Valence and crystal fields of endohedral metallofullerenes

摘要

The Raman spectra of endohedral mona-and dimetallofullerenes covering the metals Sc, Y, La, Ce, Sm, Eu, Gd, and Tm were cmpared to the response of empty C_60, D_2-C_84 and D_2d-C_84 in order to assign the metal-carbon cage vibrations. Based on these assignments we have established a well defined relationship betwee the metal-cage bond strength and the electronic state of endohedral rare earth melals. From this a 2+ state follows for Sm, En and Tm and a 3+ state is obtained for La, Ce and Gd. A very good agreement was found for the metal-cage bond strength of mono-and di-yttrium-and cermiumfullerenes indicating a rather samll metal-metal interaction. Finally by a detailed analysis of the metal-cage mode splitting we found that the unit cell of solid D_ad-Y_2@C_84 contains at least 2 molecules as previously reported for D_2d-Sc_2@C_84.