| Abstract
| - Electron paramagnetic resonance (EPR) studies at 295 K of theradical anion of buckminsterfullerene(C60•-)generated electrochemically by bulk-controlled potential electrolysisof neutral C60 in mixed toluene−acetonitrilesolvents (5−20% v/v acetonitrile with 0.1−0.2 Mn-Hex4NPF6 orn-Bu4NPF6 as the supportingelectrolyte)have shown that at least three different forms ofC60•- exist in solution.The radical anions have different gvalues and can thus be detected by EPR spectroscopy in the form ofsingle line signals with different linewidths. The familiar species with the broad line width signal(ΔHpp = 6 mT) was present in a highpercentage(ca. >95%) along with two species with narrow line width(ΔHpp = 0.16 and 0.07 mT) signals thatwerepresent between 1 and 5% of the total concentration ofC60•-. The concentrationsof the species with narrowline width EPR signals increased with increasing time so that over a20-h period their EPR signal intensityapproximately doubled. The purity of the toluene was found to bevery important in determining the numberof species detected with sharp EPR signals. Although two specieswere always detected with sharp EPRsignals, when lower purity toluene (<99%) was used, the number ofspecies with narrow line width signalsincreased to >2. The increase in the sharp EPR signals withincreasing time is not inconsistent with a slowreaction between C60•- and lowlevels of impurities in the solvent to form lower symmetryparamagneticspecies, the narrow line width signals being very similar to thosereported for substituted fullerene radicals.EPR and cyclic voltammetry experiments were conducted onC60 in the presence of several complexingagents,cyclotriveratrylene (CTV), the symmetrical tris-allyl substitutedanalogue of CTV [CTV(allyl)3], andp-benzyl-calix[5]arene. The intensity of the narrow and broadline width EPR signals decreased whenC60•- waselectrochemically generated in the presence of the complexing agents,indicating that the host−guest π−πinteractions were sufficiently strong to alter the EPR signals ofC60•-. Cyclic voltammetryexperimentsperformed on C60 in the presence of the complexing agentsshowed that the first four reduction processes ofC60 split into two new processes upon complexation, withthe time allowed for the host−guest reaction beingcritical in determining the voltammetric behavior.
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