Charge-transfer complexes reversible ionization

As for the ability of C60 to function as an electron donor, it would be difficult to obtain acceptor-type fullerene salts or charge transfer complexes because of the higher ionization potential 7p of 7.6 eV [10] for the molecule. In fact, the electrochemical oxidation of C60 in solutions is irreversible [11,12], in contrast to the reversible, six one-electron cathodic reduction in solutions [13,14]. 

These interactions are, however, more complex than has been indicated thus far. A solution of -trinitrobenzene in pyridine showed a marked increase in conductivity with time as did mixtures of -trinitrobenzene with diethylamine in ethanol (43). In the latter system a 1 1 complex is formed. Miller and Wjume-Jones (56) have discussed these results in terms of MuUiken s concept of inner and outer complexes (49) and have suggested that an outer complex forms, that this is in equilibrium with an inner complex, essentially an ion-pair, which in an ionizing solvent can dissociate into two solvated radical-ions. This is supported by the detection of a weak ESR absorption in solutions of s-trinitrobenzene in diethylamine both in the presence and absence of acetone (56). The rate of reaction between diethylamine and s-trinitrobenzene in acetone-ether (1 3 molar) has been studied by a stopped flow method (57). This rapid, reversible reaction is of first order in s-trinitrobenzene and second order in diethylamine and has been interpreted in terms of a rapid preliminary equilibrium, possibly the dimerization of the amine, and the formation of a charge-transfer complex. With aromatic amines the reactions involved proved too fast to measure. 

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