Helical tubuland diols

Another case of major enantiomer separation occurs when helical tubuland diols (Section 3.2.1) are crystallised with small phenol molecules and intimately hydrogen bonded co-crystals are produced. A typical example is (11 ) ( p-chloro-phenol) [33], The major supramolecular synthon is H-0 H-0 H-0 hydrogen bonding with eclipsed stacks of the participating molecules surrounding a pseudo-threefold screw axis (Figure 13). This chiral motif involves molecules of p-chloroplienol and only one of the enantiomers of 11. 

An analogous structure is produced when the helical tubuland diol 12 forms a 1 1 co-crystalline adduct with methanol (Figure 15). The lattice, as before, comprises stacked layers of alternating chirality, but overall is an achiral structure [34],... 

Unlike the above cases, the relationship between structural and supramolecular properties can be far more cryptic and not immediately apparent. One example is the key role played by the (at first glance unimportant) methyl groups of the helical tubuland diol hosts 59-62. Another is the closely related host behavior of hydroquinone 49 and the diol 102 in the presence of small guests. Although these are aromatic and aliphatic compounds, respectively, both of these hosts form clathrates in a similar manner namely by trapping small guests between two interpenetrated sublattices in their respective crystal structures. ... 

Bishop R (2009) Helical tubuland diols a synthetic and crystal engineering quest. Acc Chem Res 42 67... 

Helical Tubulands formed by Rigid Alkyclic Diols.143... 

In fact there is substantial structural variability among the five instances of the helical tubuland structure described above, in the form of variable placements of the diol hosts along the twofold axes, and variable a dimensions of the lattice, both of which have marked influence on the size and shape of the canals. Full analysis of these effects is provided elsewhere 8) and the major results only are reported here. As a consequence of steric repulsions between the bridge on the syn face and methyl substituents R on adjacent molecules presenting an anti face to the canal, as shown in Fig. 8, the molecules presenting the anti face are moved along the twofold axes, farther... 

The helical tubuland (HT) diols are a group of alicyclic dialcohols that show characteristic crystallisation behaviour [32,35], When a racemic sample is crystallised, then enantiomeric self-resolution occurs, yielding a conglomerate of (+)- and... 

Discovery of the inclusion properties of many channel-type compounds was mainly made by chance. The creation of crystal lattices with tailor-made properties or even the fine tuning of properties of known crystal architectures represent significant challenges for materials chemists. Worth mentioning here is a large family of alicyclic diols, called helical tubulands. These com-... 

MOLECULAR DETER14INANTS OF A NEW FAMILY OF HELICAL TUBULAND HOST DIOLS... 

ABSTRACT. The alicyclic diols (1-5) constitute the first members of a family of novel helical tubuland hosts crystallising in space group P3 21 but possessing quite different canal shapes and dimensions. Consideration of their structural data has revealed two distinct sub-classes of these materials. The molecular features necessary for a diol to crystallise with the helical tubuland structure are defined and discussed. 

Following this initial discovery we embarked on a program of systematic synthesis in order to demonstrate that additional materials of similar structure could be obtained. Recently we have described the syntheses and crystal structures 4 of further alicyclic diols (2-4) of this- type which also adopt the crystal space group P3] 21. Their structural characteristics have been analysed and reported in detail. The previously unreported diol (5) also belongs to this new family of helical tubuland host diols. 

Our program of synthesis has been planned to define the molecular features required in a host diol molecule for it to crystallise with the helical tubuland structure. The following molecular determinants have been found to be necessary. 

A network of host diol molecules (space group P3 21) is maintained by continuous helical spines of hydrogen bonds. Other diol molecules radiate from and interconnect these spines enclosing parallel open canals containing the disordered guest molecules. This tubuland structure constitutes an especially interesting example since in each crystal these canals are surrounded by a double helical array of host diol molecules of the same chirality. 

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