Molybdenum dioxide

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]

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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]

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