Вісники НТУ "ХПІ"

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The influence of singly charged ions on the translational motion of molecules in extremely dilute amide solutions
(Національний технічний університет "Харківський політехнічний інститут", 2021) Bulavin, Viktor Ivanovych; Vunik, Ivan Nikolajevych; Kramarenko, Andrii Viktorovych; Rusinov, Alexandr Ivanovych
The type of short range solvation of Li⁺ , Na⁺ K⁺ , Rb⁺ , Cs⁺ , NH₄⁺ , Cl⁻ , Br⁻ , I⁻, ClO₄⁻ ions has been determined and analyzed in formamide (FA), Nmethylformamide (MFA), N-dimethylformamide (DMF) at 298.15 K. In order to determine the type of ion solvation we used familiar-variable quantitative parameter (d – ri), where d is the translational displacement length of ion, ri is its structural radius. It was found that the difference (d – ri) is equal to the coefficient of attraction friction (CAF) of ions normalized to the solvent viscosity and hydrodynamic coefficient. The sign of the CAF is determined by the sign of the algebraic sum of its ion-molecular and intermolecular components. In amide solutions the studied cations are cosmotropes (positively solvated ((d – ri) > 0), structure-making ions) and anions are chaotropes (negatively solvated ((d – ri) < 0 ), structurebreaking ions). In the amide series, regardless of the sign (d – ri), the near-solvation enhances, which can be explained by the weakening of the specific interaction between the solvent molecules. The decrease of d and respectively (d – ri) with increasing cation radius in a given solvent is the result of weakening of its coordinating force due to the decrease of charge density in the series Li⁺–Na⁺–K⁺–Rb⁺–Cs⁺ . The increase of d (and (d – ri), correspondingly) for the ions studied in the series FA-MFA-DMF can be explained by the weakening of intermolecular interactions in this series, which leads to the strengthening of solvation. It was found that for the halide ions in the series FA-MFA-DMF the regular growth of d parameter is explained by the weakening of the solvent structure. It was shown that Li⁺ ion with the lowest diffusion coefficient among cations and the highest d value forms kinetically stable complexes in amide solutions.
Near hydration of singly charged monoatomic ions in extremely diluted solutions: the effect of temperature and pressure
(Національний технічний університет "Харківський політехнічний інститут", 2021) Bulavin, Viktor Ivanovych; Vunik, Ivan Nikolajevych; Kramarenko, Andrii Viktorovych; Rusinov, Alexandr Ivanovych
The diffusion coefficient 0iD and the distance of translational displacement of Li+, Na+K+, Cs+, Cl– and Br– ions d in water at 298.15 K –423.15 K (25 K step) and pressure from 0.0981 to 784.5 MPa (98.1 MPa step) were calculated from the literature data on limiting molar electrical conductivity. The 0iD values for these ions increase with pressure growth from 0.0981 to 98.1 MPa at 298.15 K. Further pressure increase (up to 785 MPa) leads to decrease in 0iD. Temperature growth under isobaric conditions leads to an increase in 0iD. Parameter (d – ri) (deviation from the Stokes–Einstein law, riis ion structural radius) was used as a criterion for the type of ion solvation. It is shown that Li+ and Na+ ions behave as cosmotropes, or positively solvated structure–forming ions having (d– ri) > 0. The Cs+, Cl–, Br– ions behave as chaotropes, or negatively solvated structure–breaking ions having (d– ri) < 0. For the K+ ion, the (d – ri) deviation is alternating. At 0.0981 MPa and 298.15 K, the K+ ion is a chaotrope. But at 320 K (Tlim) parameter (d – ri) = 0. It corresponds to the transition from negative to positive solvation. Above Tlimat P = const, the K+ ion is a cosmotrope. At 298.15 K and up to 98.1 MPa, the pressure causes the same change in the (d – ri) deviation as the temperature. On the contrary, at 320 K and higher, the pressure affects the near hydration in the direction opposite to the temperature.

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