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Durham e-Theses
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Structural studies of novel molecular systems

Burke, Jacquelyn Marie (2002) Structural studies of novel molecular systems. Doctoral thesis, Durham University.



This work investigates two main areas of interest. The first is the synthesis and study of a variety of Lewis acid-Lewis base adducts of general formula X(_3)B-PR(_3) (X = CI, Br; R= alkyl or aryl). The (^11)B-P and (^10)B-P NMR coupling phenomena are investigated. The partial dissociation of some of these compounds in solution is probed by (^31)P and (^11)B NMR. The crystal structures of many of these compounds are presented and analysed for correlations between the properties of the phosphines and B P bond length. It was found that only the Tolman cone angle gave a good correlation to B P bond length. A compound containing a novel B2O2 ring was synthesised during these studies, and theoretical calculations performed to gain an insight into the planarity of this unusual 4- membered ring. The first crystallographically characterised example of the tri(o-toly)phosphonium cation is also presented. The related compounds X(_3)B pyridine, X(_3)B-2-picoline and X(_3)B 4-picohne (X = CI, Br) are investigated by various analytical methods. Crystal structures of these B-N adducts are presented. It is found that the structure of CI3B 4-picoline exhibits an interesting phase transition from orthorhombic Pnma at higher temperatures to monoclinic space group P2i/n below ca. 170K.The second area of work involves crystal structure analyses of a variety of co-crystals of his(phenylethynyl)benzene compounds, of general type R-Ph-CC-Ph-CC-Ph-R, with R = H, F, MeO, MeS, CH3 and CF3 and a varying fluorinadon pattern on the phenyl rings. The effect of these para substituents on the arene-peifluoroarene interaction was investigated. The effect of each substituent was found to be subtle. In most cases, the co-crystallisation induced an arene-perfluoroarene interaction that was not present in the individual components. Starting materials for the bis(phenylethynyl)benzene compounds often include halogenated tolans of the form Ph-CC-Ph-X (X = CI, Br, I), with either the halogenated or the non-halogenated ring fluorinated. Crystal structures of PhF(_5)-CC-Ph-X (X = I, Br, CI), Ph-CC-PhF4-I and Ph-CC-PhF4-CC-SiMe3 are presented and the arene- perfluoroarene interaction investigated. It is found that the PhPg-CC-Ph-X (X = I and Br) compounds show no evidence of the interaction. The dominating intermolecular force is a Type n halogen -halogen short contact. In contrast, the structure of the chloro analogue is dominated by the arene-perfluoroarene interaction, with no halogen -halogen short contacts. Neither intermolecular force is present in the Ph-CC- PhF(_4)-I or Ph-CC-PhF(_4)-CC-SiMe(_3) structures.

Item Type:Thesis (Doctoral)
Award:Doctor of Philosophy
Thesis Date:2002
Copyright:Copyright of this thesis is held by the author
Deposited On:26 Jun 2012 15:26

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