Entropic and Enthalpic Contributions to the Solvent Dependence of the Thermodynamics of Transition-Metal Redox Couples II. Couples Containing Ammine and Ethylenediamine Ligands.
MICHIGAN STATE UNIV EAST LANSING DEPT OF CHEMISTRY
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We have been examining the solvent dependence of the thermodynamics of simple transition-metal redox couples as part of an experimental program exploring the role of the solvent in the kinetics and thermodynamics of outer-sphere electron transfer reactions. One-electron redox couples containing substitutionally inert complexes form especially tractable systems for this purpose since the influence of variations in the outer-shell solvent contributions can be assessed separately from the inner-shell metal-ligand coordination shell effects. Our general approach is to determine the formal potential Ef of each redox couple in a range of solvents having suitably varied chemical and physical properties. In addition, the temperature dependence of Ef is monitored in each solvent using a nonisothermal cell arrangement, yielding values of the reaction entropy of the redox couple equals the difference between the absolute ionic entropies of the reduced and oxidized forms. These measurements yield estimates of the free energy, entropy, and enthalpy of transferring the redox couple from water to other solvents.
- Organic Chemistry
- Atomic and Molecular Physics and Spectroscopy