Search

Chemical reduction of the Li + @C 60 cation by decamethylferrocene was carried out to obtain neutral Li + @C 60 •– (simply denoted as Li@C 60 ). The method is scalable and does not demand long reaction times unlike electrolytic reduction routes. Powder X-ray diffraction and Raman and EPR spectroscopic measurements of the Li@C 60 solid sample are consistent with the presence mainly of (Li@C 60 ) 2 dimers together with remaining Li + @C 60 •– monomer species due to lack of crystallization time in the course of formation and precipitation.

The photoion yield spectra of an endohedral metallofullerene Pr@C 82 were measured in the photon energy range of 100–150 eV by using time-of-flight mass spectrometry. Parent ions Pr@C 82 + , Pr@C 82 2+ and Pr@C 82 3+ were observed in the mass spectra. The photoion yield spectra of Pr@C 82 2+ showed a broad peak at 120–140 eV that was assigned to the 4 d –4 f giant dipole resonance of the encapsulated Pr atoms. Absolute photoabsorption cross sections of Pr@C 82 were evaluated from the photoion yield spectra to be 37±12 Mb at 110 eV (off-resonance) and 52±13 Mb at 130 eV (on-resonance). These cross sections of Pr@C 82 were compared with the results of Ce@C 82 , the only metallofullerene whose photoionization properties have ever been studied near the 4 d edge of the encapsulated metal atom. The enhancement of photoabsorption due to the giant resonance was found to be similar in Pr@C 82 and Ce@C 82 , but there are marked differences in the peak shapes, which can be explained as due to interference effects between the fullerene cage and the encapsulated metal atoms.

The photoion yield curves for Dy@C 82 z + ( z = 1 and 2) from Dy@C 82 are measured by using synchrotron radiation in the photon energy range from 24.5 to 39.5 eV. Correction has been made to compensate the effect of transient change of the density of Dy@C 82 in the interaction region, with the help of the yield curve of C 60 z + produced from C 60 remaining as a trace impurity in the sample. The yield of Dy@C 82 + exhibits a gradually descending curve with a flat region at 30–33 eV, similarly to the yield curve of C 60 + from C 60 . The total photoabsorption cross section of Dy@C 82 was evaluated to be (1.2 ± 0.4) × 10 −20 m 2 at the photon energy of 39.5 eV.

Location of the Dy ion in the minor isomer of Dy@C 82 was determined by Dy L III -edge EXAFS. The Dy ion is found to lie near the fused bond between the two hexagon rings. This finding is consistent with that predicted by a quantum-chemical calculation [Chem. Phys. Lett. 282 (1998) 325].

Two isomers of Dy@C 82 were separated by high performance liquid chromatography (HPLC), and their UV–VIS absorption spectra were measured to characterize these isomers. The crystalline powder of Dy@C 82 was obtained by removing the solvent (toluene) at 250°C under vacuum. The X-ray diffraction pattern can be indexed with fcc crystal lattice, as that in La@C 82 . The lattice constant a at 298 K, 15.86(1) A, is close to that of La@C 82 , 15.78 A. The distances between Dy and the first and second nearest C atoms are determined to be 2.52(2) and 2.86(2) A, respectively, on the basis of Dy L III -edge EXAFS. The XANES shows that the valence of the Dy atom in Dy@C 82 is +3.

The structure of La2@C80 is studied by La K-edge XAFS from 40 to 295 K. The distances between the La atom and the first nearest C atoms have been determined to be 2.42(1) A at 40 K and 2.44(2) A at 295 K, and those between the La atom and the second nearest C atoms to be 2.97(2) A at 40 K and 2.98(3) A at 295 K. The La–La distance has been determined to be 3.90(1) A at 40 K and 3.88(2) A at 295 K. The temperature dependence of the mean-square displacement of La–C is also studied to get an insight into the dynamical behavior of two La atoms in the C80 cage.

Eu endohedral C60, Eu@C60, has been extracted with aniline from soot prepared by arc-heating of a graphite/Eu2O3 composite rod and obtained at high concentration by combining sublimation and repeated high-performance liquid chromatography. The laser desorption time-of-flight mass spectrum showed a pronounced peak of Eu@C60+. The UV–VIS absorption spectrum of this sample has a red-shift in the onset (>900 nm) in comparison with those for C60 and C70, as expected from electron transfer from the Eu atom to the C60 cage. The valence state of the Eu atom in Eu@C60 has been determined to be +2 by Eu LIII-edge XANES.

Temperature dependence of Raman scattering in a pressure-induced superconductor Cs3C60 was studied under ambient pressure between 2 and 290 K. The contributions of the intramolecular vibration modes to electron–phonon coupling were evaluated by comparing the linewidths of the modes in Cs3C60 with those in pristine C60. The total electron–phonon coupling constant λ was ≈0.18, approximately one-third of the values for Rb3C60 and K3C60. Temperature-dependent Raman scattering in the superconductor Rb3C60 and a non-superconductor Rb6C60 was also measured for comparison.

NaC60 was prepared and identified by Raman spectroscopy. Differential scanning calorimetry showed the existence of two stable phases above and below 280 K. The high-temperature phase was supercooled down to 205 K and further transformed to a glass state below 205 K. X-ray diffraction at 295 K could be indexed by a face-centered cubic lattice. The 23 Na-NMR spectra below 252 K exhibited the second-order nuclear quadrupole effect accompanied by a descent in symmetry at the site occupied by the Na+ ion. An ESR study has shown that the fcc NaC60 becomes nonmagnetic below 180 K.