1991 Fiscal Year Final Research Report Summary
A Solvent-Independent Reference Potential in Nonaqueous Solvents
| Project/Area Number |
02640455
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
分析・地球化学
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| Research Institution | Osaka City Unversity |
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Principal Investigator |
ICHIMURA Akio Osaka City University, Faculty of Science, Lecturer, 理学部, 講師 (50047396)
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| Project Period (FY) |
1990 – 1991
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| Keywords | Reference potential / Nonaqueous solvents / Electrochemical reaction / Solvent effect / Ferrocene / Iron dicarbollyl complex |
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| Research Abstract |
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.
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