Manganese(VII) oxide
4869852
203740458
2008-04-06T13:07:23Z
78.145.83.0
{{Chembox new
| Name = Manganese(VII) oxide
| ImageFile = Mn2O7.png
<!-- | ImageSize = 200px -->
| ImageName = Manganese(VII) oxide
| ImageFile1 = Manganese-heptoxide-3D-balls.png
<!-- | ImageSize1 = 200px -->
| ImageName1 = Ball-and-stick model of manganese heptoxide
| IUPACName = Manganese(VII) oxide
| OtherNames = Manganic oxide<br /> dimanganese heptoxide
| Section1 = {{Chembox Identifiers
| SMILES = O=(O=)(O=)MnOMn(=O)(=O)=O
| CASNo = 12057-92-0
| RTECS =
}}
| Section2 = {{Chembox Properties
| Formula = Mn<sub>2</sub>O<sub>7</sub>
| MolarMass = 221.87 g/mol
| Appearance = dark red oil (room temp.)
| Density = 2.79 g/cm<sup>3</sup>
| Solubility = dec.
| MeltingPt = 5.9 °C
| BoilingPt = explodes on heating<br /> sublimes at −10 °C
}}
| Section3 = {{Chembox Structure
| Coordination = bitetrahedral
| CrystalStruct = monoclinic
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards = explosive, strong oxidizer
| RPhrases =
| SPhrases =
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Rhenium(VII) oxide|Re<sub>2</sub>O<sub>7</sub><br />]] [[Potassium permanganate|KMnO<sub>4</sub>]]<br /> [[Technetium(VII) oxide|Tc<sub>2</sub>O<sub>7</sub>]]
}}
}}
'''Manganese(VII) oxide''' is the [[chemical compound]] with the [[chemical formula|formula]] Mn<sub>2</sub>O<sub>7</sub>. This volatile liquid is highly reactive and more often discussed than observed or intentionally prepared. It is a dangerous oxidizer that was first described in 1860.<ref>Aschoff, H. Ann. Phys. Chem. Ser. 2 volume 111 (1860) page 217 and page 224.</ref>
==Key properties==
The [[crystalline]] compound is red. It is soluble in [[carbon tetrachloride|CCl<sub>4</sub>]], melts at only 5.9 °C, and sublimes at −10 °C. These 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 O<sub>3</sub>Mn-O-MnO<sub>3</sub>. 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°.<ref>Simon, A.; Dronskowski, R.; Krebs, B.; Hettich, B. "Die Kristallstruktur von Mn<sub>2</sub>O<sub>7</sub>" Angewandte Chemie 1987, volume 99, pages 160–161.</ref>
Pyrosulfate, pyrophosphate, and dichromate adopt structures similar to that of Mn<sub>2</sub>O<sub>7</sub>. Probably the most similar main group species is [[dichlorine heptoxide|Cl<sub>2</sub>O<sub>7</sub>]]. Focusing on comparisons within the transition metal series, [[technetium(VII) oxide|Tc<sub>2</sub>O<sub>7</sub>]] and Mn<sub>2</sub>O<sub>7</sub> are structurally similar but the Tc-O-Tc angle is 180°. Solid [[rhenium(VII) oxide|Re<sub>2</sub>O<sub>7</sub>]] is not molecular but consists of crosslinked Re centers with both tetrahedral and octahedral sites, <ref>Krebs, B.; Mueller, A.; Beyer, H. H. The Crystal Structure of Rhenium(VII) Oxide" Inorganic Chemistry 1969, 8, 436-443.</ref> in the vapour phase it is molecular with a similar structure to Tc<sub>2</sub>O<sub>7</sub>.<ref> Wells A.F. (1962) ''Structural Inorganic Chemistry'' 3d edition Oxford University Press </ref>
One distinction of Mn<sub>2</sub>O<sub>7</sub> is that it is charge-neutral. ''Molecular'' oxides that are neutral or cationic are often oxidants.
==Synthesis and reactions==
Mn<sub>2</sub>O<sub>7</sub> arises as a dark red oil by the addition of [[sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]] to [[potassium permanganate|KMnO<sub>4</sub>]]. The reaction initially produces permanganic acid, HMnO<sub>4</sub> (also described with the formula HOMnO<sub>3</sub>). Permanganic acid spontaneously loses water to form its [[anhydride]], Mn<sub>2</sub>O<sub>7</sub>.
:2 KMnO<sub>4</sub> + 2 H<sub>2</sub>SO<sub>4</sub> → Mn<sub>2</sub>O<sub>7</sub> + H<sub>2</sub>O + 2 KHSO<sub>4</sub>
Mn<sub>2</sub>O<sub>7</sub> can react further with sulfuric acid to give the remarkable cation MnO<sub>3</sub><sup>+</sup>, which is [[isoelectronicity|isoelectronic]] with [[chromium trioxide|CrO<sub>3</sub>]]:
:Mn<sub>2</sub>O<sub>7</sub> + 2 H<sub>2</sub>SO<sub>4</sub> → MnO<sub>3</sub><sup>+</sup>,HSO<sub>4</sub><sup>-</sup> + H<sub>2</sub>O
Mn<sub>2</sub>O<sub>7</sub> decomposes near room temperature, explosively so at >55 °C. The explosion can be initiated by striking the sample or by its exposure to oxidizable organic compounds. The products are [[manganese oxide|MnO<sub>2</sub>]] and [[oxygen|O<sub>2</sub>]].<ref>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref> [[Ozone]] is also produced, giving a strong smell to the substance.
==References==
<references/>
[[Category:Manganese compounds]]
[[Category:Oxides]]
[[cs:Oxid manganistý]]
[[de:Mangan(VII)-oxid]]
[[fr:Acide permanganique]]
[[pl:Tlenek manganu(VII)]]
[[zh:七氧化二锰]]