Electron-transfer reactions in non-aqueous media. III. Reduction of CoF(NH3)52+, CoCl(NH3)52+ and CoBr(NH3)52+ by iron(II) in N,N-dimethylformamide

The reduction of the cobalt(111) octahedral complexes CoF(NH3)52+, CoCl(NH3)52+ and CoBr(NH3)52+ by iron(11) in HCONMe2 proceeds through a mechanism involving reversible formation of a halide bridged binuclear intermediate prior to electron transfer and decomposition of the intermediate to products. Values of the activation parameters for reduction and the equilibrium constants for formation of the bridged intermediate are consistent with a tetrahedral stereochemistry for the iron(11) atom in the bridged intermediate for the chloro and bromo systems. However, for the fluoro system these values are consistent with the iron(11) atom maintaining octahedral coordination. These results are compared to those obtained in Me2S0.1,2

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Electron-transfer reactions in non-aqueous media. II. Reduction of CoF(NH3)52+, CoCl(NH3)52+ and CoBr(NH3)52+ by iron(II) in dimethyl sulphoxide-water mixtures

Australian Journal of Chemistry ◽

10.1071/ch9760097 ◽

1976 ◽

Vol 29 (1) ◽

pp. 97 ◽

Cited By ~ 15

Author(s):

BA Matthews ◽

DW Watts

Keyword(s):

Electron Transfer ◽

Aqueous Media ◽

Activation Parameters ◽

Solvent Composition ◽

Dimethyl Sulphoxide ◽

Transfer Reactions ◽

Octahedral Coordination ◽

Electron Transfer Reactions ◽

Kinetics Of

The kinetics of the reduction of the cobalt(111) octahedral complexes, CoF(NH3)52+, CoCl(NH3)52+ and CoBr(NH3)52+, by iron((11) in various Me2SO-H2O mixtures have been studied over a range of temperatures. The activation parameters obtained for the chloro and bromo systems are consistent with a change in the stereochemistry of the iron (11) atom in the bridged intermediate from octahedral in water to tetrahedral with increasing Me2SO concentration. The fluoro system, however, has activation parameters which are less sensitive to solvent composition and consistent with the iron(11) atom maintaining octahedral coordination.

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Electron-Transfer Reactions in Non-Aqueous Media. V. Solvent Effects in the Reduction of CoN3(NH3)52+ by Iron(II)

Australian Journal of Chemistry ◽

10.1071/ch9792139 ◽

1979 ◽

Vol 32 (10) ◽

pp. 2139 ◽

Cited By ~ 5

Author(s):

TJ Westcott ◽

DW Watts

Keyword(s):

Electron Transfer ◽

Aqueous Media ◽

Activation Parameters ◽

Transfer Reactions ◽

Tetrahedral Coordination ◽

First Order ◽

Precursor Complex ◽

Stage Process ◽

Pseudo First Order ◽

Reversible Formation

The reduction of CoN3(NH3)52+ by iron(II) is rate-determined by a two-stage process involving the reversible formation of an azide-bridged precursor complex prior to electron transfer in each of the solvents water, Me2SO, aqueous Me2SO and HCONMe2. The activation parameters in H2O and Me2SO, and the trends shown with increasing Me2SO concentrations in aqueous Me2SO, are similar to the properties of the previously studied CoCl(NH3)52+ and CoBr(NH3)52+ systems and contrast with the reduction of COF(NH3)52+. The results are consistent with a bridged precursor complex octahedral at both the iron and cobalt atoms in water but with tetrahedral coordination about the iron in Me2SO. In HCONMe2, as in the reduction of COF(NH3)52+, COCl(NH3)52+ and COBr(NH3)52+, the precursor complex is a significant part of the reacting solutions, and as a result the experimental pseudo-first-order rate constants for the loss of CoIII are not linearly dependent on the concentration of FeII. The initial spectra of the reacting solutions in this system also indicate significant concentrations of the precursor complex.

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Estimation of the Outer Sphere Contribution to the Activation Parameters for Homogeneous Electron Transfer Reactions Using the Mean Spherical Approximation

10.21236/ada243217 ◽

1991 ◽

Author(s):

W. R. Fawcett ◽

L. Blum

Keyword(s):

Electron Transfer ◽

Activation Parameters ◽

Outer Sphere ◽

Transfer Reactions ◽

Spherical Approximation ◽

Mean Spherical Approximation ◽

Electron Transfer Reactions ◽

The Mean

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Electron-transfer reactions in non-aqueous media. VII. Reduction of CoF(NH3)52+ and Co(HCOO)(NH3)52+ by copper(I) in dimethyl sulfoxide-water mixtures

Australian Journal of Chemistry ◽

10.1071/ch9831923 ◽

1983 ◽

Vol 36 (10) ◽

pp. 1923 ◽

Cited By ~ 2

Author(s):

JMB Harrowfield ◽

L Spiccia ◽

DW Watts

Keyword(s):

Electron Transfer ◽

Dimethyl Sulfoxide ◽

Aqueous Media ◽

Mixed Solvents ◽

Transfer Reactions ◽

Aprotic Solvents ◽

Aqueous Mixtures ◽

Electron Transfer Reactions ◽

Dipolar Aprotic Solvents ◽

Sphere Mechanism

Previous work on the reduction of a series of cobalt(III) complexes by iron(II) in dipolar aprotic solvents and in aqueous mixtures has been extended to reduction by copper(I). The greater stability of copper(I) to disproportionation in these media has permitted the study of the reduction of CoF(NH3)52+ and Co(HCOO)(NH3)52+ in range of solvents over a number of temperatures with a precision not possible in previous studies in water. The results are consistent with an inner-sphere mechanism in which the copper(I) reductant is preferentially solvated by dimethyl sulfoxide to the exclusion of water in mixed solvents.

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