Stability Of Fullerenes Research Articles

(Invited) 1,3-Dipolar Cycloadditions on Endohedral Fullerenes M3N@I h -C80 (M = Sc-Gd): Remarkable Endohedral-Cluster Regiochemical Control

Since the C60 discovery in 1985, many fullerene structures have been synthesized and a variety of experimental and computational studies regarding the fullerene stability, characterization, properties such as aromaticity, and reactivity have been reported.1 The huge interest engendered by these fullerene-based materials is mainly attributed to their potential applications in the electronics, photovoltaics, biology, and medicine fields. Obstacles to such bio-applications include their poor solubility in water necessitating the preparation of water-soluble materials by suitable modifications. One of the most useful methods to functionalize fullerenes is via 1,3-dipolar cycloaddition (i.e. Prato reaction). The complete structural, chemical and electronic properties of (metallo)fullerenes are not totally understood at the present time. Specifically, the factors controlling the regiochemistry of multiple additions remain largely unexplored and poorly understood. In this communication, we rationalize using DFT calculations both the effect of the exohedral moiety and the orientation of the encapsulated cluster on the regioselectivity of the Prato (bis)addition to the Ih-C80 based endohedral metallofullerenes, M3N@Ih -C80 (M=Sc, Lu, Y, and Gd).2-4 1M. Garcia-Borràs, S. Osuna, M. Swart, J. M. Luis, M. Solà, Chem. Soc. Rev., 2014, 43, 5089. 2S. Aroua, M. Garcia-Borràs, S. Osuna, Y. Yamahoshi, Chem. Eur. J. 2014, 20, 14032. 3S. Aroua, M. Garcia-Borràs, M. Bölter, M., S. Osuna, Y. Yamakoshi, J. Am. Chem. Soc. 2015, 137, 58. 4M. R. Cerón, M. Izquierdo, M. Garcia-Borràs, S. S. Lee, S. Osuna, L. Echegoyen, J. Am. Chem. Soc. 2015, 137, 11775. Figure 1

On the search of stable, aromatic and ionic endohedral compounds of C28: A theoretical study

The X@C28 compounds form the family of the smallest endohedral fullerenes. Currently, they consist of C28, which is endohedrally doped with group-4 elements (Ti, Zr, Hf) and U. We have studied the electronic properties, equilibrium geometries, binding energies and other properties of several X@C28 at the PBE/def2-TZVP level. These were compared with the tetraanion C284−. For this study we have chosen elements from groups 4, 14 and Sc as endohedral dopants for being many of them tetravalent. In addition, we studied by the first time the entire group-10 (Ni, Pd and Pt) as endohedral dopant of C28. To elucidate the stability of these ionic compounds, we have studied their binding energies. Our results show that a big positive binding energy is necessary but not enough to determine the stability of these endohedral fullerenes. We propose that a HOMO–LUMO gap around 2eV results in less reactive compounds, property only shown by group-4 compounds. Some compounds have aromatic character in all rings according with their NICS(0)iso and reparametrized HOMA indexes. In addition, the charge distribution have been studied with NBO and Hirshfeld population analysis as well as electrostatic potential maps in order to find similarities between them and that shown by the tetraanion C284−. The most stable compounds are the group-4 X@C28 which form compounds: energetically favorable, less reactive, ionic and aromatic. Our results are compared with available experimental information about the formation of these compounds.

Fingerprinting Electronic Molecular Complexes in Liquid.

Predicting the electronic framework of an organic molecule under practical conditions is essential if the molecules are to be wired in a realistic circuit. This demands a clear description of the molecular energy levels and dynamics as it adapts to the feedback from its evolving chemical environment and the surface topology. Here, we address this issue by monitoring in real-time the structural stability and intrinsic molecular resonance states of fullerene (C60)-based hybrid molecules in the presence of the solvent. Energetic levels of C60 hybrids are resolved by in situ scanning tunnelling spectroscopy with an energy resolution in the order of 0.1 eV at room-temperature. An ultra-thin organic spacer layer serves to limit contact metal-molecule energy overlap. The measured molecular conductance gap spread is statistically benchmarked against first principles electronic structure calculations and used to quantify the diversity in electronic species within a standard population of molecules. These findings provide important progress towards understanding conduction mechanisms at a single-molecular level and in serving as useful guidelines for rational design of robust nanoscale devices based on functional organic molecules.

Object-oriented Persistent Homology.

Persistent homology provides a new approach for the topological simplification of big data via measuring the life time of intrinsic topological features in a filtration process and has found its success in scientific and engineering applications. However, such a success is essentially limited to qualitative data classification and analysis. Indeed, persistent homology has rarely been employed for quantitative modeling and prediction. Additionally, the present persistent homology is a passive tool, rather than a proactive technique, for classification and analysis. In this work, we outline a general protocol to construct object-oriented persistent homology methods. By means of differential geometry theory of surfaces, we construct an objective functional, namely, a surface free energy defined on the data of interest. The minimization of the objective functional leads to a Laplace-Beltrami operator which generates a multiscale representation of the initial data and offers an objective oriented filtration process. The resulting differential geometry based object-oriented persistent homology is able to preserve desirable geometric features in the evolutionary filtration and enhances the corresponding topological persistence. The cubical complex based homology algorithm is employed in the present work to be compatible with the Cartesian representation of the Laplace-Beltrami flow. The proposed Laplace-Beltrami flow based persistent homology method is extensively validated. The consistence between Laplace-Beltrami flow based filtration and Euclidean distance based filtration is confirmed on the Vietoris-Rips complex for a large amount of numerical tests. The convergence and reliability of the present Laplace-Beltrami flow based cubical complex filtration approach are analyzed over various spatial and temporal mesh sizes. The Laplace-Beltrami flow based persistent homology approach is utilized to study the intrinsic topology of proteins and fullerene molecules. Based on a quantitative model which correlates the topological persistence of fullerene central cavity with the total curvature energy of the fullerene structure, the proposed method is used for the prediction of fullerene isomer stability. The efficiency and robustness of the present method are verified by more than 500 fullerene molecules. It is shown that the proposed persistent homology based quantitative model offers good predictions of total curvature energies for ten types of fullerene isomers. The present work offers the first example to design object-oriented persistent homology to enhance or preserve desirable features in the original data during the filtration process and then automatically detect or extract the corresponding topological traits from the data.

Nitric oxide adsorption on non-stoichiometric boron nitride fullerene: Structural stability, physicochemistry and drug delivery perspectives

The structural stability and physicochemical properties of the N-rich BN fullerene, B24N36, have been analyzed by means of the density functional theory at the level of the generalized gradient approximation. For this purpose, the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid density functional and the 6-31G(d) basis set were used. The results indicate that the B24N36 fullerene is stable and behaves as a semiconductor compound. It has been found that while the polarity of the B24N36 fullerene is comparable with that of C60 fullerene, its chemical reactivity is notoriously higher. The spatial charge distribution of the BN fullerene allows nitric oxide adsorption, without compromising structural stability. Although the interaction between the NO molecule and BN fullerene is through van der Waals forces (dipole–dipole attraction), it has strong influence on the dipole moment, vibrational modes, HOMO–LUMO gap and work function energy; suggesting that this nanostructure could be used as a molecular sensor or drug carrier with enhanced bioavailability.

Study of endohedral doped C60 fullerene using model potentials

In this paper, we present a study of Si, Ge, Au and Tl doped endohedral fullerenes using model potentials. We have used Brenner potential, Lennard-Jones potential and Gupta potential to describe the C–C (Si, Ge), C–metal and metal–metal interaction, respectively. We have done total energy calculations to find out the minimum energy structures. In the case of Sin@C60 complex, a maximum of nine atoms can be doped inside the fullerene cage. The addition of a tenth Si atom leads to the breaking of the fullerene cage. Similarly for Ge, Au and Tl, a maximum of four, two and two atoms, respectively, can be doped inside the fullerene cage. It has been observed that the stability of fullerene decreases with an increase in the number of dopant atoms. These calculations prove the change of characteristics of fullerenes upon doping.

Distributed curvature and stability of fullerenes.

Energies of non-planar conjugated π systems are typically described qualitatively in terms of the balance of π stabilisation and the steric strain associated with geometric curvature. Curvature also has a purely graph-theoretical description: combinatorial curvature at a vertex of a polyhedral graph is defined as one minus half the vertex degree plus the sum of reciprocal sizes of the faces meeting at that vertex. Prisms and antiprisms have positive combinatorial vertex curvature at every vertex. Excluding these two infinite families, we call any other polyhedron with everywhere positive combinatorial curvature a PCC polyhedron. Cubic PCC polyhedra are initially common, but must eventually die out with increasing vertex count; the largest example constructed so far has 132 vertices. The fullerenes Cn have cubic polyhedral molecular graphs with n vertices, 12 pentagonal and (n/2 - 10) hexagonal faces. We show that there are exactly 39 PCC fullerenes, all in the range 20 ≤n≤ 60. In this range, there is only partial correlation between PCC status and stability as defined by minimum pentagon adjacency. The sum of vertex curvatures is 2 for any polyhedron; for fullerenes the sum of squared vertex curvatures is linearly related to the number of pentagon adjacencies and hence is a direct measure of relative stability of the lower (n≤ 60) fullerenes. For n≥ 62, non-PCC fullerenes with a minimum number of pentagon adjacencies minimise mean-square curvature. For n≥ 70, minimum mean-square curvature implies isolation of pentagons, which is the strongest indicator of stability for a bare fullerene.

Colloidal stability of (functionalised) fullerenes in the presence of dissolved organic carbon and electrolytes

Influence of various parameters on the stability and size of fullerene clusters is being investigated using DLS, MALS and flow cytometry.

Persistent homology for the quantitative prediction of fullerene stability.

Persistent homology is a relatively new tool often used for qualitative analysis of intrinsic topological features in images and data originated from scientific and engineering applications. In this article, we report novel quantitative predictions of the energy and stability of fullerene molecules, the very first attempt in using persistent homology in this context. The ground-state structures of a series of small fullerene molecules are first investigated with the standard Vietoris-Rips complex. We decipher all the barcodes, including both short-lived local bars and long-lived global bars arising from topological invariants, and associate them with fullerene structural details. Using accumulated bar lengths, we build quantitative models to correlate local and global Betti-2 bars, respectively with the heat of formation and total curvature energies of fullerenes. It is found that the heat of formation energy is related to the local hexagonal cavities of small fullerenes, while the total curvature energies of fullerene isomers are associated with their sphericities, which are measured by the lengths of their long-lived Betti-2 bars. Excellent correlation coefficients (>0.94) between persistent homology predictions and those of quantum or curvature analysis have been observed. A correlation matrix based filtration is introduced to further verify our findings.

High Stability of Faceted Nanotubes and Fullerenes of Multiphase Layered Phosphorus: A Computational Study.

We present a paradigm in constructing very stable, faceted nanotube and fullerene structures by laterally joining nanoribbons or patches of different planar phosphorene phases. Our abinitio density functional calculations indicate that these phases may form very stable, nonplanar joints. Unlike fullerenes and nanotubes obtained by deforming a single-phase planar monolayer at substantial energy penalty, we find faceted fullerenes and nanotubes to be nearly as stable as the planar single-phase monolayers. The resulting rich variety of polymorphs allows us to tune the electronic properties of phosphorene nanotubes and fullerenes not only by the chiral index but also by the combination of different phosphorene phases. In selected phosphorene nanotubes, a metal-insulator transition may be induced by strain or by changing the number of walls.

First results of the ORGANIC experiment on EXPOSE-R on the ISS

AbstractThe ORGANIC experiment on EXPOSE-R spent 682 days outside the International Space Station, providing continuous exposure to the cosmic-, solar- and trapped-particle radiation background for fourteen samples: 11 polycyclic aromatic hydrocarbons (PAHs) and three fullerenes. The thin films of the ORGANIC experiment received, during space exposure, an irradiation dose of the order of 14 000 MJ m−2 over 2900 h of unshadowed solar illumination. Extensive analyses were performed on the returned samples and the results compared to ground control measurements. Analytical studies of the returned samples included spectral measurements from the vacuum ultraviolet to the infrared range and time-of-flight secondary ion mass spectrometry. Limited spectral changes were observed in most cases pointing to the stability of PAHs and fullerenes under space exposure conditions. Furthermore, the results of these experiments confirm the known trend in the stability of PAH species according to molecular structure: compact PAHs are more stable than non-compact PAHs, which are themselves more stable than PAHs containing heteroatoms, the last category being the most prone to degradation in the space environment. We estimate a depletion rate of the order of 85 ± 5% over the 17 equivalent weeks of continuous unshadowed solar exposure in the most extreme case tetracene (smallest, non-compact PAH sample). The insignificant spectral changes (below 10%) measured for solid films of large or compact PAHs and fullerenes indicate a high stability under the range of space exposure conditions investigated on EXPOSE-R.

Maximum aromaticity or maximum pentagon separation; which is the origin behind the stability of endohedral metallofullerenes?

Two different interpretations have been recently proposed to rationalize the stabilization of some hosting cages in endohedral metallofullerenes as a consequence of the larger localization of the negative charge on pentagonal rather than on hexagonal faces. We try to figure out the physical origin that mainly governs the stability of charged fullerenes; is it aromaticity or electrostatics?

Endohedral Metallofullerenes Based on Spherical Ih-C80 Cage: Molecular Structures and Paramagnetic Properties

Fullerenes are carbon cages assembled from fused hexagons andpentagons that have closed networks and conjugated π systems. The curve of the fullerene structure requires that the constituent carbon atoms take on a pyramidal shape and produces extra strain energy. However, the highly symmetrical geometry of the fullerene decreases the surface tension in these structures, so highly symmetrical fullerenes are usually very stable. For example, C60 with icosahedral symmetry (Ih) is the most stable fullerene molecule. However, another highly symmetrical fullerene, Ih-C80, is extremely unstable. The reason for this difference is the open-shell electronic structure of Ih-C80, which has a 4-fold degenerate HOMO occupied by only two electrons. Predictably, once the degenerate HOMO of Ih-C80 accepts six more electrons, it forms a closed-shell electronic structure similar to Ih-C60 and with comparable stability. Because the hollow structure of fullerenes can encapsulate metal atoms and those internal metals can transfer electrons to the fullerene cage, the encapsulation of metal clusters may provide an ideal technique for the stabilization of the Ih-C80 fullerenes. In this Account, we focus on the molecular structures and paramagnetic properties of spherical Ih-C80 endohedral fullerenes encaging a variety of metal moieties, such as metal atoms (Mn), metal nitride (M3N), metal carbide (MnC2), metal carbonitride (M3CN), and metal oxides (M4Om). We introduce several types of endohedral metallofullerenes such as Sc4C2@Ih-C80, which exhibits a Russian-doll-like structure, and Sc3CN@Ih-C80, which encapsulates a planar metal carbonitride cluster. In addition, we emphasize the paramagnetic properties of Ih-C80-based metallofullerenes, such as Sc3C2@Ih-C80, Y2@C79N, and M3N@Ih-C80, to show how those spin-active species can present a controllable paramagnetism. This Account highlights an inspiring molecular world within the spherical Ih-C80 cages of various metallofullerenes.

Study of the fullerene C60 stability in biological substrates using in vitro model system

This paper presents the results of an in vitro study of the unmodified fullerene C60 stability in samples of biological substrates obtained from Wistar rats. The known amounts of fullerene C60 at various concentrations are added to the freshly prepared samples of rat whole blood, homogenates, and liver microsomal fractions; the decrease in its concentration over a day is studied using HPLC. The data testify to the instability of fullerene C60 in biological media in situations reproducing with some degree of approximation the processes of biodegradation of the substance taking place in a living organism (nitrogen-oxygen atmosphere, +37°C, in the dark).

Fullerene matrices in the MALDI-TOF mass spectroscopic characterisation of organometallic compounds

The use of MALDI-TOF mass spectrometry with fullerene matrices in the characterisation of insoluble, air-sensitive organolanthanides is described. The issues of matrix, sample preparation, fullerene stability, calibration, comparisons with other matrices, oxygen sensitivity and adduct formation of samples, radical chemistry, aggregation, the detection of triple-decker compounds, and complications in recording the spectra are discussed. The fullerene matrix is found to provide the basis for excellent characterisation for these compounds, and the technique is potentially of general utility.

Enhancement in the Stability of 36-Atom Fullerene through Encapsulation of a Uranium Atom

With an objective to rationalize the experimentally observed intense U@C36 peak in the mass spectrum of U@C2n metallofullerene, structural, stability, and spectroscopic aspects of the uranium doped C36 fullerene have been studied in a unified and systematic way using density functional theory (DFT) and its time-dependent variant. Relativistic effects have been taken into account within the framework of zeroth-order regular approximation using scalar and spin–orbit-based approaches. Among all of the 15 possible classical isomers reported for the C36 fullerene cage system, singlet D2d and triplet D6h structures are found to be isoenergetic and most stable. Encapsulation of uranium atom into various C36 cages leads to 15 distinct isomers with considerable energy differences. It has also been shown that this encapsulation process results in significant gain in thermodynamic stability. The most stable U@C36 isomer is found to be associated with C6v symmetry and closed-shell electronic configuration, derived from the open-shell D6h structure of C36. The next stable isomer is associated with Cs symmetry and obtained from the corresponding singlet D2d structure of the C36 cage. Distinct changes have also been found in the calculated vibrational and UV–visible spectra of the U@C36 cluster as compared to the corresponding bare C36 cage. All of the calculated quantities reported here suggest that the stability of the U@C36 cluster is high enough for possible formation of cluster-assembled material leading to synthesis of this metallofullerene experimentally.

Selecting boron fullerenes by cage-doping mechanisms

So far, no boron fullerenes were synthesized: more compact sp(3)-bonded clusters are energetically preferred. To circumvent this, metallic clusters have been suggested by Pochet et al. [Phys. Rev. B 83, 081403(R) (2011)] as "seeds" for a possible synthesis which would topologically protect the sp(2) sector of the configuration space. In this paper, we identify a basic pentagonal unit which allows a balance between the release of strain and the self-doping rule. We formulate a guiding principle for the stability of boron fullerenes, which takes the form of an isolated filled pentagon rule (IFPR). The role of metallic clusters is then reexamined. It is shown that the interplay of the IFPR and the seed-induced doping breaks polymorphism and its related problems: it can effectively select between different isomers and reduce the reactivity of the boron shells. The balance between self and exterior doping represents the best strategy for boron buckyball synthesis.

The Stability of Cosmic Fullerenes and Fullerenic Aggregates

AbstractEstablishing the stability of cosmic fullerenes and fullerenic aggregates is extremely relevant for a variety of reasons. For instance, the emission features of C60 and C70 fall in the same spectral region as the Un-identified InfraRed (UIR) bands, which they could contribute to. To be able to contribute to the UIR emission, however, fullerenes must be able to survive long enough against the destruction mechanisms operating in the interstellar medium. In this study we focus on the effects of collisional processing, i.e., the bombardment by energetic ions and electrons. A recent experimental/theoretical study has shown that ion collisions with C60 clusters result in the dissociation of the cluster with the simultaneous formation of covalent fullerene dimers, which could play a role as DIBs carriers. We present here our first results about the collisional processing of C60 molecules and clusters by H, He and C ions in interstellar shocks. We have adapted the models that have previously been developed to successfully treat the collisional processing of PAHs in space. The nature of the interaction and the similarities between PAHs and fullerenes make this approach appropriate. In addition, our study shows that the formation of covalent dimers following ion collisions with C60 clusters is compatible with the astrophysical conditions under consideration.

Fullerene Genetic Code: Inheritable Stability and Regioselective C2 Assembly

A bottom-up topological pathway was established to elucidate the growth of small fullerenes and the generation of Ih-symmetric C60. In contrast to countless growth mechanisms, the model described herein has two distinctive features. First, each fullerene on the route possesses the lowest potential energy or exhibits a predominant molar fraction at elevated temperatures in the corresponding series. Second, a C2 insertion without any high-barrier rearrangement process (such as Stone–Wales transformation) can connect two adjacent molecules on the route directly. These two characteristics imply that the fullerene stability can be inherited through continuous insertion of a C2 cluster during carbon-cage enlargement. Various adducts can be generated from different active sites on the parent fullerene surface. Therefore, an investigation of the regioselectivity of C2 addition using density functional theory is reported herein for the first time. A systematic simulation demonstrates that the reaction to the most ...

Fullerene based endohedral metallocenes

In this study, the density functional theory (DFT)-based Becke’s three parameter hybrid exchange functional and Lee–Yang–Parr correlation functional (B3LYP) and dispersion corrected B3LYP (B3LYP-D) calculations have been performed to predict the structure and stability of fullerene based endohedral sandwich complexes. The role of confinement on the structure of half-sandwich complex (i.e. (η5-Cp)Fe+ (Cp=cyclopentadienyl anion)) has also been probed using energy decomposition analysis. The standard redox potential has been calculated to understand the electrochemical property of newly designed endohedral sandwich complexes. Results have been compared with exohedral sandwich complexes and ferrocene.