Hydrides and dimers of C58 fullerenes: structures and stabilities

A density functional theory (DFT) study of fullerene hydrides C58H2x (2x = 2,4,...,34) is presented. We consider two relevant isomers, the most stable classical isomer C-58-C-3v and the energetically close non-classical isomer C-58-C-s, which contains a heptagonal ring. Iterative pairwise addition of hydrogen atoms to only the energetically favoured products of the previous iteration yields a set of low energy structures for each composition. From these, low energy pathways are extracted. Analysis of the C-H binding energies along the reaction pathways is performed to identify particularly stable hydride compositions. These are 2x = 6,18,28,34 for C-58-C-s and 2x = 10,26,30 for C-58-C-3v. We therefore suggest that these hydrides are preferably formed in hydrogenation experiments and that it should be possible to distinguish between the two C-58 isomers. We further investigate the dimer formation based on low energy C58H2 addition patterns. All dimers show binding energies of more than 1 eV whereby dispersion interactions play a significant role. Both C-58 isomers can also undergo further aggregation. This leads us to the conclusion that in the absence of other reactant molecules C-58 will form intercage bonds and cannot be isolated in molecular form, which is in accordance with experimental results.