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We have applied density functional theory calculations to devise stable arrangements of chlorofluorofullerenes (CFFs). In the case of C60ClF and C60Cl2F2, an extensive isomer search shows that the most stable configurations are those with two halogens located on the corannulene-like structure. In general, 1,2-adduct is more stable than 1,4-adduct and 1,2 addition across 6–6 bonds is more stable than 1,2 addition across 5–6 bonds. The formation of a CFF from chlorofullerene is exothermic while chlorination of a fluorofullerene is endothermic. For C60Cl18-3nF3n (n = 0, 1, 2, 3, 4, 5, and 6), the binding energies decrease as the number of Cl atoms increases and the energy differences between isomers with the same formula are small. The 13C NMR patterns of C60Cl18-3nF3n (n = 0, 1, 2, 3, 4, 5, and 6) are divided into two parts: δiso values of chlorinated and fluorinated carbons shift to low field and appear in the range of 65.1–100.2 and 84.5–97.4 ppm; two peaks related to C sites on the cyclohexatriene pole and the flattened equatorial belt separating the two hemispheres appear at 120.2–123.4 and 125.8–129.1 ppm, respectively. Negative nucleus independent chemical shift (NICS) in interior positions of rings or cages indicates the presence of induced diatropic ring currents which suggests that cyclohexatriene poles can be considered as benzenoid fragments. NICS yields minor value (−2.7 ppm) at the ring center of polar pentagons of C60Cl10F10, and significantly negative values in the cage center.
KeywordsChlorofluorofullerenes Binding energy DFT NMR NICS
We are grateful to Professor Seik Weng Ng for making us available his software (G98W) and hardware (machine time) facilities. The financial support of Research Council of Shahid Beheshti University is gratefully acknowledged.
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