Investigation of ion-pairing phenomenon in BaF2 aqueous solution: Experimental and theoretical studies

The ion-pair association constant values, related to the reaction Ba2+ + F− ⇆ [BaF]+, are determined by means of NMR spectroscopy. The values for thermodynamic functions of the ion-pairing process are calculated on the basis of the NMR results. In addition, the association entropy has been found to be dependent on temperature. Comparing the experimental data and Fuoss theory, it is found that [BaF]+ contact ion-pair is formed in the BaF2 aqueous solution. Also, hydration of barium-fluoride ion-pair is investigated by the DFT method. The hydration number of barium-fluoride ion-pair is determined by comparing the experimental and theoretical results. The effect of number of water molecules on the properties of ion-pairs is investigated by determining NQR and NMR parameters. Also, the relation between the chemical shifts and the energy gap between the highest occupied molecular orbital (HOMO) and low-lying virtual molecular orbital (LUMO) is investigated.