The crystal structures of Mn 5 O 8 and Cd 2 Mn 3 O 8 are determined from single crystal and high resolution X ‐ray powder data. Both structures have very similar monoclinic unit cells, space group C – C 2/m, and are isotypic: equation image Hence, the true formula of Mn 5 O 8 is Mn Mn O 8 . The crystal structure consists of pseudohexagonal Mn IV sheets ( bc ) with similar oxygen sheets on either side, giving a distorted octahedral coordination to the Mn IV . As every fourth Mn IV is missing in these “main layers”, their composition becomes Mn 3 O 8 , and chains of coordination octahedra linked by common edges become distinct. Above and below the empty Mn IV sites are either Mn II or Cd II completing the composition Mn Mn O 8 or Cd 2 Mn 3 O 8 respectively. Examples of similar “double layer” structures are given.
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Oswald et al. (1967) studied this question.
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