Tetrachloronickelate

However in other organic solvents, or molten salts the tetrachloronickelate ion can form.

[2] Organic ammonium salts of the type (R3NH)2[NiCl4] are often thermochromic (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 [NiCl4]2−, the intensity being a consequence of the Laporte selection rule.

The yellow color results from a polymer consisting of octahedral Ni centers.