Homochiral coordination polymers constructed from aminocarboxylate derivates: Effect of bipyridine on the amidation reaction

Article abstract of DOI:10.1016/j.jssc.2012.04.025

Using aminocarboxylate derivates (S)-N-(4-cyanobenzoic)-glutamic acid (denoted as cbg, 1a) and (S)-N-(4-nitrobenzoic)-glutamic acid (denoted as nbg, 1b) as chiral ligands, five new homochiral coordination polymers formulated as [Cu(cbg)(H₂O)

Full text of DOI:10.1016/j.jssc.2012.04.025

Journal of Solid State Chemistry 192 (2012) 255–262
Contents lists available at SciVerse ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Homochiral coordination polymers constructed from aminocarboxylate
derivates: Effect of bipyridine on the amidation reaction
Jianshan Chen, Tianlu Sheng, Shengmin Hu, Shengchang Xiang, Ruibiao Fu, Qilong Zhu, Xintao Wu n
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Using aminocarboxylate derivates (S)-N-(4-cyanobenzoic)-glutamic acid (denoted as cbg, 1a) and
(S)-N-(4-nitrobenzoic)-glutamic acid (denoted as nbg, 1b) as chiral ligands, five new homochiral coordination
polymers formulated as [Cu(cbg)(H2O)2]n (3), [Cu(cbop)2(4,40-bipy)(H2O)]n (4) (cbop¼(S)-N-(4-cyanoben-
zoic)-5-oxoproline, 4,40-bipy¼4,40-bipyridine), {[Cu(nbop)2(4,40-bipy)] ꢀ 4H2O}n (5) (nbop¼(S)-N-(4-nitroben-
zoic)-5-oxoproline), {[Cd(nbop)2(4,40-bipy)] ꢀ 2H2O}n (6), and [Ni(nbop)2(4,40-bipy)(H2O)2]n (7) have been
hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction study reveals that
the original chirality of aminocarboxylate derivates is maintained in all these complexes. Complexes 3, 4, and
7 are one-dimensional infinite chain coordination polymers, while complexes 5 and 6 possess two-
dimensional network structures. In situ cyclization of 1a and 1b was taken place in the formation of
complexes 4–7, which may be due to the competition of 4,40-bipyridine with chiral ligands during the
coordination process. Preliminary optical behavior investigation indicates that ligands 1a, 1b, and complexes
6, 7 are nonlinear optical active.
Received 11 January 2012
Received in revised form
9 April 2012
Accepted 15 April 2012
Available online 24 April 2012
Keywords:
Metal–organic complex
Homochiral
Amino acid
In situ cyclization
Nonlinear optical active
& 2012 Elsevier Inc. All rights reserved.
1. Introduction
The natural amino acids are a rich pool of chiral ligands because
they: (1) are cheap and readily available; (2) possess several
Metal–organic coordination networks have attracted much
interest in these decades, because they show numerous inherent
advantages over traditional inorganic zeolites. By choice and
modification of organic linkers and metal centers, metal-organic
coordination networks exhibit varieties of interesting molecular
topologies, which permits incorporation of many specific proper-
ties [1–8]. Although lots of metal–organic coordination networks
have been successfully synthesized so far, it is still a challenge to
design and synthesize metal-organic coordination networks with
expected structures and properties.
Our interest is focused on the synthesis of homochiral metal–
organic polymers, because homochiral polymers show potential
applications on enantioselective catalysis [9–14], separations
[15–19], and second-order nonlinear optical applications [20–23].
Homochiral coordination polymers can be prepared from chiral
ligands and templates, which is a most direct and efficient method
[24–28]. Despite the fact that hydrothermal techniques have been
used widely in preparation of metal organic complexes, most chiral
coordination complexes were obtained using conventional solution
synthesis techniques, because the chirality may lost under hydro-
thermal conditions [29–31].
functional groups in one molecule; (3) are relevant to biological
systems. Therefore, amino acids are often used to construct new
chiral materials [32–37]. Modifying natural amino acids endows
the resulting chiral ligands with more structural diversities, as
well as fascinating properties, which are helpful for the synthesis
of chiral metal–organic polymers with expected functionalities
[38–43]. N-(2-hydroxybenzyl)-amino acids, which contain term-
inal and bridging coordination modes that favor the coordination
of metal ions, have been used as building blocks in MOF construc-
tion [44–46]. However, studies on their analogs synthesized from
benzaldehyde derivates without hydroxy group are relatively few
[47–50].
In this work, two new amino acid derivates 1a and 1b were
obtained from
L-glutamic acid and used as chiral ligands in
constructing homochiral metal–organic complexes. The chirality
of ligands retain in the target complexes even under hydrothermal
condition. As expected, the metal-organic complexes possess
second-order harmonic generation properties due to their chirality.
2. Experimental
2.1. Materials and methods
n Corresponding author. Fax: þ86 591 8371 4946.
E-mail address: wxt@fjirsm.ac.cn (X. Wu).
Commercially available reagents were used as received without
further purification. Chiral ligands 1a–1b were synthesized under
0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jssc.2012.04.025

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J. Chen et al. / Journal of Solid State Chemistry 192 (2012) 255–262
28.6
D
nitrogen atmosphere. Ligand 2 and complexes 3–7 were synthe-
sized in 25 mL Teflon-lined stainless steel vessels under autogenous
pressure. The reactants were stirred homogeneously before heating.
1H NMR and 13C NMR were carried out with Bruker 400 MHz
AVANCE III spectrometers. Melting points were obtained on a SGW
X-4 microscope without temperature correction. Element analyses
were carried out with a Vario EL III element analyzer. Infrared
spectra were obtained on a Nicolet Magna 750 FTIR spectrometer.
Optical rotation values were measured at the sodium-D line
(589 nm) with a SGW-1 polarimeter without temperature correc-
tion. Solid-state circular dichroism (CD) spectra were recorded on a
J-800 spectropolarimeter (Jasco, Japan). Thermogravimetric ana-
lyses (TGA) were performed on a NETZSCH STA449C under nitrogen
gas flow at a heating rate of 15 1C minꢁ1 from room temperature to
800 1C. Second harmonic generations (SHG) were measured by
using the Kurtz and Perry method [51] with a Nd:YAG laser of
1064 nm wavelength.
50 1C. Yield: 24 g (85.0%). Mp. 207–208 1C;
[a]
¼ ꢁ6.461
(c 0.005, 0.025 M NaOH). Anal. Calcd. for C12H14N2O6 1b: C,
51.06(50.99); H, 5.00(4.96); N, 9.93(9.96). IR (KBr, cmꢁ1):
3505.73 m; 1712.54s; 1614.73s; 1528.56s; 1351.18s; 1270.61m;
1234.72w; 859.24m. 1H-NMR (400 MHz, DMSO, 27 1C):
d¼8.176–
8.219(m, 2H, H-arom), 7.500–7.522(m, 2H, H-arom), 4.645–
4.882(m, 1H, –CH), 4.039–4.066(m, 2H, –CH2), 2.499–2.517(m,
2H, –CH2), 2.310–2.402(m, 2H, –CH2), 1.978–2.031(m, 1 H, –NH)
ppm. 13C-NMR (400 MHz, DMSO, 21 1C):
174.56(–COOH), 148.19(C-arom), 147.00(C-arom),
d
¼175.07(–COOH),
129.61
(C-arom), 124.02(C-arom), 59.95(C-alkyl), 50.38(C-alkyl), 30.88
(C-alkyl), 27.79(C-alkyl) ppm.
2.2.3. N-(4-Cyanobenzoic)-5-oxoproline (2)
A
mixture of 1a (59.5 mg, 0.25 mmol) and H2O (5 mL,
0.28 mol) was sealed in a 25 mL Teflon lined stainless steel
container and heated at 80 1C for 48 h. After the mixture was
cooled slowly to ambient temperature, colorless prism-shaped
crystals of 2 were obtained. The crystals were filtered, washed
with distilled water, and dried at ambient temperature. A suitable
crystal was selected for single-crystal X-ray diffraction studies.
The yield was 61.5% (37.4 mg) based on 1a. Anal. Calcd. for
2.2. Preparation
2.2.1. (S)-N-(4-cyanobenzoic)-glutamic acid (1a)
L-Glutamic acid (11.7 g, 0.08 mol) was dissolved in an aqueous
C
13H11N2O3 2: C 63.93, H 4.95, N 11.47. Found: C 64.27, H 4.90,
solution of sodium hydroxide (0.16 mol, 80 mL). A solution of
4-cyanobenzaldehyde (10.5 g, 0.08 mol) in ethanol (40 mL) was
added dropwise and then the mixture was cooled to 0 1C. Sodium
borohydride (1.0 g, 0.025 mol) was added in small portions and
the mixture was stirred at room temperature for 1.5 h. Stirring
was continued for 30 min after a second portion of 4-cyanoben-
zaldehyde (2.1 g, 0.016 mol) was added. Finally, a second portion
of sodium borohydride (0.2 g, 4.8 mmol) was added, and the
mixture was stirred for another 30 min before it was extracted
with diethyl ether to remove excess 4-cyanobenzaldehyde. And
then the aqueous layer was acified at 0 1C to pH 3 with concen-
trated HCl, at which point the compound precipitated as a white
powder. The suspension was filtered, and washed with cold
N 11.55. IR (KBr pellet, cmꢁ1): 2515.29m, 2235.02m, 1721.67s,
1630.44s, 1467.55m, 1420.85m, 1362.05m, 1280.08m, 1225.89s,
1172.64w, 988.84w, 866.33m, 654.64m.
2.2.4. [Cu(cbg)(H2O)2]n (3)
A mixture of Cu(CH3COO)2 ꢀ 2H2O (100 mg, 0.5 mmol), 1a
(59.5 mg, 0.25 mmol), and NaOH (10 mg, 0.25 mmol) in H2O
(5 mL, 0.28 mol) was sealed in a 25 mL Teflon lined stainless steel
container and heated at 80 1C for 48 h. After the mixture was
cooled slowly to ambient temperature, blue needle-shaped crys-
tals of 3 were obtained. The crystals were filtered, washed with
distilled water, and dried at ambient temperature. A suitable
crystal was selected for single-crystal X-ray diffraction studies.
The yield was 48.9% (44.0 mg) based on 1a. Anal. Calcd. for
water. The white powder was dried under reduced pressure at
31.7
50 1C. Yield: 14.7 g (70.0%); Mp. 155–157 1C; [
a]
D
¼ ꢁ5.721
(c 0.005, 0.025 M NaOH). Anal. Calcd. for C13H13N2O4 1a: C
59.54, H 5.38, N 10.68. Found: C 59.23, H 5.44, N 10.61. IR (KBr,
cmꢁ1): 3511.38m, 2233.08m, 1716.58s, 1613.60s, 1582.55s,
C
13H16CuN2O6 3: C 43.39, H 4.48, N 7.79. Found: C 43.49,
H 4.37, N 7.81. IR (KBr pellet, cmꢁ1): 3458.51m, 3239.82m,
2227.72m, 1653.80s, 1612.84s, 1549.27s, 1416.41m, 1381.98s,
1323.70m, 984.19w, 857.43w.
1488.87w,
1397.04w,
1342.33m,
1277.68m,
1231.26w,
1081.81w, 855.35w. 1H-NMR (400 MHz, DMSO, 20 1C):
d
¼13.037(s, 1H, –COOH), 7.799–7.815(m, 2H, H-arom), 7.416–
2.2.5. [Cu(cbop)2(4,40-bipy)(H2O)]n (4)
7.795(m, 2H, H-arom), 4.808–4.848(m, 1H, –CH), 4.017-4.141
(m, 2H, –CH2), 2.499–2.517(m, 2H, –CH2), 2.286–2.399(m, 2H,
–CH2), 1.956–2.048(m, 1H, –NH) ppm. 13C-NMR (400 MHz, DMSO,
A mixture of copper carbonate (29.2 mg, 0.25 mmol), 1a
(59.5 mg, 0.25 mmol), and 4,40-bipyridine (39 mg, 0.25 mmol) in
H2O (5 mL, 0.28 mol) was sealed in a 25 mL Teflon lined stainless
steel container and heated at 80 1C for 48 h. After the mixture was
cooled slowly to ambient temperature, blue prism-shaped crys-
tals of 4 were obtained. The crystals were filtered, washed with
distilled water, and dried at ambient temperature. A suitable
crystal was selected for single-crystal X-ray diffraction studies.
The yield was 22.5% (40.8 mg) based on 1a. Anal. Calcd. for
22 1C):
d¼175.34(–COOH), 173.69(–COOH), 143.15(C-arom),
132.85(C-arom), 129.02(C-arom), 119.26(–CN), 110.47(C-arom),
59.31(C-alkyl), 45.14(C-alkyl), 29.25(C-alkyl), 23.04(C-alkyl) ppm.
2.2.2. (S)-N-(4-nitrobenzoic)-glutamic acid (1b)
L-Glutamic acid (14.7 g, 0.1 mol) was dissolved in an aque-
C
36H32CuN6O7 4: C 59.71, H 4.45, N 11.60. Found: C 59.58,
ous solution of sodium hydroxide (0.2 mol, 100 mL). A solution
of 4-nitrobenzaldehyde (15.1 g, 0.1 mol) in methanol (50 mL)
was added dropwise and then the mixture was cooled to 0 1C.
Sodium borohydride (1.2 g, 0.03 mol) was added in small portions
and the mixture was stirred at room temperature for 1.5 h.
Stirring was continued for 30 min after a second portion of
4-nitrobenzaldehyde (3.02 g, 0.02 mol) was added. Finally, a
second portion of sodium borohydride (0.24 g, 6 mmol) was
added, and the mixture was stirred for another 30 min. And then
the aqueous layer was acified at 0 1C to pH 3 with concentrated
HCl, at which point the compound precipitated as a pale yellow
powder. The suspension was filtered, and washed with cold
water. The white powder was dried under reduced pressure at
H 4.35, N 11.54. IR (KBr pellet, cmꢁ1): 3387.90m, 2228.48m,
1672.56s, 1606.67s, 1413.72m, 1275.86m, 809.77m, 639.10w.
2.2.6. {[Cu(nbop)2(4,40-bipy)] ꢀ 4H2O}n (5)
A mixture of copper carbonate (29.2 mg, 0.25 mmol), 1b
(70.5 mg, 0.25 mmol), and 4,40-bipyridine (39 mg, 0.25 mmol) in
H2O (5 mL, 0.28 mol) was hated at 120 1C for 12 h. After the
mixture was cooled slowly to ambient temperature, blue prism-
shaped crystals of 5 were obtained. The crystals were filtered,
washed with distilled water, and dried at ambient temperature.
A suitable crystal was selected for single-crystal X-ray diffraction
studies. The yield was 30.6% (62.5 mg) based on 1b. Anal. Calcd.

J. Chen et al. / Journal of Solid State Chemistry 192 (2012) 255–262
257
for C34H38CuN6O14 5: C 49.91, H 4.68, N 10.27. Found: C 49.58,
Table 1
H 4.48, N 10.15. IR (KBr pellet, cmꢁ1): 3445.32m, 1676.09s,
1610.40s, 1520.32m, 1414.39m, 1347.03s.
Crystallographic data and structural refinements for 2–4.
2
3
4
2.2.7. {[Cd(nbop)2(4,40-bipy)] ꢀ 2H2O}n (6)
Empirical formula
Crystal system
Space group
C13H11N2O3
Orthorhombic
P212121
C13H16CuN2O6
Monoclinic
P21
C36H32CuN6O7
Monoclinic
C2
A mixture of cadmium carbonate (43.1 mg, 0.25 mmol), 1b
(70.5 mg, 0.25 mmol), and 4,40-bipyridine(39 mg, 0.25 mmol) in
H2O (5 mL, 0.28 mol) was sealed in a 25 mL Teflon lined stainless
steel container and heated at 100 1C for 24 h. After the mixture
was cooled slowly to ambient temperature, pale yellow prism-
shaped crystals of 6 were obtained. The crystals were filtered,
washed with distilled water, and dried at ambient temperature.
A suitable crystal was selected for single-crystal X-ray diffraction
studies. The yield was 21.0% (43.6 mg) based on 1b. Anal. Calcd.
for C34H34CdN6O12 6: C 49.14, H 4.12, N 10.11. Found: C 49.18,
H 3.54, N 10.07. IR (KBr pellet, cm-1): 3421.34m, 1677.45s,
1659.26s, 1591.70s, 1519.79s, 1448.35w, 1414.63m, 1347.46s,
1297.32w, 1218.68w, 814.28m, 708.26m, 627.58m.
5.071(2)
7.2547(14)
27.967(12)
˚
a (A)
13.152(6)
17.641(8)
7.3221(11)
13.748(3)
5.779(2)
˚
b (A)
22.193(9)
˚
c (A)
a
b
g
(1 )
(1)
(1)
90
90
90
90
100.432(13)
90
114.499(6)
90
90
3
1176.5(9)
718.2(2)
3264(2)
˚
V (A )
Z
4
2
4
Formula weight
243.24
1.373
0.100
0.71073
359.82
1.664
1.552
0.71073
724.22
1.474
0.730
0.71073
Dc (g cmꢁ3
)
m
(mmꢁ1
˚
)
L
(A)
Temperature (K)
Rint
R1a, wR2b(I42d(I))
293(2)
0.0345
293(2)
0.0413
293(2)
0.0264
R1¼0.0440,
wR2¼0.1049
R1¼0.0482,
wR2¼0.1036
R1¼0.0426,
wR2¼0.0915
2.2.8. [Ni(nbop)2(4,40-bipy)(H2O)2]n (7)
A
mixture of nickel carbonate (33.3 mg, 0.25 mmol), 1b
R1, wR2 (all data)
R1¼0.0565,
R1¼0.0640,
R1¼0.0500,
(70.5 mg, 0.25 mmol), and 4,40-bipyridine(39 mg, 0.25 mmol) in
H2O (5 mL, 0.28 mol) was sealed in a 25 mL Teflon lined stainless
steel container and heated at 120 1C for 12 h. After the mixture
was cooled slowly to ambient temperature, green prism-shaped
crystals of 7 were obtained. The crystals were filtered, washed
with distilled water, and dried at ambient temperature. A suitable
crystal was selected for single-crystal X-ray diffraction studies.
The yield was 29.1% (56.5 mg) based on 1b. Anal. Calcd. for
wR2¼0.1124
wR2¼0.1178
wR2¼0.0975
Flack parameter
GOF
0.00 (2)
1.053
ꢁ0.005 (11)
1.040
1.069
P
P
a
R¼ (||Fo|ꢁ|Fc||)/ |Fo|.
P
P
wR¼{ w[(F2o ꢁF2c)2]/ w[(F2o)2]}0.5y.
b
C
34H34N6NiO12 7: C 52.53, H 4.41, N 10.81. Found: C 52.48,
Table 2
Crystallographic data and structural refinements for 5–7.
H 4.29, N 10.80. IR (KBr pellet, cmꢁ1): 3314.65m, 1669.52s,
1608.17s, 1516.30m, 1418.05m, 1401.41m, 1343.35s, 1305.34m,
732.62w.
5
6
7
Empirical formula
Crystal system
Space group
C34H38CuN6O14
Orthorhombic
P212121
C34H34CdN6O12
Monoclinic
P21
C34H34N6NiO12
Monoclinic
C2
2.3. Single-crystal X-ray diffraction
11.129(7)
11.759(7)
15.444(11)
˚
a (A)
X-ray data of 2–7 were collected on a Rigaku Mercury CCD/AFC
17.624(11)
19.353(12)
8.819(5)
11.308(7)
10.076(7)
˚
b (A)
diffractometer using graphite monochromated Mo K radiation
a
18.246(11)
˚
˚
c (A)
(
l
(Mo K ) 0.71073 A) at 293(2) K. Data were reduced with
a
a
b
g
(1)
(1)
(1)
90
90
90
CrystalClear version 1.3. These structures were solved by direct
methods and refined by full-matrix least-squares techniques on
F2 using SHELXTL-97 [52]. All non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were generated geometri-
cally. Crystal data, as well as details of the data collection and
refinement for the complexes are summarized in Tables 1 and 2.
90
104.066(10)
90
104.115(9)
90
90
3
3796(4)
1835.4(18)
1706(2)
˚
V (A )
Z
4
2
2
Formula weight
818.24
1.432
0.650
0.71073
831.07
1.504
0.665
0.71073
777.38
1.513
0.643
0.71073
Dc (g cmꢁ3
)
m
l
(mmꢁ1
)
˚
(A)
Temperature (K)
293(2)
293(2)
293(2)
3. Results and discussion
Rint
0.1124
0.0452
0.0326
b
R1a, wR2 (I42d(I))
R1¼0.0911,
wR2¼0.2208
R1¼0.0429,
wR2¼0.0946
R1¼0.0402,
wR2¼0.0746
3.1. Synthesis
R1, wR2 (all data)
R1¼0.1550,
R1¼0.0583,
R1¼0.0501,
Ligands (S)-N-(4-cyanobenzoic)-glutamic acid (1a) and (S)-N-
(4-nitrobenzoic)-glutamic acid (1b) were obtained from conden-
sation of one equivalent of sodium glutamate and one equivalent
of corresponding aldehyde in water/alcohol solution, followed by
in situ reduction of the unstable imine bond via sodium borohy-
dride (Scheme 1). Acidifying the solution with hydrochloric acid
at low temperature precipitated the products from water. Strong
peaks at approximately 1717, 1614, 1583 cmꢁ1 in the IR spectra
of 1a and 1b suggest the presence of carboxyl groups. Reduction
of the imine group is supported by the 1H NMR chemical shift at
about 2.0 ppm, which indicates the presence of a secondary
amine group. Although racemization was observed during the
synthesis process of analogous ligands [46], ligands 1a and 1b
wR2¼0.2838
wR2¼0.1018
wR2¼0.0799
Flack parameter
GOF
ꢁ0.03 (3)
ꢁ0.03 (3)
0.002 (14)
1.003
1.052
0.990
P
P
a
R¼ (||Fo|ꢁ|Fc||)/ |Fo|.
P
P
b
wR¼{ w[(F2o ꢁF2c)2]/ w[(F2o)2]}0.5y.
Complex [Cu(cbg)(H2O)2]n (3) was obtained as a pure phase by
reacting copper acetate with 1a and sodium hydroxide under
hydrothermal condition. Single crystal X-ray diffraction analysis
reveals that complex 3 is a 1D infinite structure.
4,40-Bipyridine is often used as bridge ligand in constructing
metal-organic frameworks. A new chiral 2D network would be
expected when 4,40-bipyridine was introduced into complex 3.
preserve the S-configuration of
L-glutamic acid testified by optical
rotation and solid-state CD spectrum (Fig. 1(A)).

258
J. Chen et al. / Journal of Solid State Chemistry 192 (2012) 255–262
as a Lewis catalyst [39]. Although the possible role of metal ions
in cyclization reaction cannot be excluded completely, we pre-
sume metal ions may not be the key factor of in situ ligand
condensation, because ligand 1a keeps its original structure with
Cu2þ as metal ion, as can be seen from complex 3. On the other
hand, under similar reaction condition without metal ions, con-
densation of 1a also happens and yields 2.
We have speculated that ligand 1a in complex 3 kept its
configuration in order to connect neighboring metals with the
g
Scheme 1. Preparation of ligands 1a and 1b.
-carboxyl group when no other bridge ligand such as 4,40-bipyr-
idine was used. In order to find out the main reason of in situ
cyclization, complexes 5-7 were synthesized, too. Blue prism crys-
tals of complex 5 were obtained by reacting ligand 1b with basic
copper carbonate and 4,40-bipyridine at 120 1C for 12 h. To our
surprise, although little difference between raw materials, com-
plexes 4 and 5 show absolutely different structures. In complex 5,
ligand 1b also experiences in situ cyclization. However, the con-
densed ligand nbop coordinates metal ions not only with the
a-
carboxyl group but also with the carbonyl group on the five member
ring, thus forms a 2D network. Reacted 1b and 4,40-bipyridine with
either cadmium carbonate or nickel carbonate under hydrothermal
conditions, complexes 6 and 7 were crystallized from the reaction
mixtures. The coordination mode of complex 6 is similar to that of
complex 5. However, despite the difference in metal and ligand,
complex 7 shows similar structure to complex 4. These facts indicate
that, condensation of glutamic derivate ligands has occurred against
the impact of metal and ligand. Crystals of 6 in KBr pellets give clear
signals in solid-state CD spectroscopy (Fig. 1(B)), which indicates
that the chirality of ligand is preserved in the complex even at
temperature up to 100 1C.
Excluding those factors mentioned above, 4,40-bipyridine may
play a key role in the condensation of 1a or 1b during the
formation of 4-7. We speculate that the coordination ability of
4,40-bipyridine is slightly stronger than 1a or 1b. Thus, in com-
plexes 4-7, 4,40-bipyridine coordinates with metal prior to the
chiral ligand, resulting to the condensation of 1a or 1b. When
4,40-bipyridine is absent in the reaction, just as in complex 3, 1a
or 1b coordinates with metal ions quickly and maintains its
original structure. Adding other auxiliary ligand into the reaction,
such as isonicotinic acid, whose coordination ability is even
stronger than 4,40-bipyridine, the product crystals would be the
complex constructed from metal and isonicotinic acid. Ligand 1a
or 1b does not participate in the reaction in that case.
3.2. Structure descriptions
The coordination mode and the crystallographic data of 3 are
exhibited in Figs. 2 and 3 and Table 1, respectively. Complex 3
crystallizes in P21 chiral space group. In complex 3, the copper (II)
ions are five-coordinated with four oxygen atoms and one nitro-
gen atom to form a slightly distorted square-pyramidal geometry
Fig. 1. CD data of (A) ligand 1b and (B) complex 6 obtained from a transparent
disk made from a mixture of 1b or 6 (2 mg) and KBr (50 mg).
However, under the same synthetic procedure except addition
of 4,40-bipyridine, only complex 4 with 1D infinite chain was
obtained. Besides, 1a in 4 undergoes in situ cyclization forming a
new chiral ligand (S)-N-(4-cyanobenzoic)-5-oxoproline (cbop, 2).
Complex 4 can also be synthesized from 1a, 4,40-bipyridine, and
basic copper carbonate with 1:1:1 mol ratio in water solution.
Ligand 2 can be obtained by directly heating ligand 1a in water
to 80 1C for 48 h. Intramolecular amidation happens to the second
(Fig. 2). Ligand 1a retains the coordination ability of
acid and acts as a tridentate ligand with the amino group and
-carboxyl group to chelating Cu2þ ion, and
-carboxyl group
coordinating another Cu2þ ion. The bond length of Cu–N is
L-glutamic
a
g
˚
2.017(4) A, which is parallel to that reported by Vittal [44] using
˚
1a analog as ligand (Cu–N¼1.978 A), while the bond lengths of
˚
amine group and the
g-carboxyl group of 1a, and forms a stable
Cu–O (1.897(4)–1.902(4) A) is shorter than those in Cu-1a analog
2þ
˚
five-member heterocyclic ring. Intramolecular amidation is con-
firmed by the peaks at approximate 1722, 1630 cmꢁ1 in the IR
spectrum. Intramolecular amidation is a common feature of
glutamic acid and its derivates [53], because thermodynamically
more stable five-membered structure is achieved by cyclization.
Rosseinsky et al. synthesized ligand bgxH4 and coordinated it
with copper and 4,40-bipyridine. In situ cyclization of the ligand
was considered to be the effect of metal ion, which probably acted
(1.921–1.969 A). The two remaining coordination sites of Cu
are occupied by water molecules. The bond distance between
metal center and coordination water molecules at the planar
˚
position of square pyramid is 1.959(4) A, and the distance at the
˚
axial position is slightly longer (2.396(4) A). Two neighboring
Cu2þ ions are bridged by 1a to form a one-dimensional infinite
left-handed helical chain along the a-axis (Fig. 3). The successful
in situ reduction of the imine in the ligand is evident from the

J. Chen et al. / Journal of Solid State Chemistry 192 (2012) 255–262
259
Fig. 2. The ORTEP diagram of complex 3 with a numbering scheme.
Fig. 4. The ORTEP diagram of complex 4 with a numbering scheme.
Fig. 5. Packing of the 1D chain polymer of complex 4. Hydrogen atoms have been
omitted for clarity.
In complex 5, each Cu2þ ion is coordinated by two nitrogen atoms
from 4,40-bipyridine and three oxygen atoms from 1b to form a
distorted square pyramidal structure. Ligand 1b also experiences
in situ cyclization and the cyclized ligand nbop maitains the
S-configuration of 1b, just as in complex 4. The ligand nbop
coordinates with Cu2þ by two modes. One nbop coordinates with
Fig. 3. (A) Packing of the 1D chain polymer. Hydrogen atoms have been omitted
for clarity. (B) Chiral helix of complex 3.
˚
C(6)–N(1) distance (1.495 A) when compared with usual C–N
˚
amine bonds (1.47–1.50 A). In addition to the asymmetric center
at atom C(6), the coordination of the ligand to the metal ion gives
rise to an asymmetric secondary nitrogen atom N(1) with
R-absolute configuration, which is a subsequent induction of the
neighboring homochiral carbon center.
metal ion in a single non-bridge mode only by
a
-carboxyl group.
The bond distance of Cu–O is 1.970(6) A. The other two nbop act
as bidentate linkers bridging neighboring metals with -carboxyl
˚
a
group and the carbonyl group on the five membered ring to form
X-ray diffraction analysis reveals that complex 4 is a mono-
clinic C2 space group and also exhibits slightly distorted square-
pyramidal five-coordinate geometry. In complex 4, each Cu2þ ion
is coordinated by two nitrogen atoms from 4,40-bipyridine
a 1D infinite chain along b axis. The Cu–carboxyl bond distance is
˚
˚
1.963(6) A, while the Cu–carbonyl group distance is 2.399(6) A.
At the same time, two bipyridine molecules also link the neigh-
boring metal ions to form a 1D chain along a axis (Cu–N¼1.995–
˚
˚
(Cu–N¼2.05(2) A), two oxygen atoms from the condensed ligand
2.025(6) A), thus resulting in a 2D network structure. The four
2 (Cu–O¼1.95(2) A), and one water molecule (Cu–O¼2.18(4) A)
(Fig. 4 and Table 1). The four planar positions are occupied by
4,40-bipyridine and ligand 2, and the water molecule binding at
the apex completes the coordination sphere. The amine group of
ligand 2 loses its coordination property because it is a tertiary
amine. As a result, ligand 2 coordinates to metal ion only with the
planar positions of square pyramid are occupied by 4,40-bipyr-
idine and carboxyl groups from nbop. The carbonyl group on the
five member ring occupies the axial position. As can be seen from
the structure of complex 5, nbop coordinates metals by carbonyl
group of the heterocyclic ring, although the Cu–O bond is
relatively weak. This result reverses our previous speculation that
glutamic derivates keep their carboxyl side chains in order to
bridge adjacent metals.
Complex 6 crystallizes in a monoclinic P21 space group with
coordination mode similar to that of complex 5 (Fig. 9, Table 2).
Each Cd2þ ion is coordinated by five oxygen atoms from three
nbop ligands and two nitrogen atoms from 4,40-bipyridine to
form an approximate pentagonal bipyramidal geometry. Ligand
nbop coordinates to Cd2þ with two modes. Two of them act
˚
˚
oxygen atom from
a
-carboxyl group. The neighboring Cu2þ ions
are bridged by 4,40-bipyridine to form a 1D infinite chain along
c-axis in complex 4 (Fig. 5). The crystals of ligand 2 can be isolated
as pure colorless prism. The isolated ligand 2 crystallizes in
orthorhombic P212121 space group (Fig. 6 and Table 1).
Complex 5 crystallizes in an orthorhombic P212121 space
group. The coordination mode and the crystallographic data of
complex 5 are exhibited in Figs. 7 and 8 and Table 2, respectively.

260
J. Chen et al. / Journal of Solid State Chemistry 192 (2012) 255–262
˚
as tridentate linkers bridging neighboring metals with
group and the carbonyl group on the five membered ring to
form a 1D infinite chain. The Cd–carboxyl bond distances is
a
-carboxyl
ligands nbop (Ni–O¼2.061 A), and the other two come from water
molecules (Ni–O¼2.089). 4,40-Bipyridine bridges neighboring metal
ions to form a 1D infinite chain structure.
˚
2.367(4)–2.441(4) A, and the bond length of Cd–carbonyl group
˚
is 2.396(4) A. The third nbop coordinates metal ion only with the
3.3. SHG properties
˚
oxygen atoms of carboxyl group (Cd–O¼2.339(4)–2.438(3) A).
Furthermore, 4,40-bipyridine bridges the neighboring Cd2þ and
In ligands 1a and 1b, the amino group of glutamic acid was
connects the 1D chain to form a new 2D network (Cd–N¼2.35
modified with substituted phenyl groups, which help to construct
˚
(3) A).
P-conjugated systems in these compounds. At the same time, the
Different from complex 6, complex 7 crystallizes in a mono-
cyano- or nitro- group on the 4-position of the phenyl, accom-
panied with the amino group from glutamic acid, acting as the
acceptor and the donor of electron respectively, forms a good
clinic C2 space group with coordination mode similar to that of
complex 4 (Fig. 10, Table 2). Each Ni2þ ion is coordinated by four
oxygen atoms and two nitrogen atoms forming an octahedral
geometry. Two of the oxygen atoms come from two condensed
donor-P-acceptor system. Besides, the chirality of glutamic acid
ensures ligands 1a and 1b crystallizing in noncentrosymmetric
space groups, which is an essential requirement for SHG response.
Therefore, 1a and 1b would be expected to possess second-order
nonlinear effect. On the other hand, reducing the imine bond will
result in the decrease of conjugation, leading to a lower second
harmonic generation (SHG) response. Using the methods pro-
posed by Kurtz and Perry, the SHG efficiencies of 1a and 1b
were estimated. The experimental results indicate that the SHG
responses of both are about 1.1 times as high as that of potassium
dihydrogen phosphate (KDP). Preliminary SHG measurement of
the complexes constructed from 1a and 1b reveals that com-
plexes 6 and 7 display SHG responses close to that of KDP.
The decrease in SHG responses may due to disorder of the dipole
arrangement in the complexes.
4. Conclusions
In summary, two new chiral aminocarboxlate derivates 1a and 1b
have been synthesized and used as ligands in constructing homo-
chiral metal organic complexes 3–7. All these complexes synthesized
under hydrothermal conditions were proved to be optically pure.
Complex 3 is a 1D helical infinite chain bridged by ligand 1a.
Complexes 4–7 possess 1D and 2D structures respectively, in which
the chiral ligands 1a and 1b experience in situ intramolecular
amidation. For the ligand condensation, competitive coordination
Fig. 6. The ORTEP diagram of ligand 2 with a numbering scheme.
Fig. 7. The ORTEP diagram of complex 5 with a numbering scheme.

J. Chen et al. / Journal of Solid State Chemistry 192 (2012) 255–262
261
Fig. 8. Packing of the 2D polymer of complex 5 viewed along the c axis. Hydrogen atoms have been omitted for clarity.
Fig. 9. Ball and stick representation of the coordination spheres of Cd ions in complex 6. The hydrogen atoms are omitted for clarity.

262
J. Chen et al. / Journal of Solid State Chemistry 192 (2012) 255–262
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This work was supported by grants from the 973 Program
(2007CB815301), the National Science Foundation of China
(20733003, 20871114 and 20801055), the Science Foundation of
CAS (KJCX2-YW-H20) and of Fujian Province (2009HZ0006-1,
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Appendix A. Supporting information
Supplementary data associated with this article can be found in
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