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Title: Acid:base Co-crystal formation in crystal engineering and supramolecular design
Author: Batchelor, E.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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The chemical and physical properties of organic molecular crystals depend on both the molecular and crystal structure. The systematic approach to understanding and controlling crystal structure lies in the field of "crystal engineering". One strategy to emerge within crystal engineering has been the utilisation of specific interactions or couplings / synthons to predictably build supramolecular arrays such as tapes, ribbons or sheets. These arrays form a subset of the crystal structure. While many couplings take the form of cyclic motifs in which component interactions are of comparable strength, a cyclic coupling consisting of an O-- H...N and a C-H...O interaction was noted as having a potential use in designing supramolecular arrays. This type of strong / weak coupling is possible upon the interaction of an N-heterocycle with a carboxyl group. The following research describes the co-crystallisation of various N-heterocyclic bases with a number of olefinic and aliphatic dicarboxylic acids. The crystal structures of various complexes of phenazine, 1,10-phenanthroline and quinoxaline were solved from single-crystal X-ray diffraction data and are discussed. Two distinct strong / weak couplings were identified within the three sets of co-crystals. A comparison of the relative stabilities of the two couplings was made using the quinoxaline system. Supramolecular tapes were observed in all of the phenazine co-crystals and in three of the four quinoxaline co-crystals. (The stoichiometry of the phenazine co-crystals may be related to the position of the carboxyl groups on the participating acid.) The packing of the tapes is discussed with particular reference to tape topography and inter-tape C-H...O interactions. Proton transfer occurred in four of the five co-crystals of 1,10-phenanthroline. Co-crystals were prepared via two methods: by growth from a solution and by grinding of a physical mixture of the starting components. Solid-state grinding was found to be a viable method for the preparation of co-crystals. Complexes of 1,10-phenanthroline prepared via the two routes were analysed using solid-state 13C MAS NMR and the effects of protonation on certain carbon resonances is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available