Complexation of higher fullerenes by calix[5]arene-based host molecules

The binding abilities of calix[5]arene-based host molecules for higher fullerenes (C-76, C-78, and C-84) were investigated in organic solvents. The binding abilities of double-calix[5]arenes to higher fullerenes are high. In particular, their association constants to C-76 and C-78 in toluene reached at the order of 10(5) 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 C-76 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.