Tetraiodonickelate Explained

Tetraiodonickelate is a complex ion of nickel with four iodide ions [NiI<sub>4</sub>]2− arranged in a tetrahedron. [NiI<sub>4</sub>]2− is red in solution. This colour is due to absorption around 530 nm and below 450 nm. Maximum light transmission is around 620 nm, which is red. A broad weak absorption in the near infrared is at 740 nm. The magnetic moment is anomalously low.[1]

A mixture of lithium iodide and nickel iodide in water or methanol can partition NiI42− ions into a cyclohexane-amine mixture. The solution formed is blood red.[2]

History

Already in 1909 Cambi had noticed that a mixture of nickel iodide and sodium iodide dissolved in acetone has a red colour. This red colour was due to the presence of tetraiodonickelate.[3]

Salts

Bis-triphenylmethylarsonium tetraiodoronickelate [(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>CH<sub>3</sub>As]2NiI4 is red in colour.[3] It can be made from triphenylmethylarsonium iodide and nickel iodide in hot ethanol. The red flakes that precipitate must be filtered before the alcohol cools, else the compound decomposes.[3]

Bis(tetraethylammonium) tetraiodonickelate has a molecular weight of 826.8135 and a CAS number of 13927-28-1.[4]

1,2,6-trimethyl-pyrazinium-tetraiodonickelate has CAS 88227-96-7.

Notes and References

  1. Hollebone. B. R.. Pseudo-halide complexes of transition metals. Part II. Spectra, structure, and nature of bonding. Journal of the Chemical Society A: Inorganic, Physical, Theoretical. 1971. 484. 10.1039/J19710000481.
  2. Florence. T. M.. Farrar. Yvonne J.. Liquid-liquid extraction of nickel with long-chain amines from aqueous and nonaqueous halide media. Analytical Chemistry. July 1968. 40. 8. 1200–1206. 10.1021/ac60264a010.
  3. Gill. Naida S.. Nyholm. R. S.. 802. Complex halides of the transition metals. Part I. Tetrahedral nickel complexes. Journal of the Chemical Society (Resumed). 1959. 3997. 10.1039/JR9590003997.
  4. Web site: bis(tetraethylammonium) tetraiodonickelate. webbook.nist.gov. 14 June 2016.