Theoretical Aspects Associated with Charge-transfer Kinetics across Interfaces between Two Immiscible Electrolyte Solutions (original) (raw)
Related papers
Structural Effects on Intermolecular Electron Transfer Reactivity
Journal of The American Chemical Society, 2000
Rate constants (k ij ) measured by stopped flow are reported for 50 additional intermolecular electron transfer reactions between 0 and 1+ oxidation states of various compounds, enlarging our data set to 141 reactions between 45 couples in acetonitrile containing 0.1 M tetrabutylammonium perchlorate at 25°C. Hydrazines with both saturated and unsaturated substituents, ferrocene derivatives, and heteroatom-substituted aromatic compounds are included in the couples studied. Least-squares fit of all the reactions to simple Marcus cross-reaction theory provides an internally consistent set of best fit intrinsic barriers ∆G ‡ ii (fit) (for selfelectron transfer of each couple) covering a range of over 19 kcal/mol (rate constant range 2 × 10 14 ) that predicts the k ij rather accurately. All reactions have ratios of calculated to observed k ij in the range 0.3-3.3 and 95% fall in the range 0.5-2.0. These results require that the preexponential factor for a cross reaction is close to the geometric mean of those for the self-reactions, which is not expected. Changes in internal reorganization energy (λ v ) have major effects on ∆G ‡ ii (fit), and changes in electronic overlap (H ab ) have easily detectable ones, but the reactions studied are clearly not strongly nonadiabatic, even though in many cases the only electronic overlap at the transition state is between nonbonded alkyl groups. It is argued that these reactions occur in the "elbow region" between nonadiabatic and adiabatic electron transfer.
Journal of Physical Chemistry B, 2002
The dynamics of photoinduced heterogeneous electron transfer between a series of ferrocene derivatives and the heterodimer zinc meso-tetrakis(p-sulfonatophenyl)-porphyrin (ZnTPPS 4-) and zinc meso-tetrakis(Nmethylpyridyl)porphyrin (ZnTMPyP 4+ ) were studied at the polarized water/1,2-dichloroethane interface. The photocurrent responses originating from the heterogeneous quenching of the heterodimer showed a welldefined dependence on the formal Gibbs energy of electron transfer (∆G°′ et ). The use of various ferrocene derivatives with different redox potentials and potentiostatic control over the Galvani potential difference across the interface allowed modifying ∆G°′ et over a range of 1 eV. The photocurrent as a function of ∆G°′ et can be unambiguously described in terms of a Marcus-type behavior of the phenomenological bimolecular electron-transfer rate constant (k et II ). The solvent reorganization energy was estimated to be 1.05 eV, from which an average distance of 0.8 nm between the redox species can be evaluated within the framework of the Marcus model for sharp liquid/liquid boundary. These studies also provided an estimate of the activation-less limit of k et II of 3 × 10 -19 cm 4 s -1 , which reflects a rather nonadiabatic behaviour of the charge-transfer process. The origin of this nonadiabaticity is connected to the average distance separating the redox species across the interface. Finally, the implications of the observed potential dependence of k et II on current debates about structure and potential distribution across the interface are briefly highlighted.
Journal of Molecular Structure: THEOCHEM, 1996
Important energy quantities governing electron transfer (ET) kinetics in polar solutions (reorganization energy, E,, and net free energy change, AU) are evaluated on the basis of quantum-chemical self-consistent reaction-field (SCRF) models. Either self-consistent field (SCF) or configuration interaction (CI) wavefunctions are used for the solute, which occupies a molecular cavity of realistic shape in a dielectric continuum. A classical SCRF model together with unrestricted Hartree-Fock SCF wavefunctions based on the semiempirical PM3 Hamiltonian is applied to the calculation of the solvent portion of E, (denoted E,) for two different series of radical ion ET systems: radical cations and anions of biphenylyl/naphthyl donor/acceptor (D/A) pairs linked by cyclohexane-based spacer groups and trans-staggered radical anions of the type (CH,),, m = 2-5. Results for E, based on two-configurational CI wavefunctions and an alternative reaction field (the so-called Born-Oppenheimer model, which recognizes the fast timescales of solvent electrons relative to those involved in ET) are also noted. Results for innersphere (i.e. intra-solute) reorganization, Ei, and for AU are also reported. The semiempirical E, results are quite similar to corresponding ab initio results and display the form of the two-sphere Marcus model for E, as a function of D/A separation. Nevertheless, in the one case where direct comparison is possible, the calculated E, result is more than twice the magnitude of the estimate based on experimental ET kinetic data. To reconcile this situation, a generalized SCRF model is proposed, which assigns different effective solute cavity sizes to the optical and inertial components of the solvent response, using ideas based on non-local solvation models.
Ion-pairing effects in intramolecular electron transfer
Chemical Physics Letters, 2002
The effect of electrolyte on the rate of intramolecular electron transfer (ET) was analyzed within the framework of ionic association. A unified approach combining the ionic atmosphere and specific ion pairing contributions to the reorganization energy has been developed. The weighing of the free ion and ion pairing contributions is based on the appropriate mass action law. In the limit of weak association the model converges to the Debye-H€ u uckel-Bjerrum picture of electrolytes. In the limit of strong association the ion-pairing dominates. In accordance with experiment, this results in a remarkable decrease of ET rates even at very low electrolyte concentrations. Ó
The Journal of Physical Chemistry B, 2013
We explore solvent dynamics effects in interfacial bond breaking electron transfer in terms of a multimode approach and make an attempt to interpret challenging recent experimental results (the nonmonotonous behavior of the rate constant of electroreduction of S 2 O 8 2− from mixed water−EG solutions when increasing the EG fraction; see Zagrebin, P.A. et al. J. Phys. Chem. B 2010, 114, 311). The exact expansion of the solvent correlation function (calculated using experimental dielectric spectra) in a series predicts the splitting of solvent coordinate in three independent modes characterized by different relaxation times. This makes it possible to construct a 5D free-energy surface along three solvent coordinates and one intramolecular degree of freedom describing first electron transfer at the reduction of a peroxodisulphate anion. Classical molecular dynamics simulations were performed to study the solvation of a peroxodisulphate anion (S 2 O 8 2− ) in oxidized and reduced states in pure water and ethylene glycol (EG) as well as mixed H 2 O−EG solutions. The solvent reorganization energy of the first electrontransfer step at the reduction of S 2 O 8 2− was calculated for several compositions of the mixed solution. This quantity was found to be significantly asymmetric. (The reorganization energies of reduction and oxidation differ from each other.) The averaged reorganization energy slightly increases with increasing the EG content in solution. This finding clearly indicates that for the reaction under study the static solvent effect no longer competes with solvent dynamics. Brownian dynamics simulations were performed to calculate the electron-transfer rate constants as a function of the solvent composition. The results of the simulations explain the experimental data, at least qualitatively.
Theory of Electrochemical Electron Transfer
Introduction to Marcus Theory of Electron Transfer Reactions, 2020
INTRODUCTION References CHAPTER 2 ELECTRON TRANSFER REACTIONS: CLASSIFICATION AND EXAMPLES 2.1 Introduction 2.2 Outer and Inner Sphere ET Reactions 2.3 Adiabatic and Nonadiabatic ET Reactions References CHAPTER 3 HISTORICAL BACKGROUND 3.1 Introduction 3.2 Classical Theory of Electron Transfer 3.3 Quantum Me.chanical Treatment of Electron Transfer 3.4 Other Developments References CHAPTER 4 THE ROLE OF SOLVENT DYNAMICS IN ELECTRON TRANSFER 4.
The Journal of Physical Chemistry C, 2019
We report a combined experimental and computational study on the heterogeneous electron transfer kinetics for a simple one electron transfer reaction (ferrocene/ferrocenium Fc + /Fc couple) in a series of molecular solvents and ionic liquids. We focus on the diagnostics of the electron transfer regime (adiabatic vs. nonadiabatic) and assess the parameters of the quantum mechanical electron transfer theory, which determine the observed tendencies in the solvent effect on the electron transfer rates. The applicability of the linear plots of the electron transfer rate constant vs. longitudinal relaxation time (or solvent viscosity) for distinguishing between different ET kinetic regimes is analyzed. Classical molecular dynamics simulations were performed to calculate the potential of mean force for Fc and Fc +. The structure of reaction layer derived from molecular dynamics is thoroughly investigated. The experimental dielectric spectra for the both type of solvents are used for quantum corrections of the outer-sphere reorganization energy, as well as for estimations of the effective frequency factor in the limit of strong and weak electronic coupling. The electron transfer rate constants are calculated and discussed in the viewpoint of available experimental data.