PURIFICATION OF C-60 AND C-70 BY SELECTIVE COMPLEXATION WITH CALIXARENES

MOLECULAR complexation of fullerenes in host-guest complexes has the potential to afford efficient large-scale purification of fullerenes(1). This method would avoid the losses inherent in the chromatographic techniques currently in use, which arise from irreversible absorption on the stationary phase(2). Several host-guest interactions have been reported for C-60, including the formation of complexes with 1,4-hydroquinone(3,4), azacrown compounds(5), certain water-soluble macrocycles such as gamma-cyclodextrin(6-8), and complexation between C-60 and an iridium phosphine in which pendant groups attached to a phosphorus atom form a cradle for an adjacent C-60 molecule(9). Other relevant studies are the inclusion of C-60 into a microporous aluminophosphate(10) and the formation of a charge-transfer complex between C-60 and a thiafulvalene(11). Here we show that both C-60 and C-70 Will form discrete complexes with calixarenes, howl-shaped macrocycles with hydrophobic cavities. Complexation of p-Bu'-calix[8]arene with a mixture of the toluene extract of 'crude' fullerene soot, followed by a series of recrystallizations, affords >99.5% pure C-60. Our approach could lead to a substantial reduction in the cost of purifying C-60 and C-70.