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The smallest borafullerene U@C27B has been synthesized using a laser vaporization cluster source. The U atom, placed in the middle of the cage and interacting with all the 28 atoms, is formally described as highly oxidized U(vi).

A synthetic strategy featuring dicyanometalates [M(CN)2]- (M = Ag, Au) as N-coordinating ditopic linkers connecting partially blocked FeII centers has been employed to produce heterometallic hexanuclear complexes, which exhibit spin-crossover (SCO) behavior at the FeII sites. The reaction between tris(2-pyridylmethyl)amine (tpma)-capped FeII ions and [Ag(CN)2]- proceeded with partial decomposition of the dicyanoargentate and led to the formation of {[Fe(tpma)]4(μ-CN)2[μ-Ag(CN)2]2}(ClO4)4·3H2O (1), in which both [Ag(CN)2]- and CN- act as bridging ligands, and the opposite [Ag(CN)2]- bridges are engaged in a pronounced argentophilic d10-d10 interaction. In an analogous synthesis, the more stable [Au(CN)2]- species remained intact and furnished the complex {[Fe(tpma)]2[μ-Au2(CN)4]2} (2), which features two FeII centers bridged by two [Au2(CN)4]2- dimers. The use of S,S'-bis(2-pyridylmethyl)-1,2-thioethane (bpte) as a mixed-donor, N2S2-coordinating capping ligand yielded {[Fe(bpte)]2[μ-Au2(CN)4]2} (3), with a structure analogous to that of 2. Variable-temperature magnetic susceptibility measurements revealed that complexes 1-3 exhibit an onset of SCO above 350 K. Measurements above 400 K further confirmed the occurrence of a gradual spin-state conversion for complex 2.

The functionalization of endohedral metallofullerenes by halogenation has not been previously reported and remains a challenging endeavor in carbon nanoscience. In this work, we show that halogenation of endohedral metallofullerenes is predicted to be feasible based on thermodynamic grounds by means of DFT computations, combined with in situ experimental investigations. Computed bond energies for the chlorination, fluorination and hydrogenation of endohedral metallofullerenes that span a range of cage sizes are found to be comparable to those of known halogenated and hydrogenated empty fullerenes. Therefore, we propose that new forms of functionalized metallofullerenes should be synthesized under appropriate experimental conditions, despite many prior unsuccessful attempts. Indeed, we experimentally show for the first time that M@C2n (M = metal) metallofullerenes and the prototypical Sc3N@C80 clusterfullerene can be fluorinated by two different routes under the typical ‘harsh’ gas phase conditions of metallofullerene plasma synthesis, and at lower extents that could avoid cage degradation. The combination of halogenation and metal encapsulation offers the potential to create new radical-quenched, functionalized endohedral metallofullerenes that possess stable, large-gap carbon cages. These results open new avenues for the synthesis and stabilization of encapsulated molecular nanocarbons.

Endohedral metallofullerenes (EMF), i.e. fullerenes that contain metal atoms or metal clusters in their inner void space, have been intensively studied since the isolation of La@C82.1 In 1999, the synthesis and characterization of the first clusterfullerene Sc3N@C80 using the Krätschmer-Huffman method was a milestone in the field of EMF.2 Since this pioneering work, many EMF have been obtained and characterized,3 among them actinide endofullerenes,4 as for example the dimetallic U2@C80.5 In this compound, the metal-metal distance from X-ray diffraction was found to be ranged between 3.46 and 3.79 Å, quite a long bond distance to suppose the presence of a strong metal-metal bond, as observed previously for dimetallic (lanthanide)2@C2n. This experimental confirmation of a weak U-U bonding interaction in a molecular structure is certainly very encouraging, but we were wondering whether it is possible to isolate a compound with a strong U-U bond or not. In this communication we analyze the characteristic electronic structure of a family of endohedral actinidofullerenes related to U2@C80 and discuss about the challenging task of synthesizing new systems showing strong actinide-actinide interaction in the confined space of a fullerene. References 1. Chai, Y.; Cuo, T.; Jin, C.; Haufler, R. E.; Felipe Chibante, L. P.; Fure, J.; Wang, L.; Alford, J. M.; Smalley, R. E. J. Phys. Chem. 1991, 95, 7564-7568. 2. Stevenson, S.; Rice, G.; Glass, T.; Harich, K.; Cromer, F.; Jordan, M. R.; Craft, J.; Hadju, E.; Bible, R.; Olmstead, M. M.; Maitra, K.; Fisher, A. J.; Balch, A. L.; Dorn, H. C., Nature 1999, 401, 55. 3. Popov, A. A.; Yang, S.; Dunsch, L. Chem. Rev. 2013, 113, 5989-6113. 4. a) Wang, Y.; Morales-Martínez, R. et al.J. Am. Chem. Soc., 2017, 139, 5110-5116; b) Cai, W. C.; Morales-Martínez, R. et al. Chem. Sci. 2017, 8, 5282-5290; c) Cai, W.; Abella, L. et al.J. Am. Chem. Soc., 2018, 140, 18039-18050. 5. Zhang, X.; Wang, Y.; Morales-Martínez, R.; Zhong, J.; de Graaf, C.; Rodríguez-Fortea, A.; Poblet, J. M.; Echegoyen, L.; Feng, L.; Chen, N. J. Am. Chem. Soc., 2018, 140, 3907-3915.

The formation of the smallest fullerene, C28, was recently reported using gas phase experiments combined with high-resolution FT-ICR mass spectrometry. An internally located group IV metal stabilizes the highly strained non-IPR C28 cage by charge transfer (IPR = isolated pentagon rule). Ti@C44 also appeared as a prominent peak in the mass spectra, and U@C28 was demonstrated to form by a bottom-up growth mechanism. We report here a computational analysis using standard DFT calculations and Car–Parrinello MD simulations for the family of the titled compounds, aiming to identify the optimal cage for each endohedral fullerene and to unravel key aspects of the intriguing growth mechanisms of fullerenes. We show that all the optimal isomers from C26 to C50 are linked by a simple C2 insertion, with the exception of a few carbon cages that require an additional C2 rearrangement. The ingestion of a C2 unit is always an exergonic/exothermic process that can occur through a rather simple mechanism, with the most energetically demanding step corresponding to the closure of the carbon cage. The large formation abundance observed in mass spectra for Ti@C28 and Ti@C44 can be explained by the special electronic properties of these cages and their higher relative stabilities with respect to C2 reactivity. We further verify that extrusion of C atoms from an already closed fullerene is much more energetically demanding than forming the fullerene by a bottom-up mechanism. Independent of the formation mechanism, the present investigations strongly support that, among all the possible isomers, the most stable, smaller non-IPR carbon cages are formed, a conclusion that is also valid for medium and large cages.

The combination of a 3 K cryogenic radiofrequency ion trapping apparatus and a laser vaporization source is described. This instrument was constructed for the synthesis and characterization of gas phase molecules, particularly those that are difficult to make using traditional organic chemistry routes. The flexible time scale for storage and relaxation afforded by the trap enables spectroscopic investigation of ions that are challenging to cool using supersonic expansions. Routine in situ tagging of cations with helium facilitates one-photon experiments. The potential of this instrument is demonstrated by providing data on the 2B2 ← X 2A1 electronic transition of cyclic C6+, a system that had thus far evaded spectroscopic interrogation in the gas phase.

Since the discovery of buckminsterfullerene in 1985,1 intensive research has been devoted to this family of closed-cage carbon nanostructures. Endohedral metallofullerene La@C60 was already detected the same year and La@C82 was isolated few years later.2 In 1999, the synthesis, isolation and characterization of the first clusterfullerene Sc3N@C80 using the Krätschmer-Huffman method was a milestone in the field of endohedral metallofullerenes (EMF).3 The characteristic structural and electronic properties of EMFs, as well as their reactivity, have been extensively analyzed by experimental and theoretical groups.4 In particular, different rules to predict the relative stability of fullerene cages, based on the ionic model, were proposed.5 A different way to modify the properties of fullerenes is by replacing a carbon atom in the caged network with a heteroatom. The resulting heterofullerene shows distinct electronic structure and, therefore, properties from the all-carbon cage precursor. Nitrogen-doped heterofullerenes have received much more attention and investigation than boron-doped heterocages.6 Few years ago, Dunk et al. reported facile gas-phase formation of C59B by atom exchange resulting from exposure of C60 to boron vapor by means of a pulsed laser vaporization cluster source, which was the first report of borafullerene formation directly from pristine C60.7 Recent application of this technique to endohedral monometallofullerenes and clusterfullerenes at the National High Magnetic Field Laboratory in Florida lead to the formation of boron-doped EMFs with exciting electronic properties. We here analyze the characteristic electronic structure of observed B-doped metalloheterofullerenes, rationalize their stabilities and discuss about their properties. References Kroto, H. W.; Heath, J. R.; O’Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162-163. a) Heath, J. R.; O’Brien, S. C.; Zhang, Q.; Liu, Y.; Curl, R. F.; Kroto, H. W.;Tittel, F. K.; Smalley, R. E. J. Am. Chem. Soc. 1985, 107, 7779-7780; (b) Chai, Y.; Cuo, T.; Jin, C.; Haufler, R. E.; Felipe Chibante, L. P.; Fure, J.; Wang, L.; Alford, J. M.; Smalley, R. E. J. Phys. Chem. 1991, 95, 7564-7568. Stevenson, S.; Rice, G.; Glass, T.; Harich, K.; Cromer, F.; Jordan, M. R.; Craft, J.; Hadju, E.; Bible, R.; Olmstead, M. M.; Maitra, K.; Fisher, A. J.; Balch, A. L.; Dorn, H. C., Nature 1999, 401, 55. a) Rodríguez-Fortea, A.; Balch, A. L.; Poblet, J. M. Chem. Soc. Rev. 2011, 40, 3551-3563; b) Popov, A. A.; Yang, S.; Dunsch, L. Chem. Rev. 2013, 113, 5989-6113. a) Rodríguez-Fortea, A.; Alegret, N.; Balch, A. L.; Poblet, J. M., Nature Chem. 2010, 2, 955-961; b) Garcia-Borràs M., Osuna S., Swart M., Luis J.M., Solà M. Angew. Chem. Int.. Ed. 2013, 52, 9275-9278; c) Wang, Y.; Díaz-Tendero, S.; Martín, F. and Alcamí, M. J. Am. Chem. Soc., 2016, 138, 1551-1560. Lamparth, I.; Nuber, B.; Schick, G.; Skiebe, A.; Grosser, T.; Hirsch, A. Angew. Chem. Int. Ed. Engl. 1995, 34, 2257. Dunk, P. W.; Rodríguez-Fortea, A.; Kaiser, N. K.; Shinohara, H.; Poblet, J. M.; Kroto, H. W. Angew. Chem. Int. Ed. 2013, 52, 315-319.

Fullerenes that encapsulate clusters of atoms represent a fundamental interest in chemistry, materials, and carbon science due to their unique properties and nanoscale structures. Numerous cages that feature a combination of carbon, metal, and heteroatom-based clusters have been discovered since, for example, Sc3NC@C80 was first reported. Nanocarbon reactions that underlie formation of such compounds, however, are not well understood. Here, we experimentally investigate intramolecular reactions of metallofullerenes in the gas phase by means of laser-based techniques, analyzed by high magnetic field Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. A variety of structurally defined clusterfullerene cages (e.g., Sc3N@C68, Sc3N@C78, etc.) are probed under energetic conditions to decipher reactions that may lead to encapsulation of C atoms, as well as clusterfullerenes that include metal-loss products. An aim of the present work is to identify mechanistic processes and principles that guide formation of metallofullerenes that entrap carbon, metal, and heteroatom-based clusters.

Fullerenes have been studied for nearly three decades and enormous advances have been made. Mass spectrometry is commonly used for investigations on the distribution of fullerenes formed from evaporated graphite targets, and soot produced from such targets. We report distributions of fullerenes formed by graphite evaporation by use of a pulsed supersonic cluster source and compare them to certain distributions synthesised by other techniques, such as arc discharge and combustion methods. We highlight the fact that physical processes can occur during the mass spectral analysis of fullerenes under certain conditions that may skew the observed distribution of cage sizes present in a sample. In some cases, an analysis of fullerene-containing soot can greatly exaggerate the relative abundance of large fullerenes compared to C60 and medium-sized fullerenes, depending on the particular experimental setup.

International audience; Carbonaceous presolar grains of supernovae origin have long been isolated and are determined to be the carrier of anomalous (22)Ne in ancient meteorites. That exotic (22)Ne is, in fact, the decay isotope of relatively short-lived (22)Na formed by explosive nucleosynthesis, and therefore, a selective and rapid Na physical trapping mechanism must take place during carbon condensation in supernova ejecta. Elucidation of the processes that trap Na and produce large carbon molecules should yield insight into carbon stardust enrichment and formation. Herein, we demonstrate that Na effectively nucleates formation of Na@C60 and other metallofullerenes during carbon condensation under highly energetic conditions in oxygen- and hydrogen-rich environments. Thus, fundamental carbon chemistry that leads to trapping of Na is revealed, and should be directly applicable to gas-phase chemistry involving stellar environments, such as supernova ejecta. The results indicate that, in addition to empty fullerenes, metallofullerenes should be constituents of stellar/circumstellar and interstellar space. In addition, gas-phase reactions of fullerenes with polycyclic aromatic hydrocarbons are investigated to probe "build-up" and formation of carbon stardust, and provide insight into fullerene astrochemistry.

A β-4-β′ C70 bis-adduct regioisomer and an uncommon mono-adduct β-malonate C70 derivative were synthesized by using a Diels–Alder cycloaddition followed by an addition–elimination of bromo-ethylmalonate and a retro-Diels–Alder cycloaddition reaction. We also report the regioselective synthesis and spectroscopic characterization of Cs-symmetric tris- and C2v-symmetric tetra-adducts of C70, which are the precursors of the mono- and bis-adduct final products.

We have observed new mechanistic insight into the formation of metallic nitride clusterfullerenes from doped graphite by use of laser-based plasma synthesis techniques, analyzed by ultrahigh resolution 9.4 tesla Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. These online chemical sampling techniques provide a route to investigate underexplored nanocarbon reactions that take place under the harsh conditions of metallofullerene synthesis, and are expected to be applicable to macroscopic production methods. Here, we report efforts to form various clusterfullerenes by laser vaporization and extend these techniques as new avenues for investigation of exohedral functionalization (e.g., fluorination of Sc3N@C80) and heteroatom-doping of endohedral fullerenes. This work was supported by NSF Division of Materials Research through DMR-11-57490 and the State of Florida.

The chemical processes that result in self-assembly of nitride clusterfullerenes are largely unknown because in situ experimental studies are not possible by conventional arc plasma discharge techniques. Here, we report the gas-phase formation of Group III-containing nitride clusterfullerenes by laser vaporization of graphite-, metal-, and heteroatom-based starting materials, conducted by online chemical sampling techniques and analyzed by ultrahigh resolution 9.4 tesla Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Further, structurally defined clusterfullerenes are exposed to carbon vapor produced from graphite under characteristic physicochemical synthesis conditions to elucidate cluster-cage and structural effects on nanocarbon reactions that control formation.

An understanding of chemical formation mechanisms is essential to achieve effective yields and targeted products. One of the most challenging endeavors is synthesis of molecular nanocarbon. Endohedral metallofullerenes are of particular interest because of their unique properties that offer promise in a variety of applications. Nevertheless, the mechanism of formation from metal-doped graphite has largely eluded experimental study, because harsh synthetic methods are required to obtain them. Here we report bottom-up formation of mono-metallofullerenes under core synthesis conditions. Charge transfer is a principal factor that guides formation, discovered by study of metallofullerene formation with virtually all available elements of the periodic table. These results could enable production strategies that overcome long-standing problems that hinder current and future applications of metallofullerenes. An understanding of the formation mechanism of endohedral metallofullerenes may pave the way towards targeted synthesis of these nanomaterials. Here, the authors investigate their bottom-up synthesis and determine that charge transfer plays a key role in their formation.

Two Fe(II) complexes, {[(tpma)Fe(μ-CN)]4}X4 (X = ClO4(-) (1a), BF4(-) (1b); tpma = tris(2-pyridylmethyl)amine), were prepared by reacting the {Fe(tpma)}(2+) building block with (Bu4N)CN. The crystal structures of 1a and 1b feature a tetranuclear cation composed of cyanide-bridged Fe(II) ions, each capped with a tetradentate tpma ligand. The Fe4(μ-CN)4 core of the complex is strongly distorted, assuming a butterfly-like geometry. Both complexes exhibit gradual temperature-driven spin crossover (SCO) associated with the high-spin (HS) ↔ low-spin (LS) transition at two out of four metal centers. The evolution of HS and LS Fe(II) ions with temperature was followed by a combination of X-ray crystallography, magnetic measurements, and Mossbauer spectroscopy. Only the Fe(II) ions surrounded by six N atoms undergo the SCO. A comparison of the temperature-dependent SCO curves for the samples stored under solvent and the dried samples shows that the former exhibit a much more abrupt SCO. This finding was interpreted in terms of the increased structural disorder and decreased crystallinity caused by the loss of the interstitial solvent molecules in the dried samples.

Introducing boron: Heterofullerenes that incorporate boron have been scarcely studied because a formation route from C60 is not known. It is now reported that C59B−, an electronically closed-shell species, is formed directly from pristine C60 in the gas-phase by facile atom exchange reactions.

Introducing boron: heterofullerenes that incorporate boron have been scarcely studied because a formation route from C(60) is not known. It is now reported that C(59)B(-), an electronically closed-shell species, is formed directly from pristine C(60) in the gas-phase by facile atom exchange reactions.

We report the first charge reversal experiments performed by tandem-in-time rather than tandem-in-space MS/MS. Precursor odd-electron anions from fullerene C60, and even-electron ions from 2,7-di-tert-butylfluorene-9-carboxylic acid and 3,3′-bicarbazole were converted into positive product ions (–CR+) inside the magnet of a Fourier transform ion cyclotron resonance mass spectrometer. Charge reversal was activated by irradiating precursor ions with high energy electrons or UV photons: the first reported use of those activation methods for charge reversal. We suggest that high energy electrons achieve charge reversal in one step as double electron transfer, whereas UV-activated –CR+ takes place stepwise through two single electron transfers and formally corresponds to a neutralization-reionization (–NR+) experiment. Open image in new window

Tremendous advances in nanoscience have been made since the discovery of the fullerenes; however, the formation of these carbon-caged nanomaterials still remains a mystery. Here we reveal that fullerenes self-assemble through a closed network growth mechanism by incorporation of atomic carbon and C(2). The growth processes have been elucidated through experiments that probe direct growth of fullerenes upon exposure to carbon vapour, analysed by state-of-the-art Fourier transform ion cyclotron resonance mass spectrometry. Our results shed new light on the fundamental processes that govern self-assembly of carbon networks, and the processes that we reveal in this study of fullerene growth are likely be involved in the formation of other carbon nanostructures from carbon vapour, such as nanotubes and graphene. Further, the results should be of importance for illuminating astrophysical processes near carbon stars or supernovae that result in C(60) formation throughout the Universe.