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Title: Discovery of novel polyoxopalladates and investigation of their supramolecular behaviour
Author: Christie, Lorna Grace
ISNI:       0000 0004 7226 5673
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2018
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Polyoxopalladates (POPds) are an emerging class of unconventional polyoxometalates (POMs) which are particularly interesting due to the catalytic properties of palladium. Until recently, POPds were limited to low nuclearity {Pd12} and {Pd15} archetypes. However, in 2012, the giant {Pd84}Ac macrocycle was discovered, becoming the largest of this family to date. One of the major barriers to the discovery of POMs in general is that the chemistry relies heavily on crystallisation. The presence of POMs in solution is often overlooked if no crystalline products emerge. Furthermore, their behaviour in solution is not well-understood. This thesis expands on the family of POPd macrocycles and explores the supramolecular behaviour of the POPd macrocycles using solution analysis techniques such as SEC-HPLC, ESI-MS and NMR spectroscopy. In the first section of work, a new synthetic route to making {Pd84}Ac is reported, whereby palladium acetate is substituted for sodium acetate, allowing the carboxylate source to be added separately. This new synthetic route was investigated to explore the formation of novel macrocycles by varying the acetate ligand. Initial results showed this to be possible by substituting acetate for propionate. This yields a smaller {Pd72}Prop macrocycle, which was characterised crystallographically. An SEC-HPLC approach was then adopted to screen many small-scale reactions for the formation of other large palladium macrocycles, using a wide variety of carboxylate sources. This led to the discovery of {Pd84}Gly, an exact structural analogue of {Pd84}Ac. IMS-MS was employed to assess the relative sizes of the new macrocycles in solution, confirming the presence of {Pd72}Prop and {Pd84}Gly. The structure of {Pd84}Gly was later confirmed crystallographically. Having shown the screening method to be successful in detecting novel POPds in solution, this approach was expanded on. In the second section, SEC-HPLC was used to screen many small-scale reactions containing different combinations of polyphosphate solutions and carboxylate ligands, in the presence of Pd(NO3)2. SEC-HPLC indicated the presence of a variety of species larger in size than {Pd84}Ac, however further analysis using ESI-MS was not able to identify these products, most likely due to their decomposition under the mass spectrometry conditions, or poor separation in the SEC column. Over this course of this work, two smaller POPd clusters containing the squarate ligand were isolated: {Pd11} and {Pd8}. In the third section, two mass spectrometry techniques were employed to analyse the real-time self-assembly of the {Pd84}Ac, {Pd72}Prop and {Pd84}Gly macrocycles. Analysis was carried out using two methods: SEC-HPLC-MS and direct injection of a desalted sample (Desalted-MS). Initial results showed the loss of acetate ligands when using SEC-HPLC-MS, which was confirmed by comparing identical crystalline samples of {Pd84}Ac analysed with each technique. The {Pd72}Prop macrocycle was found to appear in solution after five days, and exhibits building units analogous to those seen in the assembly of {Pd84}Ac, suggesting a similar build-up mechanism to {Pd84}Ac. Likewise, {Pd84}Gly was found to appear in solution after four days and also exhibits the same analogous building units. Furthermore, a {Pd30} species was observed in SEC-HPLC-MS studies of the {Pd84}Gly reaction, indicating a possible template or smaller macrocycle which has not yet been isolated. In the final section, the molecular encapsulation potential of {Pd84}Ac was explored using 1D and 2D NMR techniques. Using 1H NMR spectroscopy, interactions were observed between {Pd84}Ac and a series of polyamine guests, indicating a fast exchange regime between the free and encapsulated guest molecules. Subsequent 1H DOSY NMR spectroscopy showed the diffusion coefficient of 1,8-diamionooctane matched that of {Pd84}Ac when the compounds were mixed, confirming the strong host-guest interaction. Following this, the [Ru(bpy)3]Cl2 (Ru-bpy) complex was selected as a potential guest within the {Pd84}Ac cavity due to its suitable size and photochemical properties. 1H NMR spectroscopy showed a significant shifts in the Ru-bpy 1H signals in the presence of {Pd84}Ac, indicating a fast exchange interaction. 1H DOSY NMR spectroscopy revealed the coefficient of the Ru-bpy complex was found to decrease dramatically when in the presence of {Pd84}Ac.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry