Formation and stability of small metallocarbon clusters: what is the specificity for the formation of stable metallofullerenes?

Abstract

To clarify the specificity for the formation of stable metallofullerenes M@C 82, laser vaporization time-of-flight mass spectroscopy was applied to metal—carbon composite rods, which have been used to produce extractable metallofullerenes. Most of the metal elements in the fourth row of the periodic table (K to Zn), the group IIIA elements (La, Y, and Sc), and some of the lanthanides (Ce, Sm, Eu, Gd, Tb, and Lu) were examined. The results of mass spectra taken by three different modes (positive, negative, and post-ionization) were shown and compared with the laser desorption time-of-flight mass spectra of the metallofullerene-containing crude extract for each element. It was shown that there was a strong correlation between the formation of MC n ( n>4) and the formation of MC 82. Also, a preliminary ab initio calculation was performed, using MC 6 (M = Sc, Y, and K) as typical examples, in order to elucidate the stability and the molecular structure of MC n . It was shown that there was a difference in the binding energy and the optimized molecular structure between the cases of M = Sc, Y, and M = K. All of the above findings strongly support the view that MC n ( n>4) has an important role in the formation process of M@C 82.