity towards 2-methylfuran. On the other hand, the formed CuCo (111) sites promotes the dissociation of hydrogen, cleavage of the CO bond and reduces the diffusion barrier of hydrogen so as to advance the formation of 2-methylfuran. This work may provide a feasible strategy for the design of nanoalloy catalyst for the hydrodeoxygenation of biomass platforms to value-added chemicals.

Synthesis of inter-[60]fullerene conjugates with inherent chirality

Coalescence of [60]fullerenes potentially produces hypothetical nanocarbon assemblies with non-naturally occurring topologies. Since the discovery of [60]fullerene in 1985, coalesced [60]fullerene oligomers have only been observed as transient species by transmission electron microscopy during an oligomerization process under a high electron acceleration voltage. Herein, we showcase the rational synthesis of covalent assemblies consisting of inherently chiral open-[60]fullerenes. The crystallographic analyses unveiled double-caged structures of non-conjugated and conjugated inter-[60]fullerene hybrids, in which the two [60]fullerene cages are bounds to each other through a covalent linkage. The former one further assembles via a heterochiral recognition so that four carbon cages are arranged in a tetrahedral manner both in solution and solid state. Reflecting radially-conjugated double π-surface nature, the inter-[60]fullerene conjugate exhibits strong electronic communication in its reduced states, intense absorption behavior, and chiroptical activity with a dissymmetry factor of 0.21 (at 674 nm) which breaks the record for known chiral organic molecules.

Computational understanding of the structural characteristics of Sm-based endohedral metallofullerenes

Endohedral metallofullerenes (EMFs) containing samarium (Sm) are rich and cover all kinds of conventional endofullerene types. Herein, an exhaustive density functional theory study was conducted to understand the structural characteristics of all 21 Sm-based EMFs characterized by single-crystal X-ray diffraction. The mono-, di- and tri-EMFs have open-shell septet, 13-et and 19-et electronic states, respectively. The internal Sm atoms hold all the unpaired spins (six for each), which are completely shielded by carbon cages. A formal divalent state can be assigned to each metal but with obvious electron backdonation from cage orbitals, rendering the metal-metal and metal-cage interactions mainly ionic. Thus, their Sm positions can be easily located by the electrostatic potentials inside negatively charged hollow cages and also affected by intramolecular covalent interactions. All Sm-based EMFs are stable with large encapsulation energies and SOMO-LUMO gap energies. Interestingly, although the two Sm2+ cations are repulsive, the limited cage cavity of Sm2@D2(35)-C88 may push them to have obvious covalent interactions. While for Sm3@Ih(7)-C80, the three Sm2+ cations exhibit markedly reduced positive charges to effectively alleviate the intermetallic repulsions. Our findings rationalize the structural characteristics and favorable formation of all Sm-based EMFs, and could deepen the understanding for more types of EMFs.

Ag@Mg12@Ag20: a three-layer matryoshka structure with S 6 symmetry.

The C60 fullerene, renowned for its soccer ball-like high-symmetry configuration, has attracted extensive interest. As research on C60 progresses, the synthesis of diverse C60 derivatives and the exploration of embedding varying numbers of atoms within the carbon cage, ranging from singular atoms to entire molecules, have emerged. This trend has prompted investigations into potential high-symmetry structures formed by incorporating main group or transition metal elements. This study presents a detailed analysis of a three-layer Ag@Mg12@Ag20 structure, featuring a Mg12 icosahedron enclosed within an Ag20 dodecahedron with a singular Ag atom at its core. Employing density-functional theory, the structure underwent comprehensive scrutiny, including energy minimization resulting in the adoption of a S 6 symmetry, and subsequent evaluation of stability via vibrational frequency analysis and molecular dynamics simulations. The electronic structures and bonding characteristics of this three-layer Ag@Mg12@Ag20 architecture were explored through electron density analysis, density of states, and adaptive natural density partitioning analysis. Considering structural stability, the proposed three-layer Ag@Mg12@Ag20 structure exhibits promise as a novel constituent in the construction of other nano-materials.

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.

Non-classical (NC), heptagon-containing fullerenes obtained via chlorination-promoted cage transformations: C76(NC2a)Cl24 and C76(NC2b)Cl28.

High-temperature chlorination of C76 fullerene with SbCl5 proceeds via five Stone-Wales rearrangements, resulting in non-classical (NC) C76(NC1a)Cl24 with two heptagons and 14 pentagons partically fused in pairs and triples. C76(NC2b)Cl28 with isomeric carbon cage was obtained by chlorination-promoted cage shrinkage of C80via two C2 losses. The pathways of skeletal cage trasformations, the chlorination patterns, and formation energies are discussed in detail.

Computational insights into Diels-Alder reactions of paramagnetic endohedral metallofullerenes: M@C82 (M = Sc, Y, La) and La@C72.

In fullerene chemistry, Diels-Alder cycloaddition is an essential reaction for exohedral modification of carbon cages. M@C2v(9)-C82 (M = Sc, Y, and La), incorporating one metal atom within the fullerene cage, are key compounds for understanding the impact of both endohedral and exohedral modifications on their electronic structures. In this work, the Diels-Alder (DA) cycloaddition of cyclopentadiene (Cp) to M@C2v(9)-C82 (M = Sc, Y, and La) and La@C2(10612)-C72 was systematically studied using density functional theory. The most reactive bonds were initially chosen for detailed mechanistic exploration, considering both concerted and stepwise mechanisms. Our findings revealed that DA cycloadditions for the three metals (Sc, Y, and La) consistently exhibit the same regioselectivity, favoring the concerted attack on the [5,6] bond. This observation is in agreement with previous experimental and theoretical studies on the regioselectivity of the Diels-Alder reaction between La@C2v(9)-C82 and Cp. In the case of La@C2(10612)-C72, the most favored pathway is the concerted attack on the [6,6] bond both kinetically and thermodynamically. In toluene and ortho-dichlorobenzene, while the energy barriers and the reaction free energies increased to different extents for most pathways, the regioselectivity largely mirrored that observed in the gas phase.

Encapsulating biomass-derived SiOx with internal conductive channels in nitrogen-doped flexible carbon cages for high performance Li ion-battery anodes

N-doped flexible porous carbon encapsulated SiOx/C (p-NC/SiOx/C-3) was synthesized using rice husks as both the silicon and carbon source. When utilized as an anode for lithium ion batteries, p-NC/SiOx/C-3 delivers excellent cycling performance.

Synthetic routes to carbon substituted cobalt bis(dicarbollide) alkyl halides and aromatic amines along with closely related irregular pathways.

Carbon substituted cobalt bis(dicarbollide) alkyl halides [(1-X-(CH2)n-1,2-C2B9H10)(1,2-C2B9H11)-3,3'-Co]Me4N (X = Br, I; n = 1-3) are prepared in high yields (>90%) from their corresponding alcohols without side skeletal substitutions. These species offer access to the synthesis of aromatic cobalt bis(dicarbollide) amines, however only for particular terminal halogen substitution, the propylene pendant arm, and under appropriately controlled reaction conditions. Thus, the compounds substituted at cage carbon atoms with a propylene linker and terminal aromatic amine groups could be prepared. In other cases, numerous irregular reaction pathways occur, undoubtedly as a consequence of the bulky anionic boron cage in close proximity to the reaction site. Among them, an unusual intramolecular hydroboration forming rigidified carbon-to-boron bridged isomeric anions with an asymmetric structure that correspond to formulae [(1,8'-μ-C2H4)-(1,2-C2B9H10)(1',2'-C2B9H10)-3,3'-Co]- and [(1,7'-μ-C2H4)-(1,2-C2B9H10)(1',2'-C2B9H10)-3,3'-Co]- is described herein and the former isomer is structurally characterized. This product with a restrained geometry is widely accessible through nucleophile and/or thermally induced decomposition of (pseudo)halides attached to the cage via an ethylene linker. Surprisingly enough, also doubly bridged isomeric species [(1,8-μ-C2H4-1,2-C2B9H9)2-3,3'-Co]- and [(1,7-μ-C2H4-1,2-C2B9H9)2-3,3'-Co]- are available in good yield using these methods. Furthermore, other more typical side reactions are discussed, i.e. nucleophilic reactions of propyl halides with Me3N formed apparently by disproportionation of Me4N+ at higher temperatures or with pyridine used as a base.

Thermal stability and degradation mechanism of C60 fullerene‐based polymers

AbstractIn this paper, the thermal stability and degradation mechanisms of C60 fullerene‐based polymers, obtained by click polymerization between dialkyne‐substituted C60 derivative monomers and 1,3,5‐tris(dodecyloxy)benzene‐based diazide comonomers, were evaluated. The activation energy of the fullerene polymer C60P2 with an ethylene spacer, determined under peak degradation rate conditions, was lower than that of the counter polymer C60P1 with a methylene spacer, suggesting lower thermal stability of C60P2. The combined technique of thermogravimetric analysis—mass spectroscopy and Fourier transform infrared spectroscopy revealed that the thermal decomposition onset of the analyzed samples is accompanied by CC cleavage of the dodecyloxyside chain groups, followed by the decomposition of the 1,2,3‐triazole, dicarboxylate and benzoate moieties. It was found that no thermal decomposition of the fullerene carbon cage occurs up to 670°C. Molecular modeling with Hyperchem software version 7.5 confirmed that C60P1 is more thermally stable than C60P2.

Nd─Nd Bond in Ih and D5h Cage Isomers of Nd2 @C80 Stabilized by Electrophilic CF3 Addition.

Synthesis of molecular compounds with metal-metal bonds between 4f elements is recognized as one of the fascinating milestones in lanthanide metallochemistry. The main focus of such studies is on heavy lanthanides due to the interest in their magnetism, while bonding between light lanthanides remains unexplored. In this work, the Nd─Nd bonding in Nd-dimetallofullerenes as a case study of metal-metal bonding between early lanthanides is demonstrated. Combined experimental and computational study proves that pristine Nd2 @C80 has an open shell structure with a single electron occupying the Nd─Nd bonding orbital. Nd2 @C80 is stabilized by a one-electron reduction and further by the electrophilic CF3 addition to [Nd2 @C80 ]- . Single-crystal X-ray diffraction reveals the formation of two Nd2 @C80 (CF3 ) isomers with D5h -C80 and Ih -C80 carbon cages, both featuring a single-electron Nd─Nd bond with the length of 3.78-3.79 Å. The mutual influence of the exohedral CF3 group and endohedral metal dimer in determining the molecular structure of the adducts is analyzed. Unlike Tb or Dy analogs, which are strong single-molecule magnets with high blocking temperature of magnetization, the slow relaxation of magnetization in Nd2 @Ih -C80 (CF3 ) is detectable via out-of-phase magnetic susceptibility only below 3 K and in the presence of magnetic field.

Diels–Alder cycloadditions of fullerene: Advances in mechanistic theory

AbstractFullerene exhibits a wealth of interesting characteristics owing to its unique π‐electron configuration. The structure and properties of fullerene can be manipulated by introducing chemical groups to the carbon–carbon bonds via organic reactions, extending its application field. The Diels–Alder (DA) cycloaddition reaction is commonly used to decorate the carbon cage of fullerene. Furthermore, atoms, ions, clusters, and molecules can be inserted into the hollow carbon cage of a fullerene, thereby changing the electron transfer process within the fullerene cage and thus the reactivity of the as well as the regioselectivity of the DA cycloaddition reaction. Computer‐based theoretical modeling is an essential tool for studying chemistry. Herein, we provide a brief review of theoretical investigations into the cycloaddition mechanism of two most common fullerenes (C60 and C70), especially in terms of the effects of encapsulated chemical species based on the distortion–interaction model. We hope that the current mini review will provide a useful and interesting resource for researchers working on—or simply being interested in—the in silico investigation of fullerenes and their DA‐based modification.

Bionic Fe-N-C catalyst with abundant exposed Fe-Nx sites and enhanced mass transfer properties for efficient oxygen reduction

Transition metal and nitrogen co-doped carbon electrocatalysts are promising candidates to replace the precious metal platinum (Pt) in oxygen reduction reactions (ORR). Unfortunately, the electrochemical performance of existing electrocatalysts is restricted due to limited accessibility of active sites. Inspired by jellyfish tentacles, we design an efficient ORR micro-reactor called Fe-Nx/HC@NWs. It features abundant exposed Fe-Nx active sites dispersed on nitrogen-doped cubic carbon cages, which have a hierarchically porous and hairy structure. The accessible, atomically dispersed Fe-Nx sites and the elaborate substrate architecture synergize to provide the catalyst withremarkable ORR catalytic activity, extraordinary long-term stability, and favorable methanol tolerance in an alkaline electrolyte; overall, its performance is comparable to that of commercial carbon-supported Pt. Our synthesis is facile and controllable, paving a new avenue toward advanced non-precious metal-based electrocatalysts for energy storage and conversion.

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@C2n (2n = 72, 76, 78, and 80) and ThY@C2n (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. The ESR study of ThY@D3h(5)-C78 shows a doublet as expected for an unpaired electron interacting with Y, and a SQUID magnetometric study of ThDy@D3h(5)-C78 reveals a high-spin ground state for the whole molecule. Theoretical studies further confirm the presence of a single-electron bonding interaction between Y or Dy and Th, due to a significant overlap between hybrid spd orbitals of the two metals.

Chemistry of Carbon-Substituted Derivatives of Cobalt Bis(dicarbollide)(1-) Ion and Recent Progress in Boron Substitution.

The cobalt bis(dicarbollide)(1-) anion (1-), [(1,2-C2B9H11)2-3,3'-Co(III)](1-), plays an increasingly important role in material science and medicine due to its high chemical stability, 3D shape, aromaticity, diamagnetic character, ability to penetrate cells, and low cytotoxicity. A key factor enabling the incorporation of this ion into larger organic molecules, biomolecules, and materials, as well as its capacity for "tuning" interactions with therapeutic targets, is the availability of synthetic routes that enable easy modifications with a wide selection of functional groups. Regarding the modification of the dicarbollide cage, syntheses leading to substitutions on boron atoms are better established. These methods primarily involve ring cleavage of the ether rings in species containing an oxonium oxygen atom connected to the B(8) site. These pathways are accessible with a broad range of nucleophiles. In contrast, the chemistry on carbon vertices has remained less elaborated over the previous decades due to a lack of reliable methods that permit direct and straightforward cage modifications. In this review, we present a survey of methods based on metalation reactions on the acidic C-H vertices, followed by reactions with electrophiles, which have gained importance in only the last decade. These methods now represent the primary trends in the modifications of cage carbon atoms. We discuss the scope of currently available approaches, along with the stereochemistry of reactions, chirality of some products, available types of functional groups, and their applications in designing unconventional drugs. This content is complemented with a report of the progress in physicochemical and biological studies on the parent cobalt bis(dicarbollide) ion and also includes an overview of recent syntheses and emerging applications of boron-substituted compounds.

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 (Ih) C80 cage embedding homonuclear rare-earth bimetals, and a chemical modification of the Ih-C80 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. Four novel La-Ti heteronuclear di-EMFs were isolated, namely, LaTi@D3h(5)-C78, LaTi@Ih(7)-C80, LaTi@D5h(6)-C80, and LaTi@C2v(9)-C82, and their molecular structures were unambiguously determined by single-crystal X-ray diffraction. Upon increasing the cage size from C78 to C82, the La-Ti distance decreases from 4.31 to 3.97 Å, affording fine-tuning of the metal-metal bonding and hyperfine coupling, as evidenced by an electron spin resonance (ESR) spectroscopic study. Density functional theory (DFT) calculations confirm the existence of SEMB in all four LaTi@C2n di-EMFs, and the accumulation of electron density between La and Ti atoms shifts gradually from the proximity of the Ti atom inside C78 to the center of the LaTi bimetal inside C82 due to the decrease of the La-Ti distance. The electronic properties of LaTi@C2n heteronuclear dimetallofullerenes differ apparently from their homonuclear La2@C2n counterparts, revealing the peculiarity of heteronuclear dimetallofullerenes with the involvement of 3d-block transition metal Ti.