Recently, our group has reported anisotropic magnetism of an endohedral metallofullerene (EMF) Ce@C82 both in a pristine form and chemically functionalized form.1,2 Remarkably, the anisotropy of the magnetism which is led by the encapsulated Ce atom was slightly influenced by the carbene addition reaction. In addition, absolute position of the hydrogen atoms of the addend were assigned by the difference in the effective distance of the anisotropic magnetism, which is decreased with the cube of distance between the Ce and hydrogen atoms.
In this study, we have developed Ce@C82 derivatives that demonstrate a potential of EMFs for location recognition in molecular-scale. Five derivatives of Ce@C82 were successfully synthesized and isolated by a similar radical reaction that we reported recently.3 Addition position of the two isomers of them were unambiguously determined by a single crystal structure and/or characteristic absorption spectra. DFT calculations provide reasonable criteria to predict the addition position by the radical coupling reaction. The carbon atoms that have high SOMO density and positive charge are preferable for the addition position.
Temperature-dependent 1H-NMR measurements demonstrated unique paramagnetic shifts that are derived by the anisotropic magnetism of the Ce atom. And further analysis of the shifts revealed the dependency of the shift based on the distance and relative position from the Ce atom. This result indicates that the paramagnetic shifts provide location information of the addend. Therefore, Ce@C82 is capable to act as an molecular probe for location recognition of atoms by utilizing anisotropic magnetism of an EMF.
Reference:
1. T. Wakahara et al. J. Am. Chem. Soc. 2004, 126, 4883-4887.
2. Y. Takano et al. J. Am. Chem. Soc. 2009, 131, 9340-9346.
3. Y. Takano et al. J. Am. Chem. Soc. 2008, 130, 16224-16230.