Lithium phosphide

Lithium phosphide is an inorganic compound of lithium and phosphorus with the chemical formula Li3P. This dark colored compound is formally the lithium salt of phosphine, consisting of lithium cations Li+ and phosphide anions P(3−). It is hazardous to handle because of its high reactivity toward air.

Synthesis
Heating red phosphorus and lithium in an argon atmosphere:
 * 12 Li + P4 → 4 Li3P

Reaction of monolithium phosphide and lithium:
 * LiP + 2 Li → Li3P

Physical and chemical properties
Lithium phosphide forms red-brown crystals of hexagonal systems, space group P63/mmc, cell parameters a = 0.4264 nm, c = 0.7579 nm, Z = 2.

The compound reacts with water to release phosphine:
 * Li3P + 3 H2O → 3 LiOH + PH3

Uses
The compound is proposed to be used as a potential electrolyte for solid-state devices.

Related compounds
Reaction of lithium with red phosphorus at 870 °C gives Li3P7.

Safety
Alkali metal phosphides are dangerous compounds when exposed to oxygen or moisture.