Molybdenum trioxide

Molybdenum trioxide describes a family of inorganic compounds with the formula MoO3(H2O)n where n = 0, 1, 2. These compounds are produced on the largest scale of any molybdenum compound. The anhydrous oxide is a precursor to molybdenum metal, an important alloying agent. It is also an important industrial catalyst.[8] It is a yellow solid, although impure samples can appear blue or green.

Molybdenum trioxide
Names
IUPAC name
Molybdenum trioxide
Other names
Molybdic anhydride
Molybdite
Molybdic trioxide
Molybdenum(VI) oxide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.013.823
EC Number
  • 215-204-7
UNII
UN number 3288
  • InChI=1S/Mo.3O
    Key: JKQOBWVOAYFWKG-UHFFFAOYSA-N
  • O=[Mo](=O)=O
Properties
MoO3
Molar mass 143.95 g·mol−1
Appearance yellow solid
Odor odorless
Density 4.70 g/cm3[1]
Melting point 802 °C (1,476 °F; 1,075 K)[1]
Boiling point 1,155 °C (2,111 °F; 1,428 K)(sublimes)[1]
1.066 g/L (18 °C)
4.90 g/L (28 °C)
20.55 g/L (70 °C)
Band gap >3 eV (direct)[2]
+3.0·10−6 cm3/mol[3]
Structure[4]
Orthorhombic, oP16
Pnma, No. 62
a = 1.402 nm, b = 0.37028 nm, c = 0.39663 nm
4
see text
Thermochemistry[5]
75.0 J K−1 mol−1
77.7 J K−1 mol−1
−745.1 kJ/mol
-668.0 kJ/mol
Hazards[6]
GHS labelling:
GHS07: Exclamation markGHS08: Health hazard
Warning
H319, H335, H351
P201, P202, P261, P264, P271, P280, P281, P304+P340, P305+P351+P338, P308+P313, P312, P337+P313, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
3
0
OX
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
125 mg.kg (rat, oral)
2689 mg/kg (rat, oral)[7]
120 mg Mo/kg (rat, oral)
120 mg Mo/kg (guinea pig, oral)[7]
>5840 mg/m3 (rat, 4 hr)[7]
Related compounds
Other cations
 Chromium trioxide
Tungsten trioxide
Molybdenum dioxide
"Molybdenum blue"
Related compounds
 Molybdic acid
Sodium molybdate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Molybdenum trioxide occurs as the rare mineral molybdite.

Structure
A section of the chain comprising edge-sharing octahedra. Oxygen atoms in back and front of the chain link to other chains to build the layer.[9]

In the gas phase, three oxygen atoms are bonded to the central molybdenum atom. In the solid state, anhydrous MoO3 is composed of layers of distorted MoO6 octahedra in an orthorhombic crystal. The octahedra share edges and form chains which are cross-linked by oxygen atoms to form layers. The octahedra have one short molybdenum-oxygen bond to a non-bridging oxygen.[9][10] Also known is a metastable (β) form of MoO3 with a WO3-like structure.[11][2]

Preparation and principal reactions

MoO3 is produced industrially by roasting the compound molybdenum disulfide, the chief ore of molybdenum:[8]

2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2

The laboratory synthesis of the dihydrate entails acidification of aqueous solutions of sodium molybdate with perchloric acid:[12]

Na2MoO4 + H2O + 2 HClO4 → MoO3(H2O)2 + 2 NaClO4

The dihydrate loses water readily to give the monohydrate. Both are bright yellow in color.

Molybdenum trioxide dissolves slightly in water to give "molybdic acid". In base, it dissolves to afford the molybdate anion.

Uses

Molybdenum trioxide is used to manufacture molybdenum metal:

MoO3 + 3 H2 → Mo + 3 H2O

Molybdenum trioxide is also a component of the co-catalyst used in the industrial production of acrylonitrile by the oxidation of propene and ammonia.

Because of its layered structure and the ease of the Mo(VI)/Mo(V) coupling, MoO3 is of interest in electrochemical devices and displays. It has been described as "the most commonly used TMO in organic electronics applications ... it is evaporated at relatively low temperature (~400 °C)."[13]

Molybdite on molybdenite, Questa molybdenum mine, New Mexico (size: 11.0×6.7×4.1 cm).

References
  1. Haynes, p. 4.77
  2. Balendhran, Sivacarendran; Walia, Sumeet; Nili, Hussein; Ou, Jian Zhen; Zhuiykov, Serge; Kaner, Richard B.; Sriram, Sharath; Bhaskaran, Madhu; Kalantar-zadeh, Kourosh (2013-08-26). "Two-Dimensional Molybdenum Trioxide and Dichalcogenides". Advanced Functional Materials. 23 (32): 3952–3970. doi:10.1002/adfm.201300125. S2CID 95301280.
  3. Haynes, p. 4.134
  4. Åsbrink, S.; Kihlborg, L.; Malinowski, M. (1988). "High-pressure single-crystal X-ray diffraction studies of MoO3. I. Lattice parameters up to 7.4 GPa". J. Appl. Crystallogr. 21 (6): 960–962. doi:10.1107/S0021889888008271.
  5. Haynes, p. 5.15
  6. "Molybdenum trioxide". pubchem.ncbi.nlm.nih.gov.
  7. "Molybdenum (soluble compounds, as Mo)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  8. Roger F. Sebenik; et al. (2005). "Molybdenum and Molybdenum Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_655.
  9. "Molybdite Mineral Data". Webmineral.
  10. Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  11. McCarron, E. M. (1986). "β-MoO3: A Metastable Analogue of WO3". J. Chem. Soc., Chem. Commun. (4): 336–338. doi:10.1039/C39860000336.
  12. Heynes, J. B. B.; Cruywagen, J. J. (1986). Yellow Molybdenum(VI) Oxide Dihydrate. Inorganic Syntheses. Vol. 24. pp. 191–2. doi:10.1002/9780470132555.ch56. ISBN 9780470132555.
  13. Meyer, Jens; Hamwi, Sami; Kröger, Michael; Kowalsky, Wolfgang; Riedl, Thomas; Kahn, Antoine (2012). "Transition Metal Oxides for Organic Electronics: Energetics, Device Physics and Applications". Advanced Materials. 24 (40): 5408–5427. Bibcode:2012AdM....24.5408M. doi:10.1002/adma.201201630. PMID 22945550. S2CID 197055498.

Cited sources
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