Hydrogen-bond acceptors 4,4 -bipyridine

To determine whether it is possible to isolate a guest within 4 which, unlike 2-4(pyridine), is different than that of the substituents hydrogen bonded to the upper rim of 2, we next turned to pyridine derivatives, namely 4-picoline (monopyridine) and 1,10-phenanthroline (bipyridine). In a similar way to pyridine, both molecules possess hydrogen bond acceptors along their surfaces and 7i-rich exteriors which we anticipated would allow these units to assemble along the upper rim of 2 as stacked dimers. As shown in Figure 4, cocrystallization of 2... 

The valency of the hydrogen bond donors and acceptors can be varied to produce chiral mesophases [85]. Mixtures of the divalent 4,4 -bipyridine with 4-[(S)-2-methylbutoxy]benzoic acid in ratios between 1 9 and 4 6 show LC behaviour, but the chiral mesophases are exhibited for only a small range of compositions [86]. Here, the cholesteric and a blue LC phase were observed. The association of the acid to the bipyridine was confirmed by a crystal structure of the 1 2 complex. 

Within the Hush formalism of electron transfer [129], the electronic coupling through hydrogen bond interfaces may be deduced from the intensity of a mixed-valence transition between juxtaposed donor-acceptor pairs. We highlight the only such detailed study in this section. Curtis and coworkers have studied a collection of hydrogen-bonded mixed-valence adducts formed between ruthenium(II) electron-donor and ruthenium(III) electron-acceptor complexes in solution [130]. Using acetonitrile or nitromethane as a solvent, hydrogen-bonded assemblies of the type [(tpy)(bpy)Ru (CN)]2, (en)2Ru (bpy) 5+ 45 (bpy = 2,2 -bipyridine, tpy = 2, 6", 2 -terpyridine, en = ethylenediamine) and [(bpy)2Ru (CN)2]2, (en)2Ru (bpy) +... 

The use of hydrogen bonding for mesogenic network formation has been expected for the formation of dynamic mesomorphic states due to the induction of dynamic properties, e.g. reversibility and fast exchange of the H-bonding [108-111]. Supramolecular liquid-crystalline networks have been prepared by the self-assembly of a polyacrylate with a benzoic acid moiety and 4,4 -bipyridine [108]. Complexes 46 form dynamically cross-linked structures obtained by the complexation of a carboxyl-functionalized polyacrylate and a mixture of a stilbazole, which has the single H-bond acceptor, and a bipyridine, which has the two acceptors. 

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