Electron Transfer Processes and the Oxidation–Reduction Reactions of Hexacyanoferrate (III) Ion in Aqueous Solutions

1952 ◽  
Vol 56 (7) ◽  
pp. 858-862 ◽  
Author(s):  
Arthur W. Adamson

It has been realized for some time that simple electron-transfer processes play an important part in the mechanism of many oxidation-reduction reactions in solution. An attempt has been made to give a quantum-mechanical interpretation of these processes on the basis of the earlier theories of electron transfer in the gaseous state (Landau 1932; Bates & Massey 1943). The present treatment for solutions takes into account the role of the solvent, with particular reference to the operation of the Franck—Condon principle and it also leads to some definite picture of the transition state for the electron transfer process. A number of examples are discussed, including electron transfer between like ions of different valency and also reactions involving complex ions, e.g. metal porphyrins, the reactions of which are of importance in certain biochemical processes. It appears that the application of certain theoretical principles leads to a satisfactory understanding of electron-transfer processes in solution from a qualitative and, in some cases, also from a semi-quantitative point of view.


The flash photolysis of halide solutions yields unstable species believed to be the dihalide ion the absorption spectrum of which we have observed and photographed. This transient has been noted during the photolysis of ( а ) the aqueous solutions of KCl, KBr, KI, HCl, NaCl, NaBr, NH 4 C1, MgCl 2 , HgCl 2 , CaCl 2 and SrCl 2 , ( b ) the ethyl and methyl alcoholic solutions of KBr and KI, ( c ) the methyl cyanide solution of KI. The effect of the addition of sulphuric acid, potassium hydroxide and Mn 2+ ion to certain of the solutions has also been studied. Our interpretation of the results of the flash photolysis of KI in solution, based on the Rigg & Weiss mechanism of electron transfer, involves the postulation of the splitting of the solvent molecule. In water solution, this would mean the formation of hydrogen. The production of hydrogen in aqueous solutions of KI of pH 6 to 7 has been confirmed by an investigation of the steady state photolysis.


Author(s):  
Abraham Nitzan

Electron transfer processes are at the core of all oxidation–reduction reactions, including those associated with electrochemistry and corrosion. Photoelectrochemistry and solar energy conversion, organic light emitting diodes, and molecular electronic devices, all dominated by electron transfer and electron transmission in molecular systems, are presently subjects of intensive research at the interface of science and technology. Similarly, electron transfer processes constitute fundamental steps in important biological phenomena such as photosynthesis and vision. This chapter is an introduction to the general phenomenology and theoretical concepts associated with these processes. Electron transfer is one of the most important, and most studied, elementary chemical processes. This most fundamental oxidation–reduction process lies at the core of many chemical phenomena ranging from photosynthesis to electrochemistry and from the essential steps governing vision to the chemical processes controlling corrosion. As other molecular phenomena that involve charges and charged particles, the natural environment for such processes is a polar solution; the solvation energy associated with the polarization of the environment is a major component in the energetics of such processes. Noting that in vacuum typical molecular ionization potentials are of the order of (100–400)kBT for T = 300 K, it appears that the stabilization of ionic species by the solvent environment is the reason why electron transfer processes in solution can take place at room temperature. When we try to go beyond this general statement, questions arise.


2010 ◽  
Vol 49 (6) ◽  
pp. 1014-1022 ◽  
Author(s):  
M. Laura Dántola ◽  
Mariana Vignoni ◽  
Constanza González ◽  
Carolina Lorente ◽  
Patricia Vicendo ◽  
...  

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