352Diphosphine is an analogue of hydrazine. Compounds containing P=P double bonds have
also been observed, although they are rare.
Phosphides
The phosphide ion is P3-. Phosphides arise by reaction of metals with red phosphorus.
Salts of P3- do not exist in solution and these derivatives are refractory, reflecting their high
lattice energy. Illustrated by the behavior calcium phosphide, many metal phosphides
hydrolyze in water with release of phosphine:
Ca 3 P 2 + 6 H 2 O → 2 PH 3 + 3 Ca(OH) 2Schreibersite is a naturally occurring phosphide found in meteorites. Many
polyphosphides are known such as derivatives of OsP 2. These can be structurally complex
ranging from Na 3 P 7 and derivatives of P 26 4-. Often these species adopt cage-like structures
that resemble fragments of violet phosphorus.