The suitability of microporous compounds for applications such as Beta-Lapachone exchange and selective adsorption is assisted by their ability to change their pore dimensions reversibly and reproducibly with temperature, as well as having good thermal stability. This field has seen rapid growth in recent years with much of the effort being directed to the new field of metal organic frameworks ,  and  as well as to zeolites and zeolitic materials ,  and . An important factor that influences the effect of temperature change on the pore size/geometry is the presence of guest molecules in the pores. The cyanide-bridged framework structure for Cd(CN)2·nCCl4 displays a change from positive thermal expansion (PTE) to negative thermal expansion (NTE) as the CCl4 guest occupancy is decreased . Similar effects are observed for water molecules in the pores. The 3D frameworks in ZnPt(CN)6·nH2O  and in LnCo(CN)6·nH2O  switch from PTE to NTE behaviour when the water is removed.