Carbon aggregates of various nuclearities have been recently the subject of renewed interest [1]. Despite an intense research, effort no molecular level characterization of C60 and related molecules has been reported yet [1,2]. Moreover, the chemical properties of these materials is virtually unknown. In this paper we report briefly the preparation, electrochemical and structural characterization of crystalline C60/70 solvates [3].

An extremely simple and inexpensive apparatus for preparation of the C60 and C70 fullerenes is described. An efficient separatory technique is described which implements a phenylglycine based HFLC column for preparation of high purity (99.99%) C60 and C70 samples. Treatment of C60 with osmium tetroxide and pyridine gives the osmate ester (2:1 adduct) and establishes that oxygen functionality can be added to C60 without disrupting the carbon framework. Raman spectroscopy of high purity C60 indicates that several lines previously not assigned to C60 (D.S.Bethune, G.Meijer, W.C.Tang, and H.J.Rosen, Chem.Phys.Lett.174, 219(1990)) are attributable to C60.

The high-resolution He I photoelectron spectrum of C60 in the gas phase is reported and compared with the photoelectron spectrum of C60as a thin film prepared by vapor deposition (one to three monolayers) on gold. The spectra show low valence ionization bands that are very sharp and well-separated for a molecule of this size, consistent with the highly symmetric truncated icosahedral structure and theoretical calculations. The total band widths of the valence ionizations from the thin film samples are comparable to those from the gas phase species, showing that the electronic interactions between the molecules and with the surface do not significantly influence these measurements of the molecular electronic structure. The gas phase photoelectron spectra also show vibrational fine structure in the first and second ionization bands with spacings that are consistent with the two totally symmetric vibrational modes of C60. The first vertical ionization energy relative to the vacuum level is determined to be 7.61 ± 0.02 eV from these gas phase measurements.

C60 and C70 were synthesized and purified according to published procedures. Both nanosecond and picosecond laser desorption from coated substrates gave copious positive and negative ions. Mass spectra (TOF and FTMS) with excellent signal to noise, showing only the C60 and C70 mass peaks, have been observed. Well-resolved isotopic structure was seen in the FTMS spectra in agreement with the natural abundance of carbon. Laser desorption and multiphoton ionization/photodissociation of the neutral species, as well as electronic absorption, FTIR, and fluorescence spectra, have been obtained.

Newly developed empirical hydrocarbon potentials and self-consistent first-principles local density functional methods are used to investigate possible isomers and the electronic structure of C60H36. Within the high symmetry Th structure conjectured by the groups at Rice University there are two inequivalent sets of hydrogen atoms containing twelve and twenty-four atoms respectively. Binding each set either inside or outside of the C60 cage leads to four isomers of C60H36 with inequivalent strain energies. Although we find that placing twelve hydrogens inside the cage can lead to a metastable structure, our calculated total energies suggest that the isomer with all the hydrogens on the outside of the cage is the energetically most stable.

We have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the “soccer ball” model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions.

The physical and chemical properties of large carbon clusters, Cn(n>40), have been studied extensively over the past six years. The spherical nature of these clusters has been debated and inferred from both experimental and theoretical studies until the recent isolation and subsequent spectroscopic identification of bulk C60 and C70. Although the n=60 and 70 cluster ions are anomalously abundant (“magic numbers”) in the mass spectra and are proposed to be highly symmetric species, the other “magic number” clusters have yet to be isolated.

Carbon-13 NMR spectra of powder samples of pure C60 and of a mixture of C60 and C70 provide information about molecular motions in the solid state. At room temperature, C60 molecules rotate rapidly and isotropically. The transition from a rapidly rotating to a stationary (on the time scale of the experiment) system occurs over a temperature range from 120 K to 60 K, suggesting a distribution of activation energies. C70 molecules also rotate rapidly at room temperature, but more anisotropically.

STM topographical images of C60 are reported. The images are consistent with a molecule approximately 9 Å in diameter possessing the now-famous soccer ball structure. With the molecule deposited on gold, its atomic structure is not resolved. On graphite the structure of the within the borders of the C60 molecule is dominated by that of the graphite forming a moiré-like pattern. Some evidence of atomic structure is seen in multilayers of C60 where some five- and six-membered rings are visible. These may, however, be features of fragments of the fullerene rather than whole molecules.

We have investigated the structure and dynamics of C60 and C70 with 13C NMR spectroscopy. In solution, high-resolution spectra reveal that C60 has a single resonance at 143 ppm, indicating a strained, aromatic system with high symmetry. This is strong evidence for a C60 “soccer ball” geometry. A 2D NMR INADEQUATE experiment on 13C-enriched C70 reveals the bonding connectivity to be a linear string, in firm support of the proposed “rugby ball” structure with D5h symmetry, and furnishes resonance assignments. Solid state NMR spectra of C60 at ambient temperatures yield a narrow resonance, indicative of rapid molecular reorientation. Variable temperature T1 measurements show that the rotational correlation time is ∼ 10−9s at 230 K. At 77 K, this time increases to more than 1 ms, and the 13C NMR spectrum of C60 is a powder pattern due to chemical shift anisotropy (tensor components 220, 186, 40 ppm). At intermediate temperatures a narrow peak is superimposed on the powder pattern, suggesting a distribution of barriers to molecular motion in the sample, or the presence of an additional phase in the solid state. A Carr-Purcell dipolar experiment on C60 in the solid state allows the first precise determination of the C60 bond lengths: 1.45 and 1.40Å.

Images of monolayer coverages of C60 on gold substrates, using scanning tunneling microscopy, reveal intermolecular arrangement and intramolecular features. In this paper we concentrate on the interpretation of these internal features, present a model showing that they arise from local charge density variations of high-lying π orbitals on approximately every other carbon atom, and discuss also other possible mechanisms for this effect.

We report the first structure optimization and quantum molecular dynamics simulations for solid C60. The symmetry-unconstrained optimization results in nearly ideal buckminsterfullerene structure. This is due to the closed shell nature of C60 and the weakness of the intermolecular interactions in the solid. The lack of substantial intermolecular interactions allows for rotations at relatively low temperatures and these rotations are observed during simulations. Although the zero temperature structure consists of alternating single and double bonds, this distinction becomes blurred at moderate temperatures. However, computer generated movies show that the cage structure is preserved even at high temperatures, despite vibrational motion with substantial amplitude.

We have developed a new cluster ion source that can generate intense beams of metal and semiconductor clusters of a very wide-size range. With the source, we have observed intense beams of carbon clusters with mean cluster sizes of up to 4000 atoms/clusters. However, we have found that for generating small fullerenes, such as C60 and C70, the recently discovered technique by Kraetschmer et al. is much more efficient. By improving the technique, we have generated gram quantities of C60 and C70 and systematically investigated their thermal desorption properties. During the heating process, we have discovered that at high temperatures the bulk fullerenes, fullerite, transformed to another form of carbon, which still evaporates at temperatures above 700 C, but does not dissolve in benzene.