New metallomesogens core. New copper complexes with calamitic mesophases using tropolone based ligands. Crystal structure of bis(5-octyloxytropolonato)copper

Article abstract of DOI:10.1039/a707255d

A new class of metallomesogens based on 5-substituted tropolones with both enantiotropic and monotropic mesophase behaviour are prepared, the mesogenic properties are in line with the rod-like, calamitic nature of bis(5-octyloxytropolonato)copper shown in its crystal structure.

Full text of DOI:10.1039/a707255d

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New metallomesogens core. New copper complexes with calamitic mesophases
using tropolone based ligands. Crystal structure of
bis(5-octyloxytropolonato)copper
John R. Chipperfield, Steve Clark, James Elliott and Ekkehard Sinn*
Department of Chemistry, University of Hull, Hull, UK HU6 7RX
A new class of metallomesogens based on 5-substituted
tropolones with both enantiotropic and monotropic meso-
phase behaviour are prepared, the mesogenic properties are
in line with the rod-like, calamitic nature of bis(5-
octyloxytropolonato)copper shown in its crystal structure.
very fine needles are obtained. Crystallisation of bis(5-
octyloxytropolonato)copper from 1,4-dioxan containing 10%
acetic acid in a similar way to that used for bis(tropolonato)-
copper(ii)15 yielded a suitable crystal for an X-ray diffraction
study.‡ The CuO
4
centre is required by crystallographic
symmetry to be precisely planar, and the entire molecule is
planar within 7%. The ligand plane O(1)C(1)C(7)O(2) attached
to the Cu makes an angle of 2° with the tropolone ring. The
molecular structure shown in Fig. 1 confirms the calamitic
nature of the tropolone derivatives, while the packing in the
crystal shows a similar arrangement to that in the smectic C
phase. No solvent molecules are incorporated into the structure
and there is no Cu–Cu interaction, the closest Cu···Cu approach
being along the c-axis at 6.413(4) Å. The alkyl chain thermal
parameters are interesting in that they exhibit partial melting at
room temperature.
NMR analysis of 5-alkoxy tropolones confirmed their
structure. Satisfactory analyses were obtained for the com-
plexes. Over a period of time, the copper complexes are prone
to hydrate, making them difficult to dry. However, because of
the high transition temperatures, all water will have evaporated
from the copper complex and have no effect on the mesophase
behaviour. This is confirmed by uniform phase identification
Most metallomesogens1–4 have made use of benzene rings as
integral parts of the rigid core. Seven-membered ring cores in
metallomesogens are reported here for the first time. Tropolone-
based organic liquid crystals have been reported by Uemura
5
6–9
et al., and Mori et al.
Tropolone forms complexes with
10
many metals in a manner analogous to acetylacetone, but none
were reported to be metallomesogens. We report here the first
syntheses and studies of mesogenic complexes 1 based on
tropolone.
OH
O
O
RO
M
OR
RO
O
O
O
1
R = CnH2n +1 (n = 8, 10, 12, 14, 16); M = Cu, Ni, VO
2a R = H,
b R = alkyl
8
We have modified the literature method to make 5-substi-
(
and transition temperatures) of the copper complexes when dry
tuted tropolones, 2b, from 5-hydroxytropolone, 2a, by using
and hydrated. IR data for bis[5-(decyloxy)tropolonato]-
copper(ii) (KBr disc): 2918s, 2850s, 1516s, 1432vs, 1350s,
1241s, 1204s, 789w.
dimethylimidazolidinone (DMI) as solvent for alkylation of the
8
5
-position to replace the carcinogenic HMPA. DMI has in the
11–14
past been reported as replacement for HMPA,
but we
believe that this is the first reported use for tropolone derivatives
Scheme 1.
Table 1 Phase transition temperatures and corresponding enthalpies
OH
21
(kJ mol ) of copper tropolonate complexes
O2, hn
HO
haematoporphyrin IX
O
Cu
O
O
O
RO
OR
RBr
NaH
DMI
O
O
Alkyl chain R
C10H21
OH
O
250 °C (32.51)
O
O
O
O
M(OAc)2
K
I
I
RO
M
OR
RO
151 °C
11.10)
248 °C
(18.42)
SB
(
Scheme 1
2
39 °Ca
242 °Ca
C12H25
C14H29
K
SC
235 °Ca
The copper complexes of these 5-substituted tropolones (1,
M = Cu) have been synthesised in the usual way† and their
mesomorphic nature has been studied using polarised optical
microscopy and differential scanning calorimetry. Variable
temperature X-ray powder studies are in progress.
1
79 °C
163 °C
B
SB
(7.71)
(4.09)
34 °Ca
236 °Ca
2
K
SC
I
The decyl substituted copper complex displays a monotropic
183 °C
235 °Ca
1
48 °C
B
SB
S
B
phase. Both the dodecyl and tetradecyl copper complexes
mesophase (which despite the high
temperatures are stable) as well as S and crystal G phases. The
hexadecyl substituted copper complex exhibits a S phase and
(9.01)
(5.67)
exhibit a short range S
C
233 °C (34.80)
B
C16H33
K
I
B
an anisotropic plastic crystal phase which cannot be pinpointed.
The mesogenic data are summarized in Table 1.
141 °C
232 °C
(26.80)
1
80 °C
(13.77)
G/J
SB
(
6.30)
Long chain alkoxy derivatives are very difficult to crystallise
in forms suitable for X-ray structure determination. Generally
a
Overlapping peaks, enthalpies could not be resolved.
Chem. Commun., 1998
195

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C(5)
C(6)
O(2)
Cu
C(9)
C(8)
C(11)
C(13)
C(7)
C(3)
C(4)
C(10)
C(15)
C(1)
C(12)
O(1)
C(2)
C(14)
Fig. 1 View of bis(5-octyloxytropolonato)copper(ii) from X-ray data
Nickel and oxovanadium(iv) complexes of the 5-substituted
tropolone ligands have been prepared. However, despite having
melting points which are 50 and 90 °C lower respectively than
their copper complex counterparts, none have displayed any
mesophases. For the nickel complexes, IR spectra suggest
octahedral nickel.
While mesophases are still at high temperatures, appropriate
substitution on the tropolone rings enables the length-to-breadth
ratio to be adjusted, and initial work gives the promise of
metallotropolonates with much lower mesophase transition
temperatures. The use of tropolone derivatives in medicine
tometer. The small crystal size led to a relatively small data set. The copper,
oxygen and ring carbons were refined with anisotropic thermal parameters.
Cu lies on a special position (origin): Cu–O(1) 1.916(2) Å, Cu–O(2)
1
.902(9) Å; O(1)–Cu–O(2) 85.0(4)°. CCDC 182/694.
1
2
A.-M. Giroud-Godquin and P. M. Maitlis, Angew. Chem., Int. Ed. Engl.,
991, 30, 375.
P. Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano and E. Sola,
1
Coord. Chem. Rev., 1992, 117, 215.
3 D. W. Bruce, J. Chem. Soc., Dalton Trans., 1993, 2983.
4 S. A. Hudson and P. M. Maitlis, Chem. Rev., 1993, 93, 861.
5
6
7
8
9
T. Uemura, S. Takenaka, S. Kusabayashi and S. Seto, Mol. Cryst. Liq.
Cryst., 1983, 95, 287.
A. Mori, K. Katahira, K. Kida and H. Takeshita, Chem. Lett., 1992,
(
colchicine is a valuable anti-tumour agent while hinokitiol has
strong biocidal properties), indicates potential uses for metal
tropolonate derivatives outside the field of display devices.
The authors would like to thank EPSRC for financial support,
and Professor J. Goodby and Dr P. Styring for help with phase
identification.
1
767.
A. Mori, H. Takeshita, K. Kida and M. Uchida, J. Am. Chem. Soc., 1990,
12, 8635.
1
A. Mori, N. Kato, H. Takeshita, M. Uchida, H. Taya and R. Nimura,
J. Mater. Chem., 1991, 1, 799.
A. Mori, H. Taya and H. Takeshita, Chem. Lett., 1991, 579.
1
0 Comprehensive Coordination Chemistry, ed. G. Wilkinson, R. D.
Gillard and J. McCleverty, Pergamon, 1987, vol. 2, p. 397.
Footnotes and References
*
†
E-mail: e.sinn@chemistry.hull.ac.uk
Example: bis[5-(decycloxy)tropolonato]copper(ii): 5-decyloxytropolone
11 B. J. Barker, J. Rosenfarb and J. A. Caruso, Angew. Chem., Int. Ed.
Engl., 1979, 18, 503.
12 D. D. MacNicol, P. R. Mallinson, A. Murphy and G. J. Sym,
Tetrahedron Lett., 1982, 23, 4131.
(0.18 g, 0.71 mmol), sodium acetate (0.1 g, 1.4 mmol) and copper acetate
3
(0.072 g, 0.359 mmol) were dissolved in methanol (15 cm ). The mixture
was refluxed for 3 h before cooling and filtration of the copper complex as
a green powder. Recrystallisation in dichloromethane yielded bis[5-
13 D. Seebach, R. Henning and T. Mukhopadhyay, Chem. Ber., 1982, 115,
1705.
14 D. Seebach, Chem. Br., 1985, 21, 632.
15 J.-E. Berg, A.-M. Pilotti, A.-C. Soederholm and B. Karlsson, Acta
Crystallogr., Sect. B, 1978, 34, 3071.
(
‡
decycloxy)tropolonato]copper(ii) as green needles.
¯
6
Crystal data: C80H42CuO , triclinic, space group P1, a = 7.607(4), b =
1
5.871(8), c = 6.413(4) Å, a = 96.32(4), b = 105.46(3), g = 97.449(3)°,
3
21
U = 731(1) Å , Z = 1, T = 24 °C, m(Mo-Ka) = 7.84 cm , R, R
for 990 independent reflections collected on a Rigaku AFC6S diffrac-
w
= 0.055
Received in Cambridge, UK, 7th October 1997; 7/07255D
196
Chem. Commun., 1998