Guest-host structure

It is not easy to control the steric course of photoreactions in solution. Since molelcules are ordered regularly in a crystal, it is rather easy to control the reaction by carrying out the photoreaction in a crystal. However, molecules are not always arranged at an appropriate position for efficient and stereoselective reaction in their crystals. In these cases inclusion chemistry is a useful technique, as it can be employed to position molecules appropriately in the host-guest structure. Chiral host compounds are especially useful in placing prochiral and achiral molecules in suitable positions to yield the desired product upon photoirradiation. Some controls of the steric course of intramolecular and intermolelcular photoreactions in inclusion complexes with a host compound are described. 

Phthalocyanines have attracted particular attention as potential surface modifiers due to their stability and tendency to form ordered structures directed by dispersion forces. They are inherently host-guest structures with a readily interchangeable coordinating metal ion, which in the solid state results in a tunable bandgap. At a surface, in addition to possibly interesting electronic... 

Mechanisms of interactions between cyclodextrins and enantiomers were reported by Parker and Kataky [15,16]. The complexes have a 1 1 stoichiometry and they all have a host-guest structure. 

The cocrystallization of molecules of different shapes may lead to a host/ guest structure where the guests are included in more or less open cavities... 

One of the first formal definitions of a supramolecular cage-like host-guest structure was proposed by... 

A large number of host-guest structures are known, but a reversible guest exchange or chemical transformation of the guest inside a coordination polymer framework has been described for only a few (257, 281-283). In most cases the integrity of the inclusion lattice cannot be effectively maintained in the absence of guest molecules... 

Reinhoudt s preparation of diastereomeric complexes 15 guest, each differing in the orientation of the contained guest, provided means for the discovery of a new form of stereoisomerism, carceroisomerism [26]. Application of these novel host-guest structures as molecular switches has been suggested [25, 26]. 

Table 3 Watersoluble Host-Guest Structures for the Incorporation of Fullerenes...

It should be mentioned that unusual cationic clusters may be stabilized in certain host-guest structures in the solid state. For instance, the extremely electron-poor clusters Ins and Ins have been claimed to form in zeolite A (see ref. 111). 

A possibility to prove the molecular inclusion of the guest in the host cavity, at least in the crystalline state, is given by X-ray analysis There are different fundamental types of host/guest structures that have to be distinguished ... 

These composite structures are also known as intergrowth or host-guest structures. Figure 1.3-9 illustrates an example of a host with channels along a, in which atoms of the substructure with a periodicity Xa reside as a guest. 

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