Novel copper coordination compounds of amino acids and pyridines : synthesis, characterisation, physical properties, and future prospects for gas adsorption

Fellows, Simon Matthew

September 2017

Thesis or dissertation

© 2017 Simon Matthew Fellows. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

The primary goal of the work discussed in this thesis was to assess the capability of cheap, readily available ligands, e.g. pyridines and amines, to produce new coordination compounds, primarily with copper, that could lead to the development of novel materials for gas adsorption. Chapters 1 and 2 introduce the topic and methods respectively, results are contained within chapters 3-6.

Chapter 3 describes the synthesis, polymorphism and solid-gas reactions of [CuCl₂(RPy)₂] and (RPy-H)[CuCl₄] (RPy: R = 4-CO₂H, 4-CONH₂, 3-CONH₂). The polymeric [CuCl₂(RPy)₂] compounds appear blue, while the equivalent (RPy-H)[CuCl₄] salts appear yellow or green depending on the geometry of the [CuCl₄]²⁻ ion. Exchange between the two types of compound is possible through the gain and loss of HCl, although the exact mechanism and what causes the observed differences in reaction is uncertain. [CuCl₂(RPy)₂] compounds could be developed further into porous materials through the use of simple tris(pyridine) ligands.

Chapter 4 discusses a facile synthetic method for [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] compounds via the oxidation of CuCl in the presence of [CuCl₂(RPy)₂]n (RPy: R = 4-Me, 4-NH₂, 4-NMe₂). The production of the [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] cluster only seems to occur for compounds where the [CuCl₂(RPy)₂] complex is non-polymeric or at least weakly polymeric. Only one porous [Cu₄(μ⁴-O)(μ²-Cl)6(RPy)₄] compound is known with 1,4-diazabicyclo[2.2.2]octane, but there is potential for others to be discovered. However, these compounds are not as stable as other compounds that might be used for gas adsorption and are better suited for catalysis applications.

Chapter 5 focuses on the copper and zinc coordination chemistry of amino acids with general formula CO₂H-(CH₂)n-NH₂ (where n = 1-5 and 7). Amino acids are a good potential ligand for CO₂ capture given their similarity with monoethanolamine: the most common chemical used in industrial technologies. However, their flexibility and propensity to form zwitterions means that the majority of compounds produced were adducts of copper halides, and those which were not appeared too dense for application in CO₂ adsorption. The copper halide adducts showed similar HCl/HBr gas uptake as the [CuCl₂(RPy)₂] compounds in chapter 3, although the reverse reaction was much slower with very little change observed over several months.

Lastly, chapter 6 details the novel coordination compounds created using Cu and a combination of various benzoic acid based and pyridine-based ligands. Most of the novel compounds have only been structurally characterised and no general conclusions can be made about their structures due to the lack of data. One compound made with 4-hydroxybenzoic acid and pyrazine in methanol showed promise for methanol adsorption, however the compound could not be made reliably or quantities large enough to study the phenomenon further.

Department of Chemistry, The University of Hull
Prior, Timothy J.
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