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Ammonium perrhenate

Ammonium perrhenate
Ammonium perrhenate
Ammonium perrhenate.jpg
Names
Other names
Ammonium perrhenate,
Ammonium perrhenate(VII)
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.033.690
EC Number 237-075-6
PubChem CID
Properties
NH4ReO4
Molar mass 268.2359 g/mol
Density 3.97 g/cm3, solid
Melting point °C
2.8 g/100 mL (0 °C), 6.2 g/100 mL (20 °C), 12.0 g/100 mL (40 °C), 20.7 g/100 mL (60 °C), 32.3 g/100 mL (80 °C), 39.1 g/100 mL (90 °C)
Structure
scheelite
N/A
Hazards
Not listed.
Flash point Non-flammable
Related compounds
Other anions
Ammonium manganate; ammonium pertechnetate
Other cations
Sodium perrhenate; perrhenic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
Infobox references

Ammonium perrhenate (APR) is the ammonium salt of perrhenic acid, NH4ReO4. It is the most common form in which rhenium is traded. It is a white, water-soluble salt. It was first described soon after the discovery of rhenium.

The crystal structure of APR is that of scheelite, in which the atomic cation is replaced by the ammonium molecular cation. It undergoes a molecular orientational ordering transition on cooling without change of space group, but with a highly anisotropic change in the shape of the unit cell, resulting in the unusual property of having a positive temperature and pressure Re NQR coefficient.

NH4ReO4 can be regarded as the prototype structure of a family of ammonium scheelites, which include the pertechnetate (NH4TcO4), periodate (NH4IO4), tetrachlorothallate (NH4TlCl4) and tetrachloroindate (NH4InCl4).

Ammonium perrhenate may be prepared from virtually all common sources of rhenium. The metal, oxides, and sulfides can be oxidized with nitric acid and the resulting solution treated with aqueous ammonia. Alternatively an aqueous solution of Re2O7 can be treated with ammonia followed by crystallisation.

Pure rhenium powder can be produced from APR by heating it in the presence of hydrogen:

Heating must be done slowly because ammonium perrhenate decomposes to volatile Re2O7 starting at 250 °C. When heated in a sealed tube at 500 °C, APR decomposes to rhenium dioxide:


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