Intercalated guest

The family of true clathrates based on hydrocarbons only is further enriched by the inclusion compounds of 48 with benzene (1 1) and p-xylene (2 1) 90> (Table 19). Figure 28 illustrates the structure of 48 benzene (1 1). The structure of the p-xylene clathrate shows intercalated guest molecules at centers of symmetry in the crystal lattice. Both clathrates are rather unstable at ambient temperatures and decompose easily, e.g. on exposure to X-rays (even in the presences of mother liquor). The 48 p-xylene clathrate is unstable to such a degree that decomposition occurs at low temperature. 

Fig, 11. Diagrammatic representation of a planar intercalating guest molecule complexed between adjacent base pairs of the double helical DNA host structure. The base pairs and intercalator are represented by stippled rods. Note the increased base pair separation caused by complexation with the guest. 

Zinc me.w-tetrakis (p-carboxyphenyl)porphyrin (ZnTPPC), a neutral molecule, can be readily intercalated into the Li-Al LDH-myristate interlayers by replacing the myristate ions [101b], However, the uptake of the ZnTPPC into this material was minimal. The diffraction pattern showed that, as is the case with other porphyrins, ZnTPPC intercalates with its plane perpendicular to the metal hydroxide layer. The emission spectrum (excitation at 407 nm) of the intercalated guest is similar to that of nonaggregated ZnTPPC in solution (Fig. 53), suggesting that ZnTPPC is solubilized in the LDH in a dispersed form and not as an aggre-... 

Most of the zeolite syntheses carried out under hydrothermal conditions directly results in the formation of three-dimensional crystalline frameworks. However, several zeolites, like MCM-22 or ferrierite, can be synthesized in the form of layered precursors, which can be transformed by further thermal treatment into the three-dimensional crystal structure. These layered solids arouse an interest due to their ability to intercalate guest molecules between two neighboring zeolite layers. Using a proper treatment, layered zeolite materials can be delaminated while the structure of layers is preserved, which makes accessible all active sites located on the external surface of such catalyst. By adding proper inorganic guest molecules functioning as pillars, the control of the interlayer distance can be achieved. Such materials... 

Intercalation Through Electron Transfer. The direct intercalation of electrically neutral molecules in layered neutral crystals is only possible if these guest molecules are Lewis bases (organic amines, phosphines, thiols, etc) or strong electron donors (alkali metals) and if the host lattice is reducible. Indeed, the electron transfer mechanism from the intercalated guest to the host lattice is governed... 

More complex intercalate guests can be introduced as well, eitha- by ion exchange or by delamination of the compounds and subsequent reaggregation with new intercalate guests. Some examples of such compounds will be discussed further in the application section. 

A good example of a photochemical reaction of an intercalated guest species is the trans-cis isomerization of the azo dye shown here in magadiite ... 

An entropy effect may also contribute to the enhanced reactivity of the hydrated acids. The displacement of water molecules, i.e the transfer of water molecules from the constrained interlayer space into the dispersion medium, compensates or even overcompensates for the loss of entropy of the intercalated guest molecules. In contrast, the penetration of guest molecules between the layers of dehydrated acids is accompanied by a loss of entropy. 

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