Interactions between cation-encapsulated single-walled carbon nanotubes M+@SWNT (M+ = H, Li, Na) and nucleophiles

The intermolecular forces between cation-encapsulated single-walled carbon nanotubes M+@SWNT (M+ = H, Li, Na) and five nucleophiles (H2O, CH3OH, HF, CH3SH and CH3NH2) were studied in the frame of the density functional theory. It was shown that molecular adsorptions of CH3OH and H2O on lithium, sodium and hydrogen cations encapsulated within SWNT are stabilized by ion-mediated interactions. Furthermore, they are preferred as compared to the corresponding adsorptions of HF, CH3SH and CH3NH2. The diffusion of ions into the SWNT cavity was not observed because their presence was the main factor in promoting a highly selective stability in the complexes formed. The bond dissociation enthalpies favor the stability of the complexes interacting with H2O and CH3OH in ca. 2 and 4 kcal mol−1. This fact shows that the doping of pristine carbon nanotubes with ions can strongly enhance interactions with nucleophiles that contain –OH electronegative groups. However, with HF, CH3SH and CH3NH2, the dissociation occurs spontaneously and the nucleophiles react with SWNT whenever the ions do not form part of the complexes. The degree of attractive interaction for the ions follows this order: Li+ ≈ Na+ > H+.