Molybdenum dioxide

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IUPACName = molybdenum(IV) oxide
OtherNames = molybdenum dioxide
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CASNo = 18868-43-4
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Section2 = Chembox Properties
Formula = MoO₂
MolarMass = 127.939 g/mol
Appearance = brownish violet
Density = 6.5 g/cm³
MeltingPt = 1100 °C(decomposes)
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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 ["Oxides: Solid state chemistry" McCarroll W.H. Encyclopedia of Inorganic Chemistry Ed R. Bruce King, (1994), John Wiley & sons ISBN 0-471-93620-0 ] .
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 [ Cotton&Wilkinson6th]

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

Molybdenum oxide is a constituent of "technical molybdenum oxide" produced during the industrial processing of MoS₂ [ "Metallurgical furnaces" Jorg Grzella, Peter Sturm, Joachim Kruger, Markus A. Reuter, Carina Kogler, Thomas Probst, Ullmans Encyclopedia of Industrial Chemistry ] :

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

MoO₂ has been reported as catalysing the dehydrogenation of alcohols [A. A. Balandin and I. D. Rozhdestvenskaya, Russian Chemical Bulletin, 8, 11, (1959), 1573 doi|10.1007/BF00914749 ] and the reformation of hydrocarbons ["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] . Molybdenum nano-wires have been produced by reducing MoO₂ deposited on graphite ["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]

Mineralogical form of this compound is called tugarinovite, only very rarely found.

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