Electrode kinetics of Eu3+/Eu2+ reaction by cyclic voltammetry

1982 ◽  
Vol 47 (7) ◽  
pp. 1773-1779 ◽  
Author(s):  
T. P. Radhakrishnan ◽  
A. K. Sundaram
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Outer Sphere ◽  
Electrode Reaction ◽  
Transfer Reactions ◽  
Cyclic Voltammetric ◽  
Edta Solution ◽  
Kinetics Of ◽  
Activated Complex ◽  
Good Agreement

The paper is a detailed study of the cyclic voltammetric behaviour of Eu3+ at HMDE in molar solutions of KCl, KBr, KI, KSCN and in 0.1M-EDTA solution with an indigenously built equipment. The computed values of the rate constants at various scan rates show good agreement with those reported by other electrochemical methods. In addition, the results indicate participation of a bridged activated complex in the electron-transfer step, the rate constants showing the trend SCN- > I- > Br- > Cl- usually observed for bridging order of these anions in homogeneous electron-transfer reactions. The results for Eu-EDTA system, however, indicate involvement of an outer sphere activated complex in the electrode reaction.

Electron transfer kinetics of cobaloxime complexes

1996 ◽  
Vol 74 (5) ◽  
pp. 658-665 ◽  
Author(s):  
Kefei Wang ◽  
R.B. Jordan
Keyword(s):  
Electron Transfer ◽  
Exchange Rate ◽  
Rate Constants ◽  
Ph Dependence ◽  
Outer Sphere ◽  
The Self ◽  
Oxidation Of Co ◽  
Reduction Potentials ◽  
Inner Sphere ◽  
Kinetics Of

The rates of oxidation of CoII(dmgBF2)2(OH2)2 by CoIII(NH3)5X2+ (X = Br−, Cl−, and N3−) have been studied at 25 °C in 0.10 M LiClO4. The rate constants are 50 ± 9, 2.6 ± 0.2, and 5.9 ± 1.0 M−1 s−1 for X = Br−, Cl−, and N3−, respectively, in 0.01 M acetate buffer at pH 4.7. The relative rates are consistent with the inner-sphere bridging mechanism established earlier by Adin and Espenson for the analogous reactions of CoII(dmgH)2(OH2)2. The rate constants with CoII(dmgBF2)2(OH2)2 typically are ~103 times smaller and this is attributed largely to the smaller driving force for the CoII(dmgBF2)2(OH2)2 complex. The outer-sphere oxidations of cobalt(II) sepulchrate by CoIII(dmgH)2(OH2)2+ (pH 4.76–7.35, acetate, MES, and PIPES buffers) and CoIII(dmgBF2)2(OH2)2+ (pH 3.3–7.42, chloroacetate, acetate, MES, and PIPES buffers) have been studied. The pH dependence gives the following rate constants (M−1 s−1) for the species indicated: (1.55 ± 0.09) × 105 (CoIII(dmgBF2)2(OH2)2+); (5.5 ± 0.3) × 103 (CoII(dmgH)2(OH2)2+); (3.1 ± 0.5) × 102 (CoIII(dmgH)2(OH2)(OH)); (2.5 ± 0.3) × 102 (CoIII(dmgBF2)2(OH2)(OH)). The known reduction potentials for cobalt(III) sepulchrate and the diaqua complexes, and the self-exchange rate for cobalt(II/III) sepulchrate, are used to estimate the self-exchange rate constants for the dioximate complexes. Comparisons to other reactions with cobalt sepulchrate indicates best estimates of the self-exchange rate constants are ~2.4 × 10−2 M−1 s−1 for CoII/III(dmgH)2(OH2)2and ~5.7 × 10−3 M−1 s−1 for CoII/III(dmgBF2)2(OH2)2. Key words: electron transfer, cobaloxime, inner sphere, outer sphere, self-exchange.

Outer-sphere electron-transfer reactions of ascorbate anions

1982 ◽  
Vol 35 (6) ◽  
pp. 1133 ◽  
Author(s):  
NH Williams ◽  
JK Yandell
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Exchange Rate ◽  
Ionic Strength ◽  
Rate Constants ◽  
Outer Sphere ◽  
The Self ◽  
Transfer Reactions ◽  
Redox Potentials ◽  
The One

Rate constants for the one-electron oxidation of ascorbate dianion (A2-) by bis(terpyridine)cobalt(III)ion (8.5 × 106 dm3 mol-1 s-1) and pentaammine(pyridine)ruthenium(III) ion (6.0 × 109 dm3 mol-1 s-1), and of the monoanion (HA-) by tetraammine (bipyridine)ruthenium(III)ion (2.1 × 105 dm3 mol-1s-1) have been determined in aqueous solution at 25�C and ionic strength 0.1 (NaNO3 or NaClO4). It is shown that these rate constants, and other published rate constants for oxidation of HA- and A2-, are consistent with the Marcus cross relation, on the assumption that the self-exchange rate constants for both the HA-/HA and A2-/A-couples are 106 dm3 mol-1 s-1. One electron redox potentials for the ascorbate/dehydroascorbate system have been derived from scattered literature data.

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 mechanisms of the oxidation of ascorbic acid and benzene diols by nickel(III)tetraazamacrocycles in aqueous perchloric acid

1983 ◽  
Vol 61 (6) ◽  
pp. 1120-1125 ◽  
Author(s):  
A. McAuley ◽  
T. Oswald ◽  
R. I. Haines
Keyword(s):  
Ascorbic Acid ◽  
Perchloric Acid ◽  
Rate Constants ◽  
Cross Correlation ◽  
Outer Sphere ◽  
Transfer Reactions ◽  
Aqueous Perchloric Acid ◽  
Kinetics Of Reaction ◽  
Kinetics Of ◽  
Sphere Mechanism

The kinetics of reaction of ascorbic acid, hydroquinone, and catechol (H2A) with nickel(III) macrocycles (NiL3+) (L = cyclam, meso-(5,12)-7,7,14,14-Me6-14-ane-1,4,8,11-N4 (tet-a), and rac-(5,14)-7,7,12,12-Me6-14-ane-1,4,8,11-N4 (tet-c):[Formula: see text]have been investigated in aqueous perchloric acid solutions using the stopped-flow technique. The data are consistent with a rate-determining one-electron transfer reactions:[Formula: see text]followed by a rapid oxidation of the radical formed. In the reaction with ascorbic acid, for Ni(cyclam)3+, k1 = 250 M−1 s−1 (25 °C), k4Ka = 680 s−1; Ni(tet-c)3+, k1 = 2.52 × 103 M−1 s−1, k4Ka = 1.06 × 104 s−1; and Ni(tet-a)3+, k1 = 2.85 × 103 M−1 s−1 (21.95 °C), k4Ka = 1.26 × 104 s−1. With catechol, k1 = 6.98 × 102 M−1 s−1, 1.73 × 104 M−1 s−1, and 3.3 × 104 M−1 s−1 respectively in reactions with Ni(cyclam)3+, Ni(tet-c)3+, and Ni(tet-a)3+. With hydroquinone, k1 = 1.09 × 104 M−1s−1 (Ni(cyclam)3+) and 2.49 × 105 M−1 s−1 (20.9 °C) (Ni(tet-c)3+). The reactions are considered to take place via an outer-sphere mechanism and rate constants are discussed in terms of the Marcus cross correlation. Use has been made of predicted rate constants to identify reaction pathways in the hydrogen-ion dependent systems.

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