Molecular motions in the hydration sphere of the F−ion in aqueous solution. (with some results for HF, HF2, and BF)

Experimental results for the F19nuclear magnetic relaxation rate in aqueous solutions of NaF, KF, RbF and CsF as a function of the concentration are reported. Using these data together with the proton relaxation behaviour in the same solutions three models for the hydration sphere are discussed: A long‐lived rigid and non‐rigid hydration sphere and a short‐lived hydration sphere. Then, experimental results for the self‐diffusion coefficient of the F−ion in aqueous solution together with the corresponding H2O self‐diffusion coefficients are reported. The analysis of all these data yields the result that the F−hydration sphere is non‐rigid and probably fairly short‐lived. ThepH dependence of the F−relaxation is evaluated to give the reorientational correlation times of HF and HF and from the F relaxation in NaBF4solution we derive the reorientational correlation time of the BF ion.