Structural studies of ionic liquids and ionothermally-prepared materials

Fused salts;X-rays--Diffraction

Byrne, Peter Joseph ; Morris, Russell Edward ; Morris, Russell Edward

University:University of St Andrews

Department:Chemistry (School of)

关键词: Fused salts;    X-rays--Diffraction;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/780/Peter%20J.%20Byrne%20PhD%20thesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

The aim of this thesis was to examine materials using high resolution X-raydiffraction techniques. Initial work involved the synthesis of various metalphosphates to investigate their suitability for charge density work. Many of thesewere discovered to be of insufficient quality for further study. Much of the phosphatesynthesis work performed at the moment utilises an ionic liquid both as a solvent andstructure directing agent which dictates the topology of the structure due to its sizeand charge density. As such the ionic liquid 1-ethyl-3-methylimidazoliumhexafluorophosphate used in the synthesis process was examined with highresolution X-ray diffraction as it was possible to produce large pure crystals whichcould be examined further. A high resolution data set was also collected from themetal organic framework SIMOF-1 which produced a preliminary multipole modelhowever further data collections are required to improve the quality of the model.A multi-technique investigation involving X-ray diffraction, solid state NMR andfirst principles calculations was carried out on the aluminophosphate material AlPO₄-15. A synchrotron X-ray single crystal diffraction study was carried out on the samesample as that used in solid state NMR studies. The model from the single crystalstudy, together with a model from a literature high resolution study of the samematerial, were used as starting points for the first-principles calculations of the NMRparameters. This enabled the ³¹P and ²⁷Al NMR spectra to be unambiguouslyassigned and all the NMR parameters calculated agreed well with the experimentalspectra 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 positionswould not change too drastically.Other aspects of this thesis involved investigations into other ionothermally preparedsystems such as the use of different phosphonate sources to provide functionality tothe materials. This work resulted in some interesting findings such as the ionic liquidbreaking down and being incorporated into the framework via the metal. Many of thestructures produced were of a layered nature however a molecular structure was alsosynthesised which is unlike the vast majority of hydrothermally preparedphosphonates, which are layered.The negligible vapour pressure provided by the ionic liquid has enabled synthesisreactions 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 andcompare microwave assisted reactions against a conventional heating method, theresults indicate that two different types of reactions are occurring resulting indifferent intermediates which is due to the way the reagents are heated. Themicrowave assisted reactions also result in larger purer crystals which highlights theimportance of the method in materials synthesis.The use of a specially designed environmental gas cell was used to investigate theadsorption properties of the metal organic framework CPO-27-Co in-situ. Using thecell it was possible to locate sulfur dioxide physisorbed and chemisorbed sites within 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 metalorganic framework however due to the low scattering factor and disorder from thegas it was not possible to locate the physisorbed sites.