Further insights in DFT calculations of redox potential for iron complexes: The ferrocenium/ferrocene system

We report DFT calculations of the redox potential for the ferrocenium/ferrocene couple in acetonitrile. This system is generally used as an internal reference for non-aqueous solutions and is commonly used for redox potential determination of metal complexes. The set of functionals evaluated includes PBE, B3LYP, M05, M06, MO6L and omega B97X-D along with different basis sets. Solvent effects were considered through PCM and SMD continuum models. Also, the multireference character of the system was tested. For all functionals considered structural and energetic analysis were performed in order to explain the calculated redox potentials. Results of multireference test show that a single reference treatment is adequate. A comparison between calculated and experimental parameters suggests that omega B97X-D functional in combination with SDD/cc-pVTZ basis functions and the PCM solvation model provides the best description of the redox potential and the structural and energetic parameters. Thus, a confident prediction of redox potential for the Fc(+)/Fc system was obtained (0.685 V/SHE vs an experimental range of 0.624-0.650 V/SHE), which shows new insights for the widespread use of DFT calculations in the study of redox potentials for similar systems. (C) 2016 Elsevier B.V. All rights reserved.