Novel Nanomaterials Based on Inorganic Molybdenum Octahedral Clusters

In this contribution, we present a review of our recent works about the design of phosphor nanoparticles and materials based on [Mo6X14]2− cluster units (X = Cl, Br, I) as well as the functionalization of monocrystalline Si(111) surfaces by Mo6 clusters. Our purpose was to use the specific properties of cluster units found in inorganic solids for the design of new nanomaterials with potential applications in nanotechnologies (e.g. phosphor dyes for bio labelling, light emitting diodes, redox active molecular junctions…) using soft chemistry techniques. Phosphor Cs2Mo6X14@SiO2 nanoparticles emitting in 550–900 nm upon photo-excitation were synthesised using a ‘water in oil’ microemulsion technique. They exhibit a regular shape (~45 nm) and are based on [Mo6X14]2− cluster units and Cs+ counter cations embedded in a silica matrix. ((n–C4H9)4N)2Mo6Br14@ZnO colloids and nanopowders are based on the association of ZnO crystalline nano-particles with Mo6 cluster units adsorbed on their surface. They exhibit a large emission window in the visible region that can be tuned by modulation of the excitation wave length in order to selectively obtain the emission of either clusters units or ZnO nanocrystals or of both entities. Functionalized surfaces were obtained by the attachment of cluster units on a Si(111) surface through pyridine end capped organic chains using a multi-step procedure. Modified surfaces were characterized by X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM), IR and electrochemical analysis. The surface coverage can be modulated by the controlled introduction of inert organic chains among pyridine end-capped ones before the cluster anchoring step.