Molybdenum trioxide

Molybdenum trioxide describes a family of inorganic compounds with the formula MoO₃(H₂O)_n where n = 0, 1, 2. The anhydrous compound is produced on the largest scale of any molybdenum compound since it is the main intermediate produced when molybdenum ores are purified. 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
CAS Number	1313-27-5 anhydrous Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30627
ChemSpider	14118
ECHA InfoCard	100.013.823
EC Number	215-204-7
PubChem CID	14802
UNII	22FQ3F03YS Y
UN number	3288
CompTox Dashboard (EPA)	DTXSID7020899
InChI InChI=1S/Mo.3O Key: JKQOBWVOAYFWKG-UHFFFAOYSA-N
SMILES O=[Mo](=O)=O
Properties
Chemical formula	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]
Solubility in water	1.066 g/L (18 °C) 4.90 g/L (28 °C) 20.55 g/L (70 °C)
Band gap	>3 eV (direct)[2]
Magnetic susceptibility (χ)	+3.0·10−6 cm3/mol[3]
Structure[4]
Crystal structure	Orthorhombic, oP16
Space group	Pnma, No. 62
Lattice constant	a = 1.402 nm, b = 0.37028 nm, c = 0.39663 nm
Formula units (Z)	4
Coordination geometry	see text
Thermochemistry[5]
Heat capacity (C)	75.0 J K−1 mol−1
Std molar entropy (S⦵298)	77.7 J K−1 mol−1
Std enthalpy of formation (ΔfH⦵298)	−745.1 kJ/mol
Gibbs free energy (ΔfG⦵)	-668.0 kJ/mol
Hazards[6]
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H319, H335, H351
Precautionary statements	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)	3 0 OX
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	125 mg.kg (rat, oral)[citation needed] 2689 mg/kg (rat, oral)[7]
LDLo (lowest published)	120 mg Mo/kg (rat, oral) 120 mg Mo/kg (guinea pig, oral)[7]
LC50 (median concentration)	>5840 mg/m3 (rat, 4 hr)[7]
Related compounds
Other cations	Chromium trioxide Tungsten trioxide
Related molybdenum oxides	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). N verify (what is YN ?) 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

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

MoO₃ is produced industrially by roasting the mineral molybdenite (molybdenum disulfide), the chief ore of molybdenum:^[8]

2 MoS₂ + 7 O₂ → 2 MoO₃ + 4 SO₂

Similar procedures apply to the recovery of molybdenum from spent catalysts. The resulting trioxide can be purified by sublimation. The laboratory synthesis of the dihydrate entails acidification of aqueous solutions of sodium molybdate with perchloric acid:^[12]

Na₂MoO₄ + H₂O + 2 HClO₄ → MoO₃·2H₂O + 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 [transition metal oxide] in organic electronics applications ... it is evaporated at relatively low temperature (~400 °C)."^[13] It has favourable electronic and chemical properties for use as interfacing layers, p-type dopants and hole transport materials in OLEDs, organic solar cells and perovskite solar cells,^[14] especially when forming an ohmic contact to organic semiconductors.^[15]

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.
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. ISBN 978-3527306732.
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.
14. White, Robin T.; Thibau, Emmanuel S.; Lu, Zheng-Hong (2016-02-16). "Interface Structure of MoO3 on Organic Semiconductors". Scientific Reports. 6 (1): 21109. Bibcode:2016NatSR...621109W. doi:10.1038/srep21109. ISSN 2045-2322. PMC 4754744. PMID 26880185.
15. Gong, Yongshuai; Dong, Yiman; Zhao, Biao; Yu, Runnan; Hu, Siqian; Tan, Zhan'ao (2020). "Diverse applications of MoO 3 for high performance organic photovoltaics: fundamentals, processes and optimization strategies". Journal of Materials Chemistry A. 8 (3): 978–1009. doi:10.1039/C9TA12005J. ISSN 2050-7488. S2CID 213237371.

Cited sources

• Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 978-1439855119.

External links

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
• U.S. Department of Health and Human Services National Toxicology Program
• International Molybdenum Association
• Los Alamos National Laboratory – "Molybdenum"