Long-term Stability of Manganese(III) Complexes in Aqueous Soil Slurries

The long-term stability of some manganese(II) and (III) complexes in soil slurries was studied. The thermodynamically very stable manganese(III) complexes with X,X'-[alkylenebis(iminomethyl)]-2,2'-dihydroxybenzoate, X,X'=2-7 (1-6), were stable in aqueous sandy loam slurries with pH 6 for months and up to 3 weeks in an aqueous slurry of calcareous clay with pH 7.5. The addition of manganese(III) 1-6 complexes to aqueous soil slurries caused no exchange reactions with iron, as observed when the manganese(II)-EDTA complex was added to the same soil slurries. This confirms that the manganese(III) 1-6 complexes are thermodynamically more stable than the corresponding iron(III) complexes.