TY - JOUR
T1 - Solvent-Dependent Redox Thermodynamics of Metal Amine Complexes. Delineation of Specific Solvation Effects
AU - Lay, Peter A.
AU - McAlpine, Neale S.
AU - Hupp, Joseph T.
AU - Weaver, Michael J.
AU - Sargeson, Alan M.
PY - 1990/1/1
Y1 - 1990/1/1
N2 - Solvent-dependent formal potentials, Ef, and reaction entropies, ΔSrc°, for four reversible Co(III/II) couples featuring macrobicyclic “cage” ligands have been obtained. These are utilized, together with corresponding data for other Co(III/II) and Ru(III/II) amine couples and for M(III/II) polypyridine couples, to unravel effects on the redox thermodynamics arising from specific ligand-solvent and other interactions. The solvent dependencies of Ef(vs ferrocenium-ferrocene) for each redox couple are fitted by using a multiparameter approach, incorporating various well-known empirical quantities describing solvent basicity, acidity, polarity, and internal ordering. For most amine couples, solvent basicity appears to play a prevailing role, associated with interactions involving the amine hydrogens, although solvent polarity also exerts a substantial, albeit less solvent-dependent, influence upon Ef. The presence of a deprotonated amide group in the Co(III/II) amine couple is signaled by the additional presence of a significant solvent acidity component in the multiparametric fit. The solvent basicity and other specific contributions to the Ef-solvent behavior for the polypyridine couples are markedly smaller than for the amines. While the inclusion of a “solvent internal ordering” term does not exert a statistically significant influence on the Ef-solvent dependence for any of the redox couples, the ΔSrc°-solvent dependencies are correlated most successfully with this parameter. Besides identifying the major specific solvation factors upon the redox thermodynamics for such inorganic redox couples, the present multiparametric solvent-dependent analysis also provides a novel, although approximate, means by which the extent of such obfuscating influences upon Efcan be assessed.
AB - Solvent-dependent formal potentials, Ef, and reaction entropies, ΔSrc°, for four reversible Co(III/II) couples featuring macrobicyclic “cage” ligands have been obtained. These are utilized, together with corresponding data for other Co(III/II) and Ru(III/II) amine couples and for M(III/II) polypyridine couples, to unravel effects on the redox thermodynamics arising from specific ligand-solvent and other interactions. The solvent dependencies of Ef(vs ferrocenium-ferrocene) for each redox couple are fitted by using a multiparameter approach, incorporating various well-known empirical quantities describing solvent basicity, acidity, polarity, and internal ordering. For most amine couples, solvent basicity appears to play a prevailing role, associated with interactions involving the amine hydrogens, although solvent polarity also exerts a substantial, albeit less solvent-dependent, influence upon Ef. The presence of a deprotonated amide group in the Co(III/II) amine couple is signaled by the additional presence of a significant solvent acidity component in the multiparametric fit. The solvent basicity and other specific contributions to the Ef-solvent behavior for the polypyridine couples are markedly smaller than for the amines. While the inclusion of a “solvent internal ordering” term does not exert a statistically significant influence on the Ef-solvent dependence for any of the redox couples, the ΔSrc°-solvent dependencies are correlated most successfully with this parameter. Besides identifying the major specific solvation factors upon the redox thermodynamics for such inorganic redox couples, the present multiparametric solvent-dependent analysis also provides a novel, although approximate, means by which the extent of such obfuscating influences upon Efcan be assessed.
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U2 - 10.1021/ic00346a031
DO - 10.1021/ic00346a031
M3 - Article
AN - SCOPUS:0002098963
SN - 0020-1669
VL - 29
SP - 4322
EP - 4328
JO - Inorganic chemistry
JF - Inorganic chemistry
IS - 21
ER -