Molybdenum dioxide explained

Molybdenum dioxide is the chemical compound with the formula MoO. It is a violet-colored solid and is a metallic conductor. The mineralogical form of this compound is called tugarinovite, and is only very rarely found.

Structure

It crystallizes in a monoclinic cell, and has a distorted rutile, (TiO₂) crystal structure. In TiO the oxide anions are close packed and titanium atoms occupy half of the octahedral interstices (holes). In MoO the octahedra are distorted, the Mo atoms are off-centre, leading to alternating short and long Mo – Mo distances and Mo-Mo bonding. 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]

Preparation

MoO can be prepared :

• by reduction of MoO₃ with Mo over the course of 70 hours at . The tungsten analogue, WO, is prepared similarly.

2 MoO + Mo → 3 MoO

• by reducing MoO with H₂ or NH₃ below

Single crystals are obtained by chemical transport using iodine. Iodine reversibly converts MoO₂ into the volatile species MoOI.^[2]

Uses

Molybdenum dioxide is a constituent of "technical molybdenum trioxide" produced during the industrial processing of MoS₂:^{[3] [4]}

2 MoS + 7 O → 2 MoO + 4 SO

MoS + 6 MoO → 7 MoO + 2 SO

2 MoO + O → 2 MoO

MoO has been reported as catalysing the dehydrogenation of alcohols,^[5] the reformation of hydrocarbons^[6] and biodiesel.^[7] Molybdenum nano-wires have been produced by reducing MoO deposited on graphite.^[8] Molybdenum dioxide has also been suggested as possible anode material for Li-ion batteries.^{[9] [10]}

Notes and References

1. Oxides: Solid state chemistry McCarroll W.H. Encyclopedia of Inorganic Chemistry Ed R. Bruce King, (1994), John Wiley & sons
2. Conroy, L. E.; Ben-Dor, L. "Molybdenum(IV) Oxide and Tungsten(IV) Oxides Single-Crystals" Inorganic Syntheses 1995, volume 30, pp. 105–107.
3. Metallurgical furnaces Jorg Grzella, Peter Sturm, Joachim Kruger, Markus A. Reuter, Carina Kogler, Thomas Probst, Ullmans Encyclopedia of Industrial Chemistry
4. "Thermal Analysis and Kinetics of Oxidation of Molybdenum Sulfides" Y. Shigegaki, S.K. Basu, M.Wakihara and M. Taniguchi, J. Therm. Analysis 34 (1988), 1427-1440
5. A. A. Balandin and I. D. Rozhdestvenskaya, Russian Chemical Bulletin, 8, 11, (1959), 1573
6. Molybdenum based catalysts. I. MoO as the active species in the reforming of hydrocarbons A. Katrib, P. Leflaive, L. Hilaire and G. Maire Catalysis Letters, 38, 1–2, (1996)
7. Catalytic partial oxidation of a biodiesel surrogate over molybdenum dioxide, C.M. Cuba-Torres, et al, Fuel (2015),
8. 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
9. Shi. Yifeng. Guo. Bingkun. Corr. Serena A.. Shi. Qihui. Hu. Yong-Sheng. Heier. Kevin R.. Chen. Liquan. Seshadri. Ram. Stucky. Galen D.. 2009-12-09. Ordered Mesoporous Metallic MoO2 Materials with Highly Reversible Lithium Storage Capacity. Nano Letters. 9. 12. 4215–4220. 10.1021/nl902423a. 19775084. 1530-6984.
10. Kim. Hyung-Seok. Cook. John B.. Tolbert. Sarah H.. Dunn. Bruce. 2015-01-01. The Development of Pseudocapacitive Properties in Nanosized-MoO2. Journal of the Electrochemical Society. en. 162. 5. A5083–A5090. 10.1149/2.0141505jes. 1370243. 0013-4651.