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

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...

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Bibliographic Details
Published in:Journal of solution chemistry 2018-06, Vol.47 (6), p.993-1020
Main Authors: Mabe, Takuya, Doseki, Fumiaki, Yagyu, Takeyoshi, Ishihara, Koji, Inamo, Masahiko, Takagi, Hideo D.
Format: Article
Language:English
Subjects:
Acetonitrile
Chemistry
Chemistry and Materials Science
Condensed Matter Physics
Coordination compounds
Dependence
Dielectric properties
Diffusion rate
Electron transfer
Electron transfer reactions
Electrons
Geochemistry
Industrial Chemistry/Chemical Engineering
Inorganic Chemistry
Ionic liquids
Ions
Oceanography
Permittivity
Physical Chemistry
Rate constants
Refractivity
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Summary: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 × 10 9 , 3.65 × 10 7 , 2.63 × 10 7 , and 2.01 × 10 7 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.
ISSN:0095-9782
1572-8927
DOI:10.1007/s10953-018-0772-6