Supramolecular hexagons

Transition metal supramolecular arrays can be constructed with the aid of n-bonding interactions by using various [2n]cyclophanes and polymetallic clusters. This area is only in its infancy and its potential is illustrated by the formation of a supramolecular hexagonal two-dimensional network by using metal centers linked through the [2.2.2]paracyclophane ligand [102],... 

Scheme 8. Supramolecular hexagon. Reproduced from reference 5. Copyright 2000 American Chemical Society.

Supramolecular hexagons via either a three-by-three angle-angle approach similar to that of the two-by-two squares or a six-by-six angle-side approach similar to that of the four-by-four squares are much more common tlm the five-by-five pentagons (5,30-33). As such, a host of research into these types of systems appears in the literature, and many interesting species abonnd. 

Scheme 9. Supramolecular hexagons formed with three-by-three angle-angle methodology. Adapted from reference 33. Copyright 2007 American Chemical...

Fig. 3. An idealized representation of the supramolecular cylinder self-assembled from a single chain of the dendrimer derived from monomer 9 (R=OC12H25, n=3) in the hexagonal columnar phase, assuming one single backbone per cylinder, drawn to proportion with existing experimental data a tilted side view b top view. Reproduced with permission from references 5 a...

Trzaska and co-workers showed a similar propeller mechanism for the formation of helical columns from disclike metallomesogens (29-31).34 These metallomesogens also have C3 symmetry and 30 and 31 are provided with chiral side chains. In the hexagonal columnar mesophase these chiral side chains induce a Cotton effect in the chromophore of the helically arranged core. Heating the mesophase to the isotropic liquid results in the disappearance of the Cotton effect because of the loss of helical order. This effect illustrates the need for the molecules to be positionally ordered in order for the side-chain chirality to be transferred to the supramolecular column. 

The supramolecular transformation from sphere to cylinder is supported by X-ray data indicating that the spherical polymers adopt a cubic phase, whereas the cylindrical polymers adopt a hexagonal phase [23b]. Further studies involving a library of dendritic macromonomers led to the conclusion that the effect of DP on polymer shape is a general phenomenon [24], More recently, scanning... 

Hexagold heteronuclear cluster compounds, X-ray crystallography, 39 369-371 Hexagonal framework supramolecular complexes, 46 204-219 Hexahalochalcogen acids, 35 264 Hexahalochalcogenates (IV), 35 251-253... 

The columnar order in 52a,b was explained by molecular folding the molecules are assumed to be in their U- (or wedge-) shaped conformation and six molecules self-assemble to a supramolecular disc. These discs are stacked in columns and arranged within a columnar hexagonal lattice (Fig. 8). Folding of similar mesogens was also seen by Heiney [65]. 

Upon addition of NaOTf, columnar hexagonal mesophases could be induced. For 68, 0.4 equiv. of salt were needed while for 67, only 0.2 equiv. of NaOTf were needed for mesophase induction. Upon complexation, the complexed crown ether moieties and the anions self-assemble within a supramolecular tube and the taper-shaped side groups stack over each other in the periphery. X-Ray scattering... 

Fig. 12 Neat melamine Hekates 40, their 1 1 host-guest complexes 41,42 and the 1 3 aggregates of a melamine core with three arms 43 and 44. The disk-shaped aggregates 41 stack in a Colrd phase [99]. The Janus-type Hekate 42 arrange in a Colh phase with hexagonal superstructure of the nanosegregated semi-perfluorinated chains [105]. The supramolecular Hekate discs 43-45 self-assemble by hydrogen bonding of the three arms around a melamine core...

Recombinant [oil (VIII) ] 3 and [a2(VIII)]s molecules form highly ordered supramolecular assemblies. These assemblies may be formed by four triple-helical collagen VIII molecules that come together to form a tetrahedron via the hydrophobic patches on their G-termini. It has also been suggested that these tetrahedral structures may further associate to form hexagonal lattices, with the N-terminals of individual molecules interacting with either the N-terminals or with the triple-helical portion of molecules in other tetrahedrons (Stephan et al., 2004). 

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