Solubility of fullerenes



The solubility of fullerenes is generally low. Carbon disulfide dissolves 8g/L of C60, and the best solvent (1-chloronaphthalene) dissolves 53 g/L. up Still, fullerenes are the only known allotrope of carbon that can be dissolved in common solvents at room temperature. Besides those two, good solvents for fullerenes include 1,2-dichlorobenzene, toluene, p-xylene, and 1,2,3-tribromopropane. Fullerenes are highly insoluble in water, and practically insoluble in methanol.

Solutions of pure C60 (buckminsterfullerene) have a deep purple color. Solutions of C70 are reddish brown. Larger fullerenes C76 fullerene to C84 fullerene have a variety of colors. C76 fullerene has two optical forms, while other larger fullerenes have several structural isomers.

General considerations
Some fullerene structures are not soluble because they have a small band gap between the ground and excited states. These include the small fullerenes, and. The structure is also in this class, but the endohedral version with a trapped lanthanide-group atom is soluble due to the interaction of the metal atom and the electronic states of the fullerene. Researchers had originally been puzzled by being absent in fullerene plasma-generated soot extract, but found in endohedral samples. Small band gap fullerenes are highly reactive and bind to other fullerenes or to soot particles.

Solubility of in some solvents shows unusual behaviour due to existence of solvate phases (analogues of crystallohydrates). For example, solubility of in benzene solution shows maximum at about 313 K. Crystallization from benzene solution at temperatures below maximum results in formation of triclinic solid solvate with four benzene molecules ·4H6 which is rather unstable in air. Out of solution, this structure decomposes into usual face-centered cubic (fcc) in few minutes' time. At temperatures above solubility maximum the solvate is not stable even when immersed in saturated solution and melts with formation of fcc. Crystallization at temperatures above the solubility maximum results in formation of pure fcc. Millimeter-sized crystals of and  can be grown from solution both for solvates and for pure fullerenes.

Solubility table
The following are some solubility values for and  from the literature, in grams per liter.