Interaction Between C60 Fullerene and Alkali Metals Demonstrating Superconductivity

A discret summation method [1] has been used to calculate the van der Waals dispersion interactions between an alkali metal atom and individual C₆₀ fullerene molecules, as well as between an intercalated alkali metal atom and the face-centred-cubic lattice of solid fullerite. It is known [2, 3] that the conductivities observed in the doped C₆₀ films vary considerably for different alkali atoms. Our interest was to investigate any correlation between these conductivities and the long range potential field behaviour. In the present study, we have obtained interaction potential curves of the C₆₀ fullerene molecule including within its cage, as well the potential field topography within the overall C₆₀ fullerite solid unit cell. We have found that for all intercalated alkali metals, except Cs, there are voids within the unit-cell of fullerite where the dopant experiences attractive interactions. Whereas on the other hand, inside the fullerene cage only Li and Na experience attractive forces. Importantly, it has been shown that the localization of the crystallographic sites [4] of doped alkali metals in fullerite coincide with the potential energy minima of long range van der Waals forces.     

Disruptive influence of the host cage C60 on the guest He–H+ bond and bonding in H3+

Although a helium atom prefers to stay at the centre of a fullerene (C₆₀) cage and a proton binds with one of the carbon atoms from inside, DFT(MN15)/cc-pVTZ and DLPNO-MP2/def2-TZVP calculations show that the helium atom and the proton in HeH⁺ prefer to stay away from the centre of the cage, weakening the He–H⁺ covalent bond considerably. Both the helium atom and the proton exhibit noncovalent interactions with the carbon atoms of two pentagons at the opposite ends of the fullerene cage. Our calculations also show that a linear arrangement of H₃⁺ (inside C₆₀), pointing towards the centres of two pentagons opposite to each other, with the proton breaking away from H_2, is energetically more favored over the equilateral triangle geometry of free H₃⁺.     

Nature of C60 and C70 fullerene encapsulation in a porphyrin- and metalloporphyrin-based cage: Insights from dispersion-corrected density functional theory calculations

The search for efficient synthetic hosts able to encapsulate fullerenes has attracted attention with regard to the purification and formation of ordered supramolecular architectures. This study of a porphyrin-based cage as an extension of the well-described ExCage⁶⁺ and BlueCage⁶⁺, involving viologen as sidearms, provides an interesting scenario where the oblate C₇₀ fullerene is preferred in comparison to the spherical C₆₀. Our results expose the nature of the fullerene-cage interaction involving ∼50% of dispersion-type interactions evidencing the strong π⋯π surface stacking, with a complementary contribution by the electrostatic and orbital polarization character produced by a charge reorganization with a charge accumulation facing the porphyrin macrocycles and a charge depletion along the equator formed by the viologens sidearms. Interestingly, the central N₄H₂ ring from each porphyrin contributes to the dispersion term via N-H⋯π interactions, which is decreased when the metallate N₄Zn is evaluated. Thus, the formation of stable and selective fullerene encapsulation can be achieved by taking into account two main driving forces, namely, (a) the extension of the π⋯π and X-H⋯π stacking surface and (b) charge reorganization over the fullerene surfaces, which can be used to control fine tuning of the encapsulation thanks to the introduction of more electron-deficient and electron-rich groups within the host cage.     

On the interatomic potentials for noble gas mixtures

Recently, a relatively simple scheme for the construction of isotropic intermolecular potentials has been proposed and tested for the like species interactions involving He, Ne, Ar, Kr and H₂. The model potential has an adjustable parameter which controls the balance between its exchange and Coulomb energy components. The representation of the Coulomb energy contains a damped multipolar dispersion energy series (which is truncated through O(R^?10) and provides additional flexibility through adjustment of the dispersion energy coefficients, particularly C₈ and C₁₀, within conservative error estimates. In this paper the scheme is tested further by application to interactions involving unlike noble gas atoms where the parameters in the potential model are determined by fitting mixed second virial coefficient data as a function of temperature. Generally the approach leads to potential of accuracy comparable to the best available literature potentials which are usually determined using a large base of experimental and theoretical input data. Our results also strongly indicate the need of high quality virial data.     

Collisional fragmentation of Ar@C60

The fragmentation patterns resulting from collisions between (Ar@C₆₀)⁺ or (Ar@C₆₀)⁻ ions and H₂, He, CH₄, Ne, Ar and Kr target gases have been measured. The ion-source material Ar@C₆₀ was synthesized by heating C₆₀ under 3000 atm of argon gas, leading to a 10⁻³ concentration of endohedral fullerenes. The fragmentation spectra (charged molecules only) are dominated by positive ions both when positive or negative endohedrals break up. Endohedral fragment ions Ar@C_n⁺ (48n60) as well as all carbon fragments are observed. For collisions involving (Ar@C₆₀)⁻, ejection of the Ar atom together with two electrons, without permanently damaging the fullerene cage, is a prominent reaction channel, indicating that a ‘window' or a deformation in the form of e.g. a large hole, through which the argon atoms can exit, is opened during the collision.     

Packed to the Rafters: Filling up C60 with Rare Gas Atoms

How many rare gas atoms can be placed into a fullerene cage until the pressure becomes large enough to break the C₆₀ framework? The answer given by density functional and ab initio computations is surprising and underlines the high stability of this unique carbon structure.     

Nouvelle méthode de préparation pour les complexes endoédriques atome de gaz rare–fullerène C60

New route for preparation of endohedral complexes of rare gas atom–C₆₀. Preparation of endohedral complexes of a rare gas atom–fullerene is described, in which a sample of C₆₀ powder, surrounded by a high pressure rare gas, is sublimated and excited by a strong nanosecond pulse laser beam. Experiments were carried out with the following rare gases: pure ⁴He, a mixture of 2 % of ³He in ⁴He, and pure Ar. Macroscopic quantities of these complexes were obtained in estimated concentations up to 20 %.     

First Synthesis and Characterization of CH4@C60

The endohedral fullerene CH₄@C₆₀, in which each C₆₀ fullerene cage encapsulates a single methane molecule, has been synthesized for the first time. Methane is the first organic molecule, as well as the largest, to have been encapsulated in C₆₀ to date. The key orifice contraction step, a photochemical desulfinylation of an open fullerene, was completed, even though it is inhibited by the endohedral molecule. The crystal structure of the nickel(II) octaethylporphyrin/ benzene solvate shows no significant distortion of the carbon cage, relative to the C₆₀ analogue, and shows the methane hydrogens as a shell of electron density around the central carbon, indicative of the quantum nature of the methane. The ¹H spin‐lattice relaxation times (T₁) for endohedral methane are similar to those observed in the gas phase, indicating that methane is freely rotating inside the C₆₀ cage. The synthesis of CH₄@C₆₀ opens a route to endofullerenes incorporating large guest molecules and atoms.     

Photolytic cage effect of iodine in gases at high pressures

The photolysis of iodine has been studied in the gas phase using laser flash photolysis at 6943 A. The dependence of the quantum yield on the pressure has been investigated in the range 0.1–1000 atm for several inert gases. For Kr, Xe, O₂, CO₂, CH₄, C₂H₆ and C₃H₈ a decrease of the quantum yield with increasing pressure was obtained; for He, Ne, Ar and H₂ no effect could be observed. These results may correspond to a photolycitc cage effect of iodine in the gas phase analogous to that known from the liquid phase.     

Etudes par spectroscopie dans l'ultra-violet et le visible, du fullerène C60 en solution dans le n-hexane ou adsorbé sur des solides diélectriques

Ultraviolet and visible spectroscopy studies of the fullerene C₆₀ melted in n-hexane or adsorbed on dielectric solids. Experiments of spectroscopy have been carried out, between the far ultraviolet and the near infrared, with pure C₆₀ or containing endohedral complexes rare gas atom-C₆₀, melted in n-hexane, and also pure C₆₀ adsorbed on surfaces of solids.Several phenomena have been observed: 1. a charge transfer due to the influence of interactions between the molecules of C₆₀ and surfaces of solids, yielding new transitions observed in the far ultraviolet ; and interpreted as super excited states of Rydberg type; 1.1. red and blue shifts for some transitions of adsorbed C₆₀, interpreted on the basis of attractive, or turned repulsive, dispersion forces; 1.1.1. emission processes for several transitions of adsorbed C₆₀, explained on the basis of a resonant coupling between these transitions and modes of the surface plasmon induced by the collective excitations of the C₆₀ molecule; this kind of process might be drawn to the Faraday instability in acoustics.     

Encapsulation of the interstellar abundant H3+ in a C60 fullerene

The possible encapsulation of the interstellar abundant H₃⁺ ion inside a C₆₀ fullerene cage has been examined by using the Hartree‐Fock (HF) and the second order Møller‐Plesset perturbation (MP2) methods both with the 6‐31G** basis set. It was found that H₃⁺ forms various stable endohedral complexes inside the cage. Six configurations have been examined among which four were stable compared with the separated initial species, the dissociated H₂ + H⁺ inside the cage being the most stable. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Quantum chemical studies of non-covalent interactions between the ethyl cation and rare gases

By taking into consideration the facts that rare gases (Ar, He, Kr, and Ne) are practically inert and that the structure of the ethyl cation (C₂H₅⁺) is stabilized through the hyperconjugation effect, a theoretical study at the B3LYP/6-311 + +G(d,p) level of calculation was carried out here in order to investigate the formation of the C₂H₅⁺···Ar, C₂H₅⁺···He, C₂H₅⁺···Kr, and C₂H₅⁺···Ne complexes. The charge transfers among H and Ar, He, Kr or Ne prove that the loss of electronic density on the rare gases are clearly noticeable. Additionally, the synergism between the structural changes and the vibration shifts have been demonstrated and justified on the basis of the Bent rule and QTAIM calculations. In complement, the interaction strength in H⁺···Ar, H⁺···He, H⁺···Kr, and H⁺···Ne was examined, although the covalent character is completely null because these contacts are very weak.     

Potential energy surfaces for the benzene–rare gas systems

A harmonic expansion representation of the intermolecular interaction has been exploited to obtain the potential energy surface (PES) for the C₆H₆–He, –Ne, –Ar, –Kr and –Xe systems in an analytical form. Basic data employed are binding energy, equilibrium distance and long-range attraction predicted by a semi-empirical method for selected configurations of the complexes. For those favorable cases where additional information are available the proposed PESs exhibit features in good agreement with those derived from spectroscopy and scattering experiments and/or ab initio calculations. The availability of realistic PESs expressed in an analytical form opens new perspectives of calculations in molecular dynamics and spectroscopic simulations where the benzene molecule and rare gas atoms are involved.     

In-silico exploration of noble gas dimer enforced by noncovalent interaction

Density functional calculations have been carried out to investigate the possibility of trapping of noble gas dimers by cyclo[18]carbon dimer. Parallel-displaced conformation of the cyclo[18]carbon dimer is found to be the minimum energy structure. Noncovalent interaction is found to hold the noble gas dimers. The lighter noble gases (He, Ne) posses weaker attractive interactions while the heavier one (Ar, Kr) are held by stronger attractive interactions forming genuine bonds. Each of the noble gas atoms in turn forms noncovalent interaction with the cyclo[18]carbon monomers. The bond dissociation energy of the noble gas dimers dramatically increases inside the cyclo[18]carbon dimer. Energy decomposition analysis reveals that dispersion plays the major role toward the stabilization energy.     

Endofullerenes: size effects on structure and energy

The geometric and energy characteristics of endohedrals X@C _n (X = He, Ne, Ar; n = 20, 24, 30, 32, 40, 50, 60) were calculated by the density functional theory. The insertion of the helium atom leads to only a slight change in the geometry of the fullerene cage of the endohedrals. As the size of the trapped atom increases, the average C—C bond length increases in proportion to the radii of these atoms (by 0.05 for Ne@C₂₀ and 0.12 for Ar@C₂₀). The inclusion energies of endofullerenes and the pressure of the cage exerted on the endo atom were calculated for all the above-mentioned endohedrals.     

Angle and bond-length dependent C6 coefficients for H2 interacting with H,Li, Be and rare gas atoms

Summary Accurate new C₆ dispersion energy coefficients, and their dependence on the diatom orientation and bond length, are calculated for molecular hydrogen interacting with an atom of H, Li, Be, He, Ne, Ar, Kr or Xe. They are generated from accurateab initio pseudo dipole oscillator strength distributions (DOSD) for H₂, H, He and Be, and reliable semiempirical ones for Li, Ne, Ar, Kr and Xe. Compact power series expansions for the diatom bond-length dependence of these coefficients, suitable for incorporation into representations of full potential energy surfaces for these systems, are determined and assessed.     

Can a Single Molecule of Water be Completely Isolated Within the Subnano‐Space Inside the Fullerene C60 Cage? A Quantum Chemical Prospective

Based on an experimental observation, it has been controversially suggested in a study (Kurotobi et al., Science 2011 , 33, 613) that a single molecule of water can completely be localized within the subnano‐space inside the fullerene C₆₀ cage and, that neither the H atoms nor the O lone‐pairs are linked, either via hydrogen bonding or through dative bonding, with the interior C‐framework of the C₆₀ cage. To resolve the controversy, electronic structure calculations were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population and bond orbital analyses, and the results were analyzed by using varieties of recommended diagnostics often used to interpret noncovalent interactions. The present results reveal that the mechanically entrapped H₂O molecule is not electronically innocent of the presence of the cage; each H atom of H₂O is weakly O? H???C₆₀ bonded, whereas the O lone‐pairs are O???C₆₀ bonded regardless of the conformations investigated. Exploration of various featured properties suggests that H₂O@C₆₀ may be regarded as a unique system composed of both inter‐ and intramolecular interactions.     

Design and application of a multicoefficient correlation method for dispersion interactions

A new multicoefficient correlation method (MCCM) is presented for the determination of accurate van der Waals interactions. The method utilizes a novel parametrization strategy that simultaneously fits to very high-level binding, Hartree-Fock and correlation energies of homo- and heteronuclear rare gas dimers of He, Ne, and Ar. The decomposition of the energy into Hartree-Fock and correlation components leads to a more transferable model. The method is applied to the krypton dimer system, rare gas-water interactions, and three-body interactions of rare gas trimers He3, Ne3, and Ar3. For the latter, a very high-level method that corrects the rare-gas two-body interactions to the total binding energy is introduced. A comparison with high-level CCSD(T) calculations using large basis sets demonstrates the MCCM method is transferable to a variety of systems not considered in the parametrization. The method allows dispersion interactions of larger systems to be studied reliably at a fraction of the computational cost, and offers a new tool for applications to rare-gas clusters, and the development of dispersion parameters for molecular simulation force fields and new semiempirical quantum models.