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Date: 11-2-2016
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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.
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