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 to C₈₄ have a variety of colors. C₇₆ 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 C₂₈,^[1] C₃₆ and C₅₀. The C₇₂ 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 C₇₂ 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 C₆₀ in some solvents shows unusual behaviour due to existence of solvate phases (analogues of crystallohydrates). For example, solubility of C₆₀ 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 C₆₀·4C₆H₆ which is rather unstable in air. Out of solution, this structure decomposes into usual face-centered cubic (fcc) C₆₀ 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 C₆₀. Crystallization at temperatures above the solubility maximum results in formation of pure fcc C₆₀. Millimeter-sized crystals of C₆₀ and C₇₀ can be grown from solution both for solvates and for pure fullerenes.^[2][3]

Solubility table

The following are some solubility values for C₆₀ and C₇₀ from the literature, in grams per liter.^{[4][5][6][7][8]}

See also

• Fullerene chemistry

References

1. ^ Guo, T.; Smalley, R.E.; Scuseria, G.E. (1993). "Ab initio theoretical predictions of C₂₈, C₂₈H₄, C₂₈F₄, (Ti@C₂₈)H₄, and M@C₂₈ (M = Mg, Al, Si, S, Ca, Sc, Ti, Ge, Zr, and Sn)". Journal of Chemical Physics. 99 (1): 352. Bibcode:1993JChPh..99..352G. doi:10.1063/1.465758
2. ^ Talyzin, A.V. (1997). "Phase Transition C₆₀−C₆₀*4C₆H₆ in Liquid Benzene". Journal of Physical Chemistry B. 101 (47): 9679–9681. doi:10.1021/jp9720303
3. ^ Talyzin, A.V. & Engström, I. (1998). "C₇₀ in Benzene, Hexane, and Toluene Solutions". Journal of Physical Chemistry B. 102 (34): 6477–6481. doi:10.1021/jp9815255
4. ^ Beck, Mihály T. & Mándi, Géza (1997). "Solubility of C₆₀". Fullerenes, Nanotubes and Carbon Nanostructures. 5 (2): 291–310. doi:10.1080/15363839708011993
5. ^ Bezmel'nitsyn, V.N.; Eletskii, A.V.; Okun', M.V. (1998). "Fullerenes in solutions". Physics-Uspekhi. 41 (11): 1091–1114. Bibcode:1998PhyU...41.1091B. doi:10.1070/PU1998v041n11ABEH000502
6. ^ Ruoff, R.S.; Tse, Doris S.; Malhotra, Ripudaman; Lorents, Donald C. (1993). "Solubility of fullerene (C₆₀) in a variety of solvents". Journal of Physical Chemistry. 97 (13): 3379–3383. doi:10.1021/j100115a049
7. ^ Sivaraman, N.; Dhamodaran, R.; Kaliappan, I.; Srinivasan, T. G.; Vasudeva Rao, P. R. P.; Mathews, C. K. C. (1994). "Solubility of C₇₀ in Organic Solvents". Fullerene Science and Technology. 2 (3): 233–246. doi:10.1080/15363839408009549
8. ^ Semenov, K. N.; Charykov, N. A.; Keskinov, V. A.; Piartman, A. K.; Blokhin, A. A.; Kopyrin, A. A. (2010). "Solubility of Light Fullerenes in Organic Solvents". Journal of Chemical & Engineering Data. 55: 13–36. doi:10.1021/je900296s