H-Bonded metallomesogens derived from salicyladiminates

Article abstract of DOI:10.1016/j.tet.2010.06.002

A series of new mesogenic compounds 1a-b (n=8, 10, 12, 14, 16) derived from salicyladimines and their palladium 2a, 2b, vanadyl 2a, and copper complexes 3a, 3b were prepared and their mesomorphic properties investigated by optical microscopy, differential

Full text of DOI:10.1016/j.tet.2010.06.002

Tetrahedron 66 (2010) 6101e6112
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
H-Bonded metallomesogens derived from salicyladiminates
Sih-Yeh Li a, Chun-Jung Chen a, Po-Yuan Lo b, Hwo-Shuenn Sheu c,
,
Gene-Hsiang Lee d, Chung K. Lai a
*
a Department of Chemistry, National Central University, Chung-Li 32001, Taiwan, ROC
b Industrial Technology Research Institute, Hsinchu 300, Taiwan, ROC
c National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
d Instrumentation Center, National Taiwan University, Taipei 10660, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 April 2010
Received in revised form 26 May 2010
Accepted 1 June 2010
Available online 12 June 2010
A series of new mesogenic compounds 1aeb (n¼8, 10, 12, 14, 16) derived from salicyladimines and their
palladium 2a, 2b, vanadyl 2a, and copper complexes 3a, 3b were prepared and their mesomorphic
properties investigated by optical microscopy, differential scanning calorimetry and powder X-ray dif-
fractometry. Pd2þ and VO2þ ions formed mononuclear complexes, whereas, Cu2þ ion formed binuclear
complexes due to the relative acidic strength of Schiff base. Single crystallographic analysis of non-
mesogenic compound 2a (n¼8) confirmed its coordination geometry at Pd2þ as square plane. It crys-
tallizes in a triclinic space group Pꢀ1 with a Z¼1. As expected, the Pd2þ was coordinated via a trans-N2O2
donor set of phenoliceO and imine-N atoms, leaving two hydroxyl groups intact and uncoordinated. The
two alkoxy chains, pointing to the opposite direction were parallel, and the molecule was considered as
twisted Z-shaped. Both hydroxyl-OH groups attached on C17 and C18-Schiff imines participate in the H-
bonds in the lattice. Interestingly, a pseudo polymeric structure was observed, in which H-bonded dimer
was continuously extended by another H-bonded dimer in the lattice. Compounds 1 exhibited smectic A
phases, and Pd and VO complexes and Cu complexes 3b exhibited smectic A or/and smectic X phases,
however, Cu complexes 3a formed crystal phases. Intermolecular H-bonds might be attributed to the
difference observed on the mesomorphic properties in these compounds. Copper complexes 2b were not
active on ESR spectroscopy.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
van der Waals force and others might be concomitant. In contrast,
metallomesogenic materials2 approached by same concept were
The use of intermolecular attraction induced (or stabilized) by
hydrogen-bonds to generate organic mesogenic materials has been
well demonstrated during the past years. The approach by H-
bonding allowed us to tailor molecular engineering for functional
organic liquid crystals. Numerous novel examples1 prompted by
either intermolecular or/and intramolecular were described, in
which both using single component or multiple components were
all accessible. There is often a competition between inter-molecular
and intra-molecular H-bonding. In order to achieve a stable
mesogenic state, a balance between the tendency of the molecules
to melt or to segregate into a crystalline state becomes crucially
important. H-bond interaction; considered as a relatively weak
force might not be the principle attraction in forming the meso-
relatively limited. The presence of one or more hydroxyl groups in
the organic moiety is truly compulsory in order to induce such
attractive H-bonds. Likewise, the hydroxyl groups were also an
excellent coordination sites toward most of transition metals, thus
leaving no free hydroxyl group to be induced in mesogenic states.
Diamagnetic palladium (d8-Pd2þ) and paramagnetic oxovanadium
or vanadyl (d1-VIVO2þ) ions were considered exclusively as a few
metal ions. Pd2þ ion is often considered as soft Lewis acid, whereas,
VO2þ is then regarded as harder Lewis acid. These two metal ions
will not coordinate to the hydroxyl groups with a less acidic
strength, particularly to the primary-OH (1ꢁ), and secondary-OH
(2ꢁ) of the alkyl alcohols. However, they do coordinate to the
phenolic hydroxyl group.
phase. Other interactions, as well as
p
ep
interaction, weal dipole,
Recently, we have been interested in this type of stabilized
H-bonded metallomesogens, and
a
few H-bonded metal-
lomesogens 4,3 54 have been prepared and reported by this
group. Complexes 4 formed smectic A phases, however, com-
plexes 5 exhibited hexagonal columnar phases. Interestingly,
single crystallographic analysis indicated that a dimeric structure
* Corresponding author. Tel.: þ886 03 4259207; fax: þ886 03 4277972; e-mail
address: cklai@cc.ncu.edu.tw (C.K. Lai).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.06.002

6102
S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
in compounds 4 and a tetrameric structure in compound 5 by
H-bond were observed in the crystal states, and the formation of
mesophases induced might be attributed to such H-bond in the
mesophases. A smectic A phase and hexagonal phase was ob-
served by H-bonded dimeric and tetrameric structure for com-
pounds 1 and 4, respectively. An appropriate aspect ratio or/and
resulting complementary shape effect were probably improved
by H-bonds. A removal of hydroxyl group then led to the loss of
liquid crystallinity in both complexes. In addition, the position
(or location) of the hydroxyl groups has a significant impact on
the liquid crystalline behavior; changing their position often
dramatically alters their geometries needed to induce the H-
bond interactions. Salicyladimine Schiff bases are one of the
organic moieties that have been studied the most, and many
mesogenic palladium complexes5 were reported. Interestingly,
a series of mononuclear copper(II) complex6 derived from azo-
containing salicylaldimines was prepared and studied by Rezvani
and co-workers. A free hydroxyl group on ethanolamine Schiff
base was remained as uncoordinated, however, whether H-bond
existing was uncertain due to the lack of single crystallographic
analysis.
In this work, a new series of mesogenic compounds 1 (n¼8, 10,
12, 14, 16) derived from salicyladimines and their palladium,
vanadyl, and copper complexes 2, 3 were prepared and their me-
somorphic properties studied. Single crystallographic analysis of
non-mesogenic compound 2a (n¼8) confirmed the square planar
geometry at Pd2þ center, and also a pseudo-polymeric structure
induced by intermolecular H-bonds were formed. Both hydroxyl-
OH groups are important since they all participate in the H-bonds
in the crystal lattice. Palladium 2a, 2b and vanadyl complexes 2a
are mononuclear complexes; however, copper complexes 3a, 3b are
binuclear complexes. A structurally similar bimetallomesogens 67a,
b, 77c were also reported by this group. Single crystallographic data
indicated that these copper complexes were all dinuclear co-
ordinated with one copper atom lying above and below the central
plane.
RO
X
O
N
OH
M
HO
N
O
X
OR
M = Pd, VO; R = (CH2)nH
2a; X = OH
2b; X = H
RO
RO
OH
O
O
N
N
O
N
N
O
OH
OH
Pd
Pd
HO
OH
RO
OR
5
4
X
RO
RO
Y
X
O
N
O
O
O
N
Cu
Cu
Cu
O
N
O
O
O
N
Cu
Y
X
OR
OR
X
6; X = H, CH3
7; X, Y = H, OR

S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
6103
RO
HO
RO
b
a
OH
N
X
OH
O
OH
O
HO
1a; X = OH
1b; X = H
d
c
RO
RO
X
O
O
N
N
O
O
Cu
Cu
O
N
OH
X
M
HO
N
O
X
X
OR
OR
M = Pd, VO
2a; X = OH
2b; X = H
3a; X = OH
3b; X = H
Scheme 1. Reactions and reagents. (a) KHCO3 (2.0 equiv), KI, RBr (1.1 equiv), refluxing in acetone, 16 h, 40%. (b) 3-Amino-propane-1,2-diol (1.1 equiv) or 3-amino-propanol
(1.1 equiv), refluxing in THF/absolute ethanol, 3 h, 90%. (c) M(OAC)2 (M¼Pd, VO; 0.55 equiv), refluxing in C2H5OH, 6 h. 75%. (d) Cu(OAC)2 (1.1 equiv), refluxing in ethanol, 6 h, 80%.
2. Results and discussion
peak appeared at ca. d 8.02e8.13, assigned for an imine-H (eC]NH)
of compounds 1a, 1b was observed. Metal complexes 2, 3, prepared
by the reactions of Schiff bases 1 with vanadyl(IV) sulfate, palla-
dium(II) acetate or copper acetate refluxing in ethanol were
obtained after recrystallization twice from THF/methanol. All pal-
ladium and vanadyl complexes were isolated as yellow and gray-
green solids; however, all binuclear copper complexes were
obtained as pale green solids. These bicopper d9-[Cu2þ]2 complexes
2.1. Synthesis and characterization
The synthetic pathways to compounds 1a, 1b and their palla-
dium(II) 2a, 2b, vanadyl 2a and copper(II) complexes 3a, 3b are
summarized in Scheme 1. All intermediates and Schiff bases were
characterizes by 1H and 13C NMR spectroscopy. A characteristic
Figure 1. The IR spectra measured at 25.0 ꢁC of the compounds: 1a (n¼10; top), VO complex 2a (n¼10) and Pd complex 2a (n¼10; bottom).

6104
S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
3a, 3b and monovanadyl d1-VIVO2þ 2a are all paramagnetic, and
their 1H NMR spectra displayed only one broad alkoxy signals. All
other proton signals close to paramagnetic metal center were not
all well observed. In addition, these paramagnetic d9-[Cu2þ
]
2
complexes showed no signal at 77 K and 298 K on solid-samples
EPS spectroscopy due to the super exchange behavior.
The IR spectral frequencies of a few compounds 1a (n¼10) and 2a
(M¼VO, Pd; n¼10) were obtained using KBr pellets. In the com-
pounds 1a (n¼10), the imine eC]N and the hydroxyl eOH groups
were observed at nC]N¼1656 cmꢀ1, and nOH¼3250e3450 cmꢀ1, as
shown in Figure 1. Upon complexation, the VO complexes 2a (n¼10)
has a nC]N frequency shifted to lower 1608 cmꢀ1, and another n(V]O)
frequency was observed at 979 cmꢀ1, indicative of the formation of
the mononuclear five-coordinatewith square-pyramid geometries.8
On the other hand, the phenolic eOH group often, occurred at
nOH¼3200 cmꢀ1 was slightly superimposed with the two lateral
eOH groups observed at nOH¼3320 cmꢀ1. Infrared data were much
less informative for the palladium complexes 2a (C]N and N]N
stretching modes overlapped in the same region). All vanadyl
complexes were only slightly soluble in polar solvents; however,
they were not quite stable in such solvents. The solution changed to
red in color in few minutes when dissolved in THF, and this might be
associated to the coordination of THF to the vanadyl center as the
sixth ligand. Removal of THF would not lead back to the original
structure. In order to evaluate electrochemical properties of the
bicopper complex, the cyclic voltammetry (CV) measurements
(Fig. 2) were performed in a dry dichloromethane solution of
Bu4NPF6 (0.1 M) with a scan rate of 100 mV sꢀ1 at roomtemperature.
Compound 3a (n¼16) showed a quasi-reversible peak9 ate0.65 V and
Figure 3. An ORTEP plot for compound 2a (n¼8) with the numbering scheme, and the
thermal ellipsoids of the non-hydrogen atoms are drawn at the 50% probability level.
Table 1
Crystallographic and experimental data for compound 2a (n¼8)
Compound
2a (n¼8)
C36H56N2O8Pd
751.23
Empirical formula
Formula weight
T/K
150 (2)
Crystal system
Space group
a/Å
b/Å
c/Å
Triclinic
Pꢀ1
5.3975 (2)
9.5122 (4)
17.8000 (4)
78.796 (2)
88.670 (3)
84.599 (2)
892.48 (5)
1
e0.71 V, E1/2¼0.61 V (
d
EP¼65 mV). The one-electron reduction can be
ascribed to the oxidation reaction of bicopper complexes as
ꢁ
ꢁ
[(Cu2þCu2þ)L]þeꢀ4[(CuþCu2þ)L]ꢀ.
a
/
b
/
ꢁ
/
g
U/Å3
Z
F (000)
396
1.398
Dc/Mg mꢀ3
Crystal size/mm3
Range for data collection/ꢁ
Reflection collected
Data, restraints, parameters
Independent reflection
Final R1, wR2
0.32ꢂ0.06ꢂ0.02
2.19e25.00
9252
3139/0/227
3139 [R (int)¼0.0671
0.0443, 0.1044
plane. The two angles of N1AePdeO1A and O1ePdeN1A aree91.90
(10)ꢁ ande88.10 (10)ꢁ, respectively, which showan almost ideal angle
of 90ꢁ as expected for a square planar coordination. The other two
angles of N1ePdeN1A and O1ePdeO1A were also perfect ofe180ꢁ.
Selected bond distances and angles for compound 2a (n¼8) were
listed in Table 2.
Figure 2. Cyclic voltammogram of copper complex 3a (n¼16) in CH2Cl2/0.1 M Bu4NPF6
at 25 ꢁC.
2.2. Single crystal structure of palladium complex of 3-[(2-
hydroxy-4-octyloxy benzylidene)amino]propane-1,2-diol (2a;
n[8)
Table 2
Selected bond distances [Å] and angles [ꢁ] for compound 2a (n¼8)
In order to confirm the geometry at central Pd2þ ion, and also
understand the possible effect of the two hydroxyl groups (eOH) on
the formation of mesophases, a single crystal of the non-mesogenic
palladium complex 2a (n¼8) suitable for crystallographic analysis
was obtained by slow vaporization from THF/methanol at room
temperature and it structure resolved. As expected, the palladium
ion was coordinated via a trans-N2O2 donor set of phenolic-O and
imine-N atoms, leaving the two hydroxyl groups intact and un-
coordinated. Figure 3 shows the molecular structure with the atomic
numbering schemes. Table 1 lists its crystallographic and structural
refinement data. It crystallizes in a triclinic space group Pꢀ1 with
a Z¼1. The geometry at palladium center is a nearly perfect square
Bond distances
N(1)ePd
O(1)ePd
C(1)eC(2)
C(1)eN(1)
C(16)eN(1)
2.022 (3)
1.983 (2)
1.434 (5)
1.287 (4)
1.471 (4)
C(2)eC(3)
1.412 (5)
1.317 (4)
1.535 (5)
1.322 (7)
1.403 (6)
C(3)eO(1)
C(16)eC(17)
C(17)eO(3)
C(18)eO(4)
Bond angles
O(1)ePdeN(1)
O(1)ePdeN(1)A
C(3)eO(1)ePd
N(1)eC(1)eC(2)
N(1)eC(16)eC(17)
91.90 (10)
88.10 (10)
126.1 (2)
128.2 (3)
112.8 (3)
O(1)AePdeN(1)A
O(1)AePdeN(1)
C(1)eN(1)ePd
O(3)eC(17)eC(18)
O(4)eC(18)eC(17)
91.90 (10)
88.10 (10)
122.7 (2)
113.6 (4)
108.0 (4)
Symmetry transformations used to generate equivalent atoms: #1ꢀx, ꢀyþ2, ꢀz.

S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
6105
Two phenyl rings were parallel; however, they were not co-
planar with the central plane defined by N1eO1ePdeN1AeO1A
atoms. A dihedral angle of 16.03ꢁ was measured. The two alkoxy
chains were almost perpendicular to the central Pd plane with an
angle ofe89.67ꢁ. There was no interaction between the neighboring
This intermolecular H-bond between two dimeric structures has
apparently enhanced the molecular interaction between the layers.
2.3. Mesomorphic properties
ꢀ
ꢀ
PdePd atoms (de5.40 A) and PdeO atoms (de4.38 A). The two chains
The liquid crystalline behavior of ligands 1a, 1b, bicopper
complexes 3a, 3b, vanadyl, and palladium complexes 2a, 2b were
characterized and studied by differential scanning calorimetry
(DSC) and polarized optical microscope (POM). The phase transi-
tions and thermodynamic data are summarized in Table 3e5. The
only derivative 1a with a shorter chain (n¼8) exhibited mono-
tropic behavior, whereas all other derivatives 1a (n¼10, 12, 14, 16)
with longer alkoxy carbon chains showed enantiotropic phases.
Under optical microscope they exhibited oily streak textures
(Fig. 6) with a large area of homeotropic domains, which was
characteristic of a layer smectic A phase expected for the rod-like
molecules. The phases were tentatively assigned as smectic A
phases based on POM observation. The clearing temperatures
were all ranged at Tcl¼124.4 ꢁC (n¼8)e132.9 ꢁC (n¼14), while all
melting temperatures remained at T¼119.8 ꢁC (n¼10)e114.5 ꢁC
(n¼16). On the other hand, the temperature range of mesophase
ꢀ
were parallel (d w3.929 A) aligned, pointing to the opposite di-
rection (or a trans arrangement). It led to an overall molecular
shape considered as a Z-shaped molecule, and the molecular length
ꢀ
was ca. e24.27 A (C15eC15A). The middle length and side length
ꢀ
were 17.0 and 7.7 A, giving a total possible fully extended molecular
ꢀ
ꢀ
length of 17.0þ2ꢂ7.7 A¼32.4 A. Unsurprisingly, two types of inter-
molecular H-bonds formed by two hydroxyl groups attached on C17
and C18 Schiff imine were in fact observed in the lattice. Both types
are intermolecular H-bonds. The first H-bond was induced by two
neighboring molecules above-and-below planes; and the second
H-bond was formed by two side-by-side molecules. The first H-
ꢀ
bond lengths of above-and below molecules were ofe1.828 A (O4-
ꢀ
H4/O3) and the second one wase2.030 A (H3A/O4). The two bond
angles, :O3eH4eO4 and O4-H3eO3 were of 153.97ꢁ and 163.90ꢁ,
respectively. A pseudo dimeric structure formed by H-bond was
arranged by a style of cis arrangement (Fig. 4). This dimeric struc-
ture was formed by interlocking two molecules via two symmetric
H-bonds; one was C18O4/H3AC17A and other one was
increased slightly with carbon length of alkoxy chains,
D
T¼20.8 ꢁC
(n¼8)>40.1 ꢁC (n¼12)>41.7 ꢁC (n¼16) on cooling process. The
transition enthalpies of SmA-to-Iso transitions were relatively
C17O3H3/ O4AC18A. On the other hand, no
tween molecules were observed. The H-bonds facilitated the for-
mation of a layer smectic phase observed in compounds 2a (Fig. 5).
pep interaction be-
small, and also decreased with carbon length,
D
HSmA/I¼1.87
(n¼10)e1.87 kJ/mol (n¼16). In contrast, all derivatives 1b (n¼8, 12,
16) formed monotropic behavior. The clearing temperatures were
Figure 4. Inter-molecular H-bonds in compound 2a (n¼8) observed in the unit cell.

6106
S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
Figure 5. The molecular arrangements into layer structures in 2a (n¼8) viewed from different axes.
all much lower than those for derivatives 1a by ca. 82.3 ꢁC (n¼8)e
41.6 ꢁC (n¼16). However, the temperature range of mesophases
bonding might be induced in both compounds 1a, 1b. However,
Intermolecular H-bonds induced or/and formed by an extra hy-
droxyl group at C17 in derivatives 1a have apparently enhanced
the intermolecular attraction, leading a higher clearing tempera-
ture, and mesophase were also improved.
for derivative 1b remained
D
T¼9.4 ꢁC (n¼8)e23.3 ꢁC (n¼8),
slightly narrower than those of derivatives 1a. The phases were
also identified as smectic A phases. A relatively lower enthalpy,
D
H¼0.85 (n¼16)e2.19 kJ/mol (n¼8) for 1a and
D
H¼3.09 (n¼8)e
Palladium complexes derived from 1a, 1b, and vanadyl com-
plexes derived from 1a were also prepared and studied. All Pd
compounds, 2a, 2b except for those with shorter alkoxy chains
(n¼8) were mesogenic, and both Pd complexes 2a, 2b have a much
3.83 kJ/mol (n¼12) for 1b of transition of smectic phase-to-iso-
tropic was also consistent for SmA phases. The difference in the
mesomorphic temperatures might be attributed to H-bonds. H-
Table 3
Phase temperature and enthalpiesa of compounds 1a and 1b
a
n is the carbon numbers of terminal alkoxy groups. Cr1, Cr2¼crystal, SmA¼smectic A, and I¼isotropic phase.

S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
6107
Table 4
Phase temperatures and enthalpiesa of compounds 2
a
n is the carbon numbers of terminal alkoxy groups. Cr1, Cr2, and Cr3¼crystal, SmX¼smectic X, SmA¼smectic A, and I¼isotropic phase.
b
Obtained by optical microscope.
higher clearing temperature than those of compounds 1a, 1b by
Table 5
Phase temperatures and enthalpiesa of compounds 3
a
D
Tcl¼65.8 ꢁC (n¼12)e73.3 ꢁC (n¼14) and
D
Tcl¼40.5 ꢁC (n¼16)e
76.0 ꢁC (n¼8), respectively. Likewise, Pd complexes 2a also have
a higher clearing temperature than that of Pd complexes 2b by
a
D
Tcl¼70.9 ꢁC (n¼12)e74.1 ꢁC (n¼16). This lowering in clearing
temperatures observed in 2b over 2a might be attributed to the
dramatic weakening or loss of H-bonds in Pd complexes 2b. Com-
pounds 2a formed smectic X and smectic A phases, however,
compounds 2b formed smectic A phase. An oily streak texture, as
characteristic textures of smectic A phases was observed under
optical microscope, in which a large area of homeotropic domain
was also observed (Fig. 7). Compounds 2a (n¼10, 12, 14, 16) have
a higher clearing temperature than that of compounds 2b by ca.
D
Tcl¼73.9 ꢁC (n¼14)e81.4 ꢁC (n¼12). The higher clearing temper-
atures might be attributed to the H-bond formed by an extra hy-
droxyl group at C17 of Schiff bases. Both series of compounds have
a
n is the carbon numbers of terminal alkoxy groups. Cr¼crystal, SmA¼smectic A,
and I¼isotropic phase.
a temperature range of mesophase at ca.,
D
TSmA¼58.4 ꢁC (n¼10)e
74.1 ꢁC (n¼12) and
D
TSmA¼55.8 ꢁC (n¼14)e73.7 ꢁC (n¼16) for
Figure 6. The optical textures observed. SmA phase by 1a (n¼10; top) at 125.0 ꢁC, SmA phase by 1b (n¼8; bottom) at 29.0 ꢁC.

6108
S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
Figure 7. The optical textures observed. SmA phase by 2a/Pd (n¼10; left) at 192.0 ꢁC and SmX phase by 2a/Pd (n¼10; right) at 175.0 ꢁC.
compounds 2a and 2b, respectively. An extra highly ordered SmX
phase was also observed for compounds 2a at lower temperatures,
of which were not studied further for its phase classification. All VO
complexes 2a (n¼8, 12, 14, 16) were kinetically unstable in meso-
phase behavior and they all exhibited monotropic behavior. Com-
pound with a n¼16 was nonmesogenic. The clearing temperatures
The bicopper complexes 3a, 3b with a central bridging oxygen
were also prepared and studied. A structurally similar copper
complexes derived from 4-alkoxy-N-(3-hydroxypropyl) salicyl-
aldimines and 3,5-bis-(3,4,5-trialkoxybenzyloxy)phenyl-2-(3-
hydroxypropyl)imino propylketones 6, 7 have been prepared and
investigated in this group. The geometry of these bicopper com-
plexes was perfectly square pyramid, in which two copper atoms
were slightly lower than those of Pd complexes by ca.
DTcl¼1.7
(n¼10)<3.3 (n¼12)<9.7 ꢁC (n¼14). The temperature range of
mesophase was also slightly narrower by 19.8 (n¼12)e19.8 ꢁC
(n¼14) that those of Pd complexes 2a. The mesophase were also
assigned as SmA phases based on POM textures.
were found lying 3.0375 (5) A apart, one 0.018 A above and the
ꢀ
ꢀ
ꢀ
other 0.018 A. The center core was nearly flat, which facilitated the
molecular arrangement. Copper complexes have a relatively larger
core size, so a higher clearing temperature might be expected. From
Figure 8. The powder X-ray diffraction plots for compounds. Top: 1a (n¼14) at 25.0 ꢁC (left) and at 125.0 ꢁC (right); bottom: 2a/Pd (n¼12) at 25.0 ꢁC (left) and at 196.0 ꢁC (right).

S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
6109
DSC analysis, all compounds 3a were not mesogenic, and a phase
transition from crystal-to-isotropic state was only observed at 243.1
(n¼8)e222.1 ꢁC (n¼16). All compounds 3a were also slightly
decomposed above their clearing temperatures. In contrast, all
compounds 3b exhibited monotropic behavior. The clearing tem-
peratures were drastically lower that those of compounds 3a,
which might be attributed to the structural effect. The temperature
range of mesophases was quite short, ca. 4.80 (n¼8)e17.3 ꢁC
(n¼12). A too strong intermolecular H-bonding induced by two
hydroxyl groups in compounds 3a destroyed the liquid crystallinity.
On the other hand, a weakening of H-bond interaction by only one
hydroxyl group in compounds 3b reached a well-balanced force
needed to form the mesophases.
2.4. Variable-temperature powder XRD diffraction data
The mesophase structures for two compounds 1a (n¼14), 2a
(Pd, n¼12) were also confirmed by use of variable-temperature
powder XRD experiments. For compound 1a (n¼14) at T¼125.0 ꢁC
a diffraction pattern with one strong peak, one weak peak and
ꢀ
ꢀ
one very broad peat with a d-spacing of ca. e39.3 A, e19.7 A, and
ꢀ
e4.59 A was observed (Fig. 8). The first two diffraction peaks
Figure 9. The schematic diagram showing the molecular arrangements proposed for compounds 1a (top) and Pd complexes 2a (bottom) both in Cr and SmA phase.

6110
S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
Table 6
corresponded to a layer structure, assigned as 001 and 002 in-
Elemental analysisa of compounds 1e3
ꢀ
dices. The very broad weak of de4.59 A at wide angle region was
due to halo diffraction. This diffraction pattern was typically
characteristic of layer structures observed for a SmA phase. The
Compounds
C (%)
H (%)
1a (n¼8)
66.83 (66.84)
68.31 (68.34)
69.52 (69.62)
70.83 (70.72)
71.53 (71.68)
57.54 (57.55)
59.51 (59.23)
61.05 (61.20)
62.65 (62.69)
63.89 (64.01)
60.33 (60.12)
63.72 (63.56)
64.73 (64.95)
66.11 (66.18)
56.14 (56.16)
60.01 (59.91)
62.81 (62.81)
58.48 (58.59)
61.90 (62.16)
64.40 (64.90)
9.10 (9.04)
9.54 (9.46)
9.85 (9.83)
10.23 (10.14)
10.40 (10.41)
7.51 (7.51)
7.98 (7.99)
8.38 (8.40)
8.87 (8.77)
9.08 (9.09)
8.01 (7.85)
8.82 (8.73)
9.00 (9.08)
9.36 (9.40)
7.06 (7.07)
8.10 (8.00)
8.72 (8.78)
7.45 (7.38)
8.30 (8.28)
8.86 (9.00)
ꢀ
1a (n¼10)
layer d-spacing of 39.3 A (1a; n¼14) is much larger than the
ꢀ
1a (n¼12)
monomeric molecular length ofe25.0 A, a distance calculated for
1a (n¼14)
a fully extended molecule by MM2 model. However, it is much
1a (n¼16)
ꢀ
closer to the dimeric molecular length ofe45.0 A (1a; n¼14), in-
2aePd (n¼8)
2aePd (n¼10)
2aePd (n¼12)
2aePd (n¼14)
2aePd (n¼16)
2bePd (n¼8)
2bePd (n¼12)
2bePd (n¼14)
2bePd (n¼16)
3a (n¼8)
dicating that the formation of a smectic phase was induced or/
and formed by a H-bonded dimeric structure with all alkoxy
chains partially interdigitated.
XRD diffractions for palladium complex 2a (n¼12) both at
196.0 ꢁC at 25.0 ꢁC were also obtained. At 196.0 ꢁC, a strong and
ꢀ
ꢀ
a very weak diffraction peak at d¼30.4 A and d¼15.2 A assigned
as 001 was observed. This diffraction pattern also confirmed the
SmA phases. This d-spacing was close to the molecular length of
3a (n¼12)
ꢀ
31.3 A, obtained from single crystallographic data of complex 2a
3a (n¼16)
(n¼8) with four methylene moieties (CH2)4 on both sides added
for complex 2a (n¼12). A molecular arrangement in the meso-
phase was therefore proposed in Figure 9.
3b (n¼8)
3b (n¼12)
3b (n¼16)
a
With calculated values in parentheses.
3. Conclusions
4.2. X-ray crystallography
Two series of new Schiff bases 1a, 1b and their palladium,
vanadyl, and copper complexes 2, 3 were prepared and their
mesomorphic properties investigated to demonstrate the possi-
ble effect of induced H-bonds. Single crystallographic analysis of
palladium complexes 2a (n¼8) confirmed the single crystal and
molecular crystal structures. A dimeric structure with a better
aspect ratio was induced by intermolecular H-bond, which led to
the formation and facilitation of mesophases in compounds 2a.
All compounds 1 exhibited smectic A phases, in contrast, all metal
complexes 2, 3 formed smectic A and/or smectic X phases. Pd and
VO complexes 2a, 2b exhibited similar mesomorphic behavior.
The presence of a hydroxyl group at C17- and C18-position of Schiff
imines played a significant role in forming the mesomorphic
properties. Both palladium complexes 2a, 2b were mesogenic.
However, compounds 2a with two hydroxyl-OH groups attached
on C17 and C18 have a higher clearing temperature than those of
X-ray diffraction data were collected at 150 (2) K on a Nonius
Kappa CCD X-ray diffractometer unit using graphite-mono-
ꢀ
chromated Mo K
a
radiation (
l
¼0.71073 A) from crystals mounted
on glass fibers and quickly coated in epoxy resin. Cell parameters
were retrieved and refined using DENZO-SMN software on all ob-
served reflections. Data reduction was performed with the DENZO-
SMN software. The program package SHELXTL was used for space
group determination, structure solution, and refinement.
Refinement was performed against F2 by weighted full-matrix
least-square, and empirical absorption correction (SADABS) were
applied. H atoms were placed at calculated positions using suitable
riding models with isotropic displacement parameters derived
from their carrier atoms. Crystal data, selected bond distances, and
angles are provided in Tables 1 and 2.
4.2.1. 4-Dodecyloxy-2-hydroxybenzaldehyde (n¼12). White solid,
compounds 2a with only one hydroxyl group attached on C18
indicating a stronger intermolecular interaction in 2a.
,
yield 40%. 1H NMR (300 MHz, CDCl3):
d 0.86 (t, eCH3, 3H,
J¼6.80 Hz), 1.24e1.43 (m, eCH2, 18H), 1.74e1.84 (m, eOCH2CH2,
2H), 3.97 (t, eOCH2, 2H, J¼6.58 Hz), 6.38 (S, AreH, 1H), 6.49 (dd,
AreH, 1H, J¼2.10 Hz), 6.50 (dd, AreH, 1H, J¼2.15 Hz), 6.49 (dd,
AreH, 1H, J¼2.10 Hz), 7.38 (d, AreH, 1H, J¼8.50 Hz), 9.67 (s, eCHO,
4. Experimental section
4.1. General
1H), 11.45 (s, AreOH, 1H). 13C NMR (75 MHz, CDCl3):
d 14.12, 22.70,
25.93, 25.98, 26.06, 28.20, 28.79, 28.94, 29.32, 29.36, 29.46, 29.55,
29.56, 29.59, 29.64, 31.93, 32.87, 33.99, 68.61, 101.06, 108.76, 115.02,
135.17, 164.55, 166.47, 194.25.
3-Amino-1,2-propanediol
alcohol
and
2,4-dihydroxy-
benzaldedyde were purchased from Acros used as received. The 1H
and 13C NMR spectra were measured on a BUKER 300 UltraShieldÔ
operated at 300 MHz with CDCl3-d1 as solvent with tetrame-
thylsilane as the reference. 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 (Table 6) were conducted at Instrumentation Center, Na-
tional Taiwan University on a Heraeus CHNeO-Rapid elemental
analyzer. The powder X-ray diffraction data were collected from the
Wiggler-A beam line of the National Synchrotron Radiation Re-
search Center. The electrochemical experiment (CV) was carried
out with a CHI 627C electrochemistry workstation (CHI, USA). A
conventional three-electrode electrochemical system was used for
the electrochemical experiment; this consisted of a working elec-
trode, a platinum wire auxiliary electrode and a saturated Ag/AgCl
reference electrode.
4.2.2. 4-Hexadecyloxy-2-hydroxybenzaldehyde (n¼16). White solid,
yield 45%. 1H NMR (300 MHz, CDCl3):
d 0.86 (t, eCH3, 3H,
J¼6.38 Hz), 1.23e1.58 (m, eCH2, 26H), 1.70e1.81 (m, eOCH2CH2,
2H), 3.98 (t, eOCH2, 2H, J¼6.53 Hz), 6.48 (dd, AreH, 1H, J¼2.30 Hz),
6.52 (dd, AreH, 1H, J¼2.15 Hz), 6.48 (dd, AreH, 1H, J¼2.30 Hz), 7.39
(d, AreH, 1H, J¼8.62 Hz), 9.68 (s, eCHO, 1H), 11.46 (s, AreOH, 1H).
13C NMR (75 MHz, CDCl3):
d 14.10, 22.68, 25.90, 28.90, 29.29, 29.51,
29.55, 29.65, 29.67, 31.91, 68.60, 101.03, 108.78, 114.99, 135.18,
164.51, 166.46, 194.28.
4.2.3. 3-[(2-Hydroxy-4-dodecyloxybenzylidene)amino]propane-1,2-
diol (1a; n¼12). The mixture of 4-dodecyloxy-2-hydroxy-
benzaldehyde (1.0 g, 2.63 mmol) dissolved in 5.0 mL of dried THF
was added 3-amino-1,2-propanediol (0.25 g, 2.77 mmol) dissolved
in 10 mL of absolute ethanol. The solution was refluxed for 3 h
under nitrogen atmosphere. The solids were collected, and the

S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
6111
products, isolated as bright yellow solids were obtained after re-
crystallization from ether or hexane/THF at ice bath temperature.
(t, eCH3, 3H, J¼6.9 Hz), 1.27e1.79 (m, eCH2, 10H), 1.95 (m,
eOCH2CH2, 2H), 3.61 (t, eCH2NC, 2H, J¼6.6 Hz), 3.74 (t, eCH2OH,
2H, J¼6.0 Hz), 3.92 (t, eOCH2, 2H, J¼6.6 Hz), 6.3 (d, AreH, 1H,
J¼2.10 Hz), 6.34 (s, AreH, 1H), 7.05 (d, AreH, 1H, J¼8.4 Hz), 8.11(s,
Yield 89%. 1H NMR (300 MHz, CDCl3):
d
0.86 (t, eCH3, 3H, J¼6.9 Hz),
1.24e1.45 (m, eCH2,18H), 1.70e1.80 (m, eOCH2CH2, 2H), 3.55e3.79
(m, eCH2NC, eCH2OH, 4H), 3.93 (t, eOCH2, 2H, J¼6.6 Hz),
3.96e4.04 (m, eCHOH, 1H), 6.36 (b, AreH, 2H), 7.06 (d, AreH, 1H,
-NCH, 1H). 13C NMR (75 MHz, CDCl3):
d 14.11, 22.64, 25.96, 29.03,
29.52, 31.54, 31.88, 33.27, 53.15, 59.69, 68.04, 101.90, 106.80, 111.60,
132.70, 163.90, 168.10.
J¼9.3 Hz), 8.11 (s, eNCH, 1H). 13C NMR (75 MHz, CDCl3):
d 14.10,
22.68, 25.98, 29.06, 29.34, 29.57, 31.91, 59.41, 64.55, 68.16, 71.32,
101.99, 107.24, 111.67, 133.13, 164.20, 165.57.
4.2.10. N-(3-Hydroxypropyl)-4-hexadecyloxysalicylaldimine
(1b;
n¼16). Yellow needle crystal, yield 82%. 1H NMR (300 MHz,
CDCl3):
d
0.86 (t, eCH3, 3H, J¼6.9 Hz), 1.28e1.79 (m, eCH2, 26H),
4.2.4. 3-[(2-Hydroxy-4-octyloxybenzylidene)amino]propane-1,2-diol
1.93 (m, eOCH2CH2, 2H), 3.64 (t, eCH2NC, 2H, J¼6.6 Hz), 3.75 (t,
eCH2OH, 2H, J¼6.0 Hz), 3.93 (t, eOCH2, 2H, J¼6.6 Hz), 6.31 (d,
AreH, 1H, J¼2.40 Hz), 6.35 (s, AreH, 1H), 7.06 (d, AreH, 1H,
(1a; n¼8). Bright yellow solid, yield 86%. 1H NMR (300 MHz, CDCl3):
d
0.86 (t, eCH3, 3H, J¼6.9 Hz),1.26e1.46 (m, eCH2,10H),1.71e1.76 (m,
eOCH2CH2, 2H), 3.50e3.74 (m, eCH2NC, eCH2OH, 4H), 3.93 (t,
eOCH2, 2H, J¼6.6 Hz), 3.96e4.03 (m, eCHOH,1H), 6.28 (b, AreH, 2H),
7.02 (d, AreH, 1H, J¼9.3 Hz), 8.02 (s, -NCH, 1H). 13C NMR (75 MHz,
J¼8.7 Hz), 8.13 (s, -NCH, 1H). 13C NMR (75 MHz, CDCl3):
d 14.09,
22.65, 25.97, 29.03, 29.32, 29.52, 29.57, 29.61, 29.63, 29.65, 31.54,
31.88, 33.27, 53.14, 59.69, 68.0, 101.90, 106.80, 111.60, 132.70,
163.80, 168.20.
CDCl3): d 14.08, 22.64, 26.00, 29.06, 29.21, 29.33, 31.80, 58.76, 64.53,
68.15, 71.25, 102.15, 107.28, 111.46, 133.34, 164.50, 165.27.
4.3. Palladium and vanadyl complex of 3-[(2-hydroxy-4-
dodecyloxybenzylidene)amino] propane-1,2-diol (2a; n[12)
4.2.5. 3-[(2-Hydroxy-4-decyloxybenzylidene)amino]propane-1,2-
diol (1a; n¼10). Bright yellow solid, yield 91%. 1H NMR (300 MHz,
CDCl3):
d
0.86 (t, eCH3, 3H, J¼6.9 Hz), 1.25e1.46 (m, eCH2, 14H),
The mixture of 3-[(2-hydroxy-4-dodecyloxybenzylidene)
amino]propane-1,2-diol (0.50 g, 0.58 mmol) and palladium (II) ac-
etate (0.065 g, 0.29 mmol) or VOSO4 (0.047 g, 0.29 mmol) was
stirred in 20 mL of THF for 6 h. The solids were collected and the
products, isolated as yellow solids for vanadyl complexes or light
gray-green for palladium complexes were obtained after re-
crystallization from THF/methanol at ice bath temperature. Yield
70e76%. Vanadyl complexes were only slightly soluble in THF, and
it was not stable in THF. The color changed to red in a few minutes.
1.72e1.76 (m, eOCH2CH2, 2H), 3.51e3.75 (m, eCH2NC, eCH2OH, 4H,),
3.94 (t, eOCH2, 2H, J¼6.0 Hz), 3.96e4.01 (m, eCHOH, 1H), 6.29 (b,
AreH, 2H), 7.03(d, AreH, 1H, J¼8.4 Hz), 8.05 (s, eNCH, 1H). 13C NMR
(75 MHz,CDCl3):d14.08, 22.65,25.98,29.05,29.30,29.37, 31.87, 57.92,
64.46, 68.13, 71.14, 102.26, 107.26, 111.26, 133.51, 164.40, 165.01.
4.2.6. 3-[(2-Hydroxy-4-tetradecyloxybenzylidene)amino]propane-
1,2-diol (1a; n¼14). Bright yellow solid, yield 87%. 1H NMR
(300 MHz, CDCl3):
d
0.86 (t, eCH3, 3H, J¼6.9 Hz), 1.24e1.46 (m,
eCH2, 22H), 1.72e1.77 (m, eOCH2CH2, 2H), 3.53e3.79 (m, eCH2NC,
eCH2OH, 4H,), 3.95 (t, eOCH2, 2H, J¼6.6 Hz), 3.98e4.00
(m, eCHOH, 1H), 6.35 (b, AreH, 2H), 7.07(d, AreH, 1H, J¼9.0 Hz),
4.4. Copper complex of 3-[(2-hydroxy-4-dodecyloxybenzyli-
dene)amino]propane-1,2-diol (3a; n[12)
8.13 (s, eNCH, 1H). 13C NMR (75 MHz, CDCl3):
d 14.11, 22.68, 25.97,
The mixture of 3-[(2-hydroxy-4-dodecyloxybenzylidene)
amino]propane-1,2-diol (0.50 g, 0.58 mmol) and copper(II) acetate
(0.11 g, 0.58 mmol) was refluxed in THF for 6 h. The solids were
collected, and the products, isolated as green powder were
obtained after recrystallization from THF/methanol at ice bath
temperature. Yield 80%.
29.06, 29.35, 29.65, 31.91, 60.08, 64.54, 68.16, 71.37, 101.85, 107.20,
111.85, 132.98, 164.53, 165.85.
4.2.7. 3-[(2-Hydroxy-4-hexadecyloxybenzylidene)amino]propane-
1,2-diol (1a; n¼16). Bright yellow solid, yield 90%. 1H NMR
(300 MHz, CDCl3):
d
0.85 (t, eCH3, 3H, J¼6.9 Hz), 1.23e1.45 (m,
eCH2, 26H), 1.72e1.76 (m, eOCH2CH2, 2H), 3.53e3.79 (m, eCH2NC,
eCH2OH, 4H), 3.92 (t, eOCH2, 2H, J¼6.3 Hz), 3.97e4.03 (m, eCHOH,
1H), 6.34 (b, AreH, 2H), 7.08 (d, AreH, 1H, J¼9.3 Hz), 8.14 (s, eNCH,
4.4.1. Palladium complex of N-(3-hydroxypropyl)-4-dodecyloxy-
salicylaldimine (2b; n¼12). The mixture of N-(3-hydroxypropyl)-4-
dodecyloxysalicylaldimine (0.50 g, 1.38 mmol) dissolved CHCl3 was
added palladium(II) acetate (0.15 g, 0.69 mmol) dissolved in
10.0 mL of ethanol. The mixture was refluxed for 8 h. The solution
was concentrated and the products, isolated as yellow solids were
obtained after recrystallization from hexane/dichloromethane.
Yield 75%.
1H). 13C NMR (75 MHz, CDCl3):
d 14.09, 22.67, 25.97, 29.06, 29.34,
29.65, 31.91, 60.34, 64.54, 68.16, 71.41, 101.80, 107.18, 111.93, 132.91,
163.72, 165.98.
4.2.8. N-(3-Hydroxypropyl)-4-dodecyloxysalicylaldimine
(1b;
n¼12). The mixture of 4-dodecyloxy-2-hydroxybenzaldehyde
(1.0 g, 2.63 mmol) and 3-amino- propan-1-ol (0.21 g, 2.77 mmol)
was refluxed in 15 mL of absolute ethanol for 3 h. The solution was
cooled and the solids were collected. The products, isolated as
yellow needle crystals were obtained after recrystallization from
4.4.2. Copper
complex
of
N-(3-hydroxypropyl)-4-dodecylox-
ysalicylaldimine (3b; n¼12). The mixture of N-(3-hydroxypropyl)-
4-dodecyloxysalicylaldimine (0.50 g, 1.38 mmol) dissolved in
5.0 mL of CHCl3 was added copper(II) acetate (0.25 g, 1.38 mmol)
dissolved in 10 mL of ethanol. The mixture was refluxed for 1 h. The
solution was concentrated and the product, isolated as brown
solids was obtained after recrystallization from ethyl acetate/
methanol. Yield 86%.
hexane. Yield 85%. 1H NMR (300 MHz, CDCl3):
d 0.86 (t, eCH3, 3H,
J¼6.9 Hz), 1.27e1.78 (m, eCH2, 18H), 1.94 (m, eOCH2CH2, 2H), 3.64
(t, eCH2NC, 2H, J¼6.6 Hz), 3.74 (t, eCH2OH, 2H, J¼6.0 Hz), 3.93 (t,
eOCH2, 2H, J¼6.6 Hz), 6.31 (d, AreH, 1H, J¼2.10 Hz), 6.34 (s, AreH,
1H), 7.05 (d, AreH, 1H, J¼8.4 Hz), 8.12 (s, -NCH, 1H). 13C NMR
(75 MHz, CDCl3):
d 14.11, 22.64, 25.96, 29.03, 29.31, 29.52, 29.61,
Acknowledgements
31.54, 33.27, 53.14, 59.69, 68.03, 101.90, 106.80, 111.60, 132.70,
163.80, 168.10.
We thank the National Science Council of Taiwan, ROC (NSC98-
2815-C-008-021-M & NSC98-2752-M-008-010-PAE) and Industrial
Technology Research Institute of Taiwan, ROC (ITRI-99-B-069351-
A-A-5130) in generous support of this work.
4.2.9. N-(3-Hydroxypropyl)-4-octyloxysalicylaldimine (1b; n¼8).
Yellow needle crystal, yield 85%. 1H NMR (300 MHz, CDCl3):
d 0.87

6112
S.-Y. Li et al. / Tetrahedron 66 (2010) 6101e6112
} }
5. (a) Bilgin-Eran, B.; Yuror, C.; Tschierske, C.; Prehm, M.; Baumeister, U. J. Mater.
Chem. 2007, 17, 2319e2328; (b) Bilgin-Eran, B.; Tschierske, C.; Diele, S.; Bau-
meister, U. J. Mater. Chem. 2006, 16, 1136e1144; (c) Murillas, D. L.; Pinol, R.; Ros,
References and notes
ꢁ
1. (a) Coco, S.; Cordovilla, C.; Domínguez, C.; Donnio, B.; Espinet, P.; Guillon, D.
Chem. Mater. 2009, 21, 3282e3289; (b) Lavigueur, C.; Foster, E. J.; Williams,
V. E. J. Am. Chem. Soc. 2008, 130, 11791e11800; (c) Kutsumizu, S.; Mori, H.;
Fukatami, M.; Naito, S.; Sakajiri, K.; Saito, K. Chem. Mater. 2008, 20,
3675e3687; (d) Barberá, J.; Puig, L.; Romero, P.; Serrano, J. L.; Sierra, T. J. Am.
Chem. Soc. 2006, 128, 4487e4492; (e) Barberá, J.; Puig, L.; Romero, P.;
Serrano, J. L.; Sierra, T. J. Am. Chem. Soc. 2005, 127, 458e464; (f) Yagai, S.;
Nakajima, T.; Kishikawa, K.; Kohmoto, S.; Karatsu, T.; Kitamra, A. J. Am. Chem.
Soc. 2005, 127, 11134e11139; (g) Chen, B.; Baumeister, U.; Diele, S.; Das, M. K.;
Zeng, X.; Ungar, G.; Tschierske, C. J. Am. Chem. Soc. 2004, 126, 8608e8609; (h)
Prehm, M.; Diele, S.; Das, M.; Tschierske, C. J. Am. Chem. Soc. 2003, 125,
614e615.
B.; Serrano, J. L.; Sierra, T.; Fuente, M. R. J. Mater. Chem. 2004, 14, 1117e1127; (d)
Hegmann, T.; Kain, J.; Diele, S.; Schubert, B.; Bogela, H.; Tschierske, C. J. Mater.
}
Chem. 2003, 13, 991e1003; (e) Díez, L.; Espinet, P.; Miguela, J. A.; Rosb, M. B.
J. Mater. Chem. 2002, 12, 3694e3698.
6. Rezvani, Z.; Divband, B.; Abbasi, A. R.; Nejati, K. Polyhedron 2006, 25, 1915e1920.
7. (a) Lai, C. K.; Leu, Y. F. J. Chin. Chem. Soc. 1997, 44, 89e91; (b) Lai, C. K.; Lu, M. Y.;
Lin, F. J. Liq. Cryst. 1997, 23, 313e315; (c) Lai, C. K.; Lin, R.; Lu, M. Y.; Kao, K. C.
Dalton Trans. 1998, 1857e1862.
8. (a) Mohebbi, S.; Bakhshi, B. J. Coord. Chem. 2008, 61, 2615e2628; (b) Krish-
namurthy, S. S.; Soundarajan, S. J. Inorg. Nucl. Chem. 1966, 28, 1689e1692; (c)
Kasahara, R.; Tsuchimoto, M.; Ohba, S.; Nakajima, K.; Ishida, H.; Kojima, M.
Inorg. Chem. 1996, 35, 7661e7665; (d) Zhao, H. Y.; Xing, Y. H.; Cao, Y. Z.; Li, Z.
P.; Wei, D. M.; Zeng, X. Q.; Ge, M. F. J. Mol. Struct. 2009, 938, 54e64; (e)
Chang, C. J.; Labinger, J. A.; Gray, H. R. Inorg. Chem. 1997, 36, 5927e5930; (f)
Ooi, S.; Nishizawa, M.; Matsumoto, K.; Kuroya, H.; Saito, K. Bull. Chem. Soc.
Jpn. 1979, 52, 452e457; (g) Mohan, M.; Stephen, M. H.; Butcher, R. J.; Jasinski,
J. P.; Carano, C. J. Inorg. Chem. 1992, 31, 2029e2034.
2. (a) Miao, J.; Zhu, L. Chem. Mater. 2010, 22,197e206; (b) Vera, F.; Serrano, J. L.; Sierra,
T. Chem. Soc. Rev. 2009, 38, 781e796; (c) Giménez, R.; Elduque, A.; López, J. A.;
Barberá, J.; Cavero, E.; Lantero, I.; Oro, L. A.; Serrano, J. L. Inorg. Chem. 2006, 45,
_
10363e10370; (d) Massiot, P.; Imperor-Clerc, M.; Veber, M.; Deschenaux, M. Chem.
Mater. 2005, 17, 1946e1951; (e) Ziessel, R.; Pickaert, G.; Camerel, F.; Donnio, B.;
Guillon, D.; Cesario, M.; Prange, T. J. Am. Chem. Soc. 2004, 126, 12403e12413.
3. Wang, Y. J.; Song, J. H.; Lin, Y. S.; Lin, C.; Sheu, H. S.; Lee, G. H.; Lai, C. K. Chem.
Commun. 2006, 4912e4914.
9. (a) Lintvedt, R. L.; Ranger, G.; Schoenfelner, B. A. Inorg. Chem.1984, 23, 688e695; (b)
Zehetmair, J. K.; Lintvedt, R. L. Inorg. Chem.1990, 29, 2201e2204; (c) Wang, M. Y.; Xu,
X. Y.; Yang, F.; Zhang, S. Y.; Yang, X. J. J. Appl. Electrochem. 2008, 38, 1269e1274.
4. Tetrahedron 2010. doi:10.1016/j.tet.2010.03.04