Degree Type

Dissertation

Date of Award

1992

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

R. A. Jacobson

Abstract

Two methods--SUPSYMM and MMXRAY--for the determination of crystal structures that have resisted solution through normal crystallographic methods have been developed. SUPSYMM needs only a list of Patterson superposition peaks as its starting point. Using distance analysis and vector projections, symmetry relationships between the superposition peaks are identified. These relationships are exploited to identify probable peak positions which can then be employed as a starting point for least-squares crystallographic refinement;MMXRAY helps to solve large organometallic structures by taking advantage of the strengths of Patterson superposition techniques and molecular mechanics methods. Patterson superposition techniques can usually locate at least the heavy atoms in the structure. For large organometallic structures, these few atoms may not phase the reflections well enough to reveal the rest of the structure. Molecular mechanics is used to model the remaining organic parts of the structure. MMXRAY converts the modeled structure to the original crystallographic reference system and allows for crystallographic refinement of the structure;Two programs designed to teach the basics of both powder and single crystal X-ray diffraction methods to undergraduate Physical Chemistry; students are presented in the Appendix. In addition, several crystal structures solved through routine crystallographic routes are discussed there.

DOI

https://doi.org/10.31274/rtd-180813-9684

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Catherine Lucia Day

Language

en

Proquest ID

AAI9301999

File Format

application/pdf

File Size

138 pages

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