KMn8O16

KMn8O16 is a potassium manganese oxide belonging to the hollandite family. Its formula represents one potassium ion per eight manganese atoms balanced by sixteen oxide ions. The hydrated form is known in nature as cryptomelane, commonly written as KMn8O16·nH2O.

Structure and properties

Hollandite-type KMn8O16 has a tetragonal framework in which MnO6 octahedra share corners and edges to form a three-dimensional network with 2x2 channels along the c-axis. Potassium ions reside in these channels, giving rise to a one-dimensional guest-host system. The manganese atoms exist in mixed oxidation states, typically Mn3+ and Mn4+, which leads to mixed-valence behavior that can influence electronic conductivity and redox properties. The material is generally a dark solid with notable chemical stability in oxidizing environments, though its exact properties depend on hydration level and synthesis method.

Occurrence and synthesis

In nature, the hydrated mineral cryptomelane is a common example of KMn8O16·nH2O, found in oxidized zones of manganese-rich deposits and nodules. The anhydrous KMn8O16 can be prepared by dehydration of cryptomelane or by high-temperature solid-state synthesis from potassium and manganese precursors under controlled conditions. The open-framework hollandite structure accommodates various cations, which can influence the material’s stability and properties.

Applications and context

Like other hollandite-type manganese oxides, KMn8O16 is studied for catalytic oxidation reactions and as a potential electrode material for rechargeable batteries and supercapacitors, where its channels can host mobile ions. Its redox-active manganese framework also makes it of interest in electrochemical research and materials science.

Safety

Handling KMn8O16 and related manganese oxides should follow standard laboratory safety practices. Avoid inhalation of powders and contact with skin or eyes; manganese compounds can be hazardous if misused.