Polyoxometalate Clusters in a Supramolecular SelfOrganized Environment: Steps Towards Functional Nanodevices and Thin Film Applications

Abstract

A review. Polyoxometalates (POMs) represent a well-defined class of inorg. compds. with potential applications in fundamental and applied science. To implement POMs in functional materials and nanotechnol. devices it will be of paramount importance to control the surface chem. properties of the primarily water-sol. clusters. Two different approaches toward this goal are presented here, which are primarily based on ion-exchange of POM countercations with suitable surface-active compds. In the first method, the POM countercations are replaced by charged surfactants, leading to discrete hydrophobic surfactant-encapsulated clusters (SECs). These materials combine the physicochem. properties of the inorg. POM core with the diverse assets of org. compds. including wetting, adhesion, soly. as well as bio-compatibility. Using Langmuir-Blodgett techniques, it is feasible to deposit SEC mono- and multilayers and thus to engineer highly-ordered POM arrays that approach macroscopic length scales. In the second method, multi-layered thin films of POMs and polyelectrolytes are co-assembled on arbitrary substrates by a sequential deposition process. These films are robust and permeable, which renders them potentially attractive for applications in heterogeneous catalysis, electrochem. and mol. recognition devices, such as sensors. [on SciFinder (R)]