A chiral layered Co(II) coordination polymer with helical chains from achiral materials

Article abstract of DOI:10.1039/b417184e

A layered coordination polymer Co(PDC)(H₂O)₂· H₂O containing two helical chains was synthesized, and the resultant crystals were not racemic as evidenced by the observation of strong signals in vibrational circular dichroism (VCD) spectra. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b417184e

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A chiral layered Co(II) coordination polymer with helical chains from
achiral materials{
Ge Tian,a Guangshan Zhu,*a Xiaoyu Yang,a Qianrong Fang,a Ming Xue,a Jinyu Sun,a Yan Wei*b and
Shilun Qiu*a
Received (in Cambridge, UK) 16th November 2004, Accepted 5th January 2005
First published as an Advance Article on the web 26th January 2005
DOI: 10.1039/b417184e
VCD spectra were measured with the Bruker PMA 37 spectro-
meter. A Perkin-Elmer TGA 7 thermogravimetric analyzer
was used to obtain the TG curve in air with a heating rate of
A layered coordination polymer Co(PDC)(H2O)2?H2O con-
taining two helical chains was synthesized, and the resultant
crystals were not racemic as evidenced by the observation of
strong signals in vibrational circular dichroism (VCD) spectra.
20 uC min21
.
Single-crystal X-ray analysis{ shows that the compound is a 2-D
layer coordination polymer which possesses two types of helical
chains. As shown in Fig. 1, Co(II) displays a distorted octahedral
coordination environment with one nitrogen atom (N1) and three
oxygen atoms (O1, O3, O4) from three H2PDC ligands, and other
two oxygen atoms (O5, O6) from two water molecules, there is one
guest water molecule (O7) in the compound. The compound is
stable in air and insoluble in water and common organic solvents.
[Co(PDC)(H2O)2?H2O]: Anal. Calc. for C7H9NO7Co: Co 21.49,
C 30.30, H 3.51, N 5.08. Found: Co 21.12 C 30.26, H 3.26, N
5.04%.
Helical structures through self-organization are an essence of life
and are of interest in supramolecular chemistry because helical
structures are reminiscent of DNA molecules. The design and
synthesis of chiral inorganic–organic materials have attracted great
attention for their potential applications in enantioselective
separation and catalysis.1,2 It is known that the aluminosilicate
zeolite b and the titanosilicate ETS-10 are multiphasic with one
polymorph crystallized in a chiral space group.3 The chiral
compounds can be synthesized by using chiral reactants, solvents
and/or auxiliary agents, by spontaneous resolution, or by the
influence of chiral physical environment such as polarized light.4,5
Recently, chiral templates such as chiral metal complexes have
been used to form chiral metal phosphates.6 The transformation
was achieved by chirality direction and chirality transfer. The
phenomenon of spontaneous resolution is unusual in coordination
chemistry, and the products are normally a racemic mixture of left-
and right-handed helical chains, although the each crystal is a
single enantiomer.7
The compound crystallizes in the chiral space group P212121 and
there are two types of twofold screw axes along the crystal-
lographic b axis. Each carboxylate of the H2PDC ligands bridges
two Co(II) ions in syn-anti coordination mode to form infinite
right-hand helical –C–O–Co– chains (Fig. 2(a)). The PDC ligands
also bridge the cobalt center to form a further tpye of helical –Co–
PDC– chains with helical orientation opposite to the former helical
chains (Fig. 2(a)). The distance of the repeating parts is about
˚
9.422 A. The two types of helical chains are interconnected to
In this work, we employed an achiral ligand pyridine-2,5-
dicarboxylic acid (H2PDC) and synthesized a 2-D layer coordina-
tion polymer Co(PDC)(H2O)2?H2O containing two helical chains.8
The synthesis did not involve any chiral reactant or solvent or
other auxiliary agent. To our surprise, the resultant crystals were
not racemic as evidenced by the observation of strong signals in
vibrational circular dichroism (VCD) spectra. VCD spectroscopy
is a relatively new but powerful technique to obtain conforma-
tional information of chiral molecules.9
each other through the cobalt center to produce an interesting
As a typical preparation procedure, a mixture of H2PDC
(0.5 mmol) and Co(CH3COO)2?4H2O (0.5 mmol) was suspended
in 8 ml deionized water and sealed in a 20-ml Teflon-lined
autoclave. Upon heating at 180 uC for three days, the autoclave
was slowly cooled to room temperature. The pink crystals were
collected, washed with deionized water and dried in air (0.083 g,
yield 60%). The single-crystal data were collected on a Bruker
SMART CCD diffractometer using graphite-monochromated
˚
Mo-Ka radiation (l 5 0.71073 A). FTIR spectra were obtained
on a Nicolet Impact 410 FTIR spectrometer using a KBr pellet.
Fig. 1 Thermal ellipsoid plot (50%) showing an asymmetric unit of
˚
Co(PDC)(H2O)2?H2O. The N(1)–Co(1) distance is 2.149(4) A. The Co–O
˚
distances are 2.062(3)–2.182(3) A. The angles around the cobalt atom
{ Electronic supplementary information (ESI) available: xm vs. T and 1/xm
vs. T plots of Co(PDC)(H2O)2?H2O. See http://www.rsc.org/suppdata/cc/
b4/b417184e/
*sqiu@mail.jlu.edu.cn (Shilun Qiu)
range from 76.97(14) to 173.71(13)u. The H atoms are omitted for clarity.
1396 | Chem. Commun., 2005, 1396–1398
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Thermogravimetric analysis (TGA) showed that compound was
stable up to 200 uC. The TG curve showed three weight loss steps.
The first weight loss of 7.1% from 100 to 200 uC corresponds to the
loss of one guest water molecule. The second weight loss of 17.5%
between 200 and 250 uC is attributed to the loss of two water
molecules. The third step between 300 and 510 uC corresponds to
the loss of all organic ligands and a weight gain of the residue is in
accordance with conversion to CoO.
We have obtained VCD spectra in the mid-IR region of the 2-D
layer coordination polymer. Fig. 3 shows the VCD and IR spectra
of the Co(PDC)(H2O)2?H2O crystals. The IR spectrum of the
compound is assigned as follows: the bands at 1290, 1363, 1394
and 1658 cm21 are attributed to the CLO stretch vibrations; the
bands at 1479, 1583 and 1600 cm21 are assigned to the skeleton
vibrations of aromatic ring. The experimental VCD bands at
1288–1394 and 1658 cm21 correspond to CLO stretch vibrations,
and the bands at 1471–1611 cm21 correspond to the skeleton
vibration of aromatic ring. The bond of the CLO group and the
aromatic ring construct the two types of helical chains: the right-
hand helical –C–O–Co– chains, and the left-hand –PDC–Co–
helical chains. There is a good agreement between VCD and IR
absorption spectra. The vibrational modes were identified and
conformational information also can be observed in the VCD
spectra. The strong VCD signals indicate that the crystals of
Co(PDC)(H2O)2?H2O were chiral. The experiment was repeated
on the compound obtained from different autoclave experiments
six times.
The pyridine-2,5-dicarboxylic acid ligand may play a key role in
the two chains. As shown in Fig. 2, the organic ligand acts as the
structure directing agent to form the chiral coordination polymer
of the right-handed and left-handed helical chains.
In order to understand the reason for the observed enantiomeric
excess in the Co(PDC)(H2O)2?H2O product, we have checked all
the reagents and solvents as well as the mother-liquor, and found
Fig. 2 (a) A space-filling view of the right-handed helical chain of –C–O–
Co– and a cylindrical view of the left-handed helical chain of –PDC–Co–
along the b axis. (b) The 2D structure including two types of helical chains.
(c) Packing of the undulating layers along the [100] direction. The H atoms
are omitted for clarity. Color code: Co: pink; C: grey; N: blue; O: red.
two-dimensional layered structure (Fig. 2(b)) The two coordinated
water molecules and two coordinated carboxylate oxygen atoms
…
˚
form intralayer H-bonds with an O5 O1 distance of 2.691 A and
…
˚
an O6 O3 distance of 2.693 A. One coordinated water molecule
and the uncoordinated carboxylate oxygen atom of an adjacent
…
layer form an interlayer H-bond with an O5 O2 distance of
˚
2.687 A. The guest water molecule and one coordinated water
…
˚
form an H-bond with an O7 O6 distance of 2.623 A. Therefore,
…
the O–H O hydrogen bonds further extend the 2-D undulating
layers in to a 3-D supramolecular framework (Fig. 2(c)).10
Fig. 3 VCD (top) and IR absorption (bottom) spectra.
Chem. Commun., 2005, 1396–1398 | 1397
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1.792 mm21, Flack parameter 5 0.0032, R 5 0.0284, 2225 reflections
measured, 1374 unique (Rint 5 0.0288) which were used in all calculations.
The final wR(F2) was 0.0822 (all data). CCDC 252681. See http://
www.rsc.org/suppdata/cc/b4/b417184e/ for crystallographic data in .cif or
other electronic format.
that none had optical rotation. There was no VCD signal for the
starting materials, H2PDC and Co(CH3COO)2?4H2O, or the
solids obtained by evaporating the mother-liquor. So far we have
made independent preparations using different autoclaves and all
yielded crystals with essentially the same VCD signals. We have
also checked for and eliminated the possibility of a physical chiral
environment effect including light, magnetic field and stirring
directions (clockwise or counterclockwise). The enantiomeric
excess may be explained by the fact that the initial crystals formed
may seed the handedness of the bulk product, and thus the
particular handedness of the bulk depends on which random hand
is formed by the initial few crystals. Further investigation is in
progress to extend the synthesis to other metal and ligand systems
and to elucidate the reasons for the observed enantiomeric excess.
The variable-temperature (4–300 K) magnetic susceptibility
measurement of the compound is shown in Fig. S1 (ESI{).
Between 4 and 300 K, xm continuously increases with decreasing
temperature. In the 1/xm vs. T plot, the susceptibility can be fitted
to the Curie–Weiss law with C 5 3.045 cm3 K mol21. The Weiss
temperature, h 5 26.58 K, indicates that antiferromagnetic
interactions exist between metallic Co centers.
1 (a) O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae,
M. Eddaoudi and J. Kim, Nature, 2003, 423, 705; (b) S. Kitagawa,
R. Kitaura and S. Noro, Angew. Chem., Int. Ed., 2004, 43, 2334.
2 (a) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon and K. Kim,
Nature, 2000, 404, 982; (b) R. Xiong, X. You, B. F. Abrahams, Z. Xue
and C. Che, Angew. Chem., Int. Ed., 2001, 40, 4422; (c) G. Cao,
E. G. Maurie, A. Monica, F. B. Lora and E. M. Thomas, J. Am. Chem.
Soc., 1992, 114, 7574; (d) S. J. Lee, A. Hu and W. Lin, J. Am. Chem.
Soc., 2002, 124, 12948; (e) E. M. Thomas and A. G. Julia, Acc. Chem.
Res., 1998, 31, 209.
3 (a) M. W. Anderson, O. Terasaki, T. Ohsuna, A. Philippou,
S. P. MacKay, A. Ferreira, J. Rocha and S. Lidin, Nature, 1994, 367,
347; (b) M. M. J. Treacy and J. M. Newsam, Nature, 1988, 332, 249.
4 (a) C. J. Kepert, T. J. Prior and M. J. Rosseinsky, J. Am. Chem. Soc.,
2000, 122, 5158; (b) T. J. Prior and M. J. Rosseinsky, Inorg. Chem.,
2003, 42, 1564.
5 (a) L. Carlucci, G. Ciani, D. M. Proserpio and S. Rizzato, Chem.
Commun., 2000, 1319; (b) J. D. Ranford, J. J. Vittal, D. Wu and
X. Yang, Angew. Chem., Int. Ed., 1999, 38, 3498; (c) T. Ezuhara,
K. Endo and Y. Aoyama, J. Am. Chem. Soc., 1999, 121, 3279; (d)
K. Biradha, C. Seward and M. J. Zaworotko, Angew. Chem., Int. Ed.,
1999, 38, 492; (e) Y. Cui, H. L. Ngo and W. B. Lin, Chem. Commun.,
2003, 1388.
6 (a) Y. Wang, J. Yu, M. Guo and R. Xu, Angew. Chem., Int. Ed., 2003,
42, 4089; (b) Y. Wang, J. Yu, Q. Pan, Y. Du, Y. Zou and R. Xu, Inorg.
Chem., 2004, 43, 559.
We are grateful to the financial support by the State Basic
Research Project and the National Natural Science Foundation of
China. The authors thank Dr T. Ben and H. Cao for collecting
and analyzing the VCD spectra.
7 (a) M. Kondo, M. Miyazawa, Y. Irie, R. Shinagawa, T. Horiba,
A. Nakamura, T. Naito, K. Maeda, S. Utsuno and F. Uchida, Chem.
Commun., 2002, 2156; (b) E. Gao, Y. Yue, S. Bai, Z. He and C. Yan,
J. Am. Chem. Soc., 2004, 126, 1419.
8 We thank a referee for attracting our attention to the fact that the
structure described here is essentially that of Co(PDC)(H2O)3
(M. J. Plater, M. R. St. J. Foreman, R. A. Howie and
E. E. Lachowski, J. Chem. Res. (S), 1998, 754), and we emphasize
the chirality of the structure and the VCD result.
Ge Tian,a Guangshan Zhu,*a Xiaoyu Yang,a Qianrong Fang,a
Ming Xue,a Jinyu Sun,a Yan Wei*b and Shilun Qiu*a
aState Key Laboratory of Inorganic Synthesis and Preparative
Chemistry, Department of Chemistry, Jilin University, Changchun,
130012, China. E-mail: sqiu@mail.jlu.edu.cn; Fax: +86-431-5168331;
Tel: +86-431-5168331
bDepartment of Chemistry, Drexel University, Philadelphia, PA 19104,
USA. E-mail: weiyan@drexel.edu
9 (a) V. Setnicka, M. Urbanova, P. Bour, V. Kral and K. Volka, J. Phys.
Chem. A, 2001, 105, 8931; (b) H. Izumi, S. Yamagami, S. Futamura,
L. A. Nafie and R. K. Dukor, J. Am. Chem. Soc., 2004, 126, 194.
10 (a) X. Shi, G. Zhu, Q. Fang, G. Wu, G. Tian, R. Wang, D. Zhang,
M. Xue and S. Qiu, Eur. J. Inorg. Chem., 2004, 185; (b) Y. Cui,
H. L. Ngo, P. S. White and W. B. Lin, Chem. Commun., 2003, 994.
Notes and references
{ Crystal data for Co(PDC)(H2O)2?H2O: C7H9NO7Co, M 5 278.08,
orthorhombic, space group P212121 (no. 19), a 5 7.363(2), b 5 9.422(3),
3
c 5 13.976(4) A, V 5 969.6(5) A , T 5 293(2) K, Z 5 4, m(Mo-Ka) 5
˚
˚
1398 | Chem. Commun., 2005, 1396–1398
This journal is ß The Royal Society of Chemistry 2005