Solvent Effects on the Electrochemistry of C₆₀. Thermodynamics of Solvation of C₆₀ and Fullerides

Abstract

The previously published solvent dependence of the electrochemistry of C60 has been extended and reanalyzed. The potentials have been measured against the decamethylferrocenium/decamethylferrocene (Me10Fc+/0) couple, which is much less solvent-dependent than the ferrocenium/ferrocene (Fc+/0) couple, and hence gives a more accurate reflection of the solvent dependence of the C60 n -/( n +1)- couples. The formal redox potentials of the C60 n -/( n +1)- couples exhibit substantial dependences on the solvent and become more solvent-dependent as the charge increases. This dependence arises from two main interactions with the solvents: hydrogen-bonding interactions with acidic functionality and electrostatic interactions with solvent dipoles. The strength of the hydrogen-bonding interaction increases as the square of the solute charge due to the increase in basicity of the fullerides. In addition to the contribution of the hydrogen-bonding acidity and the solvent dipoles, the potentials of the C60 0/1- couple are influenced by the Lewis basicities of the solvents. The latter is likely to be due to ion-pair formation between the fullerides and the Bu4N+ ion and/or interactions between the Lewis basicity of the solvent and the Me10Fc+ ion of the reference couple. This interaction is much smaller compared to the solvent/solute interaction. π-Stacking interactions between C60 and aromatic solvents results in a significant contribution of polarizability to the first reduction. The solvent dependences of the fullerenes can be used to model electrode/solvent interactions in which the surface (albeit a distorted one) goes from the point-of-zero-charge (C60) to a variety of discrete negative surface charges (fullerides).

Discrete Fulleride Anions and Fullerenium Cations

“…0.45 V for the successive reductions is striking. It is a particular feature of fullerenes as a class of molecules, reflecting their delocalized LUMOs, and is observed in C 70 , C 76 , C 78 , and C 84 . 9,51,[55][56][57][58][59] It has also been calculated using density functional theory.…”

“…69,78 The effect of solvent on the redox potentials of C 60 is more substantial than the effect of electrolyte. Early indications of a correlation of the first reduction potential with solvent donicity 51,69 (e.g., Gutmann donor number) have held up to more detailed analysis, 78 but the interpretation of experimental data has turned out to be less straightforward than originally believed. The basic problem lies in obtaining statistically significant data that are not compromised by the solvent dependence of the reference couple used.…”

“…The basic problem lies in obtaining statistically significant data that are not compromised by the solvent dependence of the reference couple used. For this reason, Lay and co-workers 78 have used the decamethylferrocene/decamethylferrocenium couple rather than the ferrocene/ferrocenium (Fc/Fc + ) couple as a reference, reinterpreting the data of Kadish and co-workers 69 to produce statistically valid analyses. Data are listed in Table 2.…”

Electrocatalytic Properties and Sensor Applications of Fullerenes and Carbon Nanotubes

“…0.4 V, depending on experimental conditions. Moreover, these potentials are largely influenced by solvation [11, 32 ± 37] and, to some extent, by ion pairing [34,35]. This is why these potentials can be conveniently tuned by selecting proper solvent and/or salt of a supporting electrolyte [11], as depicted in Figure 1 for six C 60 n/(nÀ1) redox couples.…”

EPR Spectroscopy in Electrochemistry

“…Electrochemical EPR has been undertaken in toluene|acetonitrile mixtures [118], but it is notoriously difficult to unambiguously interpret these spectra [119,120].…”