Fullerenols revisited as stable radical anions.
The first exhaustive purification and characterization of the much-studied "fullerenols", prepared by reaction of C(60) 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 C(60) but rather is a structurally and electronically complex C(60) radical anion with a molecular formula of Na(+)(n)[C(60)O(x)(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 mu(B) values in aqueous solution of 1.9-2.1 B.M. at 0.5 T and 300 K and R(1) proton relaxivities of 0.55-0.77 mM(-1)s(-1) at 20 MHz and 40 degrees 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 C(60) surface that protects a cyclopentadienyl radical center on the fullerene.
Husebo
Lars O
LO
Department of Chemistry and Center for Nanoscale Science and Technology, MS-60, Rice University, Houston, Texas 77251-1892, USA.
Sitharaman
Balaji
B
Furukawa
Ko
K
Kato
Tatsuhisa
T
Wilson
Lon J
LJ
D000838:Anions / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry* / Q000302:isolation & purification; D008280:Magnetics; D046529:Microscopy, Electron, Transmission; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012972:Sodium Hydroxide / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods; D014050:Toluene / Q000737:chemistry
D000838:Anions; D005609:Free Radicals; D037741:Fullerenes; D000644:Quaternary Ammonium Compounds; C108127:fullerenol; D014050:Toluene; D012972:Sodium Hydroxide; C009405:tetrabutylammonium; C069837:fullerene C60