Metal oxide-based networks

A. Muller, P. Kogerler, and C. Kuhlmann, A variety ofcombinatorially linkable units as disposition from a giant icosahedral keplerate to multi-functional metal-oxide based network structures, Chem. 

Despite their solid appearance, within the gel the liquid component is mobile and is only held by capillary forces. The solid network can be either a covalent polymer or a supramolecular assembly of small molecules. The latter class of compound, termed low molecular weight gelators (LMWG) of which 14.11 14.15 are examples, is perhaps of most interest to supramolecular chemists. Perhaps the most well known gels are metal oxide based polymeric materials produced by the sol-gel process. The sol-gel process involves the hydrolysis and polycondensation of monomeric metal salts such as early transition... 

Soler-Illia, G.J.A.A. Sanchez, C. Lebeau, B. Patarin, J. Chemical strategies to design textured silica and metal oxide-based organised networks from nanostructured networks to hierarchical structures. Chem. Rev. 2002, 102, 4093. 

Catalysis by sol gel doped silica-based materials has become in the last 20 years a prominent tool to synthesize a vast number of useful molecules both in the laboratory and in industrial plants.12 The underlying basic concept of all sol-gel applications is unique one or more host molecules are entrapped by a sol-gel process within the cages of an amorphous metal oxide where they are accessible to diffusible reactants through the inner pore network, which leads to chemical interactions and reactions (Figure 5.3). 

A glass is an ionic solid with an amorphous structure resembling that of a liquid. Glass has a network structure based on a nonmetal oxide, usually silica, Si02, that has been melted together with metal oxides that act as network modifiers. ... 

As the example of molecular magnetism shows, modern magnetochemistry is now seeing more efforts toward the directed design and synthesis of novel magnetic materials, usually based on molecular building blocks as opposed to traditional two-or three-dimensional solid-state networks (bulk metals, metal oxides, etc.). 

This type of reaction leads to the formation of an inorganic polymer or a three-dimensional network formed of metal oxianions. The above-described process is called metal alkoxide-based sol-gel. The literature contains excellent reports providing in-depth analyses of this method [100,223]. The sol-gel process allows for very good chemical homogeneity and offers the possibility of obtaining metastable phases, including the amorphous phase. This process normally promotes the formation of amorphous metal oxides, which require thermal or hydrothermal treatment to promote crystallization. Several factors affect the sol-gel process, including the kind... 

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