Procedures for collecting data on a diffractometer equipped with an area detector from samples held within the diamond anvil cell have been developed. The cell construction limits access to reciprocal space and leads to contamination of the diffraction patterns, leading to problems in indexing, data processing and refinement; these effects have been investigated and some strategies for overcoming these are described. Compression studies of the amino acid glycine show the formation of a new polymorph below 8 kbar via a single crystal – single crystal phase transition from the known β-phase of glycine. The formation of this new polymorph can be rationalised on topological grounds by changes in the packing of the molecules to a more favourable body centred cubic based arrangement. γ-glycine was found to undergo a phase transition, characterised using powder diffraction at high pressure. The behaviour is consistent with the formation of δ-glycine. The crystal structure of the amino acid l-alanine is stable to the effects of pressure to at least 70 kbar. The hydrogen-bonding network undergoes significant distortion; this distortion can be explained by the structure adopting a more body centred cubic packing arrangement with increasing pressure. Crystal growth at high pressure from liquid resulted in the formation of new polymorphs of formamide and pyridine. Growth of crystals of the N-methylated analogues of formamide, N-methyl formamide and N,N-dimethyl formamide, did not. The structure of the high pressure polymorph of formamide formed at 4.4 kbar is closely related to the previously known phase. At 10.8 kbar pyridine crystallises in a much simpler structure than that observed at low temperature, matching the structure observed for the perdeuterated molecule. A novel hemi-hydrate of piperidine is observed when grown from liquid at 3.1 kbar.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:649229 |
| Date | January 2003 |
| Creators | Dawson, Alice |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12179 |
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