Understanding the Decamethylferrocene FeIII/IV Oxidation Process in Tris(pentafluoroethyl)trifluorophosphate-Containing Ionic Liquids at Glassy Carbon and Boron-Doped Diamond Electrodes
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-07-12 |
| Journal | Inorganic Chemistry |
| Authors | Miguel A. GonzĂĄlvez, Luke Gundry, Laura GarciaâQuintana, SiâXuan Guo, Alan M. Bond |
| Institutions | Monash University |
Abstract
Section titled âAbstractâUnder voltammetric conditions, the neutral decamethylferrocene ([Me<sub>10</sub>Fc]) to cationic ([Me<sub>10</sub>Fc]<sup>+</sup>) Fe<sup>II/III</sup> process is a well-known reversible outer-sphere reaction. A companion cationic [Me<sub>10</sub>Fc]<sup>+</sup> to dicationic [Me<sub>10</sub>Fc]<sup>2+</sup> Fe<sup>III/IV</sup> process has been reported under direct current (DC) cyclic voltammetric conditions at highly positive potentials in liquid SO<sub>2</sub> at low temperatures and in a 1.5:1.0 AlCl<sub>3</sub>/1-butylpyridinium chloride melt. This study demonstrates that in room-temperature ionic liquids containing the hard to oxidize and hydrophobic tris(pentafluoroethyl)trifluorophosphate anion, the [Me<sub>10</sub>Fc]<sup>+/2+</sup> process can be detected as a quasi-reversible reaction at glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Large amplitude Fourier-transformed alternating current (FT-AC) voltammetry minimizes background current contributions occurring at potentials similar to those of the Fe<sup>III/IV</sup> process in the second and higher-order harmonics. This enables a straightforward determination of the thermodynamics and kinetics for both the Fe<sup>II/III</sup> and Fe<sup>III/IV</sup> processes. Unlike the ideal outer-sphere Fe<sup>II/III</sup> process, the parameters of the Fe<sup>III/IV</sup> process may be impacted by ion-interaction effects. For the faster Fe<sup>II/III</sup> process, heterogeneous rate constants are approximately 10 times smaller at BDD than those at GC electrodes. This electrode dependence is less pronounced for the slower Fe<sup>III/IV</sup> process. The slower BDD kinetics may be attributed in part to a density of states lower than that at GC.