Novel preparation of endohedral metallofullerenes via laser vaporization of fullerene/metal pellets
Bailey, John Anderson
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Electric-arc vaporization of graphite rod/metal (or metal oxide) mixtures in an inert He atmosphere has been the method of choice for the production of endohedral metallofullerenes (Am@C2n). However, yields of endohedral metallofullerenes have been limited to only a few percent of the total fullerene yield, making the production and isolation of macroscopic quantities (grams) difficult. In the present study, fullerene/metal mixtures have been vaporized using a CO2-laser beam. The sample pellets employed in the laser vaporization were prepared from empty-cage fullerenes (C60, C70, C76, C78, C84, ..• ) and small percentages, by weight, of metal or nletal oxide (La203, SC203, Y 203, Sc, Y, Er). In addition, a sample mixture of a scandium endohedral metallofullerene extract, prepared by electric-arc vaporization, was subjected to the laser. Vaporized samples were analyzed by negative-ion chemical ionization mass spectrometry and by normal phase HPLC. Inert atmospheres of helium, argon, and xenon were compared for optimization of yields of endohedral metallofullerenes, as well as for production of unique endohedral species not observed by production via electric-arc vaporization. Scandium, yttrium, and erbium endohedral metallofullerenes were synthesized by vaporization of fullerene mixtures and the appropriate metal. Optimum conditions were realized with pellet temperatures greater than or equal to 3000°C and inert gas pressures of -100 Torr. This method of CO2 laser vaporization also served as a valuable tool to analyze the production mechanisms of fullerenes and endohedral metallofullerenes, such as production pathways (Le., C60 -> higher fullerenes -> endohedral metallofullerenes).
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