Manganese(III) and its hydroxo- and chloro-complexes in aqueous perchloric acid: comparison with similar transition-metal(III) complexes

Abstract

At 25°C the formation constant of MnCl²⁺ is found by spectrophotometry to be 13.2 ± 0.9 dm³ mol^–1 at ionic strength 3.26 mol dm^–3; for MnCl⁺₂ the value is 1.1 ± 0.7 dm³ mol^–1. Increase in the number of chloride ions in complexes results in longer wavelengths for the corresponding absorption maxima. In the absence of chloride the hydrolysis constant of Mn^III at ionic strength 5.6 mol dm^–3 is found from voltammetry and potentiometry to be 1.0₅± 0.2₆ mol dm^–3. Aged managanese(III) is found to be 15–25% polymeric, from both kinetic and e.m.f. measurements. Comparison of formation constants for halogeno- and hydroxo-complexes of M³⁺(first transition series) shows that a combination of charge-transfer, ligand-field and coulomb interactions underlies the observed sequences; the dipole moment of OH^– is also a factor.