Investigating the solvation behavior of some perchlorates in non-aqueous medium and predicting their ion-solvation thermodynamics using Born formula

Abstract

A systematic study of volumetric, acoustic properties and thermodynamics of ion solvation, from appropriate data of sound velocity, density and conductivity of RNH3ClO4 (R is Ethyl, n-Propyl, n-Hexyl and n-Octyl) in binary mixtures of acetonitrile (AN) and dimethyl sulfoxide (DMSO) has been made at different temperatures. Various acoustical parameters like relaxation strength (r), Rao’s constant (R), Wada’s constant (W), available volume (Va), van der Waals constant (b) and apparent molal volume (Vɸ) were assessed through the experimental data of density and sound velocity at T = (298, 308, 318 and 328) K and at P = 0.1 MPa pressure. From the data of apparent molal volume, other parameters like limiting apparent molal expansibilities ϕEο and Hepler’s constant (∂ϕEο/∂T)p that helps in determining the structure making and structure breaking ability of solute in the solutions, were evaluated. In the second part of this work, the solvated radii (ri) of alkylammonium (RNH3+) and perchlorate (ClO4-) ions have been determined in the binary mixtures of AN-DMSO solvent system at four investigated temperatures. The solvated radii data is then fitted to modified Born equations, whose provenance and implications are discussed and is utilized to evaluate thermodynamics of solvation in terms of free energy change (ΔGI-S), entropy change (ΔSI-S) and enthalpy change (ΔHI-S) of ion–solvent interactions. It is shown that, the plot of ΔGI-S as a function of 1/ri is linear, indicating the investigated system to follow Born equations. Overall, the results obtained from volumetric, acoustic and thermodynamic data, indicates the possibility of effective solute–solvent interactions amidst the investigated system.