Metallic phase in the metal-intercalated higher fullerene Rb8.8(7)C84

A new material of higher fullerene, RbxC84, was synthesized by intercalating Rb metal into C-84 crystals. The RbxC(84) crystals showed a simple cubic (sc) structure with lattice constant, a, of 16.82 (2) angstrom at 6.5 K, and 16.87 (2) angstrom at 295 K. The Rietveld refinements were achieved with the space group, Pa (3) over bar, based on a model that the C-2 axis of D2d-C84 aligned along [111]. The sample composition was determined to be Rb-8.8(7) C-84. The ESR spectrum at 303 K was composed of a broad peak with peak-to-peak linewidth Delta H-pp of 220 G, and a narrow peak with Delta H-pp of 24 G. Temperature dependence of the broad peak clearly showed a metallic behavior. The metallic behavior was discussed based on a theoretical calculation. This finding of new metallic phase in a higher fullerene is the first step for a development of new types of fullerene materials with novel physical properties such as superconductivity.</p

Theoretical Study of Structures and Chemical Functionalization of Endohedral Metallofullerenes

　Endohedral metallofullerenes (fullerenes encapsulating metal atoms inside the hollow spherical cages)have long attracted wide interest because of the promising material, catalytic, and biomedical applications. The electronic properties and reactivities of endohedral metallofullerenes have been extensively investigated both theoretically and experimentally. It is currently the focus of interest to determine the cage structures and metalpositions, since these are fundamental in the investigation and application of endohedral metallofullerenes. 　In this thesis, she has disclosed (1) the cage structures of the representative trimetallofullerene Sc3 C82 and dimetallofullerene Sc2C84, (2) the metal positions for Ce@C82, Eu@C82, Eu@C82 and Gd@C82, (3) how the encapsulation of La2 and Sc3N indside C80 tunes the reactivities of the C80 cage, and (4) how the rotationalmotion of La2 and Sc3N inside C80 in controllable by exohedral chemical functionalization, by using densityfunctional calculations in collaboration with experiment.　(1) It is widely accepted that the maximum entropy method (MEM)/Rietveld analysis of synchrotron X-ray powder diffraction data is powerful for structural determination of endohedral metallofullerenes. Since the first application to Y@C82, the structured of many representative metallofullerenes have been determined and reported by the MEM/Rietveld method. For example, the MEM/Rietveld analysis of Sc3C82 shows that three Sc atoms are encapsulated inside a C3v isomer of C82 as a trimer. However, this Sc3@C82 structure does not correspond to an energy minimum. From density functional calculrations and 13C NMR data, it has been disclosed that the cage structure of Sc3C82 originates from the Ih isomer of C80 (not from the C3v isomer of C82)and two C atoms as well as three Sc atoms are encaged inside the C80 fullerene, the Sc3C2@C80 structure being much more stable than the Sc3@C82 structure determined by the MEM/Rietveld analysis. This noticeable finding has been corroborated by the single-crystal X-ray diffraction analysis of a carbine derivative of Sc3C2@C80. The carbide metallofullerene, Sc3C2@C80, is noteworthy since the number of encapsulated atomsis the largest known up to now. As another interesting example, it has been disclosed that Sc2C84 takes the from of Sc2C2@C82, though Sc2C84 has been believed to have the form of Sc2@C84 from the MEM/Rietveld analysis. These results suggest that the structures of endohedral metallofullerenes determined by the MEM/Rietveld analysis are not always reliable enough, though the determined structures have been widely employed to explain the electronic properties and reactivities as well as spectroscopic data.　(2)Since the first successful extraction of La@C82(M=Sc, Y, and La ) has been known as atypical monometallofullerene. The M atom is mostly encapsulated inside the C2v cage of C 82 and located at an off-centered position near a hexagonal ring along the C2 axis. From the MEM/Rietveld analysis, however, it has been very recently claimed that Eu@C82 and Gd@C82 have exceptionally an anomalous endohedral structure since the metal atom having f electrons is located near the C-C double bond on the opposite side of the C2v-C82 cage along the C2 axis. To provide theoretical insight to this exception, density functional calculations were performed for Eu@C82 and Gd@C82 as well as Ce@C82. For all these metallofullerenes, it was found that the metal positions near the C-C double bond on the opposite side are highly unstable and do not correspond to energy minima, as also supported from the analysis of electrostatic potentials. The Eu, Gd, and Ce atoms move without any barrier to the positions near the hexagonal ring. The metal positions near the hexagonal ring are 30,52, and 50 kcal/mol more stable for Eu@C82, Gd@C82, and Ce@C82, respectively, than those near the C-Cdouble bond. These results suggest that Eu@C82, Gd@C82, and Ce@C82 have a normal endohedral structure, as found for M@C82(M=Sc, Y, and La). In collaboration with experiment, the normal structure of Ce@C82has been verified from the paramagnetic NMR spectral analysis of the anion.　(3)Both La2@C80 and Sc3N@C80 have the same carbon cage that originates from the Ih isomer of C80 andthe electronic structures are formally described as (La2)6＋C806- and (Sc3N)6+C806- as a result of six-electron transfer to the C80 cage. However, Sc3.However, Sc3N@C80 has a much higher LUMO level than La2@C80. The LUMO of Sc3N@C80 is delocalized not only on the Sc3N cation but also on the C80 anion, while the LUMO of La2@C80 islocalized on the La cation and more suitable as an electron accommodation. These suggest that La2@C80 is more reactive toward nucleophiles than Sc3N@C80. In fact, the different reactivities of La2@C80 and Sc3N@C80 have been verified for the reactions with disilirane. As this example shows, it is interesting that the reactivities of metallofullerenes are tunable by encapsulated species.　(4) For La2@C80 and Sc3N@C80, it is known that the two La atoms and the Sc3N cluster rotate freely inside the round Ih-C80 cage at room temperature. By density functional calculations, however, it was found that the two La atoms stand still at a specific position upon the exohedral chemical functionalization of La2@C80 by azomethine ylides, while the three-dimensional random motion of the Sc3N cluster in Sc3N@C80 is fixied in the plane perpendicular to the equator by attaching electron-donating molecules such as disilirane. These theoretical findings have been recently confirmed by experiment. Control of motion of encapsulated species within a hollow cage is expected to be helpful in designing molecular devices with electronic or magnetic properties

Exceptional Chemical Properties of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ Probed with Adamantylidene Carbene

It has been an interesting finding that reactions of M@<i>C</i>_2<i>v</i>(9)–C₈₂ (M = Y, La, Ce, Gd) with diazirine adamantylidene (AdN₂, <b>1</b>) gave rise to only two monoadduct isomers, indicating that the cage reactivity of monometallofullerenes is not dependent on the type of the internal metal. However, we found here that Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ shows an exceptional chemical reactivity toward the electrophile <b>1</b>, affording four monoadduct isomers (<b>2a</b>–<b>d</b>). Single-crystal X-ray diffraction crystallographic results of the most abundant isomer (<b>2a</b>) confirm that the addition takes place at a [6,6]-bond junction which is very close to the internal metal ion. Theoretical calculations reveal that 2 out of the 24 nonequivalent cage carbons of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ are highly reactive toward <b>1</b>, but only one cage carbon of the other M@<i>C</i>_2<i>v</i>–C₈₂ (M = Y, La, Ce, Gd) is sufficiently reactive. The exceptional chemical property of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ is associated with the small ionic radius of Sc³⁺, which allows stronger metal–cage interactions and makes back-donation of charge from the cage to the metal more pronounced. Our results have provided new insights into the art of altering the chemical properties of fullerene molecules at the atomic level, which would be useful in the future in utilizing EMFs in quantum computing systems

Exceptional Chemical Properties of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ Probed with Adamantylidene Carbene

It has been an interesting finding that reactions of M@<i>C</i>_2<i>v</i>(9)–C₈₂ (M = Y, La, Ce, Gd) with diazirine adamantylidene (AdN₂, <b>1</b>) gave rise to only two monoadduct isomers, indicating that the cage reactivity of monometallofullerenes is not dependent on the type of the internal metal. However, we found here that Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ shows an exceptional chemical reactivity toward the electrophile <b>1</b>, affording four monoadduct isomers (<b>2a</b>–<b>d</b>). Single-crystal X-ray diffraction crystallographic results of the most abundant isomer (<b>2a</b>) confirm that the addition takes place at a [6,6]-bond junction which is very close to the internal metal ion. Theoretical calculations reveal that 2 out of the 24 nonequivalent cage carbons of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ are highly reactive toward <b>1</b>, but only one cage carbon of the other M@<i>C</i>_2<i>v</i>–C₈₂ (M = Y, La, Ce, Gd) is sufficiently reactive. The exceptional chemical property of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ is associated with the small ionic radius of Sc³⁺, which allows stronger metal–cage interactions and makes back-donation of charge from the cage to the metal more pronounced. Our results have provided new insights into the art of altering the chemical properties of fullerene molecules at the atomic level, which would be useful in the future in utilizing EMFs in quantum computing systems

Bis-Silylation of Lu₃N@<i>I</i>_<i>h</i>‑C₈₀: Considerable Variation in the Electronic Structures

Photochemical reactions of Lu₃N@<i>I</i>_<i>h</i>-C₈₀ with disiliranes <b>1</b> and <b>2</b> produce several isomeric adducts. Spectroscopic analyses characterize the most stable isomers as 1,4(AA) adducts, which consist of paired twist conformers at rt. The electrochemical and theoretical studies reveal that the HOMO–LUMO energy gaps of the 1,4(AA) adducts are smaller than that of Lu₃N@<i>I</i>_<i>h</i>-C₈₀ because the electron-donating groups effectively raise the HOMO levels

Mechanistic Study of the Diels–Alder Reaction of Paramagnetic Endohedral Metallofullerene: Reaction of La@C₈₂ with 1,2,3,4,5-Pentamethylcyclopentadiene

The reaction mechanism of the Diels–Alder reaction of paramagnetic endohedral metallofullerene, La@C₈₂, and 1,2,3,4,5-pentamethylcyclopentadiene was studied theoretically and experimentally. Theoretical calculations revealed that this reaction proceeds via a concerted mechanism that includes formation of a stable intermediate. The activation energy of a retro-Diels–Alder reaction was also studied experimentally, which is in good agreement with theoretical results

The enunciation of 'terrorism' as a kind of power and its distribution in the West

This paper is motivated by the assumption that ‘terrorism’ is a loaded and politically significant term, the use of which exudes and produces power relations. It acknowledges this, and also argues that not everyone has an equal right to use the term. This leads to an examination into the kind of power that is manifested in the use of the term, by putting the social constructivist framework to work and placing the semantic field of terrorism within that framework. It identifies a kind of power attached to the enunciation of the term ‘terrorism’ and argues that it is unequally distributed between perceived potential victims of terrorism and perceived potential perpetrators of terrorism. Drawing on Nietzsche’s genealogical analysis of morality, I argue that it is counterproductive to deny potential perpetrators the power of enunciation around the term ‘terrorism’ on the basis that this leads to a kind of slave revolt in terrorism. Redistributing the power of enunciation around the term ‘terrorism’ might remove the line that separates potential victims from potential perpetrators of terrorism and work towards reducing the threat of terrorism itself by allowing those potential perpetrators to exercise this capability within mainstream society, as opposed to seeking alternative communities to do so outside of it