Engineering functional nano-architectures utilising polyoxometalate based synthons

The host - guest chemistry of the isopolyoxometalate {W36} crown – like cluster is investigated. Previous reports showed that the cluster can specifically bind primary amines via a central binding pocket formed by six terminal oxo ligands on the all - inorganic, cation binding host. This assembly strategy was transformed to utilise the incorporation of long chain alkyl diammonium guest cations to physically define the supramolecular structure of the clusters with respect to each other and demonstrate the structure direction as a function of alkyl chain length. The systematic variation of chain length gave access to five unprecedented supramolecular assemblies. Diprotonated 1,8-diaminooctane molecules link the {W36} clusters into infinite 1-D zig - zag chains whereas huge trimeric assemblies were observed for 1,9-diaminononane and 1,10-diaminodecane linkers. Dumb - bell shaped dimeric units as a result of direct centre – to - centre linkages between the {W36} clusters using diprotonated 1,12-diaminododecane were prepared and triply protonated bis(hexamethylene)triamine was employed to obtain linear 1-D chains of directly connected {W36} cluster units. In an alternative approach, the linking of polyoxometalate – based secondary building blocks was investigated using transition metal linkers in organic solvents. It has been previously shown that Ag(I) is an excellent candidate due to its versatility and ability to readily adopt a wide variety of coordination environments. A series of novel architectures have been prepared including a supramolecular dimer based on decavanadate {V10}, an interconnected 2-D network incorporating the decatungstate species {W10}, extensively interconnected systems based on the unique {W19} cluster and unusual, highly symmetrical frameworks incorporating non – classical Dawson type units {SbW18} and {BiW18}. The newly discovered silver - tungstate systems, which feature varying degrees of attractive argentophilic silver - silver interactions, have proven to be effective precursors for the formation of interesting nano / sub - micro materials. For the ultimate study, three titanium embedded polyoxotungstates with unprecedented structural features are presented: a monotitanium containing tungstoantimonate featuring an unusual {Ti=O}2+ moiety, a hexatitanium containing tungstoarsenate featuring a highly charged {Ti4(H2O)10}16+ core and a decatitanium containing tungstoarsenate exhibiting the second largest structure of its type ever reported. Due to their highly unique nature, the systems have been fully investigated using DFT calculations yielding important results. The first cluster has been optimised with five sodium cations in the belt position, which in addition to reducing the high charge, influence a stabilisation of the antimony lone pairs. Furthermore, electrostatic potential calculations highlight the high electronegativity of the terminal oxygen on the single titanium centre, enhancing real potentiality as a reactive site for catalysis. The second cluster could also be isolated as an n-tetrabutylammonium salt and has been thoroughly investigated by ESI-MS studies providing direct information on the protonation state of the overall system