Searching for stable hept‐C 62 X 2 (X = F, Cl, and Br): Structures and stabilities of heptagon‐containing C 62 halogenated derivatives

To determine the geometries of the most stable hept‐C 62 X 2 (X = F, Cl, and Br) isomers, all 967 possible hept‐C 62 F 2 isomers have been orderly optimized using AM1, HF/STO‐3G, B3LYP/3‐21G, and B3LYP/6‐31G* methods, and chlorofullerenes and bromofullerenes, which are isostructural with five most stable hept‐C 62 F 2 isomers, were regarded as candidates of the most stable isomer, and optimized at the B3LYP/6‐31G* level. The results reveal that 2,9‐ and 9,62‐hept‐C 62 X 2 (X = F, Cl, and Br) are the two most stable isomers with slight energy difference. The halogenation releases strain energy of hept‐C 62 , and all halogenated fullerenes are more chemically stable than hept‐C 62 with lower E HOMO and higher E LUMO . All five most stable hept‐C 62 X 2 (X = F, Cl, and Br) isomers are energetically favorable, and their thermodynamic stability decreases along with the increase of sizes of addends. Only hept‐C 62 F 2 isomers show high thermodynamic stability, and they are potentially synthesized in experiments. 59,62‐squ‐C 62 X 2 (X = F, Cl, and Br) were computed for comparison, and they are found to be more stable than their heptagon‐containing isomers. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008