A Solvent-Independent Reference Potential in Nonaqueous Solvents

为了研究溶剂对非水溶剂中电化学反应氧化还原电位和动力学参数的影响，有必要建立与溶剂无关的电位标度。我们在此提出，[Fe(cp)_2]^<+/0>(A^<+/0>)和[Fe(cp)(cb)]^<0/->(B^<0/->)对的氧化还原电位的平均值（E^< 0 '>）是一个与溶剂无关的参考电位（E_<ref>），其中cp=环戊二烯，cb=(3)- 1,2 -二羰基。(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)使用Bom-Haber周期,精灵可以表示如下。FE_<ref>=(Ip + Ea)/2-(DELTAG^s_A-DELTAG^S_B)/2+(DELTAG^S_<A+>-DELTAG^S_<B->)/2+K+Ljp(4)，其中Ip为[Fe(cp)_2]的电离势，Ea为[Fe(cp)(cb)]的电子亲和力，DELTAG^S_i为配合物i的溶剂化能。K为所使用的参比电极的能量，Ljp为液结电位。[Fe(cp)_2]和[Fe(cp)(cb)]在结构上非常相似，表明中性物质的溶剂化能几乎相等。在十种非质子溶剂和六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_<A+>=DELTAG^S_<B->。因此，方程4中右边的溶剂化能项被消去了，因此E_<ref>与溶剂无关。在低介电常数的溶剂中，离子对的形成使E^<o'>_A和E^<o'>_B发生移位。然而，E^<o'>_A和E^<o'>_B的电位位移大小相同，符号相反。因此，即使在介电常数较低的溶剂中，E^<o'>_A和E^<o'>_B的平均值E_<ref>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.