Vyacheslav G. Kremenetsky

Charge-transfer kinetics in the Nb(V)/Nb(IV) couple in alkali-metal molten chlorides

Charge-transfer standard rate constants ks for Nb(V)/Nb(IV) redox couple in KCl-NbCl5 and CsCl-NbCl5 chloride melts at glassy carbon and platinum electrodes are determined. The Nb(V) electro-chemical reduction process in the NaCl-KCl (equimolar mixture)-NbCl5 melt was shown being reversible even at high polarization scan rate (v = 2.0 V s−1); hence, the determination of ks appeared impossible. Values of ks in KCl-NbCl5 melts are higher than those in CsCl-NbCl5 melts. Quantum-chemical calculations done in nM+[NbCl6]—model systems by the Discrete Fourier Transformation method showed that the calculated ratio of charge-transfer activation energies in the K+-Cs+ series corresponds to changes in the experimental charge-transfer rate constants. The charge-transfer standard rate constants increase with the increasing of temperature and with the passing from glassy carbon electrode to platinum one.

Ab Initio Estimation of NbF− 6 , NbClF2− 6 , and NbF2− 7 Complexes Stability in Alkali Chloride Melts

Quantum-chemical calculations of the parameters of the nM+・NbClF2−6 type particles have been performed, where M stands for Na, K, Cs and n = 0 - 6. Under certain conditions such particles may exist in melts of alkali metal chlorides.Within the framework of this approximation, compositions for themost stable particles in molten salts were obtained. Relative stability of the particles containing the NbF−6 , NbClF2−6 , and NbF2−7 complexes has been calculated. Energies and some other characteristics of the electron structure and the particle geometry structure were determined depending on the n and M values. For estimation of the third sphere’s influence, the systems (M2NbF7 +8MCl) and (M2NbF7 +15MCl) are surveyed. The chlorine anion enters the first coordination sphere in the Nasystem only, i. e. in this system the true complex NbClF3−7 is formed.

Quantum-Chemical Study of the Charge Transfer Mechanism in the MgTiF6–12MgCl2 System

A quantum-chemical analysis of frontier molecular orbitals is used to propose a mechanism for the electrochemical electron transfer in the model system MgTiF6 + 12MgCl2. The geometric structure of the transient state is shown not to be intermediate between the initial and final states of the system. The contraction of the Ti–F bonds during totally symmetrical vibrations is found to be the most probable version providing electron transfer to the system.

Analysis of electrochemical electron transfer mechanisms in molten salts by the frontier orbital method

It has been demonstrated that the application of the frontier orbital method to the quantum-chemical analysis of possible variants of electron transfer in electrochemical systems makes it possible to sharply narrow the search for the transition state and to reduce computational burden by several orders of magnitude. The high informativity of the method allows us to recommend it as a tool for verifying any hypotheses about the mechanism of charge transfer in electrochemical systems.

Comparison of Model Systems (M

On the basis of quantum-chemical calculations the most stable particle compositions are estimated in such model systems as (M

Influence of the outer-sphere shell on the parameters of niobium complexes: Quantum-chemical calculation

The interaction of the complexes NbF61− and NbF62− with their outer-sphere shell consisting of alkaline metal atoms is considered. The calculated parameters characterizing the state of the complexes in the composition of particles nM+·NbF61− and nM+ · NbF62− (M = Na, K, Cs; n = 0–4), respectively, are analyzed using the concept of the “counterpolarizing” effect of the outer-sphere cations on a complex.

Quantum-Chemical Estimation of Outersphere Cations Influence on Charge Transfer at the NbF7 2– Reduction. I. Electronic Structure of Complexes

Quantum-chemical calculations of the parameters of the nM+ ・ NbF7 q− type particles, where M stands for Na, K, Cs; q = 2,3 and n = 0 - 7 have been performed. Within the framework of this approximation, compositions for the most stable particles in molten salts were obtained. It is shown that electron transfer onto the particle results in a different redistribution of the electron density with the Na and K-particles on one hand and Cs-containing particles on the other hand. Energies and some other characteristics of the electron structure and particle geometry were determined depending on the n and M values.

Model of Sodium Chloride Premelting

A model for the premelting of alkali chlorides is proposed. It is shown that diminishing of the free length of phonons under temperature increase may bring about the instability of the crystal lattice near the melting point. A probable structure of a lattice near this temperature been examined.