Dianin inclusion compounds

Polar and coordinatively active functional groups are structural elements frequently found in the constitution of crystal inclusion hosts, mainly including conventional host molecules7 . Typical examples are urea (2), thiourea (5), hydroquinone (4), Dianin s compound (5), deoxycholic add (6) or simply water (Fig. 1). This was the reason to assume that functional groups play an important part in the construction of crystal inclusion compounds. 

Fig. 4. Inclusion cage of Dianin s compound (5). The matrix is constructed via a cyclic H-bonded hexagonal system of host molecules (on top and on bottom of the macrocage O atoms as bold dots, H-bonds as dotted lines) bulky parts of the host molecules interlock (equatorial of the cage). The cage can be filled with molecules of fitting size (e.g. one molecule of chloroform) (Adapted from Ref. 16)...

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. 

Figure 3. The shape and size of the cavity/channel of Dianin s compound, (a) The cage formed by two sets of hexamers. (b) The top or bottom half of the cage, hexamers are held together by hydrogen bonds, (c) Schematic illustration of the cage/channel. The stacking is along the c axis. (Reproduced with permission from D. D. MacNicol in Inclusion Compounds, Vol. 2, J. L. Atwood, J. E. D. Davies, and D. D. MacNicol, Eds., Academic Press, New York, 1984, p. 1.)...

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. 

Dianin s compound 8 is a famous example of a lattice inclusion host from the early days of inclusion chemistry [26,27], It is usually prepared as the race-mate and forms inclusion compounds with many guests in space group R3. Six molecules of 8 assemble by means of their phenolic groups into a near-planar hydrogen-bonded (-0-H)6 cycle, with alternate molecules being orientated up... 

One of the well-studied inclusion compounds is trimethylchroman. 1, commonly known as Dianin s compound. First prepared in 1914 by the Russian chemist A. P. Dianin, this compound has attracted considerable attention due to its ability to tenaciously hold on to certain organic solvents. A cage structure was predicted in the adducts of 1 based on space group, unit cell dimensions and packing considerations and was confirmed by detailed X-ray single crystal structure smdies on the chloroform and ethanol adducts of 1 after 15 years. Irrespective of the guest, the 1... 

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... 

Fig. 4. Inclusion matrix of Dianin s compound (i) (schematic representation) Individual Dianin molecules are represented by a specified hydroxy group attached to an elUpsoid. The characteristic hydrogen bridge networks are indicated by the shaded hexagons (H-bonds in dotted lines). The hatched sphere in the centre of the cavity pictures an included guest molecule, e.g. chloroform...

Fig. 6. Hexa-host strategy Close connection between (a) a hydrogen-bonded hexamer unit typical of phenolic hosts (hydroquinone, Dianin s compound cf. Fig. 4) and (b) of a hexasubstituted benzene analogue (follow up the shaded hexagons) (c) characteristic constitution of hexa-host molecules and (d) host-guest packing of a representative clathrate inclusion compound (dioxane clathrate of I3a, 1 1 dioxane molecules hatched)...

Numerical considerations dealing with the total number of individual components in a chemical sense, e,g. binary (b), ternary (t), etc. and with the number of particles [host, guest separately, e.g. monomolecular (Im), binuclear (2n), respectively] are also practicable Thus, the clathrate formed between Dianin s compound (5) and chloroform (see Fig. 4) is identified as binary, hexamolecular, and mononuclear. The full description of this inclusion compound applying the complete set of symbols and designations explained above, hence follows as b, 6m, In-cryptato-clathrate . 

Interstitial primary solid solutions are rare among inclusion compounds but not unknown. Thus a-quinol contains small amounts of gas in solid solution, while Dianin s compound forms inclusion compounds of primary solid solution-type, with only small differences in cell dimensions between neat crystals and interstitial solid solutions. The same situation occurs in a-TMA. 

MacNicol. D.D. Structure and Design of Inclusion Compounds The Clathrates of Hydroquinone. Phenol. Dianin s Compound and Related Systems. In Inclusion Compounds, Atwood. J.L.. Davies. J.E.D.. MacNicol. D.D.. Eds. Academic Press London, 1984 Vol. 2. 1-45. 

Hofmann-type clathrates Werner clathrates clathrate hydrates inclusion compounds of urea, thiourea, and selenourea cyclodextrins calixarenes gossypol hexa-hosts hydroquinone phenol and Dianin s compounds graphite intercalates natural and pillared clays and others. Such studies contributed to the birth of supramolecular chemistry, with relevance to a new understanding of the world of materials that was emphasized with a Nobel Prize. 

This type of structure is an example of an organic multimolecular inclusion complex, dependent on the entire packing arrangement of host molecules providing void spaces which can be occupied by guest molecules. Such materials include th familiar examples of he clathrates formed by Dianin s compound, and by hydroquinone, and the canal complexes formed by urea with n-alkanes. ... 

As a natural development of the successful molecular inclusion concept, which involved electrostatic as well as van der Waals forces between the interacting host and guest entities, an increasing interest has been shown in the systematic study of lattice-inclusion type systems. A considerable effort has been devoted to the design of new hosts for the formation of stable crystaUine clathrates and the improvement of selective complexations with potential guests. Suitable examples of clathrates studied in recent years include hosts such as Dianin s compounds , perhydrotriphenylene , cyclotriveratrylene triphenylmethane hexakis-(arylthio) and -(arylthiomethyl)benzenes tri-o-thymotide (TOT) and choleic acids (cf. Fig. 1 in Ch. 1 of Vol. 140). Selected series of such clathrate inclusion systems have particularly been useful in research of photochemical reactions in the solid state and of selective molecular complexation that is central to biological phenomena... 

Many further cases of inclusion materials were discovered by happy accident during the next two centuries, for example, additional clathrate hydrates, the Hofmann clathrates, phenol inclusion compounds, Dianin s compound, urea tubulates, choleic acids, cyclodextrins, aud interpenetrated hydroquinone inclusion compounds. These substances remained problematic despite being the object of much painstaking scientific study. Mauy were unstable under ambient conditions and therefore it proved difficult to determine accurate ratios of their two components A and B. Furthermore, the substances did not follow the usual rules of covalent bonding, leading to their representation in the fonn (A)x (B)y. It was surmised that one component somehow trapped the other, but no experimental methods were available to analyze this phenomenon. 

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... 

The hexa-host molecules are the first synthetic clathrands with no direct structural relationship to a previously known host. They were designed from scratch in the first supramolecular clathrand synthesis. MacNicol realized that appropriate hexa-substituted benzenes would be more robust analogs of the (0-H)6 hydrogen-bonded motif found in inclusion compounds such as the j6-structure of hydro-quinone 49 " and Dianin s compound 8 (Section S)." If the aromatic substituents were attached to the central core by a flexible linker atom or group (L e.g., S or CH2-O), then the new molecule would act as a covalent mimic of the earlier hydrogen-bonded motif (Figure 13). 

There is also a close relationship between the inclusion crystal structures of hydroquinone 49, Dianin s compound 8, and the alicyclic diol 103. This is revealed if the two motifs used by MacNicol in the hexa-host design, namely the aromatic ring and (0-H)6 cycle structures, are regarded as equivalent supramolecular nodal points. The network connectivity (see Network and Graph Set Analysis, Supramolecular Materials Chemistry) and familial relationship of these three lattices is then revealed. ... 

---