SPring-8, the large synchrotron radiation facility

Speaker:
  (1) Dr. Wolfgang Schmitt
  (2) Dr. Lionel Vayssieres
Affiliation: National Institute for Materials Science ICYS

Abstract (1)
　　The synthesis of hybrid organic-inorganic supramolecular structures is one of todayÅfs most active areas in chemical and materials research. The concept of hybrid inorganic/organic materials presents a way to tailor physical and chemical properties by reducing the dimensions and by influencing the devolution pattern of classical inorganic materials in the crystal structures. Nanosized structural motifs - embedded in organic matrixes - are regarded to display unusual physical properties significantly different to the bulk materials due to the coexistence of classical and quantum-mechanical phenomena.
　　Our work investigates structure directing effects of iminodiacetic acid substituted phenols and corresponding naphthyl derivates. These complexing agents (L) containing hydrophilic and hydrophobic parts react with FeIII salts to give dinuclear complexes where the transition metal ions are doubly bridged by hydroxo-, oxo- and carbonate groups, [Fe₂(μ-OH)(μ-CO₃)L₂]^3– and [Fe₂(μ-O)(μ-CO₃)L₂]^4–/6–. Their alkali counterions bind through O-donors to these negatively charged FeIII complexes and are linked to each other via water molecules forming supramolecular cross-linked coordination assemblies where self-assembling processes organize vast areas of different polarities. By using different newly synthesized organic complexing agents we obtained a series of unprecedented compounds with a variety of 3D architectures; we investigated these structures using single crystal X-ray analysis and scanning and transmission electron microscopy. Variation of the shape and functionality of the organic ligand provides a means to engineer different motifs of supramolecular coordination assemblies where the packing of hydrophilic and hydrophobic portions results for instance in bilayer arrangements, dense hexagonal arrays or porous networks. Thermal decomposition of the synthesized coordination networks in different atmospheres allows the preparation of nanomaterials. Total oxidation of the organic components results in purely inorganic phases. In an opposite process under strongly reducing conditions the organic components of the inorganic/organic structure can get activated and the organic areas of the structure provide potential reaction vessels for the organic components to react to carbon polymerization products. By applying this thermal decomposition we obtain new types nanosized materials or micro-capsules containing nanomaterials.
　　A further part of our work focuses on the synthesis of FeIII molecular clusters, particles and composites trying to associate structural motifs with useful magnetic properties such as hysteresis behavior. We studied the formation processes of ligand- stabilize oxo-clusters. These “0-dimensional” hybrid organic- inorganic structures are molecular ferrimagnetic systems and often reveal inter-cluster coupling combined with the properties of single molecule magnets (SMM).

Abstract (2)
　　The ability to design anisotropic nanoparticles with tailored aspect ratio and to order them into large 3-D arrays is an important challenge scientists have to face to create smart and functionalized nanomaterials. Our approach to control the size and shape of nanoparticles as well as the overall texture of particulate thin films is to tune their direct aqueous hydrolysis-condensation growth onto substrates by monitoring the interfacial thermodynamics of nanocrystals as well as their kinetics of heteronucleation. This is achieved by minimizing the surface energy at the water/oxide interface according to a general quantitative model based on Gibbs adsorption equation. Indeed, growing materials at very low interfacial tension, i.e. at thermodynamically stable conditions, allows the experimental control of the extension and rate of the nucleation stage and therefore different sizes, shapes, and orientations can be generated onto various substrates. Consequently, the design and fabrication of novel devices with tailored and engineered three-dimensional architecture can be obtained without template, surfactant, applied field, or undercoating. Such ideas will be demonstrated and illustrated on transition metal oxides based materials at nano-, meso-, and micro-scale, their growth as 2-, and 3-D arrays with controlled orientations onto various substrates as well as the characterization of their electronic structure, photoelectrochemical and magnetic properties.