Ag1.8Mn8O16: Square Planar Coordinated Ag⊕ Ions in the Channels of a Novel Hollandite Variant

A promising new ion‐conducting material, the title compound, can be prepared from AgMnO4 and Ag2O (1:1) at 970 °C under 5 kbar O2. The Mn8O16 framework forms channel‐like cavities of face‐sharing cubes. The Ag⊕ ions occupy the bottle‐necks of this one‐dimensional diffusion channel as regular lattice sites. This constitutes the first example of square‐planar coordinated Ag⊕‐ions.