Journal of Physical Chemistry B, Vol.101, No.33, 6350-6358, 1997
Solvent Effects on the Electrochemistry of C-60 - Thermodynamics of Solvation of C-60 and Fullerides
The previously published solvent dependence of the electrochemistry of C-60 has been extended and reanalyzed. The potentials have been measured against the decamethylferrocenium/decamethylferrocene (Me(10)Fc(+/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 C-60(n-/(n+1)-) couples. The formal redox potentials of the C-60(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 C-60(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 Me(10)Fc(+) ion of the reference couple. This interaction is much smaller compared to the solvent/solute interaction. pi-Stacking interactions between C-60 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 (C-60) to a variety of discrete negative surface charges (fullerides).
Keywords:JAHN-TELLER DISTORTION;REPORTING ELECTRODE-POTENTIALS;X-RAY STRUCTURE;APROTIC-SOLVENTS;REDOX COUPLES;BUCKMINSTERFULLERENE;C-70;ELECTROREDUCTION;FULLERENES;PARAMETERS