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This point has been further substantiated by the qualitative comparison of the pyridine,
bipyridine and terpyridine Schiff-based ligands bearing phasmidic tails.
A key element of this work involves the use of segmented polytopic ligands bear-
ing a vacant coordination site. This facilitates the formation of symmetrical metal-
lohelicates that remain in labile conformations. The fluctional motion of the ligands
gliding across the metal centers provides for the low-temperature mesogenic phase
and for the stabilization of higher valence states. This suggests ways to generate
new metallomesogens displaying highly desirable properties. It is clear from the few
examples of liquid-crystalline materials obtained from these artificial molecular
architectures that the list of novel assemblies will grow rapidly in the near future,
despite the difficulty in ensuring the targeted properties and properly characterizing
the emerging mesophases. The self-assembly process is very versatile and allows the
preparation of a great number of discrete supramolecular species with well defined,
pre-designed shapes and geometries. The most important advantages of this approach
are its wide applicability and the large and different number of potentially suitable
transition metal complexes and multidentate nitrogen- or oxygen-containing ligands
available as building blocks. Excellent product yields and the high thermodynamic
stability constants of the formed complexes that are inherent to such self-assembly
processes have been observed in many cases. These results demonstrate two key
points with respect to the design of self-assembling systems. First, it is possible to
combine imino functions with bipyridine and terpyridine fragments to create stable
supramolecular complexes in a productive fashion. Second, judicious tailoring of the
ligand with flexible alkyl chains can produce macroscopically organized phases with
textures strongly dependent on the architecture of the rigid frame.
7.4 Outlook and Perspectives
Up to date, there has been a steady and progressive interest in the synthesis of oligopyr-
idines and an impressive number of such substances are now known. These compounds
are not especially appealing on their own, although there are some interesting synthetic
facets, and certain compounds form stable complexes with many cations. It is this interest
for the synthesis of metal complexes that has driven research into finding new and
improved oligopyridines, and such complexes figure prominently in historical accounts of
both coordination chemistry and analysis. More recently, metal oligopyridines have been
used to construct exotic molecular architectures, to sensitize photoelectrochemical cells,
and to label biomaterials as the basis for selective sensors and as magnetic materials. In
the future oligopyridines will find even more applications, especially as materials scien-
tists seek to develop miniaturized devices. We have argued the case that Schiff-base tem-
plates endow certain metal complexes with special properties and this claim is the result
of a determined and sustained effort to produce a comprehensive catalogue of suitably
functionalized compounds. In the present survey, we have outlined a synthetic strategy
for grafting imino groups to a variety of different oligopyridines. The synthetic routes
have been adapted to ensure that various terminal groups (from one to three paraffinic
chains) can be attached and to provide means by which to tune the flexibility and micro-
segregation behavior of the emerging material. Throughout this work, we have become
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