Theoretical Study of Host-Guest Interaction in Model Endohedral Fullerenes with Tetrahedral Molecules and Ions of MH4 Hydrides inside the C_(60)H_(36), C_(60)H_(24), C_(84), and C_(60) Cages

摘要

The equilibrium geometrical parameters, dissociation energies, normal vibration frequencies, ion-ization potentials, electron affinities, and magnetic shielding constants of a series of model endohedral fullerenes with hydride molecules and ions MH_4 = BH~(-)_4, CH_4, NH~(+)_4, A1H~(-)_4, SiH_4, and PH~(-)_4 inside the C_(60)H_(36) (T), C_(60)H_(24) (T), C_(84) (T_d), and C_(60) cages were calculated by the density functional theory B3LYP method with the 6-31G and 6-31G* basis sets. The effect of the steric and electronic factors (the charge and size of the encapsulated particle and the shape of the cavity, etc.) on the host-guest interaction and its manifestations in the properties of endofullerenes were studied. The encapsulation of neutral MH_4 hydrides slightly affects the properties of the cages; however, it is accompanied by the contraction of the guest, large hypsochromic shifts of its stretching vibration frequencies delta nu, and a significant increase in the magnetic shielding constants of the guest atoms(delta sigma). The encapsulation of MH~(+ -)_4 ions leads to redistribution of electron density between the guest and the cage and to considerable shifts of frequencies delta nu and constants delta sigma of the cage atoms. These shifts increase with an increase in the size and negative charge of the guest and decrease as the cage becomes larger and as the match between the cage and guest shapes becomes better; however, these shifts remain considerable even in the "spacious" clusters MH_4@C_(84_ and can easily be monitored by IR and Raman spectroscopy and NMR.