Tetrachloronickelate is the

metal complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or ...

with the formula iCl₄sup>2−. Salts of the complex are available with a variety of cations, but a common one is

tetraethylammonium Tetraethylammonium (TEA) is a quaternary ammonium cation with the chemical formula , consisting of four ethyl groups (, denoted Et) attached to a central nitrogen atom. It is a counterion used in the research laboratory to prepare lipophilic salt ...

. When concentrated lithium chloride and nickel chloride solution in water is mixed, only a pentaaquachloro complex is formed: i(H₂O)₅Clsup>+. However in other organic solvents, or molten salts the tetrachloronickelate ion can form. Nickel can be separated from such a solution in water or

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

, by partitioning it into a cyclohexane solution of amines. Organic ammonium salts of the type (R₃NH)₂ iCl₄are often

thermochromic Thermochromism is the property of Chemical substance, substances to change color due to a change in temperature. A mood ring is an example of this property used in a consumer product although thermochromism also has more practical uses, such as b ...

(R = Me, Et, Pr). Near room temperature, these salts are yellow , but these solids become blue when heated to near 70 °C. The bright blue color is characteristic of tetrahedral iCl₄sup>2−, the intensity being a consequence of the

Laporte selection rule The Laporte rule is a rule that explains the intensities of absorption spectra for chemical species. It is a selection rule that rigorously applies to atoms, and to molecules that are centrosymmetric, i.e. with an inversion centre. It states that ...

. The yellow color results from a polymer consisting of octahedral Ni centers. The corresponding tetrabromonickelates are also thermochromic with a lower transition temperatures.

History

The blue colour due to the tetrachloronickelate ion was first observed in 1944 when Remy and Meyer melted caesium chloride and caesium nickel trichloride together.

Compounds

Related substances

tetrabromonickelate The tetrabromonickelate anion contains a doubly-charged nickel atom (Ni2+) surrounded by four bromide ions in a tetrahedral arrangement. The formula is iBr4sup>2−. The anion combines with cations to form a series of salts called tetrabromonicke ...

References

{{chlorine compounds Nickel complexes Inorganic chlorine compounds Chlorometallates