Master of Science / Department of Chemistry / Mark D. Hollingsworth / Most urea inclusion compounds (UICs) are known to share a common packing arrangement in which the urea host forms helical ribbons held together by hydrogen bonds to form a series of linear, hexagonal tunnels. Because UICs can encapsulate a wide variety of linear guest molecules, they serve as useful model systems for probing mechanisms of crystal growth and molecular recognition. In this thesis, the syntheses (or attempts thereof) of six compounds that will serve as consequential guest molecules in studies of UICs are presented. These compounds are (5S,6S)-2,9-decanedione-d2, 1,6-dicyanohexane-1,1,6,6-d4, 1,11-undecanedioic acid, bis(3-oxobutyl) adipate, 2,16-heptadecanedione, and 2-eicosanone. With the exception of (5S,6S)-2,9-decanedione-d2, whose synthesis remains incomplete, detailed synthesis and crystal growth of the UICs of these compounds are discussed. Ongoing studies with the UICs containing these guests include the determination of the absolute configuration of UICs, the study of guest conformer population changes via solid-state NMR, the development and identification of novel ferroelastic UICs, and the classification of guest ordering in a series of alkanedione UICs.

Doctor of Philosophy / Department of Chemistry / Mark D. Hollingsworth / Urea inclusion compounds (UICs) are classic examples of nanoporous, host:guest materials in which the linear channels of the honeycomb structure of the urea host can include various types of long-chain compounds (the guests). By using synchrotron X-ray radiation sources, a deeper understanding of these materials is made possible through detailed structural studies. In particular, this dissertation describes a series of structural phase transitions that occur upon cooling two related UICs containing alkanedione guest molecules. UICs may be classified as either commensurate or incommensurate structures, depending on whether the repeat lengths of the host (c[subscript h]) and guest (c[subscript g]) along the channel axis are related by a small whole number ratio. Crystals of 2,8-nonanedione/urea and 2,11-dodecanedione/urea, which are incommensurate structures at room temperature, undergo "lock-in" phase transitions below room temperature to generate commensurate structures in which the guest repeat lengths are elongated. Upon nucleation and growth of these elongated, commensurate phases, other molecules in the same channels are compressed to give successively shorter guest repeat lengths. Further lock-in phase transitions give a multitude of commensurate and incommensurate phases during cooling. The crystal structures of two of these commensurate phases have been determined using synchrotron sources. The "self-compression" observed in these 1-D crystals serves as a paradigm for understanding solid-state reactions in three-dimensional crystals.