Valence state of paramagnetic centers in fullerenes

Abstract

Charge distribution on individual carbon atoms of a fullerene molecule C n depends on the number of atoms it comprises, n. Only C60 has the same charge on all its carbon atoms while other molecules containing from n = 32 to n = 84 molecules are characterized by a variety of charge distributions. A neutral C60 molecule is diamagnetic and does not show EPR signal. Charged C60 v molecules, where vis the valence taking values from v = -6 to v = +1, show EPR signals for odd v and for v = 2 when a fullerene molecule is in the triple state. EPR lines of isolated fullerene ions are narrow in the whole temperature range whereas EPR lines of MexC60 v in ionic compounds MexC60 are wide and their width decreases with temperature. A model of paramagnetic centers and an empirical formula relating g-factor to valence have been given.

Second Harmonic Generation of C60Incorporated in Alkali Metal Ion Zeolites and Mesoporous MCM-41 Silica

“…To determine the nature of this photochemically generated intermediate, EPR measurements were carried out. As expected in view of the precedents in the literature, [55][56][57] EPR spectroscopy reveals the presence of C 60 radical cation in all the samples of porous silicate containing C 60 as assessed by the observation of a signal at g ) 2.0022 that agrees relatively well with the g value of 2.0027 ( 0.0002 reported in the literature for the C 60 •+ incorporated in FeY zeolite. 58,59 This g value is significantly different to the g value of C 60 •that appears at g ) 2.0000; therefore, the radical anion that is the C 60 transient species more frequently observed in solution can be firmly ruled out in our case.…”

ESE Studies of Pristine Paramagnetic Species of C60 Powder Samples

“…Sharp signals have been observed in several C 60 samples and derivatives. In solid pristine samples this signal was attributed to a C 60 cation doublet (S = 1/2) species . Triplet species (S = 1) were also observed in powder C 60 by continuous wave electron paramagnetic resonance (CW-EPR).…”

“…In solid pristine samples this signal was attributed to a C 60 cation doublet (S ) 1/2) species. 6 Triplet species (S ) 1) were also observed in powder C 60 by continuous wave electron paramagnetic resonance (CW-EPR). These species are attributed to a photonassisted reaction with molecular oxygen of the air.…”

EPR and MMMA Study of C60upon K-Doping

“…A comparison of such results with the data obtained from EPR studies of electrochemically produced C60 radicals with different valences (υ) in solution [6][7][8] would permit verification of the EPR signals due to ion radicals of speciflc valence which are known to occur in pure C60 or in Me x C60 admixtured with alkali metals [2,9,10]. Therefore we could ascribe the following g-factor values: g+ .^.s 2.0025, g1-1.9998, g3-2.0014 to the C 6 0, CL and C ion radicals, respectively.…”