Electronically interesting materials formed from redox-active ligands
AuthorSutton, Ashley Leyton
AffiliationSchool of Chemistry
Document TypePhD thesis
Access StatusThis item is embargoed and will be available on 2021-11-15.
© 2019 Ashley Leyton Sutton
The work described in this thesis is targeted towards generating coordination frameworks with redox-active ligands. Redox-active coordination polymers are anticipated to possess interesting and useful electronic properties. Described in chapter two are approaches undertaken towards the generation of coordination polymers with favourable charge-transport. The first approach involves the novel and potentially redox-active ligand 2,3,7-trihydroxyfluorone which was synthesised and structurally characterised. Although the original intent was to generate porous coordination frameworks with this ligand, these efforts were unfortunately unsuccessful. A series of [4+4] Mo and W based metallocycles with the trianion of the 2,3,7-trihydroxyfluorone ligand were synthesised and characterised. The second approach described in chapter two focuses on improving charge transport in coordination polymers through the use of soft donor ligands. The synthesis and structures of several potential thio pro-ligands are reported. In-situ cleavage of the alkyl thiols was not achieved, however several 1D Cu(I) and Ag(I) polymers were structurally characterised with several of the pro-ligands. Whilst the overall focus of the project was coordination frameworks, several systems were explored in which the redox-active ligands were uncoordinated. In the first half of chapter three, charge-transfer complexes of 7,7,8,8-tetracyanoquinodimethane, TCNQ, and its derivatives were examined. Based on structural and spectroscopic characterisation the complexes were found to exist in a mixed-valent state, with the TCNQ/F4TCNQ molecules present in an oxidation state between the dianion and radical monoanion. The second half of the chapter examines an unusual Fe-based coordination polymer with radical TCNQ counter anions. Moessbauer spectroscopy indicates the Fe exists as Fe(III) and the compound exhibits the unusual Goldanskii-Karyagin effect. Magnetic measurements indicate weak antiferromagentic ordering. Chapter 4 is predominately a synthetic and structural study of X4TCNQ2- (X = H or F) based coordination polymers. Products include neutral and anionic metal-X4TCNQ2- coordination polymers. The X4TCNQ2- ligand can act as a tetradentate, tridentate and bidentate bridging ligand allowing for a range of coordination polymers. Co-ligands have been shown to compete for metal coordination sites and may have a significant structure directing influence on the resultant coordination polymer. When nitrile arms are uncoordinated there is a clear tendency for them to participate in hydrogen bonding with solvent molecules or co-ligands. Chapter 5 describes the exploration of the host-guest chemistry of the [MnII(F4TCNQ-II)(py)2] framework. Selective uptake of CO2 occurs, with in-situ powder X-ray diffraction experiments revealing a ’gating’ mechanism. Intercalation of the framework with various electron acceptors is associated with significant changes to the spectroscopic and electrical properties. A correlation is observed between the strength of the electron acceptor and the optical bandgap of the host-guest material. A similar trend is apparent for the electrical conductivity of the framework. Solid-state density functional theory calculations aid in the rationalisation of these experimental observations. Chapter 6 gives a brief overview of the experimental results and provides a discussion of the overarching themes encountered in this thesis.
KeywordsX-ray crystallography; Coordination polymers; Electrical conductivity; Metal organic framework; MOF; TCNQ; F4TCNQ
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