Electron transfer reactions of nickel complexes of 1,4,7-triazacyclodecane

1985 ◽  
Vol 63 (11) ◽  
pp. 2983-2989 ◽  
Author(s):  
M. G. Fairbank ◽  
A. McAuley ◽  
P. R. Norman ◽  
O. Olubuyide
Keyword(s):  
Electron Transfer ◽  
Exchange Rate ◽  
Proton Transfer ◽  
Electrochemical Oxidation ◽  
Rate Constant ◽  
Aqueous Media ◽  
Nickel Complexes ◽  
Outer Sphere ◽  
The Self ◽  
Transfer Reactions

The preparation of [Ni(1,4,7-triazacyciodecane)2]3+, (Ni(10-aneN3)23+) is described. The existing procedure has been modified leading to good yields of the ligand trihydrochloride. The nickel(II) analogue (reported previously) is oxidised in a facile manner, either by Co3+aq in acidic aqueous media or by NO+ in CH3CN. Since the octahedral NiN6, chromophore is retained upon electron transfer, outer sphere reactions both of the Ni(II) and Ni(III) species have been studied. Rates of oxidation by various nickel(III) macrocycles have been measured and details are provided. Electrochemical oxidation of the Ni(II) complex is consistent with E0(Ni(10-aneN3)23+/2+) = 0.997 V (vs. NHE). The data have been used in a Marcus correlation, leading to the self-exchange rate k11 for the couple (Ni(10-aneN3)23+/2+) = (2 ± 1) × 104 M−1 s−1. This value is compared with other data derived using octahedral Ni(II)/Ni(III) centres. The oxidation of the Ni(II) complex by Co(III)aq has been studied in both protonated and deuterated media. There is no evidence for any proton transfer (from the N—H) being coupled to the electron transfer step. The observed rate constant for the reaction of Co3+ with Ni(II)(10-aneN3)22+ (550 M−1 s−1) may be compared with the calculated outer sphere rate (270 M−1 s−1). An estimate of k11 (CoOH2+/+) ~ 3 M−1 s−1 for the CoOH2+/+ exchange is discussed.

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.

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.

Cobalt, Iron and Ruthenium Complexes of Picolinic and Dipicolinic Acids: Syntheses, Solution Properties and Kinetics of Electron Transfer Reactions With Cytochrome C(II) and Some Inorganic Reductants

1989 ◽  
Vol 42 (1) ◽  
pp. 1 ◽  
Author(s):  
RM Ellis ◽  
JD Quilligan ◽  
NH Williams ◽  
JK Yandell
Keyword(s):  
Exchange Rate ◽  
Cytochrome C ◽  
Rate Constant ◽  
Order Rate Constant ◽  
The Self ◽  
Transfer Reactions ◽  
Solution Properties ◽  
Cobalt Iron ◽  
Exchange Rate Constant ◽  
Kinetics Of

Tris picolinate complexes of CO111 and RU111 have been synthesized, and their standard potentials measured (432 �10, 403 �2 mV) at 25�C and ionic strength 0.1 mol dm-3. The self-exchange rate constant of Ru ( pic )3O/- was found to be (1 .4 �0.9)×108 dm3 mol-1 s-l, from reaction with cytochrome C(II), Co( bpy )32+ and ~Co( phen )32+. For the reaction between Fe( dipic )2- and cytochrome ~(II), at 2S260C, pH 5.5 and I 0.1 mol dm-3 (KNO3), the second-order rate constant was (3.2 �0.l)×105 dm3 mol-1 s-1,with ΔH+ 19.9 �0.9 kJ mol-1 and ΔS+ -72.8 �.7 J K-1 mol-l. The self-exchange rate constant of Fe( dipic )2-/2- was reevaluated as (5.8 �0.2)×106 dm3 mol-l s-1.

Electron transfer in non-oxovanadium(IV) and (V) complexes: Kinetic studies of an amavadin model

2009 ◽  
Vol 81 (7) ◽  
pp. 1241-1249 ◽  
Author(s):  
Jeremy M. Lenhardt ◽  
Bharat Baruah ◽  
Debbie C. Crans ◽  
Michael D. Johnson
Keyword(s):  
Electron Transfer ◽  
Exchange Rate ◽  
Rate Constant ◽  
Exchange Process ◽  
Kinetic Studies ◽  
Electron Transfer Reaction ◽  
The Self ◽  
Synthetic Analog ◽  
Vanadium Complex ◽  
Exchange Rate Constant

Electron-transfer reactions of the eight-coordinate vanadium complex, bis-(N-hydroxyiminodiacetate)vanadium(IV) [V(HIDA)2]2–, a synthetic analog of amavadin with ascorbic acid and hexachloroiridate(IV), have been studied. The self-exchange rate constant for this analog has been calculated from oxidation and reduction cross-reactions using Marcus theory and directly measured using 51V NMR paramagnetic line-broadening techniques. The average self-exchange rate constant for the bis-HIDA vanadium(IV/V) couple equals 1.5 × 105 M–1 s–1. The observed rate enhancements are proposed to be due to the small structural differences between the oxidized and reduced forms of the HIDA complex and inner-sphere reorganizational energies. The electron-transfer reaction of this synthetic analog is experimentally indistinguishable from amavadin itself, although significant differences exist in the reduction potential of these compounds. This suggests that ligand modification effects the thermodynamic driving force and not the self-exchange process.

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