Organically functionalized metallic oxo-clusters: Structurally well-defined nanobuilding blocks for the design of hybrid organic-inorganic materials

Hybrid organic-inorganic materials, in which organic and inorganic components are combined over a length scale ranging from a few Angstroms to a few tens of nanometers, are nanocomposites which offer huge potentialities for high added value applications. Numerous hybrid organic-inorganic materials have been developed in the past few years, mainly by taking advantage of the mild chemical conditions of the sol-gel process. Yet, the sol-gel process generally yields amorphous materials which exhibit some polydispersity in the size and composition of the inorganic components of the hybrids. Moreover, controlling the interactions between the inorganic and organic components is not an easy task. One possible solution to overcome the polydispersity problem and achieve better control of the interactions is to use perfectly defined inorganic nanobuilding blocks such as metal ore-clusters which exhibit sizes around 10 Angstrom. When properly functionalized, they can be assembled, without being damaged, into various types of structures. Examples taken from polyhedral oligomeric silsesquioxanes, monoorganotin ore-clusters, transition metal oxo-clusters and organically modified polyoxometalates will be presented and discussed relative to their synthesis, functionalization and assembling strategies.