Isolation of two seven-membered ring C-58 fullerene derivatives: C58F17CF3 and C58F18

Fluorination of C-60 at 550 degrees C leads to milligram quantities of two stable fullerene derivatives with 58-carbon cage structures: C58F18 and C58F17CF3. The compounds were characterized by mass spectrometry and fluorine nuclear magnetic resonance spectroscopy, and the data support a heptagonal ring in the framework. The resulting strain, which has hindered past attempts to prepare these smaller quasi-fullerenes, is mitigated here by hybridization change of some of the carbons in the pentagons from sp(2) to sp(3) because of fluorine addition. The loss of carbon from C-60 is believed to occur via sequential fluorine addition to a C-C single bond and an adjacent C=C bond, followed by loss of a :CF2 carbene.