Web Release Date: September 4,
Fullerenols Revisited as Stable Radical Anions
and
Contribution from the Department of Chemistry and Center for Nanoscale Science and Technology, MS-60, Rice University, Houston, Texas 77251-1892, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan, and Faculty of Science, Josai University, Keyakidai 1-1, Sakado 350-0295, Japan
Received April 26, 2004
Abstract:
The first exhaustive purification and characterization of the much-studied "fullerenols", prepared
by reaction of C60 in toluene with an oxygenated, aqueous NaOH solution using tetrabutylammonium
hydroxide as a phase transfer catalyst, has been performed. The resulting fullerenol is not simply
polyhydroxylated C60 but rather is a structurally and electronically complex C60 radical anion with a molecular
formula of Na+n[C60Ox(OH)y]n- (where n = 2-3, x = 7-9, and y = 12-15) for three different, but identical,
preparations. Surprisingly, Na+-fullerenol is paramagnetic, exhibiting 
B values in aqueous solution of 1.9-2.1 B.M. at 0.5 T and 300 K and R1 proton relaxivities of 0.55-0.77 mM-1s-1 at 20 MHz and 40 
C, values
both slightly higher than those expected for a pure S = 1/2 spin system. ESR studies (ESE-FS and 2D
nutation) of frozen aqueous solutions at 1.5 and 5.0 K establish that Na+-fullerenol is mainly S = 1/2 with
a minor, but significant, component of S = 1. Thus, this is the first report to characterize these widely
studied, water-soluble fullerenols as stable radical anions. The stability of the S = 1/2 Na+-fullerenol radical
is likely due to a highly derivatized C60 surface that protects a cyclopentadienyl radical center on the fullerene.
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