Metal imidazolates [M(Im)
2] have received much recent attention as a promising class of metal coordination polymer especially as microporous phases for separation technology. Notably they have chemical stability because of strong metal-nitrogen bonds which also leads to exceptional framework thermal stabilities of 300°C-500°C. They are also of interest as direct topological analogues of silica SiO
2. Chapter One surveys the background to successful design and preparation of ZIFs and their potential applications such as gas storage and separation. Moreover, guest-inclusion of ZIFs was surveyed and computational studies of ZIFs were introduced. In Chapter Two a total of 18 cadmium bisbenzimidazolate phases were formed solvothermally by varying a wide range of solvents. Those compounds possess a number of different topologies, such as 2D sheet, 2D double six-membered layer, ABW and SOD. The 2D sheet could be chiral or centro by using different solvents. The 2D D6R frameworks are totally new in Zeolite Imidazolate Frameworks. Interestingly, we obtained two conformational isomers of [Cd(BzIm)
2]
n with ABW topology due to the different orientations of benzimidazolate, and they are templated by different solvents. When using Cycloketones as solvents, two SOD frameworks with different lowered symmetries were obtained. These are conformational isomers of each other. Chapter Three explores the group 12 metal polymers from mixed imidazolate-benzimidazolate ligands. Many of them are polymorphs of the new 2D double layer D6R structural types. When using acetone as solvent in the imidazolate-benzimidazolate system, a new double layer topology with D4R and D8R was obtained. When changing cadmium to zinc, the 2-MeIm/BzIm system gives a modified SOD framework with cubic space group. Chapter Four studies the cadmium polymers from a mixed imidazolate/ 2-Methylbenzimidazolate system. This is quite distinct from that explored in Chapter 3 with the 2-Me on the imidazole. Firstly, however, the [Cd(2-MeBzIm)
2]
n system was been studied in depth. All solvents give the same condensed product [Cd(2-MeBzIm)
2]
n 4-1 with dia topology. Then the mixed system was explored by using different solvent templates, which give lon, BCT, cag and DFT topological types. These included interesting regio-chemical isomers for the cag frameworks in which Im and 2-MeBzIm positions were interchanged. Chapter Five discusses the phase transformations of the two systems [Cd(BzIm)
2]
n and [Cd(Im)(2-MeBzIm)]
n these are consistent with dissolution and then recrystallisation processes. Finally selective absorption properties of [Zn(2-MeIm)
4/3(BzIm)
2/3]
n with cubic SOD structure were studied. It shows highly selective absorption of morpholine to 1,4-dioxane compared with known ZIF-8 [Zn(2-MeIm)
2]
n . This may be due to N-H···Cg interaction of morpholine with the inner surface of host framework. The thermodynamics of this selective absorption are being investigated.
| Date of Award | 2013 |
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| Original language | English |
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| Awarding Institution | - The Hong Kong University of Science and Technology
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