Phosphides

Most elements combine with phosphorus to give binary phosphides; exceptions include Hg, Pb, Sb, Bi and Te.  Types of solid state phosphides are very varied,† and simple classification is not possible. Phosphides of the dblock metals tend to be inert, metallic-looking compounds with high melting points and electrical conductivities. Their formulae are often deceptive in terms of the oxidation state of the metal and their structures may contain isolated P centres, P₂ groups, or rings, chains or layers of P atoms.

   The group 1 and 2 metals form compounds M₃P and  M₃P₂ respectively which are hydrolysed by water and can be considered to be ionic. The alkali metals also form phosphides which contain groups of P atoms forming chains or cages, the cages being either [P₇]^3- (14.18) or [P₁₁]^3- (e.g. LiP contains infinite helical chains, K₄P₃ contains [P₃]^4- chains, Rb₄P₆ has planar [P₆]^4- rings, Cs₃P₇ contains [P₇]^3- cages, and Na₃P₁₁ features [P₁₁]^3- cages. The latter examples are phosphorus-rich species. Some other members of this class such as Ba₃P₁₄ and Sr₃P₁₄ contain [P₇]^3- cages, while phosphides such as BaP₁₀, CuP₇ , Ag₃P₁₁, MP₄ (e.g. M = Mn, Tc, Re, Fe, Ru, Os) and TlP₅ containmore extended arrays of P atoms, two examples  of which have already been mentioned.