STEREOCHEMICAL PATTERNS IN BROMOFULLERENES, C60BR12 TO C60BR24

The stabilities of different isomers of C60Brn have been calculated fo r n = 14-24. Two types of structure are found to be important. The fir st type involves the linking of alternating 1,4-C6Br2 rings and 1,3-C6 Br2 rings, forming -Br-BrBr-Br- strings over the molecule. Additional stability is achieved if the string ends are eliminated by the formati on of cyclic strings, and particularly stable structures incorporate t he Br-12 cycle of S-6 symmetry. The strings may branch at 1,3,5-C6Br3, rings with the formation of polycyclic string structures, culminating in the rhombicuboctahedral bromine pattern in C60Br24 These patterns are related to the conformation of the Cg rings, which form shallow bo ats in 1,4-C6Br2 and chairs in 1,3,5-C6Br3. A second important structu ral feature is the presence of discrete Br-6 skew pentagonal pyramids, one in C60BT6, two in C60Br12 and three in C60Br18 These results indi cate the possibility of forming C60Br12 and C60Br18 under the appropri ate conditions.