NEAR SOLVATION OF TETRAALKYLAMMON IONS IN ETHYLENE GLYCOL AND IN WATER

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Diffusion coefficients and microscopic characteristics of the length (), time (τ), and the rate of diffusion shift (drift) of tetraalkylammonium ions (TAA) (Me4N+, Et4N+, Pr4N+, Bu4N+, Pe4N+) in ethylene glycol (EG) and in water at temperature 298.15 K are calculated from literature data on the limiting molar electrical conductivity of these ions. From analysis of the calculated data, it was found that the value for TAA ions in ethylene glycol and in water depends on the structural radius of the ion and on the solvent. For the above ions, the parameter in the EG is less than in water, which indicates a more significant inhibitory effect of the EG on the drift of TAA ions compared to water. A correlation was established between the sign of the deviation of the length of the discrete diffusion displacement from the structural radius of the ion (ri) in the form of (– ri) and the solvability of ions according to Samoilov. When parameter exceeds the crystallographic (structural) radius of the ion, the latter is positively solvated. If value is less than the crystallographic radius of the ion, negative solvation is observed. The essence of the phenomenon of negative solvation according to Samoilov is that the ion-molecule bonds of the solvent are weaker than the bonds of the solvent molecules to each other. Our correlation between the deviation sign (– ri) from the Stokes – Einstein law and the short-range solvation of ions according to Samoilov in solvents with a spatial network of H-bonds (EG, water) indicates that ion diffusion is associated with short-range solvation, and the parameter is its quantitative characteristic, i.e. we propose a deviation from the Stokes-Einstein law (– ri) as a measure of the near solvation of ions. For the ions studied, the parameter (– ri) has positive values, and in the EG a negative value of the parameter (– ri) is observed only for the Me4N+ ion, which indicates its negative solvation. The parameter τ in the EG exceeds the same values in water by 9-14 times, which indicates the inhibitory effect of the drift of TAA ions, also caused by the influence of solvent viscosity. The rate of translational displacement of TAA ions in water is 6-12 times higher than in the EG.