Nets and MOFs

This approach has been taken further, using as linkers diamine ligands that contain within them sites that themselves coordinate to catalytically active metals that are accessible to molecules from within the pore space.This approach, which is discussed further in Chapter 9, has been used to include enantioselective catalytic sites into MOFs. 

The diversity of ordered porous solids increases at an astonishing rate, particularly among the readily crystallised MOFs, and continues to olfer novel materials properties. There is no obvious barrier to the synthesis of a myriad of new zeolite, zeotype or hybrid structures. Challenges remain, however. For zeolitic aluminosilicates, the 10 A pore size restriction remains an important barrier, and an enantiomerically pure zeolite is still out of reach. For nonsilicate crystalline microporous solids, thermal and hydrothermal stability, rather than framework geometry, limit their applicability, since fully crystalline germanates and carboxylates with pores in the mesoporous range now exist, and these solids have enormous specific surface areas. In these hybrid solids the ability to choose chirality in the building units indicates that it will be possible to prepare these in chiral form the first examples have already been prepared. 

Mesoporous silicas can possess intercage windows within the microporous region, but their stability and acid strength are low compared to those of zeolites. One current approach to this particular problem is the use of partially crystallised zeolite nuclei as starting materials in the synthesis of mesoporous solids, in an attempt to prepare a solid with structural features of both microporous and mesoporous solids. Such solids are said to possess hierarchical porosity, and are discussed further in Chapter 10. 

Baerlocher, W. M. Meier and D. H. Olson, Atlas of Zeolite Framework Types , 5th Ed., Elsevier, Amsterdam, 2001. 

Diaz-Cabanas, J. Martinez-Triguero, F. Rey and J. Rius, 

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