Tetraiodonickelate

Tetraiodonickelate is a complex ion of nickel with four iodide ions [NiI₄]²⁻ arranged in a tetrahedron.^[1] [NiI₄]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.^[1] The magnetic moment is anomalously low.^[2]

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.^[3]

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.^[1]

Salts

Bis-triphenylmethylarsonium tetraiodoronickelate [(C₆H₅)₃CH₃As]₂NiI₄ is red in colour.^[1] 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.^[1]

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.

References