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Title: Understanding the reorganisation of lacunary [γ-SiW10O36]8- during the synthesis of transition metal substituted polyoxotungstates
Author: Winter, Ross S.
ISNI:       0000 0004 5360 7463
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2014
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One of the biggest challenges in chemistry is the selective synthesis of molecular structures in a controlled and predictive manner. Within polyoxometalate chemistry this is especially true and there is still much left unknown regarding how and why particular architectures form and how specific structures can be selected for. The lacunary Keggin polyoxotungstate K8[γ-SiW10O36]•12H2O is a very versatile starting material in the synthesis of transition metal substituted polyoxometalates. It is capable of undergoing several isomerisations and changes in nuclearity as it reacts, but the process is poorly understood. This thesis examines the interplay between the reaction conditions and the final architectures obtained when using {γ-SiW10O36}, with the intention to understand the mechanisms that underpin its reactivity. Using high pH reaction conditions {γ-SiW10O36} readily reorganised and it was capable of forming some of the most sophisticated transition metals substituted polyoxometalate structures known to date in which three unique Keggin are found concurrently around a cubane-like transition metal core. Furthermore, high pH conditions lead to the discovery of the first clusters containing the previously unreported {γ-SiW9O36} species, which was able to trap a highly transition metal substituted Keggin core. The synthesis of the {γ-SiW9O36} containing cluster was particularly interesting as within the crystallisation, “intermediate” crystals could be obtained which were shown by microscopy to be sacrificial nucleation sites for crystal growth of the final products. The final and intermediate products were composed of isomeric building blocks, which varied only in the positions within the architecture that were occupied by transition metal. Using a limited parameter synthetic approach with only two reaction components, it was shown that we could selectively produce each type of isomer and hence could for the first time control the exact positioning of transition metals within a polyoxometalate. The building blocks were also shown to dimerise when the concentration of transition metal was increased. Using {γ-SiW10O36} it was possible to synthesize {M2(B-β-SiW8)2} clusters (M = Mn, Fe, Co, Ni, Cu, Zn) and use these as clusters as the first known {B-β-SiW8} based starting materials. This opened up the potential for studying the solution phase behaviour of {B-β-SiW8} for the first time in POM history.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry