Carbon nanotube container: Complexes of C ₅₀H ₁₀ with small molecules

The stability of complexes of a recently synthetized (Scott et al. J. Am. Chem. Soc.2011, 134, 107) opened nanocontainer C ₅₀H ₁₀ with several guest molecules, H ₂, N ₂, CO, HCN, H ₂O, CO ₂, CS ₂, H ₂S, C ₂H ₂, NH ₃, CH ₄, CH ₃CN, CH ₃OH, CH ₃CCH, 2-butyne, methyl halides, and with noble gas atoms, has been examined by means of symmetry-adapted perturbation theory of intermolecular interactions, which fully incorporates all important energy components, including a difficult dispersion term. All complexes under scrutiny have been found stable for all studied guests at 0 K, but entropic effects cause many of them to dissociate into constituent molecules under standard conditions. The estimation of temperature at whichthe Gibbs free energy δG = 0 revealed that the recently observed (Scott et al. J. Am. Chem. Soc.2011, 134, 107) complex CS ₂@C ₅₀H ₁₀ is the most stable at room temperature while the corresponding complexes with HCN and Xe guests should decompose at ca. 310 K and that with CO ₂ at room temperature (ca. 300 K). In agreement with the δG estimation, molecular dynamics simulations performed in vacuum for the CS ₂@C ₅₀H ₁₀ complex predicted that the complex is stable but decomposes at ca. 350 K. The MD simulations in CHCl ₃ solution showed that the presence of solvent stabilizes the CS ₂@C ₅₀H ₁₀ complex in comparison to vacuum. Thus, for the complexes obtained in solution the CO ₂ gas responsible for the greenhouse effect could be stored in the C ₅₀H ₁₀ nanotube.