Ammonium perrhenate

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Ammonium perrhenate
Ammonium perrhenate
Ammonium perrhenate.jpg
Identifiers
CAS number 13598-65-7 YesY
ChemSpider 2341271 YesY
Jmol-3D images Image 1
Properties
Molecular formula NH4ReO4
Molar mass 268.2359 g/mol
Density 3.97 g/cm³, solid
Melting point °C
Solubility in water 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
Crystal structure scheelite
Coordination
geometry
N/A
Hazards
EU classification Not listed.
Flash point Non-flammable
Related compounds
Other anions Ammonium manganate; ammonium pertechnetate
Other cations Sodium perrhenate; perrhenic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Ammonium perrhenate (APR) is the ammonium salt of perrhenic acid, NH4ReO4. This 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.[1]

Structure[edit]

The crystal structure of ammonium perrhenate with orientationally ordered ammonium ions (blue) and ReO4 (grey) tetrahedra.

The crystal structure of APR is that of scheelite, in which the atomic cation is replaced by the ammonium molecular cation.[2] 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.[3]

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).[2]

Preparation[edit]

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.[4][5]

Reactions[edit]

Pure rhenium powder can be produced from APR by reducing it with hydrogen with heat:[4]

2 NH4ReO4 + 7 H2 → 2 Re + 8 H2O + 2 NH3

Heating must be done slowly because ammonium perrhenate decomposes to volatile oxides starting at 250 °C. In a sealed tube at 500 °C, APR decomposes to the dioxide:[4]

NH4ReO4 → ReO2 + N2 + H2O

References[edit]

  1. ^ J. Noddack and W. Noddack "Die Sauerstoffverbindungen des Rheniums" Zeitschrift für anorganische und allgemeine Chemie 1929, volume 181, pages 1–37. doi:10.1002/zaac.19291810102
  2. ^ a b I. P. Swainson and R. J. C. Brown (1997). "Refinement of ammonium perrhenate structure using a pseudo-spin model for the ammonium ion orientation". Acta Crystallographica B53: 76–81. doi:10.1107/S0108768196011160. 
  3. ^ R. J. C. Brown and S. L. Segel (1977). "187Re, 14N, and 2H nuclear quadrupole couplings in NH4ReO4: Evidence for a possible phase transition". Journal of Chemical Physics 67 (7): 3163–7. doi:10.1063/1.435229. 
  4. ^ a b c O. Glemser "Ammonium Perrhenate" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, New York. vol. 1. p. 1476–85.
  5. ^ Richard J. Thompson (1966). "Ammonium Perrhenate". Inorganic Syntheses 8: 171–173. doi:10.1002/9780470132395.ch44.