Guest exchange successive

M4L4 Tetrahedra with Successive Guest Exchange. 88... 

Van Koten et al. successfully prepared silicon-based dendrimers with a polyca-tionic branching shell. The dendrimer type shown in Fig. 4.37 consists of a non-polar core (tetraarylsilane) bearing an ionic layer which, in turn, is surrounded by a less polar polyether shell [67]. Such dendrimers are predestined for potential inclusion of anionic guests - with anion exchange - in the positively charged host scaffold. 

Cation exchanged zeolites are successfully applied as catalysts or selective sorbents in separation technologies. " For both catalytic and sorption processes a concerted action of polarizing cations and basic oxygen atoms is important. In addition, transition metal cation embedded in zeolites exhibit peculiar redox properties because of the lower coordination in zeolite cavities compared to other supports." " Therefore, it is important to establish the strength and properties of active centers and their positions in the zeolite structure. Various experimental methods and simulation techniques have been applied to study the positions of cations in the zeolite framework and the interaction of the cations with guest molecules.Here, some of the most recent theoretical studies of cation exchanged zeolites are summarized. 

There are a number of techniques that have been successfully applied to synthesize modified hydrotalcites (48). The most commonly method used is the co-precipitation of two metal salts in alkaline solution at a constant pH value of about 10. Another method uses the classical ion exchange process in which the guest anions are exchanged with the anions in the interlayer spaces of preformed layered double hydroxides to produce specific anion intercalated modified hydrotalcites. StiU another method is a lattice reconstruction after heating, i.e., calcination, which is based on the structural memory effect of these materials, due to which the original structure is reproduced after rehydration. 

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