Molybdenum dioxide
Chemical compound
From Wikipedia, the free encyclopedia
Molybdenum dioxide is the chemical compound with the formula MoO2. 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.
| Names | |
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| IUPAC name
Molybdenum(IV) oxide | |
| Other names
Molybdenum dioxide Tugarinovite | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.038.746 |
| EC Number |
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PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |
| MoO2 | |
| Molar mass | 127.94 g/mol |
| Appearance | brownish-violet solid |
| Density | 6.47 g/cm3 |
| Melting point | 1,100 °C (2,010 °F; 1,370 K) decomposes |
| insoluble | |
| Solubility | insoluble in alkalies, HCl, HF slightly soluble in hot H2SO4 |
| +41.0·10−6 cm3/mol | |
| Structure | |
| Distorted rutile (monoclinic) | |
| Octahedral (MoIV); trigonal (O−II) | |
| Hazards | |
| 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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure
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 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
MoO2 can be prepared :
- by reduction of MoO3 with Mo over the course of 70 hours at 800 °C (1,470 °F). The tungsten analogue, WO2, is prepared similarly.
- 2 MoO3 + Mo → 3 MoO2
Single crystals are obtained by chemical transport using iodine. Iodine reversibly converts MoO2 into the volatile species MoO2I2.[3]
Uses
Molybdenum dioxide is a constituent of "technical molybdenum trioxide" produced during the industrial processing of MoS2:[4][5]
- 2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2
- MoS2 + 6 MoO3 → 7 MoO2 + 2 SO2
- 2 MoO2 + O2 → 2 MoO3
MoO2 has been reported as catalysing the dehydrogenation of alcohols,[6] the reformation of hydrocarbons[7] and biodiesel.[8] Molybdenum nano-wires have been produced by reducing MoO2 deposited on graphite.[9] Molybdenum dioxide has also been suggested as possible anode material for Li-ion batteries.[10][11]