ENDOHEDRAL CHEMISTRY - ELECTRONIC-STRUCTURES OF MOLECULES TRAPPED INSIDE THE C60 CAGE

Ab initio electronic structure calculations, carried out at the Hartree-Fock level, reveal that the C60 carbon cage (''footballene'') is capable of encapsulating small molecules to form endohedral (''inside a cage'') complexes in which the guest molecules remain positioned close to the center of the cage while being able to tumble freely. In these unusual systems, the cage acts as a polarizable sphere that stabilizes the polar molecules and destabilizes the nonpolar ones. This conclusion is drawn from studies on the C60.H2, C60.N2, C60.CO, C60.HF, C60.LiH, and C60.LiF complexes for which the equilibrium bond lengths of the guests, the frequencies of vibrational and librational motions, the stabilization energies, the GAPT charges, and the dipole moments were calculated. The present study raises the possibility of the existence of endohedral complexes in which the guest molecules are expected to exhibit properties radically different from those in the gas phase.