Systematic computational analyses and novel search procedures for crystallographic information
This thesis describes work in two distinct areas of crystallographic research. In chapters 3 and 4, a number of novel crystal structures are reported. Eight new potential dyotropic rearrangement precursors are discussed in chapter 3. A comparison with other known structures is given. Three conjugated zwitterionic TCNQ type derivatives are discussed in chapter 4. All three molecules show good second order hyperpolarisability and so have potential uses in non-linear optical applications. Chapter 6 and chapter 7 use the Cambridge Structural Database in novel ways to derive new information. In chapter 6 the estimated standard deviations of the 3D crystallographic coordinates have been used to derive more accurate precision indicators, as functions of the R-factor and the chemical constitution by correlation and regression methods. This research has shown that it is possible to provide effective improve precision indicators within the CSD for the circa 50,000 entries that do not possess coordinate e.s.d's. In chapter 7 a re-analysis of space group frequencies is given. New software has been written to search the CSD and derive the lowest symmetry point group utilised by the independent residues within each crystal structure. With this analysis it has been possible to produce matrices which rationalise space group frequency as a function of point group utilised within the crystal. The requirement of mirror plane occupation in mirror-symmetric space groups has been confirmed. Further trends are also noticed.