Reaction mechanisms in molten salts. Part I. Ligand replacement in chromium(III) complexes dissolved in hydrogen sulphate melt and in 100% sulphuric acid
Abstract
Spectral shifts in the crystal-field bands of a variety of chromium(III) complexes dissolved in 100% sulphuric acid at 40 °C show that the ligands water, oxalate, acetylacetonate, and chloride, but not ammonia and ethylenediamine, are easily substituted by (protonated) sulphate ligands. By selecting appropriate ligands in the co-ordination sphere, it is possible to generate and record the spectra of the (solvated) species Cr(en)33+, Cr(en)23+, Cr(en)3+, and Cr3+ in 100% sulphuric acid. These data are used for studying the decomposition of the [Cr(en)3]3+ ion in molten NH4HSO4–KHSO4 at 142°. It is shown that the first and second ethylenediamine ligands are removed rapidly from the co-ordination sphere and that removal of the third is probably a one-stage process. Comparison is made with the decomposition of the complex in 100% sulphuric acid at the same temperature.
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