Browsing by Author "Oliver, Clive L"

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    A Cambridge structural database search for entangled MOFS and the synthesis and analysis of the non-entangled counterparts of a set of entangled MOFs
    (2024) Bambiso, Lungelo Tervin; Oliver, Clive L; Mogodi, Wilson M
    Metal-organic frameworks (MOFs) have become a fast-growing field of research in the areas of synthetic chemistry, crystal engineering, materials science and supramolecular chemistry in recent years. The synthesis and characterization of novel MOFs have been of particular interest to researchers around the world due to their potential in several applications, such as gas sorption and separation, drug delivery and catalysis. The focus and pursuit in the early stages of MOF research was to design materials with as large pore volumes as possible, which lead to the phenomenon called entanglement. Entanglement in MOFs, of which interpenetration is a subtype, refers to when networks within the same crystal structure cannot be hypothetically separated from one another without breaking chemical bonds. This has a significant impact on the porous nature, structure, and functional applications of MOFs. Thus, initially entanglement was viewed as undesirable, however, it has since been recognized that entanglement could be advantageous, since these MOFs may be more stable. The primary objective of this work was (i) to data mine the Cambridge Structural Database (CSD) for entangled MOFs and (ii) to investigate the structural, thermal and sorption properties of a set of non-entangled MOFs with their previously published isoreticular and entangled counterparts. The first section of this thesis, the computer-based section, presents the MOFs (not discriminating between entangled and non-entangled MOFs) belonging to seven different families extracted (using the CSD version 5.37 - May 2016 update) according to the search criteria used by Moghadam and Fairen-Jimenez et al. In this thesis, these seven families were updated using the CSD version 5.43 - April 2021. These families formed the basis sets from which entangled MOF structures were searched using search criteria based on intermolecular, non-bonded contacts such as hydrogen bonding, π–π and C–H⋯π interactions. The average of the two success rate indicators, showed that the percentage of retrieved entangled MOF structures from the four MOF families that had entangled structures, ranged from 13.6 – 38.6%, 11.8 – 38% and 4.4 – 34%, respectively, for the three search criteria. The second section of this thesis, the experimental section, describes two novel non-entangled two-dimensional (2D), 2-periodic isoreticular fluorinated MOFs of formulae [Cu2(hfipbb)2(DMF)2]n·n(DMF)4 (1), [Cu(hfipbb)(DEF)]n·n(DEF)2 (2), where hfipbb = 4,4′-(hexafluoroisopropylidene)bis(benzoate), DMF = N,N′-dimethylformamide and, DEF = N,N′-diethylformamide. These structures are compared to their entangled, isoreticular counterparts published by Chatterjee et al. in terms of their syntheses, structures, thermal and sorption properties. The entangled structures had decomposition temperatures of 310 °C and 400 °C for the MOFs obtained from DMF and for DEF, respectively whilst the non-entangled MOFs had decomposition temperatures of 350 °C and 370°C for 1 and 2, respectively. The non-entangled MOFs had contact surface potential void space of 39% and 40.4% for 1 and 2, respectively, significantly higher than those of entangled MOFs with contact surface potential void spaces of 8.2% and 12.5% for the entangled MOFs obtained from DMF and DEF, respectively. Despite the lack of entanglement in 1 and 2, as compared to their entangled counterparts, their 195 K CO2 sorption isotherms also display inflection points and significantly increased sorption, as well as large extents of hysteresis, of 35% and 39% obtained for 1 and 2, respectively, whilst both entangled MOFs displayed extents of hysteresis of 44%. Interestingly, the activated phase of a third MOF, [Cu2(hfipbb)2(H2O)2]n (3), synthesized through DMF ligand exchange with water in 7 days, does not display an inflection point in its 195 K CO2 isotherm and subsequent increased sorption, despite also being non-entangled. This confirms that subtle differences in the desolvated phases can lead to marked differences in the sorption behaviour of isoreticular MOFs.
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    Characterisation and topological analysis of novel metal-organic frameworks
    (2011) Davies, Kate; Bourne, Susan A; Oliver, Clive L
    The investigation of complexes in the solid state has developed exponentially over the past few decades in terms of both crystal engineering and supramolecular chemistry. The preparation of new metal-organic frameworks and coordination polymers has been of particular interest due to the large variety of structural topologies as well as the varying functionalities they offer. A study of the preparation of new metal-organic frameworks from common starting materials was undertaken to increase the understanding of the preparative methods for these compounds.
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    Crystal engineering and sorption studies of cyclotriveratrylene and C-methylcalix[4]resorcinarene solvates
    (2019) Payne, Richard Michael; Oliver, Clive L
    Cyclotriveratrylene compounds crystallised from acetonitrile (1) and 2-butanone (4) are shown to be nearly isostructural, resulting in the formation of dimeric capsules, while the compound which crystallised from chloroform (3) results in the formation of layers of cyclotriveratrylene molecules separated by layers of chloroform molecules. 1 is found to undergo a single-crystal-to-single-crystal transformation following desolvation. Consecutive single-crystal X-ray diffraction experiments on 1 at 50 °C reveal that the rotation of a unique, single methoxy group of the host molecule may permit the escape of the solvent molecules from the apparently nonporous crystal. C-methylcalix[4]resorcinarene has been shown previously to form either channel-type structures or hexameric, spherical assemblies when crystallised from various alcohol molecules. The effect of the length of the alkyl chain of the solvent alcohol was studied. It was established that the short-chain alcohols favour the formation of channel-type structures while the longer-chain alcohols favour the formation of the hexameric, spherical assemblies. A hexameric assembly structure crystallised from 1-propanol (8) displays a ~25% increased interior volume over known assemblies and is found to be the first of these types of assemblies to form by vapour sorption. A hexameric assembly structure crystallised from 1-butanol (9) has already been published in the literature. However, SCXRD studies for this work revealed additional structural information not apparent in the literature structure. Another hexameric assembly structure, this time crystallised from 1-pentanol (10), was shown to be similar to the structure of 9, with certain differences. Characterization of these structures was performed by single-crystal X-ray diffraction, powder X-ray diffraction, hot stage microscopy and thermal analysis. All compounds were shown to maintain crystallinity upon heating and desolvation – however, several transitioned through an amorphous phase. Gas and vapour sorption analysis was performed on all activated compounds. Some of these compounds were found to resolvate to their original solvated structures merely upon exposure of the desolvated powders to the solvent vapours.
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    Crystal engineering of 2-periodic Ni- and Co-based, isoreticular, mixed ligand metal-organic frameworks for sorption studies
    (2023) Baloyi, Nonhlanhla; Oliver, Clive L
    The study of porous materials has been the subject of vast research, with Metal-Organic Frameworks (MOFs) being the front-runner. A MOF is composed of metal ions and organic ligands, and the type of ligand can affect or control pore size, shape, geometry, inner surface, and structural rearrangement of the materials. This allows for tailoring of the structure/properties, and this one of the most appealing features of MOFs and can be of benefit in many applications, for example, enhancing gas sorption capacities. MOFs consisting of mixed ligands, i.e., more than one type of ligand, open the possibility of varying pore directional features in three dimensions independently, thus allowing for further tailoring of properties. This thesis reports the synthesis of novel two-periodic, isoreticular, Ni and Co isoreticular MOFs, of the formulae [Ni(2-nta)(bpe)(H2O)2]n·2(DMA)n (1), [Ni(2-bta)(bpe)(H2O)2]n·2(DMF)n (2), [Co(2-nta)(bpe)(H2O)2]n·2(DMA)n (3) and [Co(2-ata)(bpe)(H2O)2]n·3(DMA)n·(H2O)n (4). These were synthesized from 1,2-bis(4-pyridyl) ethane and terephthalate ligands (2-nitroterephthalic acid, 2-bromoterephthalic acid, 2-aminoterephthalic acid) with functionalities of varying sizes and polarizabilities (-NO2, -Br, -NH2). The possible effects of the functionalities (-Br, -NO2 and -NH2) of the terephthalate ligands on the stability, porosity and sorption properties of the MOFs were investigated. It was found that MOFs 1 − 4 are all isoreticular to each other, although with void spaces ranging from 36 – 52%, with those containing the nitro functionalities, displaying the smaller void spaces. Although, 2 and 4 display higher void spaces than 1 and 3, 1ʹ and 3ʹ show higher sorption, especially in the case of carbon dioxide sorption and water sorption, which were accompanied by hysteresis upon desorption, with 1ʹ showing superior water sorption with a favourable “S-shaped” isotherm. The differences in sorption could not be fully attributed to the group functionalities in terms of their polarities, however the relative degrees of crystallinity of the MOFs (before and after activation) seemed to be the major factor in explaining the large degree of variation in their sorption properties.
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    Crystal engineering of mixed-ligand metal-organic frameworks
    (2016) Tahier, Tayyibah; Oliver, Clive L
    Research of solid state complexes has grown and developed exponentially over the past few years in terms of supramolecular chemistry and crystal engineering. The synthesis and characterisation of metal organic frameworks (MOFs) have attracted widespread attention owing to their potential in various applications. This includes gas sorption, which could aid in alleviating serious environmental issues such as global warming by sequestrating greenhouse gases. Advances in the design of these materials using the mixed ligand approach add to variation in structures and thus provide a further means of tailoring of properties. A novel two dimensional, mixed ligand MOF has been synthesised based on 1,3,5 benzenetricarboxylic acid, 4,4' bipyridine N,N' dioxide and zinc sulfate with the formula [Zn3(BTC)(4,4' bpdo)(OH)(SO4)(H2O)3]n·n(H2O)2.33 (1). The 2D layers of 1 arrange in a polar fashion with adjacent layers forming isolated cavities. Variable temperature powder X ray diffraction (VT PXRD) analysis showed that the crystallinity of the compound was retained and the crystalline phase remained unchanged as the temperature was increased. Variable temperature single crystal X ray diffraction (VT SCXRD) analysis of 1 revealed that the dehydration and rehydration processes occur via single crystal to single crystal transformations. Water vapour sorption experiments showed a type I isotherm, typical of microporous materials. A two dimensional, interpenetrated, mixed ligand MOF has been synthesised based on 5 nitro 1,3 benzenedicarboxylic acid, 1,2 bis(4 pyridyl)ethane and cadmium nitrate with the formula [Cd(bpe)1.5nbdc]·DMF (2). VT PXRD analysis shows subtle differences in the compound as the temperature is increased. VT SCXRD experiments show that the most notable change in the structure occurs at 373 K. These changes include the removal of the guest molecule and a change in the crystal system, along with changes in the orientation of the pyridyl ring of the organic ligand. Carbon dioxide sorption experiments at 195 K showed a type IV isotherm, which is usually associated with mesoporous materials. Both 1 and 2 were synthesised using the solvothermal method and fully characterised using X ray diffraction studies (SCXRD, PXRD, VT SCXRD and VT PXRD), thermal analysis (thermogravimetric, differential scanning calorimetry, hot stage microscopy), elemental analysis and FT IR spectroscopy. The porosity of the compounds was tested using carbon dioxide (273 K and 193 K), nitrogen, water vapour and liquid sorption experiments.
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    Structural and Electrochemical Studies of Cobalt(II) and Nickel(II) Coordination Polymers with 6-Oxonicotinate and 4,4′-Bipyridine
    (2021-12-10) Škugor Rončević, Ivana; Vladislavić, Nives; Chatterjee, Nabanita; Sokol, Vesna; Oliver, Clive L; Kukovec, Boris-Marko
    The 6-oxonicotinate (6-Onic) salts of a one-dimensional cationic cobalt(II) or nickel(II) coordination polymers with 4,40 -bipyridine (4,40 -bpy), namely {[Co(4,40 -bpy)(H2O)4 ](6-Onic)2 ·2H2O}n (1) and {[Ni(4,40 -bpy)(H2O)4 ](6-Onic)2 ·2H2O}n (2), were prepared hydrothermally by reactions of cobalt(II) nitrate hexahydrate or nickel(II) nitrate hexahydrate, respectively, 6-hydroxynicotinic acid and 4,40 -bipyridine in a mixture of ethanol and water. In the hydrogen-bonded frameworks of 1 and 2, the one-dimensional polymeric chains of {[M(4,40 -bpy)(H2O)4 ] 2+}n (M = Co, Ni), the 6-oxonicotinate anions and the lattice water molecules were assembled via strong intermolecular O–H···O and N–H···O hydrogen bonds and π–π interactions, leading to the formation of the representative hydrogen-bond ring motifs: trimeric R 2 3 (10) motif, the centrosymmetric tetrameric R 2 4 (8) and R 2 4 (12) motifs and the pentameric R 4 5 (12) motif. The isostructural coordination polymers 1 and 2 exhibited a different electrochemical behavior, as observed by cyclic voltammetry, which can be attributed to the nature of the metal ions (cobalt(II) vs. nickel(II)).
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    Topological studies of three related metal-organic frameworks of Gd III and 5-nitroisophthalate
    (2012) Davies, Kate; Bourne, Susan A; Öhrström, Lars; Oliver, Clive L
    The reaction of 5-nitroisophthalic acid (H(2)NIA) with Gd(NO(3))(3)·6H(2)O in DMF afforded three new metal-organic frameworks: [Gd(NIA)(1.5)(DMF)(2)]·DMF (I), [Gd(2)(NIA)(3)(DMF)(4)]·xH(2)O (II) and [Gd(4)(NIA)(6)(DMF)(5.5)(H(2)O)(3)]·4DMF·H(2)O (III). These compounds can be prepared through a variety of methods. Compounds (I) and (II) are more reproducibly formed than compound (III). Network analysis revealed (I) to have a (4(12).6(3))-pcu topology, while (II) displays a (4(2).8(4))(4(2).8(4))-pts topology. Compound (III) was found to present the uncommon 4,5,6T11 topological net, which combines aspects of both the pcu and pts topologies. The short symbol of this net is (4(4).6(2))(4(6).6(4))(2)(4(8).6(6).8).