Ammonium perrhenate

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Ammonium perrhenate
Ammonium perrhenate
Ammonium perrhenate.jpg
Names
Other names
Ammonium perrhenate,
Ammonium perrhenate(VII)
Identifiers
13598-65-7 YesY
3D model (Jmol) Interactive image
ChemSpider 2341271 YesY
ECHA InfoCard 100.033.690
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 verify (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.[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 heating it in the presence of hydrogen:[4]

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

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:[4]

2NH4ReO4 → 2ReO2 + N2 + 4 H2O

References[edit]

  1. ^ Noddack, J.; Noddack, W. (1929). "Die Sauerstoffverbindungen des Rheniums". Zeitschrift für anorganische und allgemeine Chemie. 181: 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.