Reaction entropies and acid-base behavior of transition-metal complexes in recast nation films

Michael H. Schmidt, Nathan S Lewis

Research output: Contribution to journalArticle

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Abstract

The effect of Donnan potentials on the apparent formal potentials of polymer-bound metal ions has been investigated for recast Nafion films and for spin-cast Nafion films on graphite electrodes. For the probe ions Ru(NH3)6 3+/2+ and Ru(bpy)3 3+/2+, the behavior generally correlates with Donnan potentials expected for ideally permselective domains, and plots of the apparent E°′ vs ionic strength (μ) have slopes of 59 mV/(decade increase in μ) for 1:1 monovalent electrolytes. The observed reaction entropies, ΔSobsdave been determined as a function of solution ionic strength. The measured ΔSobsd values are found to consist of the intrinsic reaction entropy for the reaction and an entropy of transfer term. The latter term arises from the permselectivity properties of the Nafion films. Extraction of the intrinsic reaction entropy, ΔSrc, yields a revised interpretation of the reaction entropy behavior of Ru complexes in Nafion films. The pH vs E1/2 properties of Nafion-bound Ru(NH3)5(H2O)3+/2+, Ru(NH3)5(isna)3+/2+ (isna = isonicotinic acid), and Ru(NH3)5(pz)3+/2+ (pz = pyrazine) have been investigated, and apparent pka, values have been determined for these complexes. Apparent pKa, values in Nafion are generally higher than those in aqueous media by 1.5-2 pK units.

Original languageEnglish
Pages (from-to)2018-2022
Number of pages5
JournalJournal of Physical Chemistry
Volume92
Issue number7
Publication statusPublished - 1988

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Coordination Complexes
Metal complexes
Transition metals
Entropy
transition metals
entropy
acids
Acids
Ionic strength
Isonicotinic Acids
ion probes
Graphite electrodes
pyrazines
Pyrazines
Metal ions
casts
metal ions
graphite
Electrolytes
plots

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Reaction entropies and acid-base behavior of transition-metal complexes in recast nation films. / Schmidt, Michael H.; Lewis, Nathan S.

In: Journal of Physical Chemistry, Vol. 92, No. 7, 1988, p. 2018-2022.

Research output: Contribution to journalArticle

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