Hydration of tetraphenylphosphonium and tetraphenylborate ions by dielectric relaxation spectroscopy
Wachter, W., Buchner, R. and Hefter, G. (2006) Hydration of tetraphenylphosphonium and tetraphenylborate ions by dielectric relaxation spectroscopy. Journal of Physical Chemistry B, 110 (10). pp. 5147-5154.
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A systematic study of the dielectric relaxation spectra of aqueous solutions of NaBPh4 and Ph4PCl has been made at solute concentrations of 0.02 ≤ c/M ≤ 0.82 and 0.20, respectively, and over a wide range of frequencies (0.2 ≤ v/GHz ≤ 89) at 25°C. The spectra were best described by a superposition of four Debye processes, consisting of a very small ion-pair contribution with an average relaxation time of about 300 ps, a "slow"-water relaxation at 17 ps, and two bulk-water relaxations at 8 ps and 0.25 ps, respectively. The slow-water process has been assigned to the presence of a sheath of water molecules surrounding BPh4- and Ph4P+, whose structure has been enhanced by its proximity to the bulky hydrophobic phenyl rings. A structure-making effect on the remaining solvent water can also be observed at low concentrations. More importantly, BPh4- and Ph4P+ show almost identical hydration characteristics, which provides indirect support for the use of the tetraphenylphosphonium tetraphenylborate reference electrolyte assumption in deriving single-ion thermodynamic properties.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Chemical and Mathematical Science|
|Publisher:||American Chemical Society|
|Copyright:||© 2006 American Chemical Society.|
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