Molybdic acid

Molybdic acid refers to hydrated forms of molybdenum trioxide and related species. The monohydrate (MoO3·H2O) and the dihydrate (MoO3·2H2O) are well characterized. They are yellow diamagnetic solids.

Molybdic acid
Names
Other names
Molybdic(VI) acid
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.063
EC Number
  • 231-970-5
Properties
MoO3·H2O
Molar mass 161.95 g mol−1 [1]
Density 3.1 g cm−3 [1]
Melting point 300 °C (572 °F; 573 K)[1]
1510 mg dm−3 Soluble in 10% ammonia 35gm/lt[2]
Hazards
R-phrases (outdated) R36/37/38 [1]
S-phrases (outdated) S24/25, S22 [1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Structure of the solids
Portion of one layer of hydrated molybdic acid, MoO3·(H2O)2.

Solid forms of molybdic acid are coordination polymers. The monohydrate MoO3·H2O consists of layers of octahedrally coordinated MoO5·(H2O) units where 4 vertices are shared.[3] The dihydrate (image shown above) has the same layer structure with the "extra" H2O molecule intercalated between the layers.[4]

Structure of molybdic acid in solution

In acidified aqueous solutions of molybdic acid, the complex MoO3(H2O)3 is observed. Once again, molybdenum adopts octahedral molecular geometry, probably with three oxo ligands and three aquo ligands.[5]

The salts of molybdic acid are called molybdates. They arise by adding base to solutions of molybdic acid.

Applications

Many molybdenum oxides are used as heterogeneous catalysts, e.g. for oxidations. Molybdic acid and its salts are used to make the Froehde reagent for the presumptive identification of alkaloids.

References
  1. "Molybdic acid | 7782-91-4". Chemicalbook.com. Retrieved 2012-08-23.
  2. http://www.chemspider.com/RecordView.aspx?rid=e75000d7-a392-4602-8ca4-f2bd1f94b31c
  3. Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
  4. Krebs, B. (1972). "Die Kristallstruktur von MoO3(H2O)2". Acta Crystallographica B. 28: 2222–2231. doi:10.1107/S0567740872005849.
  5. Solution structure of molybdic acid from Raman spectroscopy and DFT analysis, Oyerindea O.F., Week C.L., Anbarb A.D., Spiro T.G. Inorganica Chimica Acta, 361, 4, (2008), 1000-1007, doi:10.1016/j.ica.2007.06.025


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