NCI analysis of the interaction cation⋯π in complexes with molecular bowls derived from fullerene

A systematic study based on the non-covalent interactions (NCI) index was carried out in order to analyze the characteristics of the cation⋯π interaction in complexes formed by alkaline cations (Li+, Na+, K+, Rb+, and Cs+) and molecular bowls of increasing size, going from corannulene, C20H10, to the fully closed buckminsterfullerene, C60. For this purpose all the possible inner complexes with the cation on the bottom of the bowl were studied. SCF densities were employed at the B3LYP/6-31 + G∗ level (LANL2DZ effective core potential basis set was included for Rb+ and Cs+). NCI plots allowed to visualize the characteristics of the cation⋯π interaction; showing the spatial arrangement of the interaction and locating the regions of different interaction strength. Moreover, when the comparison of NCI plot is carried out in an adequate way, an excellent correlation with the calculated complexation energies was found. Finally, in order to obtain complementary data, QTAIM calculations were carried out for several complexes, locating critical points and bond paths.