Phosphide

Phosphide is a term used for compounds that contain the phosphide ion, P3−, or phosphorus in a negative oxidation state within a compound. In practice, the label covers both ionic phosphides formed with electropositive metals and covalent phosphides in which phosphorus behaves as a centralized, negatively charged species within a lattice.

Ionic phosphides include salts such as sodium phosphide (Na3P) and calcium phosphide (Ca3P2), produced by direct reaction of phosphorus with alkali or alkaline-earth metals. Covalent phosphides include materials like gallium phosphide (GaP) and indium phosphide (InP), which are important III–V semiconductors. Metal-rich phosphides occur across transition-metal and rare-earth systems (for example FeP, Fe3P, Ni2P) and often exhibit complex crystal structures. Natural phosphides appear as minerals such as schreibersite (Fe3P), found in meteorites.

Reactivity: Many phosphides react with water or acids to release phosphine gas (PH3), a toxic and flammable substance. For instance, Ca3P2 reacts with water to yield calcium hydroxide and phosphine. This reactivity affects how phosphides are handled and stored.

Applications: Phosphide semiconductors such as GaP and InP are used in optoelectronics, solar cells, and high-speed electronics. Transition-metal phosphides like Ni2P and CoP serve as catalysts in hydrogenation and hydrodesulfurization and are studied for other catalytic applications.

Preparation: Phosphides form by direct combination of phosphorus with metals at high temperature or by precipitation from suitable precursors; many intermetallic phosphides are prepared using metallurgical routes.