Journal of Solution Chemistry

, Volume 47, Issue 6, pp 993–1020 | Cite as

Behavior of Ionic Liquids Around Charged Metal Complexes: Investigation of Homogeneous Electron Transfer Reactions Between Metal Complexes in Ionic Liquids

  • Takuya Mabe
  • Fumiaki Doseki
  • Takeyoshi Yagyu
  • Koji Ishihara
  • Masahiko InamoEmail author
  • Hideo D. TakagiEmail author


The second-order electron transfer reaction between the photo-excited triplet state of [Zn(TPP)]* (TPP = 5,10,15,20-tetraphenylporphyrin) and [Co(sep)]3+ (sep = sepulchrate = 1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane) was investigated in three ionic liquids (ILs, 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with R = butyl, pentyl, and hexyl) and in acetonitrile. Results of electrochemical and kinetic measurements indicated that ILs dissociate in the vicinity of charged metal complexes and at electrodes, although the dissociated anionic and cationic components of the ILs seem to exist as pairs around the metal complexes. Second-order rate constants for the electron transfer reaction are 1.88 × 109, 3.65 × 107, 2.63 × 107, and 2.01 × 107 kg·mol−1·s−1 in acetonitrile and in the butyl, pentyl and hexyl ILs, respectively, at 298 K, after correction of the contribution of diffusion. The average slope of the plot of the logarithmic second-order rate constants observed in acetonitrile and ILs against the logarithmic viscosity of each solvent was − 0.84. However, the slope of the same plot was much steeper (− 4.1) when data for only the three ILs were used. Detailed analyses of the experimental results on the basis of the Latner–Levin cross relation and the Marcus theory lead to the conclusion that the solvent properties such as the dielectric constant and refractive index around the polarized/charged transition states are different from those for the bulk ILs: observed self-exchange rate constants did not exhibit the Pekar factor dependence when dielectric constants and refractive indices for bulk ILs are used.


Ionic liquid Electron transfer reaction Metal complexes 



We wish to thank JSPS KAKENHI Grant Numbers 16K05865 and 15K05451for financial support.


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Authors and Affiliations

  1. 1.Research Center for Materials ScienceNagoya UniversityNagoyaJapan
  2. 2.Department of Life Science and Applied Chemistry, Graduate School of EngineeringNagoya Institute of TechnologyNagoyaJapan
  3. 3.Department of Chemistry, School of Science and EngineeringWaseda UniversityTokyoJapan
  4. 4.Department of EducationAichi University of EducationKariyaJapan

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