The structures of C60F36 and new possible structures for C60H36

The structures and stabilities of various isomers of C60F36 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-C6F3 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 C5F3 faces and all isolated carbon-carbon double bonds are on pent-hex edges. Two isomers are known experimentally for C60F36 The major isomer appears consistent with the most stable C-3 structure and the minor isomer with the T structure. In contrast to C60F36, the most stable isomer for C60H36 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). (C) 1999 Elsevier Science B.V. All rights reserved.