Valence π-bonding  Dewar Structures and Free π-Radical Structures of Metallofullerenes
CHIU Ying-Nana, XIAO Ji-Mei, XIAO Xing-Cai, HUANG Wen-Xiu, LI Norman N.
Chem. J. Chinese Universities . 1997, (7): 1147 -1152 .