A Solvent-Independent Reference Potential in Nonaqueous Solvents

为了研究非水溶剂体系中氧化还原电位和电化学反应动力学参数的溶剂效应，有必要建立一个与溶剂无关的电位标度。本文提出[Fe（cp）_2]^&lt;+/0&gt;（A^&lt;+/0&gt;）和[Fe（cp）（cb）]^&lt;0/-&gt;（B^&lt;0/-&gt;）对的平均氧化还原电位（E^&lt;o '&gt;）是一个不依赖于溶剂的参考电位（E_<ref>）。[Fe（cp）_2]^++e =[Fe（cp）_2] E^&lt;o '&gt;_A（1）[Fe（cp）（c B）]+e^-=[Fe（cp）（c B）]^- E^&lt;o'&gt;_B（2）E_<ref>=（E^o '&gt;_A+E^o'&gt;_B）/2（3）使用Bom-Haber循环，ELf可以表示如下。<ref>（Ip + Ea）/2-（DELTAG ^s_A-DELTAG ^S_B）/2+<B->其中Ip是[Fe（cp）_2]的电离电势，Ea是[Fe（cp）_2]的电子亲和势，（c B）]，DELTAG^S_i为络合物i的溶剂化能。K是所使用的参比电极的能量，并且Ljp是液体接界电势。[Fe（cp）_2]和[Fe（cp）（cb）]的结构相似性表明它们的溶剂化能几乎相等。在10种非质子溶剂和6种质子溶剂中的伏安和电导结果证实了DELTAG^S_A=DELTAG^S_B和DELTAG^S_&lt;A+&gt;=DELTAG^S_<B->。因此，方程4中右侧的溶剂化能项被抵消，因此E_<ref>是溶剂无关的。在低介电常数的溶剂中，离子对的形成使E^&lt;o '&gt;_A和E^&lt;o'&gt;_B移动。然而，E^&lt;o '&gt;_A和E^&lt;o'&gt;_B的电势位移大小相同，符号相反。因此，<ref>即使在低介电常数的溶剂中，E_、E^&lt;o '&gt;_A和E^&lt;o'&gt;_B的平均值也不受离子对形成的影响。

In order to study on solvent effect on the redox potential and kinetic parameters of electrochemical reactions in nonaqueous solvents, it is necessary to establish a solvent-independent potential scale. We propose here that the average of redox potentials (E^<o'>) of the[Fe(cp)_2]^<+/0>(A^<+/0>) and [Fe(cp)(cb)]^<0/->(B^<0/->) couples, where cp=cyclopentadienyl and cb=(3)-1, 2-dicarbollyl, is a solvent-independent reference potential (E_<ref>).[Fe(cp)_2]^++e =[Fe(cp)_2] E^<o'>_A (1)[Fe(cp)(cb)]+e^-=[Fe(cp)(cb)]^- E^<o'>_B (2)E_<ref> =(E^<o'>_A+E^<o'>_B)/2 (3)Using the Bom-Haber cycle, ELf can be expressed as follows.FE_<ref>=(Ip + Ea)/2-(DELTAG^s_A-DELTAG^S_B)/2+(DELTAG^S_<A+>-DELTAG^S_<B->)/2+K+Ljp (4)where Ip is the ionization potential of [Fe(cp)_2], Ea the electron affinity of[Fe(cp)(cb)], and DELTAG^S_i the solvation energy for the complex i. K is the energy of the reference electrode used and ljp is the liquid junction potential. The very close structural resemblance between[Fe(cp)_2] and[Fe(cp)(cb)]suggests that the solvation energies for the neutral species are almost equal to each other. Voltammetric and conductometric results in ten aprotic and six protic solvents confirm DELTAG^S_A=DELTAG^S_B and DELTAG^S_<A+>=DELTAG^S_<B->. Thus the solvation energy terms of the right hand side in equation 4 are canceled out, ane therefore E_<ref> is solvent-independent. In the solvents with low dielectric constant the ion-pair formation shifts E^<o'>_A and E^<o'>_B. The potential shifts of E^<o'>_A and E^<o'>_B, however, are the same in magnitude and opposite in sign each other. Therefore E_<ref>, the average of E^<o'>_A and E^<o'>_B is not affected by the ion-pair formation even in the solvents with low dielectric constant.