Organic-inorganic hybrid materials : new functionalised polyoxotungstates

Polyoxometalates are the polyoxoanions of the early transition metals, especially tungsten, molybdenum and vanadium. Although they were first described in the 19th century, their development was slow until modern experimental techniques enabled a greater understanding of their structures and properties. In the last 40 years a large variety of shapes, sizes and compositions have been investigated; functionalisation via covalent grafting of organic groups onto the polyoxometalate clusters is less investigated and provides a method of fine tuning the properties of these materials towards desired applications. Polyoxotungstates (polyoxometalates with tungsten as the metal) are investigated here, those with the Keggin structure being of interest due to the relatively easy formation of lacunary anions which have a highly nucleophilic surface and can react with electrophilic groups to add functionality to the cluster. Organophosphonyl and organosilyl derivatives are prepared with formulae (NR¹₄)₃Hn[XW₁₀O₃₆(R²PO)₂], (NBu₄)₃[XW₉O₃₄(R³SiO)₃(R³Si)], (NBu₄)₃Hn[XW₉O₃₄(tBuSiOH)₃], (NBu₄)₃Hn[XW₉O₃₄(tBuSiO)₃(SiR⁴)], (NBu₄)₃Hn[XW₉O₃₄(R²PO)₂] or (NBu₄)₃Na[SiW₉O₃₄(R²PO)₃] (X = Si or P; R¹ = Bu or Et; R² = Et, H₂C=CH, H₂C=CHCH₂, H₂C=CHC₆H₄, HOOC(CH₂)m (m = 1 or 2) or H₃CCOC₆H₄; R³ = H₂C=CH or H₂C=CHCH₂; R⁴ = R³ or (CH₂)₃Br; n=0 or 1). The structures are confirmed and investigated using multinuclear NMR (¹H, ³¹P and ²⁹Si), IR, MS, EA, single crystal X-ray diffraction and Cyclic Voltammography. The derivatised polyoxotungstate clusters have the potential to take part in further reactions using the organic functionalities to create inorganic-organic hybrid materials which retain the electrochemical properties of the polyoxotungstate units. Examples include the polymerisation of carbon double bonds and condensation reactions of carboxylic acids and amines; both are investigated here. Radical polymerisation is successful in creating polymeric materials, either through single reaction of the polyoxotungstate cluster or a co-polymerisation reaction with a second co-monomer. Reaction with amines did not proceed as expected, instead one of the RPO groups was removed from the cluster, producing a new set of singly derivatised clusters, [SiW₁₀O₃₆(R²PO)]⁶⁻ from [SiW₁₀O₃₆(R²PO)₂]⁴⁻. These create potential for a product with asymmetrically functionised polyoxotungstates containing a mixture of R groups [SiW₁₀O₃₆(R²PO)(R²bPO)]⁴⁻, thus providing greater control over the organic functionality on the cluster and increasing the number of potential derivatives available.EThOS - Electronic Theses Online ServiceGBUnited Kingdo