Potassium phosphides

Phosphine reacts with a solution of potassium in liquefied ammonia to form potassium dihydrophosphide, KH₂P, white crystals decomposed by moist air with evolution of phosphine. On heating, it is converted into tripotassium phosphide, K₃P. A solution of potassium in liquefied ammonia reacts with red phosphorus to form potassium pentaphosphide, KP₅. The black product formed from potassium and phosphorus loses its excess of metal in vacuum at 400° to 450° C., yielding dipotassium pentaphosphide, K₂P₅. It is a lemon-yellow substance with a density of about 2, is unstable in air, and is decomposed by water with formation of solid phosphorus hydride.