Assoziationsverhalten und Dipolmomente von Tetra(n-Butyl)-Ammoniumpertechnetat und Tetra(n-Butyl)Ammoniumperchlorat in Benzol

At very low concentrations tetra-n-butylammonium pertechnetate and tetra-n-butylammonium perchlorate form ion pairs in benzene Solutions. At room temperature, formation of dimers and larger aggregates begins to occur at concentrations of 10⁻⁵ mol/1. This behaviour has been investigated quantitatively by the determination of the molecular weight in the case of the perchlorate salt, and by the concentration-dependence of the pertechnetate phase equilibrium between water and benzene. It could be demonstrated that Bu₄NClO₄-dimers and larger aggregates have no apparent dipole moment. Knowing the relative concentration of the monomers from the extraction experiments, the dipole moment of 16.6 Debye has been calculated for the ion pair. Applying an extrapolation method, the dipole moment of Bu₄NCIO₄ was found to be 16.2 Debye. The similarity of the dipole moments is in good agreement with the similar ionic radii of the TcO₄⁻ and the ClO₄⁻ ions. The charge separation in the ion pairs however, calculated from the dipole moments, is smaller than the sum of cationic and anionic radii.