Broadband dielectric relaxation spectroscopy (DRS) has been used to investigate aqueous solutions of MgCl2 and CaCl2 up to concentrations of about 1.8 mol L–1 at 25 °C over the frequency range 0.07 ≤ ν/GHz ≤ 89. Detailed analysis of the dominant solvent mode centered at ∼20 GHz showed that both Mg2+ and Ca2+ are strongly solvated, each immobilizing ∼20 water molecules on the DRS timescale. This is consistent with the formation of two well-defined hydration layers around both cations. The hydration shell of Ca2+(aq) was found to be slightly more labile compared with Mg2+(aq). Two or three low-intensity solute-related modes were observed at frequencies ≲10 GHz for MgCl2(aq) and CaCl2, respectively. Two of these modes were attributed to the formation of double-solvent-separated and solvent-shared 1:1 ion pairs. The third mode (observed at very low frequencies and only for some CaCl2 solutions) was thought to be due to an ion-cloud relaxation. No evidence was found for “slow” water or, consistent with the strong cation hydration, for contact ion pairs. The overall association constants for MgCl+(aq) and CaCl+(aq) calculated from the ion-pairing constants were very small but in good agreement with literature values obtained from other techniques.

Dilute l-glutamate affects water dynamics beyond its 1st hydration shell but above 0.4 M only H2O surrounding carboxylate moieties is involved.

Aqueous solutions of five lanthanide salts: LaCl3, La(NO3)3, La2(SO4)3, Eu(NO3)3 and Eu2(SO4)3 have been studied at 25 °C by dielectric relaxation spectroscopy over the frequency range 0.05 ≤ ν/GHz ≤ 89. Detailed analysis of the solvent-related modes located at higher frequencies showed that both La3+ and Eu3+ are strongly hydrated, even including partial formation of a third hydration shell similar to that of Al3+(aq). Up to two solute-related modes could be detected at lower frequencies, due to the formation of various types of 1 : 1 ion pairs (IPs). All five salts showed modest levels of association in the order Cl- < NO3- ≪ SO42-, mostly in the form of double-solvent-separated IPs with small amounts of solvent-shared IPs. Overall association constants, , calculated from the stepwise IP formation constants were consistent with literature values.

Alkyltrimethylammonium alkanecarboxylates, [CxMe3N]+[Cy]−, with medium to long alkyl chains on both cation and anion (x,y = 6–10), were investigated in aqueous solution by density and zeta potential measurements, ITC, and DRS.