Kinetic Solvation of Singly Charged Ions in Infinitely Dilute Solutions in Ethylene Glycol: Effect of Temperature

Abstract

To quantitatively describe the kind of interaction between ion and solvent, it is convenient to use the concept of negative or positive solvation. We have established earlier that diffusion displacement distance ($\overline{d}$) of an ion correlates with its solvation type. The ion is solvated positively if the average $\overline{d}$ value exceeds the crystallographic (structural) radius of an ion $r_i$; otherwise, ion solvation is negative. In this paper, we have estimated the length, time and velocity of ion diffusion displacement (hop) for singly charged ions $\text{Li}^+$, $\text{Na}^+$, $\text{K}^+$, $\text{Rb}^+$, $\text{Cs}^+$, $\text{Me}_4\text{N}^+$, $\text{Et}_4\text{N}^+$, $\text{Bu}_4\text{N}^+$, $\text{F}^-$, $\text{Cl}^-$, $\text{Br}^-$, $\text {BPh}_{4}^{-}$ over the temperature range from 273.15 K to 473.15 K and for ions $\text{Pr}_4\text{N}^+$, $\text{I}^-$, $\text {NO}_{3}^{-}$, $\text {ClO}_{4}^{-}$ at 298.15 K in ethylene glycol. The fact of the negative solvation of almost all ions studied (except $\text{Li}^+$, $\text{Na}^+$, $\text{F}^-$) in ethylene glycol has been established for the first time. It has been shown that $\text{Me}_4\text{N}^+$ ion has turned out solvated solvophilically in EG as well as in water while ions $\text{Et}_4\text{N}^+$, $\text{Bu}_4\text{N}^+,$ and $\text {BPh}_{4}^{-}$ appeared to be solvated solvophobically. We have estimated the temperature of transition $T_\text {tr}$ (from negative to positive ion solvation) for $\text{K}^+$ and $\text{Rb}^+$ ions. It physically corresponds to the absence of solvation of the ion ($\overline{d}=r_i$).