Auride

Auride is an ion made from a gold atom with one extra electron. It has the chemical formula .mw-parser-output .template-chem2-su{display:inline-block;font-size:

Auride
The left picture shows a solution of caesium auride in ammonia. The right picture shows yellow caesium auride crystals.

Auride is an ion made from a gold atom with one extra electron. It has the chemical formula Au−. It is a rare example of a single metal atom making a negatively charged ion.[1]

Although auride is more stable than other metal anions, only a few aurides have been made, using alkali metals and the organic ion tetramethylammonium. Aurides have no applications outside research.

Chemistry

Gold has a highly negative electron affinity of −222.8 kJ/mol. This is more negative than any other element other than the halogens, including most nonmetals. This allows the Au− anion to be more stable than other metal anions, which normally only exist as Zintl ions that spread the charge out over many atoms, or need to use host-guest chemistry to stop the metal from losing its extra electrons.

Computer simulations predict that auride acts like a halide ion, somewhere between bromide and iodide.[2]

Auride ions react with water, but make stable solutions in ammonia.[3]

History

The first auride solutions were probably made by Eduard Zintl's research group in 1931, but they did not think it contained auride.[3] In 1938, chemists discovered that an alloy of gold and caesium had much less volume than the separate metals, suggesting it made a chemical compound.[4] This compound was found to have the same crystal structure as caesium chloride, and to act like a semiconductor, not a metal.[5]

References

  1. ↑ Jansen, Martin (2008). "The chemistry of gold as an anion". Chemical Society Reviews. 37 (9): 1826–1835. doi:10.1039/B708844M. PMID 18762832.
  2. ↑ Belpassi, Leonardo; Tarantelli, Francesco; Sgamellotti, Antonio; Quiney, Harry M. (2006). "The Electronic Structure of Alkali Aurides. A Four-Component Dirac−Kohn−Sham Study". The Journal of Physical Chemistry A. 110 (13): 4543–4554. Bibcode:2006JPCA..110.4543B. doi:10.1021/jp054938w. PMID 16571062.
  3. ↑ 3.0 3.1 Peer, William J.; Lagowski, J. J. (1978). "Metal-ammonia solutions. 11. Gold(1-), a solvated transition metal anion". Journal of the American Chemical Society. 100 (19): 6260–6261. Bibcode:1978JAChS.100.6260P. doi:10.1021/ja00487a064.
  4. ↑ Biltz, Wilhelm; Weibke, Friedrich; Hans-Joachim Ehrhorn, Versuchen; Wedemeyer, Roman; Weibke, Friedrich (1938). "Über Wertigkeit und chemische Kompression von Metallen in Verbindung mit Gold". Zeitschrift für Anorganische und Allgemeine Chemie. 236: 12–23. Bibcode:1938ZAACh.236...12B. doi:10.1002/zaac.19382360104.
  5. ↑ Spicer, W. E.; Sommer, A. H.; White, J. G. (1959). "Studies of the Semiconducting Properties of the Compound CsAu". Physical Review. 115: 57–62. Bibcode:1959PhRv..115...57S. doi:10.1103/PhysRev.115.57.

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