Molybdenum(IV) oxide
IUPAC name	Molybdenum(IV) oxide
Other names	Molybdenum dioxide Tugarinovite
Identifiers
CAS number	18868-43-4 Y
Properties
Molecular formula	MoO2
Molar mass	127.94 g/mol
Appearance	brownish-violet solid
Density	6.47 g/cm3
Melting point	1100 °C decomp.
Solubility in water	insoluble
Solubility	insoluble in alkalies, HCl, HF slightly soluble in hot HSO4
Structure
Crystal structure	Distorted rutile (tetragonal)
Coordination geometry	Octahedral (MoIV); trigonal (O–II)
Hazards
EU Index	Not listed
Flash point	Non-flammable
Related compounds
Other anions	Molybdenum disulfide
Other cations	Chromium(IV) oxide Tungsten(IV) oxide
Related molybdenum oxides	"Molybdenum blue" Molybdenum trioxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox 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]

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

[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 ed.), 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

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