| Popis: |
Molecules pack in accordance with Kitaigorodsky's theory of close packing to minimise empty space between molecules. The mode of packing is dependent on molecular shape, such that the bumps on one molecule fit roughly into the grooves of a neighbouring molecule. It is possible to extend the close packing theory to ask the following question: Is it possible to interchange substituents of similar shape and size, such as chlorine and methyl (Cl-Me interchange), on a molecule without causing it to adopt a different crystalline structure? This thesis summarises attempts to answer this question. Chapter 2 summarises methods for finding the frequency of isostructural Cl-Me interchange by retrieving as many examples as possible from the Bath Information and Data Services and the Cambridge Structural Database (CSD). However, given the large number of crystal data entries within the CSD, the frequency was approximated from that database. Approximately 23% of all examples retrieved from the CSD are isostructural, which illustrates that factors other than the size and shape of interchanged substituents determine crystal structure. Chapter 3 summarises attempts at finding intermolecular and molecular factors that govern isostructural CL-Me interchange and concludes that minimising the intermolecular interactions of Cl and Me can facilitate isostructurality. Chapters 4, 5 and 6 go on to summarise three approaches for reducing the intermolecular contacts of Cl and me with successful examples of forced isostructurality through co-crystallisation. Finally, chapter 7 discusses the formation of supramolecular tapes - common structures formed by crystal engineers, and illustrates how small changes in the size and shape of acid spacers can effect tape structure and crystal structure. |
