Molybdenum dioxide

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Molybdenum dioxide
IUPAC name molybdenum(IV) oxide
Other names molybdenum dioxide
Identifiers
CAS number [18868-43-4]
Properties
Molecular formula MoO2
Molar mass 127.939 g/mol
Appearance brownish violet
Density 6.5 g/cm3
Melting point

1100 °C(decomposes)
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Molybdenum dioxide is the chemical compound with the formula MoO2. It is a violet-colored solid and is a metallic conductor. It crystallizes in a monoclinic cell, and has a distorted rutile, (TiO2) crystal structure. In TiO2 the oxide anions are close packed and titanium atoms occupy half of the octahedral interstices (holes). In MoO2 the octahedra are distorted, the Mo atoms are off-centre, leading to alternating short and long Mo – Mo distances. The short Mo – Mo distance is 251 pm which is less than the Mo – Mo distance in the metal, 272.5 pm. The bond length is shorter than would be expected for a single bond. The bonding is complex and involves a delocalisation of some of the Mo electrons in a conductance band accounting for the metallic conductivity[1].
MoO2 can be prepared :

  • by reduction of MoO3 with Mo over the course of 70 hours at 800 °C. The tungsten analogue, WO2, is prepared similarly.
2 MoO3 + Mo → 3 MoO2
  • by reducing MoO3 with H2 or NH3 below 470°C [2]

Single crystals are obtained by chemical transport using iodine. Iodine reversibly converts MoO2 into the volatile species MoO2I2[3].

Molybdenum oxide is a constituent of "technical molybdenum oxide" produced during the industrial processing of MoS2[4]:

2 MoS2 + 7O2 → 2MoO3 + 4SO2
MoS2 + 6MoO3 → 7MoO2 + 2SO2
2 MoO2 + O2 → 2MoO3

MoO2 has been reported as catalysing the dehydrogenation of alcohols[5] and the reformation of hydrocarbons[6]. Molybdenum nano-wires have been produced by reducing MoO2 deposited on graphite[7]

[edit] References

  1. ^ Oxides: Solid state chemistry McCarroll W.H. Encyclopedia of Inorganic Chemistry Ed R. Bruce King, (1994), John Wiley & sons ISBN 0-471-93620-0
  2. ^ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th Edn.) New York:Wiley-Interscience. ISBN 0-471-19957-5.
  3. ^ Conroy, L. E.; Ben-Dor, L. "Molybdenum(IV) Oxide and Tungsten(IV) Oxides Single-Crystals" Inorganic Syntheses 1995, volume 30, pp. 105-107. ISBN 0-471-30508-1
  4. ^ Metallurgical furnaces Jorg Grzella, Peter Sturm, Joachim Kruger, Markus A. Reuter, Carina Kogler, Thomas Probst, Ullmans Encyclopedia of Industrial Chemistry
  5. ^ A. A. Balandin and I. D. Rozhdestvenskaya, Russian Chemical Bulletin, 8, 11, (1959), 1573 doi:10.1007/BF00914749
  6. ^ Molybdenum based catalysts. I. MoO2 as the active species in the reforming of hydrocarbons A. Katrib, P. Leflaive, L. Hilaire and G. Maire Catalysis Letters, 38, 1-2, (1996) doi:10.1007/BF00806906
  7. ^ Synthesis of Molybdenum Nanowires with Millimeter-Scale Lengths Using Electrochemical Step Edge Decoration M. P. Zach, K. Inazu, K. H. Ng, J. C. Hemminger, and R. M. Penner Chem. Mater. (2002),14, 3206 doi:10.1021/cm020249a