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|Title: ||Structural studies of ionic liquids and ionothermally-prepared materials|
|Authors: ||Byrne, Peter Joseph|
|Supervisors: ||Morris, Russell E.|
|Issue Date: ||2009|
|Abstract: ||The aim of this thesis was to examine materials using high resolution X-ray
diffraction techniques. Initial work involved the synthesis of various metal
phosphates to investigate their suitability for charge density work. Many of these
were discovered to be of insufficient quality for further study. Much of the phosphate
synthesis work performed at the moment utilises an ionic liquid both as a solvent and
structure directing agent which dictates the topology of the structure due to its size
and charge density. As such the ionic liquid 1-ethyl-3-methylimidazolium
hexafluorophosphate used in the synthesis process was examined with high
resolution X-ray diffraction as it was possible to produce large pure crystals which
could be examined further. A high resolution data set was also collected from the
metal organic framework SIMOF-1 which produced a preliminary multipole model
however further data collections are required to improve the quality of the model.
A multi-technique investigation involving X-ray diffraction, solid state NMR and
first principles calculations was carried out on the aluminophosphate material AlPO₄-15. A synchrotron X-ray single crystal diffraction study was carried out on the same
sample as that used in solid state NMR studies. The model from the single crystal
study, together with a model from a literature high resolution study of the same
material, were used as starting points for the first-principles calculations of the NMR
parameters. This enabled the ³¹P and ²⁷Al NMR spectra to be unambiguously
assigned and all the NMR parameters calculated agreed well with the experimental
spectra even without relaxing the X-ray derived structural models. Highlighting that as long as a good data set has been collected in the first place the atomic positions
would not change too drastically.
Other aspects of this thesis involved investigations into other ionothermally prepared
systems such as the use of different phosphonate sources to provide functionality to
the materials. This work resulted in some interesting findings such as the ionic liquid
breaking down and being incorporated into the framework via the metal. Many of the
structures produced were of a layered nature however a molecular structure was also
synthesised which is unlike the vast majority of hydrothermally prepared
phosphonates, which are layered.
The negligible vapour pressure provided by the ionic liquid has enabled synthesis
reactions to be investigated with glass vessels on an energy dispersive beam line.
This work highlighted how it is possible to study the synthesis process in-situ and
compare microwave assisted reactions against a conventional heating method, the
results indicate that two different types of reactions are occurring resulting in
different intermediates which is due to the way the reagents are heated. The
microwave assisted reactions also result in larger purer crystals which highlights the
importance of the method in materials synthesis.
The use of a specially designed environmental gas cell was used to investigate the
adsorption properties of the metal organic framework CPO-27-Co in-situ. Using the
cell it was possible to locate sulfur dioxide physisorbed and chemisorbed sites with
in the framework which could be removed by the application of a vacuum and heat.
It was also possible to locate the chemisorbed sites for nitric oxide within the metal
organic framework however due to the low scattering factor and disorder from the
gas it was not possible to locate the physisorbed sites.|
|Publisher: ||University of St Andrews|
|Appears in Collections:||Chemistry Theses|
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