Academic literature on the topic 'Crystallography'

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005.<br>Includes bibliographical references (p. 51).<br>AtomicControl is a software package designed to aid in the teaching of crystallography and x-ray diffraction concepts to materials science students. It has the capability to create an arbitrary crystal structure based on the user's specification of a space group and atomic coordinates. It also can generate a simulated powder diffractogram based on the user's generated crystal. The program is fully interactive and allows the user to view the effects of changes to lattice and atoms in a 3D visualization of the crystal. AtomicControl's x-ray diffraction patterns have been shown to match well with experimental data, proving the validity of the algorithm. AtomicControl is available online.<br>by Edward S. Barnard.<br>S.B.

Crystallographic disorder is common in the solid state but it is rarely investigated explicitly despite having a fundamental impact on the solid-state structure of a material. In this work, nuclear magnetic resonance (NMR) crystallography methods are utilised to achieve a detailed understanding of the structure and dynamics of solid organic systems containing disorder. Several new cocrystal systems are studied, each containing a topical drug molecule (caffeine, naproxen or furosemide) and each serving to demonstrate how NMR crystallography can be applied to a variety of structural questions. Hydrogen bonding motifs are identified using single crystal X-ray diffraction experiments, where possible, and are subsequently verified by solid-state NMR. Alternative hydrogen bonding models are ruled out by comparison of experimental solid-state NMR data with density functional theory calculated shieldings, and proton transfer can be investigated by monitoring the energy of the system with respect to proton position. In a particularly challenging case, 2D solid-state NMR experiments go some way to identify the hydrogen bonds in a system that cannot be crystallised. Dynamic disorder of fragments and solvent molecules are characterised by variable temperature solid-state NMR, including analysis of relaxation times to establish energy barriers and rates of motion. A mechanism of motion is also proposed for dynamic acetone molecules in a new cocrystal solvate, which is supported by good agreement between experimental and simulated 2H static NMR line shapes. Finally, the current limit of NMR crystallography is identified with respect to the reproducibility of calculated NMR parameters following geometry optimisation. It is shown that the geometry optimisation protocol does not affect standard NMR crystallography investigations pertaining to atom assignment, but it is significant for cases where very subtle structural features are probed, such as NMR linewidths. Overall, NMR crystallography investigations allow a deeper understanding of solid materials to be achieved than would be possible with any single technique and this work highlights the applicability of such methods to complex materials containing disorder.