Marcus cross relationship applications

The acid dependence observed in the reduction of trans-[Co(Me4[14]tetraeneN4)(N3)2] by Fe (aq) is attributed to the greater reactivity of the oxidant upon protonation of an azide ligand. The application of the Marcus cross-relationship to the data for the reduction of [Co(tmen)3] (tmen = tetramethylethylenediamine) by [Ru(H20)6] " yields a self-exchange rate constant of 10 s for the [Co(tmen)3] couple. Studies of the spectroscopic... 

Electrochemical measurements of the Cu(II/I) potentials with the nS4 ligands (n = 12-16) indicate that the Cu(II) and Cu(I) species each exist in two different conformational states [170]. Conformational rearrangement may either precede or succeed electron transfer. Rorabacher and coworkers interpreted their results in light of a square mechanistic scheme that neatly reconciles the sweep rate dependence of the cyclic voltammograms with the requisite change in coordination geometry at Cu. Kinetic studies on the electron transfer [149, 170, 176-177] support this scheme application of the Marcus cross relationship to reduction of Cu(II) and oxidation of Cu(I) yields widely discrepant values, presumably because of the different conformational states involved. 

The fact that methyl transfers in water are elementary reactions suggests that they should be a better ground to test the applicability of free-energy relationships in 8 2 reactions. Albery and Kreevoy made an extensive smdy of such reactions and attempted to interpret their free-energy dependence using the Marcus cross-reaction scheme. According to the Marcus cross-relation, the free energy of activation of the cross-reaction... 

A, direct measurement of the exchange reaction B, estimate of the self-exchange rate by application of the Marcus relationship to cross reactions. 

The rate constants and activation parameters (including AV ) for electron self-exchange in the [Mn(CNC(CH)3)6]-"/ -" and [Mn(CNC6Hu)6] couples have been determined by Mn NMR line broadening in several pure and binary organic solvent systems. The values of A V cover a range of about 12 cm moP (-9 to -21 cm mol ) with no simple correlation with solvent parameters observed. A self-exchange rate constant of 0.7 0.4 M" s" has been calculated for the [Mn(edta)(H20)] and [Mn(cdta)(H20)] couples from the application of the Marcus relationship to outer-sphere cross-reactions with a variety of metal complexes in aqueous solution. Deviations from the correlation were observed for the nonadiabatic reactions with osmium tris(polypyridine) complexes. 

The kinetics of several electron transfer reactions of the molybdenum cuboidal system [Mo4S4(edta)2]" ( = 2, 3, 4) with cross-reactants such as [Co(edta)]-, [Fe(edta)]-, [Co(dipic)2] , [Fe(H20)e], and [Pta ] -, have been investigated. The electron self-exchange rate constants determined for the [Mo4S4(edta)2] and [Mo4S4(edta)2] couples, by an application of the Marcus relationship, are 1.5 x 10 and 7.7 x 10 M s , respectively. The rate constants for the outer-sphere oxidation of two dimeric complexes, [MoW 0)2(p-edta-AT,lV )]2- and [W2(0)2(p-0)(p-S)(p-edta-Ar,iV )] -, by [IrCl ] in addic aqueous solution have been measured. While the oxidation of the former complex shows a simple second-order rate law, the kinetics of the oxidation of the latter complex exhibited a rate retardation in the presence of the [IrCl6] complex. 

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