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Solvation and association of 3:1 electrolytes in N, N-dimethylformamide

Fuchs, A., Buchner, R. and Hefter, G. (2013) Solvation and association of 3:1 electrolytes in N, N-dimethylformamide. The Journal of Physical Chemistry B, 117 (46). pp. 14468-14476.

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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 C using dielectric relaxation spectroscopy over the frequency range of 0.1 ν/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 ∼15 GHz due to the solvent and one or (for AlTf3 solutions) two solute-related processes at lower frequencies (νmax 2 GHz). Effective solvation numbers, Zib, calculated from the solvent relaxation process indicated that all three cations were strongly solvated by DMF with Zib 0 values at infinite dilution 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 solutions was assigned to the rotational diffusion of solvent-shared ion pairs (SIPs) of 1:1 stoicheometry; the additional slower process for AlTf 3 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-Hückel considerations, the KA values decreased rapidly with increasing solute concentration.

Item Type: Journal Article
Murdoch Affiliation: School of Veterinary and Life Sciences
Publisher: American Chemical Society
Copyright: © 2013 American Chemical Society.
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