Oscillations, Waves, and Interactions - GWDG

Multistep association of cations and anions 353
4.2 Uncommon complexation of zinc(II)chloride
Similar to aluminium sulfate aqueous solutions (Fig. 12), the dielectric spectra of
aqueous solutions of zinc chloride show two relaxation regions (Fig. 18). Again the
high-frequency region reflects the reorientational motions of the solvent molecules.
The additional low-frequency relaxation verifies in an obvious manner the existence
of (dipolar) ion complex structures in transition metal halide aqueous solutions, as
suggested from the ɛ1 data of such systems (sect. 4.1). Because of the intriguing
thermodynamic, structural, and transport properties of zinc chloride solutions these
structures have been discussed for long time [86–88]. A multitude of different ion
complexes has been identified using a variety of experimental techniques. In general
the complex reaction scheme shown in Fig. 19 has to be considered when discussing
Figure 18. Real part ɛ ′ (ν) and negative imaginary part ɛ ′′ (ν) of the dielectric spectrum of
water (+) and of a 2.04 mol/l solution of ZnCl2 in water (•) at 25 ◦ C [22,23]. Dashed lines
show the subdivision of the spectrum for the salt solution according to Eq. (15) with h2 ≡ 0.