Crossover phase behavior (discotic to calamitic) in liquid-crystalline copper complexes. Dependence on the length and position of alkoxy chains in new polycatenar Bis[5-(dialkoxybenzylidine)aminotropolonato]copper(II) complexes

Article abstract of DOI:10.1021/ic001475u

New polycatenar metallomesogens have been synthesized containing a tropolone core joined to benzylidine terminal rings. Variation of the position, number, and nature of alkoxy substituents on the terminal rings allows for the control of the phase behavior

Full text of DOI:10.1021/ic001475u

6390
Inorg. Chem. 2001, 40, 6390-6396
Crossover Phase Behavior (Discotic to Calamitic) in Liquid-Crystalline Copper Complexes.
Dependence on the Length and Position of Alkoxy Chains in New Polycatenar
Bis[5-(dialkoxybenzylidine)aminotropololonato]copper(II) Complexes
James M. Elliott,† John R. Chipperfield, and Stephen Clark
Department of Chemistry, University of Hull, Hull HU6 7RX, U.K.
Ekkehard Sinn*
Department of Chemistry, University of MissourisRolla, Rolla, Missouri 65409
ReceiVed December 29, 2000
New polycatenar metallomesogens have been synthesized containing a tropolone core joined to benzylidine terminal
rings. Variation of the position, number, and nature of alkoxy substituents on the terminal rings allows for the
control of the phase behavior of the compounds. In particular, for copper complexes with 3,4-dialkoxy substitution,
a change from calamitic to discotic (columnar) behavior is seen as the chain lengths are increased.
Introduction
separation of the tropolone-based compounds, colchicine and
trimethylcolchicinic acid.4
Calamitic liquid-crystalline molecules have rigid cores with
terminal flexible alkyl groups. The majority of the rigid cores
of organic liquid crystals are based upon benzene rings. In metal-
based liquid crystals (metallomesogens), rigid chelate rings also
form part of the rigid cores. Metallomesogens based on Schiff
bases use phenyl rings as rigid cores with alkyl chains, all of
which are necessarily located opposite but off-center to the
metal. To place one substituent in an opposite site, we have
replaced one of the benzenes by five- and seven-membered rings
and have formed the first metallomesogens (1)1 based on
tropolone (2-hydroxycyclohepta-2,4,6-trienone). This work was
While the tropolone core is aromatic, it is some 13% broader
than benzene and is, therefore, likely to impart different packing
arrangements on complexes. The tropolone complexes 1 have
high transition temperatures, but for many (though not all) of
the applications of metallomesogens, low transition temperatures
are desirable. To reduce these temperatures, the tropolone
ligands need modification. One successful way of lowering
mesophase transition temperatures is by the incorporation of
m-alkyl chain substituents on benzene rings as well as the usual
p-alkyl chains: Berdague et al.5 have synthesized Schiff-base
complexes with both para and ortho substituents and also with
both para and meta chains. Table 1 shows that the transition
temperatures of both of these are reduced when lateral chains
are added. The complexes 2 (X ) Y ) H) have extended cores,
subsequently confirmed by Mori et al.2 Tropolone is a versatile
chelating agent with a complexing ability akin to that of
â-diketones (log K1 for tropolonate-Cu2+ is 8.35, and for
acetylacetonate-Cu2+ it is 8.16). Tropolones are also of interest
as the cores of the natural products hinokitiol (â-thujaplicin and
4-isopropyltropolone), a powerful fungicide, and colchicines,
which show strong antitumor and antigout activity. This high-
binding constant explains why copper(II) tropolonate is a
classical complex which can readily be used for the purification
of tropolone by reversing complexation (e.g., with cyanide).3
Copper complexes can also be used for the chromatographic
† Present address: University of Missouri-Rolla.
(1) Chipperfield, J. R.; Clark, S.; Elliott, J. M.; Sinn, E. Chem. Commun.
1998, 195.
(2) Mori, A.; Takemoto, M.; Mori, R.; Takeshita, H.; Ujiie, S.; Vill, V.
Chem. Lett. 1998, 601.
which are rodlike in character and consistent with calamitic
liquid-crystal properties. However, the introduction of ortho or
meta substitution in the terminal benzene rings makes the
(3) Roberts, J. D.; Caserio, M. C. Basic Principles of Organic Chemistry,
2nd ed.; W. A. Benjamin, Inc.: Menlo Park, CA, 1977. Lloyd, D.
Nonbenzenoid Conjugated Carbocyclic Compounds; Elsevier:
New York, 1984.
(4) Lacey, E.; Brady, R. J. Chromatogr. 1984, 315, 233.
(5) Berdague, P.; Perez, F.; Courtieu, J.; Bayle, J. P. Bull. Soc. Chim. Fr.
1994, 131, 335.
10.1021/ic001475u CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/06/2001

Liquid-Crystalline Cu Complexes
Inorganic Chemistry, Vol. 40, No. 25, 2001 6391
Table 1. Effects of Substitution on the Phase Properties of 2
para chain only
ortho and para chains
meta and para chains
R
2 (X ) Y ) H)
2 (X ) OR, Y ) H)
cryst 138 iso
cryst 92.8 iso
cryst 52.5 N 61.5 iso
cryst 75 iso
2 (X ) H, Y ) OR)
cryst 171.5 SC 177.5 iso
cryst 138 S 158.5 iso
cryst 115.5 S 141 iso
cryst 109.5 S 140 iso
C4H9
C8H17
C12H25
C16H33
cryst 231 N 261 iso
cryst 195 N 257 iso
cryst 173 N 248 iso
cryst 158 N 233 iso
suspended in ethanol (100 cm3). A total of 5% of palladium/charcoal
(20 mg) was added as a catalyst, and the reaction was stirred under a
hydrogen atmosphere at room temperature for 8 h. No further hydrogen
was taken up in a further 24 h. The dark-green solution was filtered to
reclaim the catalyst, and the solvent was removed to give a hard-orange
powder. Sublimation (95 °C at 0.5 mmHg) and recrystallization gave
5-aminotropolone (1.96 g, 92%) as orange needles, mp 178 °C (from
ethyl acetate; lit.22 177-178 °C. IR υmax/cm-1 (KBr disk): 3440, 3370,
complexes broader and lowers mesophase transitions. In par-
ticular, alkoxy groups ortho to the ester link cause a substantial
lowering of the temperature.
The first liquid crystals which showed a crossover from
calamitic to discotic (columnar) behavior dependent on the chain
length were described by Malthete and co-workers6,7 and called
phasmids (named after the stick insect, the phasma). It is of
great interest to discover such crossover behavior in metal-
lomesogens. The first biforked hybrids were described by
Nguyen et al.8 and later termed, from the number of alkyl chains
present, polycatenars.9,10 Although most polycatenars are organic
liquid crystals, metal-containing polycatenars include 1,3-
butadiene iron carbonyl complexes11 and stilbazole complexes
of silver(I),12 palladium, and platinum.13,14 Recently Ohta et al.15
has reported a series of substituted bis(diphenylglyoximato)-
nickel(II) complexes 3 where, as the alkyl chains were shortened,
mesophase behavior changed from columnar to lamellar, though
these materials are not polycatenar. Polycatenars are represented
by compounds recently reported by Tschierske,16,17 Ziessel,18,19
and Swager20,21 and their co-workers. In our work to extend
the range of metallomesogen cores, we have synthesized a series
of 5-(alkoxybenzylidine)tropolones (4) and prepared complexes
5 from them. The complexes show how the subtle interactions
between the core nature and chain length affect the melting
behavior and have given rise to a novel series of metallome-
sogens showing phase-crossover behavior.
1
3220 br, 1675, 1540 s, 1460 vs, 1421 vs, 1220 vs, 780. H NMR δ
(400 MHz, DMSO-d6, Me4Si): 7.09 (2H, d, J ) 12.0, trop), 6.70 (2H,
d, J ) 12.0, trop), 6.25 (2H, s, trop-NH2). MS m/z: 137 (M+, 38%),
109 (100), 91 (6), 82 (21), 80 (82), 68 (7), 63 (21), 58 (9), 55 (19), 53
(54), 52 (64), 45 (6). J values are given in hertz throughout.
2-Hydroxy-4-dodecyloxybenzaldehyde. This was prepared in bu-
tanone from 2,4-dihydroxybenzaldehyde and bromododecane in the
presence of potassium bicarbonate in a manner similar to that
reported.23,24 The change in the solvent from acetone24 to butanone
increased the yield. 2-Hydroxy-4-dodecyloxybenzaldehyde was obtained
(overall yield 75%) as white needles, mp 40 °C (from ethyl acetate;
1
lit.24 39 °C), with H NMR agreeing with the reports.23,24
2-Hydroxy-4-hexadecyloxybenzaldehyde. This was made similarly
in 60% yield as pale-yellow needles, mp 51 °C (from ethyl acetate).
IR υmax/cm-1 (KBr disk): 3201-3000, 2923, 2855, 1681, 1578, 1508,
1395, 1355, 1321, 1298, 820. 1H NMR δ (400 MHz, CD2Cl2, Me4Si):
0.87 (3H, t, J ) 7.0, -CH3), 1.20-1.48 (26H, m, (CH2)13), 1.75-1.88
(2H, m, Ar-O-CH2-CH2-R), 4.01 (2H, t, J ) 6.6, Ar-O-CH2-
R), 6.40 (1H, s, Ar), 6.53 (1H, d, J ) 8.6, Ar), 7.44 (1H, d, J ) 8.6,
Ar), 9.70 (1H, s, OdCH-Ar), 11.46 (1H, s, HO-Ar). MS m/z: 362
(M+, 36%), 245 (18), 333 (14), 277 (16), 207 (15), 179 (12), 151 (22),
138 (100), 123 (16), 69 (35). Although previously reported,25 there are
no data in the literature.
(6) Malthete, J.; Levelut, A. M.; Nguyen, H. T. J. Phys., Lett. 1985, 46,
L875.
(7) Malthete, J.; Nguyen, H. T.; Destrade, C. Liq. Cryst. 1993, 13, 171.
(8) Nguyen, H. T.; Destrade, C.; Levelut, A. M.; Malthete, J. J. Phys.
(Paris) 1986, 47, 553.
(9) Gasparoux, H.; Hardouin, F.; Destrade, C.; Nguyen, H. T. New J.
Chem. 1992, 16, 295.
(10) Nguyen, H. T.; Destrade, C.; Malthete, J. AdV. Mater. 1997, 9, 375.
(11) Jacq, P.; Malthete, J. Liq. Cryst. 1996, 21, 291.
(12) Donnio, B.; Heinrich, B.; Gulik Krzywicki, T.; Delacroix, H.; Guillon,
D.; Bruce, D. W. Chem. Mater. 1997, 9, 2951.
(13) Donnio, B.; Bruce, D. W. J. Chem. Soc., Dalton Trans. 1997, 2745.
(14) Neve, F.; Ghedini, M.; Francescangeli, O. Liq. Cryst. 1996, 21, 625-
630.
(15) Ohta, K.; Higashi, R.; Ikejima, M.; Yamamoto, I.; Kobayashi, N. J.
Mater. Chem. 1998, 8, 1979.
(16) Hegmann, T.; Peidis, F.; Diele, S.; Tschierske, C. Liq. Cryst. 2000,
27, 1261.
(17) Hegmann, T.; Neumann, B.; Kain, J.; Diele, S.; Tschierske, C. J. Mater.
Chem. 2000, 10, 2244.
(18) El-ghayoury, A.; Douce, L.; Skoulios, A.; Ziessel, R. Angew. Chem.,
Int. Ed. Engl. 1988, 37, 2205.
(19) Ziessel, R.; Douce, L.; El-ghayoury, A.; Harriman, A.; Skoulios, A.
Angew. Chem., Int. Ed. 2000, 39, 1489.
(20) Trzaska, S. T.; Zheng, H. X.; Swager, T. M. Chem. Mater. 1999, 11,
130.
(21) Levitsky, I. A.; Kishikawa, K.; Eichhorn, S. H.; Swager, T. M. J.
Am. Chem. Soc. 2000, 122, 2474.
(22) Uemura, T.; Takenaka, S.; Kusabayashi, S.; Seto, S. Mol. Cryst. Liq.
Cryst. 1983, 95, 287.
(23) Binnemans, K.; Galyametdinov, Y. G.; Collinson, S. R.; Bruce, D.
W. J. Mater. Chem. 1998, 8, 1551.
(24) Lai, C. K.; Chang, C.-H.; Tsai, C.-H. J. Mater. Chem. 1998, 8, 599.
(25) Cerrada, P.; Marcos, M.; Serrano, J. L. Mol. Cryst. Liq. Cryst. 1989,
170, 79.
Experimental Section
5-Aminotropolone. This was prepared using a modification of
Uemura’s method.22 5-Nitrosotropolone (2.32 g, 15.36 mmol) was

6392 Inorganic Chemistry, Vol. 40, No. 25, 2001
Elliott et al.
2-Hexyloxy-4-dodecyloxybenzaldehyde (6a). 2-Hydroxy-4-dodec-
yloxybenzaldehyde (2.00 g, 6.53 mmol), potassium carbonate (0.91 g,
6.60 mmol), and 1-bromohexane (1.15 cm3, 7 mmol) were added to
DMF (100 cm3) and refluxed for 4 h. The solvent was removed using
a rotary evaporator, and the brown residue was extracted into diethyl
ether (100 cm3) and then filtered before being washed with water (3 ×
100 cm3) and a saturated sodium chloride solution (2 × 100 cm3). The
diethyl ether layer was then dried with calcium chloride before removing
the solvent and washing the solid with cold light petroleum (bp 40-
60 °C, 2 × 10 cm3) to yield 6a (2.38 g, 93%) as a white powder, mp
50 °C (from hexane). IR υmax/cm-1 (KBr disk): 2915 vs, 2840 vs, 1670
3,4-Dioctyloxybenzaldehyde (6h). 3,4-Dihydroxybenzaldehyde (3.00
g, 21.74 mmol), potassium bicarbonate (4.45 g, 44.00 mmol), potassium
iodide (0.10 g), and 1-bromooctane (8.49 cm3, 44.00 mmol) were
suspended in butanone (120 cm3) and refluxed for 18 h under a nitrogen
atmosphere. The suspension was cooled, and the solvent was removed
to give a yellow solid, which was extracted into dichloromethane (100
cm3). The extract was washed with 1 M hydrochloric acid (2 × 100
cm3) and water (100 cm3) and then dried with magnesium sulfate, and
the solvent was removed. The solid residue was washed with ethanol
(2 × 10 cm3) to yield 6h (5.43 g, 69%) as white prisms, mp 51 °C
(from hexane/methanol, 4:1). IR υmax/cm-1 (KBr disk): 2925 vs, 2854
1
1
s, 1601 vs, 1462 s, 1293 s, 1260 s, 1190 s, 1110 s. H NMR δ (400
s, 1680, 1608 s, 1516 s, 1467 s, 1433 vs, 1356 s, 1266 s, 1179 w. H
MHz, CD2Cl2, Me4Si): 0.88 (3H, t, J ) 7.0, -CH3), 0.91 (3H, t, J )
7.0, -CH3), 1.20-1.52 (24H, m, (CH2)3 + (CH2)9), 1.75-1.88 (2H,
m, Ar-O-CH2-CH2-R), 1.87 (2H, m, Ar-O-CH2-CH2-R), 3.99
(2H, t, J ) 6.4, Ar-O-CH2-R), 4.02 (2H, t, J ) 6.3, Ar-O-CH2-
R), 6.42 (1H, s, Ar), 6.49 (1H, d, J ) 8.6, Ar), 7.71 (1H, d, J ) 8.6,
Ar), 10.28 (1H, s, OdCH-Ar).
NMR δ (400 MHz, CD2Cl2, Me4Si): 0.89 (3H, m, 2 × -CH3), 1.21-
1.56 (20H, m, 2 × (CH2)5), 1.83-1.94 (4H, m, 2 × Ar-O-CH2-
CH2-R), 4.03 (2H, t, J ) 6.6, Ar-O-CH2-R), 4.07 (2H, t, J ) 6.6,
Ar-O-CH2-R), 6.97 (1H, d, J ) 8.3, Ar), 7.37 (1H, s, Ar), 7.42
(1H, d, J ) 8.3, Ar), 9.81 (1H, s, OdCH-Ar).
Aldehydes 6i-m were made similarly. Their characterization
follows.
Aldehydes 6b-g were made similarly. Their characterization follows.
2-Decyloxy-4-dodecyloxybenzaldehyde (6b) was prepared in an
3,4-Didecyloxybenzaldehyde (6i) was prepared in a 72% yield as
white prisms, mp 64 °C (from hexane/methanol, 4:1). IR υmax/cm-1
(KBr disk): 2925 vs, 2854 s, 1680, 1608 s, 1516 s, 1467 s, 1433 vs,
1356 s, 1266 s, 1179 w. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.88
(6H, m, 2 × -CH3), 1.18-1.53 (28H, m, 2 × (CH2)7), 1.82 (2H, m,
Ar-O-CH2-CH2-R), 1.85-1.94 (2H, m, Ar-O-CH2-CH2-R),
4.03 (2H, t, J ) 6.6, Ar-O-CH2-R), 6.97 (1H, d, J ) 8.3, Ar), 7.36
(1H, s, Ar), 7.41 (1H, d, J ) 8.3, Ar), 9.80 (1H, s, OdCH-Ar).
3,4-Didodecyloxybenzaldehyde (6j) was prepared in a 67% yield
as a white powder, mp 70 °C (from hexane/ethanol, 4:1). IR υmax/cm-1
(KBr disk): 3432 w, 2930 vs, 2858 s, 1705 s, 1680, 1601 s, 1465 s,
1300, 1170 s, 1059, 721. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.88
(6H, t, 2 × -CH3), 1.14-1.60 (36H, m, 2 × (CH2)9), 1.82-1.92 (4H,
m, 2 × Ar-O-CH2-CH2-R), 4.03 (2H, t, J ) 6.6, Ar-O-CH2-
R), 4.06 (2H, t, J ) 6.6, Ar-O-CH2-R), 6.97 (1H, d, J ) 8.0, Ar),
7.36 (1H, s, Ar), 7.42 (1H, d, J ) 8.0, Ar), 9.80 (1H, s, OdCH-Ar).
3,4-Ditridecyloxybenzaldehyde (6k) was prepared in a 65% yield
as a yellow powder, mp 73 °C (from chloroform/methanol, 2:1). ΙR
85% yield as a light-brown powder, mp 55 °C (from hexane). IR υmax
/
cm-1 (KBr disk): 2922 vs, 2840 vs, 1670 s, 1601 vs, 1462 s, 1293 s,
1
1260 s, 1190 s, 1110 s. H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.89
(6H, t, J ) 7.0, 2 × -CH3), 1.20-1.52 (32H, m, (CH2)7 + (CH2)9),
1.80 (2H, m, Ar-O-CH2-CH2-R), 1.75-1.88 (2H, m, Ar-O-CH2-
CH2-R), 3.99 (2H, t, J ) 6.4, Ar-O-CH2-R), 4.04 (2H, t, J ) 6.3,
Ar-O-CH2-R), 6.42 (1H, s, Ar), 6.49 (1H, d, J ) 8.6, Ar), 7.71
(1H, d, J ) 8.6, Ar), 10.23 (1H, s, OdCH-Ar).
2-Propyloxy-4-hexadecyloxybenzaldehyde (6c) was prepared in a
77% yield as a white powder, mp 44 °C (from hexane). ΙR υmax/cm-1
(KBr disk): 2922 vs, 2840 vs, 1670 s, 1601 vs, 1462 s, 1290 s, 1260
1
s, 1200 s, 1110 s. H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.88 (3H,
t, J ) 7.0, -CH3), 1.20-1.52 (29H, m, -CH3 + (CH2)13), 1.80 (2H,
m, Ar-O-CH2-CH2-R), 1.71-1.88 (2H, m, Ar-O-CH2-CH2-
R), 3.97 (2H, t, J ) 6.4, Ar-O-CH2-R), 4.03 (2H, t, J ) 6.3, Ar-
O-CH2-R), 6.42 (1H, s, Ar), 6.48 (1H, d, J ) 8.6, Ar), 7.71 (1H, d,
J ) 8.6, Ar), 10.23 (1H, s, OdCH-Ar).
2-Hexyloxy-4-hexadecyloxybenzaldehyde (6d) was prepared in a
υ
max/cm-1 (KBr disk): 2930 vs, 2851 s, 1706, 1680 s, 1601 s, 1465 s,
77% yield as a white powder, mp 42 °C (from ethyl acetate). IR υmax
/
1300, 1170 s, 1059, 721, 710 w. 1H NMR δ (400 MHz, CD2Cl2, Me4-
Si): 0.88 (6H, t, 2 × -CH3), 1.20-1.58 (40H, m, 2 × (CH2)10), 1.81-
1.94 (4H, m, Ar-O-CH2-CH2-R), 4.03 (2H, t, J ) 6.6, Ar-O-
CH2-R), 4.06 (2H, t, J ) 6.6, Ar-O-CH2-R), 6.97 (1H, d, J ) 8.0,
Ar), 7.37 (1H, s, Ar), 7.42 (1H, d, J ) 8.0, Ar), 9.81 (1H, s, OdCH-
Ar).
cm-1 (KBr disk): 2920 vs, 2835 vs, 1670 s, 1602 vs, 1462 s, 1290,
1
1260 s, 1200 s, 1110 s. H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.88
(3H, t, J ) 7.0, -CH3), 0.92 (3H, t, J ) 7.0, -CH3), 1.24-1.47 (32H,
m, (CH2)3 + (CH2)13), 1.75-1.88 (2H, m, Ar-O-CH2-CH2-R), 1.85
(2H, m, Ar-O-CH2-CH2-R), 3.97 (2H, t, J ) 6.4, Ar-O-CH2-
R), 4.03 (2H, t, J ) 6.3, Ar-O-CH2-R), 6.44 (1H, s, Ar), 6.52 (1H,
d, J ) 8.6, Ar), 7.71 (1H, d, J ) 8.6, Ar), 10.23 (1H, s, OdCH-Ar).
2-Decyloxy-4-hexadecyloxybenzaldehyde (6e) was prepared in a
3,4-Ditetradecyloxybenzaldehyde (6l) was prepared in a 62% yield
as a yellow powder, mp 74 °C (from chloroform/methanol, 2:1). IR
υ
max/cm-1 (KBr disk): 2930 vs, 2851 s, 1706 s, 1680, 1601 s, 1465 s,
78% yield as a white powder, mp 40 °C (from ethyl acetate). ΙR υmax
/
1300, 1170 s, 1059, 721, 712 w. 1H NMR δ (400 MHz, CD2Cl2, Me4-
Si): 0.87 (6H, t, 2 × CH3), 1.20-1.58 (44H, m, 2 × (CH2)11), 1.82-
1.94 (4H, m, 2 × Ar-O-CH2-CH2-R), 4.03 (2H, t, J ) 6.6, Ar-
O-CH2-R), 4.06 (2H, t, J ) 6.6, Ar-O-CH2-R), 6.97 (1H, d, J )
8.0, Ar), 7.36 (1H, s, Ar), 7.41 (1H, d, J ) 8.0, Ar), 9.80 (1H, s,
OdCH-Ar).
cm-1 (KBr disk): 2915 vs, 2835 vs, 1671 s, 1603 vs, 1462 s, 1290,
1
1260 s, 1200 s, 1108 s. H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.87
(6H, t, J ) 7.0, 2 × -CH3), 1.22-1.51 (40H, m, (CH2)9 + (CH2)13),
1.78-1.88 (2H, m, J ) 6.8, Ar-O-CH2-CH2-R), 1.85 (2H, m, Ar-
O-CH2-CH2-R), 4.01 (2H, t, J ) 6.4, Ar-O-CH2-R), 4.06 (2H, t,
J ) 6.4, Ar-O-CH2-R), 6.44 (1H, s, Ar), 6.53 (1H, d, J ) 8.6, Ar),
7.71 (1H, d, J ) 8.6, Ar), 10.23 (1H, s, OdCH-Ar).
3,4-Dihexadecyloxybenzaldehyde (6m) was prepared in a 69% yield
as a white powder, mp 81 °C (from chloroform/ethanol, 1:1). ΙR υmax
/
2,4-Dihexadecyloxybenzaldehyde (6f) was prepared in an 82% yield
as a white powder, mp 58 °C (from ethyl acetate). IR υmax/cm-1 (KBr
disk): 2920 vs, 2835 vs, 1671 s, 1603 vs, 1462 s, 1290, 1260 s, 1195
cm-1 (KBr disk): 2920 vs, 2851 s, 1680, 1617 s, 1516 s, 1467 s, 1433
1
vs, 1356 vs, 1266 s, 1170 w. H NMR δ (400 MHz, CD2Cl2, Me4Si):
0.87 (6H, t, 2 × CH3), 1.20-1.55 (52H, m, 2 × (CH2)13), 1.82-1.94
(4H, m, 2 × Ar-O-CH2-CH2-R), 4.03 (2H, t, J ) 6.6, Ar-O-
CH2-R), 4.06 (2H, t, J ) 6.6, Ar-O-CH2-R), 6.96 (1H, d, J ) 8.0,
Ar), 7.36 (1H, s, Ar), 7.41 (1H, d, J ) 8.0, Ar), 9.80 (1H, s, OdCH-
Ar).
3,5-Dihexadecyloxybenzaldehyde (6n). 3,5-Dihydroxybenzaldehyde
(1.00 g, 7.25 mmol), potassium bicarbonate (1.50 g, 15.00 mmol),
potassium iodide (ca. 0.10 g), and 1-bromohexadecane (4.58 cm3, 15.00
mmol), were suspended in butanone (120 cm3), and the mixture was
refluxed for 4 h before being cooled to room temperature and water
was added (200 cm3). The crude product was extracted from the aqueous
solution with dichloromethane (8 × 20 cm3) and washed with 1 M
hydrochloric acid (10 × 50 cm3), a saturated sodium bicarbonate
solution (4 × 100 cm3), and water (2 × 100 cm3). The dichloromethane
1
s, 1108 s. H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.87 (6H, t, J )
7.0, 2 × -CH3), 1.21-1.49 (52H, m, 2 × (CH2)13), 1.78-1.89 (4H,
m, 2 × Ar-O-CH2-CH2-R), 3.96 (2H, t, J ) 6.4, Ar-O-CH2-
R), 4.06 (2H, t, J ) 6.4, Ar-O-CH2-R), 6.44 (1H, s, Ar), 6.53 (1H,
d, J ) 8.6, Ar), 7.71 (1H, d, J ) 8.6, Ar), 10.21 (1H, s, OdCH-Ar).
2,4-Dipropyloxybenzaldehyde (6g) was prepared in 94% yield as
white crystals, mp 52 °C (from ethanol). IR υmax/cm-1 (KBr disk): 2921
vs, 2835 vs, 1670 s, 1603 vs, 1462 s, 1290, 1260 s, 1195 s, 1108 s. 1H
NMR δ (400 MHz, CD2Cl2, Me4Si): 1.04 (6H, m, 2 × -CH3), 1.79
(2H, m, 2 × Ar-O-CH2-CH2-CH3), 1.85 (2H, t, J ) 6.8, Ar-O-
CH2-CH2-CH3), 3.99 (2H, t, J ) 6.4, Ar-O-CH2-R), 4.02 (2H, t,
J ) 6.4, Ar-O-CH2-R), 6.45 (1H, s, Ar), 6.54 (1H, d, J ) 8.6, Ar),
7.73 (1H, d, J ) 8.6, Ar), 10.21 (1H, s, OdCH-Ar).

Liquid-Crystalline Cu Complexes
Inorganic Chemistry, Vol. 40, No. 25, 2001 6393
layer was dried with calcium chloride, and the solvent was removed.
The crude product was washed with ethanol (2 × 10 cm3) and light
petroleum (bp 40-60 °C, 10 cm3) to yield 6n (3.18 g, 75%) as a white
powder, mp 59 °C (from chloroform/ethanol, 2:1). IR υmax/cm-1 (KBr
disk): 2927 vs, 2857 s, 1701, 1604, 1471 s, 1358, 1301, 1190, 1067
w, 720. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.87 (6H, t, 2 ×
-CH3), 1.18-1.50 (52H, m, 2 × (CH2)13), 1.78-1.90 (4H, m, 2 ×
Ar-O-CH2-CH2-R), 3.98 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R),
6.69 (1H, s, Ar), 6.96 (2H, s, Ar), 9.87 (1H, s, OdCH-Ar).
1145. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.87 (6H, t, 2 × -CH3),
1.18-1.50 (52H, m, 2 × (CH2)13), 1.80-1.92 (4H, m, Ar-O-CH2-
CH2-R), 4.01 (2H, t, J ) 6.6, Ar-O-CH2-R), 4.03 (2H, t, J ) 6.6,
Ar-O-CH2-R), 6.47 (1H, s, Ar), 6.55 (1H, d, J ) 8.8, Ar), 7.23
(2H, d, J ) 12.0, trop), 7.33 (2H, d, J ) 12.0, trop), 8.00 (1H, d, J )
8.8, Ar), 8.73 (1H, s, NdCH).
5-(2,4-Dipropyloxybenzylidine)aminotropolone (4g) was prepared
in a 92% yield as yellow needles, mp 46 °C (from ethanol). IR υmax
/
cm-1 (KBr disk): 3300-3100 br, 2924 vs, 2850 s, 1660, 1620, 1541
1
5-(2-Hexyloxy-4-dodecyloxybenzylidine)aminotropolone (4a). Com-
pound 6a (1.00 g, 2.57 mmol), acetic acid (5 drops), and 5-ami-
notropolone (0.33 g, 2.40 mmol) were suspended in toluene (60 cm3).
A Dean-Stark trap was fitted to the reaction vessel, and the reaction
mixture was refluxed under a nitrogen atmosphere for 4 days before
the removal of the solvent by rotary evaporation. The yellow solid
produced was washed with ethanol (2 × 10 cm3) and cold diethyl ether
(10 cm3) and dried under vacuum for 2 h to yield 4a (1.03 g, 84%) as
a yellow solid, mp 71 °C (from ethanol). IR υmax/cm-1 (KBr disk):
3300-3100 br, 2920 vs, 2850 s, 1660, 1620, 1540 vs, 1515 s, 1450
vs, 1518 s, 1429 vs, 1433 s, 1383 s, 1361 vs, 1144. H NMR δ (400
MHz, CD2Cl2, Me4Si): 1.03 (6H, m, 2 × -CH3), 1.82-1.94 (4H, m,
2 × Ar-O-CH2-CH2-CH3), 3.94 (2H, t, Ar-O-CH2-Et), 3.97 (2H,
t, Ar-O-CH2-Et), 6.47 (1H, s, Ar), 6.55 (1H, d, J ) 8.8, Ar), 7.23
(2H, d, J ) 12.0, trop), 7.33 (2H, d, J ) 12.0, trop), 8.00 (1H, d, J )
8.8, Ar), 8.73 (1H, s, NdCH).
5-(3,4-Dioctyloxybenzylidine)aminotropolone (4h) was prepared
in a 90% yield as a yellow powder, mp 115 °C (from ethanol). IR
υ
max/cm-1 (KBr disk): 3300-3100 br, 2921 vs, 2850 s, 1660, 1622,
1
1540 vs, 1515 s, 1450 vs, 1430 s, 1379 s, 1362 vs, 1145. H NMR δ
(400 MHz, CD2Cl2, Me4Si): 0.86 (6H, t, J ) 7.0, 2 × -CH3), 1.22-
1.51 (20H, m, 2 × (CH2)5), 1.81-1.88 (4H, m, 2 × Ar-O-CH2-
CH2-R), 4.03 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R), 6.92 (1H, d, J )
8.3, Ar), 7.23-7.32 (3H, m, 2 trop + 1 Ar), 7.38 (2H, d, J ) 12.0,
trop), 7.52 (1H, s, Ar), 8.25 (1H, s, NdCH).
1
vs, 1431 s, 1379 s, 1362 vs, 1144. H NMR δ (400 MHz, CD2Cl2,
Me4Si): 0.86 (3H, t, -CH3), 0.87 (3H, t, -CH3), 1.20-1.50 (24H, m,
(CH2)3 + (CH2)9), 1.81-1.93 (4H, m, 2 × Ar-O-CH2-CH2-R), 4.02
(2H, t, J ) 6.6, Ar-O-CH2-R), 4.04 (2H, t, J ) 6.6, Ar-O-CH2-
R), 6.46 (1H, s, Ar), 6.56 (1H, d, J ) 8.8, Ar), 7.22 (2H, d, J ) 12.0,
trop), 7.33 (2H, d, J ) 12.0, trop), 8.00 (1H, d, J ) 8.8, Ar), 8.73 (1H,
s, NdCH).
5-(3,4-Didecyloxybenzylidine)aminotropolone (4i) was prepared
in an 86% yield as a yellow powder, mp 112 °C (from ethanol). IR
Schiff bases 4b-n were made similarly. Their characterization
follows.
υ
max/cm-1 (KBr disk): 3300-3100 br, 2920 vs, 2852 s, 1660, 1620,
1
1541 vs, 1510 s, 1450 vs, 1425 s, 1372 s, 1362 vs, 1144. H NMR δ
(400 MHz, CD2Cl2, Me4Si): 0.86 (6H, t, J ) 7.0, 2 × -CH3), 1.21-
1.51 (28H, m, 2 × (CH2)7), 1.81-1.88 (4H, m, 2 × Ar-O-CH2-
CH2-R), 4.03 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R), 6.92 (1H, d, J )
8.3, Ar), 7.23-7.32 (3H, m, 2 trop + 1 Ar), 7.38 (2H, d, J ) 12.0,
trop), 7.52 (1H, s, Ar), 8.25 (1H, s, NdCH).
5-(2-Decyloxy-4-dodecyloxybenzylidine)aminotropolone (4b) was
prepared in an 81% yield as a yellow powder, mp 75 °C (from ethanol).
IR υmax/cm-1 (KBr disk): 3300-3100 br, 2921 vs, 2850 s, 1660, 1620,
1
1540 vs, 1515 s, 1450 vs, 1430 s, 1379 s, 1362 vs, 1145. H NMR δ
(400 MHz, CD2Cl2, Me4Si): 0.86 (3H, t, -CH3), 0.87 (3H, t, -CH3),
1.20-1.50 (32H, m, (CH2)7 + (CH2)9), 1.81-1.93 (4H, m, 2 × Ar-
O-CH2-CH2-R), 4.02 (2H, t, J ) 6.6, Ar-O-CH2-R), 4.04 (2H, t,
J ) 6.6, Ar-O-CH2-R), 6.46 (1H, s, Ar), 6.56 (1H, d, J ) 8.8, Ar),
7.22 (2H, d, J ) 12.0, trop), 7.33 (2H, d, J ) 12.0, trop), 8.00 (1H, d,
J ) 8.8, Ar), 8.73 (1H, s, NdCH).
5-(3,4-Didodecyloxybenzylidine)aminotropolone (4j) was prepared
in an 82% yield as a yellow powder, mp 110 °C (from ethanol/
chloroform, 5:1). IR υmax/cm-1 (KBr disk): 3300-3100 br, 2924 vs,
2850 s, 1660, 1620, 1541 vs, 1520 s, 1429 vs, 1433 s, 1383 s, 1366 vs,
1144. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.86 (6H, t, J ) 7.0, 2
× -CH3), 1.21-1.51 (36H, m, 2 × (CH2)9), 1.82-1.92 (4H, m, 2 ×
Ar-O-CH2-CH2-R), 4.03 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R),
6.92 (1H, d, J ) 8.3, Ar), 7.23-7.32 (3H, m, 2 trop + 1 Ar), 7.38
(2H, d, J ) 12.0, trop), 7.52 (1H, s, Ar), 8.25 (1H, s, NdCH).
5-(3,4-Ditridecyloxybenzylidine)aminotropolone (4k) was prepared
in a 73% yield as a yellow powder, mp 108 °C (from ethanol/
chloroform, 4:1). IR υmax/cm-1 (KBr disk): 3300-3100 br, 2918 vs,
2850 s, 1660, 1620, 1539 vs, 1510 s, 1450 vs, 1425 s, 1372 s, 1362 vs,
1144. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.86 (6H, t, J ) 7.0, 2
× -CH3), 1.21-1.50 (40H, m, 2 × (CH2)10), 1.82-1.92 (4H, m, 2 ×
Ar-O-CH2-CH2-R), 4.03 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R),
6.92 (1H, d, J ) 8.3, Ar), 7.23-7.32 (3H, m, 2 trop + 1 Ar), 7.38
(2H, d, J ) 12.0, trop), 7.52 (1H, s, Ar), 8.25 (1H, s, NdCH).
5-(3,4-Ditetradecyloxybenzylidine)aminotropolone (4l) was pre-
pared in a 68% yield as a yellow powder, mp 107 °C (from ethanol/
chloroform, 4:1). IR υmax/cm-1 (KBr disk): 3300-3100 br, 2917 vs,
2849 s, 1660, 1620, 1540 vs, 1515 s, 1454 vs, 1425 s, 1372 s, 1362 vs,
1141. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.86 (6H, t, J ) 7.0, 2
× -CH3), 1.21-1.50 (44H, m, 2 × (CH2)11), 1.82-1.94 (4H, m, 2 ×
Ar-O-CH2-CH2-R), 4.03 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R),
6.92 (1H, d, J ) 8.3, Ar), 7.23-7.33 (3H, m, 2 trop + 1 Ar), 7.38
(2H, d, J ) 12.0, trop), 7.52 (1H, s, Ar), 8.25 (1H, s, NdCH).
5-(3,4-Dihexadecyloxybenzylidine)aminotropolone (4m) was pre-
pared in a 64% yield as a yellow powder, mp 105 °C (from ethanol/
cloroform, 3:1). IR υmax/cm-1 (KBr disk): 3300-3100 br, 2924 vs,
2850 s, 1660, 1620, 1541 vs, 1520 s, 1429 vs, 1433 s, 1383 s, 1366 vs,
1144. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.86 (6H, t, J ) 7.0, 2
× -CH3), 1.21-1.51 (52H, m, 2 × (CH2)13), 1.82-1.90 (4H, m, 2 ×
Ar-O-CH2-CH2-R), 4.03 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R),
6.92 (1H, d, J ) 8.3, Ar), 7.23-7.33 (3H, m, 2 trop + 1 Ar), 7.38
(2H, d, J ) 12.0, trop), 7.52 (1H, s, Ar), 8.25 (1H, s, NdCH).
5-(3,5-Dihexadecyloxybenzylidine)aminotropolone (4n) was pre-
pared in a 34% yield as a yellow powder, mp 47 °C (from butanol/
5-(2-Propyloxy-4-hexadecyloxybenzylidine)aminotropolone (4c)
was prepared in a 75% yield as a yellow powder, mp 54 °C (from
ethanol). IR υmax/cm-1 (KBr disk): 3300-3100 br, 2920 vs, 2850 s,
1660, 1620, 1541 vs, 1515 s, 1450 vs, 1430 s, 1379 s, 1362 vs, 1143.
1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.86 (3H, t, -CH3), 1.04 (3H,
t, -CH3), 1.20-1.50 (26H, m, (CH2)13), 1.81-1.93 (4H, m, 2 × Ar-
O-CH2-CH2-R), 4.02 (4H, m, 2 × Ar-O-CH2-R), 6.46 (1H, s,
Ar), 6.56 (1H, d, J ) 8.8, Ar), 7.22 (2H, d, J ) 12.0, trop), 7.33 (2H,
d, J ) 12.0, trop), 8.00 (1H, d, J ) 8.8, Ar), 8.73 (1H, s, NdCH).
5-(2-Hexyloxy-4-hexadecyloxybenzylidine)aminotropolone (4d)
was prepared in a 83% yield as a yellow powder, mp 60 °C (from
methanol/chloroform, 4:1). IR υmax/cm-1 (KBr disk): 3300-3100 br,
2920 vs, 2850 s, 1660, 1620, 1539 vs, 1510 s, 1450 vs, 1425 s, 1372
s, 1362 vs, 1144. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.86 (3H, t,
-CH3), 0.87 (3H, t, -CH3), 1.20-1.50 (32H, m, (CH2)3 + (CH2)13),
1.81-1.93 (4H, m, 2 × Ar-O-CH2-CH2-R), 4.02 (2H, t, J ) 6.6,
Ar-O-CH2-R), 4.04 (2H, t, J ) 6.6, Ar-O-CH2-R), 6.46 (1H, s,
Ar), 6.56 (1H, d, J ) 8.8, Ar), 7.22 (2H, d, J ) 12.0, trop), 7.33 (2H,
d, J ) 12.0, trop), 8.00 (1H, d, J ) 8.8, Ar), 8.73 (1H, s, NdCH).
5-(2-Decyloxy-4-hexadecyloxybenzylidine)aminotropolone (4e)
was prepared in a 72% yield as a yellow powder, mp 63 °C (from
ethanol/chloroform, 4:1). IR υmax/cm-1 (KBr disk): 3300-3100 br,
2918 vs, 2861 s, 1660, 1620, 1540 vs, 1515 s, 1449 vs, 1430 s, 1382
s, 1362 vs, 1145. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.86 (6H, t,
2 × -CH3), 1.20-1.50 (40H, m, (CH2)7 + (CH2)13), 1.81-1.93 (4H,
m, 2 × Ar-O-CH2-CH2-R), 4.02 (2H, t, J ) 6.6, Ar-O-CH2-
R), 4.04 (2H, t, J ) 6.6, Ar-O-CH2-R), 6.46 (1 H, s, Ar), 6.56 (1H,
d, J ) 8.8, Ar), 7.22 (2H, d, J ) 12.0, trop), 7.33 (2H, d, J ) 12.0,
trop), 8.00 (1H, d, J ) 8.8, Ar), 8.73 (1H, s, NdCH).
5-(2,4-Dihexadecyloxybenzylidine)aminotropolone (4f) was pre-
pared in a 67% yield as a yellow powder, mp 65 °C (from ethanol/
chloroform, 3:1). IR υmax/cm-1 (KBr disk): 3300-3100 br, 2924 vs,
2851 s, 1660, 1620, 1533 vs, 1515 s, 1450 vs, 1431 s, 1380 s, 1362 vs,

6394 Inorganic Chemistry, Vol. 40, No. 25, 2001
Elliott et al.
Table 2. Synthesis of 5-(Dialkoxybenzylidine)aminotropolones
aromatic ring substituents
2-R1
3-R2
4-R3
5-R4
aldehyde no.
Schiff base no.
mp Schiff base/°C
Cu complex no.
C6H13O
C10H21O
C3H7O
C6H13O
C10H21O
C16H33O
C3H7O
H
H
H
H
H
H
H
H
H
H
H
H
C12H25O
C12H25O
C16H33O
C16H33O
C16H33O
C16H33O
C3H7O
C8H17O
C10H21O
C12H25O
C13H27O
C14H29O
C16H33O
H
H
H
H
H
H
H
H
H
H
H
H
H
H
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
71
75
54
60
63
65
46
115
112
110
108
107
105
47
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
C8H17O
C10H21O
C12H25O
C13H27O
C14H29O
C16H33O
C16H33O
H
H
C16H33O
Scheme 1. Synthesis of Ligands
choroform, 4:1). IR υmax/cm-1 (KBr disk): 3300-3100 br, 2924 vs,
2850 s, 1660, 1620, 1541 vs, 1520 s, 1429 vs, 1433 s, 1383 s, 1366 vs,
1144. 1H NMR δ (400 MHz, CD2Cl2, Me4Si): 0.87 (6H, t, J ) 7.0, 2
× -CH3), 1.18-1.50 (52H, m, 2 × (CH2)13), 1.78-1.90 (4H, m, 2 ×
Ar-O-CH2-CH2-R), 3.99 (4H, t, J ) 6.6, 2 × Ar-O-CH2-R),
6.59 (1H, t, J ) 2.4, Ar), 7.01 (2H, d, J ) 2.4, Ar), 7.26 (2H, d, J )
11.9, trop), 7.35 (2H, d, J ) 11.9, trop), 8.30 (1H, s, NdCH).
Bis[5-(2-hexyloxy-4-dodecyloxybenzylidine)aminotropolonato]-
copper(II) (5a). Compound 4a (0.30 g, 0.59 mmol) was added to a
solution of anhydrous NaOAc (82 mg, 1.00 mmol) in ethanol (40 cm3)
and stirred for 10 min. A solution of Cu(OAc)2‚H2O (60 mg, 0.30 mmol)
in ethanol (20 cm3) was added to the reaction mixture, and the mixture
was refluxed for 2 h. The mixture was cooled in an ice bath, and the
yellow solid was filtered off. The solid was washed in diethyl ether
(10 cm3) and cold tetrahydrofuran (2 × 10 cm3) before being dried
under vacuum (0.5 mmHg) for 4 h. The crude product was purified
twice by a Soxhlet extraction with hexane to yield 5a (0.27 g, 84%) as
a yellow powder, mp 152 °C (from toluene). Anal. Calcd for
CuC64H92N2O8: C, 71.11; H, 8.58; N, 2.59. Found: C, 71.32; H, 8.47;
N, 2.51. IR υmax/cm-1 (KBr disk): 3600-3350, 2925 s, 2855 s, 1655,
1605 s, 1515 s, 1471 s, 1433 vs, 1364 s, 1312 s, 1181 w.
Copper complexes 5b-n were prepared similarly. As is common
with copper(II) chelate complexes, traces of water were very hard to
remove. Complex 5o was made from 4m and NiCl2‚6H2O, and 5p was
prepared from 4m and ZnCl2‚2H2O, similarly.
and identification of the substituted benzaldehydes not in the
literature are given in the Experimental Section. The alkoxylated
benzaldehydes and 5-aminotropolone were then condensed to
give the Schiff bases.22 Two copper complexes were readily
prepared from the 5-(alkoxybenzylidine)tropolones by reaction
with copper(II) acetate in the presence of sodium acetate. The
compounds synthesized are given in Table 2. The identity and
purity of all of the ligands was assessed by NMR, MS, and
TLC. Elemental analyses were satisfactory for all of the copper
complexes (Table 3).
Phase Studies. The phase behavior of the complexes was examined
by using an Olympus BH2 polarizing microscope in conjunction with
a Mettler FP5 hot stage and controller. Phase-transition enthalpies were
measured using a Perkin-Elmer DSC-2C with a PC 3600 thermal
analysis data station. The heating rates used were normally 10 °C min-1
,
and the measured onset of the indium standard was 156.66 °C, ∆H )
28.50 J g-1 (standard2626 value is 156.60 °C, ∆H ) 28.45 J g-1).
Results and Discussion
Melting Behavior of Complexes. (a) 2,4-Substituted Com-
plexes. For copper complexes 5a-g with substituents in the 2
and 4 positions of the benzylidine ring, there are no mesophases,
but melting points are much lower than the clearing temperatures
of the 5-alkoxytropolone derivatives previously reported1 (Table
4and Figure 1).
As expected, the length of the alkoxy chains, whether at the
2 or the 4 position, affects the melting points, which are the
lowest when both of the chains are the longest.
Synthesis. Scheme 1 shows the synthesis of 5-(alkoxybenz-
ylidine)tropolones. A supply of 5-aminotropolone is readily
synthesized. Tropolone is first treated with sodium nitrite to
form 5-nitrosotropolone,22 which is then reduced with hydrogen
over 5% palladium/charcoal in ethanol to yield 5-aminotropolo-
ne. The alkoxylated benzaldehydes 6 were prepared from the
appropriate hydroxybenzaldehyde.27-32 Details of preparation
Changing the metal atom from copper to nickel to zinc
produced little change in the melting point (Table 5).
(b) 3,5-Substituted Complexes. Scheme 2 shows the melting
behavior of bis[5-(3,5-dialkoxybenzylidine)tropolonato]copper
(5n; R1 ) R3 ) H and R2 ) R4 ) OC16H33).
The spread-out chains confer a disklike structure, and
microscopy confirmed a columnar-hexagonal disordered phase.
This agrees with the columnar phases identified in 3,4-
substituted polycatenar silver(I) complexes.33
(26) CRC Handbook of Physics and Chemistry, 68th ed.; Weast, R. C.,
Ed.; CRC Press: Boca Raton, FL.
(27) Donnio, B.; Bruce, D. W. J. Chem. Soc., Dalton Trans. 1997, 2745.
(28) Destrade, C.; Nguyen, H. T.; Alstermark, C.; Lindsten, G.; Nilsson,
M. Mol. Cryst. Liq. Cryst. 1990, 180, 265.
(29) Hoshino, N.; Takahashi, H.; Matsunaga, Y.; Okamoto, H.; Mitani, T.
Mol. Cryst. Liq. Cryst. 1992, 216, 265.
(30) Kosteyn, F.; Zerban, G.; Meier, H. Chem. Ber. 1992, 125, 893.
(31) Zerban, G.; Meier, H. Z. Naturforsch., B: Chem. Sci. 1993, 48, 171.
(32) Kretzschmann, H.; Muller, K.; Kolshorn, H.; Schollmeyer, D.; Meier,
H. Chem. Ber. 1994, 127, 1735.

Liquid-Crystalline Cu Complexes
Inorganic Chemistry, Vol. 40, No. 25, 2001 6395
Figure 2. Melting behavior of 3,4-substituted copper complexes 5h-
m. There is a general decrease in the melting point/clearing point with
the chain length irrespective of the nature of the mesophase (the nature
of the mesophases is in Scheme 3).
Figure 1. Melting behavior of 2,4-substituted copper complexes 5a-
g. The length of the 2 chain is much more important than that of the
4 chain in influencing the melting point (detailed data is in Table 4).
Scheme 2. Mesomorphism of Bis[5-(3,5-dihexadecyloxy-
benzylidine)tropolonato]copper (5n)
Table 3. Elemental Analysis of Complexes
%C
%H
%N
no.
formula
exptl calcd exptl calcd exptl calcd
5a C64H92CuN2O8
5b C72H108CuN2O8
5c C66H96CuN2O8‚0.5H2O 70.95 70.90 8.72 8.74 2.61 2.51
71.32 71.11 8.47 8.58 2.51 2.59
72.55 72.48 9.20 9.12 2.14 2.34
Scheme 3. Mesomorphism of
Bis[5-(3,4-dialkoxybenzylidine)aminotropolonatocopper(II)
5d C72H108CuN2O8
5e C80H124CuN2O8
5f C92H148CuN2O8
5g C40H44CuN2O8
5h C60H84CuN2O8
5i C68H100CuN2O8
5j C76H116CuN2O8
5k C80H124CuN2O8
5l C84H132CuN2O8‚0.5H2
72.93 72.47 9.45 9.12 2.36 2.35
73.26 73.60 9.85 9.42 2.22 2.15
74.87 74.98 9.95 10.12 1.98 1.90
64.69 64.55 5.95 5.96 3.91 3.76
70.88 70.31 8.55 8.26 2.80 2.73
71.88 71.82 8.96 8.87 2.50 2.46
73.23 73.07 9.60 9.36 2.25 2.24
73.44 73.60 9.95 9.77 2.08 2.06
73.51 73.61 9.95 9.78 2.08 2.04
[Enthalpies (kJ mol-1) in Parentheses]
5m C92H148CuN2O8‚0.5H2O 74.49 74.52 10.61 10.13 1.88 1.89
5n C92H148CuN2O8‚0.5H2O 74.52 74.52 10.05 10.13 1.82 1.89
5o C92H148N2NiO8‚0.5H2O 74.55 74.77 10.21 10.16 1.80 1.90
5p C92H148N2O8Zn‚H2O
73.81 73.98 10.24 10.12 1.60 1.88
Table 4. Melting Behavior of Bis[5-(2,4-dialkoxybenzylidine)-
tropolonato]copper Complexes 5a-g
temp of
cryst-iso
transition (°C)
R1 ) OCnH2n+1
R3 ) OCmH2m+1
compd no.
n
m
5a
5b
5c
5d
5e
5f
12
12
16
16
16
16
3
6
10
3
152
146
241
141
138
126
270 (dec)
6
10
16
3
5g
Table 5. Melting Behavior of Bis[5-(2,4-dihexadecyloxy-
benzylidine)tropolonato] Derivatives of Metals
compd no.
cryst-iso (°C) compd no.
cryst-iso (°C)
5o
5p
Ni
Zn
135
138
5f
Cu
126
changeover from lamellar to columnar. There is a competition
in these complexes between the columnar behavior expected
for complexes with lateral alkoxy chains and the lamellar
behavior expected for the rodlike molecules containing 4-alkoxy
substitutents. This phase changeover fits in well with previous
considerations on the significance of the curvature of the
interface between the rigid core and the alkyl chains.34-38 With
short chains, there is no imbalance between the volumes of the
(c) 3,4-Substituted Complexes. The melting behavior of the
copper complexes 5h-m is given in Scheme 3. The bar chart
(Figure 2) shows that mesophase transition temperatures de-
crease fairly uniformly with an increase in the chain lengths.
With a chain length below 13, the transition is to a smectic C
phase. With a chain length of 13 or greater, the mesophase is
a columnar-hexagonal disordered phase. These complexes
provide a fine example of polycatenar molecules with a phase
(34) Charvolin, W. J. Chim. Phys. Phys.-Chim. Biol. 1983, 80, 15.
(35) Hendrikx, Y.; Levelut, A.-M. Mol. Cryst. Liq. Cryst. 1988, 165, 233.
(36) Skoulis, A.; Guillon, D. Mol. Cryst. Liq. Cryst. 1988, 165, 317.
(37) Tschierske, C. J. Mater. Chem. 1998, 8, 1551.
(33) Donnio, B.; Bruce, D. W. New J. Chem. 1999, 23, 275.

6396 Inorganic Chemistry, Vol. 40, No. 25, 2001
Elliott et al.
Table 6. Variation of Melting Behavior with the Substitution
Pattern
new series of dinuclear copper bis(terpyridine) complexes, which
are mesogenic, and the first example of a metallomesogen with
a terpyridine core. Observation of these terpyridine complexes
with optical microscopy showed a schlieren texture that was
indicative of a biaxial smectic phase. Crystallographic data for
the core structure has shown the molecules to be aligned in
parallel rows, indicative of a lamellar packing of molecules.
Further characterization with XRD studies show the organization
of the individual molecules into a columnar stack with lamellar
morphology. The change in the design of the core, from a
bipyridine to a terpyridine structure, has resulted in crossover
phase behavior in the molecules from discotic to calamitic
mesophases.
Tschierske et al.16 have utilized two molecular subunits, the
calamitic disubstituted 2-phenylpyrimidine core and the half-
disk shape of a 1,3-diketonate with alkyl chains, to give
palladium complexes of an intermediate shape between a rod
and a disk. These novel palladium complexes are mesogenic,
and a sequential increase in the number of alkyl chains has led
to a discontinuous crossover in phase behavior from lamellar
(4 or 5 chains) to columnar (7 or 8 chains). These mononuclear
ortho-palladated phenylpyrimidine-1,3-diketonato organyls are
the first to show thermotropic columnar mesophase behavior.
Further work by Tschierske et al.17 has again utilized the idea
of fusing two submolecular units via ortho palladation to create
metallomesogens which exhibit a crossover phase behavior
between lamellar and columnar. Using a rodlike p-cyclophane
core with 1,3-diketonates, the subsequent palladium complexes
again show a discontinuous crossover phase behavior between
lamellar (4 chains) and columnar (8 chains). Moreover, these
p-cyclophane derivatives are the first to show thermotropic,
columnar mesophase behavior.
positions
compd of C16H33O
transition
θ (°C) transition θ (°C)
5f
5n
5m
2,4
3,5
3,4
cryst-iso
colhd-iso
colhd-iso
126
127
190
cryst-colhd
cryst-colhd
40
146
rigid core and the alkyl chains, and lamellar phases are found.
With longer alkyl chains, the volume required by the chains
becomes much greater than that required by the core, and
columnar phases result. It is noteworthy that the analogous
nickel and zinc complexes, although melting at lower temper-
atures, do not give rise to mesophases. This indicates that the
molecular environment required for mesophases is very de-
manding. 3,4-Substituted polycatenar silver complexes showed
cubic and columnar phases but no calamitic N or SC phases.33
The 2,4-substituted series gave no mesophases but had lower
melting points than those of the analogous 3,4-substituted
complexes (Table 6).
From Table 6, it can be seen that the 3,5-dialkoxy ring
produces the lowest melting point. The two lateral long alkoxy
chains destabilize packing well.
Conclusions
This new series of metallomesogens provides further evidence
for the subtle balance between the chain length and molecule
breadth required to give mesophases. Our results can be
summarized in terms of terminal chains (alkoxy substitution at
the 4 position) and lateral chains (substitution at the 3 and 5
positions). When there are no terminal chains (3,5 substitution),
only columnar behavior is seen. With both terminal and lateral
chains, mixed behavior is seen, depending upon the chain length.
Substitution at the 2 position so disrupts packing that no
mesophases are seen, even with long terminal chains. The bis-
(tropolonato)copper(II) core is a good base on which to graft
further ring systems where molecule length and breadth can be
varied. Copper complexes of alkoxy-substituted ligands often
show alkoxy oxygen-copper interactions perpendicular to the
chelate plane, which partly determine the three-dimensional
packing.1
Although these are fine examples of compounds that show
crossover phase behavior, they all involve a change in the core
design of the complexes to get the jump. Our complexes are an
example of the crossover phase behavior of a more fundamental
sense, with crossover seen within a single series of compounds
and with no change to the core. The design of our complexes
fits the model laid down for polycatenars by Malthete et al.10
and is a true example of copper-complex tetracatenars.
Ziessel et al.19 reported metallomesogens based around a
polypyridine core. Copper complexes synthesized with a bipy-
ridine core have exhibited columnar mesophases. They have
extended this core, using a further bipyridine ring to form a
Acknowledgment. Financial support from the EPSRC is
gratefully acknowledged.
Supporting Information Available: Micrographs of the various
phases, labeled according to chain lengths and phases. This material is
available free of charge via the Internet at http://pubs.acs.org.
(38) Roll, C. P.; Donnio, B.; Weigand, W.; Bruce, D. W. Chem. Commun.
2000, 709.
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