Solvent Effect on Redox Potentials of Polynuclear Metal Complexes

The redox behavior of multi-metal complexes exhibits usually the multi-step one-electron transfer processes。The redox potentials are mainly dependent on the degree of interaction among central metal ions and the solvation energy of reductant and oxidant species.In this report，we have studied the solvent effect on the redox potentials for the two one-electron oxidation processes of biferrocene([Fc-Fc])and 1，2-differocenylethane([FcCH I D22 ii D2]CH I D 22 ii D 2 Fc])。The electrode reaction entropies were determined from the temperature dependence on the redox potentials for each oxidation step。The ratio of entropyΔS I D10 I D 1 I D 22 I D 2/ΔS D 10 I D 1 D 21 I D 2 for the biferrocene redox system，whereΔS I D 10 I D 1 I D 21 I D 2 andΔS D 10 I D 1 I D 22 I D 2 are the electrode reaction entropies for the first one-electron oxidation of[Fc-Fc]I D 1+I D 1/([Fc-Fc])and the second one-electron oxidation of the first one-electron oxidation of[Fc-Fc]I D 1+I D 1/([Fc-Fc])and the second one-electron oxidation of[Fc-Fc]I D 1+I D 1(Fc-Fc)Respectively，is nearly2，whereas that for the 1，2-differrocenylethane system is nearly1.Furthermore，ΔS I D10 I D1 I D 21 I D 2([Fc-Fc]I D 1+I D 1/([Fc-Fc])is smaller than，ΔS I D 10 I D 1 I D 21 I D 2([FcCH I D 22 I D 2 CH I D 22 I D 2 Fc]I D 1+I D 1/([([FcCH D 22 E])D 2 CH D 22 D 2 Fc D.These results suggest that the solvation for[Fc-Fc]+and[Fc-Fc]2+is represented as charge delocalized([Fc-Fc]I D1+I D1)(S)I D 2 p D 2 and([Fc-Fc]I D 12+D 1)(S)I D 2 q d 2，respectively，where S represents a solvent molecule，And that the solvation for[FcCH D 22个D 2 CH D 22个D 2 Fc]I D 1+I D 1 and[FcCH I D 22 I D 2 CH D 22 I D 2 Fc]I D 12+I D 1 is represented as charge localized(S)D 2τD 2 D 2 D 1+I D 1[FcCH D 22 I D 2 CH I D 22 D 2 Fc]I D 1+I D 1 and(S)I D 2τD 2 D 2 Fc D 2 D 2 D D 2 Fc D 2 D 2 D D 2 Fc D 2D 1+D 1(S)D 2τD 2，Respectively。

The redox behavior of multi-metal complexes exhibits usually the multi-step one-electron transfer processes. The redox potentials are mainly dependent on the degree of interaction among central metal ions and the solvation energy of reductant and oxidant species. In this report, we have studied the solvent effect on the redox potentials for the two one-electron oxidation processes of biferrocene ([Fc-Fc]) and 1,2-differocenylethane ([FcCHィイD22ィエD2]CHィイD22ィエD2Fc]). The electrode reaction entropies were determined from the temperature dependence on the redox potentials for each oxidation step. The ratio of entropy ΔSィイD10ィエD1ィイD22ィエD2/ΔSィイD10ィエD1ィイD21ィエD2 for the biferrocene redox system, where ΔSィイD10ィエD1ィイD21ィエD2 and ΔSィイD10ィエD1ィイD22ィエD2 are the electrode reaction entropies for the first one-electron oxidation of [Fc-Fc]ィイD1+ィエD1/([Fc-Fc]) and the second one-electron oxidation of [Fc-Fc]ィイD12+ィエD1/([Fc-Fc]ィイD1+ィエD1), respectively, is nearly 2, whereas that for the 1,2-differrocenylethane system is nearly 1. Furthermore, ΔSィイD10ィエD1ィイD21ィエD2([Fc-Fc]ィイD1+ィエD1/([Fc-Fc]) is smaller than, ΔSィイD10ィエD1ィイD21ィエD2([FcCHィイD22ィエD2CHィイD22ィエD2Fc]ィイD1+ィエD1/([([FcCHィイD22ィエD2CHィイD22ィエD2Fc]) . These results suggest that the solvation for [Fc-Fc]+ and [Fc-Fc]2+ is represented as charge delocalized ([Fc-Fc]ィイD1+ィエD1)(S)ィイD2pィエD2 and ([Fc-Fc]ィイD12+ィエD1)(S)ィイD2qィエD2 , respectively, where S represents a solvent molecule, and that the solvation for [FcCHィイD22ィエD2CHィイD22ィエD2Fc]ィイD1+ィエD1 and [FcCHィイD22ィエD2CHィイD22ィエD2Fc]ィイD12+ィエD1 is represented as charge localized (S)ィイD2τィエD2ィイD1+ィエD1[FcCHィイD22ィエD2CHィイD22ィエD2Fc]ィイD1+ィエD1 and (S)ィイD2τィエD2ィイD1+ィエD1[FcCHィイD22ィエD2CHィイD22ィエD2Fc]ィイD1+ィエD1(S)ィイD2τィエD2, respectively.