Relative Yields of Endohedral Lanthanide Metallofullerenes by Arc Synthesis and Their Correlation with the Elution Behavior

Fourteen endohedral lanthanide metallofullerenes were synthesized using the arc-discharge method under identical conditions, and their relative yields and elution behavior have been studied by mass spectrometry and HPLC. The eluate around the M@C 82 peak (M = lanthanide metal) was collected in two fractions of equal amount. The DCI negative ion mass spectrum of each metallofullerene in each collected fraction was well resolved on the basis of the characteristic isotopic distribution. The relative yield of these metallofullerenes was found to be in the following order: Ce > Pr > Tb > Gd > Nd > La ∼ Er > Ho > Dy > Lu ≫ Tm ∼ Sm ∼ Eu ∼ Yb. The order of their retention times (Tb > Gd > Pr > Ce > Er ∼ Lu > La ∼ Ho > Nd > Dy ≫ Tm ∼ Sm ∼ Eu ∼ Yb) was also obtained by comparing the mass peak intensities of each metallofullerene from the two HPLC fractions. A fairly good correlation between these two sequences is identified and discussed.