From molecular assemblies to extended frameworks of polyoxometalates through secondary metal ion coordination

The work detailed in this thesis is presented and discussed in three distinct chapters, which constitute a general and progressive study into polyoxometalate (POM) chemistry. This began with the development of a new synthetic strategy towards a family of transition metal-substituted POMs (TMSPs), continued through the study of POM physical properties in solution, and culminated in the empirical analysis of a new family of structures. During this work, the focus was primarily on crown-type POMs and their function as supramolecular inorganic hosts, both as discrete ‘zero-dimensional’ structures, and as an integral part of porous multi-dimensional frameworks. Four iso-structural triple Wells-Dawson-type phosphotungstate compounds, which incorporate six transition metal (TM) centres are discussed, with two of the compounds presented for the first time. An in-depth comparative study of the structures of the four TMSPs has been conducted, and related back to the synthetic conditions which gave rise to their formation. Electrochemical and electrocatalytic studies of the four compounds are also detailed. Although a great number of TMSPs of various shapes, sizes and composition is already known, the establishment of iso-structural TMSP families is still rare. In the second chapter, the application of isothermal titration calorimetry to assess the binding properties of the crown-type POM, [P8W48O184]40- ({P8W48}), is discussed. To facilitate these studies, {P8W48} was prepared in the absence of potassium to give two new mixed lithium/ammonium salts. Distortion of the {P8W48} ring, previously only observed in compounds with TM substitution, was observed both in solution and in the solid state, whilst this investigation also revealed ‘super-crown’ behaviour of the compound. {P8W48} is also an ideal building block for the construction of inherently-porous framework materials. However, the coordination of 1st-row TMs to this POM ring has so far proven unpredictable, and established compounds are often difficult to reproduce. Comprehensive analysis of {P8W48}-based frameworks was therefore performed to unite a group of previously disparate compounds. This class of inorganic framework materials is termed POMzites due to members’ all-inorganic POM scaffolds, their oxygen-rich and anionic nature, and their micro-scale porosity