In our program of fluorinating fullerenes by metal fluorides under vacuum followed by HPLC separation of the products, we have isolated and in many cases fully characterized the following: C 60 F 2 , [1] C 60 F 16 , [2] C 60 F 18 , [3,4] C 60 F 36 (two isomers), [5] C 60 F n O (n 4, 6, 8), [6] C 60 F 18 O (three isomers), [7,8] C 60 F 18 O 2 (seven isomers), [9] C 60 F 17 CF 2 CF 3 , [10] C 60 F 17 CF 3 (two isomers), [10] forty-nine derivatives of [70]fullerene, [11] C 76 F n (n 36, 38, 40, 42, 44), C 78 F n (n 38, 42), C 82 F 44 , C 84 F 40 , and C 84 F 44 . [12] The success in this work is due to the high polarity of the fluorofullerenes, which results in the derivatives having significantly different retention times. Moreover, they have substantial solubility in both toluene and alkanes, which further facilitates the separations.
Many of these components have been formed through fluorination with K 2 PtF 6 under vacuum at approximately 465 8C, the major product under these conditions being C 60 F 18 . During preparation of a larger amount of this material, we isolated many other components, including a number of ethers (oxahomofullerenes) and bis-ethers. [7±9] One of the latter was accompanied by a shoulder peak of 75 min retention time which gave a mass spectrum showing the presence of C 60 F 20 with the typical À n F fragmentation pattern, but the amount was insufficient for further characterization.
Subsequently we have scaled-up the preparation through the use of an MnF 3 /KF fluorinating mixture. Whereas fluorination of [60]fullerene with MnF 3 gives mainly C 60 F 36 , [5] addition of an equimolar amount of KF reduces the overall fluorinating ability and gives greater yields of products with lower fluorine content, including C 60 F 18 and C 60 F 20 . The isolated amount of the latter (1 ± 2 mg) was sufficient for spectroscopic study and we now report its extraordinary structure.