molybdenum dioxide
{{redirect|MoO2|the videogame|Master of Orion II: Battle at Antares{{!}}Master of Orion II: Battle at Antares}}
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 361075238
| IUPACName = Molybdenum(IV) oxide
| OtherNames = Molybdenum dioxide
Tugarinovite
|Section1={{Chembox Identifiers
| CASNo = 18868-43-4
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID = 27268
| EC_number = 242-637-9
| PubChem = 29320
| StdInChI=1S/Mo.2O
| StdInChIKey = QXYJCZRRLLQGCR-UHFFFAOYSA-N
| SMILES = O=[Mo]=O
}}
|Section2={{Chembox Properties
| Formula = MoO2
| MolarMass = 127.94 g/mol
| Appearance = brownish-violet solid
| Density = 6.47 g/cm3
| MeltingPtC = 1100
| MeltingPt_notes = decomposes
| Solubility = insoluble
| SolubleOther = insoluble in alkalies, HCl, HF
slightly soluble in hot H2SO4
| MagSus = +41.0·10−6 cm3/mol
}}
|Section3={{Chembox Structure
| CrystalStruct = Distorted rutile (monoclinic)
| Coordination = Octahedral (MoIV); trigonal (O−II)
}}
|Section4={{Chembox Thermochemistry
}}
|Section7={{Chembox Hazards
| FlashPt = Non-flammable
}}
|Section8={{Chembox Related
| OtherAnions = Molybdenum disulfide
| OtherCations = Chromium(IV) oxide
Tungsten(IV) oxide
| OtherFunction = "Molybdenum blue"
Molybdenum trioxide
| OtherFunction_label = molybdenum oxides
}}
}}
Molybdenum dioxide is the chemical compound with the formula MoO{{sub|2}}. 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{{sub|2}} the oxide anions are close packed and titanium atoms occupy half of the octahedral interstices (holes). In MoO{{sub|2}} 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.Oxides: Solid state chemistry McCarroll W.H. Encyclopedia of Inorganic Chemistry Ed R. Bruce King, (1994), John Wiley & sons {{ISBN|0-471-93620-0}}
Preparation
MoO{{sub|2}} can be prepared :
- by reduction of MoO3 with Mo over the course of 70 hours at {{convert|800|C}}. The tungsten analogue, WO{{sub|2}}, is prepared similarly.
:2 MoO{{sub|3}} + Mo → 3 MoO{{sub|2}}
- by reducing MoO{{sub|3}} with H2 or NH3 below {{convert|470|C}} {{Cotton&Wilkinson6th}}
Single crystals are obtained by chemical transport using iodine. Iodine reversibly converts MoO2 into the volatile species MoO{{sub|2}}I{{sub|2}}.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}}
Uses
Molybdenum dioxide is a constituent of "technical molybdenum trioxide" 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"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
:2 MoS{{sub|2}} + 7 O{{sub|2}} → 2 MoO{{sub|3}} + 4 SO{{sub|2}}
:MoS{{sub|2}} + 6 MoO{{sub|3}} → 7 MoO{{sub|2}} + 2 SO{{sub|2}}
:2 MoO{{sub|2}} + O{{sub|2}} → 2 MoO{{sub|3}}
MoO{{sub|2}} 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 }} the reformation of hydrocarbonsMolybdenum based catalysts. I. MoO{{sub|2}} 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}} and biodiesel.Catalytic partial oxidation of a biodiesel surrogate over molybdenum dioxide, C.M. Cuba-Torres, et al, Fuel (2015), {{doi|10.1016/j.fuel.2015.01.003}} Molybdenum nano-wires have been produced by reducing MoO{{sub|2}} 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}} Molybdenum dioxide has also been suggested as possible anode material for Li-ion batteries.{{Cite journal|last1=Shi|first1=Yifeng|last2=Guo|first2=Bingkun|last3=Corr|first3=Serena A.|last4=Shi|first4=Qihui|last5=Hu|first5=Yong-Sheng|last6=Heier|first6=Kevin R.|last7=Chen|first7=Liquan|last8=Seshadri|first8=Ram|last9=Stucky|first9=Galen D.|date=2009-12-09|title=Ordered Mesoporous Metallic MoO2 Materials with Highly Reversible Lithium Storage Capacity|journal=Nano Letters|volume=9|issue=12|pages=4215–4220|doi=10.1021/nl902423a|pmid=19775084|bibcode=2009NanoL...9.4215S |issn=1530-6984}}{{Cite journal|last1=Kim|first1=Hyung-Seok|last2=Cook|first2=John B.|last3=Tolbert|first3=Sarah H.|last4=Dunn|first4=Bruce|date=2015-01-01|title=The Development of Pseudocapacitive Properties in Nanosized-MoO2|journal=Journal of the Electrochemical Society|language=en|volume=162|issue=5|pages=A5083–A5090|doi=10.1149/2.0141505jes|osti=1370243|issn=0013-4651|url=https://www.osti.gov/biblio/1370243}}