Manganese heptoxide

Properties

The crystalline form of this chemical compound is dark green. The liquid is green by reflected light and red by transmitted light. It is soluble in carbon tetrachloride, and decomposes when in contact with water.

Structure

Its solubility properties indicate a nonpolar molecular species, which is confirmed by its structure. The molecules consist of a pair of tetrahedra that share a common vertex. The vertices are occupied by oxygen atoms and at the centers of the tetrahedra are the Mn(VII) centers. The connectivity is indicated by the formula O3Mn−O−MnO3. The terminal Mn−O distances are 1.585 Å and the bridging oxygen is 1.77 Å distant from the two Mn atoms. The Mn−O−Mn angle is 120.7°.

Pyrosulfate, pyrophosphate, and dichromate adopt structures similar to that of . Probably the most similar main group species is . Focusing on comparisons within the transition metal series, and are structurally similar but the Tc−O−Tc angle is 180°. Solid is not molecular but consists of crosslinked Re centers with both tetrahedral and octahedral sites; in the vapour phase it is molecular with a similar structure to Tc2O7.

Synthesis and reactions

Manganese heptoxide () arises as a dark green oil by the addition of cold concentrated sulfuric acid () to solid potassium permanganate (). The reaction initially produces permanganic acid, (structurally, ), which is dehydrated by cold sulfuric acid to form its anhydride, : :

Manganese heptoxide can react further with sulfuric acid to give the remarkable manganyl(VII) cation , which is isoelectronic with : :

Manganese heptoxide decomposes near room temperature, explosively so above 55 C. The explosion can be initiated by striking the sample or by its exposure to oxidizable organic compounds. The products are manganese dioxide () and oxygen (). Ozone is also produced, giving a strong smell to the substance. The ozone can spontaneously ignite a piece of paper impregnated with an alcohol solution.

Manganese heptoxide reacts with hydrogen peroxide in presence of sulfuric acid, liberating oxygen and ozone: :

References

References

1. Aschoff, H. Ann. Phys. Chem. Ser. 2 volume 111 (1860) page 217 and page 224.
2. H. Lux. (1963). "Handbook of Preparative Inorganic Chemistry, 2nd Ed.". Academic Press.
3. (1987). "The Crystal Structure of Mn₂O₇". [[Angew. Chem. Int. Ed. Engl.]].
4. (1969). "The Crystal Structure of Rhenium(VII) Oxide". [[Inorganic Chemistry (journal).
5. Wells A.F. (1962) ''Structural Inorganic Chemistry'' 3d edition Oxford University Press
6. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN. 0-12-352651-5.