The structure of K_1.33Mn₈O₁₆ and cation ordering in hollandite-type structures

A possible evolutionary origin for the Mn 4 cluster of the photosynthetic water oxidation complex from natural MnO 2 precipitates in the early ocean

“…Sizable single crystals of these minerals are difficult to find; several of the structures are determined or inferred on the basis of the analysis of powder diffraction measurements and by analogy to similar structures with better definition. However, single crystal diffraction of hollandite (57) and a synthetic analog (58) have been reported. The disorder, together with the presence of cations, also reflects the presence of Mn oxidation states other than Mn(IV).…”

Strong Enhancement of deSoot Activity of Transition Metal Oxides by Alkali Doping: Additive Effects of Potassium and Nitric Oxide

“…For all samples, the diffraction peaks were labeled with Miller indexes. The manganese catalysts, i.e., spinel, cryptomelane (tunneled structure), and birnessite (layered structure), were indexed in the Pmab (ICSD-30005 [34]), I4/m (ICSD-59159 [35]) and R3m (ICSD-152290 [36]) space groups, respectively. Some reflections originating from an excess of potassium carbonate are only detectable in the case of the birnessite phase (marked with violet diamonds).…”

Pb2+ cation ordering in Pb3(Mo4O6)4

“…It then appears that the state of the order in the tunnels in the structure of AxMo406 is critically dependent upon the valency and radius of the ternary metal cation. Similar to the hollandite-type compounds, the symmetry of the structure is to some extent related to the size of the cation (Vicat, Fanchon, Strobel & Qui, 1986). Distortion to orthorhombic symmetry was observed in the crystals of KMo406-I and Bao.62Mo406 because of the large K + and Ba 2+ cations.…”