Phosphides of metals

The structures of the alkal-metal phosphides, arsenides, etc. are shown in Table 19.2, where N stands for the Na3As structure and L for the Li3Bi structure (p. 1035). The NasAs structure is somewhat reminiscent of an alloy structure. As having 11 Na neighbours at distances from 2-94 to 3-30 A, and that of Li3Bi is a typical intermetallic structure. With the Group VB metalloids Li also forms 1 1 

P-P groups in compounds with the pyrites or marcasite structures, discrete P4 rings in IrP3 etc. (C0AS3 structure), chains in PdP2, layers in CdP4. 

In all these compounds the P-P bond length is close to 2-2 A (single bond). In some of the transition-metal phosphides P-P has rather larger values, 2-4 A (NIP), and 2-6-2-7 A (CrP, MnP, FeP, CoP). 

Pyrites or Marcasite P2 groups PtP2,(2 ) NiP2 (h.p.)(2) PeP2,(ia) OSP2, RuP2 

Examples of relatively simple structures include a-CdPj CdP4 

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