Lattice inclusion compounds

Structural aspects of inclusion compounds formed by organic host lattices , Inclusion Compounds, Vol. 2, (Eds. J. L. Atwood, J. E. D. Davies, D. D. MacNicol), Academic, London, 1984. 

The formation of lattice inclusion compounds has long been regarded as a fascinating area of chemistry. In the early days it was a rare and unpredictable phenomenon that was difficult to explain [1,2]. Nowadays, although such behaviour is more familiar and better understood, it still carries with it an air of mystery. 

These various possibilities are examined here in the context of lattice inclusion compounds. 

The racemic alicyclic diol 10 can form two types of lattice inclusion compounds on crystallisation, ellipsoidal clathrates (Section 3.1.2) or helical tubulates (Section 3.2.1). Small guests give the former, and large guests give the latter, lattice. 

Host inolecules may be broadly classified into two main types those that form molecular complexes by fitting convex guests into the concave cavity of the host (examples include cyclodextrins, cyclophanes. calixar-enes, cycloveratrylenes, and various carcerands ) and those that form lattice inclusion compounds by packing in such a manner as to leave cavities, channels, or layers in the crystal structure so as to accommodate various guest... 

Thus, the host molecules dominate clathrate compounds, and the host-guest (and guest-guest) interactions are a secondary factor. The term clathrate has gradually been applied more broadly over the years, and today the descriptors clathrate, lattice inclusion compound, and solvate tend to be used interchangeably by many. 

T. Fri 6ic, Towards mechanochemical synthesis of metal-organic frameworks (MOFs) from coordination polymers and lattice inclusion compounds to porous materials, in Metal-Organic Frameworks Design and Application , ed. L. R. MacGillivray, John Wiley Sons, Inc., 2010. 

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...

Extramolecular Cavity Inclusions Lattice-Type Inclusion Compounds, Clathrates... 

Inclusion Compounds of Macrocyclic and Oligocyclic Lattice Hosts. As a common feature, all these hosts (Fig. 15) belong to the trigonal class of symmetry and most inclusions are of channel stmcture. 

Shielding and Stabilization. Inclusion compounds may be used as sources and reservoirs of unstable species. The inner phases of inclusion compounds uniquely constrain guest movements, provide a medium for reactions, and shelter molecules that self-destmct in the bulk phase or transform and react under atmospheric conditions. Clathrate hosts have been shown to stabiLhe molecules in unusual conformations that can only be obtained in the host lattice (138) and to stabiLhe free radicals (139) and other reactive species (1) similar to the use of matrix isolation techniques. Inclusion compounds do, however, have the great advantage that they can be used over a relatively wide temperature range. Cyclobutadiene, pursued for over a century has been generated photochemicaHy inside a carcerand container (see (17) Fig. 5) where it is protected from dimerization and from reactants by its surrounding shell (140). 

In case of the bianthrylmonocarboxylic acid 20, one may predict the formation of a lattice inclusion at least with dimethylformamide, but we did not succeed in obtaining it37. Instead a stable 1 1 stoichiometric inclusion compound of 20 is readily obtainable (Table 3). The bianthryldicarboxylic acid 21, which is a direct analogue of 1, is not available in sufficient quantity to be tested in respect to its lattice inclusion properties. 

According to the coordinatoclathrate predict, the Spiro compound 23 will not allow the formation of inclusion compounds with dimethylformamide and other polar solvents, but with benzene, tetrahydrofuran, and 1-bromopentane (Table 3). Due to the limited number of guest inclusions, a lattice cavity of rather restricted dimensions is suggested for 23 e.g. toluene, cyclohexane or dioxane are not suitable guest partners for 23, whereas lower homologues (cf. benzene, tetrahydrofuran) are readily included 37). The behavior of a reduced analogue of 23, the hydroxymethyl — substituted spiro compound 24, is in some way comparable since an inclusion compound with benzene is the only one known interestingly it is formed exclusively with optically resolved but not with racemic 24 49). 

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