Biologically inspired polyoxometalate-surfactant composite materials.: Investigations on the structures of discrete, surfactant-encapsulated clusters, monolayers, and Langmuir-Blodgett films of (DODA)40(NH4)2[(H2O)n⊂Mo132O372(CH3CO2)30(H2O)72]

A detailed analysis of the supramolecular architecture of the nanoporous surfactant-encapsulated cluster (SEC) with theempirical formula (DODA)(40)(NH4)(2)[(H2O)(n)subset of Mo132O372(CH3CO2)(30)(H2O)(72)] 1 (n approximate to 50) is presented. The open framework architecture of the Keplerate cluster is investigated by means of small angle neutron scattering (SANS) in CDCl3 solutions containing discrete SECs. A simplifying core-shell model of 1 is developed, which describes the SEC as a solvent-filled nanocavity, surrounded by two concentric shells (a first polyoxometalate shell of 2.96 nm outer diameter, and a consecutive surfactant shell of 6.18 nm outer diameter, respectively). The model is successfully applied to probe the content of H2O/D2O guest molecules in the Keplerate host. Different surface analytical techniques are applied to characterize the hierarchical structures of monolayers and thin films of 1. Monolayers at the air-water interface are investigated by means of optical ellipsometry and Brewster angle microscopy. Electron density profiles of the monolayers of 1 are gained from synchrotron X-ray reflectance (XRR) measurements that provide further evidence for the supramolecular core-shell architecture of the SEC. Within the spatial resolution limits of these analytical methods, the current data support a monolayer model consisting of hexagonal close-packed arrays of discrete SECs, floating at the air-water interface. Langmuir-Blodgett (LB) transfer of compressed monolayers on to a solid substrate leads to homogeneous multilayers. In the XRR spectra of LB multilayers of 1 multiple Bragg reflections appear, thus indicating an intrinsic tendency of the SECs to adapt a 3-dimensional, highly ordered solid state structure. Considering the huge variety of structurally different polyoxometalates and the possibility to tailor the surfactant shell by means of classic organic synthesis, the self-organization of hierarchically structured thin films and solids based on SECs bears promising perspectives towards the engineering of functional materials.