Complex Phosphates and Space-Containing Structures

The synthesis and discovery of new phosphate structures have accelerated greatly over the past two decades. It is now evident that phosphates will surpass silicates both in variety and in complexity, although their thermal stability is often less than that of the latter. 

Because of the large range and complex variety of inorganic phosphate structures now known, their systematic classification on a purely geometrical and structural basis is a somewhat daunting task. Nevertheless some of the simpler types can be picked out. 

In the various structural schemes, oxygen coordination is sometimes completed by (OH) or H2O molecules if they are present in the crystal formula. A recent example is provided by the mineral Cu(H20)2[B2P20g(0H)3] whose crystalline structure can be regarded as built from [PO4] and [B03(0H)1 tetrahedra, and [Cu02(0H)2(H20)2] octahedra. 

As the foregoing parts of this chapter have indicated, all these linked polyhedral networks may form characteristic structural units such as chains, sheets or 3D networks. Holes or cavities may also be present in the resulting arrangements. The subject of cavity structures is now very important in the rapidly growing field of materials science (Chapter 12). 

---