Lithium Cation Isolated Within Fullerene

Japanese scientists have for the first time isolated and determined the molecular and crystal structure of a cationic metallofullerene, Li@C₆₀ (Nat. Chem., DOI: 10.1038/nchem.698). Although fullerenes with a metal or other small molecule inside the soccer-ball-like structure are nothing new, the lithium in this fullerene cage is both charged and, notably, off-center. Hiroshi Sawa of Nagoya University and Hiromi Tobita of Tohoku University note the ion state has not been seen before in conventional metallofullerenes. Their compound forms (Li@C₆₀)(SbCl₆) crystals (shown) that are 99% pure, a level not reached before, the researchers point out. Metallofullerenes are promising in the field of electronics, but their utility may be limited by their reactivity toward empty fullerenes that coexist in soot and solvent extracts. The crystalline structure prepared by the researchers stabilizes the electrostatic force between the Li⁺ cations and the SbCl₆ ^– anions, preventing unwanted reactions with empty fullerenes. “Such position control by an external field can be widely used in electronics applications, including the single molecular switch and ferroelectric sheets,” Sawa writes.