The HSAB principle as a means to interpret the reactivity of carbon nanotubes

Polycyclic curved aromatic fragments (C₂₄H₁₂) have been employed as models of the single-walled carbon nanotubes (n,0), where n varies from 4 up to 30. Those structures were chosen on the basis of the analysis of the strain energy values calculated for the models possessing various sizes. The flat coronene structure has been chosen as a molecular fragment topologically resembling the honeycomb lattice in order to investigate the relation between the curvature and reactivity of the sidewalls of SWNTs. In the current study we took into account the interaction of CO and NH₂ (treated as probe molecules) with the exterior surface of nanotubes. Obtained results illustrate that both total as well as local hardness and/or molecular electrostatic potential (MEP) can be a good measure for the reactivity if the influence of geometrical changes is considered. The systematic theoretical studies also show that the calculated interaction energies of sorbed CO on those models are related to the both types of hardness. On the other hand, in the case of amidogen sorbed on the nanotube surface the correlation between the binding energy and MEP is visible. Those differences can be explained by various kinds of the adsorption mechanism, i.e. physical or chemical adsorption, respectively.