La[Fe(CN)6] ion pairing in aqueous solution. A dielectric relaxation study

Abstract

Complex permittivity spectra of aq. La[Fe(CN)6] solns. at 25° over the frequency range 0.2 ≤ ν ≤ 89 GHz are presented. Because of the large assocn. const. of La ferricyanide, KA = 5300, and its high ion-pair dipole moment, μIP = 77.7 D, dil. solns. in the range 0.0026≤c/mol dm-3≤0.0485 could be studied. The current models for the anal. of the ion-pair dispersion amplitude are reliable. The data reveal that the formation of contact ion-pairs is at a nearly diffusion controlled rate, and suggest that the ion-pair activity coeff. deviates from ideality. The effective solvation no. of the electrolyte is detd. from the solvent permittivity.