Über Oxidhydroxide des vierwertigen Mangans mit Schichtengitter 2. Mitteilung: Mangan (III)-manganat (IV)

The preparation and probable structure of managanese (III)-manganate (IV) Mn₇O₁₃, 5H₂O (a₀ = 2,84, c₀ = 7,27 Å) and manganous (II)-manganate (IV) Mn₇O₁₂, 6H₂O are described. Both consist of platelets. Digesting in diluted HNO₃ leads to γ-MnO₂ (nsutite). Manganese (III)-manganate (IV) is much less stable than the sodiummanganese (II, III)-manganate-(IV) described earlier and looses water easily when heated or in vacuo. Water loss results in breaking down of the double layer lattice, and the product is only two-dimensionally ordered, producing only prism reflections on the X ray diagramm. Heating results in a continuous transition to the two-dimensionally ordered phase, then to a finely divided and very disordered γ-MnO₂, and eventually to a finely divided and disordered β-MnO₂ (pyrolusite). The transition is topotactical so far, but further heating produces δ-Mn₂O₃ without obvious topotactical relations to the earlier products. The so-called ‘δ-MnO₂’ (birnessite) appears to be a family of finely divided and very disordered varieties of such manganates (IV) with part of the Mn³⁺ substituted by Mn⁴⁺. Since such products usually contain remarkable amounts of alkali ions, they are rather varieties of the earlier described sodiummanganese (II, III)-manganate (IV). A provisional explanation of the streaking in the electron diffractions of these manganate (IV). A provisional explanation of the streaking in the electron diffractions of these manganates (IV) is given. With respect to these results the so-called ‘δ-MnO₂’ can no longer be attributed to the true manganese dioxides.