Complexation of Higher Fullerenes by Calix[5]arene-Based Host Molecules

The binding abilities of calix[5]arene-based host molecules for higher fullerenes (C₇₆, C₇₈, and C₈₄) were investigated in organic solvents. The binding abilities of double-calix[5]arenes to higher fullerenes are high. In particular, their association constants to C₇₆ and C₇₈ in toluene reached at the order of 10⁵ M⁻¹. In contrast, the binding abilities of simple calix[5]arenes decreased as increasing the size of the fullerenes. Accordingly, linking two calix[5]arenes with the covalent bonds creates the large cavities, complementary to higher fullerenes. The structure of the host-guest complex of double-calix[5]arene and C₇₆ was discussed. The carbons of the polar end of C₇₆ characteristically shifted upfield more than the other carbons in the host-guest complex, indicating that these polar carbons reside most deeply inside the cavity of the calix[5]arene.