Dianin clathrates

A single C label at the methyl group of p-xylene was used to estabhsh 13c 13c distances between guest molecules and hosts with naturally abundant C, using the 2D RFDR approach [91]. Other Dianin ICs, with -hexane and n-pentanol guest molecules, have been reported [92]. Eckhardt and coworkers investigated Dianin clathrates containing two ethanol molecules and a heptanol, [93] as well as 1,6 hexanediol, 1,5 pentenediol and 1-heptanol [94]. 

The robust nature of the Dianin clathrates encouraged systematic modification of the host to attempt the synthesis of further clathrands. Baker et al. prepared the methylated derivative 9 but found that the inclusion behavior of Dianin s compound was not duplicated. This experiment is believed to be the first ever attempt to dnplicate clathrate... 

Clathration is the third sorption situation. Guests are incorporated during the growth of the host lattice. Their liberation occurs on heating or lowering the pressure with lattice breakdown. This situation is found for water, phenol, quinol, cresol, urea, and Dianin s compound. 

Some phenolic compounds can form flat hexagonal structures with the aromatic rings facing outward, and linked by hydrogen bonds. The internal space thus formed contains solvent. Such compounds are called inclusion compounds or clathrates. An example is dianin (2.14), which can form clathrates in more than 50 different solvents. 

Figure 7.43 (top) 129Xe CP-MAS NMR solid-state spectra for a the xenon clathrate of Dianin s compound obtained at 1 atmosphere pressure (bottom) the DQ filtered spectrum showing only the resonance due to the doubly occupied cavity. (Reproduced by permission of The Royal Society of Chemistry). 

Hydroquinone and phenol based clathrates including Dianin s compound are based upon cages made up of 6-membered hydrogen bonded rings of hydroquinone and are subject to considerable synthetic variation. 

One of the most revealing applications of single crystal 2H NMR has been reported by Haeberlen et al. [176]. Advantages provided by this technique were used to study the dynamic properties of the host structure in the clathrate of Dianin s compound with ethanol as the guest molecule. 

Fig. 9 Schematic representation of the two hydrogen bonding arrangements involved in concerted rotation of the hydroxyl groups about the C-0 bonds in the clathrate of Dianin s compound [176]...

Crystals which can exhibit microporosity on the scale of molecules include layer silicates such as smectites and vermiculites zeolites porosils aluminium phosphates (AlPO s) some Werner coirpounds and cyanometallates and clathrates. A short historical account of zeolites and some features of porosils and AlPO s have been given. As an example of a zeolitic Werner compound 8-tNi11, Coll) - (4-methylpyridine)4(SCN)2 is cited, and as zeolitic cyanometallates three complex cyanides are referred to. Dianin s catpound, a chroman, exemplifies a zeolitic, organic, clathrating host structure. The intracrystalline micropores in the 3-dimensional 4-connected nets of some zeolites, porosils and AlPO s have been compared in terms of the windows controlling access to the micropores their volumes and internal dimensions and the total intracrystalline pore volumes per cm3 or per g of crystal. 

Clathrates differ from zeolites in that the host structures are not usually stable in the absence of the guest. An exception is Dianin s compound (a chroman) where the porous hydrogen-bonded framework persists with no guest molecules to stabilise it. This is also true of a, B- and y- cyclodextrins, where the individual host molecules are like truncated sections of a hollow, gently tapering cone. 

The n.m.r. spectra of a number of 2-substituted 4-chromanols and l-thio-4-chromanols in DMSO show that the OH proton resonates at higher field when it is pseudo-axial than when pseudo-equatorial its coupling constant with CH is lower in the pseudo-axial than in the pseudo-equatorial position. The observations may be explained in terms of conformational equilibria of the C—O bond. Dianin s compound (116 = Me, R = OH) forms clathrates with... 

Thiochromans and Thiochromones.—The spirothiochroman (175) has been synthesized from 3-methylene-l/7-2-benzothiopyran-4(3//)-one (176) and its stereochemistry has been examined, using X-ray crystallography. Modifications which have been made to Dianin s compound (see also under Chromans ) include replacement of the ring oxygen by sulphur. Some such compounds retain the clathrate-forming ability of the original molecule. 

The chemistry of inclusion compounds also looks back on a lively history There are many events of significance in the area of inclusion chemistry till the middle of the twentieth century including the discovery of new inclusion compounds and hosts (Fig. 1), among them the graphite intercalates, the P-quinol and cyclodextrin inclusion compounds, the Hofmann-type clathrates as well as the inclusion compounds of tri-o-thymotide, Dianin s compound, the choleic acids, of phenols, of urea and others specified in comprehensive monographs... 

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