Lattice inclusion complexes

It should be noted that not all host-guest phane complexes are of the type just described. Indeed, a significant number of lattice inclusion complexes also occur. In these, the host molecules stack such that a channel running between hosts is formed. Guest molecules occupy this channel. As expected, such an arrangement is usually reflected by relatively poor host-guest selectivity. 

Two other types of system undergo solid-state polymerization which is to a considerable extent lattice controlled. One such type consists of lattice inclusion complexes ... 

Fig. 2. Classification/nomenclature of host—guest type inclusion compounds, definitions and relations (/) coordinative interaction, (2) lattice barrier interaction, (J) monomolecular shielding interaction (I) coordination-type inclusion compound (inclusion complex), (II) lattice-type inclusion compound (multimolecular/extramolecular inclusion compound, clathrate), (III) cavitate-type inclusion compound (monomolecular/intramolecular inclusion...

On the other hand, the crystallization process of diolefin compounds often plays a significant role in determining their topochemical behaviour, by changing their crystal structure or by forming solvent inclusion complexes. Furthermore, topochemical photoreactions of crystals with )8-type packing are accompanied by thermal processes under moderate control by the reacting crystal lattice (see p. 140). These factors seriously complicate the whole reaction scheme. 

The possibility to resolve the two enantiomers of 27a (or 26) by crystalline complexa-tion with optically active 26 (or 27a) is mainly due to differences in topological complementarity between the H-bonded chains of host and guest molecules. In this respect, the spatial relationships which affect optical resolution in the above described coordination-assisted clathrates are similar to those characterizing some optically resolved molecular complexes S4). This should encourage additional applications of the lattice inclusion phenomena to problems of chiral recognition. 

From these observations, we have noticed the similarity of the simple lattice inclusions to the more sophisticated assemblies of molecules (e.g. cyclodextrins 76 and proteins 78 where the formation of H-bonded loops was first detected and described. Conclusively the motive for the formation of simple inclusion crystals and of more complex associates between high and low molecular weight compounds, such as enzyme-substrate complexes, can be traced back to the same source. 

On irradiation, all complexes except 81 gave P-lactam derivatives. Irradiation time, yields, and ratios of products are summarized in Table 10 30). In all irradiations, the P-lactam derivatives 75a-c and 76a-c were prbduced exclusively. The reason for the efficient control in the inclusion complexes is not clear. A plausible interpretation is that the crystal lattices of the inclusion complexes are too compact to produce oxazolidin-4-ones (cf. 73) which have a five-membered ring, compared to the P-lactams which contain a smaller four-membered ring. 

An important advantage of the inclusion complexes of the cyclodextrins over those of other host compounds, particularly in regard to their use as models of enzyme-substrate complexes, is their ability to be formed in aqueous solution. In the case of clathrates, gas hydrates, and the inclusion complexes of such hosts as urea and deoxycholic acid, the cavity in which the guest molecule is situated is formed by the crystal lattice of the host. Thus, these inclusion complexes disintegrate when the crystal is dissolved. The cavity of the cyclodextrins, however, is a property of the size and shape of the molecule and hence it persists in solution. In fact, there is evidence that suggests that the ability of the cyclodextrins to form inclusion complexes is dependent on the presence of water. Once an inclusion complex has formed in solution, it can be crystallized however, in the solid state, additional cavities appear in the lattice, as in the case of the hosts previously mentioned, which enable the inclusion of further guest molecules. ... 

As discussed in detail in Ref. 36, for use in optoelectronics only systems crystallizing in non-centrosymmetric crystal lattices are of interest if the use of expensive enantiomers of chiral molecules is to be avoided. This considerably limits the available crystal lattices since most organic achiral molecules crystallize into centrosymmetric space groups. An interesting example of enantioselective inclusion complexation was reported by Gdaniec and coworkers [37]. 

Dianin s Compound. The unit cells of inclusion complexes in Dianin s compound and of the guest-free compound are almost the same, and there is no doubt that the guest-free lattice contains the same voids as those in which guests are present. 

Comparatively, the walls of a reaction cavity of an inclusion complex are less rigid but more variegated than those of a zeolite. Depending upon the constituent molecules of the host lattice, the guest molecules may experience an environment which is tolerant or intolerant of the motions that lead from an initial ketone conformation to its Norrish II photoproducts and which either can direct those motions via selective attractive (NB, hydrogen bonding) and/or repulsive (steric) interactions. The specificity of the reaction cavity is dependent upon the structure of the host molecule, the mode of guest inclusion, and the mode of crystallization of the host. 

Lattice Inclusion Host-Guest Complex or Clathrate (solid-state only)... 

Inclusion compound (or inclusion complex) — A complex in which one component, the host, forms a cavity or, in the case of a crystal, a crystal lattice containing spaces in the shape of long tunnels or channels in which... 

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