Quantum chemical calculations and NMR spectroscopic data suggest that the two isomers of Y@C82(CF3)5 prepared by trifluoromethylation of the endohedral metallofullerene (EMF) contain chains of four 1,4‐C6(CF3)2 edge‐sharing hexagons (see picture). In striking contrast to the empty fullerenes, which form complex mixtures with up to 22 CF3 groups, EMF Y@C82 only forms products with one, three, and five CF3 groups.

We have examined various parameters of the electric arc synthesis of endohedral metallofullerenes (EMFs or M@C2 n ). The influence of some experimental parameters (M/C ratio, helium vapor pressure, and values of the direct current arc) on yields of EMFs has been studied. The optimization of these parameters allows us to bring the EMF yield to a record level of 6−8% of the primary soot mass. Furthermore, a selective extraction sequence [o-xylene (five cycles) − dimethylformamide (seven cycles)] has been studied in detail in order to apply this technique to the estimation of the EMF yield. It has also been shown that polar organic solvents, among them dimethylformamide (DMF), dimethylacetamide (DMA), and dimethylsulfoxide (DMSO), are the most favorable ones for a selective extraction of EMF.