20  New compounds and structures in the solid state

Synthesis and Structure of Pillared Molybdates and Tungstates with Framework Layers

“…Examples of such materials include the zeolites, alumino- and gallophosphates, and metal organic frameworks. Structurally, the zeolites are made up from tetrahedral AlO 4 5− and SiO 4 4− building blocks which link together through all four O atoms to form the rings and cages that provide the basis of the diverse range of zeolite structures. − The alumino- and gallophosphates, where the SiO 4 4− tetrahedron in the zeolites is replaced by PO 4 3− , are structurally similar, but there is greater flexibility in the coordination environments leading to four-, five-, and six-coordinate Al 3+ centers and terminal O atoms on PO 4 3− . − The effect of this is to give the phosphate materials greater structural diversity than the zeolites with larger pore frameworks such as VPI-5 , and cloverite as well as layered − and chain structures being formed. − …”