Development and use of computer techniques in x-ray crystallographic studies
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The crystal and molecular structures of four chemically unrelated compounds have been determined by X-ray crystallography. One compound is organometallic and it crystallises in a centrosymmetric space group while the others are organic and their space groups are non-centrosymmetric. The compound bis(triphenylarsine)hexafluorobuta-1,3-diene platinum crystallises in two forms. Traditional vector methods were used to solve the structure of the isomer reported here. This is a further example of an organometallic compound where an olefin, in this case hexafluorobutadiene, is co-ordinated to the metal atom by one olefin bond to form what may be described as a 'metallo-cyclopropane'ring. Direct methods were used to determine the structures of 1,1-dichloro-2,5-diphenylcyclopropabenzene and 4,5,6-tri-O-benzoyl-2,3-di-S-ethyl-2,3-dithio-D-allose diethyl dithioacetal. In the first of these compounds the cyclopropabenzene system is not quite planar and the phenyl substituents are twisted and bent from the plane of the benzene ring in the cyclopropabenzene system. The second of these analyses confirmed the molecular configuration of the tetra-thio aldose derivative as D-allo and established that the molecule has a bent-chain conformation similar to that found in solution. The conformation of a brominated compound, extracted as an acetate derivative of formula C₃₂H₅₅O₈Br from the seaweed species Laurencia thyrsifera, has been established. The compound's structure is related to squalene and was solved using Vector methods. In addition to these analyses unsuccessful attempts to solve the crystal structures of a dinitro-imidazole derivative (C₄H₄N₄O₄) and a compound thought possibly to be a tetracyclo-decane (C₁₅H₁₂N₄) are outlined. A significant part of this project involved the further development of the X-ray crystallographic program suite of the University of Canterbury which is used in all X-ray structure analyses. Particular projects contributing to this development are discussed.