Theoretical Study of Host-Guest Interaction in Model Endohedral Fullerenes with CH_4 and He_4 into the C_(60)H_(36), C_(60)H_(24), C_(84) and C_(60) Cages

摘要

The equilibrium geometrical parameters, dissociation energies, vibrational frequencies, and magnetic shielding constants of a series of model endohedral fullerene complexes with the CH_4 molecule or four He atoms inside the C_(60)H_(36) (T), C_(60)H_(24) (T), C_(84) (T_d), and C_(60) cages were calculated at the 6-31G and 6-31G~* DFT B3LYP levels. The effect of the size and shape of the encapsulated particle and the cavity on the host-guest interaction and its manifestations in the properties of endofullerenes were studied. The calculations predict that the encapsulation of CH_4 or He_4 slightly affects the properties of the cages but is accompanied by the contraction of the guest, large hypsochromic shifts of its stretching vibration frequencies (v(CH) approx= 50-150 cm~(-1)), and an increase in the magnetic shielding constants of the guest atoms (DELTA sigma(C) approx= 5 ppm, DELTA sigma (H) approx= 7 ppm, DELTA sigma (He) approx= 8 ppm). The shifts DELTA v and DELTA sigma decrease with an increase in the size of a cage as the match between the cage and guest shapes becomes better; however, these shifts remain considerable even in the "spacious" cluster CH_4@C_(84) and can easily be monitored by IR and Raman spectroscopy and NMR.