Browsing by Author "Van Wyk, Lisa Mercene"

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    Investigating the solid-state dynamics of 1D coordination polymers
    (Stellenbosch : Stellenbosch University, 2021-03) Van Wyk, Lisa Mercene; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: The aims of this study were twofold: (i) to produce a series of 1D materials exhibiting novel solid-state packing, and (ii), to study these materials with a view to gaining insight into their structure-property relationships. Studies of the ability of the materials to undergo several single-crystal to single-crystal transformations were prioritised. Both dynamic behaviours and transformations were observed in the series produced. The first study describes the mechanochemical separation of two solvates that crystallise concomitantly under solvothermal conditions. Variation of the solvent water composition, and the introduction of aging periods before and after grinding provided various methods of preparing either solvate. A third solvate was prepared in a separate solvent system from the first two. Finally, solvent exchange allowed relatively facile interconversion between all three forms The second study focused on the transient porosity of two 1D coordination polymers. These materials show extreme contraction upon guest release equating to a reduction of up to 39% of the unit-cell volume. Importantly, these transformations progress in a single-crystal to single-crystal fashion and represent some of the largest reported lithotropic contractions. Consequently, the contortion of the conceptually linear ligand in one material far exceeds previous reports. These materials both resorb liquid guests, and one material sorbs vapours. Furthermore, greater ease of structural reopening occurs with each consecutive vapour sorption cycle. In Chapter 5, the low-temperature phase-change behaviour and structural dynamics in terms of thermal expansion of a series of materials, where only the metal centre is varied, are studied. This yielded a series of materials with analogous packing motifs. In nearly all cases, colossal linear and volumetric thermal expansion were recorded in the temperature range 100–270 K. In some cases, supercolossal linear thermal expansion was exhibited, in addition to extreme anisotropy. The results are comparable to the largest linear and most anisotropic thermal expansion reported, but far exceed that reported for 1D coordination polymers. The largest anisotropic thermal expansion occurred in solid solutions, indicating that this behaviour is tuneable. Studies of structure-property relationships and solid-state dynamics require firstly single-crystal to single crystal transformations and secondly bulk phase purity. In 1D coordination polymers both these criteria are often problematic. This work addresses both these concerns, providing methods to overcome or circumvent these hindrances. Furthermore, several of the outcomes in this work exceed or are comparable to the limits of similar solid-state dynamics reported in the literature