The structures of C 60F 36 and new possible structures for C 60H 36

Abstract

The structures and stabilities of various isomers of C 60F 36 containing a three-fold axis have been calculated using the AM1 Hamiltonian and the program MOPAC 6.0. Three isomers of C 3, T and S 6 symmetry, are significantly more stable than all other isomers. The tetrahedral T structure contains four isolated unfluorinated C 6 rings and was described previously. The more stable C 3 structure is closely related, but one of the C 6 rings is converted to a 1,3,5-C 6F 3 ring in a chair conformation with three radiating carbon–carbon double bonds. In the S 6 structure there are two unflourinated C 6 rings on opposite sides of the molecule. In each structure, there are twelve C 5F 3 faces and all isolated carbon–carbon double bonds are on pent–hex edges. Two isomers are known experimentally for C 60F 36. The major isomer appears consistent with the most stable C 3 structure and the minor isomer with the T structure. In contrast to C 60F 36, the most stable isomer for C 60H 36 is the S 6 isomer, although in this case the energy difference between the ten most stable isomers is less than 15 kcal mol − 1.