Zusammenfassung
N2 - A detailed study has been made of the solvation and ion assocn. of the trifluoromethanesulfonate (Tf-) salts of aluminum-(III), scandium-(III), and lanthanum-(III) in N,N-dimethylformamide (DMF) at 25 °C using dielec. relaxation spectroscopy over the frequency range of 0.1 ⪅ ν/GHz ≤ 89. The spectra of all solns. exhibited either two (for ScTf3 and LaTf3) or three (for AlTf3) ...
Zusammenfassung
N2 - A detailed study has been made of the solvation and ion assocn. of the trifluoromethanesulfonate (Tf-) salts of aluminum-(III), scandium-(III), and lanthanum-(III) in N,N-dimethylformamide (DMF) at 25 °C using dielec. relaxation spectroscopy over the frequency range of 0.1 ⪅ ν/GHz ≤ 89. The spectra of all solns. exhibited either two (for ScTf3 and LaTf3) or three (for AlTf3) relaxation processes, a dominant mode centered at ∼15 GHz due to the solvent and one or (for AlTf3 solns.) two solute-related processes at lower frequencies (νmax ⪅ 2 GHz). Effective solvation nos., Zib, calcd. from the solvent relaxation process indicated that all three cations were strongly solvated by DMF with Zib0 values at infinite diln. in the order (Al3+ ≈ Sc3+ ≈ 10) < (La3+ ≈ 13), consistent with at least partial formation of a second solvation shell around each cation. One solute-related mode for each set of salt solns. was assigned to the rotational diffusion of solvent-shared ion pairs (SIPs) of 1:1 stoicheometry; the addnl. slower process for AlTf3 solns. in DMF was attributed to the presence of double-solvent-sepd. IPs. The overall assocn. consts. at infinite diln. for the 1:1 IPs, KA°(MTf2+), were significant, but as expected from Debye-Hueckel considerations, the KA values decreased rapidly with increasing solute concn. [on SciFinder(R)]
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