Zusammenfassung
A detailed study has been made of the solvation and ion association of the trifluoromethanesulfonate (Tf-) salts of aluminum(III), scandium(III), and lanthanum(III) in N,N-dimethylformamide (DMF) at 25 degrees C using dielectric relaxation spectroscopy over the frequency range of 0.1 less than or similar to v/GHz <= 89. The spectra of all solutions exhibited either two (for ScTf3 and LaTf3) or ...
Zusammenfassung
A detailed study has been made of the solvation and ion association of the trifluoromethanesulfonate (Tf-) salts of aluminum(III), scandium(III), and lanthanum(III) in N,N-dimethylformamide (DMF) at 25 degrees C using dielectric relaxation spectroscopy over the frequency range of 0.1 less than or similar to v/GHz <= 89. The spectra of all solutions exhibited either two (for ScTf3 and LaTf3) or three (for AlTf3) relaxation processes, a dominant mode centered at similar to 45 GHz due to the solvent and one or (for AlTf3 solutions) two solute-related processes at lower frequencies (v(max) less than or similar to 2 GHz). Effective solvation numbers, 4b, calculated from the solvent relaxation process indicated that all three cations were strongly solvated by DMF with Z(ib) values at infinite dilution in the order (Al3+ approximate to Sc3+ approximate to 10) < (La3+ approximate to 13), consistent with at least partial formation of a second solvation shell around each cation. One solute-related mode for each set of salt solutions was assigned to the rotational diffusion of solvent-shared ion pairs (SIPs) of 1:1 stoicheometry; the additional slower process for AlTf3 solutions in DMF was attributed to the presence of double-solvent-separated IPs. The overall association constants at infinite dilution for the 1:1 IPs, KA (MTf2+), were significant, but as expected from Debye Huckel considerations, the KA values decreased rapidly with increasing solute concentration.
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