Ammonium perrhenate

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]

Ammonium perrhenate

Names
Other names Ammonium perrhenate, Ammonium perrhenate(VII)
Identifiers
CAS Number	13598-65-7
3D model (JSmol)	Interactive image
ChemSpider	2341271
ECHA InfoCard	100.033.690
EC Number	237-075-6
PubChem CID	3084163
CompTox Dashboard (EPA)	DTXSID10893940
InChI InChI=1S/H3N.4O.Re/h1H3;;;;;/q;;;;-1;/p+1 Key: HOJYZCWLNWENHS-UHFFFAOYSA-O InChI=1/H3N.4O.Re/h1H3;;;;;/q;;;;-1;/p+1/rH3N.O4Re/c;1-5(2,3)4/h1H3;/q;-1/p+1 Key: HOJYZCWLNWENHS-WUACXKGRAA
SMILES [O-][Re](=O)(=O)=O.[NH4+]
Properties
Chemical formula	NH4ReO4
Molar mass	268.2359 g/mol
Density	3.97 g/cm^3, 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
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).
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Infobox references

Structure

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

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

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

1. Noddack, J.; Noddack, W. (1929). "Die Sauerstoffverbindungen des Rheniums". Zeitschrift für anorganische und allgemeine Chemie. 181 (6): 1–37. Bibcode:1929NW.....17...93N. doi:10.1002/zaac.19291810102.
2. 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. Bibcode:1977JChPh..67.3163B. doi:10.1063/1.435229.
4. 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. ISBN 9780470132395.

• Wm. T. Smith, S. Harmon Long (1948). "The Salts of Perrhenic Acid. I. The Alkali Metals and Ammonium". Journal of the American Chemical Society. 70 (1): 354–356. doi:10.1021/ja01181a110.