Bridge-assisted electron transfer

Bridge mediation mechanisms in heterogeneous outer sphere electrochemical reactions has also been theoretically treated using the pull—push and push-pull mechanistic concepts [84]. Schmidt [85] has considered theoretically homogeneous inner sphere bridge electron transfer reactions without atom or ion transfer. Bridge mediation in electron transfer reactions may also involve simultaneous atom or ion transfer. Heyrovsky [86] invoked mediation of electron transfer by formation of bridges to explain the enhancement of the rate of electroreduction of indium (III) ions in the presence of specifically adsorbed halide ions on mercury. 

Specifically adsorbed thiocyanate also accelerates the kinetics of Cr(OH2)6+ oxidation on mercury with the incorporation of the anion ligand into the inner coordination sphere of the product. The oxidation of this cation is similarly enhanced by chloride ions [87] and the rate of the electrode reaction is proportional to the surface concentration of chloride ions which, like thyocyanate, are incorporated into the 

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Fig. 3. Molecular orbitals used in the many-electron formulation of bridge-assisted electron transfer...

Experimental Test of Bridge-assisted Electron Transfer Models... 

Kharkats, Y.L, Madumarov, A.K., and Vorotyntsev, M.A. (1974) Application of density matrix method in quantum-mechanical calculation of bridge-assisted electron-transfer probability in polar media. Journal of the Chemical Society. Faraday Transactions II, 70, 1578-1590. 

Ratner M. A. (1990), Bridge-assisted electron transfer effective electronic coupling , J. Phys. Chem. 94, 4877-A883. 

Fig. 16.7 Bridge-assisted electron transfer, (a) The existence of intermediate electron binding sites between the donor and acceptor changes the effective tunneling barrier and can promote the transfer rate, (b) In a simple model of bridge-assisted transfer each of the donor, acceptor, and intermediate sites are represented by a single electronic level.

The bridge-assisted electron transfer discussed above is a coherent quantum-mechanical process. Its tunneling nature is manifested by the exponentially... 

It is instructive to compare this result for the conduction through an TV + 2 level bridge to the parallel expression for the bridge-assisted electron transfer rate (cf. Eqs (16.114) and (16.113)... 

Theoretical treatments of bridge-assisted electron transfer... 

In 1969 Schmidt made the first attempt to calculate quantum mechanically the probability of the elementary act of the bridge-assisted electron transfer reaction. However, the transitions were only taken into account for which the energy is conserved in all the states including the intermediate one. In a number of subsequent papers, a more detailed quantum mechanical calculation for the reactions of this kind was performed. Recently the theory was extended to adiabatic bridge-assisted reactions. 

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