Ab Initio Electronic Structure Calculations on Endohedral Complexes of the C₆₀ Cluster

Abstract

In one of the most spectacular chemical discoveries of the last decade, the formation of the C₆₀ cluster (known as buckminsterfullerene, fullerene, [60]-fullerene, and footballene) was first postulated to account for the unusual features in the mass spectra of species produced by laser vaporization of graphite under certain conditions [1]. The original proposal was solely based on an assumption, which was at that time of a rather speculative character, that the highly symmetrical cage structure consisting of 12 five-membered and 20 six-membered rings not only fulfills the condition of saturating all of the carbon valences, but also corresponds to the most stable isomer among the C₆₀ species. Understandably, following the initial discovery, a substantial amount of effort was directed toward either confirming or disproving the assumed structure. One of these attempts took advantage of the fact that the hollow sphere of the C₆₀ cluster should be capable of encapsulat ing small atoms and ions to form inclusion complexes that could be detected by means of mass spectroscopy. Indeed, quite a strong peak indicating the presence of the C₆₀.La molecules was observed in mass spectra of the products obtained from a laser-ablated graphite disk impregnated with LaC1₃ [2]. It is fair to state that the novel concept of endohedral (“insidethecage” [3]) complexes was born as the result of a sheer necessity to prove the cage structure of C₆₀.