Manganese(VII) oxide

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Manganese(VII) oxide
Image:Mn2O7.png
Image:Manganese-heptoxide-3D-balls.png
IUPAC name	Manganese(VII) oxide
Other names	Manganic oxide dimanganese heptoxide
Identifiers
CAS number	12057-92-0
SMILES	O=(O=)(O=)MnOMn(=O)(=O)=O
Properties
Molecular formula	Mn2O7
Molar mass	221.87 g/mol
Appearance	dark red oil (room temp.)
Density	2.79 g/cm3
Melting point	5.9 °C
Boiling point	explodes on heating sublimes at −10 °C
Solubility in water	dec.
Structure
Crystal structure	monoclinic
Coordination geometry	bitetrahedral
Hazards
Main hazards	explosive, strong oxidizer
Related Compounds
Related compounds	Re2O7 KMnO4 Tc2O7
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

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.^[1]

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°.^[1]

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, ^[1] in the vapour phase it is molecular with a similar structure to Tc₂O₇.^[1]

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

Synthesis 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.^[1] Ozone is also produced, giving a strong smell to the substance.

References

cs:Oxid manganistý de:Mangan(VII)-oxid fr:Acide permanganique