DIMERIZATION OF C-60 - THE FORMATION OF DUMBBELL-SHAPED C-120

The structures of three possible C-60 dimers with intact cages have be en calculated at the semiempirical (MNDO/ AM-1, PM-3) and ab initio de nsity functional theory (DFT) levels. At the DFT level, both local (LD FT) and nonlocal (NLDFT) calculations have been performed. The dimers are formed by the 1,2-, 1,4-, and 1,2+1,4-cycloadditions of a cyclohex atrienyl unit of each C-60. The energies of the dimers relative to tha t of the most stable 1,2-C-60 dimer are 74.0 kcal/mol (AM-1), 75.2 kca l/mol (PM-3), 69.7 kcal/mol (LDFT), and 76.2 kcal/mol (NLDFT) for the 1,4-C-60 dimer and 93.0 kcal/mol (AM-1), 87.0 kcal/mol (PM-3), 69.8 kc al/mol (LDFT), and 69.5 kcal/mol (NLDFT) for the 1,2+1,4-C-60 dimer. T he dimerization reaction to form the C-60 dimers from C-60 is calculat ed to be weakly endothermic only for the formation of 1,2-(C-60)(2), a nd for the others, the reaction is predicted to be strongly endothermi c. This result suggests that 1,2-cycloaddition is the most plausible s cheme for the dimerization and polymerization of C-60 molecules, if th e cages remain intact.