Manganese(VII) oxide

Manganese(VII) oxide

Chembox new
Name = Manganese(VII) oxide
ImageFile = Mn2O7.png ImageName = Manganese(VII) oxide
ImageFile1 = Manganese-heptoxide-3D-balls.png ImageName1 = Ball-and-stick model of manganese heptoxide
IUPACName = Manganese(VII) oxide
OtherNames = Manganic oxide
dimanganese heptoxide
Section1 = Chembox Identifiers
SMILES = O=(O=)(O=)MnOMn(=O)(=O)=O
CASNo = 12057-92-0
RTECS =

Section2 = Chembox Properties
Formula = Mn2O7
MolarMass = 221.87 g/mol
Appearance = dark red oil (room temp.)
Density = 2.79 g/cm3
Solubility = dec.
MeltingPt = 5.9 °C
BoilingPt = explodes on heating
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 = Re2O7
KMnO4
Tc2O7

Manganese(VII) oxide is the chemical compound with the formula Mn2O7. 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. [Aschoff, H. Ann. Phys. Chem. Ser. 2 volume 111 (1860) page 217 and page 224.]

Key properties

The crystalline compound is red. It is soluble in CCl4, 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 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°. [Simon, A.; Dronskowski, R.; Krebs, B.; Hettich, B. "Die Kristallstruktur von Mn2O7" Angewandte Chemie 1987, volume 99, pages 160–161.]

Pyrosulfate, pyrophosphate, and dichromate adopt structures similar to that of Mn2O7. Probably the most similar main group species is Cl2O7. Focusing on comparisons within the transition metal series, Tc2O7 and Mn2O7 are structurally similar but the Tc-O-Tc angle is 180°. Solid Re2O7 is not molecular but consists of crosslinked Re centers with both tetrahedral and octahedral sites, [Krebs, B.; Mueller, A.; Beyer, H. H. The Crystal Structure of Rhenium(VII) Oxide" Inorganic Chemistry 1969, 8, 436-443.] in the vapour phase it is molecular with a similar structure to Tc2O7. [ Wells A.F. (1962) "Structural Inorganic Chemistry" 3d edition Oxford University Press ]

One distinction of Mn2O7 is that it is charge-neutral. "Molecular" oxides that are neutral or cationic are often oxidants.

ynthesis and reactions

Mn2O7 arises as a dark red oil by the addition of H2SO4 to KMnO4. The reaction initially produces permanganic acid, HMnO4 (also described with the formula HOMnO3). Permanganic acid spontaneously loses water to form its anhydride, Mn2O7.:2 KMnO4 + 2 H2SO4 → Mn2O7 + H2O + 2 KHSO4

Mn2O7 can react further with sulfuric acid to give the remarkable cation MnO3+, which is isoelectronic with CrO3::Mn2O7 + 2 H2SO4 → MnO3+,HSO4- + H2O

Mn2O7 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 MnO2 and O2. [Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.] Ozone is also produced, giving a strong smell to the substance.

References


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