 | ||
Tetrachloronickelates are a class of chemical compounds containing anions consisting of a nickel atom surrounded by four chloride ions. [NiCl4]2−
Contents
When concentrated lithium chloride and nickel chloride solution in water is mixed, only a pentaaquachloro complex is formed: [Ni(H2O)5Cl]+. 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, by partitioning it into a cyclohexane solution of amines.
Substituted ammonia tetrachloronickelates can be thermochromic. At room temperature they can be in a polymeric yellow coloured form, but when heated become bright blue, as the form changes to a tetrahedral arrangement of chlorine around the nickel atom. Yet other amine salts of tetrachloronickelate, such as [(NC3H7)3NH]2NiCl4, are blue liquids at room temperature. The trimethylammonium and diethylammonium salts have thermochromic temperatures at 70 °C. The corresponding tetrabromonickelates are also thermochromic with a transition at lower temperatures.
Some tetrachloronickelates can be ionic liquids at room temperature.
History
The blue colour due to the tetrachloronickelate ion was first observed in 1944 when Remy and Meyer melted cesium chloride and cesium nickel trichloride together.