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Browsing Department of Chemistry and Polymer Science by browse.metadata.advisor "Barbour, Leonard J."
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- ItemCharacterisation and sorption study of a highly symmetrical porous metal-organic framework(Stellenbosch : Stellenbosch University, 2020-02) Wei, Xueting; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Supramolecular chemistry is a young yet rapidly growing interdisciplinary field. A class of compounds called metal-organic frameworks (MOFs) has attracted increasing attention over the last two decades. One of the reasons for this is their porous and dynamic nature, which make them attractive candidates for various applications. In this study the MOF CdK34pba, is investigated. In particular, we focused on the characterisation of CdK34pba and explored its sorption properties. The first section discusses the characterisation of CdK34pba. The as-synthesised framework forms large 1D channels along the crystallographic c axis, with offset face-to-face (OFF) π‒π interactions between two nearby ligands, thus stabilising the structure. The 1D channels comprise approximately 43% of the unit-cell volume. The porous nature is maintained by potassium ions binding the channel walls together, thus preventing interpenetration. The channels in the as-synthesised CdK34pba contain water and DMF, which can be successfully removed without any structural changes. The material absorbs moisture from the ambient environment. CdK34pba undergoes two thermal events, one during heating and one during cooling. The thermal event during heating could be caused by a sudden decrease in volume. The second thermal event during cooling could be due to the change in gradient at which the volume decreases. However, further investigation is required to definitively explain these events. The second section investigates the sorption properties of CdK34pba. Guest exchange experiments, using the as-synthesised CdK34pba, with a variety of organic solvents indicate that CdK34pba does not undergo structural changes with selected solvent exchanges. The guest occupancy is dependent on the physicochemical identity of the solvent molecule, which suggests the potential for solvent separation. Gas sorption experiments revealed the uptake capacity for CO2, N2, methane, ethylene, propane, and butane. The isotherms suggest that at 20 bar CdK34pba has not reached its maximum capacity for selected gases. Further higher pressure gas sorption experiments could be carried out to establish the maximum gas loading capacity. The capability of CdK34pba to sorb xylene isomers was explored using xylene solvents and vapours. The xylene solvent sorption experiments showed that the uptake is the highest for m-xylene. The m-xylene guest was successfully modelled; it is hydrogen bonded to the nitrate counter ion as well as a water molecule, possibly absorbed from the environment. Lastly, a proof of concept dye sorption experiment was performed. CdK34pba can extract 10 ppm of sunset yellow dye from EtOH solvent under 24 hours at 40 °C. The structure and thermal properties of CdK34pba were explored. Sorption and exchange experiments established the uptake capacity of CdK34pba for various guests. Further investigations should be performed to explain any unanswered questions.
- ItemA combined computational and experimental study of dichromic crystals(Stellenbosch : Stellenbosch University, 2018-03) Myburgh, Dirkie; Barbour, Leonard J.; Esterhuysen, Catharine; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: A combination of theoretical and experimental techniques were used in three studies related to dichromic crystals. The first study involves a porous crystal of a Schiff base-containing trianglimine compound undergoing a yellow-to-red colour conversion above a humidity of 55%. Schiff bases are well known for undergoing enolimine-ketoenamine transformations as iono-, solvato-, thermo- or photochromic processes, altering the visible colour properties of the system. In this study a similar transformation occurs owing to the combination of a sorptiochromic and a hydrochromic process, which are both considered as subcategories of solvatochromism. The enolimine-ketoenamine transformation is caused by H-bond formation between water and the oxygen atom of the enol group. This weakens the OH bond allowing a proton transfer from the oxygen to the nitrogen atom. In the presence of H2O the ketoenamine state is thermodynamically preferred, whereas in the gas phase the enolimine is preferred. Secondly, a phase study was performed on a diarylethene compound (1,2-bis(5-pyridyl-2-propyl-3-thienyl)perfluorocyclopentene), DA-2-[o]. Diarylethenes are well known for undergoing a ring-closure reaction under UV light and have been shown to exhibit photochromic behaviour in the crystalline state, as is the case for the three polymorphic phases identified for DA-2-[o], DA-2-[o]-α, DA-2-[o]-β and DA-2-[o]-γ. The first two are obtained by recrystallisation from acetone and hexane, while the third can be obtained by heating of either DA-2-[o]-β above 70 °C or DA-2-[o]-α above 100 °C. The DA-2-[o]-α phase is converted to the DA-2-[o]-β phase by heating above 100 °C and subsequent cooling to room temperature. The opposite conversion can be achieved by leaving DA-2-[o]-β in a cupboard under ambient conditions for a period of six months. This result combined with lattice-energy calculations suggests that the DA-2-[o]-α phase is the thermodynamically preferred phase. The final study provides a fundamental explanation for the photoisomerisation reaction of diarylethenes. This was done by developing a method whereby all the major parameter differences between the ring-opened and ring-closed forms are scanned followed by the calculation of the excited state potential energy surface map. This method was then used to illustrate how various structural modifications will affect the ring-closure or ring-opening reaction. The photochromism of the open form was ascribed to the formation of an electron hole after electron excitation from the HOMO to the LUMO. This results in an attractive force between the two adjoining carbon atoms and a downward energy gradient, over the conical intersection, towards the closed form. For the ring-opening it was observed that a twisting action is required before the ring-opening can take place making this an asynchronous process.
- ItemComputational assessment and visualization of guest inclusion in porous crystalline materials.(Stellenbosch : Stellenbosch University, 2020-11) Van Heerden, Dewald Pepler; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Host-guest systems are a central feature of supramolecular chemistry and an improved understanding of guest inclusion phenomena (i.e., transport and accommodation) may lead to the development of improved functional porous materials. However, the generally greater degree of thermal motion of guest molecule(s) relative to the host often impedes their accurate modelling in crystal structures. Furthermore, activation, the act of removing the guest to yield the empty apohost phase, often results in a loss of single crystallinity. Physical stimuli such as temperature, light, mechanical pressure, gas and liquid sorption, and electric and magnetic fields can induce structural transformations; however, the scarcity of in situ or in operando single-crystal X-ray diffraction (SCXRD) data encumbers the direct elucidation of underlying mechanisms. The work presented in this thesis contribute to the collective understanding of inclusion and dynamic phenomena in the solid state. Results are presented as two manuscripts, both of which have been submitted for peer review. The first manuscript describes the systematic derivation of a fractional occupancy factor θ that allows for “back-of-the-envelope” estimation of host/guest ratios in crystal structures. A common method of evaluating guest-occupiable space involves in silico sampling of free space by means of a spherical probe in van der Waals contact with the host structure. In addition to discussing caveats pertaining to reporting guest-occupiable space, we propose the terms probe-traversable volume (PTV) and probe-accessible volume (PAV) to refer to the regions mapped out by the center and surface of the probe, respectively. High-throughput analysis of close to 40 000 solvates yielded a weighted mean θ value of 51.1(4)%, where θ is the ratio of the molecular volume of the solvent to the PAV. The utility of our methodology is demonstrated through application to case studies encompassing 0D organic and organometallic, as well as metal-organic framework (MOF) materials. As part of an ongoing investigation in our group, the second manuscript reports on a combined theoretical and in situ SCXRD structural analysis of a flexible MOF subjected to methane, ethane, propane and butane gas pressures. Whereas subnetwork displacement is induced by sorption of ethane, distinctly stepped sorption isotherms for propane and butane are associated only with linker rotation; i.e., true gate opening. A turnstile mechanism is elucidated whereby neighboring pockets are temporarily fused to allow diffusion of guest molecules through the seemingly nonporous system.
- ItemCrystal engineering of porosity(Stellenbosch : University of Stellenbosch, 2006-12) Lloyd, Gareth Owen; Barbour, Leonard J.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.Inclusion and porosity properties of the following supramolecular solid-state hosts were investigated: • 2,7-dimethylocta-3,5-diyne-2,7-diol • 2-methyl-6-phenylhexa-3,5-diyn-2-ol • Dianin’s compound • p-tert-butyl-calix[4]arene • 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxy-2,8,14,20- tetrathiacalix[4]arene • Two discrete coordination metallocycles, [Ag2IMID2](BF4)2 and [Cu2(BITMB)2(Cl)4] All of these compounds form well-defined crystalline host structures. Inclusion phenomena involving encapsulation of liquids were studied using single-crystal x-ray diffraction methods. Several guest-free host structures (α phases) were structurally elucidated and their gas sorption properties were investigated. Studies of the sorption properties of seemingly nonporous materials were carried out to provide insight into this rare phenomenon. Water and iodine sorption by a polymorph of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxy-2,8,14,20- tetrathiacalix[4]arene shows that the conventional perception of sorption through the solid-state requires reassessment. Gas sorption studies were carried out using apparatus devised and presented here. These include sorption apparatus and a device to determine single-crystal structures under controlled gas atmospheres.
- ItemDefect engineering of UiO-66 metal-organic framework (MOF) for improved hydrogen storage applications(Stellenbosch : Stellenbosch University, 2021-03) Ledwaba, Mpho Violet; Barbour, Leonard J.; Ren, Jianwei; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Metal–organic frameworks (MOFs) as a relatively new class of porous crystalline materia ls have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applicatio ns . Several modifying strategies for engineering MOF crystals have been developed based on their desired features and applications. In nature there are no "ideal crystals" with an infinite periodic repetition or ordering of the same groups of atoms in space. The structure of "real crystals" often deviates from the ideal arrangement and includes a significant density of structural irregularities or deficiencies. Crystal irregularities may arise from compositio na l inhomogeneities, and this term is often used interchangeably. By using defective technology strategies during their synthesis, crystal imperfections may be introduced into the MOF framework, thereby enhancing their performance in the envisioned applications. Defect engineering is one of the most effective approaches that one can use to change their physical and chemical features such as thermal stability, textural properties, mechanical properties and gas adsorption abilities. In order to achieve the desired changes, it is essential to control the defects, otherwise these defects may have an adverse effect on the MOFs. Therefore, it is vitally important to apply synthetic control over defects; the exact nature and concentration of the defects may be controlled by modifying the synthetic conditions and post-synthet ic modifications. Structurally characterising inherent or engineered defects is very challenging and this challenge has not been addressed substantially. This thesis explores the experimental creation of structural defects via post-synthetic modification, the role of structural defects and their relationship to gas adsorption, with emphasis on hydrogen adsorption. Through a combination of techniques, including powder X- ray diffraction (PXRD), thermogravimetric analysis (TGA), acid-base titration and Brunauer– Emmett–Teller (BET) surface area and pore size measurements, missing linkers and missing cluster defects have been identified and analysed. In Chapter 4, we seek to understand the relationship between some of the major synthetic parameters and the physicochem ic a l characteristics of UiO-66 (Universitetet i Oslo) MOF and discover a "non-defective" sampling technique for this material. The technique produces non-defective UiO-66 MOFs at a specific temperature (493 K), with the linker ratio being greater than that of the salt previously reported by Shearer et al. As described in Chapter 5, by varying the concentrations of modulator and the linker, we demonstrate that the linker vacancies can be systematically tuned, leading to significantly increased surface areas. The defects are caused by partial terephthalic acid eplacement with smaller formate groups from the formic acid modulator. The BET surface areas of the obtained samples range from 1200 to 1600 m2.g-1, and the best sample has a surface area that is about 30% higher than the theoretical value of the surface area of defect-free UiO- 66. Additionally, linker vacancies are proven to have profound effects on the gas adsorption behaviour of UiO-66 by improving the hydrogen uptake from 1.51 wt. % to 2.0 wt. % at 77 K and 1 bar. Chapters 5 and 6 include detailed studies of two conventional methods for generating defects (i.e., de novo defect technology and post-synthetic modification (PSM)) discussed in each chapter respectively. Still in chapter 5, experimental investigations are discussed that show the impact of modulator and linker concentration on H2 adsorption and thermal stability. Chapter 6 provides insight into the impact on thermal stability and adsorption properties brought about by the post-synthetic modification methods. The resultant materials typically have high surface areas, large pore volumes and structures with hierarchical pores, which makes them more practical for hydrogen storage applications.
- ItemDirect determination of isosteric heats of sorption using pressure-gradient differential scanning calorimetry(Stellenbosch : Stellenbosch University, 2017-12) White, Kerry-Anne; Barbour, Leonard J.; Smith, Vincent; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer and Science.ENGLISH ABSTRACT: Porous materials, specifically porous coordination polymers (PCP) and metal-organic frameworks (MOFs), have shown great potential for catalysis as well as gas storage, separation and purification. Energy efficient adsorption processes utilising these porous materials are desirable for reducing the energetic cost of industrial processes. Thus characterisation of these materials in terms of their thermodynamic properties is essential for practical applications. Isosteric heat (Qst) is an approximation of the enthalpy (or heat) of sorption and indicates the affinity of a material for a specific adsorbate. Conventionally Qst is determined indirectly by plotting isosteres at various temperatures and making use of the Clausius-Clapeyron approximation (the isosteric method). By comparing Qst values from the literature, there appears to be a correlation between the Qst value and the temperature range used. The higher the temperatures in the temperature range, the larger is the Qst value. This contradicts the assumption of temperature independence by the Clausius-Clapeyron approximation. Heat-flow calorimetry employing a temperature gradient is another method that has been used to determine Qst. A calorimetric approach requires fewer assumptions regarding the interaction energies and equilibrium of the system compared to the isosteric method. Herein a method is proposed for the direct determination of Qst using pressure-gradient differential scanning calorimetry (PGDSC). The PGDSC method involves the measurement of heat flow during the sorption and desorption of a gas over a predefined pressure range. In conjunction with gas loading data derived from gas sorption isotherms, Qst can be determined directly over the entire pressure (or rather gas loading) range from the changes in measured heat flow. The sorption of CO2 by CuHKUST was chosen as a test system to validate this direct method. It was found that the PGDSC approach produces temperature-independent values that are comparable to literature values obtained using the isosteric method. Since the PGDSC method is temperature independent, it requires a less labour-intensive procedure than the isosteric method. Only one PGDSC experiment and one isotherm at the same temperature are required, as opposed to multiple isotherms at various temperatures necessary for the application of the isosteric method. PGDSC furthermore employs direct heat measurements as compared to the indirect approximation of the isosteric method. The PGDSC method was further successfully applied to a 2D-layered interdigitated PCP ([Cd(oba)(bpy)]n) that displays stepped sorption and hysteresis for CO2, N2 and CH4. Since the isosteric method is not easily applied to materials with sorption profiles other than Type I, this presents an important improvement in how Qst values are measured. Qst values can also be used to predict the selectivity of the material for a specific gas. This investigation showed that [Cd(oba)(bpy)]n has the highest affinity for CO2 over N2 and CH4.
- ItemThe dynamics of new self-assembled porous materials(Stellenbosch : Stellenbosch University, 2015-12) Nikolayenko, Varvara I.; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept of Chemistry and Polymer Science.ENGLISH ABSTRACT: principal goal of this study was to prepare a wide selection of crystalline second- and third-generation metal-organic materials in order to investigate guest sequestration and storage capabilities, as well as guest exchange and sorption-induced dynamics in the solid state. Chapters I and II contain a review of the relevant literature, as well as a description of the experimental techniques employed in this work. Chapter III describes the diversity of metal-organic frameworks (MOFs) obtained from a small selection of pyridyl-functionalised ligands (varying in length and rigidity) combined with a series of carboxylic acids (also varying in length and rigidity) in the presence of one of four transition metals. Twenty one different MOFs varying in metal coordination mode, degree of interpenetration, solvent-accessible space and guest were obtained. Four of these MOFs undergo single-crystal to single-crystal (SC-SC) transformations, including activation, gas sorption and solvent exchange. Chapter IV focuses on two isostructural MOFs. The monochromic zinc-containing framework undergoes SC-SC guest exchange, indicating a mild preference for para-xylene, while gas sorption experiments revealed a clear preference for carbon dioxide. The pleochroic crystals of the cobalt analogue showed no xylene selectivity, but gas sorption experiments revealed preferential selectivity toward methane carbon dioxide and ethane. Crystallisation from solutions containing both metals (and the same ligands) resulted in the formation of trichroic solid solutions, the colour of which could be fine-tuned by varying the ratio of the two metals. To complete the study, a homoepitaxial crystal was grown. Chapter V focuses on a modified version of the ligand described in Chapter IV, with electron-withdrawing fluorine atoms located on the central phenyl ring. Use of this ligand resulted in charaterisation of a twofold interpenetrated porous framework, differing from that described in the previous chapter. Activation, as well as guest exchange, elicited “crank-handle” conformational changes in the ligand. Sorption experiments showed the material to be selective for carbon dioxide over several linear alkanes. Reaction using the hydrochloride salt of this ligand yielded a novel interdigitated MOF. Substitution of cadmium for zinc in the reaction gave a third non-interpenetrated framework where the ligand has undergone [2 + 2] cycloaddition and is present in the anti conformation. SC-SC activation as well as guest exchange experiments revealed this framework to be less flexible than its zinc counterpart. Exposure of the activated material to carbon dioxide indicated substantial uptake of carbon dioxide. A mixture of the DMF and DMSO produced two additional isoskeletal structures differing in paddlewheel construction, ligand conformation and, as a result, in the solvent-accessible void space. Chapter VI describes the response of five MOFs based on diarylethene ligands to light. The structural changes underlying the colour change differ in each case. The first framework is a porous twofold interpenetrated MOF that undergoes change in colour and shape upon UV irradiation. When the same crystal was exposed to white light, the parameters revert back to those of the original form. The activated form of a second fourfold interpenetrated highly porous MOF showed an affinity for carbon dioxide, as well as a change in colour upon irradiation. Incorporation of a more flexible ligand gave a twofold interpenetrated porous material that showed low temperature activation but could not be evacuated without loss of crystallinity. UV irradiation induced a colour change but no structural change. The fourth framework is a twofold interpenetrated structure that collapses to a seemingly non-porous form upon removal of the solvent. UV irradiation of this material results in ring-closure of the diarylethene ligand, along with a colour change. Remarkably, all these processes occur in a SC-SC fashion. This is the first example of photo-induced ring closure of a diarylethene molecule incorporated into a MOF. The fifth framework exhibits a high degree of interpenetration (fourfold) but unlike all previous examples, irradiation with UV light induced no visible colour change and no structural change.
- ItemEvaluation of gas sorption techniques and computational methods utilized in the analysis of porous compounds(Stellenbosch : Stellenbosch University, 2014-12) Van Heerden, Dewald Pepler; Barbour, Leonard J.; Esterhuysen, Catharine; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: A recently proposed mechanism responsible for anomalous thermal expansion in a metal-organic framework (compound 1) is examined through theoretical calculations. A mechanistic model that reproduces the convergent expansion of the material’s coordination spiral is developed. In order to decide on a suitable theoretical method, specifically at the Density Functional Theory (DFT) level of theory, a tricyclicorthoamide that presents a unique nearly-eclipsed methyl group in the solid state (compound 2) is investigated. Since the anhydrous solid form of this molecule presents with the expected staggered conformation, the nearly-eclipsed conformation is ascribed to the presence of water molecules in the trihydrate form. An evaluation of the potential energy profile for rotation of the methyl group by the ab initio wave function methods HF, MP2 and CCSD revealed the global minimum to indeed be the nearly-eclipsed conformation (𝜔ℎ𝑐𝑐𝑛 ≈ 10°) with a barrier to rotation (Δ𝐸𝑟𝑜𝑡) of 1.24 kcal.mol-1 located at ~85° at the MP2/6-31+G(d) level of theory. The CCSD potential energy profiles also feature a local minimum at ~55° that is ascribed to a dispersive intramolecular interaction. Since the Kohn-Sham implementation of DFT functionals ignores the dynamic electron correlation required to describe dispersion, semi-empirical dispersion-correction schemes to the density-dependent energy are evaluated. The mechanistic model describing the thermal expansion of 1 is evaluated with the B3LYP (hybrid GGA) and M06 (hybrid meta-GGA) density functionals augmented by the GD2 and GD3 dispersion correction schemes, respectively, in addition to the dispersion-corrected ωB97XD (LC-hybrid GGA) functional in conjunction with various basis sets. The resulting energy trends are found to compare favorably to the four energies obtained by periodic DFT evaluations of the 100, 190, 280 and 370 K crystal structures of 1. The thermodynamic data for carbon dioxide adsorption measured on a previously constructed in-house volumetric isosteric sorption technique (SIT) device are compared to those obtained through conventional gravimetric instrumentation. Two metallocyclic compounds (3 and 4) that maintain their crystallinity upon generation of the porous apohost, are evaluated. A comparison of the various methodologies that exist in the literature to determine isosteric heats of adsorption (𝑄𝑠𝑡) from adsorption isotherms are presented. In particular, the temperature-dependent dual-site Langmuir and virial-type isotherm equations are compared for the first time and found to be complementary. The 𝑄𝑠𝑡 values at zero occupancy are determined to be 29.2 and 35.5 kJ.mol-1 for compounds 3 and 4, respectively, and trends in 𝑄𝑠𝑡 as a function of occupancy plots are accounted for.
- ItemGuest effects on the solid-state dynamics of selected inclusion compounds(Stellenbosh : Stellenbosch University, 2016-12) Engel, Emile R.; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Guest inclusion has always been a central feature of supramolecular chemistry. The present work describes guest effects on particular properties of selected inclusion compounds. Guest replacement is demonstrated as a means of modifying thermal expansion behaviour and porosity. The body of this thesis consists of three manuscripts (two published and one under review). The first manuscript describes a nitromethane solvate of 18-crown-6 that was investigated by means of temperature-resolved single-crystal X-ray diffraction. The compound exhibits exceptionally large positive thermal expansion in two axial directions and exceptionally large negative thermal expansion along the third. The underlying mechanism relies exclusively on weak electrostatic interactions to yield a linear thermal expansion coefficient of −129×10−6 𝐾−1, which is, to the best of our knowledge, the largest negative value yet recorded for an organic inclusion compound. Our discovery of a reported analogue with acetonitrile led us to prepare an isoskeletal series of compounds for further inquiry. The second manuscript demonstrates that guest replacement in a series of isoskeletal organic inclusion compounds can produce remarkable changes in thermal expansion behaviour. The three inclusion compounds have 18-crown-6 as host molecule and nitromethane, acetonitrile or iodomethane as guests. Along principal axis X1 the linear component of thermal expansion is negative for the nitromethane and acetonitrile solvates but zero for the iodomethane solvate. The compounds show varying degrees of large volumetric thermal expansion, with coefficients of 378(22), 226(3) and 256(8)×10−6 𝐾−1 for the nitromethane, acetonitrile and iodomethane solvates, respectively. Crystal structure analysis and computational methods were used to elucidate general features of the underlying mechanism of thermal expansion for the series. Interestingly, the thermosalient effect was observed for the acetonitrile version. To our knowledge this is the first example of thermosalience reported for an inclusion compound. The success with molecular organic crystals prompted similar experimentation with a different class of materials. As inorganic inclusion compounds, MOFs are an obvious choice for experiments involving guest replacement because of their proven capability for guest exchange, and the great interest in MOFs as potential porous sorbents for molecular storage and separation in industry. The final manuscript describes a non-interpenetrated MOF with a paddle-wheel SBU that has been activated by direct thermal evacuation, guest exchange with a volatile solvent, and supercritical CO2 drying. Conventional thermal activation results in a mixture of crystalline phases and some amorphous content. Exchange with a volatile solvent and subsequent vacuum activation produces a pure breathing phase with high sorption capacity, selectivity for CO2 over N2 and CH4, and substantial hysteresis. Supercritical drying can be used to access a guest-free open phase. Pressure-resolved differential scanning calorimetry was used to investigate the systematic loss of sorption capacity by the breathing phase as a function of successive cycles of sorption and desorption.
- ItemGuest uptake in porous metallocyclic host compounds(Stellenbosch : Stellenbosch University, 2020-01) Du Plessis, Marike; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The general aim of the work discussed in this dissertation is to contribute to scientific knowledge, thereby broadening our understanding of the relationships between the structure of a solid, crystalline material and its properties. Only when we truly understand the principles of supramolecular chemistry might we be able to design crystals for targeted applications at will. Metallocycles are a sub-class of supramolecular materials studied by the Barbour group for their potential porosity. In this regard, we selected three previously reported metallocycles, known to be porous, with the specific aim of further probing their porosity by means of guest exchange experiments. The first metallocycle studied is a silver-based acetonitrile solvate with the formula [Ag2L12](BF4)2•2CH3CN, where L1 is the ligand 1,4-bis(2-methylimidazol-1-ylmethyl)benzene; we refer to this metallocycle asMC1•2CH3CN. It was shown that the acetonitrile guest molecules can be replaced by other small guest molecules, specifically acetone, dichloromethane, benzene, p-difluorobenzene and toluene by immersing the as-synthesised crystals in the liquid of the target guest. The second is a Cu-based metallocycle with dimethylsulfoxide (DMSO) coordinated to the metal centre. The formula for this metallocycle (referred to as MC2S2) is [Cu2Cl4L12S2], where S is the coordinated solvent. The coordination bond can be cleaved by replacing the DMSO with acetonitrile in a solvent exchange process. We have shown that, by exposing the acetonitrile inclusion compound (MC2•2CH3CN) to vapours of solids, inclusion compounds with pyrazine, p-benzoquinone, p-dichlorobenzene and naphthalene can be obtained. While MC1•2CH3CN and MC2S2 are constructed using the same ligand, the third metallocycle, [Cu2L22Cl4] or MC3, contains the ligand 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (L2). Guest exchange experiments were carried out with MC3 and the three isomers of xylene. We have shown that p-xylene is selectively included from a mixture of the xylene isomers and that this metallocycle can be used to purify commercially pure o-xylene by extracting p-xylene impurities. All of the guest exchanges occurred as single-crystal to single-crystal transformations, allowing us to obtain crystal structures of the new inclusion compounds using single-crystal X-ray diffraction techniques. The crystal structures were analysed and insights gained from the crystal structures as well as supporting techniques such as thermogravimetric analysis, powder X-ray diffraction, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, vapour sorption, gas chromatography and nuclear magnetic resonance spectroscopy are discussed in this dissertation.
- ItemGuest-induced flexibility in crystals(Stellenbosch : Stellenbosch University, 2012-03) Heyns, Anneli; Barbour, Leonard J.; Stellenbosch University. Faculty Sciences. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The primary goal of the work presented here was to prepare both organic and metal-organic porous crystals (using crystal engineering strategies) in order to study the guest-induced flexibility of such seemingly rigid materials. The first section describes the structural modification of a known oxacalix[4]arene compound and the ability of the novel derivatives to encapsulate guest molecules in the solid state. Although it was not possible to obtain porous guest-free forms of any of the hosts, an apohost phase of a 2,3-naphthalene-derivative was obtained from dimethyl sulfoxide. This host uses the same principle as a molecular tweezer by capturing the guests between its offset eclipsing naphthalene moieties; a series of solvate structures were obtained. The flexible nature of the host molecule, when enclosing guests of different shapes and sizes, has been illustrated by a systematic conformational study. The work dealing with metal-organic compounds was shown to be the more successful of the two parts and forms the largest portion of the work. A series of discrete metallocycles was synthesised and their ability to function as porous materials was investigated. In all instances the metallocyclic hosts included the solvent of crystallisation within the ring. Desolvation of the included solvent did not occur as a single-crystal to single-crystal process and in some instances desolvation coincided with decomposition of the metallocyclic host even though the guests are situated within continuous channels. Although it was not possible to examine the permeability of the empty host, single-crystal to single-crystal guest exchange occurs rapidly when exposing the acetonitrile solvated metallocycle to several solvents. Significant adjustment of the host conformation, as well as the guest-accessible volume, accompanies the uptake of the different guests. Remarkably, this exchange process can also occur upon exposure to small gaseous guests such as I2, CO2, C2H2 and C2H3Cl. The physico-chemical properties of a known seemingly nonporous metallocycle were investigated in order to formulate a mechanism of transport from one discrete cavity to the next. Crystals of the apohost were shown to be permeable to a series of solvents despite the lack of conventional channels in the host structure. Accurate sorption isotherms measured at four different temperatures revealed host:guest ratios that are comparable to the host:guest ratio inferred from the single-crystal structures. The thermodynamic parameters of sorption ΔHad and ΔSad could be derived from the isotherms and revealed essential information on the affinity of the hosts for particular guests. Significant deviation in the centroid-to-centroid distance between the imidazole rings suggest that the transport of molecules is facilitated by “flapping” of the imidazole rings. The extent of the host flexibility was explored by studying the permeation of relatively large volatile solids such as naphthalene and p-dichlorobenzene. Kinetic sorption isotherms in conjunction with precise single-crystal data revealed a possible mechanism of transport, which was confirmed by molecular mechanics calculations.
- ItemHost-guest dynamics in copper-based metal-organic frameworks(Stellenbosch : Stellenbosch University, 2017-12) Bezuidenhout, Charl X.; Barbour, Leonard J.; Esterhuysen, Catharine; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: A vast number of metal-organic framework materials (MOFs) and structures have been reported in the literature. These materials are of interest as they exhibit a wide range of remarkable properties such as porosity, magnetism, chromism, thermal expansion and dynamic phase-change behaviour. However, many of the reports do not include investigations of all these possible properties, which provides an opportunity to revisit such materials. This study reports three sets of related MOFs that were studied in order to gain insight into their properties and dynamic host-guest interactions. In the first section three isoreticular copper(II)glutarate based 3D MOFs, whose pore dimensions vary according to the length of the 4,4´-bipyridyl linkers, allows exploration of the effect of increasing pore dimensions on the sorption behaviour of the frameworks. These MOFs capture CO2 under supercritical conditions and retain the gas under ambient conditions. The retention of the CO2 makes it possible to model the positions of the molecules within the channels of the frameworks using single-crystal X-ray diffraction analysis (SCXRD). Comparison of the CO2 gas sorption isotherms with the trend in thermal evolution of the CO2 adducts provided insight into the dynamics of the host-guest interactions within the MOFs. Theoretical models constructed from crystallographic data were used to calculate framework electrostatic potential maps through DFT and semi-empirical methods. The maps yielded a detailed picture of the electrostatic interactions prevailing at the sorption sites, which shows an electrostatic complementarity between the sorption sites and the CO2 molecules for two of the MOFs. The δ+ carbon of the CO2 molecules interacts with the δ– carboxylate moieties of the framework. Furthermore, both δ– oxygen atoms of each of the CO2 molecules interact with several δ+ hydrogen atoms of the framework. This electrostatic complementarity between CO2 and the sorption site results in a strong interaction, which stabilises the gas within these MOFs. The second set of MOFs studied comprises two 3D Cu(II)-glutarate-based MOFs with flexible linkers, [Cu2(glu)2(bpa)] and [Cu2(glu)2(bpp)], that undergo spontaneous phase changes upon solvent loss at room temperature. These MOFs are an extension of the isoreticular series of the previous section. Using SCXRD, we show that the phase changes result in new narrow-channel phases, with a large reduction in solvent accessible volume as compared with the original wide-channel phases. Moreover, the [Cu2(glu)2(bpa)] MOF displays a stepped sorption isotherm upon CO2 sorption at RT. This is indicative of the framework reverting to the wide-channel phase. The positions of the CO2 molecules in the channels of the frameworks were determined using SCXRD analysis of crystals exposed to supercritical CO2. Finally, a scan of the potential energy surface using molecular mechanics was conducted to elucidate the mechanism by which the phase change occurs. This appears to be a direct enantiomeric conversion of the glutarate ligands as a result of structural constraints. The third section describes a one-dimensional porous coordination polymer (PCP) [Cu2(acetate)2(dptz)]n•2CHCl3, that possesses pleochroic properties, i.e. the crystals appear to have different colours depending on their orientation. Solvent exchange with acetonitrile and nitromethane reveals that crystals of this PCP are also solvatochromic. This allows the solvent exchange process to be monitored using optical microscopy with polarised light. The experiment revealed an unexpected double V-shaped pattern in the crystals, which could be explained using an overlay of the measured crystal facets with the crystal structure, along with modelling of crystal surface adsorption at the different crystal facets. Furthermore, we identified that the crystals must be growth twins subject to the double re-entrant corner effect.
- ItemInclusion Studies of Metal-Organic Hosts(Stellenbosch : Stellenbosch University, 2012-03) Potts, Storm Victoria; Barbour, Leonard J.; Haynes, Delia A.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The primary objective of the work presented in this thesis was to prepare and investigate the properties of novel inclusion complexes of metal-organic host materials. Two types of host materials were studied, namely 0D metallocycles and 3D metal-organic frameworks (MOFs). The first section details the synthesis and characterisation of six ditopic imidazole derived ligands. These conformationally flexible ligands were reacted with a variety of transition metal salts in a systematic manner with a view to synthesising 0D metallocycles. The structures of 29 novel coordination complexes were elucidated by single-crystal X-ray diffraction and five of these were 0D metallocycles. The thermal stability of the five metallocyclic inclusion complexes was investigated and it was found that all five of the metallocycles have remarkably high thermal stability with respect to the loss of their included volatile solvents. Indeed, in some cases the solvent is only lost when the host decomposes. This is a relatively rare phenomenon, with only a few examples of such systems reported in the literature. A computational study was undertaken in an attempt to rationalise this high thermal stability in terms of guest-guest and host-guest interaction energies. Furthermore, although the single crystals do not survive the desolvation process, all five of these systems exhibit Class II porosity (i.e. the included solvent could readily be exchanged for a different solvent guest without significant disruption to the host packing arrangement). This exchange process was monitored as a single-crystal to single-crystal transformation. The final section reports the attempted gas-phase diffusion of two organic radicals into four porous crystalline materials. The radicals diffused into only one of the four possible host systems, thereby indicating a selective inclusion process. The structures of the two new inclusion complexes were elucidated from powder X-ray diffraction data and it was demonstrated that the properties of both the organic radical as well as the host framework are modified in the new material. Furthermore, the host framework acts as a “vessel” in which the organic radicals, which are normally highly reactive species, can be stored under ambient conditions within the channels of the host framework for a period of three months without degradation. The host framework can thus be used for controlled release of the reactive species by exposure to a suitable solvent.
- ItemInvestigating 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
- ItemInvestigation of the carbon dioxide sorption properties of selected organic macrocycles(Stellenbosch : Stellenbosch University, 2018-03) Basson, Jeanice Letitia; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The inclusion of guest molecules within host compounds has been an ever-growing interest in supramolecular chemistry. Host-guest chemistry has attracted much attention due to potential applications in drug delivery, catalysis and the separation and storage of natural gases. As a result, a large variety of porous systems such as porous coordination polymers (PCPs), porous molecular systems, covalent organic frameworks (COFs) and supramolecular organic frameworks (SOFs) have been developed. In this study, three well-known organic macrocycles, namely p-tert-butylcalix[4]arene (TBC4), cucurbit[6]uril (CB[6]) and cucurbit[8]uril (CB[8]) were investigated as hosts for gaseous carbon dioxide (CO2). The aim of this study was to gain insight into the properties of these hosts and gain a better understanding of the inclusion of CO2 in these materials. The first section discusses TBC4 as a host for CO2. The guest-free low density polymorph of TBC4 contains discrete pockets (zero-dimensional porosity) and captures CO2 in a stepwise fashion. The system undergoes a gas-induced single-crystal to single-crystal (SC-SC) transformation to a more porous phase with an increased CO2 loading capacity. The CO2 inclusion compounds were investigated in-situ using single-crystal X-ray diffraction (SCXRD). The gas-induced phase transformation was further investigated using variable-pressure powder X-ray diffraction (VP-PXRD) and pressure-ramped differential scanning calorimetry (P-DSC). Interestingly, this porous phase is preserved when the CO2 molecules are removed. However, the original guest-free phase can be regenerated under mild activation conditions. The study was extended by investigating CO2 uptake by the high density polymorph of TBC4. Despite being a close-packed structure, CO2 molecules are able to diffuse through the host to instigate a gas-induced transformation at high pressure, and a possible mechanism is discussed. The second section describes the porosity of the well-known host, CB[6]. This host undergoes various phase transformations in order to produce a framework with permanent one-dimensional porosity. The various phases were subjected to thermal and structural analysis, where possible. This host, like most molecular organic hosts, produces a more close-packed phase when activated, and it expands upon CO2 loading. The CB[6] host framework displays a large affinity for CO2 and does not undergo a structural change at high CO2 pressure. In-situ SCXRD was used to investigate the CO2 inclusion compounds at various gas pressures to study the host-guest interactions. The final section discusses CB[8] as a CO2 adsorbent. Due to the high CO2 affinity demonstrated by CB[6], CB[8] was studied as a solid-state host. This host undergoes a phase transformation during desolvation to produce a more stable polycrystalline phase of CB[8]. Although the host could not be characterized structurally, it was evident from the CO2 sorption analysis that the host framework is porous. CB[8] displays stepwise uptake and release of CO2 molecules and has a larger affinity for CO2 as compared to methane and nitrogen gas. VP-PXRD was used to investigate the dynamic nature of the host with respect to CO2 uptake and release. Several attempts at preserving the single crystallinity of CB[8] during desolvation are also discussed.
- ItemInvestigation of the co-crystallisation of N-heterocycles(Stellenbosch : University of Stellenbosch, 2009-03) Loots, Leigh-Anne; Barbour, Leonard J.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.Co-crystals are excellent materials for studying intermolecular interactions in the solid-state and can be used to further our knowledge of the balance between strong and weak intermolecular interactions. The O–H∙∙∙∙∙∙Narom synthon was chosen as the focus of this investigation of hydrogen bonding motifs. The starting materials selected all have two hydrogen bond donor and/or acceptor sites for the formation of extended networks. All molecules are also aromatic such that the influence of weaker π∙∙∙∙∙∙π interactions can be included in the study. Two 3x3 grids of related co-crystals were produced from these starting materials and are reported in this thesis as part of an ongoing investigation into a broader set of co-crystals. A part of the work describes the investigation of co-crystals prepared by the combination of related benzenediol and diazine isomers taken from a 3x3 grid. The solid-state structures of each of the six starting materials are discussed briefly to describe the nature of intermolecular interactions involved in the single component crystals. Trends in hydrogen-bonding patterns as well as the weaker interactions identified in the starting materials, can be used to recognise those in the subsequent multi-component crystals. Thirteen co-crystal compounds were obtained, of which twelve structures are novel. Each of these co-crystal structures is discussed in terms of intermolecular interactions and packing in the solid state. Hydrogen-bonding patterns and structural similarities are highlighted in related co-crystal structures as well as between co-crystals and their respective starting materials. The combination of benzenediol isomers with benzodiazine isomers yielded seven novel co-crystal structures in a second 33 grid is reported. The structure of phthalazine, which has not yet been reported, is included in addition to these co-crystals, while the structures of quinazoline and quinoxaline that were retrieved from the CSD are discussed briefly. Co-crystal structures are discussed individually, focusing on the intermolecular interactions that are significant to the structural architecture of the compound. Certain co-crystals that display structural similarities with structures of the 3x3 grid, as well as with co-crystals presented in Chapter 3, are discussed in the relevant sections. Lastly, two extended pyridyl diyne ligands that were synthesised for use in future co-crystallisation studies similar to those reported earlier are briefly highlighted. The crystal structures of the pure compounds and of a hydrate of one of the ligands were obtained and discussed briefly. To date only one of these structures has been reported in the literature.
- ItemAn investigation of the solvent-mediated properties of organic crystals with one-dimensional channels(Stellenbosch : Stellenbosch University, 2020-02) Eaby, Alan; Barbour, Leonard J.; Esterhuysen, Catharine; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Stimuli-responsive materials have become topical in the field of supramolecular chemistry in the last 20 years. Their applications include coatings, fibres, actuators, sorbents and conductors, amongst others, owing to their unique ability to adapt to their environment. Within this class are organic crystals that have demonstrated responses to pH, temperature, electromagnetic radiation, mechanical force, solvent and so on. These responses can be observed on a macroscopic level, such as chromism or mechanical motion, extending the application of molecular crystals beyond the molecular level. Developing these materials and the tools to study them should be the focal point of materials design. This work presents two molecular systems whose properties adapt to their external environment and the methods that were used to observe, characterise and utilise these properties. The first system is a series of inclusion compounds that crystallise with 2,7-dimethyl-octa-3,5- diyne-2,7-diol (1) as the host, forming 1-D channels for smaller guest molecules to occupy. These crystals grow as long needles that exhibit elastic flexibility under mechanical stress. The guest molecules can be selectively exchanged without significant change to the packing of the host. However, the crystal habits differ in size and cross-sectional shape. The aim was to determine whether the flexibility of each crystal could be altered by selectively exchanging the guest molecule in the channel, with the difference between inclusion compounds attributed to specific supramolecular interactions. An instrument was developed to determine the Young’s modulus as a measure of the relative flexibility between crystal analogues, where the difference in crystal shape and size could be taken into account with in-house developed software. The second system studied is a trianglimine compound (2) that crystallises with large, onedimensional channels. Crystals of 2 exhibit reversible hydrochromism that only occurs at relative humidities (RH) in excess of 55% RH. The colour change stems from a proton shift in the Schiff base moiety that favours the ketoenamine tautomer at high humidities. In addition to chromism, 2 also demonstrates rare water vapour sorption capabilities. With almost no water adsorption at humidities below 55% RH, adsorption to 9 wt. % occurs rapidly at the threshold RH and is indicated with the change in colour. Remarkably, desorption across this threshold RH is also rapid with no pressureinduced hysteresis. This reduces the energy cost of desorption, which often is the primary limitation for desiccant regeneration. The rapid adsorption is related to the prototropy, as these hydroxyl groups are the primary nucleation sites during adsorption.
- ItemNegative thermal expansion of organic compounds(Stellenbosch : Stellenbosch University, 2011-03) Greyling, Guillaume Hermanus; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The primary objective of the work was to investigate the negative thermal expansion of organic materials and to determine the mechanisms governing this phenomenon by using the principles of crystal engineering. To this end, the following three compounds were studied in detail: • 4,4'-Diiodobiphenyl • 4-Iodobenzoic acid • Methyl Paraben The rationale behind this work was to determine the mechanisms responsible for the observed negative thermal expansion and to uncover the structural factors that induce negative thermal expansion. Single-crystal X-ray diffraction was employed as the primary analytical tool, owing to the unique information it can provide regarding intermolecular interactions in the solid state. A total of twenty organic compounds were analysed, of which three exhibited negative thermal expansion. Each compound employs a specific mechanism for negative thermal expansion, two of which are closely related and the third distinct.
- ItemPolar ordering of guest molecules in host-guest inclusion complexes(Stellenbosch : Stellenbosch University, 2011-12) Bezuidenhout, Charl Xavier; Barbour, Leonard J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: 2,7-dimethylocta-3,5-diyne-2,7-diol forms inclusion complexes with various guests molecules, where the guest molecules are polar-ordered. A Cambridge Structural Database (CSD) search revealed ten inclusion complexes where the guest molecules were polar-ordered. Using Density Functional Theory (DFT) computational methods (in the absence of the host), we evaluated the intra-channel and lateral guest-guest interactions between the guest molecules. Two polar-ordered inclusion complexes ((1,4,7-cyclohexane-1,2,4,5,7,8-hexaoxonane)·CHCl3 and (2,4,6-(endolongifolyl)-1,3,5-trioxane)·CDCl3) were singled out in the CSD search for further studies along with 2,7-dimethylocta-3,5-diyne-2,7-diol. Synthesis of any 1,2,4,5,7,8-hexaoxonane and 1,3,5-trioxane derivatives was attempted to establish whether the polar-ordering ability extends into the family of compounds. We managed to produce three new polar-ordered inclusion complexes with 2,7-dimethylocta-3,5-diyne-2,7-diol (ClC(CH3)3, BrC(CH3)3 and IC(CH3)3), thus extending the series to six guest polar-ordered systems. We were only able to synthesise 1,4,7-cyclohexane-1,2,4,5,7,8-hexaoxonane and produce the CHCl3 inclusion complex and one new polar-ordered inclusion complex (CHBr3). Three 1,3,5-trioxanes was synthesised (the cyclohexyl, cyclohex-3-en-1-yl and cyclopentyl derivatives), which did not include any solvents. However, these 1,3,5-trioxanes also form polar-ordered crystals. These compounds and inclusion complexes were analysed by means of single crystal X-ray diffraction to determine their crystal structures. All the crystal structures could be solved and refined to adequate accuracy (except for 2,4,6-tri(cyclopentyl)-1,3,5-trioxane) with no disorder of the guest molecules (where applicable) and their polar-ordering property investigated. Due to their vast molecular differences, these compounds were studied separately by means of visual crystal structure analysis and computational modelling techniques (Density functional theory, molecular mechanics, molecular dynamics and molecular quench dynamics).
- ItemPreparation and coordination chemistry of bis-pyridyl diamide ligands(Stellenbosch : University of Stellenbosch, 2010-03) Batisai, Eustina; Barbour, Leonard J.; Le Roex, Tanya; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: The number of coordination complexes utilizing bis-pyridyl diamide ligands has increased significantly over the past decade. This is attributed to the relatively easy synthetic procedure of the ligands and interesting structural features such as helicity, water clusters and porosity that the coordination complexes possess. In the first part of this study, the following eight structurally related bis-pyridyl diamide ligands: • N,N'-bis(pyridin-4-ylmethyl)isophthalamide (ISO); • N,N'-bis(pyridyl-4-ylmethyl)terephthalamide (TER); • N,N'-bis(pyridin-4-ylmethyl)hexanediamide (ADI); • N,N'-bis(pyridin-4-ylmethyl)butanediamide (SUC); • N,N'-bis(pyridin-4-ylmethyl)biphenyl-4,4'-dicarbonyl dicarboxamide (DIP); • N,N'-dipyridin-2-ylpentanediamide (GLUT); • (2E)-N,N'-bis(2-pyridin-4-ylmethyl)but-2-enediamide (FUM); • 4-(pyridin-4-ylmethyl)aminocarbonyl benzoic acid (TER-A). were synthesized and characterized by NMR, FTIR, MS and SCD. In the second part, the synthesized ligands were reacted with a variety of transition metal salts to yield fifteen novel coordination polymers and one discrete complex. SCD analysis showed that of the sixteen complexes thirteen formed 1-D chains, two formed 2-D networks, and one formed a discrete unit. Hydrogen bonding interactions between water molecules, the counterions and the amide groups resulted in connection of the lower dimension entities into higher dimension networks. The synthesized ligands were co-crystallized with trimesic acid and a novel co-crystal consisting of ADI and trimesic acid was obtained. SCD analysis showed that the co-crystal featured the amide homosynthon as well as the pyridine/carboxylic acid heterosynthon.