Self-assembly of two one-dimensional zinc polymers based on (+)-N-tosyl-l-glutamic acid

Article abstract of DOI:10.1016/j.ica.2012.12.031

Two novel zinc (II) coordination polymers [Zn(Him)(H₂O)(L)] _n (1) and {[Zn(2,4′-bipy)(H₂O)](L)}_n (2) (H₂L = (+)-N-tosyl-l-glutamic acid, Him = imidazole, and 2,4′-bipy = 2,4′-bipyridine) were synthesized and then structurally characterized by elemental, infrared, thermogravimetric, and X-ray crystallography analyses. Compound 1 crystallized in the chiral space group P2₁ and had a ladder-like one-dimensional double-chain structure. Compound 2 crystallized in the achiral space group P2₁/c and had a one-dimensional single-chain framework. Both compounds assembled to form two-dimensional supramolecular structures through hydrogen-bonding interactions. The two compounds also showed intense fluorescence at room temperature.

Full text of DOI:10.1016/j.ica.2012.12.031

Inorganica Chimica Acta 399 (2013) 6–11
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Self-assembly of two one-dimensional zinc polymers based on
(+)-N-tosyl-L-glutamic acid
⇑
Lili Wu, Huihua Song , Rong He, Haitao Yu
College of Chemistry and Material Science, Hebei Normal University, Shijiazhuang, Hebei 050016, China
a r t i c l e i n f o
a b s t r a c t
Two novel zinc (II) coordination polymers [Zn(Him)(H2O)(L)]n (1) and {[Zn(2,40-bipy)(H2O)](L)}n (2)
Article history:
Received 14 June 2012
Received in revised form 5 December 2012
Accepted 6 December 2012
Available online 25 January 2013
(H2L = (+)-N-tosyl-L
-glutamic acid, Him = imidazole, and 2,40-bipy = 2,40-bipyridine) were synthesized
and then structurally characterized by elemental, infrared, thermogravimetric, and X-ray crystallography
analyses. Compound 1 crystallized in the chiral space group P21 and had a ladder-like one-dimensional
double-chain structure. Compound 2 crystallized in the achiral space group P21/c and had a one-dimen-
sional single-chain framework. Both compounds assembled to form two-dimensional supramolecular
structures through hydrogen-bonding interactions. The two compounds also showed intense fluores-
cence at room temperature.
Keywords:
Zinc(II) compounds
N-p-tolylsulfonyl-L-glutamic acid
Crystal structure
Ó 2013 Elsevier B.V. All rights reserved.
Fluorescent properties.
1. Introduction
2. Experimental
Chiral coordination polymers have drawn considerable atten-
tion in recent years because of their interesting structures as well
as potential applications in luminescence, enantioselective cataly-
sis, magnetism, and gas separation [1–6]. Generally, chiral coordi-
nation polymers can be obtained by stereoselective synthesis using
chiral species or by spontaneous resolution from achiral materials.
Recently, they have been mainly prepared using chiral organic li-
gands [7–15] or chiral metal complexes [16–17]. In this work, we
selected the most straightforward and reliable process of using a
chiral organic ligand to synthesize new chiral materials. The ligand
2.1. Materials and analyses
All reagents were commercially available and used as received
without further purification. Elemental (C, H, and N) analyses were
performed with an Elemental Vario EL elemental analyzer. Infrared
(IR) spectra were recorded using KBr pellets from 4000 to 400 cmꢀ1
on a Fourier-transform infrared-8900 spectrometer. Thermogravi-
metric analysis (TGA) was performed on a TGA-7 instrument at a
heating rate of 15 °C minꢀ1. Fluorescence spectra were measured
with a Hitachi F-4600 luminescence spectrometer.
used was (+)-N-tosyl-L-glutamic acid, which is well known to form
coordination polymers with transition metals because of its multi-
ple N and O donors. Accordingly, we successfully obtained two no-
vel zinc (II) compounds with different nitrogen-containing ligands:
[Zn(Him)(H2O)(L)]n (1) and {[Zn(2,40-bipy)(H2O)](L)}n (2)
2.2. Preparations
2.2.1. Synthesis of [Zn(Him)(H2O)(L)]n (1)
Zn(CH3COO)2ꢁ2H2O (0.0220 g, 0.1 mmol), H2L (0.0151 g,
0.05 mmol), and Him (0.0078 g, 0.1 mmol) in H2O/MeOH (1:1,
10.0 ml) were mixed. The solution was adjusted to pH 6.0 with
the addition of a dilute aqueous 2 M NaOH solution. After stirring
for 10 min, a colorless solution was obtained and filtered. The sol-
vents were then allowed to evaporate slowly from the filtrate at
room temperature. After about 3 days, colorless needle-shaped
crystals suitable for X-ray analysis were obtained in 56% yield
(based on Zn). Anal. Calc. for C15H19N3O7SZn: C, 39.96; H, 4.25; N,
9.32. Found: C, 39.81; H, 4.15; N, 9.21%. IR (KBr pellet, cmꢀ1):
(H2L = (+)-N-tosyl-L
-glutamic acid, Him = imidazole, and 2,40-
bipy = 2,40-bipyridine). Some complexes that contain this ligand
have been reported [18–19], but the chiral characters of 1 and 2
are unclear. Thus, single-crystal X-ray analysis was performed
and results showed that 1 is chiral whereas 2 is achiral. This finding
indicated that some factors affect the chirality in addition to the
characteristics of the chiral organic ligand used to construct chiral
compounds. The fluorescent properties of 1 and 2 at room temper-
ature were also examined.
m
= 3436 (br), 3261 (w), 1602 (m), 1560 (s), 1452 (m), 1436 (w),
⇑
1330 (m), 1306 (m), 1155 (s), 1066 (w), 1001 (w), 958 (m), 916
(m), 877 (m), 819 (m), 752 (m), 677 (m), 615 (w), 545 (w), 518 (w).
Corresponding author. Tel.: +86 80787400; fax: +44 1223 336033.
E-mail address: songhuihua@mail.hebtu.edu.cn (H. Song).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.12.031

L. Wu et al. / Inorganica Chimica Acta 399 (2013) 6–11
7
2.2.2. Synthesis of {[Zn(2,40-bipy)(H2O)](L)}n (2)
L2ꢀ ligands, one oxygen atom from the coordinated water mole-
cule, and one nitrogen atom from a Him group.
The same synthetic procedure as for 1 was used, except that
Him (0.0078 g, 0.1 mmol) was replaced with 2,40-bipy(0.01560 g,
0.1 mmol), thereby yielding colorless bar-shaped crystals of 2 in
68% yield (based on Zn). Anal. calc. for C22H23N3O7SZn: C, 49.03;
H, 4.30; N, 7.80. Found: C, 49.15; H, 4.64; N, 7.62%. IR (KBr pellet,
The trigonality index calculated for the distorted trigonal bipy-
ramidal geometry of the Zn (II) ions in 1 is 0.16 [21–22]. The Zn–O
bond lengths range from 1.956(2) to 2.219(2) Å, and the Zn–N
bond length is 2.013(2) Å. The 2.219(2) Å value of the Zn1–O1 dis-
tance indicates the strong steric hindrance from Him. In this struc-
ture, the Him ligand only acts as a decorating ligand ligated to
cmꢀ1):
m = 3429 (br), 3210 (w), 1618 (s), 1588 (w), 1508 (w),
1464 (m), 1421 (s), 1325 (m), 1302 (s), 1221 (w), 1158 (s), 1119
(w), 1095 (m), 1069 (w), 992 (m), 916 (m), 813 (m), 780 (s), 733
(m), 669 (s), 650 (w), 618 (w), 565 (s), 550 (w).
connect one Zn (II) metal ion. The L2ꢀ anions act as l3 g1 g1 g1
– – – ,
bridging tridentate ligands through their carboxylate groups to-
ward three Zn (II) cations (Scheme 1a) and involving three carbox-
ylic oxygens (two carboxylic oxygen from the
and one oxygen from the -carboxyl group). Based on the above
coordination modes, all Zn centers are bridged by - and -car-
a-carboxyl group
2.2.3. Crystal structure determination
c
Colorless needle-shaped crystals of
1 with dimensions of
0.29 ꢂ 0.09 ꢂ 0.07 mm3 and colorless bar-shaped crystals of 2 with
dimensions of 0.32 ꢂ 0.12 ꢂ 0.09 mm3 were subjected to single-
crystal X-ray diffraction using a Bruker SMART-CCD area detector
a
c
boxyl groups of L2ꢀ ligands to form ladder-like one-dimensional
(1D) double chains along the b-direction (Fig. 1b). These 1D chains
are further extended into a two-dimensional (2D) supramolecular
architecture through hydrogen-bonding interactions between the
coordinated water molecule (O7) and the uncoordinated oxygen
atom (O6) of the L2ꢀ ligand, the uncoordinated nitrogen atom
(N3) from the Him ligand, and the uncoordinated oxygen atom
(O6) of the L2ꢀ ligand [O7ꢁ ꢁ ꢁO6(x ꢀ 1, y ꢀ 1, z) 2.746(3) Å;
N3ꢁ ꢁ ꢁO4(x ꢀ 1, y ꢀ 1, z) 3.017(4) Å] (Fig. 1c).
diffractometer with graphite-monochromatized Mo K
(k = 0.71073 Å) at 298(2) K according to the scan technique.
a radiation
x–u
The structures were solved by direct methods using the SHELXS-97
program. All non-hydrogen atoms were anisotropically refined by
the full-matrix least-square methods on F2 using the SHELXL-97 pro-
gram. Hydrogen atoms were added in geometrical positions and
not refined. A semi-empirical absorption correction was applied
to the intensity data using SADABS [20]. A summary of the crystallo-
graphic data and refinement parameters is presented in Table 1.
Compound 2 crystallizes in the space group P21/c and contains
one Zn atom, one 2,40-bipy, two halves of two L2ꢀ ligands, and one
coordinated water molecule (Fig. 2a). Each Zn2+ ion is four-coordi-
nated in a distorted tetrahedral environment (ZnO2N2) by two oxy-
gen atoms from two L2ꢀ ligands, one nitrogen atom from one 2,40-
bipy, and one oxygen atom from the coordinated water molecule
(N2–Zn1 = 2.021(5) Å, O2–Zn1 = 1.954(4) Å, O7–Zn1 = 1.985(4) Å,
3. Results and discussion
3.1. Crystal structure
Zn1–O4#2 = 1.949(4) Å). 2,40-Bipy exhibits
and is ligated to one Zn (II) cation, whereas the L2ꢀ ligands act as
1, bridging bidentate ligands through their carboxylate
groups toward two Zn (II) cations (Scheme 1b), involving two car-
boxylic oxygens (one carboxylic oxygen from the -carboxyl group
a disordered ligand
Single-crystal X-ray diffraction analysis shows that 1 crystal-
lizes in chiral space group P21, and that each asymmetric unit crys-
tallographically consists of one Zn atom, one Him group, one L2ꢀ
ligand, and one coordinated water molecule (Fig. 1a). Each Zn (II)
ion of 1 is located in a distorted trigonal bipyramidal geometry
(ZnO4N) coordinated by three oxygen atoms from three different
l2– –g
g1
a
and one oxygen from the
c-carboxyl group). It bridges the adjacent
Table 1
Summary of crystal data and details of intensity collection and refinement.
Compound
1
2
Empirical formula
Formula weight
T (K)
C
15H19N3O7SZn
C22H23N3O7SZn
538.86
298(2)
0.71073
monoclinic
P2(1)/c
10.3068(18)
9.4653(16)
450.76
298(2)
0.71073
monoclinic
P2(1)
10.431(3)
4.9185(12)
17.662(4)
90
k (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
25.245(4)
90
a
(°)
b (°)
91.686(3)
90
905.8(4)
2
1.653
464
99.671(3)
90
2427.8(7)
4
1.474
1112
1.144
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
F(000)
l
(mmꢀ1
)
1.515
h range for data collection (°)
Limiting indices
1.95–25.49
1.64–25.50
ꢀ12 6 h 6 12,ꢀ5 6 k 6 5,ꢀ15 6 l 6 21
4772/3049 (0.0263)
99.6%
0.9013 and 0.6677
3049/2/245
ꢀ12 6 h 6 12,ꢀ10 6 k 6 11,ꢀ26 6 l 6 30
12280/4505 (0.0508)
99.6%
0.9040 and 0.7109
4505/84/307
Reflections collected/unique (Rint
Completeness to h = 25.50°
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit (GOF)
)
0.983
1.073
R1, wR2 [I > 2
r
(I)]a
0.0305, 0.0604
0.0334, 0.0612
0.015(12)
0.342 and ꢀ0.268
0.0721, 0.1530
0.0969, 0.1651
0.00(2)
0.602 and ꢀ0.551
R1, wR2 (all data)a
Flack parameters
Largest difference peak and hole (e Åꢀ3
)
a
2
R1 = |Fo ꢀ Fc|/
R
Fo, wR2
=
R
[w(Fo ꢀ Fc2)2]/
R .
[w(Fo2)]1/2

8
L. Wu et al. / Inorganica Chimica Acta 399 (2013) 6–11
Fig. 1. (a) Molecular structure of 1; (b) the 1D double chain of 1 (H atoms omitted for clarity. Symmetry codes: #3 ꢀx + 1, y ꢀ 1/2, ꢀz; #4 x, y ꢀ 1, z); (c) the 2D layer structure
of 1.

L. Wu et al. / Inorganica Chimica Acta 399 (2013) 6–11
9
Zn (II) centers to form –Zn–L–Zn–L–chains (Fig. 2b). These chains
are further connected to a 2D layer (Fig. 2c) parallel to the ab plane
by hydrogen-bonding interactions between the coordinated water
carboxyl group of the L2ꢀ ligand, the coordinated oxygen atom
(O4) of the -carboxyl group, and the uncoordinated nitrogen atom
c
(N1) [O7ꢁ ꢁ ꢁO3(ꢀx + 1, y + 1/2, ꢀz + 1/2) 2.861(5) Å; N1ꢁ ꢁ ꢁO4(ꢀx,
molecule (O7) and the uncoordinated oxygen atom (O3) of the c-
y + 1/2, ꢀz + 1/2) 2.930(6) Å].
Fig. 2. (a) Molecular structure of 2; (b) the 1D chain of 2 (H atoms omitted for clarity. Symmetry codes: #2 x, y + 1, z); (c) the 2D layer structure of 2 (the tosyl groups of L2ꢀ
ligands omitted for clarity).

10
L. Wu et al. / Inorganica Chimica Acta 399 (2013) 6–11
3.3. Fluorescent properties
The emission spectra of 1, 2, and the H2L ligand in MeOH solu-
tion at room temperature are shown in Fig. 3. Upon excitation at
276 nm, the strongest emission peak of ligand H2L is at 315 nm,
whereas Him and 2,40-bipy do not show any emission peak. The
excitation leads to intense emission bands at 315 nm for 1
(kex = 276 nm) and 312 nm for 2 (kex = 276 nm), respectively. Com-
pared with other d10 metal coordination polymers [25–26], Zn (II)
ion is difficult to oxidize or reduce. Thus, the fluorescent emissions
of 1 and 2 are neither metal-to-ligand charge transfer nor ligand-
to-metal charge transfer, which may be assigned to the intraligand
Scheme 1. The observed coordination modes of H2L ligand for 1.
p⁄
–p transitions of the aromatic ring systems of the H2L ligands
[27–28]. A Apparently, the presence of Zn does not change the fluo-
rescent properties of the ligand.
4. Conclusion
Two Zn (II) compounds were successfully synthesized from (+)-
N-tosyl-L-glutamic acid with different nitrogen-containing ligands.
Compound 1 features ladder-like 1D double chains, and compound
2 has a 1D single chain. Both self-assemble to form 2D supramolec-
ular structures through hydrogen-bonding interactions. Compound
1 crystallizes in the chiral space group P21, whereas compound 2
crystallizes in the achiral space group P21/c, which may be due to
the distorted ligand 2,40-bipy. At room temperature, they exhibit
strong fluorescence emission bands at 315 and 312 nm, respec-
tively. The presence of Zn does not change the fluorescent proper-
ties of the ligand. The success achieved in this work prompts us to
synthesize more chiral materials, which hopefully lead to break-
throughs in chiral synthesis.
Fig. 3. The luminescent spectra of 1 and 2.
Acknowledgments
One of the most notable findings is that the chains of 1 and 2 are
This work was supported by the Natural Science Foundation of
China (Grants Nos. 20601007, 21141002, 20772022, 21072043,
and 20971035), the Natural Science Foundation of Hebei Education
Department (Grant No. ZH2006002), the Natural Science Founda-
tion of Hebei Province (Grant Nos. B2008000143, B2010000362
and B2012205040), and the Doctoral Foundation of Hebei Normal
University (Grant No. 130374).
fundamentally different. The Zn centers are bridged by
a- and
c
-carboxyl groups of the L2ꢀ ligands to form the ladder-like 1D
double chains in 1, whereas Zn are linked by the L2ꢀ ligands to
form –Zn–L–Zn–L– single chains in 2. We believe this situation is
due to the different steric hindrances of the second ligand Him
and 2,40-bipy.
Careful analysis of the structural features of 1 and 2 proves that
1 crystallizes in the chiral space group P21, whereas 2 crystallizes
in the achiral space group P21/c. Obviously, the chirality of 2 has
disappeared. We believe that two main factors influence the
assembly of the title coordination polymers according to related
literature: (i) the symmetrical structures can tune the space group,
and the whole crystal is racemic [23], and (ii) the lack of coopera-
tion of the distorted molecules in the layers may change the space
group [24]. In 1, no distorted molecule is present, but the 2,40-bipy
in 2 is distorted.
Appendix A. Supplementary material
CCDC 757302 (1) and 760113 (2) contains the supplementary
crystallographic data for compounds (1) and (2). These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Sup-
plementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.ica.2012.12.031.
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