Crystal Structure Analysis of Salts and Derivatives of Cationic Lithium Endohedral Fullerene

Monday, 25 May 2015: 10:00
Lake Ontario (Hilton Chicago)
S. Aoyagi (Nagoya City University), H. Ueno (Nagoya University), H. Kawakami (The University of Tokyo), K. Nakagawa (Osaka University), H. Okada (The University of Tokyo), N. Ikuma, K. Kokubo (Osaka University), Y. Matsuo (The University of Tokyo), and T. Oshima (Osaka University)
Cationic lithium endohedral fullerene, Li+@C60, has a high tendency to form ion-pair states with anions. The strong intermolecular electrostatic attraction builds unique crystal structures such as the rock-salt structure [1]. The coordinated anions in the crystal affect the position and thermal motion of the encapsulated Li+ cation. The endohedral structure of Li+ cation should be also affected by chemical functionalization. Recently we synthesized a cyclohexadiene adduct of Li+@C60 by the Diels-Alder reaction [2]. The lower LUMO level of Li+@C60 accelerates the reaction late 2,400 times faster than that of empty C60. The salt of Li+@C60(C6H8) with TFPB- (tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) was crystallized by a vapor diffusion method. The single crystal structure analysis was performed by means of the synchrotron-radiation X-ray diffraction. The crystal structure shows that the addition of C6H8 to the C60 cage occurred at the [6,6]-bond to have Cs symmetry. On the other hand, the encapsulated Li+ cation is localized under a six-membered ring so that the Cs symmetry of the molecule is broken in the crystal. The peculiar Li+ localization would be a result of an electrostatic interaction with the coordinated TFPB- anions and the addition of C6H8

[1] S. Aoyagi et al., Angew. Chem. Int. Ed. 2012, 51, 3377-3381.

[2] H. Ueno et al., J. Am. Chem. Soc. 2014, 136, 11162-11167