Different Extraction Behaviors between Divalent and Trivalent Endohedral Metallofullerenes

On the basis of high-yield preparation, arc-produced soot containing endohedral Y, La, Nd, Sm, Gd, Tb, Yb, Ca, and Ba fullerenes are successively extracted with carbon disulfide, N,N-dimethylformamide, pyridine, and aniline. The continuous four-step extraction procedure generates endohedral metallofullerenes (EMFs) with high content and abundant species, and novel EMFs such as Tb@C66, Yb@C60, and Tb3@C80 were extracted. This makes it possible for us to systemically study the varying extraction behaviors of divalent and trivalent metallofullerenes. Trivalent EMFs are characterized by higher content and multimetallofullerenes, whereas divalent species are characterized by lower content and solely monometallofullerenes. A positive relationship between the content and the species abundance of EMFs is proposed. The differences in extracting ability of the above solvents toward certain EMFs are summarized and explained on the basis of the number of transferred electrons from the encaged metal atom(s), the back-donation from carbon cages, and the solvent reduction of EMFs.