Small Molecules in C60 and C70: Which Complexes Could Be Stabilized?

The recent syntheses of complexes involving some small molecules in opened fullerenes and those of hydrogen molecule(s) in C60 and C70 are accompanied in the literature by numerous computations for endohedral fullerene complexes which cope with the problem of the stability of these complexes. In this contribution, stabilization energies of endohedral complexes of C60 and C70 with H2, N2, CO, HCN, H2O, H2S, NH3, CH4, CO2, C2H2, H2CO, and CH3OH guests have been estimated using symmetry-adapted perturbation theory, which, contrary to the standard DFT and some other approaches, correctly describes the dispersion contribution of the host-guest interactions. On the basis of these calculations, the endohedral complexes with all these guests were found stable in the larger fullerene, while the C60 cage was found too small to host the latter four molecules. Except for H2 and H2CO, a stabilization effect for most guests in the C60 cage is about 30 kJ/mol. For H2 and H2O guests, a typical supramolecular effect is observed; namely, the stabilization in the smaller cage is equal to or larger than that in the larger C70 host. Except for the water molecule where the induction interaction plays a non-negligible role, in all complexes the main stabilization effect comes from the dispersion interaction. The information on the stability of hypothetical endohedral fullerene complexes and physical factors contributing to it can be of importance in designing future experiments contributing to their applications.