H-Bonded metallomesogens: preparation, characterization, and mesomorphic studies of (3-hydroxypropylimino)propan-1,2-diols

Article abstract of DOI:10.1016/j.tet.2010.03.041

Two series of new Schiff bases 2 (n=8, 12, 16) derived from (3-hydroxypropyl imino)propan-1, 2-diol with a hydroxyl group at C₁₉/C₂₀-position and their palladium complexes 1 were prepared and their mesomorphic properties investigated

Full text of DOI:10.1016/j.tet.2010.03.041

Tetrahedron 66 (2010) 3583–3592
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
H-Bonded metallomesogens: preparation, characterization, and mesomorphic
studies of (3-hydroxypropylimino)propan-1,2-diols
,
Chieh Chien c, Chun-Jung Chen c, Hwo-Shuenn Sheu a, Gene-Hsiang Lee b, Chung K. Lai c
*
a National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
b Instrumentation Center, National Taiwan University, Taipei 10660, Taiwan, ROC
c Department of Chemistry, National Central University, Chung-Li 32001, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Two series of new Schiff bases 2 (n¼8, 12, 16) derived from (3-hydroxypropyl imino)propan-1, 2-diol
with a hydroxyl group at C19/C20-position and their palladium complexes 1 were prepared and their
mesomorphic properties investigated by DSC, POM, and XRD. The presence of both hydroxyl groups was
found to be crucial in forming the liquid crystalline behavior. All compounds 2a exhibited smectic A or
and C phases, in contrast, all compounds 2b formed hexagonal columnar phases. The formation of
mesophases in both compounds 1–2 was probably induced by inter-molecular H-bonds. Single crys-
tallographic data in mesogenic compound 2a (n¼8) indicated that a dimeric structure with a better linear
or rod-like molecular shape was formed by an inter-molecular H-bond (O4–O10, w1.854 Å). Another
inter-molecular H-bond (w1.903 Å) between two dimeric structures was also observed. It crystallizes in
a monoclinic space group P2(1)/c. On the other hand, all palladium complexes 1 formed enantiotropic
smectic A phases. Single crystallographic data in mesogenic compound 1a (n¼8) indicated that the
geometry at Pd2þ center was coordinated as slightly twisted square planar. It crystallizes in a monoclinic
space group P2(1)/n. An inter-molecular H-bond (w1.799 Å) between neighboring molecules were
observed, which might have facilitated the formation of mesophases. Variable-temperature powder XRD
experiments confirmed their mesophase structures.
Received 21 January 2010
Received in revised form 6 March 2010
Accepted 12 March 2010
Available online 20 March 2010
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
structures incorporated with atoms capable of binding metal
or metals are feasible to generate metallomesogens or poly-
More and more metallomesogens1 have been prepared and
studied during the past decades, and these so-called metal-con-
taining liquid crystals (MCLC’s) have now become a major sub-
field of long known traditional liquid crystals. More importantly,
many interesting LC properties1d,2 resulted from such type of
metallomesogens were in fact observed, and practical commercial
applications on electronic devices might become possible in the
near future. We have all been well aware that different meso-
phases might be formed or induced by distinct molecular shapes/
structures. Those specific molecular shapes might not be possible
or easy to approach along with classic organic molecules. Metal-
lomesogens were often generated from non-mesogenic moieties.
A variety of geometric metal centers within metallomesogenic
structures, such as linear, tetrahedron, square planar, octahedron
or others have been created. On the other hand, metal ions play an
important role in forming the mesophases. Organic moieties or
metallomesogens. Among them, oxygen, nitrogen, and sulfur
atoms were often incorporated due to their nucleophilic or basic
properties of lone pair electrons when bonded to more electro-
philic or acidic metal ion or ions. Therefore, a delicate balance or
control of intermolecular force becomes then crucially important
in obtaining the liquid crystalline phases from a particular metal
complex. Too strong or too weak a force will destroy its liquid
crystallinity.
Until now, known metallomesogens derived from enamino-
ketonates3 I, salicyldiminates4 II,
a,b
-diketonates5 III, aroylhy-
drazines6 IV, and -diketonates7 V were categories investigated
b,d
the most. Numerous examples of metallomesogens incorporated
3d transition metals exhibiting nematic, smectic or/and columnar
phases were by now known. Copper and nickel complexes8 sim-
ilar to compounds
I
with ethylenediaminate derivatives
(R¼CH2CH2) have been previously studied by this group. All
copper complexes regardless of the side chain density were non-
mesogenic, however, all nickel complexes with four or six alkoxy
groups exhibited columnar phases. The geometry at central metal
ion was attributed to the mesomorphic behavior observed by
* Corresponding author. Tel.: þ886 03 4259207; fax: þ886 03 4277972; e-mail
address: cklai@cc.ncu.edu.tw.
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.03.041

3584
C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
these metal complexes. Diamagnetic nickel ion (d8-Ni2þ) often
prefers a square-planar geometry, whereas, paramagnetic copper
ion (d9-Cu2þ) tends to be tetrahedral or slightly distorted square
plane coordinated.
was observed, leading to a better linear shape and improved
mesophases induced. An inter-molecular H-bond in compound 1a
(n¼8) was also observed, by which the formation of the meso-
phases was facilitated.
H-bonded mesogens9 have been an active subfield in liquid
crystalline research, and many examples were known. H-bonding
has now become an important tool for building molecular archi-
tectures with liquid crystalline and/or other optic-electric prop-
erties. Induction, stabilization or formation of mesophases by use
of H-bonding interaction can be twofold; complementary shapes
and intermolecular force. A better molecular shape or an appro-
priate aspect ratio might be optimized by a H-bonded dimeric,
trimeric or polymeric structure, which were often observed for
those molecules with unconventionally shaped molecules. Sec-
ondly, intermolecular interaction enhanced by H-bond might fa-
cilitate the formation of mesophases, particularly for those
molecules without a dipole group. H-bonds, compared to covalent
bonds are relatively weak; therefore, they are truly sensitive to the
structural alternation. Any structural change might have a dra-
matic impact on the propensity of these H-bond stabilized mol-
ecules. On the other hands, known examples of H-bonded
metallomesogens3b,10 have been relatively described. Studying
the relationship between the molecular structure and the meso-
morphic properties can therefore provide valuable insight for the
design of new LC’s materials.
R1
R
O
O
N
N
O
N
N
O
O
O
O
O
R2
M
R
M
M
R2
R
R1
III
I
II
H
R
N
N
H
O
O
O
O
O
O
M
O
M
M
O
H
N
N
R
H
V
IV
Structure 1
RO
RO
X
X
OH
Pd2+
O
N
N
O
OH
OH
Pd
HO
OH
N
OH
OH
X
2a; X = H
2b; X = OR
OR
1a; X = H
1b; X = OR; R = (CH2)nH
C8H17
O
X
OH
N
OH
2c: X = H
2d: X = OC8H17
Structure 2
In this work two new series of cis-enaminoketonate derivatives
with a hydroxyl group at C19- and C20-position of Schiff bases 2
and their palladium complexes 1 were prepared and mesomor-
phic properties investigated. The purpose of incorporating hy-
droxyl groups is to assess its importance or the structural effect on
the formation of mesomorphic properties. H-bonds might be
possibly formed by these hydroxy groups, and the mesophases
could be conceivably induced or formed. Results appeared that all
compounds 2a with one alkoxy group formed smectic A or/and
smectic C phases, however, all compounds 2b with two alkoxy
groups exhibited hexagonal columnar (Colh) phases. On the other
hand, all more rod-like palladium complexes 2a,2b formed
smectic A phases. The Pd2þ ion with a d8-electronic configuration
often prefers a diamagnetic state and square-planar geometry.
Also in order to understand the relationship between the struc-
ture and mesophase, two single crystals 1a and 2a all with n¼8
were resolved and their crystallographic data discussed. A dimeric
structure formed by inter-molecular H-bond in compounds 2a
2. Results and discussion
2.1. Synthesis and characterization
The synthetic pathways to compounds 2 and their palladium
complexes 1 are listed in Scheme 1. The 4- or 3,4-alkoxyphenyl-3-
oxo-3-phenylpropionaldehyde derivatives 3, obtained by the
Claisen formylation reactions were freshly prepared due to their
slight sensitivity to the oxidations. These intermediates and Schiff
bases were characterized by 1H and 13C NMR spectroscopy. A
characteristic peak at ca.
(–CHO) for compounds 3a and 3b was observed. In addition,
three characteristic peaks at ca. 6.70–6.80, 6.83–6.92, and 10.18–
10.20 assigned for an olefinic methane-H (–CH]C–), aldehyde-H
(–CHO), and imine-H (–C]NH–) were observed. The intensities of
these peaks were dependent on the solvent and the time length
due to the relative tautomeric ratio. Metal complexes, obtained by
the reactions of Schiff bases 2 with palladium(II) acetate were
d 9.91–9.93 assigned for aldehyde-H
d

C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
3585
RO
HO
HO
HO
a
O
O
b
d
RO
X
RO
RO
RO
d
c
RO
O
O
O
3a; X = H
3b; X = OR
e
RO
X
RO
X
OH
O
N
N
O
OH
OH
Pd
HO
f
OH
N
OH
OH
X
2a; X = H
2b; X = OR
OR
1a; X = H
1b; X = OR; R = (CH2)nH
Scheme 1. Reagents and conditions. (a) RBr (1.0 equiv), K2CO3 (2.0 equiv), KI, refluxing in acetone, 48 h; (b) RBr (2.0 equiv), K2CO3 (3.0 equiv), KI, refluxing in acetone, 48 h; (c) AlCl3,
acetyl chloride, CH2Cl2 (dry) at 0 ꢀC, 4 h; (d) NaOMe, DME, HCOOEt, stirring at rt, 24 h; (e) 3-amino-1,2-propanediol (1.1 equiv), refluxing in THF/EtOH, 8 h; (f) Pd(OAc)2 (0.5 equiv),
stirring in THF/MeOH at rt, 3 h.
obtained after twice recrystallizations from THF/methanol. All
palladium complexes were isolated as yellow solids. All complexes
were all characterized by elemental analysis (Table 5).
groups (–OH), two single crystals of the mesogenic ligand 2a (n¼8)
and its mesogenic palladium complex 1a (n¼8) suitable for crystal-
lographic analysis were obtained by slow vaporization from CH2Cl2/
methanol at room temperature and their structures resolved. As
expected, the acidity of primary alcohol-OH at C20 position and sec-
ondaryalcohol-OHat C19 position ofSchiff base on the Schiff bases are
not strong enough to coordinate with softer and larger metal ions,
such as Pd2þ or Pt2þ. Instead, imine-N and enaminoketone-O atoms
were bonded to Pd2þ ion, leaving the two hydroxyl groups un-
coordinated. Figure 1 shows the two molecular structures with the
2.2. Single crystal structures of 1-(4-octyloxyphenyl)-3-(3-
hydroxypropylimino)propan-1,2-diol (2a; n[8) and its
palladium complex (1a; n[8)
In order to understand the relationship between the structure and
mesomorphic properties and also the possible effect of the hydroxyl
Figure 1. Two ORTEP plots for 2a (n¼8; top) and 1a (n¼8; bottom) with the numbering scheme, and the thermal ellipsoids of the non-hydrogen atoms are drawn at the 50%
probability level.

3586
C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
atomic numbering schemes. Table 1 lists their crystallographic and
structural refinement data for the two molecules. The derivative 2a
(n¼8) crystallizes ina monoclinic space groupP2(1)/c witha Z¼4. The
overall molecular shape of crystal 2awas considered as a slightly bent
structure. Unsurprisingly, both inter-molecular H-bond (H4–O10 on
C20-positionandH30–O4onC19 position)andintra-molecularH-bond
(O1–H1) were in fact observed. A dimeric structure, leading to a more
linear shape was formed by inter-molecular H-bonds, and this was
attributed to the formation of a layer smectic phase observed in
compounds 2a (Fig. 2). The two phenyl rings in this dimeric structure
were perfectly coplanar. The bond angles of the H-bonds were ranged
between 124.8ꢀ (:N1–H1–O1) and 175.1ꢀ (:O4–H4–O10). Two hy-
droxyl groups at C19 and C20 positions were all responsible for the
inter-molecular H-bonds. The distances of two inter-molecular H-
bonds were measured as w1.854 Å (O10–H4) and w1.903 Å (O4–H30),
whereas the distance of intra-molecular H-bonds was w2.128 Å (O1–
H1). The inter-molecular H-bonds were relatively stronger than that
of the intra-molecular H-bond. In the unit cell, two more linear di-
meric structures, shown in Figure 2 were also linked by another H-
bond (O4–H30) with a distance of w1.903 Å and bond angle of
w163.7ꢀ (:O4–H30–O30). This inter-molecular H-bond between two
dimeric structures has apparently enhanced the molecular in-
teraction between the layers. The molecular length L of this dimeric
structurewasmeasuredasca. w37.394 Å,whichwasslightlylessthan
double lengths of monomeric structure (ca. w21.724 Å). The length of
37.394 Å was quite close to the d-spacing of w38.239 Å obtained by
powder XRD diffraction experiment. Therefore, alkoxy chains were
probably not interdigitated in the mesophase.
Table 1
Crystallographic and experimental data for compounds 1a and 2a (n¼8)
Compd.
2a (n¼8)
1a (n¼8)
In contrast, the palladium complex 1a (n¼8) crystallizes in
a monoclinic space group P2(1)/n with a Z¼4. The geometry at
palladium center was coordinated as distorted square planar. The
two angles of N2–Pd–O1 and N2–Pd–O5 were of 87.74ꢀ and 92.45ꢀ,
which were quite close to an angle of 90ꢀ expected for a perfect
square-planar geometry (see Table 2). The overall molecular shape
was considered as slightly bent with a length of ca. 34.957 Å. Two
phenyl rings were not coplanar to the central plane defined by
atoms of N2–O5–Pd–O1–N1. Two molecules were also linked by H-
bonding in a fashion of anti-parallel and head-to-tail arrangements.
A few inter-molecular H-bonds with a distance ranged between
1.799 and 2.4294 Å were also observed, which were also attributed
to the formation of the mesophase in compounds 1 (Fig. 3). Two
types of inter-molecular H-bonds were observed in the unit cell;
one formed from neighboring molecule via H atom at C19 and O
atom at C20, and the other one formed from above or below mol-
ecule via H-atom at C20 and O-atom at C20. In the unit cell, all
molecules were arranged with a herringbone.
Empirical formula
Formula weight
T/K
Crystal system
Space group
a/Å
C20H31NO4
349.4
150(2)
Monoclinic
P2(1)/c
20.9194(3)
8.6903(2)
11.1929(2)
90
104.2173(10)
90
1972.50(6)
4
760
C41H64N2O9Pd
835.34
200(2)
Monoclinic
P2(1)/n
5.4037(3)
18.3223(9)
43.315(2)
90
93.4745(16)
90
4280.7(4)
4
1768
b/Å
c/Å
ꢀ
ꢀ
a
/
b
/
ꢀ
g
/
U/Å3
Z
F(000)
Dc/Mg mꢁ3
1.177
1.296
Crystal size/mm3
Range for data collection/ꢀ
Reflection collected
Data, restraints, parameters
Independent reflection
Final R1, wR2
0.33ꢂ0.22ꢂ0.08
1.00 to 27.50
13,566
4533/0/229
4533 [R(int)¼0.0365]
0.0565, 0.1645
0.38ꢂ0.06ꢂ0.03
1.21 to 25.00
20,327
7538/1/474
7538 [R(int)¼0.0917]
0.0864, 0.2327
Figure 2. Two H-bonds formed in 2a (n¼8). Top plot: inter-molecular (w1.854 Å) and intra-molecular (w2.1284 Å) H-bonds in a dimeric structure, and bottom plot: inter-dimmer
bond (w1.903 Å; H atom on C19 and O atom on neighboring C20).

C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
3587
Table 2
phases, and under optical microscope they exhibited oily streak
texture (Fig. 4), characteristic of a layer smectic phase expected for
the rod-like molecules. The phases were tentatively assigned as
smectic A phases based on POM observation. For the compounds 2a
the clearing temperatures were increased with the carbon numbers
of the terminal alkyl chains, i.e. Tcl¼154.4 (n¼8)<163.6
(n¼12)<167.9 ꢀC (n¼16), however, the melting temperatures de-
creased slightly; 124.7 ꢀC (n¼8)–117.2 ꢀC (n¼16). The mesophase
temperature, also slightly increasing with carbon length was ranged
Selected bond distances [Å] and angle [ꢀ] for compound 2a and 1a (n¼8)
2a
Bond distances
C(1)–C(2)
C(2)–C(3)
C(3)–O(1)
1.3823(24)
1.4135(26)
1.2566(21)
C(4)–C(3)
N(1)–C(1)
N(1)–H(1)
1.4951(24)
1.3212(22)
0.8802(16)
Bond angles
C(1)–C(2)–C(3)
C(2)–C(3)–O(1)
C(3)–C(4)–C(9)
122.568(166)
121.449(164)
118.826(157)
C(4)–C(9)–O(1)
C(1)–N(1)–H(1)
C(2)–C(1)–N(1)
119.393(156)
119.402(169)
128.002(175)
in
D
T¼29.7 (n¼8)–50.7 ꢀC (n¼16). An extra SmC phase, ranged quite
narrow (ca. w2.9 ꢀC) was also observed for compound 2a with
a longer alkoxy (n¼16). A typical texture described as Schlieren do-
mains (Fig. 4) were easily observed under POM. This may probably be
attributed to an enhanced dispersive interaction or van deer Waals
between the terminal alkoxy chains. The formation of the layer
smectic phases was induced by the H-bonding, of which a dimeric
structure with a larger aspect ratio facilitated the formation of the
mesophases in compound 2a.
1a
Bond distances
N(1)–Pd
N(2)–Pd
O(1)–Pd
O(5)–Pd
C(1)–C(2)
C(1)–N(1)
2.0087(76)
2.0341(76)
1.9793(65)
2.0010(63)
1.3871(144)
1.3164(119)
C(2)–C(3)
C(3)–O(1)
C(21)–C(22)
C(21)–N(2)
C(22)–C(23)
C(23)–O(5)
1.3767(136)
1.2933(107)
1.3974(142)
1.3163(120)
1.3682(137)
1.3173(107)
Bond angles
However, all compounds 2b (n¼8,12,16) with two alkoxy groups
formed enantiotropic columnar phases (Col). On DSC thermographs
they all showed a typical columnar phase transition, crystal-to-
columnar-to-isotropic (Cr/Col/I). A focal-conic texture for co-
lumnar phases (Fig. 4) was observed under POM. The temperature
range of columnar phase was narrow and increased with carbon
N(1)–Pd–O(1)
N(1)–Pd–O(5)
N(2)–Pd–O(1)
N(2)–Pd–O(5)
C(1)–N(1)–Pd
C(1)–N(1)–C(18)
91.932(276)
87.871(273)
87.741(279)
92.453(277)
123.093(617)
115.656(786)
C(3)–O(1)–Pd
126.353(551)
113.804(760)
121.486(614)
117.014(785)
126.185(545)
113.675(760)
C(4)–C(3)–O(1)
C(21)–N(2)–Pd
C(21)–N(2)–C(38)
C(23)–O(5)–Pd
C(24)–C(23)–O(5)
chain length, i.e.
D
T¼5.70 ꢀC (n¼8)<
D
T¼20.2 ꢀC (n¼16) on heating
Symmetry transformations used to generate equivalent atoms.
process. In addition, a relatively small enthalpy (
D
H¼0.43–0.88 kJ/
2.3. Mesomorphic properties
mol on heating cycle) for the Colh/I transition was observed, in-
dicating that the molecular order in the columnar phase was rela-
tively low. The overall molecular shapes of compounds 2b were in
fact not disc-like, however, two or more molecules linked or cor-
related by H-bonds might lead to a more disc-like molecule, giving
to the formation of columnar phases. As expected, compounds 2c,
2d without a hydroxyl group attached at C19-position of Schiff bases
The liquid crystalline behavior of compounds 1–2 was charac-
terized and studied by differential scanning calorimetry and polar-
ized optical microscope. The phase transitions and thermodynamic
data are summarized inTables 3 and 4. All three compounds 2a (n¼8,
12, 16) with one terminal alkoxy group exhibited enantiotropic
Figure 3. Inter-molecular H-bonds in 1a (n¼8) viewed from b axis (top plot) and from a axis (bottom plot).

3588
C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
Table 3
Phase temperaturesa and enthalpies of compound 2a–2d
154.4 (2.88)
124.7 (58.4)
Cr1
2a; n = 8
SmA
I
I
105.1 (15.7)
123.0 (-5.82)
151.1 (2.91)
163.6 (1.68)
116.7(42.4)
86.9 (9.47)
Cr2
SmA
SmA
Colh
12
16
Cr1
Cr
90.6 (-10.1)
117.2 (57.9)
156.1 (1.46)
167.9 (0.96)
I
I
I
I
SmC
Cr
104.2 (0.18)
115.8 (41.4)
165.1 (0.91)
121.5 (0.43)
101.3 (18.2)
2b; n = 8
12
64.1 (28.7)
122.5 (-11.1)
119.6 (0.55)
141.4 (0.88)
109.9 (53.2)
Cr2
Cr2
Colh
Colh
Cr2
Cr
Cr1
Cr1
74.6 (53.1)
102.6 (12.3)
90.8 (-13.9)
110.3 (70.1)
138.6 (0.84)
130.5 (0.57)
16
84.4 (82.3)
124.9 (0.50)
92.6 (25.3)
78.7 (20.8)
89.1 (65.7)
53.5 (5.04)
40.7 (3.62)
I
2c
Cr1
I
2d
60.5 (53.4)
a
n is the carbon numbers of terminal alkoxy groups. Cr1 and Cr2¼crystal, SmA¼smectic A, SmC¼smectic C, Colh¼hexahonal columnar, and I¼isotropic phase.
Table 4
Phase temperaturesa and enthalpies of compounds 1a-1b
205.0 (4.72)
199.1b
213.4 (6.00)
204.2b
211.5 (6.70)
203.1b
167.3 (6.06)
186.3 (61.8)
1a; n = 8
12
Cr
Cr
SmA
SmA
I
I
98.6 (32.9)
173.8 (65.4)
103.8 (29.6)
164.2 (73.1)
SmA
SmA
SmA
SmA
I
I
I
I
Cr
16
120.8 (36.8)
148.1 (76.9)
100.2b
130.9 (5.0)
Cr
1b; n = 8
150.1b
148.4 (4.41)
125.0 (56.50
Cr2
Cr2
12
16
Cr1
Cr1
56.1b
137.6 (3.29)
126.5 (1.90)
86.2 (-19.6)
115.4 (64.2)
73.6 (37.2)
118.9 (2.29)
a
n is the carbon numbers of terminal alkoxy groups. Cr1, Cr2¼crystal, SmA¼smectic A, and I¼isotropic phase.
bobserved by optical microscope.
Table 5
compounds 1a have a higher clearing temperature than those
of compounds 2a (n¼8) by ca. 43.6 ꢀC–50.6 ꢀC. In contrast, for the
compounds 1b only the derivative (n¼8) has a higher clearing iso-
tropic temperature than that of its precursor 2b (n¼8) by 45.8 ꢀC.
The other two derivatives 1b (n¼12, 16) have slightly lower clearing
temperatures than that those of their precursors 2b (n¼12, 16). All
palladium complexes 1a,1b formed layer smectic phases. The pha-
ses were identified also as smectic A phases, and typical focal-conic
textures (Fig. 5) were easily observed under optical polarized mi-
croscope when cooling from isotropic liquid. All compounds 1a have
a smaller range of mesophase temperature.
Elemental analysis data of compounds 1–2
Compds
C (%)
H (%)
2a (n¼8)
2a (n¼12)
2a (n¼16)
2b (n¼8)
2b (n¼12)
2b (n¼16)
1a (n¼8)
68.39 (68.74)
71.04 (71.07)
72.90 (72.84)
70.31 (70.40)
73.32 (73.30)
75.29 (75.27)
59.80 (59.79)
63.01 (62.97)
65.37 (65.44)
62.99 (63.47)
67.12 (67.34)
69.77 (70.06)
8.92 (8.94)
9.75 (9.69)
10.35 (10.26)
9.88 (9.92)
10.79 (10.76)
11.40 (11.34)
7.58 (7.53)
8.34 (8.33)
9.02 (9.02)
8.74 (8.75)
9.69 (9.73)
10.44 (10.42)
1a (n¼12)
1a (n¼16)
1b (n¼8)
1b (n¼12)
1b (n¼16)
2.4. Variable-temperature powder XRD diffraction data
Theoretical values in parenthesis.
The mesophase structures for some of the compounds 1a,1b and
2a,2b were also confirmed by use of variable-temperature powder
XRD experiments. For example, for compound 2a (n¼8) at 125.0 ꢀC
a diffraction pattern with one strong peak of d w38.2 Å and one very
weak of d w19.1 Å at small angle region, and also a very weak and
broad halo diffraction peak of d w4.4 Å at wide angle region was ob-
served, as shown in Figure 6. These two diffraction peaks at lower
angle were assigned as 001 and 002, which were typically character-
istics of layer structures observed fora SmA phase. Thelayerd-spacing
were found to be non-mesogenic. A transition from crystal-to-
isotropic at 92.6 ꢀC and 89.1 ꢀC for compound 2c and 2d, re-
spectively was obtained. A decreasing of clearing temperatures for
compound 2c and 2d by a
D
Tcl¼61.8 ꢀC and 32.4 ꢀC, respectively,
with respect to those of 2a (n¼8) and 2b (n¼8). The loss of LC be-
havior might be attributed to the weakening of the H-bond in-
teraction induced only at C20-position. The phase transitions and
thermodynamic data of compounds 1 are summarized in Table 4. All

C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
3589
Figure 5. Optical textures observed by 1a (n¼12) at 191.0 ꢀC (top) and by 1b (n¼8) at
112.0 ꢀC.
corresponds to a hexagonal columnar (Colh) arrangement11 with
a lattice constant (a¼2$d10/31/2) of w39.8 Å. This lattice constant
was also quite close to the 35.0 Å obtained for the molecular length
in single crystallographic data of 1b (n¼8). The overall molecular
shapes of compounds 2b were not considered as disc-like, but
a more lath-like. However, a correlated structure having two or
more molecules with a 180ꢀ or antiparallel arrangement would
lead to a more disc-like molecule, giving a columnar phase.
The powder XRD data measured for compounds 1a (n¼8) at
180 ꢀC and 1b (n¼8) at 155.0 ꢀC confirmed the layer structures of
smectic A phases, the same with compound 2a. For example,
a diffraction pattern with a peak at 32.1 Å (assigned as d001), 16.0 Å
(d002) and also a halo peak at 4.4 Å was observed as shown in
Figure 7. Compound 1b (n¼8) showed a similar diffraction pattern
with a peak at 29.7 Å (d001), 15.0 Å (d002), 10.0 Å (d003) and 4.4 Å
(halo). The molecular arrangements of compounds 2a and 1a both
in crystal and smectic A phases are proposed in Figure 8.
Figure 4. Optical textures observed by 2a (n¼16) at 157.0 ꢀC (top) and at 103.0 ꢀ
(center), and by 2b (n¼16) at 122.8 ꢀC (bottom).
C
of 38.2 Å is quite consistent to a distance of w37.4 Å obtained for the
molecular length of the dimeric structure in single crystallographic
data of2a(n¼8), whichindicatesthattheformationofasmecticphase
was induced or/and formed by a H-bonded dimeric structure. In ad-
dition, all alkoxy chains were not probably interdigitated.
In contrast, all compounds 2b (n¼8, 12, 15) exhibited columnar
phases based on polarized optical microscope. At 110 ꢀC, a diffrac-
tion pattern of compound 2b (n¼8) with a d-spacing at 34.5 Å,
19.9 Å, 17.2 Å, and a broad diffuse peak at 4.4 Å at wide-angle region
was observed, and it is characteristic of a columnar phase with a
d-spacing ratio of 1, (1/3)1/2 and (1/4)1/2, corresponding to Miller
indices, 10, 11, and 20, respectively. Such diffraction pattern
3. Conclusions
Two series of new Schiff bases 2 and their palladium complexes
1 were prepared and their mesomorphic properties investigated.
The presence of two hydroxyl groups attached at Schiff base C19
-
and C20-position is crucial in forming the liquid crystalline behav-
ior. Two single crystallographic data of compounds 2a and 1a (n¼8)
confirmed their single and molecular structures. A dimeric struc-
ture induced by inter-molecular H-bond was attributed to the for-
mation of mesophases in compounds 2. All compounds 2a

3590
C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
Figure 6. The powder X-ray diffraction plots of compound 2a (n¼8) at 125.0 ꢀC (top)
and at rt, and compound 2b (n¼8) at 110.0 ꢀC (bottom).
Figure 7. The powder X-ray diffraction plots of compound 1a (n¼8) at 180.0 ꢀC (top)
and at rt, and compound 1b (n¼8) at 155.0 ꢀC (bottom).
exhibited smectic A or/and C phases, in contrast, all compounds 2b
formed hexagonal columnar phases.
conducted at Instrumentation Center, National Taiwan University on
a Heraeus CHN-O-Rapid elemental analyzer. The powder X-ray dif-
fraction data were collected from the Wiggler-A beam line of the
National Synchrotron Radiation Research Center. All compounds of
4-alkoxyacetopheones and 3,4-dialkoxyacetophenones were pre-
pared by literatures’ procedures.
4. Experiment section
4.1. General
The 1H and 13C NMR spectra were measured on a Bruker DRS-
200. DSC thermographs were carried out on a Mettler DSC 1 Star
System. All phase transitions are determined by a scan rate of
10.0 ꢀC/min. Optical polarized microscope was carried out on Zeiss
Axioplan 2 equipped with a hot stage system of Mettler FP90/
FP82HT. Elemental analysis for carbon, hydrogen, and nitrogen were
4.1.1. 1-(4-Octyloxyphenyl)-3-hydroxy-2-propen-1-one (3a; n¼8). Light
yellow solid, 1H NMR (300 MHz, CDCl3):
d 0.85 (t, 3H, –CH3,
J¼6 Hz), 1.24–1.81 (m, 12H, –CH2), 3.98 (t, 2H, –OCH2, J¼7 Hz),
6.12 (d, 1H, CH, J¼4 Hz), 6.90 (d, 2H, –C6H4, J¼7 Hz), 7.84 (d, 2H,

C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
3591
6H, J¼6 Hz), 1.27–1.87 (m, –CH2, 24H), 4.03 (t, –OCH2, 4H, J¼4 Hz),
6.13 (d, –(COH)CH, 1H, J¼4 Hz), 6.86 (d, –C6H3, 1H, J¼4 Hz), 7.45–
7.47 (m, –C6H3, 2H), 8.03 (d, –(CO)CH, 1H, J¼4 Hz), 9.92 (s, –COH,
1H). 13C NMR (75 MHz, CDCl3):
d 14.07, 22.66, 25.97, 26.00, 29.06,
29.19, 29.26, 29.34, 31.81, 69.08, 69.36, 97.85, 112.05, 112.16, 121.85,
127.84, 149.03, 153.62, 175.49, 188.81.
4.1.5. 1-(3,4-Bis(dodecyloxy)phenyl)-3-hydroxyprop-2-en-1-one (3b;
n¼12). White solid, 1H NMR (300 MHz, CDCl3):
d 0.86 (t, –CH3, 6H,
J¼6 Hz), 1.24–1.84 (m, –CH2, 40H), 4.03 (t, –OCH2, 4H, J¼4 Hz), 6.13
(d, –(COH)CH, 1H, J¼4 Hz), 6.86 (d, –C6H3, 1H, J¼4 Hz), 7.45–7.49
(m, –C6H3, 2H), 8.03 (d, –(CO)CH,1H, J¼4 Hz), 9.92 (s, –COH,1H). 13
C
NMR (75 MHz, CDCl3):
d 14.01, 22.60, 25.89, 25.92, 28.97, 29.11,
29.28, 29.54, 31.84, 69.00, 69.27, 97.76, 111.96, 112.07, 121.76, 127.76,
148.94, 153.53, 175.40, 188.74.
4.1.6. 1-(3,4-Bis(hexadecyloxy)phenyl)-3-hydroxyprop-2-en-1-one
(3b; n¼16). White solid, 1H NMR (300 MHz, CDCl3):
d 0.86 (t, 6H,
–CH3, J¼6 Hz), 1.24–1.845 (m, 56H, –CH2), 1.79–1.84 (m, 2H, –CH2),
4.03 (t, 2H, –OCH2, J¼6 Hz), 6.13 (d, 1H, –(COH)CH, J¼4 Hz), 6.85
(d, 1H, Ar–H, J¼8 Hz), 7.44–7.48 (m, 2H, Ar–H), 8.03 (d, 1H,
–(COH)CH, J¼4 Hz), 9.91 (s, 1H, –COH). 13C NMR (75 MHz, CDCl3):
d
14.10, 22.69, 25.99, 26.01, 29.07, 29.20, 29.38, 29.72, 31.94, 69.07,
69.35, 97.83, 112.04, 112.16, 121.84, 127.83, 149.03, 153.62, 175.51,
188.77.
4.1.7. 1-(4-Hexadecyloxyphenyl)-3-(3-hydroxypropylimino)propan-
1,2-diol (2a; n¼16). The solution of 40-hexadecyloxy-2-hydroxy-
acrylophenone (1.0 g, 2.57 mmol) dissolved in 15 mL of dry THF
was slowly added 3-amino-1,2-propanediol (0.223 g, 2.45 mmol)
dissolved in 10 mL of abs 10 ethanol under nitrogen atmosphere.
The mixture was stirred at room temperature for 8 h. The solution
was concentrated to dryness. The product, isolated as white solid
was obtained after recrystallization from CH3OH/THF. Yield 64–
70%. 1H NMR (300 MHz, CDCl3):
d
0.86 (t, 3H, –CH3, J¼7 Hz), 1.18–
1.77 (m, 28H, –CH2), 2.17 (s, 1H, –OH), 2.81 (s, 1H, –OH), 3.28–3.38
(m, 2H, –NCH2), 3.49–3.84 (m, 3H, –CH(OH)CH2(OH)), 3.97 (t, 2H,
–OCH2, J¼4 Hz), 5.68 (d, 1H, CH, J¼4 Hz), 6.87 (d, 2H, –C6H4,
J¼4 Hz), 6.92 (m, 1H, –CHN), 7.81 (d, 2H, –C6H4, J¼4 Hz), 10.20 (m,
1H, –COH).
Figure 8. Molecular arrangements proposed for compound 2a (n¼8, top) and 1a (n¼8,
bottom) both in crystal phase and smectic A phases. The two d-spacings used in Cr
phases were obtained from XRD data measured at rt (see Figs. 6 and 7).
–C6H4, J¼7 Hz), 8.10 (d, 1H, –(CO)CH, J¼4 Hz), 9.92 (s, –COH, 1H).
4.1.8. 1-(4-Octyloxyphenyl)-3-(3-hydroxypropylimino)propan-1,2-
13C NMR (75 MHz, CDCl3):
d
14.04, 22.60, 25.93, 29.04, 29.16,
diol (2a; n¼8). Off-white solid, 1H NMR (300 MHz, CDCl3):
d 0.85 (t,
29.26, 31.75, 68.18, 68.27, 68.35, 97.65, 114.34, 114.43, 129.56,
163.18, 176.50, 188.11.
3H, –CH3, J¼4 Hz), 1.26–1.76 (m, 12H, –CH2), 2.43 (s, 1H, –OH), 3.05
(s, 1H, –OH), 3.28–3.35 (m, 2H, –NCH2), 3.61–3.83 (m, 3H,
–CH(OH)CH2(OH)), 3.95 (t, 2H, –OCH2, J¼4 Hz), 5.67 (d, 1H, CH,
J¼4 Hz), 6.66 (d, 2H, –C6H4, J¼4 Hz), 6.90 (d, 1H, –CHN) 7.80 (d, 2H,
–C6H4, J¼4 Hz), 10.20 (m, 1H, –COH). 13C NMR (75 MHz, CDCl3):
4.1.2. 1-(4-Dodecyloxyphenyl)-3-hydroxy-2-propen-1-one (3a;
n¼12). Light yellow solid, 1H NMR (300 MHz, CDCl3):
d 0.86 (t, 3H,
–CH3, J¼7 Hz), 1.24–1.82 (m, 20H, –CH2), 3.99 (t, 2H, –OCH2,
J¼6 Hz), 6.12 (d, 1H, CH, J¼4 Hz), 6.91 (d, 2H, –C6H4, J¼9 Hz), 7.85(d,
2H, –C6H4, J¼9 Hz), 8.10 (d, 1H, –(CO)CH, J¼4 Hz), 9.93 (s, –COH,
d 14.07, 15.26, 22.64, 25.53, 26.01, 27.20, 29.20, 29.32, 29.47, 31.79,
51.57, 63.97, 68.13, 71.43, 90.57, 114.02, 121.49, 128.61, 129.02,
132.00, 154.33, 161.75, 189.66, 192.85, 216.76.
1H). 13C NMR (75 MHz, CDCl3):
d 14.05, 22.63, 25.91, 29.03, 29.29,
29.50, 29.52, 29.58, 31.86, 68.25, 97.62, 114.41, 127.37, 129.53,
130.76, 163.16, 176.46, 188.09.
4.1.9. 1-(4-Dodecyloxyphenyl)-3-(3-hydroxypropylimino)propan-
1,2-diol (2a; n¼12). Off-white solid, 1H NMR (300 MHz, CDCl3):
d
0.86 (t, 3H, –CH3, J¼4 Hz), 1.24–1.77 (m, 20H, –CH2), 2.50 (s, 1H,
4.1.3. 1-(4-Hexadecyloxyphenyl)-3-hydroxy-2-propen-1-one
–OH), 3.25 (s, 1H, –OH), 3.25–3.41 (m, 2H, –NCH2), 3.56–3.83 (m,
3H, –CH(OH)CH2(OH)), 3.96 (t, 2H, –OCH2, J¼4 Hz), 5.67 (d, 1H, CH,
J¼4 Hz), 6.87 (d, 2H, –C6H4, J¼4 Hz), 6.91 (d, 1H, –CHN), 7.80 (d, 2H,
–C6H4, J¼4 Hz), 10.18 (m, 1H, –COH). 13C NMR (75 MHz, CDCl3):
(3a; n¼16). Light yellow solid, 1H NMR (300 MHz, CDCl3):
d 0.86 (t,
3H, –CH3, J¼7 Hz), 1.24–1.83(m, 28H, –CH2), 3.99 (t, 2H, –OCH2,
J¼7 Hz), 6.13 (d, 1H, CH, J¼4 Hz), 6.91 (d, 2H, –C6H4, J¼9 Hz), 7.85(d,
2H, –C6H4, J¼9 Hz), 8.11 (d, 1H, –(CO)CH, J¼4 Hz), 9.93 (s, –COH,
d
14.09, 15.26, 22.68, 26.00, 29.19, 29.33, 29.58, 29.63, 31.91, 51.55,
1H). 13C NMR (75 MHz, CDCl3):
d
14.09, 22.67, 25.95, 29.07, 29.34,
63.96, 68.12, 71.43, 90.58, 114.01, 129.01, 132.00, 147.26, 154.29,
161.74, 189.65.
29.54, 29.56, 29.67, 31.91, 68.30, 97.67,114.45,127.42,129.58,130.81,
162.92, 163.20, 176.51, 188.14.
4.1.10. 1-(3,4-Octyloxyphenyl)-3-(3-hydroxypropylimino)propan-
4.1.4. 1-(3,4-Bis(octyloxy)phenyl)-3-hydroxyprop-2-en-1-one
1,2-diol (2b; n¼8). Light yellow solid, 1H NMR (300 MHz, CDCl3):
(3b; n¼8). White solid, 1H NMR (300 MHz, CDCl3):
d
0.86 (t, –CH3,
d
0.86 (t, 6H, –CH3, J¼3 Hz), 1.23–1.75 (m, 24H, –CH2), 1.98 (s, 1H,

3592
C. Chien et al. / Tetrahedron 66 (2010) 3583–3592
–OH), 2.71 (s, 1H, –OH), 3.29–3.33 (m, 2H, –NCH2), 3.57–3.83 (m,
3H, –CH(OH)CH2(OH)), 4.00 (t, 2H, –OCH2, J¼3 Hz), 5.67 (d, 1H,
CH, J¼4 Hz), 6.82 (d, 1H, –C6H4, J¼4 Hz), 6.84–6.91 (d, 1H, –CHN),
7.39–7.44 (m, 2H, –C6H4,), 10.18 (m, 1H, –COH). 13C NMR (75 MHz,
References and notes
1. (a) Metallomesogens, Synthesis, Properties and Applications; Serrano, J. L., Ed.;
VCH: Weinheim, Germany, 1996; (b) Bruce, D. W. In Inorganic Materials, 2nd
ed.; Bruce, D. W., O’Hare, D., Eds.; Wiley: Chichester, UK, 1996; Chapter 8, p 429;
(c) Donnio, B.; Bruce, D. W. Struct. Bond. 1999, 95, 193–247; (d) Binnemans, K.;
Go¨rller-Walrand, C. Chem. Rev. 2002, 102, 2303–2346; (e) Donnio, B.; Guillon,
D.; Deschenaux, R.; Bruce, D. W. In Comprehensive Coordination Chemistry II;
McCleverty, J. A., Meyer, T. J., Eds.; Elsevier: Oxford, 2003; Vol. 7, Chapter 7.9,
pp 357–627.
CDCl3):
d 14.09, 22.67, 25.95, 29.07, 29.34, 29.54, 29.56, 29.67,
31.91, 68.30, 97.67, 114.45, 127.42, 129.58, 130.81, 162.92, 163.20,
176.51, 188.14.
2. (a) Binnemans, K. J. Mater. Chem. 2009, 19, 448–453; (b) Galyametdinov, Y. G.;
Knyazev, A. A.; Dzhabarov, V. I.; Cardinaels, T.; Driesen, K.; Go¨rller-Walrand, C.;
Binnemans, K. Adv. Mater. 2008, 20, 252–257; (c) Cavero, E.; Uriel, S.; Romero, P.;
Serrano, J. L.; Gimenez, R. J. Am. Chem. Soc. 2007, 129, 11608–11618; (d) Escande,
A.; Guenee, L.; Nozary, H.; Bernardinelli, G.; Gumy, F.; Aebischer, A.; Bu¨ nzli, J. C. G.;
Donnio, B.; Guillon, D.; Piguet, C. Chem.dEur. J. 2007,13, 8696–8713; (e) Piguet, C.;
Buunzli, J.-C. G.; Donnio, B.; Guillon, D. Chem. Commun. 2006, 3755–3768; (f)
Terazzi, E.; Suarez, S.; Torelli, S.; Nozary, H.; Imbert, D.; Mamula, O.; Rivera, J. P.;
Guillet, E.; Benech, J. M.; Bernardinelli, G.; Scopelliti, R.; Donnio, B.; Guillon, D.;
4.1.11. 1-(3,4-Dodecyloxy phenyl)-3-(3-hydroxypropylimino)propan-
1,2-diol (2b; n¼12). Light yellow solid, 1H NMR (300 MHz, CDCl3):
d
0.86 (t, 6H, –CH3, J¼4 Hz), 1.23–1.75 (m, 40H, –CH2), 2.54 (s, 1H,
–OH), 3.16 (s, 1H, –OH), 3.27–3.37 (m, 2H, –NCH2), 3.60–3.83 (m,
3H, –CH(OH)CH2(OH)), 4.01 (t, 4H, –OCH2, J¼3 Hz), 5.67 (d, 1H, CH,
J¼4 Hz), 6.82 (d, 1H, –C6H4, J¼4 Hz), 6.88 (d, 1H, –CHN) 7.39–7.45
(m, 2H, –C6H4), 10.18 (m, 1H, –COH). 13C NMR (75 MHz, CDCl3):
}
}
Bunzli, J.-C. G.; Piguet, C. Adv. Funct. Mater. 2006, 16, 157–168.
d
14.10, 22.68, 26.04, 28.18, 29.17, 29.36, 29.42, 29.64, 31.92, 51.60,
ˆ
´
3. (a) Glebowska, A.; Przybylski, P.; Winek, M.; Krzyczkowska, P.; Krwczynski, A.;
Szyd1owska, J.; Pociecha, D.; Go´ recka, E. J. Mater. Chem. 2009, 19, 1395–1398;
(b) Pietrasik, U.; Szyd1owska, J.; Kro´wczyn´ ski, A. Chem. Mater. 2004, 16, 1485–
1492; (c) Yang, C. D.; Pang, Y. S.; Lai, C. K. Liq. Cryst. 2001, 28, 191–195; (d) Lai, C.
K.; Lin, R.; Lu, M. Y.; Kao, K. C. J. Chem. Soc., Dalton Trans. 1998, 1857–1862.
4. (a) Rzvani, Z.; Divband, B.; Abbasi, A. R.; Nejati, K. Polyhedron 2006, 25, 1915–
1920; (b) Abe, Y.; Nakabayashi, K.; Matsukawa, N.; Takashima, H.; Iida, M.;
Tanase, T.; Sugibayashi, M.; Mukai, B.; Ohta, K. Inorg. Chim. Acta 2006, 359,
3934–3946; (c) Nejati, K.; Rezvani, Z. New J. Chem. 2003, 27, 1665–1669; (d) Ku,
S. M.; Wu, C. Y.; Lai, C. K. J. Chem. Soc., Dalton Trans. 2000, 3491–3492; (e)
Hoshino, N. Coord. Chem. Rev. 1998, 174, 77–108; (f) Lai, C. K.; Chang, C. H.; Tsai,
C. K. J. Mater. Chem. 1998, 8, 599–602.
64.00, 69.08, 69.27, 71.44, 90.59, 112.17, 112.38, 120.80, 148.76,
154.34.
4.1.12. 1-(3,4-Hexadecyloxyphenyl)-3-(3-hydroxypropylimino)-
propan-1,2-diol (2b; n¼16). Light yellow solid, 1H NMR (300 MHz,
CDCl3):
d
0.84 (t, 6H, –CH3, J¼4 Hz), 1.14–1.60 (m, 56H, –CH2), 2.13
(s, 1H, –OH), 2.86 (s, 1H, –OH), 3.26–3.34 (m, 2H, –NCH2), 3.35–3.47
(m, 3H, –CH(OH)CH2(OH)), 4.01 (t, 4H, –OCH2, J¼3 Hz), 5.68 (d, 1H,
CH, J¼4 Hz), 6.71 (d, 1H, –C6H4, J¼4 Hz), 6.83–6.92 (d, 1H, –CHN)
7.39–7.46 (m, 2H, –C6H4), 10.18 (m, 1H, –COH). 13C NMR (75 MHz,
5. (a) Chien, C. W.; Liu, K. T.; Lai, C. K. J. Mater. Chem. 2003, 13, 1588–1595; (b) Lai,
C. K.; Pan, H. B.; Yang, L. F.; Liu, K. T. Liq. Cryst. 2001, 28, 97–101; (c) Trzaska, S. T.;
Zheng, H.; Swager, T. M. Chem. Mater. 1999, 11, 130–134; (d) Trzaska, S. T.; Hsu,
H. F.; Swager, T. S. J. Am. Chem. Soc. 1999, 121, 4518–4519; (e) Trzaska, S. T.;
Swager, T. M. Chem. Mater. 1998, 10, 428–443; (f) Zheng, H.; Xu, B.; Swager, T. M.
Chem. Mater. 1996, 8, 907–911.
CDCl3): d 14.10, 22.68, 26.00, 29.36, 29.70, 31.92, 66.38, 69.07, 90.58,
112.15, 112.37, 120.81, 189.63.
4.1.13. Palladium complex of 1-(4-octyloxyphenyl)-3-(3-hydroxypro
pylimino)propan-1,2-diol (1a; n¼8). The solution of 1-(4-octyloxy-
phenyl)-3-(3-hydroxypropylimino)propan-1,2-diol (0.50 g, 1.43
mmol) dissolved in 10 mL of dry THF and palladium (II) acetate
Pd(OAc)2 (0.168 g, 0.75 mmol) in 10 mL was mixed and then gently
refluxed for 3 h. The solution was concentrated to dryness, and the
product isolated as yellow solids was obtained after recryst-
allization from CH3OH/THF. Yield 82–85%.
6. Lai, C. K.; Tsai, C. H.; Pang, Y. S. J. Mater. Chem. 1998, 8, 1355–1360.
7. (a) Lin, R.; Tsai, C. H.; Chao, M. Q.; Lai, C. K. J. Mater. Chem. 2001, 11, 359–363; (b)
Lai, C. K.; Chen, F. G.; Ku, Y. J.; Tsai, C. H.; Lin, R. J. Chem. Soc., Dalton Trans. 1997,
4683–4687.
8. Lai, C. H.; Pang, Y. S.; Tsai, C. H. J. Mater. Chem. 1998, 8, 2605–2610.
9. (a) Coco, S.; Cordovilla, C.; Domı´nguez, C.; Donnio, B.; Espinet, P.; Guillon, D.
Chem. Mater. 2009, 21, 3282–3289; (b) Lavigueur, C.; Foster, E. J.; Williams, V. E.
J. Am. Chem. Soc. 2008, 130, 11791–11800; (c) Barbera´, J.; Puig, L.; Romero, P.;
Serrano, J. L.; Sierra, T. J. Am. Chem. Soc. 2006, 128, 4487–4492.
10. (a) Vera, F.; Serrano, J. L.; Sierra, T. Chem. Soc. Rev. 2009, 38, 781–796; (b) Wang,
y. U.; Song, J. H.; Lin, Y. S.; Lin, C.; Sheu, H. S.; Lee, G. H.; Lai, C. K. Chem. Commun.
´
2006, 4912–4914; (c) Massiot, P.; Imperor-Clerc, M.; Veber, M.; Deschenaux, M.
Acknowledgements
Chem. Mater. 2005, 17, 1946–1951; (d) Ziessel, R.; Pickaert, G.; Camerel, F.;
Donnio, B.; Guillon, D.; Cesario, M.; Prange, T. J. Am. Chem. Soc. 2004, 126,
12403–12413.
We thank the National Science Council of Taiwan, ROC (NSC98-
2815-C-008-021-M & NSC98-2752-M-008-010-PAE) in generous
support of this work.
11. (a) Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Ha¨gele, C.; Scalia, G.;
Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosonim, M. Angew. Chem.,
Int. Ed. 2007, 46, 4832–4887; (b) Kumar, S. Chem. Soc. Rev. 2006, 35, 83–109.