Caesium auride is an ionic compound containing the unusual Au⁻ ion. It is obtained by heating a stoichiometric mixture of cesium and gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

; the two metallic-yellow liquids react to give a clear product. The solution in liquid ammonia is brown, and the solid is yellow; the ammonium adduct is dark blue.

The compound reacts violently with water, yielding caesium hydroxide

Caesium hydroxide

Caesium hydroxide is a chemical compound consisting of an atom of caesium and a hydroxide group . It is a powerful base, much like other alkali metal hydroxides such as sodium hydroxide and potassium hydroxide...

and metallic gold; in liquid ammonia it can be reacted with a cesium-specific ion exchange resin to produce tetramethylammonium auride.