Biomedical Engineering Reference
In-Depth Information
Table 9.15
Phase behavior of bischelate ionic silver
complexes.
Compound
X
Phase transition behavior
68a
BF
4
Oil at 20 °C
68b
PF
6
Cr 61 I
68c
OTf
Col
h
91 I
68d
DOS
Col
h
57 I
volume measurements indicated helical twisting about the columnar axis.
Also, compounds
68c
and
68d
exhibited blue luminescence in the meso-
morphic state [101].
Terazzi
et al.
[102-104] studied the metal complexes of 2,6-di(1H-
benzo[d]imidazo-2-yl)pyridines. Out of all of these, lanthanide complexes
69-71
were found to exhibit Col phase. All the uncomplexed ligands
exhibited columnar mesophase. h e size of lanthanide ions af ects the sta-
bility of columnar phase (Table 9.16). Larger lanthanide ions Sm to Ho
display cubic phases, smaller ions Er to Lu give rise to Col-Lam phases,
while ions Pr and Nd in between the former two display both kinds of
phases. Inversion of the ester linkages is harmful for the mesomorphism.
In compounds
70a-d
, when the ester linkages were reversed, liquid crys-
talline behavior was lost. Probably, the ester spacers should be oriented in
such a way to minimize the alterance between electron-rich and electron-
poor aromatic rings.
Metallohelicate of Cu with terpyridine complex
72
has been reported
by Zeissel and coworkers [105]. h is complex contains columnar stacks
of the molecules within the smectic layers. But no π-π interactions have
been seen, which may be because the aromatic molecules are not arranged
perpendicular to the long axis.
9.3.3
Ionic Discotic Compounds of Crown Ethers
Laschat and coworkers [106-109] prepared and studied a large number
of [18]crown-6 ether complexes of terphenyl and triphenylene based on
dif erent types of R group, Metal M, and anion X (Figure 9.28). Out of
these, only two representative sets are shown in Table 9.17. A compari-
son of terphenyl compounds with triphenylene compounds indicate that
both melting point and isotropic temperature increase for the more planar
