Structural Diversity in Metal-Organic Frameworks and Metal-Organic Polyhedra with 1,3,5-Triethynyl-Benzene Based Linkers
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Eiffe, Joseph Michael, Structural Diversity in Metal-Organic Frameworks and Metal-Organic Polyhedra with 1,3,5-Triethynyl-Benzene Based Linkers, Trinity College Dublin.School of Chemistry, 2023Download Item:
Abstract:
The study of metal-organic frameworks and metal-organic polyhedra is a rapidly evolving area of research. The research presented in this thesis serves to further our understanding of these advanced materials with the primary focus on the effects of linker symmetry and functionalisation. The newly synthesised materials were then examined using physical and computational techniques to study the influence of the material's structure on its properties.
Chapter 1 summarises the available literature related to this thesis's work. This chapter introduces the reader to the various concepts regarding metal-organic frameworks (MOFs) and metal-organic polyhedra (MOPs). The aims of the thesis are also outlined.
In Chapter 2 using the newly synthesised amino functionalised organic linker 3,3',3''-((2-aminobenzene-1,3,5-triyl)tris(ethyne-2,1-diyl))tribenzoic acid (H3BTEBmmmNH2) in combination with Cu2+ ions two MOPs, [Cu36(BTEBmmmNH2)24(H2O)28(DMF)8] (1) and [Cu12(BTEBmmmNH2)8(H2O)12] (2) were synthesised. The two MOPs have the structures of a cuboctahedron and octahedron, respectively. This demonstrates the diverse range of possible structures by using the conformational flexibility of benzene-trisethynyl benzoate (BTEB) based linkers.
These newly synthesised MOPs were then implemented as structural units in the construction of MOFs. This was achieved by using the technique known as ?pillaring?. The pillaring method involves the addition of a bipyridyl ligand, in this instance 4,4?azobipyridine (Azpy), which coordinates to the apical position on {Cu2} paddlewheel SBUs within the MOPs framework. By controlling the amount of Azpy used in the synthesis, and its ratio to the H3BTEBmmmNH2 linker, the dimensionality of the pillared MOF product can be selected. Using a low mole ratio of Azpy to H3BTEBmmmNH2 led to the pillaring of 1 into a one-dimensional coordination polymer [Cu36(BTEBmmmNH2)24(Azpy)(DMF)34] (3), while a high mole ratio led to the three-dimensional framework [Cu36(BTEBmmmNH2)24(Azpy)6(DMF)30] (4). However, attempting to pillar 2 into a framework leads to an unexpected result with the MOP disassembling in solution and reforming into a pillared two-dimensional framework, [Cu6(BTEBmmmNH2)4(PPP)2(Azpy)(H2O)2] (5).
In Chapter 3 the effects of linkers with reduced symmetries on the MOFs framework are studied. A new family of BTEB-based linkers was first synthesised using various combinations of para-benzoate, meta-benzoate and isophthalate moieties. These new linkers are combined with Cu2+ ions to form a metal-organic framework. Cu2+ ions were chosen as they have a strong tendency to form the structural building unit known as a {Cu2} paddlewheel secondary building unit (SBU). This readily reproducible SBU allows for the effect of the organic linkers geometry on the structure of the MOF to be examined in isolation. A series of MOFs, 6 - 11 were then synthesised using the new symmetry reduced tritopic linkers and tetratopic linkers. The structures and properties were examined using both physical and computational techniques.
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In Chapter 4 we then focused on examining the influence of linkers with reduced symmetry on the structure and properties of the inorganic SBUs. To study these effects, metal ions that can form a broad range of inorganic SBUs in combination with the new symmetry-reduced linkers were studied. This chapter's first MOF to be discussed, [NH2(CH3)2]6[Zn9(BTEBppi)6] (12), provides an excellent example of the potential SBUs that could be synthesised using the new linkers. The MOF contains two SBUs that are uncommon in the literature, with the structure of one SBU, a 5-connected node, being reported only once before.
Using the same H4BTEBppi linker with Co2+ ions led to the new MOF, [Co2(BTEBppi)(DMF)3] (13). The inorganic SBUS within the MOF was found to be dinuclear, with one Co2+ ion coordinated by three solvent molecules. This structural aspect of the SBU is a common feature in MOFs used in catalysis. Based on this structural feature and the literature reports of cobalt-based MOFs used for catalytic electrochemical water splitting, a preliminary investigation of the MOFs to act as a water-splitting catalyst was carried out. The MOF was determined to be an active catalyst for the oxygen evolution reaction t for extended periods of time.
The final MOF to be discussed in the thesis, and the only MOF in this work containing a pentacarboxylate organic linker, is a zinc-based MOF, [Zn7(HBTEBiip4-)3(DEF)7](NO3)2 (14). In the MOFs framework, only four of the linkers carboxylate groups coordinate with the metal ions, like the literature-known compound. Where the structure of the two MOFs diverges is the remaining carboxylate group. This carboxylate group remains uncoordinated and directed towards the pores of the MOF. This is a desirable feature in MOF chemistry that typically require post-synthetic modification to achieve serving to demonstrate the considerable potential that linkers with reduced symmetry have in MOF chemistry.
Chapter 5 describes the details of experimental procedures and characterisation data of any new compounds.
The thesis concludes in Chapter 6 with a brief summary of its contained works alongside a discussion of possible avenues for further research that this work opens up.
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European Research Council (ERC)
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Author: Eiffe, Joseph Michael
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SCHMITT, WOLFGANGPublisher:
Trinity College Dublin. School of Chemistry. Discipline of ChemistryType of material:
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MOF, MOP, Metal-organic frameworks, Metal-organic polyhedraMetadata
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