Crystal structure determination and prediction of simple organic molecules, using powder diffraction methods, and modern computational techniques

Chana, Harcharn S (2006). Crystal structure determination and prediction of simple organic molecules, using powder diffraction methods, and modern computational techniques. University of Birmingham. Ph.D.

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Abstract

The research presented within this thesis highlights aspects of crystal structure determination from the combined use of powder X-ray, synchrotron and neutron diffraction and also computational crystal structure prediction from molecular structure only.
The use of DE enabled the crystal structure of 2,4-dichloro-5-sulfamoylbenzoic acid and oxamic acid to be examined from conventional laboratory X-ray diffraction.
In the case of 2,4-dichloro-5-sulfamoylbenzoic acid two comparable structures were identified each of which refined to similar extents. To correctly identify the correct crystal structure it was necessary to obtain and refine a powder neutron dataset. This presented before obscured information on the relative positions of hydrogen atoms and inevitably led to the successful elucidation of the crystal structure of 2,4-dichloro- 5-sulfamoylbenzoic acid. With reference to oxamic acid two conformations, namely ‘cis’ and ‘trans’ were identified from the refinement of laboratory X-ray diffraction. Infrared analysis and lattice energy calculations were also used to distinguish between the two conformations with some success.
With respect to computational crystal structure prediction, presented here is a new computational strategy for crystal structure prediction from molecular structure only. The traditional lattice energy output from a polymorph prediction sequence is reranked in terms of hydrogen bonding and graph set merit points. My research here has to a certain extent managed to combine these attributes and enabled the successful prediction of 8 out of the initial 11 chosen test structures obtained from the Cambridge Structural Database (CSD).

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):