Formula (NH4)6Mo7O24 Density 2.5 g/cm³ | Molar mass 1,163.9 g/mol | |
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Related compounds Appearance white to yellow-green crystalline solid | ||
Ammonium heptamolybdate is the inorganic compound, normally encountered as the tetrahydrate, whose chemical formula is (NH4)6Mo7O24·4H2O. It is a colorless solid, often referred to as ammonium paramolybdate or simply as ammonium molybdate, although "ammonium molybdate" can also refer to ammonium orthomolybdate, (NH4)2MoO4, and several other compounds. Potassium heptamolybdate, also obtained as the tetrahydrate, is very similar to the ammonium salt.
Contents
Synthesis
Ammonium heptamolybdate is easily prepared by dissolving molybdenum trioxide in an excess of aqueous ammonia and evaporating the solution at room temperature. While the solution evaporates, the excess of ammonia escapes. This method results in the formation of six-sided transparent prisms of the tetrahydrate of ammonium heptamolybdate.
Solutions of ammonium paramolybdate react with acids to form molybdic acid and an ammonium salt. The pH value of a concentrated solution will lie between 5 and 6.
Structure
The compound was first analyzed crystallographically by Lindqvist, but has been reanalyzed. All Mo centers are octahedral. Some oxide ligands are terminal, some doubly bridging, and a few are triply bridging ligands.
Uses
Safety
Ammonium paramolybdate is harmful if swallowed or inhaled. It causes irritation to the eyes, skin, and respiratory tract. It affects kidneys and blood.