Configurable Nanosized Metal Oxide Oligomers via Precise “Click” Coupling Control of Hybrid Polyoxometalates

ABSTRACT: Polyoxometalates (POMs) are discrete clusters of redox-active metal oxides, many of which can be linked to organic moieties. Here, we show how it is possible to link Mn Anderson POMs to terminal alkyne and azide groups and develop appropriate conditions for their Cu-catalyzed alkyne−azide cycloaddition (or “click” reaction). These coupling reactions are then used to link the clusters together, forming monodisperse linear Mn Anderson oligomers, here with examples ranging in size from two to five clusters. These oligomers are built up sequentially using a combination of mono- and difunction-alized clusters, giving an unprecedented level of control over the size and structure of the resulting hybrid POMs. This new synthetic methodology therefore opens the way for the synthesis of metal oxide hybrid oligomers and polymers by coupling control, minimizing side products, producing nanosized molecular hybrid organic−inorganic oxides ca. 4−9 nm in size, with molecular weights ranging 2−10 kDa. Polyoxometalates (POMs) are discrete molecular forms ofmetal oxides, displaying a variety of electronic1,2 and catalytic3,4 properties and vastly increased solubility and structural variety compared to bulk metal oxides, but their synthesis involves complex self-assembly processes and can be hard to predict or design. Many POM structures are able to form organic−inorganic “hybrids”, where the metal−oxygen cores are directly connected to organic moieties. These organic components could provide a more predictable means of manipulating POM clusters than has been previously possible, allowing them to be incorporated into devices and materials, or shaped into specific function-driven architectures. The Lindqvist [M6O19