Endohedral metallofullerenes

Abstract

Endohedral metallofullerenes (fullerenes with metal atom(s) encapsulated) are novel forms of fullerene-based materials which have attracted wide interest during the past eight years, not only in physics and chemistry but also in such interdisciplinary areas as materials and biological sciences. In this paper, advances in the production, separation (isolation) and various spectroscopic characterizations of endohedral metallofullerenes are presented in an attempt to clarify their structural, electronic and solid state properties. Endohedral metallofullerenes are normally produced by DC electric arc discharge of metal/graphite composite rods used as positive electrodes. The metallofullerenes can also be produced by the so-called laser furnace method which incorporates laser vaporization of the composite rods under high temperature (ca 1000 • C). The endohedral metallofullerenes so far produced are centred on group 2 and 3 metallofullerenes such as Sc, Y, La, Ca, Sr and Ba as well as lanthanide metallofullerenes (Ce-Lu). These metal atoms have been encapsulated in higher fullerenes, especially in C 82 . These metallofullerenes have easily been extracted by solvents from primary soot. By using an elaborate high-performance liquid chromatography technique, the metallofullerenes are completely purified and isolated like C 60 and C 70 . Synchrotron x-ray diffraction, 13 C NMR and ultra-high vacuum scanning tunnelling microscopy (UHV-STM) studies have revealed that metal atoms are indeed encapsulated by the carbon cage and that the metal atoms are not in the centre of the fullerene cage but very close to the carbon cage, indicating the presence of a strong metal-cage interaction. It has been revealed by electron spin resonance and also by theoretical calculations that substantial electron transfers take place from the encaged metal atom to the carbon cage: intrafullerene electron transfers. Good examples are lanthanum and yttrium metallofullerenes which have the charge states of La 3+ @C 3− 82

Carrier transport properties of nanocrystalline Er3N@C80

“…One of their interest properties is a charge transfer from the endohedral atoms to the fullerene cage. The charge transfer has been widely investigated, [9][10][11][12][13] as these materials are expected to display remarkable electronic and structural properties associated with this charge transfer. Among these endohedral fullerenes, trimetallic nitride endohedral fullerenes (TNEFs), such as Sc 3 N@C 80 and Er 3 N@C 80 , can be obtained in large yield and evaporated onto heated substrates 14 because of their thermal stabilities.…”

Modification of the conductance of single fullerene molecules by endohedral doping

“…8 Endohedral doping of hollow carbon cages represents a way to impose new functional properties on the fullerene-based single molecule devices due to the possibility of changing the electronic and magnetic properties of the molecules while preserving their unique highly symmetric outer shell. 9 The symmetry of metallofullerenes results in easier selforganization, and simpler bonding schemes to electrodes than observed, e.g., in molecular devices based on alkane derivatives. 10 We show that for Ce 2 @C 80 the endohedral doping reduces the conductance in a single molecule junction compared to that of C 60 .…”

Unveiling Metal-Cage Hybrid States in a Single Endohedral Metallofullerene

“…The combined technique provides promising applications in the fields of in situ characterization and diagnostics of metallofullerene-based nanodevices. DOI: 10.1103/PhysRevLett.91.185504 PACS numbers: 61.48.+c, 31.15.Ew, 68.37.Ef, 73.22.-f Endohedral metallofullerenes have been a subject of intensive investigation in recent years, not only because of their structural and electronic novelties but also because of their promising electronic, optical, and biomedical applications [1]. The location of metal atoms inside the fullerene cage and the metal-cage interaction are two central issues.…”

“…Endohedral metallofullerenes have been a subject of intensive investigation in recent years, not only because of their structural and electronic novelties but also because of their promising electronic, optical, and biomedical applications [1]. The location of metal atoms inside the fullerene cage and the metal-cage interaction are two central issues.…”