Metal organic frameworks (MOFs) have drawn increasing attention recently due to their widespread applications for example in separation technology. Analysis of MOF topologies resulting from metal nodes bridged with linker ligands can give fruitful comparison with existing simple inorganic compounds. An important family of MOFs with such an analogy are the so-called Zeolitic Imidazolate Frameworks, or ZIFs. These have typical M(Im)₂ formulation with tetrahedral metal ²⁺ ions (Co, Zn or Cd) and bent linear μ₂-imidazolate anions and can adopt a multitude of topological types that are analogous to SiO₂, with open or condensed frameworks. The strong metal-nitrogen bonds in MIm₂ result in robust frameworks with high thermal and chemical stability even for the open framework materials. Other m...[ Read more ]

Metal organic frameworks (MOFs) have drawn increasing attention recently due to their widespread applications for example in separation technology. Analysis of MOF topologies resulting from metal nodes bridged with linker ligands can give fruitful comparison with existing simple inorganic compounds. An important family of MOFs with such an analogy are the so-called Zeolitic Imidazolate Frameworks, or ZIFs. These have typical M(Im)₂ formulation with tetrahedral metal ²⁺ ions (Co, Zn or Cd) and bent linear μ₂-imidazolate anions and can adopt a multitude of topological types that are analogous to SiO₂, with open or condensed frameworks. The strong metal-nitrogen bonds in MIm₂ result in robust frameworks with high thermal and chemical stability even for the open framework materials. Other metal dioxides such as titania and tin (IV) oxide have octahedral metal and triple bridging oxide and we were interested to see whether M(μ₃-L)₂ analogues of these could be prepared. This thesis explores some novel issues with ZIFs as well as a new family of Rutile/ Cassiterite analogues, M(4-O-Py)₂ M = Cd, Ca which may have potential for small gas molecule separations.

The First Chapter introduces the background of effective ZIF design and preparation, as well as TiO₂ analogues and their prospective applications in gas storage and separation and drug delivery. In Chapter Two, ZIF structures from the Cd(BzIm)₂ system are shown to be influenced by solvent or guest molecule, resulting in two unique structures named as ABW and D6R, which are 3D and 2D open frameworks respectively. The 2D ‘double sheet’ form of silica has been sought after by materials scientists and has been prepared in small-ordered regions on the surface of ruthenium. Our analog contains aromatic guests and may be suitable for membrane applications. In Chapter Three, the quartz analogues M(2-R-Im)₂ formed by various M²⁺ with 2-alkylimidazolates are investigated and their crystallization optimized to enable piezoelectric study. Changing solvents and changing solvothermal conditions enhance phase purity and the size of single crystals. Furthermore, the quartz-like phases are extended to mixed-metal and mixed-ligand systems, resulting in a double cell quartz topology in addition to low and high quartz phases.

In Chapter Four a new stable MOF family M(4-O-Py)₂ with TiO₂ Rutile-topology structure is synthesized hydrothermally using basic conditions, metal acetate and 4-hydroxypyridine. The resulting tetragonal structure has infinite chains of [M₂O₂] rings along the short c-axis of around 3.7Å. This separation allows the deprotonated 4-hydroxypyridine bridges to π-stack in a tilted manner reminiscent of the horizontal slats in venetian blinds, an interaction that stabilizes the MOF structure. The orientation of the tilting is preserved in all sides of the structure and thus reduces the symmetry of Rutile’s P4₂/mnm to chiral P4₂2₁2. The central channel has 2.4-2.8Å hole size depending on whether the metal is Cd or Ca. Attempts are being made to engineer the pore size and lining and whilst mono-halo substituted MOFs have not yet been prepared 3,5-Cl₂-4-O-Py forms the related phase M(OH)(3,5-Cl₂-4-O-Py) which has mu-3 hydroxide as well as mu-3 O-Py ligand and still retains a Rutile based topology. Interestingly the larger size of Cl is offset by the ring expansion so that the diameter of the cavity is similar to the parent M(4-O-Py)₂ compound, but the channel walls have been modified in their electrostatic character.

In Chapter five a range of MOF architectures and compositions are explored for their potential in different applications. The MOF sponge of Fujita act as the host to absorb different organic molecules, and we have begun to explore the metal-CD MOF with natural cyclodextrin ring serves as the channel to successfully absorb the guest molecule of methylene blue. Finally, future studies and prospects are surveyed in Chapter 6. These include technical issues to address in converting MOFs into Metal-Organic layers (MOLs) as well as channel and pore engineering of the new Rutile based MOFs using expanded ligands such as 6-oxyisoquinoline and 4-pyridyl-4-phenolate and piezo-electric measurements of single crystals for the chiral quartz and Rutile MOFs.