SYNTHESIS, EXTRACTION AND ELECTRONIC-STRUCTURE OF CE-AT-C-2N

In view of the growing interest in endohedral lanthanide fullerenes, C e, as a typical +4 oxidation state lanthanide element, has been system atically studied. The synthesis, extraction and electronic structure o f Ce@C-2n are investigated. Soot containing Ce@C-2n was synthesized in high yield by carbonizing CeO2-containing graphite rods and are back- burning the CeC2-enriched cathode deposit in a DC are plasma apparatus . Ce@C-2n, dominated by Ce@C-82, can be efficiently extracted from the insoluble part of the soot after toluene Soxhlet extraction by pyridi ne at high temperature and high pressure in a closed vessel. About 60% Ce@C-2n (2n = 82,80,78,76) and 35% Ce@C-82 can be enriched in the pyr idine extract. This fact is identified by desorption electron impact m ass spectrometry (DEI MS). The electronic structure of Ce@C-2n is anal yzed by using X-ray photoemission spectroscopy (XPS) of pyridine-free film. It is suggested that the encapsulated Ce atom is in a charge sta te close to +3 and was effectively protected from reaction with water and oxygen by the enclosing fullerene cage. Unlike theoretical expecta tion, the electronic state of Ce@C-82 is formally described as Ce+3@C- 82(3-). (C) 1997 Elsevier Science Ltd.