Molybdenum(VI) oxide

Chembox new
Name = Molybdenum(VI) oxide
ImageFile = Molybdenum(VI) oxide.jpg
ImageName = Molybdenum(VI) oxide
IUPACName = Molybdenum trioxide
Molybdenum(VI) oxide
OtherNames = Molybdic anhydride
Molybdite
Molybdenum oxide
Molybdic trioxide
Name = Solid properties
Name = Liquid properties
Name = Gas properties
Section1 = Chembox Identifiers
CASNo = 1313-27-5
Section2 = Chembox Properties
Formula = MoO₃
MolarMass = 143.94 g/mol
Appearance = yellow solid
Density = 4.7 g/cm³, solid
Solubility = 0.5 g/L (20 °C)
MeltingPt = 795 °C
BoilingPt = 1155 °C
pKa =
Section3 = Chembox Structure
Coordination = distorted octahedral
CrystalStruct = orthorhombic
Section4 = Chembox Thermochemistry
DeltaHf = −745.17 kJ/mol
Entropy = 77.78 J/(mol K)
Entropy = 114.93 J/(mol K)
Entropy = 283.89 J/(mol K)
DeltaHf = −745.17 kJ/mol
Entropy = 77.78 J.K^–1.mol^–1
Section7 = Chembox Hazards
ExternalMSDS =
EUClass = Harmful (Xn)
Irritant (Xi)
RPhrases = R36/37, R48/20/22
SPhrases = S2, S22, S25
FlashPt = not applicable
Section8 = Chembox Related
OtherAnions = Molybdenum disulfide
OtherCations = Chromium trioxide
Molybdenum dioxide
Tungsten trioxide
OtherCpds = Molybdic acid
Sodium molybdate

Molybdenum(VI) oxide is chemical compound with the formula MoO₃. This compound is produced on the largest scale of any molybdenum compound. It occurs as the rare mineral molybdite. Its chief application is as an oxidation catalyst and as a raw material for the production of molybdenum metal.

The oxidation state of Molybdenum in this compound is +6.

tructure

In the gas phase, three oxygen atoms are double bonded to the central molybdenum atom. In the solid state, anhydrous MoO₃ is composed of layers of distorted MoO₆ octahedra in an orthorhombic crystal. The octahedra share edges and form chains which are cross-linked by oxygen atoms to form layers. The octahedra have one short molydenum-oxygen bond to a non-bridging oxygen. [Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.]
The image shows a section of the chain made up from edge sharing distorted octahedra. The oxygen atoms above and below the chain link to other chains to build the layer.

Preparation and principal reactions

MoO₃ is produced industrially by burning molybdenum disulfide, the chief ore of molybdenum:: 2 MoS₂ + 7 O₂ → 2 MoO₃ + 4 SO₂The laboratory synthesis entails the acidification of aqueous solutions of sodium molybdate: [Heynes, J. B. B.; Cruywagen, J. J. "Yellow Molybdenum(VI) Oxide Dihydrate" Inorganic Syntheses, 1986, volume 24, pp. 191. ISBN 0-471-83441-6.] :Na₂MoO₄ + H₂O + 2 HClO₄ → MoO₃(H₂O)₂ + 2 NaClO₄The dihydrate loses water readily to give the monohydrate. Both are bright yellow in color.

Molybdenum(VI) oxide dissolves slightly in water to give "molybdic acid." In base, it dissolves to afford the molybdate anion.

Uses

Molybdenum(VI) oxide is used to manufacture molybdenum metal, which serves as an additive to steel and corrosion-resistant alloys. The relevant conversion entails treatment of MoO₃ with hydrogen at elevated temperatures::MoO₃ + 3 H₂ → Mo + 3 H₂OIt is also a component of the co-catalyst used in the industrial production of acrylonitrile by the oxidation of propene and ammonia.

Because of its layered structure and the ease of the Mo(VI)/Mo(V) couple, MoO₃ is of interest in electrochemical devices and displays. [Ferreira, F. F.; Souza Cruz, T. G.; Fantini, M. C. A.; Tabacniks, M. H.; de Castro, S. C.; Morais, J.; de Siervo, A.; Landers, R.; Gorenstein, A. "Solid State Ionics." 2000, "136-137", 357.]

References

External links

*
* [http://ntp.niehs.nih.gov/index.cfm?objectid=070A72C6-E9C1-AE67-4BFAB97AD0F427E8/ U.S. Department of Health and Human Services National Toxicology Program]
* [http://hse.imoa.info/Default.asp?Page=156/ International Molybdenum Association]
* [http://periodic.lanl.gov/elements/42.html/ Los Alamos National Laboratory- Molybdenum]