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Polymeric examples have also been reported using similar chemistry.
Thus, dimer
a
(Fig. 18) was allowed to react with dimer
b
and also with com-
pounds
c
,
d
and
e
togivepolymerswhosedegreeofpolymerisationwas
unreported [45].
Polymers formed between
a
and
c
,
d
and
e
all failed to show any liquid-
crystalline behaviour. However, for all
a
examined (
m
=2,4,6and8),nematic
phases were observed with
b
-4 (all monotropic) - a further monotropic ne-
matic material was the copolymer of
a
-6 and
b
-3. Unidentified crystal smectic
mesophases were reported for a further three examples.
7
Future Prospects
At the time of writing, the five papers described in the preceding section
represents the sum total of published work in the area and while this vol-
ume is timely in terms of the broader field of halogen bonding, it is slightly
premature with respect to liquid crystals. Of course, this is not the end
of the story and the author alone and also in collaboration with the Mi-
lan group, has a good deal of unpublished work that will come to fruition
shortly. For example, it has been shown that iodoperfluoroalkanes will com-
plex with stilbazoles to form mesomorphic materials, again characterised by
X-ray methods with some interesting results
2
.
This area is just beginning and there is a great deal to learn from previ-
ous work with hydrogen-bonded systems. However, the need, in our view, to
obtain single crystals in order to be confident about stoichiometry will in-
evitably limit some of what can be achieved, as this author is only too well
aware of the problems associated with crystallising materials containing long
and/or multiple alkoxy chains. Nonetheless, there will be systems for which
this is not an absolute requirement and there is confidence that other ways
will be found to accommodate this issue. It is hoped that the examples given
above will whet the appetite and encourage others to join the search for ever
more imaginative materials.
References
1. Demus D, Goodby J, Gray GW, Spiess H-W, Vill V (eds) (1998) Handbook of Liquid
Crystals. Wiley-VCH, Weinheim
2. Reddy RA, Tschierske C (2006) J Mater Chem 16:907
3. Donnio B, Guillon D, Deschenaux R, Bruce DW (2003) In: McCleverty JA, Meyer TJ
(eds) Comprehensive Coordination Chemistry II, vol 7, chap 7.9. Elsevier, Oxford,
UK, pp 357-627
4. Donnio B, Bruce DW (1999) Struct Bonding 95:193
2
Metrangolo P, Bruce DW, Pilati T, Resnati G, unpublished results
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