1998 MRS Fall Meeting & Exhibit

Chairs

Sumio Iijima, NEC Corp

Symposium Support 

• Carbolex, Inc. 
  
  

* Invited paper

SESSION S1: SOLID STATE FULLERENES 
Chair: Robert C. Haddon 
Monday Morning, November 30, 1998 
America Center (W)

8:30 AM *S1.1 MECHANICAL PROPERTIES OF FULLERENE CRYSTALS:C₆₀ AND C₇₀. Kenichi Kojima , Masaru Tachibana and Isamu Okada, Yokohama City Univ, Faculty of Science, Yokohama, JAPAN. 

A study of mechanical properties of fullerene crystals has been limited in number. We have investigated a characteristics of plastic deformation and dislocation structures in C₆₀ and C₇₀ crystals. We observed photo-illumination indentation hardening in C₆₀ crystals. The micro-hardness of C₆₀ crystals drastically increased after illumination of light. The hardness increased with illumination time. A change in hardness H is defined by the difference between an intrinsic hardness and maximum hardness after illumination. The H strongly depends on wavelength of illumination of light and temperature. H increased with increasing the wavelength and reached a maximum at 700nm and disappeared above 400K. These results suggest that the origin of hardening is due to photo-induced polymerization of C₆₀ molecules in crystals. On the other hand, in case of C₇₀ crystals, a little change in the hardness appeared after long illumination! This shows that C₆₀ crystals are more active for light than C₇₀ crystals. The photo-induced products were investigated by Raman spectra and photoluminescence. It seems that these products are photo-polymerized C₆₀ molecules. Therefore, the origin of the hardening is mainly that photo-induced polymers can act as obstacles for motion and multiplication of dislocations. We also investigated characteristics of dislocations in C₆₀ crystals by experiment and simulation. Experiments show that dislocations in C₆₀ crystals have a Burgers vector [110] on (111) and can not cross-slip. This indicates that dislocations can dissociate into two partial dislocations. Moreover, our simulation of dislocation cores showed that the dislocation dissociated into two Shockley partials. These results suggest that Shockley partials with stacking fault can interact with photo-induced polymers. 

9:00 AM S1.2 
MAGNETISM AND ELECTRICAL CONDUCTIVITY OF VAPOR-PHASE GROWN CRYSTALS OF TDAE-C60. Yusei Maruyama , Ryota Yuge, Kyoko Yoshida, Etsuko Fujimoto, Hosei Univ, Dept of Materials Chemistry, Koganei, Tokyo, JAPAN; Hironori Ogata, Inst Molecular Science, Okazaki, JAPAN. 

The ferro-or antiferro-magnetic behaviors of TDAE-C60 crystals at low temperatures have recently been studied in rather elaborated way by R.Blinc et al. In the present work we have grown first TDAE-C60 crystals in the vapor-phase with subliming C60 and evaporating TDAE separately. Obtained crystals have clear indication of ferromagnetic behanior below 16K and antiferromagnetic transition at around 50K in the measurements by an SQUID magnetometer. ESR signal also shows the strong ferromagnetic component, but it shows no indication for the antiferromagnetic transition. The resistivity is 15,000 Ohm-cm at room temperature and it is almost temperature independent above 80K. The crystal structure of the new crystal has not yet been identified. 

9:15 AM S1.3 
COMPARATIVE STUDY ON THE SYNTHESIS AND ELECTRONIC PROPERTIES OF ALKALINE EARTH, RARE EARTH, AND ALKALI-ALKALINE EARTH METAL FULLERIDES. Balvinder Gogia , Fundamental Research Laboratories, NEC Corporation, Tsukuba, JAPAN; Katsumi Tanigaki, Department of Material Science, Osaka City University, Osaka, JAPAN; Hiroshi Suematsu, University of Tokyo, Department of Physics, Bunkyo-Ku, Tokyo, Japan, and Kosmas Prassides, School of Chemistry, Physics and Environmental Science, University of Sussex, UNITED KINGDOM. 

After the discovery of the framework of carbon cage structure, C₆₀ and its intercalation process with other electron donating elements, fullerides have been of great interest from the viewpoint of their curious electronic properties. In the case of alkali-metal fullerides, the correlation between structure and electronic properties is well established because of their simple cluster structure as well as the availability of highly reliable experimental data. However, details have not still been understood in the case of alkaline-earth metal fullerides due to the difficulty in preparing high quality single-phase materials. The situation becomes more complicated in the case of rare-earth metal fullerides, where less reactivity of the intercalants and the formation of carbides are serious problems for achieving single phases. 
We have studied in detail both alkaline-earth metal and rare-earth metal C₆₀ fullerides by employing various preparation methods to attain good sample quality. We will report correlation between structure and electronic properties for Sr, Ba and La doping in C₆₀. The synthesis and electronic properties of isostructural A_3-xA'_x C₆₀ (A and A' being alkali and alkaline-earth metals, respectively) with tetra- and penta-valent states will also be presented. 

9:30 AM S1.4 
ADSORPTION AND QUANTUM DYNAMICS OF HYDROGEN IN Na_xC₆₀ (x = 0,2, and 4) AND NANOTUBES. T. Yildirim , S.A FitzGerald, D.A. Neumann and L.J. Santodonato, National Institute of Standards and Technology, Gaithersburg, MD. 

Adsorption of atoms or molecules in nanopore materials has considerable fundamental interest because of two main reasons; the reduced dimensionality and technological importance, such as gas separation and hydrogen storage. We show that adsorption of hydrogen in solid Na_xC₆₀ forms an excellent system to study a quantum object with a confining potential of zero-dimension. The loading isotherm is shown to deviate significantly from a standard Langmuir response and follows instead an exponential form, increasing from 40% filling at 10MPa to 90% at 100 MPa. Diffraction data confirm that the adsorbed molecules are randomly oriented and sit exclusively at the octahedral site. Inelastic neutron scattering clearly shows the ortho to para conversion of the interstitial hydrogen, which occurs via a transition from the J = 1 to J = 0 rotational levels. We also identify the translational modes of the trapped H₂ which are remarkably high in energy and have an isotopic shift on the order of . Quantum mechanical model calculations within the self consistent phonon approximation indicate that zero-point motion of H₂ molecules in the ground state play the central role in understanding the experimental results, and in particular the high energy of the translational modes and the magnitude of their isotopic shift. Finally we report our preliminary work on the hydrogen adsorption in carbon nanotubes, a system of recent experimental interest due to one dimensional environment with particular high surface to volume ratio. We also study this problem by Monte Carlo simulation in the grand canonical ensemble as a function of nanotube radius, pressure and temperature. 

9:45 AM S1.5 
STRUCTURE AND LATTICE DYNAMICS OF K₁C₆₀ IN THE ORTHORHOMBIC PHASE: A NEUTRON SCATTERING STUDY. H.M. Guerrero, R.L. Cappelletti , Ohio Univ, Dept of Physics and Astronomy, Athens, OH; D.A. Neumann, Taner Yildirim, NIST Center for Neutron Research, Gaithersburg, MD. 

Rietveld refinement of neutron diffraction from a powder sample of K₁C₆₀ in the orthorhombic phase using a model having polymeric linking by [2+2] cycloaddition of the C₆₀ molecules yields physically reasonable bond lengths from 1.44Å to 1.54Å between C atoms in the vicinity of the link. Neutron time-of-flight inelastic scattering measurements display a band of vibrations consistent with linking between 10 and 25 meV not present in pure C₆₀ or in the fcc phase of K₁C₆₀. Diffuse scattering is accounted for in terms of rotationally disordered C₆₀ in minority phases and in unlinked boundary regions between polymer grains. 

10:30 AM S1.6 
STRUCTURAL AND ELECTRONIC PROPERTIES IN ALKALI-HYDROGEN-C₆₀ COMPOUNDS. Hironori Ogata , Seiichi Miyajima, Institute for Molecular Science, Okazaki, JAPAN. 

In alkali-hydrogen-C₆₀ systems, hydrogen can exhibit a variety of electronic states when intercalated in the host crystal lattice. An interesting feature is how the hydrogen 1s state contribute to the bulk electronic properties. K-Li-H-C₆₀ and Rb-Li-C₆₀ compounds were synthesized. ¹H NMR spectra obtained at room temperature for these samples suggest anionic hydrogen states. We will present the structural and electronic properties for K-Li-H-C₆₀ and Rb-Li-C₆₀ compounds studied by powder X-ray diffraction, magnetic susceptibility measurement and solid state NMR spectroscopy. 

10:45 AM S1.7 
X-RAY-DIFFRACTION AND MAGNETIC SUSCEPTIBILITY OF POTASSIUM FULLERIDE K_xC₇₀. Mototada Kobayashi , Toshifumi Hara, Yuichi Akahama and Haruki Kawamura, Himeji Institute of Technology, Hyogo, JAPAN; Youichi Murakami, Photon Factory, Tsukuba, JAPAN. 

Potassium fulleride K_xC₇₀ has a structure sequence of an fcc(x=0), a doped fcc(x=1), a doped fcc(x=3), a bct(x=4), a bcc(x=6) and a K-saturated fcc(x=9) phases with increasing K concentration. We have measured the temperature dependence of the magnetic susceptibility for single-phase K_xC₇₀ powdered samples synthesized by heating stoichiometric ratio of K₉C₇₀ and C₇₀. The temperature-independent small paramagnetic contributions were observed in x=1, 3 and 4. Some K₃C₇₀ specimens have shown diamagnetic contributions below 0.5 K. The temperature dependence of the x-ray-diffraction profile for these phases down to 10 K by using synchrotron radiation are also presented. We will discuss the possible metallic and superconducting phases in K_xC₇₀. 

11:00 AM *S1.8 
VALENCE VS. SUPERCONDUCTIVITY IN INTERCALATED FULLERIDES. Yoshi Iwasa , JAIST, Ishikawa, JAPAN. 

Molecular valence n of C₆₀^-n in the solid state can be changed from 0 to 12, by co-intercalation of alkali metals and alkaline earth metals. Also, intercalation of neutral molecules enables one to tune the lattice parameters with keeping n unchanged. Here we talk about the synthesis of ternary or quarternary fullerides with particular emphasis on the control of band-filling and interfullerene spacings. Synthesis of alkali-alkaline earth ternaries shows that the character of superconductivity in C₆₀salts differs between the low reduction states (n<6) and high reduction states (n>6). Furthermore, expansion of interfullerene distance by intercalation of neutral molecules uncovered the important role of the electron correlation effect on fullerene superconductors. 

11:30 AM *S1.9 
FULLERENE INTERCALATION CHEMISTRY: NEW HOSTS AND EXPANDED STRUCTURES. Katharine M. Allen, Patrik Dahlke, Mark S. Denning, Amelia J. Fowkes, Matthew J. Rosseinsky , University of Oxford, Department of Chemistry, Oxford, UK.; T. John S. Dennis, Hisanori Shinohara, Nagoya University, Department of Chemistry, Nagoya, JAPAN. 

Seven years have passed since the discoveries of conductivity and superconductivity in alkali metal-intercalated C₆₀. A wide variety of new solid state science, of particular relevance to intercalation chemistry, the physics of narrow-band systems and the search for high superconducting transition temperatures in molecular conductors, has been developed, and it is now appropriate to consider whether there is anything more of interest that these materials can teach us. The electronic properties of metal fullerides have received much attention due to the observation of superconductivity at transition temperatures of up to 40K in A₃C₆₀ compounds, where A is an alkali metal. The superconducting transition temperature increases monotonically with the volume per fulleride anion. Recent work has shown that in addition to this obvious method of chemical control, the electronic properties are extremely sensitive to slight changes in relative fulleride orientation and fulleride charge, providing renewed motivation for the preparation of new fulleride structure types. This presentation concerns three separate issues of current interest in fulleride science. Firstly, the evolution of the electronic properties of metal fullerides as the intermolecular separation is increased towards the Mott-Hubbard localised electron regime, in a series of materials with large interfulleride separations. The synthesis of new structure types will then be covered, focusing on the use of powder diffraction and multinuclear NMR techniques to study the weak intermolecular interactions which allow the preparation of these new structures. The higher fullerenes offer largely unexplored opportunities for new structural chemistry and electronic properties. The isolation and separation of the D₂ and D_2d isomers of C₈₄ at Nagoya University have allowed us to begin exploring the intercalation chemistry of these hosts. The degenerate LUMO and near-spherical shape of the D_2d isomer suggests analogies with C₆₀ which are worth investigating. The structure and properties of the f.c.c. K_8+xC₈₄ family will be presented. 

SESSION S2: MOLECULAR FULLERENES 
Chair: Stephen R. Wilson 
Monday Afternoon, November 30, 1998 
America Center (W)

1:30 PM *S2.1 
MISSING FULLERENES AND ENDOHEDRAL CALCIUM FULLERENES. T.John S.Dennis, Takayoshi Ito, Tomoyasu Nakane, and Hisanori Shinohara , Department of Chemistry, Nagoya University, Nagoya, JAPAN. 

There has been known to exist two ``missing'' fullerenes that have not yet been isolated in macroscopic amounts, i.e., C72 and C74. The C72 and C74 fullerenes have a single IPR (isolated pentagon rule) structure, D6d and D3h symmetry structure for C72 and C74, respectively. One of the salient electronic properties of the two missing fullerenes is concerned in their HOMO-LUMO gaps. C72 has a large HOMO-LUMO gap (1.388 eV) which is larger than that of C70 (1.1 eV) and comparable to that of C60 (1.6 eV). An ab initio calculation indicates that the presence of two such hexagons in the cage structure causes significant strain and thus produces a high structural instability. C74 has been observed in soot produced by arc discharge but not yet been isolated. C74 has an unusually small HOMO-LUMO gap (0.224 eV), suggesting a high chemical reactivity. This might explain the inability to extract C74 from primary soot by normal fullerene solvents. 
Here, we report the first successful production, separation and isolation of endohedral calcium fullerenes with the two missing fullerene cages, C72 and C74 (Ref.1). Unlike the hollow C72 and C74, we have found that Ca@C72 and Ca@C74 metallofullerenes are stable and even soluble in solvents and thus can be subjected to the normal HPLC purification. The calcium atoms obviously play crucial roles in stabilizing these missing cage based matallofullerenes. 

2:00 PM S2.2 
NMR CHARACTERIZATION OF HIGHER FULLERENES UP TO C₉₄. Yohji Achiba , Yoko Miyake, Hironobu Ishiwatari, Masatsune Kainosho and Koichi Kikuchi, Tokyo Metropolitan Univ, Dept of Chemistry, Tokyo, JAPAN. 

NMR characterization has been performed for the isomers of the higher fullerenes isolated by HPLC. The sizes of the isomers examined in the present work are those from C₇₆ to C₉₄. More than 30 different isomers with the same or different carbon atoms were studied by ¹³C NMR in solution. As a result, their molecular symmetries and in some cases, their molecular structures have successfully been identified. 
For example, five major isomers of C₉₂ were well separated by HPLC and characterized by ¹³C NMR in solution, showing the presence of two C₂-symmetry isomers and three D₂-symmetry isomers. According to the Fowler's theoretical treatment, even in the restriction of isolated pentagon rule, there are at least 26 different kinds of C₂-isomers and 4 kinds of D₂-isomers. However, it was found that very limited numbers of C₂ isomers are selectively formed in the process of the fullerene growth. 
Similar trends of selective formation of specific isomers of higher fullerenes have also been observed in the isomers with different sizes. Of particular interest is that the most of the isomers examined in the present work have a common nature of the network structures with 5- and 6- membered carbon rings, which might be related to the unknown growth processes of the fullerenes. 

2:15 PM S2.3 
ROOM TEMPERATURE AND LOW-TEMPERATURE SPECTROSCOPIC STUDIES OF HIGHER FULLERENES: C₇₀, C₇₆, C₇₈, C₈₄. Steven Clarke , Jessica Pollchik, Anthony Francis, Dept of Chemistry, Univ of Michigan, Ann Arbor, MI. 

Studies of the electronic spectra of fullerenes are complicated by extreme solvatochromism and other environmental effects that arise because the fullerenes are good electrophiles and form both ground and excited state complexes with many aromatic solvents. Since transitions to the lower excited states are, in general, forbidden by strong selection rules based on molecular symmetry, the symmetry-breaking effects of the environment or those arising from electron-nuclear coupling (Jahn-Teller) have dramatic spectroscopic consequences for these species. 
We have completed detailed studies of the solvent and temperature dependence of the photoluminescence spectra of C₇₀. The results are interpreted in terms of emission from nearly degenerate excited electronic states whose characters are strongly mixed by the solvent field. In addition, using semi-prep porphyrin-silica columns for separation, we have been able to isolate several higher fullerenes in amounts sufficient for spectroscopic studies. We report the room temperature and low temperature absorbance spectra of several of these fullerenes, including C₇₆, two isomers of C₇₈ and C₈₄. We have also obtained the corresponding photoluminescence spectra of these fullerenes in several solvents at 4 K and 77 K. 

2:30 PM S2.4 
PREPARATION, ISOLATION, AND CHARACTERISATION OF FLUORO DERIVATIES OF [70]FULLERENE. Olga V. Boltalina, Chemistry Department, Moscow State University, RUSSIA; Joan M. Street, Chemistry Department Southampton University, UNITED KINGDOM; Roger Taylor , The Chemistry Laboratory, CPES School, Sussex University, UNITED KINGDOM. 

The use of fluorofullerenes in materials applications, though full of early promise, has been severely hampered by the difficulty in controlling fluorination by fluorine gas. Only C₆₀F₄₈ has been made in this way.¹ However, our recent introduction of fluorination by transition metal fluorides has enabled us to prepare and fully characterise C₆₀F₁₈,² C₆₀F₃₆,³and some oxygen-containing derivatives.⁴ We now report the use of transition metal fluorides coupled with HPLC separation of the products to prepare and isolate C₇₀F₃₄, C₇₀F₃₆ (> three isomers), C₇₀F₃₈, C₇₀F₄₀, C₇₀F₄₂, C₇₀F₃₈, C₇₀F₃₄O₃, C₇₀F₃₅O.OH (three isomers), and other oxygen-containing derivatives, many of which have been characterised by ¹³C NMR spectroscopy. This opens the way to the study of the properties of these compounds, and chemistry leading to derivatives, exemplified by the recent isolation and chacterisation of triumphene, C₆₀F₁₅ Ph₃.⁵ Some fluorinated derivatives of [76]- and [84]fullerenes may also be described. 

2:45 PM S2.5 
THE SYNTHESIS OF NEW FULLERENE DIMERS: C121 AND C122. Nita Dragoe , Kentaro Nakahara, Satoru Tanibayashi, Hidekazu Shimotani, Lixin Xiao, Koichi Kitazawa, University of Tokyo, Dept of Applied Chemistry, Tokyo, JAPAN; Yohji Achiba, Koichi Kikuchi, Yoko Miyake, Tokyo Metropolitan University, Dept of Chemistry, Tokyo, JAPAN; Kazutetsu Nojima, Jeol Ltd, Tokyo, JAPAN. 

Higher fullerenes, because of the decreasing curvature, tend toward the properties of graphite. In the case of fullerene dimers, the interaction between highly conjugated and curved carbon structures may bring interesting electronic properties. Few fullerene dimers have been reported so far and only one, the dumbbell C120, is an all-carbon dimer. Theoretical calculations show that other dumbbell derivatives as C122 or C121 should be stable. We report here the synthesis and preliminary characterization of new all carbon fullerene dimers C121 and C122. The synthesis was performed in a rather unusual way, by thermal decomposition of fullerene derivatives. We propose a general synthesis method where fullerene derivatives can be used as building blocks to synthesize new fullerene based compounds with defined three dimensional geometries, as desired. 

3:30 PM S2.6 
SYNTHESIS AND MAGNETIC CHARACTERIZATION OF NEW FULLERIDE SALTS. Olinda Carreon, Alain Penicaud , Claude Coulon, Centre de Recherche Paul Pascal, UPR CNRS, Universite de Bordeaux-I, FRANCE. 

Despite the early successes in fullerene-based material research, exemplified by the A3C60 superconducting family and TDAE-C60, not many new salts have been synthetized. We believe that a strong innovative and imaginative effort is needed from the material chemistry community, parallel to that observed in fullerenes functionnalization chemistry. In our systematic search for new C60-based materials, we will present, between others, the electrochemical synthesis of Cocp2C60, one of the few members of the family of metallocenium salts of C60 and a study of its magnetic and conducting properties. In particular, a change in g-value, spin susceptibility and linewidth is seen by electron spin resonance spectroscopy around 120K, the origin of which will be discussed. Noteworthy is the fact that below 120K, the g-factor of the C60 radicals have three different principal values suggesting a lower molecular symmetry. 

3:45 PM S2.7 
ISOTOPE EFFECT IN THE C₆₀ MOLECULE. J. R. Soto, A. Calles , Dept. of Physics, Faculty of Sciencies, National University of Mexico, Mexico D. F, MEXICO.; J.L. Morán López, Institute of Physics, University of San Luis Potosi, San Luis Potosi, MEXICO. 

In the production of C₆₀ it can be found molecules with ¹³C atoms in different places instead of ¹²C. In the present work we calculate, from first principles, the vibrational spectra with one and two ¹³C atoms in the C₆₀ molecule. In order to make the necessary second derivatives of the energies we use the Hartree-Fock approximation for obtaining the force constants between the carbon atoms. The frequency shift for the isotope effect in the vibrational spectra are compared with Raman spectroscopy experiments. 

4:00 PM S2.8 
SYNTHESIS AND CHARACTERIZATION OF NOVEL CYCLOADDUCTS OF C60. Glen P. Miller , James Mack, Mark Tetreau, Christina A. Risatti, University of New Hampshire, Department of Chemistry, Durham, NH. 

The synthesis and characterization of several new cycloadducts of C60 will be described. Particular attention will be placed upon the formation of cycloadducts resulting from separate additions of electron deficient 1,2,4,5-tetrazines and linear acenes to C60. Bis- and trisadducts often accompany monoadduct formation and these have, in some cases, been isolated and characterized. 
Reaction between C60 and 3,6-di(2-pyridyl)-1,2,4,5-tetrazine largely favors bisadduct formation, even under conditions which should favor monoadduct (e.g., excess C60). Moreover, bisadduct formation is in this case stereoselective. We observe only 3 (and under some conditions, only 1!) of 8 potential bisadducts. 
Reactions between C60 and linear acenes have been studied in an attempt to cycloadd more than 1 fullerene to a given acene molecule, and to explore the reversibility of these Diels-Alder reactions as a function of diene structure. 

4:15 PM S2.9 
IRREVERSIBLE HYDROGENATION OF UNCATALYZED AND CATALYZED SOLID C60. Eric L. Brosha , John R. Davey, Fernando H. Garzon, Shimshon Gottesfeld, Los Alamos National Laboratory, Los Alamos, NM. 

The objective of this work was to evaluate hydrogen uptake by fullerene substrates and to probe the potential of the hydrogen/fullerene system for hydrogen fuel storage. The hydrogenation and dehydrogenation of pure and catalyzed C₆₀was studied up to 120 bar PH₂ using an automated hydrogen absorption system that monitored hydrogen uptake and release. C₆₀H_18.7 was prepared at 100 bar H₂ and 400C, corresponding to hydrogen uptake of 2.6 wt%. Dehydrogenation of C₆₀H_18.7 was subsequently studied using thermogravimetric and powder x-ray diffraction analysis. The C₆₀H_18.7 molecule was found to be stable up to 430C in Ar, at which point the release of hydrogen took place simultaneously with the collapse of the fullerene structure. X-ray diffraction analysis performed on C₆₀H_18.7 samples dehydrogenated at 454, 475, and 600C showed an increasing volume fraction of amorphous material due to randomly oriented, single layer graphine sheets. Evolved gas analysis using gas chromatography and mass spectroscopy confirmed the presence of both H₂ and methane upon dehydrogenation, indicating decomposition of the fullerene, The remaining carbon could not be re-hydrogenated. These results provide the first complete evidence for the irreversible nature of fullerene hydrogenation and for limitations imposed on the hydrogenation/dehydrogenation cycle by the limited thermal stability of the molecular crystal of fullerene. 

4:30 PM S2.10 
ULTRAFAST OPTICAL KERR EFFECT OF FULLERENE-POLYAMINONITRILE DERIVATIVES. Di Qiang , Xin An, Yan-Lin Song, Hui-Ying Chen, Institute of Polymer Science.

Abstract not available.