Issue 18, 1977

Characterization of inner- and outer-sphere complexes by thermodynamics and absorption spectra. Part 1. Sulphato-complexes of the first-row transition elements

Abstract

The sulphato-complexes of the transition-metal ions MnII, FeII, CoII, NiII, and CuII have been shown to be predominantly outer sphere, and [Fe(SO4)]+ has been classified as inner sphere, for I= 0 and 5 mol dm–3 at 25 °C. At I= 0, a linear free-energy relatron (I.f.e.r.) between log K1for the formation of the sulphato- and for the mono-hydroxo-complexes allows the classifications to be rationalised. The I.f.e.r. also allows the sulphate ligand to be tentatively identrfied as unidentate in the inner-sphere complexes from comparisons with n-dentate ligands (n= 1–3 ). The Fuoss equation adequately describes the K1 values for those complexes of sulphate and other ligands that are predominantly outer sphere in character. The inner- and outer-sphere character of the species at I= 5 mol dm–3, deduced from spectrophotometric measurement of the formation constants, is similar to the pattern at I= 0. Large decreases in the entropy of formation of both inner- and outer-sphere species are attributed mainly to the reduced influence of the sulphate ligand on the structure of the medium.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1977, 1701-1707

Characterization of inner- and outer-sphere complexes by thermodynamics and absorption spectra. Part 1. Sulphato-complexes of the first-row transition elements

K. G. Ashurst and R. D. Hancock, J. Chem. Soc., Dalton Trans., 1977, 1701 DOI: 10.1039/DT9770001701

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