Cocondensation methods

This article is organized primarily according to the periodic table and secondarily with regard to the importance of substrates found to react with metal vapor atoms. Tables, lists, and figmes will display many of the known compounds prepared via the metal vapor-substrate cocondensation method and give further information about physical properties, chemical behavior, spectroscopic data, and structural details. 

Table 9 Late transition metal complexes from diene, triene, and tetraene ligands, prepared by the metal atom/ligand cocondensation method...

In our study, a cocondensation method [19] was used to enable the homogeneous incorporation of functional groups (Fig. 27.5a) like e.g. alkyl chains or cyano-propyl groups which differ strongly in polarity. This resulted in a strong influence on the diffusion coefficient of the probe molecule [20]. 

Fig. 27.5. Mesoporous silica nanoparticles as novel drug delivery systems, (a) Cocondensation method to form functionalized mesoporous silica structures in a surfactant template synthesis, (b) TEM image of mesoporous silica nanoparticles and sketch of a novel drug delivery particle which contains functionalized pores, closed by a gate, and is decorated with ligands for cell targeting, (c) Cell targeting by ligand-receptor interaction at the cell membrane, endosomal uptake and controlled release after pH change from early to late endosome...

Zeidan et al. [16] incorporated arylsulfonic acid and alkylthiol groups into mes-oporous silica by a cocondensation method, where 2-(4-chlorosulfonylphenyl)-ethyl-trimethoxysilane and 3-mercaptotrimethoxysilane were added to tetraethyl orthosilicate, forming a mesoporous silica (SBA-15) material via a sol-gel process (Fig. 23.4a). The resulting catalysts exhibited far greater activity and selectivity than materials containing only the acid. These randomly distributed catalysts achieved in the best case a per site yield (defined as moles of product per mole of sulfonic acid) of 82 and a 95% selectivity for bisphenol A, compared to a per site yield of 18 and 58% selectivity for bisphenol A when using homogeneous sulfonic acid alone. 

The Grignard analogues of Ca, Sr, and Ba are much less important for synthesis. However, alkyl and aryl halides of these metals have been prepared The cocondensation method has been adapted successfully. In general, the tendency for Wurtz reactions... 

Cocondensation Methods Using Static Reactors(4-7,10), Background. 

Postsynthetic grafting and cocondensation methods both have advantages for the synthesis of ordered mesoporous organic-inorganic hybrids. However, what are the potential limitations that need to be considered for optimizing the material synthesis following these methods ... 

Cocondensation methods, on the other hand, can sometimes lead to poorly ordered solids, especially at high organic content. Furthermore, the accessibility of the functions located deep in thick walls can be questioned (especially for materials such as SB A-15 with thick silica walls). The functional groups must resist the conditions employed for the synthesis (acid, base, hydrothermal) and for the template removal (chemical extraction). Template removal might sometimes be incomplete in the case of ionic surfactants and silanol alkoxylation by alcohol solvents takes place (transesterification). In addition, the bridged silses-quioxane precursors for the synthesis of PMOs are expensive or not always readily available. 

There are two main techniques for the incorporation of atomically dispersed titanium into a mesoporous silica framework. In the cocondensation method a titanium source is added during the preparation of the silica material framework and formation proceeds via simultaneous condensation of both titanium and silicon precursors, resulting in titanium incorporation throughout the material. Conversely, postmodification involves the grafting of a titanium-alkoxide precursor to the pore surface by condensation with surface hydroxyls of a preformed silica material. This forms a surface-modified titanium silicate. 

Figure 13.3 Schematic diagram for the (a) grafting and (b) cocondensation method in the preparation of organic groups functionalized materials.

FIGURE 4.2 Schematic representation of functionalization of mesoporous sihcas by the cocondensation method. 

In conclusion, various types of ionically modified surface-functionalized silicas displaying high structiu-al regularities are accessible via template-directed hydrolysis-cocondensation methods. These methods involve the use of ionic... 

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