The synthesis, mesomorphism and mesophase structure of anisotropic imines and their complexes with rhenium(I)

Article abstract of DOI:10.1039/a908137b

Highly anisotropic imine ligands have been synthesised and complexed to Re(I). Two series of ligands and complexes were obtained with various chain lengths, showing smectic and nematic phases for the ligands and only a nematic phase for the complexes. The

Full text of DOI:10.1039/a908137b

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J O U R N A L O F
The synthesis, mesomorphism and mesophase structure of
anisotropic imines and their complexes with rhenium(I)
Xiao-Hua Liu,a,b BenoÃõt Henirich,c Ian Manners,b Daniel Guillonc and Duncan W. Bruce*a
aSchool of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD.
Fax: z44 1392 263434. E-mail: d.bruce@exeter.ac.uk
C H E M I S T R Y
bDepartment of Chemistry, University of Toronto, Toronto, M5S 3H6, Canada
cIPCMS, Groupe des Materiaux Organiques, 23 rue du Loess, BP 20CR,
67037 Strasbourg cedex, France
Received 11th October 1999, Accepted 20th December 1999
Highly anisotropic imine ligands have been synthesised and complexed to Re(I). Two series of ligands and
complexes were obtained with various chain lengths, showing smectic and nematic phases for the ligands and
only a nematic phase for the complexes. The identity of the crystal smectic phase in the ligands was studied by
X-ray diffraction and identi®ed as a crystal J phase.
complex 2 (Fig. 1) led to alkanoyloxy-substituted materials
which show monotropic nematic phases.4 All of the alkanoyl-
oxy substituted complexes melted in the range 100±124 ³C,
giving mesophases in the range 63±83 ³C. As a second strategy,
we decided to synthesise the related complexes of rhenium(I) on
account of the fact that metal complexes of 3rd row transition
elements are often much more stable than their 2nd or 1st row
counterparts. This strategy proved successful and we reported
the fact in a communication.4 In the present paper, we now
Introduction
For some time, derivatives of ferrocene (and some of
ruthenocene) were the sole examples of formally six-
coordinate, rod-like molecules which formed liquid crystal
mesophases,1 with the vast majority of literature on calamitic
metal complexes concentrating on 2- and 4-coordinate
complexes of metals taken from Groups 9±11.2 Informed by
these studies on ferrocene-based mesogens, we began to search
for rational means by which high coordination number metal
centres could be used successfully as the basis for the
construction of calamitic materials. In 1994, we reported3
that complexation of strongly mesomorphic imines to Mn(I)
centres via orthometallation led to mesomorphic octahedral
metal complexes with a rod-like shape (1, Fig. 1). The design of
these materials was based on the premise that if a large
structural perturbation (i.e. 6-coordinate metal centre) were to
be tolerated in a mesogen, then the organic part would need to
be suf®ciently anisotropic to withstand such disruption. The
strategy was successful and the manganese complexes
demonstrated a nematic mesophase in the range 120±190 ³C.
One of the problems sometimes encountered in the study of
mesomorphic metal complexes is the lack of thermal stability of
the materials at the clearing point, which can be a signi®cant
drawback in the study of their physical properties. In order to
circumvent this problem, the ®rst strategy to obtain more stable
materials was to modify the ligand to access lower melting
systems to see how a change in the ligand can affect the thermal
parameters. First of all, removing an aromatic group to form
report
a systematic investigation of the synthesis and
mesomorphism of two series of rhenium(I) complexes and
their precursor ligands to examine properly the effect that the
ligand can have on the mesomorphism of the complexes.
Preparation of the ligands and complexes
The ligands were prepared as follows and as shown in
Scheme 1. 4-Alkoxybenzoic acid was esteri®ed (using DCC
and DMAP) with 4-hydroxybenzaldehyde to give 4-alkoxy-
benzoyloxy-4'-benzaldehyde (3), and with 4-nitrophenol to give
4-alkoxybenzoyloxy-4'-nitrobenzene (4). Reduction of the
nitrophenyl ester with tin(II) chloride at re¯ux in ethanol led
to the related amine (5). The target ligands (6, 7) were then
obtained in a Schiff base condensation in toluene at room
temperature using a catalytic quantity of acetic acid. Yields for
the esteri®cation reaction were typically above 80%, while the
Schiff base condensation gave yields of 75±90%. Reduction of
the nitro group typically proceeded in yields of around 75%. In
addition, two ligands were synthesised with a trans,trans-4-
alkylcyclohexanoyloxy ring using exactly the same approach.
The complexes (8, 9) were subsequently obtained in yields of
75±85% by reaction of the ligand with [ReMe(CO)5]5 in toluene
at re¯ux, followed by puri®cation by column chromatography.
Complexation was evident from spectroscopy. Thus, in the
1H NMR spectra of the ligands, the imine proton shifted from
d 8.45 in the ligand to d 8.62 in the complex and the AA'XX'
spin system of one ring changed to an AMX system on
complexation. Further, the complexes showed CO stretching
vibrations at 2092, 1991, 1987 and 1934 cm21 compared with
2129, 2012 and 1975 cm21 for [ReMe(CO)5]. All the new Re
complexes were characterized by elemental analysis, infrared
spectroscopy, 1H and 13C{1H} NMR spectroscopy and by 2-D
NMR experiments.
Fig. 1 Structures of mesomorphic complexes of Mn(I) and Re(I).
J. Mater. Chem., 2000, 10, 637±644
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Scheme 1
homologues showed a crystal smectic phase below the smectic
C phase, and as the stability of this phase was largely constant
although it fell slightly for the longest chain lengths, then the
range of the smectic C phase increased from 35 to 188 ³C across
the phase diagram. Curiously, one homologue (6f, n~12)
showed a smectic I phase over a range of 8 ³C. The homologue
with n~8 (6d) was originally reported in our preliminary
communication where we identi®ed the crystal smectic phase as
a G phase, whereas in Table 1, we now assign it as a crystal J
phase. The original assignment was based solely on optical
microscopy, whereas the assignment as a J phase is based on
the results of detailed X-ray crystallography which is reported
below.
For the ligands 7 with the longer ®xed chain length, there was
a similar pattern of behaviour, although some differences were
evident. First, while the clearing points of ligands 7 were 10±
20 ³C lower than those of 6, the melting points were similar.
Further, the longer chain length stabilised the smectic C phase
at the expense of the nematic phase by around 40 ³C for the
smallest values of m and around 10 ³C for larger values, leading
Mesomorphic properties of the ligands
Two series of ligands were prepared. In the ®rst (6), one chain
length was ®xed (m~8), while the other chain length was varied
(n~5, 6, 7, 8, 10, 12, 14), while in the second series (7), the same
chain was ®xed at a longer length (m~12) with the other chain
again being varied (n~5, 6, 7, 10, 2, 14).
The mesomorphism of both series was similar and is
summarised in Table 1 and Fig. 2 and 3. Both series of ligands
had rather high transition temperatures with clearing points in
excess of 260 ³C, consistent with the highly anisotropic nature
of the ligand which we had initially reasoned was needed to
preserve mesomorphism when the metal tetracarbonyl group
was introduced.
The ligands 6 showed a high-temperature nematic phase
above a wide-range smectic C phase. The stability of the
nematic phase fell from around 320 ³C at the shortest chain
length (6a, n~5) to about 260 ³C for the longest chain length
(6g, n~14), while the smectic C phase stability increased from
around 120 to 220 ³C for the same range of chain lengths. All
638
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Table 1 Thermal behaviour of ligands 6, 7 and 10
n
Transition
T/³C
DH/kJ mol21
DS/J K21 mol21
6a
6b
6c
6d
6e
6f
5
6
7
8
Crys±J
J±SC
SC±N
N±Ia
106
119
154
322
25.1
4.5
0.8
Ð
66
12
2
Ð
Crys±J
J±SC
SC±N
N±Ia
101
113
167
318
20.1
3.9
1.3
Ð
54
10
3
Ð
Crys±J
J±SC
SC±N
N±Ia
106
118
183
302
20.4
3.8
1.8
Ð
54
10
3
Ð
Crys±J
J±SC
SC±N
N±Ia
116
124
202
298
25.2
3.8
1.9
2.2
65
10
4
Fig. 2 Phase diagram for ligands 6.
4
10
12
Crys±J
J±SC
SC±N
N±Ia
112
119
215
294
22.1
1.0
3.0
3.1
57
3
6
5
Crys±J
J±SI
SI±SC
SC±N
N±Ia
91
110
118
224
284
13.5
0.4
0.8
1.4
1.0
38
1
2
3
1
6g
7a
7b
14
5
Crys±J
J±SC
SC±N
N±Ia
88
99
217
262
36.0
1.2
1.3
Ð
100
3
3
Ð
Crys±J
J±SC
SC±N
N±Ia
107
111
193
298
16.7
1.5
1.2
Ð
44
4
3
Ð
Fig. 3 Phase diagram for ligands 7.
6
Crys±J
J±SI
SI±SC
SC±N
N±Ia
104
111
114
208
290
32.9
0.4
1.1
1.7
Ð
87
1
3
4
Ð
to a reduced nematic range in 7. Similarly, while the crystal
smectic phase persisted in all but the longest chain homologue,
this time the SI phase was present in all homologues except that
with the shortest chain length showing that longer chains were
also stabilising SI.
7c
7d
7e
7
10
12
Crys±J
J±SI
SI±SC
SC±N
N±I
95
106
113
213
289
16.2
0.4
1.3
1.8
1.9
44
1
3
4
3
All ¯uid phases of both 6 and 7 were identi®ed by their
characteristic optical textures, with the `®ngerprint' texture
being seen at the SC±N transition. The SI phase gave a schlieren
texture which was rather dif®cult to bring into focus.6
Finally, and for completion, we note the thermal behaviour
of two other ligands which were reported in our initial
communication on the manganese complexes.3 Thus, the two
alkylcyclohexyl derivatives (10a and 10b) were reported as
having nematic, smectic C and a crystal smectic G in the former
case, and a nematic, smectic C, smectic I and crystal J phase in
the latter. Assignments of the crystal phases were on the basis
of optical microscopy alone, although in the light of the studies
reported below, we would now assign both crystal phases as
crystal smectic J. While overall the transition temperatures are
rather similar to those observed for the related ligands with
alkoxyphenyl groups, we would note that the SC phase in 10 is
much less stable than in either 6 or 7 which may well be related
to the greater motion possible with the ¯exible cyclohexyl
group disrupting the lamellar arrangement.
Crys±J
J±SI
SI±SC
SC±N
N±Ia
95
103
115
226
271
29.8
0.3
1.7
3.6
2.0
81
1
4
7
4
Crys±J
J±SI
SI±SC
SC±N
N±I
99
105
113
234
269
32.6
0.1
1.0
3.3
1.8
88
0
3
7
3
7f
14
5
Crys±SI
SI±SC
SC±N
N±I
99
117
239
266
36.7
1.9
5.5
2.4
99
5
11
4
10a
10b
Crys±J
J±SC
SC±N
N±I
83
131
191
299
27.2
3.7
0.9
0.9
76
9
2
2
7
Crys±J
J±SI
SI±SC
SC±N
N±I
87
137
143
216
307
33.7
0.6
1.7
1.0
1.7
94
1
4
2
3
The identity of the crystal smectic phase
In our initial communication on the mesomorphism of
orthometallated imine complexes of Mn(I), we reported the
behaviour of the ligand 6d (n~m~8) and identi®ed the crystal
smectic phase as a crystal smectic G on the basis of optical
microscopy. However, in the present work, we found it
aClearing points were observed using
microscope.
a
polarizing optical
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increasingly dif®cult to assign the crystal smectic phase seen in
many derivatives as either G or J on the basis of microscopy
alone, and so we undertook a detailed study by X-ray
diffraction in order to resolve the question. In total, ®ve
complexes were studied and they were chosen as examples
where the crystal smectic phase was formed either directly from
a smectic C phase or from a smectic I phase.
First, it was possible to con®rm the existence of a smectic C
phase due to the presence of two sharp re¯ections in the ratio
1 : 2 in the small angle region corresponding to a lamellar
system. The measured layer spacing was about 50% of the
calculated molecular length suggesting a tilt angle of around
50³ in all examples studied. In the case of the smectic I phase, in
addition to the re¯ections at small angle, there was, in the wide
angle region, a slightly broad re¯ection from the packing of the
crystal G lattice; intermediate values would be found for a
crystal smectic M type of lattice (an analogue of the crystal G
and J phases in which the tilt direction is somewhere between
that found in these two phases)8 with any other orientation of
the crystallographic axes with respect to the tilt plane (Fig. 5c).
The corresponding molecular volumes Vm~Vc/2 (recall that
two molecules per unit cell are proposed) and cell parameters c
are plotted against the sum of the carbon chain lengths nzm
(oxygen being included in the rigid core for these purposes) and
compared to the calculated molecular volume, Vm, and the
molecular lengths l (Fig. 6; Vm being obtained from the well
known volume of molten aliphatic tails, from the transverse
area of the rigid core s0 deduced from the spacing of the (hk0)
re¯ection and from the rigid core length deduced from
molecular modelling). It is then clear that the lattice parameters
which are found by assuming a crystal smectic G type of
monoclinic lattice lead to a cell volume which is too small with
respect to the volume of the 2 molecules contained in the
monoclinic lattice. In contrast, the cell volume is in good
agreement with that calculated with the lattice parameter
obtained for a crystal smectic J type of monoclinic lattice. This
suggests that the arrangement is of the smectic J type or close to
it, suggesting that all samples exhibit a crystal J phase.
One particular feature of interest was found in sample 6e
(Fig. 7) which was very different from that in the other samples,
namely the occurrence of an additional, low-intensity (12)
re¯ection. In the case of a truly centred arrangement in the ab
plane, this re¯ection would be extinguished, but its presence
suggests that there must be a shift along c between adjacent
rows of molecules parallel to the tilt plane. However, an
alternative explanation, which cannot be excluded, is that a is
in fact not exactly equal to 90³ so that the lattice is actually that
of a crystal smectic M phase (i.e. a quasi-crystalline J lattice).
Ê
rigid cores which overlapped with the diffuse 4.5 A re¯ection
due to the packing of the molten alkyl chains. The width of this
peak strongly supported the assignment as SI as it is normally
the case that the re¯ection from the packing of the cores would
be broader if the phase were SF.7
The X-ray diffraction pattern for the crystal smectic phase
showed (Fig. 4), at wide angle, a diffuse re¯ection due to the
packing of the alkyl chains, an intense, ®rst order re¯ection due
to the two-dimensional hexagonal packing of the rigid cores
and several other sharp re¯ections of low intensity correspond-
ing to an (hkl) indexation with h|0 and/or k|0 and l|0. In
order to identify the phase, both a crystal smectic G and a
crystal smectic J monoclinic lattice were considered (Fig. 5),
with a and b being placed within, and normal to, the tilt plane,
respectively. It was considered that there were two molecules
per unit cell and unit cell angles of a~c~90³, b|90³ were
assumed.
From the location of the (hkl) satellite re¯ections relative to
the ®rst order (hk0) re¯ection of the hexagonal packing, the
angle b and therefore the other cell parameter and cell volume
(Vc) are readily deduced (Table 2). The largest values for Vc
and c correspond to the crystal J lattice and the smallest to the
In¯uence of chain length and temperature
The variation of d with T is less than 0.01% ³C21 within a phase
domain, with the transitions from the SC to the SI phase and
from the SI to the J phase being associated with jumps in d of
the order of 1% in the former case, there being no jump in the
latter. This corresponds to molecular areas, S, increasing
slightly with increasing T and decreasing nzm (Fig. 8). The tilt
angle, y, which is deduced from the ratio of S and of the
transverse area to the rigid part s0 (obtained from the spacing
corresponding to the (hk0) re¯ection in the case of the SI and J
phases and evaluated from the location of the diffuse re¯ection
in the wide-angle region in the case of the SC phase) lies in the
range 50³ to 55³, with a tendency to decrease with increasing
nzm (Fig. 9). It is quasi-independent of temperature in the J
and SI phases, and only a few degrees larger in the SC phase
(Fig. 10).
Fig. 4 X-Ray diffraction pattern for 6a at 115 ³C.
Fig. 5 Illustration of the relationships between the crystal G, J and M lattices.
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Table 2 Parameters for putative crystal G and J lattices
Ê
dobs/A
Ê
dcalc/A
2hs/³
I
G phase: (hkl)
J phase: (hkl)
2hcalc/³
2.55
19.91
21.72
18.25
16.89
34.6
4.46
4.09
4.86
5.24
vs
vs
w
w
vw
001
200/110
001
110/020
19.91
21.74
18.27
16.87
4.46
4.08
4.85
5.25
ꢀ
201
ꢀ
111
201
202
111
112
c
Ê
3
Vm/10 A
Ê
a/A
Ê
b/A
Ê
c/A
Ê
Ê 2
s0/A
Ê 2
Ê 2
b/³
l /A
D /A
y/³
S/A
G lattice:
J lattice:
12.0
8.14
5.14
8.91
46.6
54.7
47.8
39.2
c
c
b
b
22.9
22.9
42.2
50.8
30.9
36.3
1.07
1.25
s0~d200b; y~902b; S~(ab)/2~cos y; Vm~d001S.
Fig. 6 Plot of (a) calculated molecular volume and (b) lattice c
parameter against total chain length.
Mesomorphic properties of the complexes
The mesomorphism of the two series of Re(I) complexes, 8 and
9 formed from ligands 6 and 7, respectively was evaluated and
compared with that of examples which we had described
previously. Thermal data are collected in Table 3 and are
displayed in Fig. 11 and 12.
Fig. 7 X-Ray diffraction patterns for 6e at 100 ³C: (a) full pattern; (b)
wide angle region.
In broad terms, the mesomorphism of all of the rhenium
complexes was the same, melting to a nematic phase in the
range 130±155 ³C and clearing between 140 and
198 ³C. Interestingly, while it was found that lower clearing
points (10±20 ³C) were found for complexes 9 (m~12)
compared to complexes 8 (m~8), no such dependence of the
melting point was observed. Further, the decrease in TNI as a
function of chain length was similar in both the ligands and the
complexes as illustrated in Fig. 13. The two complexes derived
from the alkylcyclohexyl ligands (11a and 11b) also showed
only a nematic phase although it was interesting that both the
melting and clearing points were lower by some 20±30 ³C
compared with the related alkoxyphenyl complexes. By
analogy with studies on related complexes,9 we attribute this
to the removal of the oxygen of the alkoxy group and the
attendant, stabilising, molecular dipoles. It is important to note
here that we found reproducible mesomorphism after several
heat±cool cycles, demonstrating the thermal stability of these
Fig. 8 Plot of molecular area, S, as a function of temperature for 6a
and 6e.
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Table 3 Thermal behaviour of complexes 8, 9 and 11
n
Transition
T/³C
DH/kJ mol21
DS/J K21 mol21
8a
8b
8c
8d
8e
8f
5
6
7
8
Crys±N
N±I
155
198
37.2
1.4
87
3
Crys±N
N±I
159
191
42.5
1.7
98
4
Crys±N
N±I
150
182
41.0
1.2
97
3
Crys±N
N±I
154
176
32.2
1.2
75
3
Fig. 9 Plot of tilt angle (y) against total chain length at 100 ³C in the
crystal J phase.
10
12
14
5
Crys±N
N±I
128
166
29.0
1.5
72
3
Crys±N
N±I
130
164
48.0
0.9
118
2
8g
9a
9b
9c
9e
9f
Crys±N
N±I
131
152
51.3
1.3
127
3
Crys±N
N±I
150
172
41.1
1.4
98
3
6
Crys±N
N±I
160
169
55.2
1.4
128
3
7
Crys±N
N±I
159
161
42.0
1.4
97
3
10
12
14
5
Crys±N
N±I
136
153
41.4
1.2
101
3
Fig. 10 Plot of tilt angle as a function of temperature for 6a and 6e.
Crys±N
N±I
131
145
53.4
1.1
132
3
materials which is in contrast to their manganese congeners
which decompose on clearing.
9g
11a
11b
Crys±N
N±I
131
142
29.2
0.9
72.3
2
The fact that, on complexation, the mesomorphism changes
from nematic and smectic phases solely to nematic is something
we have discussed elsewhere on several occasions3,4,9 and
results from the reduction in ligand anisotropy on the
introduction of the [Re(CO)4] group. It is, however, interesting
that even at the longest chain lengths shown (nzm~26) there
is no sign of a smectic phase, although we have recently found
that smectic phases can be induced in the complexes, but only
on the introduction of two ¯uorocarbon chains.10
Crys±N
N±I
147
177
60.3
1.2
144
3
7
Crys±N
N±I
129
171
39.8
1.3
99
3
in determining the behaviour in these systems and are currently
pursuing this line of investigation.
However, an interesting comparison arises when we look at
the mesomorphism of these complexes in relation to other
octahedral Re(I) complexes of diazabutadiene (12)11 and 2,2'-
bipyridine (13)12 ligands (Fig. 14). In these last complexes, it is
a [ReX(CO)3] fragment which binds to a neutral ligand and,
in almost all cases, the melting and clearing points are not
substantially reduced, in many cases increasing on complexa-
tion. However, contrast this with the Re(I) imine complexes
where clearing points drop substantially compared to those of
the ligands. While the complexes of the diazabutadienes may
perhaps be regarded slightly differently as they exhibit a bent
structure due to the formation of a ®ve-membered ring on
complexation (although we see no real evidence of so-called
`banana' phases), the bipyridine complexes are more similar
and we can regard the [ReX(CO)3] fragment as a structural
perturbation in the same way that we discussed the [Re(CO)4]
fragment above in relation to the imine systems. Why then does
one fragment lower the clearing points of its ligands (imine
complexes) and yet raise them in others (diazabutadienes and
bipyridines)?
Experimental
Characterization
Microanalyses were performed at Department of Chemistry,
University of Shef®eld, University of Exeter and Quantitative
As yet, we do not know the answer to this question although
it is under investigation. However, one possible explanation
relates to the fact that in the case of the diazabutadiene and
bipyridine ligands, there are two lateral dipolar functions
around the metal centre, namely a cisoid diimine function and a
Re±X bond. We believe that these may have some signi®cance
Fig. 11 Phase diagram for complexes 8.
642
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equipped with a Linkam TH600 hot stage and PR600
temperature controller or a Mettler FP82 hot stage and
FP80 central processor at University of Toronto.
Synthesis
All of the ligands and complexes were made using procedures
which we have well documented elsewhere.4,9 We therefore
include only the analytical data for the new ligands (Table 4)
and complexes (Table 5).
Table 4 Analytical data for the new ligands
Calculated (Found)/%
Compound
Yield (%)
C
H
N
Fig. 12 Phase diagram for complexes 9.
6a
6b
6c
6d
6e
6f
6g
7a
7b
7c
7d
7e
7f
83.4
85.6
80.5
83.4
81.6
75.4
77.8
86.4
87.8
82.3
81.6
76.4
74.3
81.4
90.0
75.2 (75.6)
75.3 (75.8)
75.5 (76.0)
75.9 (76.2)
76.2 (76.6)
76.5 (76.9)
76.9 (77.2)
76.1 (76.4)
76.6 (76.6)
76.7 (76.7)
76.7 (77.2)
77.5 (77.5)
77.9 (77.8)
77.0 (76.8)
76.9 (77.1)
7.3 (7.1)
7.2 (7.1)
7.4 (7.4)
7.7 (7.6)
7.9 (7.9)
8.1 (8.4)
8.4 (8.3)
7.7 (7.7)
7.8 (7.9)
8.0 (8.0)
8.4 (8.3)
8.6 (8.6)
8.9 (8.8)
8.5 (8.2)
8.5 (8.5)
2.2 (2.2)
2.2 (2.2)
2.1 (2.1)
2.0 (2.1)
2.0 (2.0)
1.9 (1.9)
1.8 (1.8)
2.0 (2.0)
1.9 (2.0)
1.9 (2.0)
1.8 (1.9)
1.7 (1.8)
1.7 (1.7)
2.3 (2.2)
2.1 (2.1)
10a
10b
Fig. 13 Plot of clearing points for ligands 6 and 7 and complexes 8 and
9.
Table 5 Analytical data for the new complexes
Calculated (Found)/%
Technologies Inc., Whitehouse, NJ, Microanalytical Service.
All chemicals were used as received unless otherwise speci®ed.
Infrared spectra were recorded on a Perkin-Elmer 1600 FT
infra-red spectrophotometer (4000±450 cm21) at University of
Shef®eld and a Nicolet Magna 550 IR spectrometer at
University of Toronto. Spectra were recorded as Nujol mulls
between polythene plates, or as CH2Cl2 solutions, or as KBr
disks.1H and 13C NMR spectra were recorded on a Bruker WM
250 and a Varian Gemini 200 spectrometer; chemical shifts are
quoted relative to an internal deuterium lock. The melting
points and phase transitions of liquid crystal materials were
observed by differential scanning calorimetry (DSC) using a
Perkin-Elmer DSC7 system with a Perkin-Elmer 7000 data
station using TAS 7 software. Visual characterisation of the
liquid-crystalline properties of the bulk materials was per-
formed using a Zeiss Jenalab-pol polarising microscope
Compound
Yield (%)
C
H
N
8a
8b
8c
8d
8e
8f
8g
9a
9b
9c
9d
9e
9f
83.3
81.5
86.7
83.3
79.4
74.5
76.7
87.4
83.1
78.9
78.4
73.2
76.7
73.2
78.3
56.5 (56.6)
57.0 (57.1)
57.0 (57.5)
57.6 (57.9)
58.4 (58.7)
59.1 (59.4)
59.6 (60.1)
57.8 (58.3)
57.8 (58.6)
58.4 (59.0)
59.5 (60.1)
60.3 (60.1)
61.0 (61.4)
57.4 (57.7)
58.0 (58.1)
4.8 (4.8)
5.0 (4.9)
4.9 (5.0)
5.0 (5.2)
5.5 (5.4)
5.6 (5.7)
5.9 (5.9)
5.3 (5.3)
5.4 (5.4)
5.6 (5.6)
5.9 (5.9)
6.1 (6.1)
6.5 (6.3)
5.4 (5.4)
5.6 (5.7)
1.9 (1.5)
1.5 (1.5)
1.4 (1.5)
1.7 (1.4)
1.4 (1.4)
1.4 (1.4)
1.3 (1.3)
1.4 (1.4)
1.4 (1.4)
1.4 (1.4)
1.3 (1.3)
1.3 (1.3)
1.3 (1.3)
1.5 (1.5)
1.8 (1.5)
11a
11b
Fig. 14 Other mesomorphic complexes of octahedral Re(I).
J. Mater. Chem., 2000, 10, 637±644
643

View Article Online
6
7
G. W. Gray and J. W. Goodby, Smectic Liquid Crystals: Textures
and Structures, Leonard Hill, Glasgow, 1984.
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Acknowledgements
The authors thank H. C. Stark for a generous gift of rhenium
and X.H.L. thanks the University of Shef®eld for a scholarship.
8
9
J. E. Maclennan and M. Seul, Phys. Rev. Lett., 1992, 69, 2082;
C. Y. Chao, S. W. Hui, J. E. Maclennan, C. F. Chou and J. T. Ho,
Phys. Rev. Lett., 1997, 78, 2581.
M.-A. Guillevic, M. J. Danks, S. K. Harries, S. R. Collinson,
A. D. Pidwell and D. W. Bruce, Polyhedron, in press.
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