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Title: Photophysical and catalytic properties of a cubic coordination cage
Author: Train, Jennifer
ISNI:       0000 0004 8509 1385
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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Chapter One consists of an introduction to supramolecular chemistry and supramolecular photochemistry. With particular focus on metal-organic cages and their application in catalysis and photocatalysis. Chapter Two describes the synthesis of an Os(II) cage, photophysical properties and guest binding. Successful synthesis of water soluble [Os4Zn4(Lnap)12]X16 coordination cage complex (where Lnap = bidentate pyrdiyl-pyrazole chelating ligand with a 1,5-dinaphthalene spacer and X = perchlorate or chloride) and [Os(Lme)3]X2 (where Lme = methyl pyridyl-pyrazole and X = potassium hexafluorophospate or chloride). Both show strong visible absorption and emission at 630 nm. As well as reversible oxidation at 0.7 V and 0.6 V respectively. In addition, binding in the cavity of five guests is presented through X-ray crystallography, NMR titrations and luminescence titrations. Chapter Three displays the evidence of photoinduced electron transfer detected by UV/vis transient absorption (TA) spectroscopy of three host.guest complexes. Ultrafast TA spectroscopy measurements show formation of a charge-separated Os(III)/guest•- state, due to cage-to-guest photoinduced electron transfer. The states are formed within 13-21 ps and decay within 185-205 ps. Control experiments with a competing guest show that binding is required for the electron transfer to occur, as well as use of [Os(Lme)3]X2 which shows that the Os(II) unit needs to be assembled in the cage structure for PET to occur. Chapter Four details the study of binding of disulfide guests and looks for evidence of photoinduced electron transfer between cage and guest. The study indicates that there is a two-step binding profile for the binding of a selection of four aryl-disulfide guests. Binding with [Os4Zn4(Lnap)12]X16, [Cd8(Lw )12](NO3)16 and [Co8(Lnap)12]Cl16 has been analysed with consistent binding constants of 103 – 105 M-1 via different mediums: X-ray crystallography, NMR titration and luminescence titrations. Chapter Five describes the use of [Os4Zn4(Lnap)12]X16 to affect the catalysis of 5- nitrobenzisoxazole and the effects of changing the oxidation state of the cage. [Os4Zn4(Lnap)12]X16 and [Co8(Lw )12](BF4)16 similarly catalyse the Kemp elimination of 5- nitrobenzisoxazole with a rate enhancement of 6 and 4 respectively, at pH 8.2. Control tests using a competitive binder also show an unexplained rate enhancement. Additionally, oxidised Os(III) cage catalyses the Kemp elimination reaction at a similar rate to the Os(II) cage.
Supervisor: Ward, Michael D. ; Weinstein, Julia Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available