Manganese(VII) oxide (manganese heptoxide) is an inorganic compound with the formula . Manganese heptoxide is a volatile liquid with an oily consistency. It is a highly reactive and powerful oxidizer that reacts explosively with nearly any organic compound. It was first described in 1860.Aschoff, H. Ann. Phys. Chem. Ser. 2 volume 111 (1860) page 217 and page 224. It is the acid anhydride of permanganic acid.
Properties The crystalline form of this chemical compound is dark green. The liquid is green by reflected light and red by transmitted light.
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 . The terminal distances are and the bridging oxygen is distant from the two Mn atoms. The 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 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 .
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 manganyl(VII) cation , which is isoelectronic with :
Manganese heptoxide decomposes near room temperature, explosively so above . 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 and forming manganese(II) sulfate ():
References
External links
Demonstration of manganese heptoxide's properties on YouTube