Trapping N5 rings and N3 chains on the outer surface of fullerene C60: a theoretical study

The capture of N-3-chains and N-5-rings on the outer surface of C-60 was studied using density functional calculations. For the neutral N-5-ring, it was found that a N-5-ring trapped by a C-60 cage becomes more stable than an isolated N-5-ring radical, and a C-60-N-5 compound with a C-N bond at an exohedral position of C-60 is more stable than an isomer with the N-5-ring encapsulated in C-60. Such stability arises from the reduction in molecular strain energy, and charge transfer from C-60 to N-5. Dynamics calculations indicate that capture of the N-5-ring on the outer surface of C-60 is a barrierless process. Furthermore, the trapping sites of more N-5-rings on the C-60 were determined using condensed Fukui functions, where the N-5-rings prefer to be trapped on the surface to form addition products across 6,6-junctions. Based on the optimized geometries of C-60-(N-5) n ( n= 2, 6, 10), their chemical stabilities were found to be comparable with that of C-60 in terms of the gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals. Similar phenomena were found for an N-3-chain wrapped on the surface of C-60. However, the results of the average adsorption energies show that C-60 can capture N-5-rings more effectively than N-3-chains.