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Mass Spectrometric and in Situ ESR Vis-NIR Spectroelectrochemical Investigations of the Mechanism of the C60 Electropolymerization in the Presence of Dioxygen in Aprotic Solvents
|Piotr Pieta 1,2, Andreas Petr 2, Wlodzimierz Kutner 1, Lothar Dunsch 2
1. Polish Academy of Sciences, Institute of Physical Chemistry, Kasprzaka 44/52, Warszawa 01-224, Poland
A mechanism of the C60 fullerene electropolymerization in the presence of dioxygen, O2, in 0.1 M tetrabutylammonium perchlorate, in the toluene : acetonitrile (4 : 1, v : v) mixed solvent solution, was investigated by comparing mass spectrometric (MS) as well as simultaneous cyclic voltammetric (CV), electron spin resonance (ESR) and Vis-NIR spectroscopic behavior of products of both one- and two-electron reduction of C60 in the absence and presence of O2. For the first cathodic CV peak corresponding to the C60/C60- electroreduction, the spectro-electrochemical behavior in the presence of O2 was similar to that in its absence. That is, a Vis-NIR band at 1080 nm characteristic of C60- appeared if the potential was held at -0.445 V vs. Ag/Ag+ psuedo-reference electrode, i.e., at the first cathodic peak, indicating that C60- was electrogenerated. This anion did not chemically react with O2 present in solution as there was only one strong MS peak with m/z of 720 characteristic of C60 accompanied by weak peaks with m/z of 736 and 739 to 741 indicative of small amounts of C60O and, presumably, C60OH4. Instead, an electron transfer from C60- to O2 yielding superoxide, O2•-, was demonstrated by using in situ ESR spectroelectrochemistry combined with the spin-trap technique.
At more negative potentials, i.e., those at which C60 is electroreduced to C602- and O2 to O2•-, the 1080-nm band vanished in the Vis-NIR spectrum and no new band emerged like if the electrogenerated C602- was consumed in some following reaction resulting in a Vis-NIR inactive product. The ESR signal of the product with the g = 2.0007 value suggested the formation of some C60 derivatives. Beside the main peak at m/z of 720 in the MS spectrum of the product, several additional peaks in the m/z range 739 to 760 appeared indicating that C60O•- and C60O2•- were generated and, then, protonated. Moreover, several peaks in the m/z range 1297 to 1465 were observed. A peak with m/z of 1441.187 may indicate the formation of the [2 + 2] dimer, C120. This peak is accompanied by a series of peaks corresponding to dimers, which last Cn (n = 1, 2) or C2n (n = 2-5) carbon atoms. Apparently, C60 can spontaneously dimerize after electroreduction of C60 and O2 to C602- and O2•-, respectively. Importantly, no oxygen atom was built in the dimeric structure although superoxide radical promoted this dimerization.
Presentation: oral at 18th Conference on Physical Organic Chemistry, Symposium 2, by Piotr Pieta
See On-line Journal of 18th Conference on Physical Organic Chemistry
Submitted: 2006-05-31 22:02 Revised: 2006-08-04 19:00