Synthesis and characterization of novel octahedral coordination cages for gas storage applications
Date
2021
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Publisher
University of Delaware
Abstract
The work detailed in this dissertation describes the design, synthesis and characterization of novel carbazole-based octahedral coordination cages and their potential gas storage applications. A wide array of characterization techniques and spectroscopic methods are employed, including single crystal X-ray diffraction, powder X-ray and neutron diffraction, gas adsorption, IR and NMR spectroscopies, and thermal studies. Chapter one provides a brief introduction to supramolecular coordination chemistry and metal-organic materials. This broad field is then narrowed down and more detailed description of carbazole-based metal-organic materials and their applications is provided. ☐ Chapter 2 details a novel synthesis route to 9H-carbazole-3,6-dicarboxylate which is utilized in the construction of many of the carbazole-based materials discussed. The design, synthesis, and characterization of the ligands along this synthetic route are described in detail. The solid state structure of the ligand intermediates is investigated and the aryl-aryl interactions displayed by the ligands inspires the synthesis of a novel copper-based octahedral coordination cage which displays similar interactions in the solid state. These interactions and their effect on gas sorption and thermal stability of the cage material are investigated. ☐ Chapter 3 describes the synthesis and activation of previously reported unfunctionalized carbazole-based octahedral cages as well as a novel chromium cage based on the ligand. A known metal-organic framework is synthesized and utilized as a surrogate to interrogate the gas binding sites within these cages and cage-based materials. In this chapter the importance of correct synthesis and solvent exchange conditions which can lead to dramatic changes in gas sorption capability are discussed. The high pressure methane storage capacities of the synthesized metal-organic materials are investigated and compared to that of the “industry standard” HKUST-1. ☐ Chapter 4 documents the expansion of the synthesis of paddlewheel-based coordination cages to cobalt- and nickel-based metal nodes. In route to the synthesis of novel coordination cages the importance of ligand functionalization is discussed as a 3-dimensional and several 2-dimensional metal-organic frameworks are produced. Through the use of solubilizing functional groups novel coordination cages can be produced with these metals. The carbazole-based coordination cages that result display excellent thermal stability and maintain their porosity at activation temperatures of up to 200 °C. ☐ Chapter 5 describes the extension of the library of carbazole-based coordination cages to aryl functionalized ligands which had previously only been utilized in framework-based materials. The design, synthesis and characterization of a series of aryl-functionalized ligands and the resultant coordination cages is given. In particular, the solid state packing of the cages reveals intermolecular aryl-aryl interactions with the functional groups on one cage interacting with the aryl groups in the pore window of an adjacent cage. The stabilizing effect of these aryl-aryl interactions increases the thermal stability of these cages, with all of them maintaining porosity at activation temperatures above 100 °C and several of the materials maintaining porosity at 200 °C. ☐ The final chapter provides an overview of the most recent developments in carbazole ligand functionalization as well as the synthesis of novel octahedral coordination utilizing a metal capping strategy and carbazole ligands. The design of ligands exhibiting functional groups which would enhance the properties of the cage are given along with some preliminary work in the development of those cages. An outlook on the potential properties of these cages along with strategies for their synthesis and activation are given.
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Keywords
Coordination Cages, Diffraction, Gas Adsorption, Ligand Synthesis, Metal-Organic Materials, Surface Area