Mechanochemical synthesis and characterization of the fullerene dimer C120

The bulk synthesis of the [2 + 2] dimer of fullerene C-60 was achieved by the solid-state mechanochemical reaction of C-60 with KCN by the use of a high-speed vibration milling (HSVM) technique. This reaction took place also by the use of potassium salts such as K2CO8 and CH3CO2K, metals such as Li, Na, K, Mg, Al, and Zn, and organic bases such as 4-(dimethylamino)- and 4-aminopyridine, Under optimum conditions, the reaction afforded only the dimer C-120 and unchanged C-60 in a ratio of about 3:7 (by weight) regardless of the reagent, used. The dimer C-120 was fully characterized by IR, W-vis, C-13 NMR, and TOF MS spectroscopies, cyclic voltammetry, and differential scanning calorimetry. Comparison of the IR and C-13 NMR spectral data of C-120 with those reported for all-carbon C-60 polymers implied that, the [2 + 2] dimer Ciao represents the essential subunit of these polymers. The dimer C-120 underwent facile dissociation into two C-60 molecules by heat, HSVM treatment, exposure to room light, or electrochemical reduction. The dimer C-120 encapsulating He-3 in one of the C-60 cages was synthesized and was used to confirm the scrambling of a C-60 cage between the monomer and the dimer during the HSVM reaction. A possible mechanism for the selective formation of the dimer C-120 is proposed.