Catenar bimetallomesogens derived from quinoxaline-salicylaldimine conjugates

Article abstract of DOI:10.1016/j.tet.2014.02.030

The preparation, characterization, and mesomorphic properties of two series of tridentate N-salicylidene-2-hydroxyanilines and their metal complexes were described. The crystal and molecular structure of bis[2-hydroxy-4-propyloxy-N- (2-hydroxy-3,4-dipropy

Full text of DOI:10.1016/j.tet.2014.02.030

Tetrahedron 70 (2014) 2389e2399
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Catenar bimetallomesogens derived from
quinoxalineesalicylaldimine conjugates
Yian-Yuan Chu a, Hsiu-Ming Kuo a, Yu-Che Wu a, Chin-Yi Wu a, Hwo-Shuenn Sheu b,
,
a,
*
Gene-Hsiang Lee c, Ming-Chou Chen a , Chung K. Lai
*
a Department of Chemistry, National Central University, Chung-Li 32001, Taiwan, ROC
b National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, ROC
c 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:
The preparation, characterization, and mesomorphic properties of two series of tridentate N-salicyli-
dene-2-hydroxyanilines and their metal complexes were described. The crystal and molecular structure
of bis[2-hydroxy-4-propyloxy-N-(2-hydroxy-3,4-dipropyloxybenzylidene) aniline]copper(II) were de-
termined by means of X-ray analysis. It crystallizes in the monoclinic space group P2(1)/n and a Z¼4. The
geometry at Cu2þ ions is square pyramidal with a THF solvent molecule coordinated. The core structure
Received 14 December 2013
Received in revised form 26 January 2014
Accepted 13 February 2014
Available online 18 February 2014
ꢀ
was nearly flat, and the intramolecular CueCu atoms were separated by ca. 3.0163(6) A. All compounds
2a formed smectic C phases, and copper complexes 1aeCu were not mesogenic. In contrast, compound
2e and complexes 1beCu, 1deCu, 1eeCu, and 1eePd exhibited columnar phases. The lack of meso-
morphism in 1eeZn was attributed to a preferred tetrahedral over square planar geometry. A Ncell equal
ꢀ
to 2.44e2.92, calculated from powder XRD data within a 9.0 A thick indicated that an induced structure
correlated by two catenar-shaped molecules was formed in Colh phases.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
salicylaldehyde precursors. Also this type of Schiff-bases was con-
sidered as an excellent building block3 for obtaining a variety of
N-Salicylidene aniline (salan), often referred as Schiff-base have
been extensively studied during the past years and are now con-
sidered as important compounds1 for the preparation of hybrid
materials since they can present both solid state thermo- and
metal complexes I, some of which giving interesting mesomorphic
properties. These so-called metallomesogens4 opened up a subfield
from conventional liquid crystals. Metallomesogens derived from
salicylaldimines were among the best known complexes5 that
formed mesogenic behavior, and most of the metal complexes from
3d-block metals (excluded Sc, Ti) were known and showed meso-
morphism. Most examples forming nematic and smectic phases,
and relatively less examples giving columnar phases6 were re-
ported. A variety of unique geometric structures, such as square
planar, tetrahedral, octahedral or others resulted from a versatile
coordination numbers and oxidation states when incorporated
with transition metals was thus generated.
In contrast, N-salicylidene-2-hydroxyanilines (salan-OH) and
their metal complexes were lesser studied, and only a few non-
mesogenic complexes7 were reported. Salan-OH is also known as
a tridentate [ONO]-donor ligand system, and a bimetallic complex
II is expected when coordinated to metal ions. Among them, a few
bimetallic complexes,8 with structures IIIa,8d,e IIIc,8b IVa,8d IVb8c,d
shown in Schemes 1 and 2 were previously prepared by this
group; only compounds IIIa, IVaeb exhibiting mesomorphic be-
havior. All other compounds IIIbec were in fact not mesogenic. The
formation of mesophases was quite sensitive to the molecular al-
teration; a bulky tetrahedral methyl group (i.e., X¼CH3) attached to
photochromism. They represent
p-conjugated systems with tun-
able photophysical properties. Some salan-related derivatives2
have been investigated for the reversible solid state photochromic
or thermochromic properties. The reversible changes in the color
were attributed to a transition accompanied between two tauto-
meric structures due to an intramolecular proton transfer. Schiff-
base compounds are also often applied as chelating ligands in co-
ordination chemistry because they are generally known of their
binding modes and capabilities, and in particularly salicylaldimines
are useful for preparing transition metal complexes. Depending on
the coordination numbers and/or oxidation states of the transition
metals incorporated, numerous metal complexes with unique ge-
ometries were generated. Salan derivatives are linear tetradentate,
N2O2-coordinating ligand systems, which were easily obtained
from the condensation reactions of readily available amines and
* Corresponding authors. 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 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.02.030

2390
Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
N
O
O
N
M2+
OH
N
M
N-salicylidene-
aniline (salan)
I
N
N
O
O
M2+
M
M
O
O
or
O
M
N
OH
O
O
M
O
N
N
HO
N-salicylidene-2-hydroxyl
aniline (salan-OH)
IIa
IIb
Scheme 1. The structures of mono- and binuclear complexes obtained from bidentate N-salicylidene-aniline and tridentate N-salicylidene-2-hydroxyaniline.
RO
RO
RO
X
X
O
O
N
N
O
O
O
O
N
N
O
O
O
O
N
N
O
O
OH
Cu
Cu
Cu
Cu
Cu
Cu
X
HO
X
OR
IIIc; crystal phase
OR
OR
IIIa; X = H, SmA phase
IIIb; X = Me, crystal phase
IIId; X = H, Me, SmA phase
RO
RO
O
N
O
O
N
O
Cu
Cu
O
O
N
RO
RO
N
Cu
Cu
O
O
O
O
OR
OR
IVa; SmA phase
Scheme 2. Known bicopper complexes IIIeIV derived from N-salicyliene-2-hydroxyanilines.
OR
IVb; columnar phase
the central core in IIIb8e was believed to cause steric disorder in the
molecular arrangement, and its steric bulk greatly increased the
intermolecular layer distance. This resulted in a weakening in-
termolecular interaction, and therefore destroyed the meso-
morphism. On the other hand, a too strong intermolecular H-
bonding induced by hydroxyl group in compounds IIIc increased
their clearing temperatures; a phase transition from crystal-to-
isotropic state was observed at Tcl¼243.1 (n¼8)e222.1 ꢀC (n¼16).
Compounds IVb were the only derivatives, showing the columnar
phases. Interestingly, copper ions in complexes IV were
coordinated by
benzoate group.
m-exogenous-bridged bonds with an acetate or
In this report, we describe the synthesis, characterization and
mesomorphic properties of two new series of N-salicylidene-2-
hydroxyanilines 2aee as core group and their metal complexes,
1aeeeM (M¼Cu, Pd, Zn), structures shown in Schemes 3 and 4. In
order to understand the possible structure of the dicopper com-
plexes (i.e., two possible structures IIa and IIb shown in
Scheme 1), a single crystal of bis[2-hydroxy-4-propyloxy-N-(2-
hydroxy-3,4-dipropyloxy benzylidene)aniline]copper(II) complex

Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
2391
HO
HO
was grown and its single crystal and molecular structures were
determined by means of X-ray analysis. Structure IIa might be, at
best, speculative.
RO
a
OH
OH
d
O
OH
b
Results indicated that all copper complexes 1aeCu (n¼12, 14,
16) were not mesogenic, and the lack of mesomorphism was at-
tributed to the relatively too larger or/and too rigid core structure.
In order to improve the mesomorphic properties in this type of core
structures, a second series of quinoxaline-salicylaldimine conju-
gates 2bee and their metal complexes 1beeeM (M¼Cu, Pd, Zn)
was then prepared. Quinoxalines have been applied to produce
photoluminescent and/or efficient electroluminescent materials
RO
RO
RO
c
NO2
NH2
OH
OH
OH
O
due to their extended p-conjugated and more rigid structures. It is
an electron-transporting or hole-blocking layer in organic light-
emitting diodes (OLEDs) because of its relative ease of prepara-
tion and also thermal stability. A few columnar phases9 were ob-
tained by our group from related quinoxalines. Unsurprisingly, an
improved mesomorphic behavior was observed; compound 2e and
copper complexes 1beeeCu, and palladium complexes 1eePd
exhibited mesomorphic behavior. This type of bimetallic complexes
can be considered as catenar-shaped molecules, and some tetra-
and hexacaternar-shaped molecules10 were known to form meso-
morphic properties. This is the first examples derived from N-sal-
icylidene-2-hydroxyaniline that exhibited columnar phases.
e
RO
RO
O
N
O
O
Cu
Cu
f
RO
O
N
OR
OH
N
HO
2a
OR
OR
1a; R = (CH2)nH, n = 12, 14 16
2. Results and discussion
Scheme 3. Reactions and Reagents: (a) RBr (1.1 equiv), KHCO3 (1.5 equiv), refluxing in
acetone, 24 h, 55e62%; (b) HNO3 (con. 1.2 equiv), NaNO2 (0.2 equiv), 0 ꢀC stirring in
CH2Cl2, 6 h, 25e32%; (c) H2NNH2$H2O (1.2 equiv), Pd/C (0.1 equiv), refluxing in
C2H5OH, 4 h, 76e82%; (d) RBr (1.1 equiv), KHCO3 (1.5 equiv), refluxing in acetone, 24 h,
32e44%; (e) acetic acid (drops), refluxing in THF/C2H5OH (1/4), 24 h, 88e92%; (f)
Cu(OAc)2, refluxed in ethanol/THF, 12 h, 90%.
2.1. Synthesis and characterization
The synthetic procedures for compounds 2aee and metal
complexes 1aeeeM (M¼Cu, Pd, Zn) are summarized in Schemes 3
and 4. N-Salicylidene-2-hydroxyaniline derivatives 2a and their
copper complexes 1aeCu were similarly prepared from our
OR
OR1
O
O
O
N
N
N
a
HO
OR
OR
HO
O
OR1
OR1
N
3
4
OR
OR1
X
b
NH2
OH
O
X
OR1
N
OH
N
N
HO
O
OR1
OR1
2b; X = H; R1 = C12H25
c
OR1
2c; X = OC12H25; R1 = C4H9
2d; X = OC12H25; R1 = C8H17
2e; X = OC12H25; R1 = C12H25
X
R1O
OR1
N
O
N
R1O
R1O
O
N
M
O
X
O
OR1
OR1
O
O
M
N
O
N
O
N
R1O
OR1
1b; M = Cu; X = H; R1 = C12H25
1c; M = Cu; X = OC12H25; R1 = C4H9
1d; M = Cu; X = OC12H25; R1 = C8H17
1e; M = Cu, Zn, Pd; X = R1 = C12H25
Scheme 4. Reagents and conditions: (a) 2.4-dihydroxybenzaldehyde (1.1 equiv), DCC (1.2 equiv), DMAP (1.2 equiv), refluxing in dried THF at rt, 24 h, 75e81%; (b) refluxing in
absolute ethanol, 12 h, 84e86%; (c) M(OAc)2 (M¼Cu, Pd, Zn), refluxing in ethanol, 4 h, 82e85%.

2392
Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
previous procedures.11 In Scheme 4, the compounds of 2,3-bis-(3,4-
dialkoxyphenyl)quinoxaline-6-carboxylic acids 4 were prepared by
previous procedures.10a,b The reactions of carboxylic acids with 2,4-
dihydroxybenzaldehyde stirred in dried THF at room temperature
iminopropyl ketonato]copper(II). Some selected bond distances
and angles for single crystal were listed in Table 2.
gave
2,3-bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4-formyl-3-hydroxyphenyl esters 3 isolated as
pale yellow solids. The final compounds, 2,3-bis-(3,4-bis-didode-
cyloxy phenyl)-quinoxaline-6-carboxylic acid 4-[(4-dodecyloxy-2-
hydroxyphenylimino)-methyl]-3- hydroxylphenyl esters 2bee
were prepared by reactions of 2,3-bis-(3,4-bis-didodecylox-
yphenyl)-quinoxaline-6-carboxylic acid 4-formyl-3-hydroxyphenyl
esters and appropriate 2-amino-5-alkoxyphenols in refluxing ab-
solute ethanol. These esters isolated as pale yellow solids were
easily purified by recrystallization from acetone. The metal com-
plexes 1aeeeM were prepared by compounds 2aee and metal
acetates in refluxing ethanol for 4 h. 1H and 13C NMR spectroscopy
in CDCl3 were used to characterize all intermediates. For instance,
two characteristic singlet peaks occurred at
d 9.90 and 11.27 ppm,
assigned for eCHO and eOH groups in 2,3-bis-(3,4-bis-dialkox-
yphenyl)-quinoxaline-6-carboxylic acid 4-formyl-3-hydroxyphenyl
esters 3. In contrast, a singlet eCHO peak was then shifted to
d
8.64e8.70 ppm assigned to imine-CHN in compounds 2bee. The
phenolic peak eOH was barely observed due to the formation of
intramolecular H-bonds with imine-H groups. Elemental analysis
or/and mass spectra of all compounds 1aee and 1aeeeM was also
performed.
Fig. 1. An ORTEP drawing for dicopper complex with the numbering scheme, and
thermal ellipsoids of non-hydrogen atoms are drawn at the 50% probability level.
2.2. Single crystal structure and molecular structure of bis[2-
hydroxy-4-propyloxy-N-(2-hydroxy-3,4-
dipropyloxybenzylidene)aniline]copper(II)
Table 1
Crystallographic data for single crystal
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
C52H70Cu2N2O12
1042.18
200(2)
The reaction of bidentate N-salicylidene-2-aniline (salan) with
transition metal ions M2þ gave mononuclear complexes at the
[NO]-coordination site,3 whereas, the reaction of tridentate N-sal-
icylidene-2-hydroxylaniline (salan-OH) with metal ions M2þ often
gave homobinuclear complexes at the [ONO]-coordination site.
There are two possible coordination structures; IIaeb, as shown in
Scheme 1. The correct structure of these two structures is not easy
to be differentiated by conventional spectroscopic methods. Ex-
amples with known structures were relatively rare.
Monoclinic
P2(1)/n
a¼8.3243(1) A,
a
¼90ꢀ
ꢀ
b¼17.4636(2) A,
b
¼92.100(1)ꢀ
ꢀ
c¼33.7643(3) A,
g
¼90ꢀ
ꢀ
3
3
ꢀ
ꢀ
Volume (A ), Z
4905.10(9) A , 4
1.411
Density (calculated, Mg/m3)
Crystal size (mm3)
0.55ꢁ0.50ꢁ0.12
1.42e27.50ꢀ
24,966
q
range for data collection
In order to speculate the coordination geometry and binding
modes at metal centers, a single crystal of a dicopper complex, bis
[2-hydroxy-4-propyloxy-N-(2-hydroxy-3,4-dipropyloxy benzyli-
dene)aniline]copper(II) was obtained and its crystallographic
analysis was resolved at 200 K. The single crystals isolated as green
plates were obtained by slow evaporation from THF solution at
room temperature. Fig. 1 shows the molecular structure with the
atomic numbering scheme, and Table 1 shows the crystallographic
and structure refinement data for the molecule. A dicopper core
structure was obtained, as expected. Each copper(II) ion was co-
ordinated by three oxygen and one nitrogen atoms; two copper
Reflections collected
Independent reflections
Final R indices
7969 [R(int)¼0.0340]
R1¼0.0648, wR2¼0.1324
R1¼0.0811, wR2¼0.1377
R indices (all data)
ꢀ
ꢀ
atoms separating 3.0163(6) A apart; one sitting 0.120 A above and
ꢀ
the other one 0.120 A below the molecular plane defined by atoms
N(2), O(4), O(1), O(3), and O(1), O(3), O(2), and N(1). Two tetrahy-
drofurans as solvation molecules were also coordinated to each
copper ion opposite below and above the core plane, shown in
Fig. 2. A total number of 359.10ꢀ or 359.14ꢀ close to an ideal angle of
360ꢀ of four angles around Cu(1) and Cu(2) atoms was obtained, as
expected for a square planar geometry at copper ions. The bicop-
per core was nearly flat and the complex can be considered as
a round-shaped molecule. The distance between two copper
ꢀ
ions was ca. 3.0163(6) A, which was close to two previously pre-
ꢀ
pared similar bimetallic structures; 3.498 A in
m-exogenous-
bridged N,N-(propan-2-ol)-bis(4-alkoxysalicylald imine)copper(II)
ꢀ
and 3.0375 A in bis[3,5-dioctanoylphenyl-2-(3-hydroxypropyl)
Fig. 2. A unit cell plot for crystal when viewed from b-axis.

Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
2393
Table 2
focal-conic textures with a thicker sample or Schlieren textures
with a thinner sample between two glass slides. Such textures and
also no homeotropic behavior identified the formation of a layer
structure of smectic C phases, expected for the rod-like molecules.
DSC data showed that the clearing temperatures of all three com-
pounds 2a were ranged at Tcl¼150.2 ꢀC (n¼16)e159.9 ꢀC (n¼12),
while all melting temperatures remained at Tmp¼135.9 ꢀC (n¼16)e
140.5 ꢀC (n¼12). The temperature range of mesophase was rela-
ꢀ
ꢀ
Selected bond distances (A) and angles ( ) for single crystal
Bond lengths
Cu(1)eO(2)
Cu(1)eO(1)
Cu(2)eO(4)
Cu(2)eO(3)
Cu(1)eCu(2)
Bond angles
O(2)eCu(1)eN(1)
N(1)eCu(1)eO(1)
N(1)eCu(1)eO(3)
O(4)eCu(2)eN(2)
N(2)eCu(2)eO(3)
N(2)eCu(2)eO(1)
Cu(1)eO(1)eCu(2)
1.862(3)
1.936(2)
1.859(3)
1.932(3)
3.0163(6)
Cu(1)eN(1)
Cu(1)eO(3)
Cu(2)eN(2)
Cu(2)eO(1)
1.924(3)
1.939(2)
1.927(3)
1.964(2)
tively short;
D
TSmC¼19.4 (n¼12)>16.8 (n¼14)>14.3 ꢀC (n¼16) on
97.11(12)
83.67(12)
160.36(12)
97.27(12)
83.40(11)
160.03(12)
101.33(11)
O(2)eCu(1)eO(1)
O(2)eCu(1)eO(3)
O(1)eCu(1)eO(3)
O(4)eCu(2)eO(3)
O(4)eCu(2)eO(1)
O(3)eCu(2)eO(1)
Cu(2)eO(3)eCu(1)
174.10(12)
99.94(11)
78.38(10)
173.77(12)
100.59(11)
77.88(10)
102.38(11)
heating process and it decreased slightly with carbon length of
alkoxy chains. This shorter range of mesophase temperature might
be due to a relatively large core. The transition enthalpies of SmC-
to-Iso transitions were in the range of
DHSmC/I¼13.6e18.0 kJ/mol.
In fact, the overall-shapes of derivatives 2a were not perfectly lin-
ear. However, a more appropriate or better aspect ratio (l/d) was
probably obtained by a dimeric structure, which was formed or/and
induced by intermolecular H-bonds (Fig. 3). The formation of
mesophases induced by H-bonds has been observed in some rod-
like molecules. In contrast, all bicopper complexes 1aeCu (n¼12,
14, 16) were not mesogenic. A higher clearing temperature of
crystal-to-isotropic at Tcl¼273.6 (n¼12)e258.6 ꢀC (n¼16) was ob-
served. The lack of mesomorphism was attributed to the relatively
larger and/or rigid core in this type of bicopper structures. The
central core in complexes 1aeCu was apparently larger or/and
more rigid than those related structures shown in Scheme 2.
2.3. Thermal analysis and phase properties
The liquid crystalline behavior of Schiff-base derivatives 2aee
and their bimetal complexes 1aeeeM was characterized and
studied by differential scanning calorimetry (DSC) and polarized
optical microscope (POM). The phase transitions and thermody-
namic data are summarized in Table 3. All three derivative 2a
(n¼12, 14, 16) exhibited enantiotropic mesomorphic behavior un-
der POM observation. Under optical microscope they exhibited
Table 3
The phase transitions (ꢀC) and enthalpiesa of compounds 1e2
140.5 (20.9)
159.9 (13.6)
118.2 (25.4)
Cr2
SmC
Cr1
Cr1
Cr1
I
2a; n = 12
120.8 (15.6)
139.1 (27.9)
153.8 (11.5)
155.9 (18.0)
123.9 (30.6)
128.8 (39.6)
Cr2
Cr2
I
I
I
I
I
2a
14
SmC
SmC
Cr
153.4 (16.9)
150.2 (16.8)
125.1 (24.3)
135.9 (23.5)
2a
16
12
147.5 (15.2)
273.6 (12.9)
124.1 (27.7)
1a-Cu
259.0 (10.8)
273.5 (58.5)
1a-Cu 14
Cr
272.0 (55.6)
258.6 (68.7)
1a-Cu 16
2b
Cr
G
257.6 (67.9)
85.7 (9.42)
I
I
I
I
79.8 (5.29)
2c
2d
G
126.1 (15.8)
Cr
94.7 (15.3)
63.2b
110.7 (1.43)
Cr
Cr
Colh
2e
57.4b
125.1b
106.0 (1.29)
246.5 (39.5)
Colh
Cr
1b-Cu
1c-Cu
I
I
103.8b
232.2 (39.5)
210.5 (30.4)
190.1 (29.9)
254.5b
206.2 (21.0)
Cr
Cr
I
I
I
I
Colh
Colh
Colh
Cr
1d-Cu
1e-Cu
1e-Pd
1e-Zn
250.3b
267.9b
170.2 (13.9)
190.9 (28.1)
263.7b
208.1b
174.9 (14.1)
149.6b
Cr
204.7b
314.1b
132.7
295.3b

2394
Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
group to increase its molecular flexibility or/and lead to a better
aspect ratio required to form mesophases. Unsurprisingly, an im-
proved mesomorphic behavior was obtained; compound 2e and
bicopper complexes 1beCu, 1deeeCu and palladium complex
1eePd exhibited mesomorphic behavior. This is probably the first
examples derived from N-salicylidene-2-hydroxyaniline that
formed columnar phases.
O
O
N
O
H
O
H
Compound 2e with longer alkoxy chains (X¼OC12H25
,
H
O
H
R1¼C12H25) showed an enantiotropic phase, and three other com-
pounds 2bed with shorter side chains were nonmesogenic. Com-
pound 2e gave two transitions of crystal-to-columnar and
columnar-to-isotropic (Cr/Col/I) on DSC thermographs. The
melting and clearing temperatures were Tmp¼63.2 ꢀC and
Tcl¼110.7 ꢀC on heating process. The mesophase was first identified
as columnar (Colh) based on optical textures observed. A typical
pseudo focal-conic texture with linear birefringent defects (Fig. 4)
was observed. The overall molecular shape of compound 2e is in
fact not disc-like, however, a dimeric structure induced by H-
bonding was attributed to the formation of columnar phase in 2e.
This dimeric structure was considered as a shape more like catenar
mesogens. Many examples with a catenar-shaped are now known
to form mesophases; such as tetracatenar and hexacatenar meso-
gens forming columnar phases. Two other derivatives 2bec formed
O
N
O
O
Fig. 3. A correlated dimeric structure was induced by H-bond in salan-OH.
In order to improve the mesomorphic properties formed in this
type of bimetallic structures, a second series of compound 2bee
and their bimetallic complexes 1beeeM was prepared and their
mesomorphic properties were also investigated. In this series of
compounds 2bee, a quinoxaline moiety was incorporated as lateral
Fig. 4. Optical textures observed. SmC phase by 2a (n¼12, top left) at 140 ꢀC and SmC phase by 2a (n¼14, top right) at 150 ꢀC; Col phase by 2e (central left) at 80 ꢀC, Col phase
(central left) by 1eeCu at 230 ꢀC and Col phase (bottom) by 1eePd at 180 ꢀC.

Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
2395
Table 4
glass states, and both compounds entered their isotropic states at
Variable-temperature XRD diffraction data for compounds 1e2
Tcl¼85.7 and 79.8 ꢀC, respectively. Compound 2d was not meso-
genic, and a transition of Cr/I state at 126.1 ꢀC was obtained.
Copper complexes 1b, 1deeeCu and palladium complex 1eePd
were mesogenic. All complexes have a much higher clearing tem-
ꢀ
Compds
Mesophase
(temp; ꢀC)
Lattice
const. (A)
d-Spacing/A (obs)
Miller
indices
ꢀ
2e
Colh (95)
a¼47.17
40.85 (40.85)
4.51 (br)
37.82 (37.82)
21.90 (21.83)
18.78 (18.91)
4.77 (br)
35.20 (35.20)
20.34 (20.32)
17.65 (17.60)
4.71 (br)
37.41 (37.41)
21.60 (21.60)
18.74 (18.71)
14.20 (14.14)
4.73 (br)
100
Halo
100
110
200
Halo
100
110
200
Halo
100
110
200
210
Halo
100
110
Halo
perature than their corresponding precursors by a
D
Tcl¼126.1
1beCu
Colh (220)
a¼43.67
a¼40.65
a¼43.20
(1deCu)<157.2 (1eeCu)<160.8 ꢀC (1beCu). Three complexes
formed enantiotropic mesomorphism, and on DSC thermographs,
they gave two transitions of crystal-to-columnar and columnar-to-
isotropic states (Cr/Col/I). Both melting and clearing tempera-
tures of metal complexes were ranged in Tmp¼125.1e206.2 ꢀC and
Tcl¼246.5e267.9 ꢀC. The temperature range of mesophase was
48.3e121.4 ꢀC on heating process. Surprisingly, palladium complex
1eePd has both melting and clearing temperatures much lower
1deCu
1eeCu
Colh (230)
Colh (230)
than those of copper complex 1eeCu by
D
Tmp¼41.3 and
D
Tcl¼59.8 ꢀC, however, its temperature range of mesophase was
only slightly smaller than that of 1eeCu; i.e.,
D
TCol¼58.5<77.0 ꢀC.
1eePd
Colh (185)
a¼42.71
36.99 (36.99)
21.42 (21.36)
4.77 (br)
The exact reason for this lowering both in Tmp and Tcl was uncertain,
however, a slightly structural twisting of the central coplanarity
caused by a larger size of palladium atom might be partly re-
sponsible for it. Electronically, the Pd2þ complex is d8-configuration
and diamagnetic, while Cu2þ complex is d9 (or d1) and para-
magnetic. A combination of electronic and/or steric effect caused by
these two metals incorporated might affect their mesomorphic
properties. The mesophase was identified as hexagonal columnar
(Colh) based on optical textures observed, and similar pseudo focal-
conic textures with linear birefringent defects (Fig. 4) was clearly
observed. Zinc complex 1eeZn was not mesogenic and a transition
of crystal-to-isotropic state at a much higher temperature of
Tcl¼314.1 ꢀC was obtained. Zn2þ ions were d10-diamagnetic and
often coordinated by a tetrahedral geometry. A twisted central core
in complex 1eeZn might be unfavorable in packing the molecules
in the mesophases.
14000
40.85
7000
4.51
5
10
15
20
0
5
10
15
2 Theta
20
25
2.4. Variable powder diffraction and molecular assembly
Variable-temperature powder XRD diffraction experiments
were performed to identify the structure of the mesophases of
compounds 1e2. A summary of the diffraction peaks and lattice
constants for compounds 1e2 is listed in Table 4. For derivatives 2e,
30000
20000
10000
0
37.41
21.60
18.74
14.20
ꢀ
ꢀ
a diffraction pattern measured at 95 C with a d-spacing at 40.85 A
4.73
15
ꢀ
and a broad diffuse peak (4.51 A) at wide-angle region was ob-
served. This diffraction pattern corresponded to a hexagonal co-
lumnar arrangement, which corresponds to an intercolumnar
distance or lattice constant (i.e., a parameter of the hexagonal lat-
5
10
20
20
ꢀ
tice) of a¼47.17 A. Also the XRD of two metal complexes, 1deCu and
1eePd were also conducted and both complexes showed a similar
diffraction pattern. A diffraction pattern at 230 ꢀC with a d-spacing
5
10
15
2 Theta
25
30
ꢀ
ꢀ
of 37.41, 21.60, 18.74, 14.20 A and a halo peak at 4.73 A was obtained
for complex 1eeCu and a similar pattern at 185 ꢀC of two diffraction
peaks with a d-spacing at 36.99, 21.42 A and a halo peak at 4.77 A
was observed for complex 1eePd (see Fig. 5). Two close lattice
30000
20000
10000
0
ꢀ
ꢀ
36.99
ꢀ
21.42
constants of 43.20 and 42.71 A were consistent with their similar
structures and molecular sizes. On the other hand, the lattice
ꢀ
constant of a¼47.17 A of compound 2e was slightly larger than
those two of complexes, confirming that the dimeric structure in
mesophase was induced by H-bond in compound 2e. The lack of
any relatively peaks at wide angles excluded a more regular peri-
odicity along the columns. However, liquid-like correlations be-
4.77
6
12
18
ꢀ
tween the rigid cores occurred at wide angle regions of 4.51e4.77 A.
The number of molecules within certain columnar height h was
calculated, and the calculation equations and processes were fol-
lowed by literature. Two parameters, Ncel and Rar were obtained
according to Vcell¼hScol¼NcellVmol. Vcell is the volume of the repeat
unit (per cell) and Vmol is the molecular volume of one molecule.
Scol was calculated from lattice parameters of X-ray diffraction. Ncell
5
10
15
2 Theta
20
25
Fig. 5. Powder X-ray diffraction plots of compounds of 2e at 95 ꢀC (top plot), 1eeCu at
230 ꢀC (central plot) and 1eePd at 185 ꢀC (bottom plot). The inert.

2396
Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
is the number of molecules within a column and Rar defined as the
UVevis absorption and PL spectra of two compounds were quite
similar wavelength. The absorption lmax peaks occurred at ca.
diameter of the aromatic or hard columnar part was calculated by
Rar¼(4Sar/
p
)
1/2. A value of Ncell¼6.79 and 2.44e2.92 was obtained
381 nm (for 2e) and 395 nm (for 4) were attributed to
transitions arising from quinoxaline moiety.9a,b Other peaks at 249,
276 nm (for 2e) and 247, 280 nm (for 4) were originated from ne
pep*
for compound 2e and 1beCu, 1deeeM (Cu, Pd), respectively
(Table 5). On the other hand, an approximate double number of Ncell
p
ꢀ
in 2e compared to 1aee was stacked within a height of 9.0 A in
transitions. The PL spectra of two compounds showed one intense
and broad peak occurred at lmax¼524 nm (2e) and 518 nm (4), and
these photoluminescent emissions were originated from hetero-
column. The molecular shapes of compounds 2e were not disc-like,
therefore, a more disc-or catenar-like structure constructed by two
molecules was then correlated, required to form columnar phases.
The possible molecular arrangement in columnar phases was pro-
posed in Fig. 6, in which two catenar-shaped molecules of induced
dimers 2e and complexes 1bee lying side-by-side in columnar
phases.
cyclic quinoxaline. Quinoxaline was often considered as
p-accep-
tors and fluorophore. A slightly red-shifted emission of w6 nm by
2e often attributed to donoreacceptor transfer was observed. A
lower quantum efficiency ranged from 0.10% (2e) to 0.26% (4) was
obtained. Lower quantum efficiency in 2e might be attributed to
the effect of excited-state intramolecular proton transfer.
Table 5
The geometric parametersa determined from XRD data for compounds 1e2
3. Conclusions
2
A (A)
S (A )
Mw (g/mol)
T (ꢀC)
Ncell
Rar (A)
ꢀ
ꢀ
ꢀ
Two series of tridentate N-salicylidene-2-hydroxyanilines 2aee
and their metal complexes 1aeeeM (M¼Cu, Pd, Zn) were prepared.
Crystallographic analysis indicated that copper ion adopted geom-
etry of square pyramidal with a THF solvent molecule coordinated
as the fifth ligand. Two copper atoms were separated by ca.
2e
47.17
43.67
40.65
43.20
42.71
1926.88
1651.63
1430.72
1616.01
1579.93
1459.16
2672.74
2592.52
3041.37
3127.12
95
220
230
230
185
6.79
2.92
2.58
2.49
2.44
28.43
29.51
34.80
33.34
27.68
1beCu
1deCu
1eeCu
1eePd
a
2
ꢀ
3
ꢀ
ꢀ
ꢀ
S (A )¼columnar cross section area, Vcell (A )¼volume of the column stratum 9 A
3.0375(5) A. All compounds 2a (n¼12, 14, 16) formed smectic C
3
ꢀ
thick, Vm (A )¼molecular volume, Ncell¼the number of molecules contained in each
phases, and copper complex 1aeCu (n¼12, 14, 16) were not meso-
genic. In contrast, compound 2e and complexes 1beCu, 1deCu,
1eeCu, and 1eePd exhibited hexagonal columnar phases. The lack
2
ꢀ
ꢀ
columnar stratum 9-A thick, Sar (A )¼the surface area of hard columnar core, Rar
2
ꢀ
(A )¼the diameter of the aromatic part.
X
O
N
O
O
O
N
N
O
O
O
O
H
H
H-Bonded dimeric ligand
N
N
H
O
O
O
H
O
O
O
O
N
X
O
O
X
N
O
O
O
N
N
O
O
O
O
H
H
N
N
H
O
X
O
O
H
O
O
O
O
N
O
O
N
O
O
N
N
O
O
O
O
H
H
N
N
X
H
O
O
O
H
O
O
O
O
N
O
X
X
O
N
O
OH
N
HO
O
O
O
Induced disc-shaped molecules
N
O
Ligand 2
X
O
O
N
O
N
N
O
N
N
O
O
M
O
O
O
O
O
O
M
O
X
O
N
O
O
O
O
N
O
X
N
O
N
O
O
M
O
X
O
O
O
X
O
O
M
N
O
O
N
O
N
O
O
N
O
N
O
N
O
O
O
M
O
O
O
O
O
O
M
N
O
N
O
N
O
O
X
Metal complex 1
Fig. 6. A schematic representation of molecular organizations in columnar phases for compounds 1e2. A catenar-shaped mesogen was formed and induced in compound 2e and
a complex 1b, 1dee, and two catenar-shaped molecules lying side-by-side to generate a more disc correlated molecule was packed within a column.
2.5. Optical properties
of mesomorphism in zinc complexes 1eeZn was attributed to its
preference of tetrahedral geometry over square planar geometry. An
ꢀ
The UVevis absorption and PL spectra of the compound 2e and 4
Ncell equal to 2.44 for 1eeCu within a slice of 9.0 A thick indicated
in CH2Cl2 solution at room temperature are presented in Fig. 7. The
that an induced structure constructed by two caternar-shaped

Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
2397
2H), 8.00 (s, eArH, 1H), 11.03 (s, eOH, 1H). 13C NMR (125 MHz,
CDCl3): 14.10, 22.66, 28.81, 29.25, 29.26, 29.32, 29.49, 29.54, 29.6,
31.90, 69.12, 101.76, 109.82, 126.89, 127.51, 157.98, 166.72.
1.0
0.8
0.6
0.4
0.2
0.0
4.3. 2-Amino-5-dodecyloxyphenol
White solids; 1H NMR (500 MHz, CDCl3):
eCH3, 3H), 1.24e1.38 (m, eCH2, 18H), 1.67e1.71 (m, eOCH2CH2,
2H), 3.84 (t, J¼6.5 Hz, eOCH2, 2H), 6.42e6.45 (d, J¼7.6 Hz, eArH,
2H), 6.74 (s, eArH, 1H), 11.03 (s, eOH, 1H). 13C NMR (125 MHz,
d
0.86 (t, J¼6.7 Hz,
CDCl3):
d 14.10, 23.12, 28.81, 29.25, 29.26, 29.32, 29.5, 29.49, 29.61,
31.91, 72.28, 102.17, 107.60, 117.23, 125.64, 144.53, 162.17.
250
300
350
400
450
500
4.4. 2-Hydroxy-4-dodecyloxy-N-(2-hydroxy-4-
dodecyloxybenzylidene)aniline 2a (n[12)
Wavelength (nm)
1.0
0.8
0.6
0.4
0.2
0.0
Yellow solids; 1H NMR (500 MHz, CDCl3):
d
0.88 (t, J¼6.90 Hz,
eCH3, 6H), 1.27e1.46 (m, eCH2, 36H), 1.74e1.80 (m, eOCH2CH2,
4H), 3.94 (t, J¼6.57 Hz, eOCH2, 2H), 3.99 (t, J¼6.57 Hz, eOCH2, 2H),
6.47e6.50 (m, AreH, 3H), 6.56 (s, AreH, 1H), 7.04 (d, J¼8.77 Hz,
AreH,1H), 7.24 (t, J¼4.58 Hz, AreH, 2H), 8.51 (s, AreCH]NeAr, 1H).
13C NMR (500 MHz, CDCl3):
d 13.92, 22.58, 25.94, 25.99, 29.06,
29.21, 29.24, 29.27, 29.31, 29.47, 29.50, 29.55, 29.57, 31.84, 68.38,
68.49, 101.73, 101.83, 107.68, 107.86, 113.37, 118.12, 129.19, 133.55,
150.95, 159.65, 160.51, 162.76, 163.69. MS (FAB): Calcd for
MHþC37H60NO4: 581.4, Found: 582.1. Anal. Calcd for C37H59NO4: C,
76.37; H, 10.22. Found: C, 76.38; H, 10.29.
450
500
550
600
650
700
Wavelength (nm)
4 . 4 .1. 2 - H y d r o x y - 4 - t e t r a d e c y l o x y - N - ( 2 - h y d r o x y - 4 -
tetradecyloxybenzylidene)aniline 2a (n¼14). Yellow solids, yield
Fig. 7. Absorption and fluorescent spectra of compound 2e (black line) and 4 (red line)
in CHCl3 at room temperature. The excitation wavelength in PL spectrum used was
382 nm.
85%. 1H NMR (500 MHz, CDCl3):
d
0.92 (t, J¼6.85 Hz, eCH3, 6H),
1.32e1.51 (m, eCH2, 44H), 1.80e1.85 (m, eOCH2CH2, 4H), 3.94 (t,
J¼6.57 Hz, eOCH2, 2H), 4.04 (t, J¼6.56 Hz, eOCH2, 2H), 6.51e6.54
(m, AreH, 3H), 6.61 (s, AreH,1H), 7.09 (d, J¼8.73 Hz, AreH,1H), 7.28
(t, J¼4.58 Hz, AreH, 2H), 8.55 (s, AreCH]NeAr, 1H). 13C NMR
molecules lying side-by-side was correlated in Colh phases. The PL
spectrum of compound 2e showed one intense peak occurred at
lmax¼524 nm, which originated from quinoxaline moiety.
(500 MHz, CDCl3):
d 13.89, 22.57, 25.46, 25.93, 25.98, 29.07, 29.22,
29.24, 29.27, 29.30, 29.46, 29.49, 29.56, 29.58, 31.84, 68.39, 68.49,
101.76, 101.88, 107.69, 107.86, 113.37, 118.11, 129.18, 133.54, 150.97,
159.67, 160.46, 162.82, 163.72. MS (FAB): Calcd for MHþC41H68NO4:
637.5, Found: 638.1. Anal. Calcd for C41H67NO4: C, 77.19; H, 10.59.
Found: C, 77.19; H, 10.67.
4. Experimental section
4.1. General materials and methods
All chemicals and solvents were reagent grade from Aldrich
Chemical Co., and solvents were dried by standard techniques. 1H
and 13C NMR spectra were measured on a Bruker DRS-300. DSC
thermographs were carried out on a Mettler DSC-822 and cali-
brated with a pure indium sample. All phase transitions are de-
4 . 4 . 2 . 2 - H y d r o x y - 4 - h e x a d e c y l o x y - N - ( 2 - h y d r o x y - 4 -
hexadecyloxybenzylidene)aniline 2a (n¼16). Yellow solids, yield
82%. 1H NMR (500 MHz, CDCl3):
d
0.89 (t, J¼6.34 Hz, eCH3, 6H),
1.28e1.47 (m, eCH2, 52H), 1.77e1.82 (m, eOCH2CH2, 4H), 3.96 (t,
J¼6.50 Hz, eOCH3, 2H), 4.01 (t, J¼6.46 Hz, eOCH2, 2H), 6.51e6.54
(m, AreH, 3H), 6.58 (s, AreH, 1H), 7.06 (d, J¼8.72 Hz, AreH, 1H),
7.26 (s, AreH, 2H), 8.53 (s, AreCH]NeAr, 1H). 13C NMR data not
determined due to its poor solubility. MS (FAB): Calcd for
MHþC45H76NO4: 693.6, Found: 694.1. Anal. Calcd for C45H75NO4: C,
77.87; H, 10.89. Found: C, 77.96; H, 10.89.
termined by
a
scan rate of 10.0 ꢀC/min. Optical polarized
microscopy was carried out on Zeiss Axioplan 2 equipped with
a hot stage system of Mettler FP90/FP82HT. The UVevis absorption
and fluorescence spectra were obtained using a Jasco V-530 and
Hitachi F-4500 spectrometer. Elemental analyses were performed
on a Heraeus CHN-O-Rapid elemental analyzer. The powder dif-
fraction data were collected from the Wiggler-A beam line of the
National Synchrotron Radiation Research Center (NSRRC) with
a wavelength of 1.3263 A. The powder samples were charged in
Lindemann capillary tubes (80 mm long and 0.01 mm thick) with
an inner diameter of 1.0 mm from Charles Supper Co. The com-
pounds of 3-alkoxyphenols, 5-alkoxy-2-nitrophenols, 2-amino-5-
alkoxyphenols, and 2,3-bis-(3,4-bis-dialkoxyphenyl)-quinoxaline-
4.5. 2,3-Bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4
Yellow solid; 1H NMR (200 MHz, CDCl3):
d 0.83e0.89 (m, eCH3,
12H), 1.24e1.84 (m, eCH2, 80H), 3.82 (t, J¼4.6 Hz, eOCH2, 4H), 3.99
(t, J¼6.5 Hz, eOCH2, 4H), 6.83 (d, J¼8.3 Hz, eArH, 2H), 7.10e7.16 (m,
eArH, 4H), 8.17 (d, J¼8.7 Hz, eArH, 1H), 8.34 (dd, 3J¼8.8 Hz,
4J¼1.6 Hz, eArH, 1H), 8.94 (d, J¼1.5 Hz, eArH, 1H). 13C NMR
6-carboxylic acids were prepared by literature’ procedures5e,f,6,9a,b
.
4.2. 5-Dodecyloxy-2-nitrophenol
(200 MHz, CDCl3): d 14.09, 22.67, 26.01, 29.12, 29.19, 29.37, 29.42,
29.66, 31.92, 69.17, 113.04, 115.24, 122.26, 130.00, 131.11, 131.17,
132.64, 148.73, 150.17, 150.33, 154.29, 155.11, 170.99. IR (neat): 2953
(CeH), 2924 (CeH), 2870 (CeH), 2854 (CeH), 2572 (OeH), 1688
(C]O), 1599 (C]N), 1582 cmꢂ1 (C]N).
Light yellow solid; 1H NMR (500 MHz, CDCl3): 0.86 (t,
J¼6.7 Hz, eCH3, 3H), 1.24e1.38 (m, eCH2, 18H), 1.74e1.82 (m, eCH2,
2H), 3.99 (t, J¼6.4 Hz, eOCH2, 2H), 6.45e6.48 (d, J¼6.7 Hz, eArH,

2398
Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
4.6. 2,3-Bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4-formyl-3-hydroxy-phenyl ester 3
J¼6.5 Hz, eOCH2, 4H), 6.83 (d, J¼8.3, eArH, 2H), 6.92e7.03
(m, eArH, 4H), 7.10e7.21 (m, eArH, 6H), 7.51 (d, J¼8.5, eArH, 1H),
8.20 (d, J¼8.7, eArH, 1H), 8.41 (dd, 3J¼8.8 Hz, 4J¼1.8 Hz, eArH, 1H),
8.70 (s, eCHN, 1H), 9.01 (d, J¼1.7 Hz, eArH, 1H). 13C NMR
(R1[C12H25
)
Under nitrogen atmosphere, the mixture of 2,3-bis-(3,4-bis-
dodecyloxyphenyl)-quinoxaline-6-carboxylic acid (2.50 g,
(200 MHz, CDCl3): d 14.02, 22.62, 26.00, 29.10, 29.16, 29.31, 29.37,
29.62, 31.86, 69.12, 69.20, 110.50, 113.00, 115.34, 116.37, 117.31,
118.70, 120.74, 122.92, 123.09, 129.17, 129.35, 129.59, 131.00,
131.08, 133.46, 135.22, 139.98, 143.27, 148.70, 149.98, 150.23,
150.39, 150.39, 154.33, 154.75, 155.15, 159.90, 162.16, 162.24,
163.77. Anal. Calcd for C82H119N3O8: C, 77.26; H, 9.41, found: C,
77.86; H, 9.54. MS (FAB): calcd for MHþ C82H119N3O8: 1275.8,
found: 1275.9.
2.39 mmol) and 2,4-dihydroxybenzaldehyde (0.36 g, 2.87 mmol)
dissolved in 50 mL of CHCl3 was added in ice-bath 4-
dimethylaminopyridine (0.38 g, 3.10 mmol). The solution was
stirred for 30 min at room temperature. Then, the solution was
added N,N0-dicyclohexy-carbodiimide (0.64 g, 3.10 mmol), and
stirred at room temperature for 12 h. The solids were filtered off
and the filtrate was concentrated to give brown solids. The product
was purified by column chromatography using hexane/CH2Cl2 (1/1)
as eluent. The final product isolated as pale yellow solids was ob-
tained after recrystallization from acetone. Yield 62%. 1H NMR
4.9. 2,3-Bis-(3,4-bis-dibutoxyphenyl)-quinoxaline-6-
carboxylic acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)-
methyl]-3-hydroxyphenyl ester 2c (X[OC12H25, R1[C4H9)
(200 MHz, CDCl3): d 0.82e0.88 (m, eCH3, 12H), 1.25e1.85 (m, eCH2,
80H), 3.82 (t, J¼6.4 Hz, eOCH2, 4H), 3.99 (t, J¼6.4 Hz, eOCH2, 4H),
6.83 (d, J¼8.4 Hz, eArH, 2H), 6.96e7.01 (m, eArH, 2H), 7.09e7.18
(m, eArH, 4H), 7.64(d, J¼8.0 Hz, eArH, 1H), 8.20 (d, J¼8.8 Hz, eArH,
1H), 8.39 (dd, 3J¼8.8 Hz, 4J¼2.0 Hz, eArH, 1H), 8.99 (d, J¼1.8 Hz,
eArH, 1H), 9.90 (s, eCHO, 1H), 11.27(s, eOH, 1H). 13C NMR
1H NMR (200 MHz, CDCl3):
d 0.86e1.00 (m, eCH3, 15H),
1.25e1.81 (m, eCH2, 36H), 3.82 (t, J¼5.7 Hz, eOCH2, 4H), 3.90e4.04
(m, eOCH2, 6H), 6.48e6.52 (m, eArH, 2H), 6.82e6.95 (m, eArH,
4H), 7.09e7.18 (m, eArH, 5H), 7.42 (d, J¼8.0 Hz, eArH, 1H), 8.20 (d,
J¼8.8 Hz, eArH, 1H), 8.43 (dd, 3J¼8.8 Hz, 4J¼1.8 Hz, eArH, 1H), 8.64
(s, eCHN, 1H), 9.01 (d, J¼1.7 Hz, eArH, 1H). 13C NMR (200 MHz,
(200 MHz, CDCl3):
d 14.07, 22.65, 25.99, 29.10, 29.16, 29.35, 29.39,
29.66, 31.89, 69.16, 110.75, 112.99, 113.84, 115.21, 118.78,122.86,
123.06, 129.09, 129.18, 129.58, 130.99, 131.09, 132.70, 136.01,
140.02, 148.69, 150.23, 150.42, 154.47, 155.34, 157.45, 163.18, 163.48,
195.44. IR (neat): 2954 (CeH), 2920 (CeH), 2871 (CeH), 2850
(CeH), 1744 (C]O), 1659 (C]O), 1621 (C]N), 1600 (C]N),
1583 cmꢂ1 (C]N).
CDCl3): d 13.74, 13.81, 14.06, 19.09, 19.14, 22.62, 25.94, 29.12, 29.29,
29.34, 29.57, 31.00, 31.12, 31.85, 68.24, 68.70, 68.75, 101.94, 107.55,
110.40, 112.83, 115.20, 117.61, 118.68 122.84, 123.03, 128.05, 129.18,
129.35, 129.62, 130.94, 131.00, 132.48, 133.12, 139.98, 143.27, 148.58,
148.60, 150.18, 150.30, 151.24, 154.32, 155.15, 159.42, 159.90, 162.24,
163.86. Anal. Calcd for C62H79N3O9: C, 73.71; H, 7.88, found: C,
73.72; H, 7.89. MS (FAB): calcd for MHþ C62H79N3O9: 1011.3, found:
1011.6.
4.7. 2,3-Bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)-
methyl]-3-hydroxyphenyl ester 2e (X[OC12H25, R1[C12H25
)
4.10. 2,3-Bis-(3,4-bis-dioctloxyphenyl)-quinoxaline-6-
carboxylic acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)-
Under nitrogen atmosphere, the mixture of 2,3-bis-(3,4-bis-
didodecyloxy-phenyl)-quinoxaline-6-carboxylic acid 4-formyl-3-
hydroxyphenyl ester (0.30 g, 0.25 mmol) and 2-amino-5-
dodecyloxyphenol (0.08 g, 0.28 mmol) was dissolved in absolute
ethanol. The solution was gently refluxed for 3 h. The solution was
filtered a few times through Celite 5. The solids were concentrated,
and the product isolated as yellow solids was obtained after re-
crystallization from acetone. Yield 82%; 1H NMR (500 MHz, CDCl3):
methyl]-3-hydroxyphenyl ester 2d (X[OC12H25, R1[C8H17
)
1H NMR (200 MHz, CDCl3):
d
0.84e0.87 (m, eCH3, 15H),
1.26e1.81 (m, eCH2, 68H), 3.83 (t, J¼6.5 Hz, eOCH2, 4H),
3.91e4.03 (m, eOCH2, 6H), 6.49e6.56 (m, eArH, 2H), 6.74e6.97
(m, eArH, 4H), 7.11e7.17 (m, eArH, 5H), 7.47 (d, J¼8.3, eArH, 1H),
8.20 (d, J¼8.9 Hz, eArH, 1H), 8.43 (dd, 3J¼1.8 Hz, 4J¼8.6 Hz, eArH,
1H), 8.65 (s, eCHN, 1H), 9.01 (d, J¼1.9 Hz, eArH, 1H). 13C NMR
d
0.84e0.87 (m, eCH3, 15H), 1.25e1.81 (m, eCH2, 100H), 3.81e3.84
(200 MHz, CDCl3): d 14.06, 22.65, 26.00, 29.13, 29.19, 29.25, 29.30
(m, eOCH2, 4H), 3.94e4.00 (m, eOCH2, 6H), 6.51 (dd, 3J¼8.3 Hz,
4J¼1.9 Hz, eArH, 1H), 6.56 (d, J¼2.4 Hz, eArH, 1H), 6.83 (d,
J¼8.2 Hz, eArH, 2H), 6.92 (dd, 3J¼8.3, 4J¼2.3 Hz, eArH, 1H), 6.97 (d,
J¼2.0 Hz, eArH, 1H), 7.10e7.13 (m, eArH, 5H), 7.46 (d, J¼8.3 Hz,
eArH, 1H), 8.20 (d, J¼8.7 Hz, eArH, 1H), 8.41 (dd, 3J¼8.7 Hz,
4J¼1.8 Hz, eArH, 1H), 8.65 (s, eCHN, 1H), 9.00 (d, J¼1.7 Hz, eArH,
29.37, 29.57, 29.60, 31.81, 31.89, 68.84, 69.21, 101.89, 107.74, 110.45,
113.03, 115.29, 117.61, 118.60 122.93, 123.10, 128.22, 129.21, 129.44,
129.68, 131.0, 131.14, 132.58, 133.22, 140.08, 143.36, 148.73, 148.76,
150.24, 150.41, 151.27, 154.44, 155.23, 159.68, 160.06, 162.24,
163.20. Anal. Calcd for C78H111N3O9: C, 75.87; H, 9.06, found: C,
75.90; H, 9.19. MS (FAB): calcd for MHþ C78H111N3O9: 1234.7,
found: 1235.8.
1H). 13C NMR (500 MHz, CDCl3):
d 14.09, 22.67, 26.02, 29.13, 29.17,
29.20, 29.36, 29.42, 29.45, 29.56, 29.64, 29.66, 29.69, 29.74, 31.92,
68.36, 69.16, 69.21, 101.82, 107.78, 110.42, 113.01, 113.06, 113.14,
115.20, 115.27, 117.68, 118.56 122.91, 123.09, 128.40, 129.21, 129.46,
129.66, 131.09, 131.15, 132.59, 133.23, 140.08, 143.38, 148.73, 148.76,
150.23, 150.41, 151.25, 154.41, 155.24, 159.86, 160.10, 161.79, 163.94.
IR (neat): 3424 (OeH), 2953 (CeH), 2920 (CeH), 2872 (CeH),
2851 (CeH), 1736 (C]O), 1620 (C]N), 1600 (C]N), 1583 cmꢂ1 (C]
N). Anal. Calcd for C94H143N3O9: C, 77.37; H, 9,88, found: C, 77.10; H,
9.91. MS (FAB): calcd for MHþ C94H143N3O9: 1460.1, found: 1460.0.
4.11. Bis{2,3-Bis-(3,4-bis-dodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4-[(4-dodecyloxy-2-hydroxy-phenylimino)-
methyl]-3-hydroxyphenylester}copper(II) 1deCu
The solution of 2,3-bis-(3,4-bis-didodecyloxyphenyl)-qui-
noxaline-6-carboxylic acid 4-[(4-dodecyloxy-2-hydroxy-phenyl-
imino)-methyl]-3-hydroxy-phenyl ester (0.20 g, 0.137 mmol)
dissolved in 10 mL of ethyl alcohol/THF (10:1) was added cop-
per(II) acetate-1-hydrate (0.03 g, 0.151 mmol). The solution was
refluxed for 2 h. All green solids were collected. The final product
isolated as green solids was obtained after recrystallization from
THF/methanol. Yield 89%. IR (neat): 2954 (CeH), 2921 (CeH), 2870
(CeH), 2851 (CeH), 1736 (C]O), 1600 (C]N), 1585 cmꢂ1 (C]N).
Anal. Calcd for C188H282N6O18Cu2: C, 74.24; H, 9.35, found: C,
73.86; H, 9.31.
4.8. 2,3-Bis-(3,4-didodecyloxy-phenyl)-quinoxaline-6-
carboxylic acid 3-hydroxy-4-[(2-hydroxyphenylimino)-
methyl]phenyl ester 2b (X[H, R1[C12H25
)
1H NMR (200 MHz, CDCl3):
d
0.82e0.88 (m, eCH3, 12H),
1.24e1.99 (m, eCH2, 80H), 3.82 (t, J¼6.5 Hz, eOCH2, 4H), 3.99 (t,

Y.-Y. Chu et al. / Tetrahedron 70 (2014) 2389e2399
2399
4.12. Bis{2,3-bis-(3,4-bis-dioctyloxyphenyl)-quinoxaline-6-
References and notes
carboxylic acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)-
methyl]-3-hydroxyphenylester}copper(II) 1ceCu
1. (a) Jacquemin, P. L.; Robeyns, K.; Devillers, M.; Garcia, Y. Chem. Commun.
2014, 40, 649e651; (b) Robert, F.; Jacquemin, P. L.; Tinant, B.; Garcia, Y. RSC
Adv. 2013, 3, 6466e6471; (c) Francois, F.; Jacquemim, P. L.; Bernard, B.; Yann,
G. CrystEngComm 2012, 14, 4396e4406; (d) Inokuma, Y.; Kawano, M.; Fujita,
M. Nat. Chem. 2011, 3, 349e358; (e) Hadjoudis, E.; Chatziefthimiou, S. D.;
Mavridis, I. M. Curr. Org. Chem. 2009, 13, 269e286; (f) Wezenberg, S. T.; Kleij,
A. W. Angew. Chem., Int. Ed. 2008, 47, 2354e2364; (g) Miyasaka, H.; Saitoh, A.;
Abe, S. Coord. Chem. Rev. 2007, 251, 2622e2664; (h) Haneda, T.; Kawano, M.;
Kojima, K.; Fujita, M. Angew. Chem., Int. Ed. 2007, 46, 6643e6645; (i) Fujiwara,
T.; Harada, H.; Ogawa, K. J. Phys. Chem. B 2004, 108, 4035e4038; (j) Had-
joudis, E.; Mavridis, I. M. Chem. Soc. Rev. 2004, 3, 579e588.
Anal. Calcd for C156H218N6O18Cu2: C, 72.27; H, 8.48, found: C,
72.16; H, 8.61.
4.13. Bis{2,3-bis-(3,4-bis-dibutoxyphenyl)-quinoxaline-6-
carboxylic acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)-
methyl]-3-hydroxyphenyl ester}copper(II) 1beCu
2. Whiteoak, C. J.; Salassa, G.; Kleij, S. A. W. Chem. Soc. Rev. 2012, 41, 622e631.
3. (a) Coe, B. J. Comprehensive Coordination Chemistry II; Elsevier Pergamon: Ox-
ford, UK, 2004, Vol. 9, pp 621e687; (b) Donnio, B.; Guillon, D.; Deschenaux, R.;
Bruce, D. W. Comprehensive Coordination Chemistry II; Elsevier: Oxford, UK,
2003, Vol. 7, pp 357e627.
Anal. Calcd for C124H154N6O18Cu2: C, 69.48; H, 7.24, found: C,
69.72: H, 7.34.
4. (a) Vera, F. V.; Serrano, J. L.; Sierra, T. C. Soc. Rev. 2009, 38, 781e796; (b) Porta,
B.; Khamsi, J. K.; Noveron, J. C. Curr. Org. Chem. 2008, 12, 1e24; (c) Binnemans,
K. Chem. Rev. 2005, 105, 4148e4204; (d) Date, R. W.; Iglesias, E. F.; Rowe, K. E.;
Elloitt, J. M.; Bruce, D. W. Dalton Trans. 2003, 1914e1931; (e) Binnemans, K.;
Walrand, G. Chem. Rev. 2002, 102, 2303e2345; (f) Hoshino, N. Coord. Chem. Rev.
1998, 174, 77e108; (g) Espinet, P. M.; Esteruelas, A.; Oro, L. A.; Serrano, J. L.;
Sola, E. Coord. Chem. Rev. 1992, 117, 215e274; (h) Giroud-Godquin, A. M.; Maitlis,
P. M. Angew. Chem., Int. Ed. Engl. 1991, 30, 375e402.
4.14. Bis{2,3-bis-(3,4-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 3-hydroxy-4-[(2-hydroxy phenylimino)-
methyl]phenyl ester} copper(II) 1aeCu
Anal. Calcd for C164H234N6O18Cu2: C, 73.70; H, 8.82, found: C,
73.23; H, 8.95.
5. (a) Bhattacharjee, C. R.; Das, G.; Mondal, P. Eur. J. Inorg. Chem. 2011, 5390e5396;
(b) Chico, R.; Dominguez, C.; Donnio, B.; Coco, S.; Espinet, P. Dalton Trans. 2011,
40, 5977e5983; (c) Bhattacharjee, C. R.; Das, G.; Mondal, P. J. Coord. Chem. 2011,
64, 3273e3289; (d) Bhattacharjee, C. R.; Das, G.; Mondal, P. Liq. Cryst. 2011, 38,
441e449; (e) Chen, C. J.; Wang, I. W.; Sheu, H. S.; Lee, G. H.; Lai, C. K. Tetrahedron
2010, 67, 8120e8130; (f) Li, S. Y.; Chen, C. J.; Lo, P. Y.; Sheu, H. S.; Lai, C. K.
Tetrahedron 2010, 66, 6101e6112; (g) Chien, C.; Chen, C. J.; Sheu, H. S.; Lee, G. H.;
Lai, C. K. Tetrahedron 2010, 66, 3583e3592.
6. Lai, C. K.; Chang, C. H.; Tsai, C. H. J. Mater. Chem. 1998, 8, 599e602.
7. (a) Ali, O. A. M.; Abdel-Rahman, L. H.; Ramadan, R. M. J. Coord. Chem. 2007, 60,
2335e2342; (b) El-Medani, S. M.; Ali, O. A. M.; Ramadan, R. M. J. Mol. Struct.
2005, 738, 171e177; (c) El-Medani, S. M. J. Coord. Chem. 2004, 57, 115e122.
8. (a) Bhattacharjee, C. R.; Datta, C.; Das, G.; Mondal, P. Liq. Cryst. 2012, 39,
639e646; (b) Rao, N. V. S.; Choudhury, T. D.; Paul, M. K.; Francis, T. Liq. Cryst.
2009, 36, 409e423; (c) Ku, S. M.; Wu, C. Y.; Lai, C. K. J. Chem. Soc., Dalton
Trans. 2000, 3491e3492; (d) Lai, C. K.; Leu, Y. F. Liq. Cryst. 1998, 25, 689e698;
(e) Lai, C. K.; Lin, R.; Lu, M. Y.; Kao, K. C. J. Chem. Soc., Dalton Trans. 1998,
1857e1862.
9. (a) Lin, K. T.; Kuo, H. M.; Sheu, H. S.; Lai, C. K. Tetrahedron 2013, 69, 9045e9055;
(b) Chen, C. J.; Wu, Y. C.; Sheu, H. S.; Lee, G. H.; Lai, C. K. Tetrahedron 2011, 67,
114e124; (c) Voisin, E.; Foster, E. J.; Rakotomalala, M.; Williams, V. V. Chem.
Mater. 2009, 21, 3251e3261; (d) Foster, E. J.; Jones, R. B.; Lavigueur, C.; Williams,
V. E. J. Am. Chem. Soc. 2006, 128, 8569e8574; (e) Foster, E. J.; Lavigueur, C.; Ke, Y.
C.; Williams, V. E. J. Mater. Chem. 2005, 15, 4062e4068; (f) Bojinov, V. B.;
Grabchev, I. K. Org. Lett. 2003, 5, 2185e2187; (g) Boden, E.; Bushby, R. J.; Liu, Q.;
Lozman, O. R. J. Mater. Chem. 2001, 11, 1612e1617.
10. (a) Cardinaels, T.; Ramaekers, J.; Nockmann, P.; Driesen, K.; Hecke, K. V.;
Meervelt, L. V.; Wang, G.; Feyter, S. D.; Iglesias, E. F.; Guillon, D.; Donnio, B.;
Binnemans, K.; Bruce, D. W. Soft Mater. 2008, 4, 2172e2185; (b) He, C. F.; Ri-
chards, G. J.; Kelly, S. M.; Contoret, A. A.; O’neill, M. Liq. Cryst. 2007, 34,
1249e1267; (c) Huck, D. M.; Nguyen, H. L.; Horton, P. N.; Hursthouse, M. B.;
Guillon, D.; Donnio, B.; Bruce, D. W. Polyhedron 2006, 25, 307e324; (d) Smi-
mova, A. L.; Bruce, D. W. J. Mater. Chem. 2006, 16, 4299e4306; (e) Gharbia, M.;
Gharbi, A.; Nguyes, H. T.; Malthete, M. Curr. Opin. Colloid Interface Sci. 2002, 7,
312e325.
4.15. Bis{2,3-bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)-
methyl]-3-hydroxy-phenyl ester} palladium(II) 1dePd
The similar procedures to copper complexes 1aeCu were fol-
lowed except that palladium acetate was used. The final product
isolated as red-brown solids was obtained after recrystallization
from THF/methanol or CHCl3/methanol. Yield 75%. IR (neat): 2953
(CeH), 2922 (CeH), 2870 (CeH), 2852 (CeH), 1737 (C]O), 1601
(C]N), 1585 cmꢂ1 (C]N). Anal. Calcd for C188H282N6O18Pd2: C,
72.21; H, 9.09, found: C, 72.47; H, 9.27.
4.16. Bis{2,3-bis-(3,4-bis-didodecyloxyphenyl)-quinoxaline-6-
carboxylic acid 4-[(4-dodecyloxy-2-hydroxyphenylimino)-
methyl]-3-hydroxy-phenylester}zinc(II) 1deZn
The similar procedures to copper complexes 1aeCu were fol-
lowed except that zinc acetate was used. The final product isolated
as light yellow solids was obtained after recrystallization from THF/
methanol or CHCl3/methanol. Yield 90%. IR (neat): 2953 (CeH),
2922 (CeH), 2871 (CeH), 2852 (CeH), 1736 (C]O), 1613 (C]N),
1599 cmꢂ1 (C]N). Anal. Calcd for C188H282N6O18Zn2: C, 74.15; H,
9.33, found: C, 73.87; H, 9.39.
Acknowledgements
11. Wu, I. T.; Chaing, P. Y.; Chang, W. J.; Sheu, H. S.; Lee, G. H.; Lai, C. K. Tetrahedron
2011, 67, 7358e7369.
We thank the National Science Council of Taiwan, ROC (NSC-
102-2113-M-008-00-MY2) for generous support of this work.