Molecular Location Sensing Approach by Anisotropic Magnetism of an Endohedral Metallofullerene

Abstract

Location recognition at the molecular scale provides valuable information about the nature of functional molecular materials. This study presents a novel location sensing approach based on an endohedral metallofullerene, Ce@C82, using its anisotropic magnetic properties, which lead to temperature-dependent paramagnetic shifts in (1)H NMR spectra. Five site-isomers of Ce@C82CH2-3,5-C6H3Me2 were synthesized to demonstrate the spatial sensing ability of Ce@C82. Single-crystal structures, absorption spectra, and density functional theory calculations were used to select the plausible addition positions in the radical coupling reaction, which preferentially happens on the carbon atoms with high electron density of the singly occupied molecular orbital (SOMO) and positive charge. Temperature-dependent NMR measurements demonstrated unique paramagnetic shifts of the (1)H peaks, which were derived from the anisotropic magnetism of the f-electron in the Ce atom of the isomers. It was found that the magnetic anisotropy axes can be easily predicted by theoretical calculations using the Gaussian 09 package. Further analysis revealed that the temperature-dependent trend in the shifts is clearly predictable from the distance and relative position of the proton from the Ce atom. Hence, the Ce-encapsulated metallofullerene Ce@C82 can provide spatial location information about nearby atoms through the temperature-dependent paramagnetic shifts of its NMR signals. It can act as a molecular probe for location sensing by utilizing the anisotropic magnetism of the encapsulated Ce atom. The potentially low toxicity and stability of the endohedral fullerene would make Ce@C82 suitable for applications in biology and material science.

Construction of a Metal‐Free Electron Spin System by Encapsulation of an NO Molecule Inside an Open‐Cage Fullerene C60 Derivative

“…Akasaka and co-workers reported paramagnetic 1 HNMR chemical shifts for Ce@C 82 (3,5-dimethylbenzyl). [25] These shifts are explained as pseudocontact shifts because of the felectron spin. In contrast, our data are rationalized by considering both Fermi contact and pseudocontact terms.…”

“…[24] Therefore,t he signal appears only when NO molecules are trapped in unsymmetrical environments such as zeolites. [25] These shifts are explained as pseudocontact shifts because of the felectron spin. Figure 3.…”

Construction of a Metal‐Free Electron Spin System by Encapsulation of an NO Molecule Inside an Open‐Cage Fullerene C60 Derivative

“…Furthermore, δ fc and δ pc are the functions of 1/ T and 1/ T 2 , respectively (Figure b). Akasaka and co‐workers reported paramagnetic 1 H NMR chemical shifts for Ce@C 82 (3,5‐dimethylbenzyl) . These shifts are explained as pseudocontact shifts because of the f‐electron spin.…”

New Horizons in Chemical Functionalization of Endohedral Metallofullerenes

“…The chemical reactivity of open-shell EMFs has also been explored [8]. Results have revealed that several reactions of open-shell EMFs, particularly those involving radical species, afforded singly bonded derivatives bearing a closed-shell electronic state [53][54][55][56]. Such single-bonding derivatization ability yielding closed-shell products is apparently a general trend for open-shell EMFs, such as trivalent M@C 82 .…”