Kinetics of electron-transfer reactions of the Co(bpyO2)32+/3+ couple in acetonitrile

1992 ◽  
Vol 70 (1) ◽  
pp. 39-45 ◽  
Author(s):  
Donal H. Macartney ◽  
Samuel Mak
Keyword(s):  
Electron Transfer ◽  
Exchange Rate ◽  
Rate Constants ◽  
Marcus Theory ◽  
Transfer Reactions ◽  
Electron Transfer Reactions ◽  
Cross Reactions ◽  
The Cross ◽  
Polypyridine Complexes ◽  
Kinetics Of

The kinetics of the outer-sphere electron transfer reactions of tris(1,1′-dioxo-2,2′-bipyridine)cobalt(II) and (III) with a series of nickel polyaza macrocycles, FeL3n+ and OsL32+ complexes (L is 2,2′-bipyridine or 1,10-phenanthroline, and substituted derivatives), and Rh2(O2CCH3)4(CH3CN)2+ have been investigated in acetonitrile at 25.0 °C. An application of the Marcus theory relationship to the cross-reaction rate constants yielded apparent Co(bpyO2)32+/3+ self-exchange rate constants of 102 M−1 s−1 from the nickel macrocycle cross-reactions and 10−1 M−1 s−1 from the cross-reactions with the metal polypyridine complexes. The latter cross-reactions are considered to be non-adiabatic due to a mismatch in the donor/acceptor orbital symmetries. The electron exchange rate constant is compared with the exchange rate constants for other Co(II)/Co(III) complex couples and M(bpyO2)32+/3+ couples of other first-row transition metals, and discussed in terms of inner-sphere and solvent reorganization barriers. Keywords: electron transfer, Marcus theory relationship, cobalt(II)/(III) couples, 1,1′-dioxo-2,2′-bipyridine.

Kinetics and mechanism of the oxidation of benzenediols and ascorbic acid by bis(1,4,7-triazacyciononane)nickel(III) in aqueous perchlorate media

1985 ◽  
Vol 63 (6) ◽  
pp. 1198-1203 ◽  
Author(s):  
A. McAuley ◽  
Lee Spencer ◽  
P. R. West
Keyword(s):  
Electron Transfer ◽  
Ascorbic Acid ◽  
Exchange Rate ◽  
Rate Constants ◽  
Outer Sphere ◽  
Kinetics And Mechanism ◽  
Hydrogen Ion ◽  
Transfer Reactions ◽  
Radical Ions ◽  
Electron Transfer Reactions

The reactions of the outer-sphere electron transfer reagent, Ni(9-aneN3)23+, (bis(1,4,7-triazacyclononane)nickel(III) ion) with ascorbic acid, hydroquinone, catechol, and resorcinol have been investigated. The absence of any proton related equilibria with the oxidant provides a means of ascribing the observed inverse hydrogen ion dependences to reactions of the dissociated ascorbate or quinolate ions, (HA−). The data are consistent with the rate-determining one-electron transfer reactions:[Formula: see text]followed by rapid oxidation of the radical ions formed. In the reaction with ascorbic acid, k1 ~ 0 and k2 (T = 25° C) = 5.2 × 106 M−1 s−1 (ΔH≠ = 10.1 ± 2.5 kcal mol−1, ΔS≠ = 5.7 ± 5.1 cal mol−1 K−1). For hydroquinone, catechol, and resorcinol, k1 = 2.9 × 103, 2.8 × 102, and ~0 M−1 s−1and k2 = 6.9 × 109, 4.1 × 109, and 2.8 × 108 M−1 s−1, respectively. These data have been combined with those from other similar reactions leading, by use of a Marcus correlation, to self-exchange rate constants for the HAsc−/HAsc• couple of 3.5 × 105 M−1 s−1 and for the H2Quin0/+ and H2cat0/+ systems of 5 × 107 and 2 × 107 M−1 s−1, respectively. The importance of the effect of bond-reorganisation on electron transfer is discussed.

Electrochemical Electron Transfer Reactions of M(ttcn)23+/2+ (M = Co, Pd, Pt, Au; ttcn = 1,4,7-trithiacyclononane): the Relation of Reaction Volumes and Electron Transfer Rate Constants

1999 ◽  
Vol 54 (9) ◽  
pp. 1138-1146 ◽  
Author(s):  
Mitsuru Matsumoto ◽  
Shigenobu Funahashi ◽  
Hideo D. Takagi
Keyword(s):  
Electron Transfer ◽  
Cyclic Voltammetry ◽  
Exchange Rate ◽  
Rate Constants ◽  
Electron Exchange ◽  
Transfer Reactions ◽  
Free Energies ◽  
Simple Method ◽  
Electron Transfer Reactions ◽  
Reaction Volumes

The reaction volumes (ΔV0M), corresponding to the volume change for the half-cell reactions for a series of M(ttcn)23+/2+ couples were measured by using cyclic voltammetry at elevated pressures. The ΔV0Mvaluesreflect the changes in the bond length between M and ligands accompanying the changes in the oxidation state of M from 3+ to 2+. The values of the estimated ΔV0M are in the order of Co < Au < Pd < Pt. The reaction volume is larger for the slower ET reactions, indicating that the reaction volumes reflect the inner-sphere contribution to the activation free energies. The heterogeneous electron exchange rate constants for the M(ttcn)23+/2+ couples, kel, were measured by AC voltammetry, and by cyclic voltammetry. The latter method on the basis of the Kochi-Nicholson’s method was carried out to examine the reliability of this rather simple method by setting the scan rate very fast to make the redox system irreversible. The results obtained by these two methods are in fair agreement with each other, especially when a glassy carbon working electrode was used for the measurements. The relation between the activation free energies for the heterogeneous electron exchange rate constants, ΔG*el, and those for the homogeneous reactions, ΔG*ex, is linear, which indicates that the homogeneous electron transfer reactions of a series of M(ttcn)23+/2+ is also governed by the intrinsic structural change. However, the slope of log kel vs. log kex plot is far smaller than 0.5 as predicted by the Marcus theory.

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