Guest-directed supramolecular architectures of {W36} polyoxometalate crowns

The {W36} isopolyoxotungstate cluster provides a stable inorganic molecular platform for the binding of inorganic and organic guest molecules. This is achieved by a binding pocket formed by six terminal oxo ligands located in the central cavity of the all-inorganic cation binding host. Previously it was shown that the cluster can specifically bind primary amines and importantly, functionalized diamines through a combination of electrostatic and hydrogen bonding interactions. Here we transform this assembly strategy to utilize the binding of long-chain alkyldiammonium 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 the chain length gives access to five supramolecular assemblies which were all fully characterized using single crystal XRD, TGA, 1H NMR, and elemental analysis. In compound 1, diprotonated 1,8-diaminooctane molecules link the {W36} clusters into infinite 1D zigzag chains, whereas compounds 2 and 3 feature trimeric {W36} assemblies directly connected through protonated 1,9-diaminononane (2) or 1,10-diaminodecane (3) linkers. Compound 4 contains dumb-bell shaped dimeric units as a result of direct center-to-center linkages between the {W36} clusters formed by protonated 1,12-diaminododecane. In compound 5, triply protonated bis(hexamethylene)triamine was employed to obtain linear 1D chains of directly connected {W36} cluster units.