Cobalt(II)–halide association equilibria in ammonium nitrate–dimethyl sulfoxide melts. II. Cobalt(II) bromide

Add time:07/20/2019    Source:sciencedirect.com

The cobalt(II)–bromide complex formation in ammonium nitrate–dimethyl sulfoxide (DMSO) melts of the type NH4NO3 ∙ xDMSO at five different compositions in the range 1.0 ≤ x ≤ 5.0 have been investigated by the spectrophotometric method. Absorption spectra of cobalt(II) bromide solutions containing variable amounts of ammonium bromide at different temperatures from 308.15 to 338.15 K have been recorded in the wavelength range 400–800 nm. In the absence of bromide ions, the solutions show spectra typical for octahedral co-ordination of cobalt(II). Addition of bromide changed the absorption spectra to a tetrahedral or severely distorted octahedral co-ordination. Stability constants for the complexes [Co(NO3)2(DMSO)2], [Co(NO3)2Br2]2− and [CoBr4]2−, and the resolved species spectra for all complexes are reported. The effect of varying the DMSO/NH4NO3 mole ratio is discussed. A sharp increase of the stability constants around x = 2 is correlated to the competition between the solvent molecules or ions and the cobalt(II) ions for the ligand and to the solvation of NH4+ with two DMSO. The results are compared with those obtained for the cobalt(II) bromide and chloride complexes in different ammonium nitrate − organic solvent binary mixtures.

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