Computing fullerene encapsulation of non-metallic molecules: N₂@C₆₀ and NH₃@C₆₀

Abstract

Some endohedral fullerenes have been considered as possible candidate species for molecular memories. Recently, the encapsulation inside the fullerene cages has been extended from atoms to small molecules, for example the nitrogen molecule was placed inside the fullerene cage. The observed N₂@C₆₀ endohedral is computed in the paper together with NH₃@C₆₀, which was not yet observed. The computations are based on structural optimizations using density-functional theory (DFT) methods. In the optimized structures, the analytical harmonic vibrational analysis was carried out and the encapsulation energetics were evaluated using the second order Møller-Plesset (MP2) perturbation treatment. The lowest-energy structure has the N₂ unit oriented towards a pair of parallel pentagons so that the complex exhibits D _5d symmetry. At the MP2 level, the encapsulation of N₂ into C₆₀ brings a potential energy gain of − 9.3 kcal/mol while that for NH₃ is − 5.2 kcal/mol. The entropy term is also evaluated, yielding the standard Gibbs-energy change at room temperature for the encapsulation of N₂ and NH₃ of − 2.6 and 1.5 kcal/mol, respectively. Some computed structural and vibrational characteristics are also reported. Emerging broader landscape of future applications of such encapsulates in nanoscience and nantechnology is discussed.

Keywords:

• Endohedral fullerenes
• Bonding and stability
• Gibbs-energy evaluations
• Molecular encapsulation
• Carbon-based nanoscience

Acknowledgements

The reported research has been supported by a Grant-in-aid for NAREGI Nanoscience Project, and for Scientific Research on Priority Area (A) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, and by the Czech National Research Program “Information Society” (Czech Acad. Sci. 1ET401110505).