Ammonium perrhenate (APR) is the ammonium salt of perrhenic acid, NH₄ReO₄. It is the most common form in which

rhenium Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...

is traded. It is a white salt; soluble in ethanol and water, and mildly soluble in NH₄Cl. It was first described soon after the discovery of rhenium.

Structure

The crystal structure of APR resembles that of

scheelite Scheelite is a calcium tungstate mineral with the chemical formula Ca W O4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist K. Scheele (1742-1786). Well-formed crystals are sought by collectors ...

, with atomic cation is replaced by ammonium. The

pertechnetate The pertechnetate ion () is an oxyanion with the chemical formula . It is often used as a convenient water-soluble source of isotopes of the radioactive element technetium (Tc). In particular it is used to carry the 99mTc isotope (half-life 6 hou ...

(NH₄TcO₄),

periodate Periodate is an anion composed of iodine and oxygen. It is one of a number of oxyanions of iodine and is the highest in the series, with iodine existing in oxidation state +7. Unlike other perhalogenates, such as perchlorate, it can exist in two ...

(NH₄IO₄), tetrachlorothallate (NH₄TlCl₄), and tetrachloroindate (NH₄InCl₄) follow this motif. 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 In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

, resulting in the unusual property of having a positive temperature and pressure Re NQR coefficient. APR does not give hydrates.

Preparation

Ammonium perrhenate may be prepared from virtually all common sources of rhenium. The metal, oxides, and sulfides can be oxidized with

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

and the resulting solution treated with aqueous ammonia. Alternatively an aqueous solution of Re₂O₇ can be treated with ammonia followed by crystallisation.

Reactions

Ammonium perrhenate is weak oxidizer. It slowly reacts with hydrochloric acid: :NH₄ReO₄ + 6 HCl → NH₄ eCl₄O+ Cl₂ ↑ + 3H₂O. It is reduced to metallic Re upon heating under

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

: :2 NH₄ReO₄ + 7 H₂ → 2 Re + 8 H₂O + 2 NH₃ Ammonium perrhenate decomposes to volatile Re₂O₇ starting at 250 °C. When heated in a sealed tube at 500 °C, It decomposes to rhenium dioxide: :2NH₄ReO₄ → 2ReO₂ + N₂ + 4 H₂O The ammonium ion can be displaced with some concentrated nitrates e.g. potassium nitrate,, silver nitrate, etc.: :NH₄ReO₄ + KNO₃ → KReO₄ ↓ + NH₄NO₃ It can be reduced to nonahydridorhenate with sodium in ethanol: :NH₄ReO₄ + 18Na + 13C₂H₅OH → Na₂ eH₉+ 13NaC₂H₅O + 3NaOH + NH₃•H₂O.

References

* {{DEFAULTSORT:Ammonium Perrhenate Inorganic compounds Perrhenates Ammonium compounds