Assembly of three coordination polymers from glycolate ligands: Syntheses, crystal structures, and thermal properties

Article abstract of DOI:10.1007/s11243-013-9717-5

Three transition metal-organic polymers, [Cu(η ² -O ₂CCH₂OH)(μ ₂-O₂CCH ₂OH)(H₂O)] _n (1), [Cu(μ ₂-O ₂CCH₂OH)₂] _n (2), and [Cd(μ ₂-O₂CCH₂OH)₂] _n (3) constructed from the rigid glycolate (HO₂CCH₂OH) ligand have been isolated under hydro(solvo)thermal conditions and structurally characterized by single-crystal X-ray diffraction. Polymer 1 presents a one-dimensional zigzag chain, while polymer 2 has a two-dimensional sheet structure. Polymer 3 exhibits a similar sheet structure as 2; however, the coordination modes of the ligands in complexes 1 and 2 are different. The three-dimensional solid-state supramolecular structures of the three polymers involve intermolecular hydrogen bonds. The thermal properties of the polymers have also been investigated.

Full text of DOI:10.1007/s11243-013-9717-5

Transition Met Chem (2013) 38:503–509
DOI 10.1007/s11243-013-9717-5
Assembly of three coordination polymers from glycolate ligands:
syntheses, crystal structures, and thermal properties
•
•
•
Xue Song Lin Ya Li Sang Wei Dong Sun
Su Hua Yang
Received: 17 January 2013 / Accepted: 18 March 2013 / Published online: 29 March 2013
ꢀ Springer Science+Business Media Dordrecht 2013
Abstract Three transition metal-organic polymers,
[Cu(g2-O2CCH2OH)(l2-O2CCH2OH)(H2O)]n (1), [Cu(l2-
O2CCH2OH)2]n (2), and [Cd(l2-O2CCH2OH)2]n (3) con-
structed from the rigid glycolate (HO2CCH2OH) ligand
have been isolated under hydro(solvo)thermal conditions
and structurally characterized by single-crystal X-ray dif-
fraction. Polymer 1 presents a one-dimensional zigzag
chain, while polymer 2 has a two-dimensional sheet
structure. Polymer 3 exhibits a similar sheet structure as 2;
however, the coordination modes of the ligands in com-
plexes 1 and 2 are different. The three-dimensional solid-
state supramolecular structures of the three polymers
involve intermolecular hydrogen bonds. The thermal
properties of the polymers have also been investigated.
catalysis [12–15], and fluorescent materials [16, 17]. For
the preparation of coordination polymers, two kinds of
well-established methods (hydrothermal and solvothermal
methods) have been adopted in order to carry out these
reactions under high temperatures which favor formation
of crystalline products suitable for X-ray studies. Although
a great number of coordination polymers have been pre-
pared by hydro(solvo)thermal synthesis methods [18–21],
the factors governing the reactions and formation of the
products are complicated. We still cannot approach a level
of design control whereby a particular type of structure can
be predictably obtained. Therefore, many more coordina-
tion polymers need to be prepared under hydro(solvo)
thermal conditions.
It is well known that a coordination polymer is com-
posed of two major components: a metal center or cluster
of metal centers and an organic ligand called a linker. The
choice of both metal and linker has significant effects on
the structure and properties of the coordination polymer.
The metal’s coordination preference influences the size and
shape of voids by dictating how many ligands can bind to
the metal and in which orientations. Depending on the size
of the ligands, inorganic connecting points, and network
connectivity, the structures of such coordination polymers
can be readily tuned to afford open channels and pores with
dimensions of several angstroms to several nanometers.
In this paper, we investigated the reactions of a simple
organic glycolate ligand with transition metals, namely
Cu(II) and Cd(II), under hydro(solvo)thermal conditions.
In this way, we obtained three interesting coordination
polymers, [Cu(g2-O2CCH2OH)(l2-COOCH2OH)(H2O)]n
(1), [Cu(l2-O2CCH2OH)2]n (2), and [Cd(l2-O2CCH2OH)2]n
(3). In these polymers, the glycolate ligand shows various
coordination modes and strong coordination ability. The
thermal properties of the complexes have been investigated.
Introduction
In the last two decades, the design and construction of
various coordination polymers have attracted much atten-
tion due to their intriguing architectures and fascinating
topologies [1–4], as well as multiple applications in gas
separation and storage [5–8], chemical and biological
sensing [9], ion exchange [10, 11], chirality, magnetism,
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-013-9717-5) contains supplementary
material, which is available to authorized users.
X. S. Lin ꢀ Y. L. Sang (&) ꢀ W. D. Sun ꢀ S. H. Yang
Department of Chemistry, Chifeng University, Chifeng 024000,
Neimenggu, People’s Republic of China
e-mail: sangyali0814@126.com
123

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Transition Met Chem (2013) 38:503–509
Experimental
Materials and methods
1605 (w), 1388 (s), 1316 (s), 1120 (m), 1036 (m), 920 (w),
668 (w), 557 (w).
Synthesis of complex 2
All chemicals were of reagent grade as obtained from
commercial sources and used without further purification.
IR Spectra were recorded on a Nicolet NEXUS 470-FTIR
spectrophotometer as KBr pellets in the 400–4,000 cm-1
region. Elemental analyses (C, H, and N) were obtained out
on a FLASH EA1112 Elemental Analyzer. TGA mea-
surements were made by heating the crystalline samples
from 20 to 850 ꢁC at a rate of 10 ꢁCꢀmin-1 in air on a
Netzsch STA 409PC differential thermal analyzer.
A mixture of ethanol/water (7/1 mL) containing sodium
glycolate (9.8 mg, 0.1 mmol) and CuCl2ꢀ2H2O (17.0 mg,
0.1 mmol) was placed in a 25 mL Teflon-lined autoclave.
The pH was adjusted by addition of one drop of Et3N to
keep the mixture weakly basic. The mixture was heated for
96 h at 120 ꢁC under autogenous pressure, then allowed to
cool to room temperature at a rate of 10 ꢁC/h. Dark blue
stick-shaped crystals of 2 were collected in 62 % yield
(based on Cu), washed with deionized water, and dried in
air. Crystals of 2 are unstable in air and turn blue after
3 days. Anal. Calcd for C4H6O6Cu: C, 22.5; H, 2.8 %.
Found: C, 22.7; H, 2.6 %. IR (cm-1, KBr): 3,257 (s), 2944
(w), 1,615 (s), 1,390 (m), 1,336 (m), 1,145 (m), 1,059 (w),
905 (w), 743 (w), 646 (w).
Synthesis of complex 1
A mixture of ethanol/water (7/1 mL) containing sodium
glycolate (9.8 mg, 0.1 mmol) and Cu(NO3)2ꢀ3H2O
(24.2 mg, 0.1 mmol) was placed in a 25 mL Teflon-lined
autoclave. The pH was adjusted by addition of one drop of
Et3N to keep the mixture weakly basic. The mixture was
heated for 72 h at 160 ꢁC under autogenous pressure, then
allowed to cool to room temperature at a rate of 10 ꢁC/h.
Blue stick-shaped crystals of 1 were collected in 47 %
yield (based on Cu), washed with deionized water, and
dried in air. Crystals of 1 are stable in air. Anal. Calcd for
C4H8O7Cu: C, 20.7; H, 3.5 %. Found: C, 21.0; H, 3.8 %.
IR (cm-1, KBr): 3334 (s), 3265 (s), 3161 (m), 2924 (w),
Synthesis of complex 3
Complex 3 was prepared in a manner analogous to the
method for complex 1 except that Cd(CH3COO)2ꢀ3H2O
was used instead of Cu(NO3)2ꢀ3H2O. Light yellow cube-
shaped crystals of 3 were collected in 70 % yield (based on
Cd), washed with deionized water, and dried in air. Crys-
tals of 3 are stable in air. Anal. Calcd for C4H6O6Cd:
Table 1 Crystallographic data for polymers 1–3
Compound
1
2
3
Formula
C4H8O7Cu
231.64
C4H6O6Cu
C4H6O6Cd
Formula weight
Crystal system
Crystal size (mm3)
Space group
213.63
262.49
Orthorhombic
0.20 9 0.20 9 0.18
P2(1)2(1)2(1)
5.2248(5)
Monoclinic
Monoclinic
0.21 9 0.20 9 0.19
0.20 9 0.20 9 0.20
P2(1)/n
P2(1)/c
˚
a (A)
9.427(3)
6.8211(5)
˚
b (A)
10.8413(9)
13.5133(12)
90.00
5.1197(13)
9.3258(7)
˚
c (A)
13.911(4)
10.9037(8)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90.00
90.00
90.00
107.362(3)
93.0020(10)
90.00
90.00
90.00
3
˚
V (A )
765.44(12)
2.010
640.8(3)
692.66(9)
Dc (Mg m-3
)
2.214
2.517
Z
4
4
4
l (mm-1
)
2.852
3.386
3.133
Reflections collected/unique
Data/restraints/parameters
R indices (all data)
6,531/1,559 [R(int) = 0.0475]
1,559/2/125
R1 = 0.0414, wR2 = 0.0830
0.761
3,014/1,122 [R(int) = 0.0224]
1,122/0/108
4,037/1,580 [R(int) = 0.0177]
1,580/2/108
R1 = 0.0361, wR2 = 0.1035
1.113
R1 = 0.0265, wR2 = 0.0660
1.229
GOF on F2
-3
˚
Dqmin and Dqmax(e A
)
-0.310 and 0.358
-0.552 and 0.644
-0.805 and 0.751
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Transition Met Chem (2013) 38:503–509
505
C, 18.3; H, 2.3 %. Found: C, 18.0; H, 2.1 %. IR (cm-1
,
technique. The correction for extinction was not adopted.
The non-hydrogen atoms were refined with anisotropic
thermal parameters. The hydrogen atoms on C were posi-
tioned geometrically and refined using a riding model. The
hydrogen atoms on O were found at reasonable positions in
the differential Fourier map and located there. All the
hydrogen atoms were included in the final refinement. The
final cycle of full-matrix least squares refinement was based
on 6531 observed reflections and 125 variable parameters
for 1; 3,014 observed reflections and 108 variable param-
eters for 2; 4,037 observed reflections and 108 variable
parameters for 3. All calculations were performed using the
SHELX-97 crystallographic software package [22]. Selec-
ted bond lengths and angles are listed in Table 2.
KBr): 3326 (s), 2,927 (m), 1,611 (s), 1,417 (s), 1,336 (s),
1,174. (w), 1,032 (s), 909 (m), 720 (m), 594 (m).
X-ray crystallography
Crystal data and experimental details for polymers 1–3 are
given in Table 1. All measurements were made on a Bruker
smart APEXII CCD diffractometer with a graphite-mono-
chromated imaging plate area detector and Mo-Ka radiation
˚
(k = 0.71073 A). Suitable single crystals were selected and
mounted on a glass fiber. All data were collected at room
temperature using the x-2h scan technique and corrected
for Lorenz-polarization effects. A correction for secondary
extinction was also applied. The three structures were
solved by direct methods and expanded using the Fourier
Results and discussion
˚
Table 2 Selected bond lengths (A) and angles (deg) for 1–3
Synthesis of the complexes
1
Cu(1)–O(5)
Cu(1)–O(3)
Cu(1)–O(1)
1.951(3)
1.993(4)
2.394(5)
Cu(1)–O(4)
1.958(3)
2.005(4)
Organic ligands of low molecular weight are frequently
utilized as ancillary ligands in the crystal engineering,
especially for N-donor molecules. However, ligands con-
taining both carboxylic and hydroxyl functional groups are
superior owing to their potential chelating capacity [23–25].
In this work, we used glycolate as a single ligand to explore
its ability to construct coordination compounds. Polymers
1–3 have been synthesized under hydro(solvo)thermal
conditions with a solvent mixture solvent of ethanol and
water (v/v 7:1). We chose this solvent composition based on
the analyses of the construction of MOFs [25–29]. Solvent
volume ratio of 7:1 (ethanol: water) for 1–3 has been used,
and the suitable crystals for X-ray diffraction can be suc-
cessfully isolated. The results indicate that formation of the
frameworks of 1–3 is considerably influenced by the nature
of the solvent.
Cu(1)–O(6)
O(5)–Cu(1)–O(4)
93.09(12)
84.92(13)
177.54(18)
89.37(19)
95.26(19)
O(5)–Cu(1)–O(3) 174.99(17) O(4)–Cu(1)–O(3)
O(5)–Cu(1)–O(6)
O(3)–Cu(1)–O(6)
O(4)–Cu(1)–O(1)
O(6)–Cu(1)–O(1)
84.78(17) O(4)–Cu(1)–O(6)
97.11(16) O(5)–Cu(1)–O(1)
91.39(16) O(3)–Cu(1)–O(1)
89.80(19)
2
Cu(1)–O(4)
Cu(1)–O(5)
1.943(3)
1.989(3)
Cu(1)–O(7)
Cu(1)–O(8)
1.946(3)
1.998(3)
O(4)–Cu(1)–O(7) 176.70(12) O(4)–Cu(1)–O(5)
94.37(13)
85.39(13)
178.13(15)
O(7)–Cu(1)–O(5)
O(7)–Cu(1)–O(8)
84.87(13) O(4)–Cu(1)–O(8)
95.26(13) O(5)–Cu(1)–O(8)
3
Cd(1)–O(7)
2.236(3)
2.322(3)
2.377(2)
Cd(1)–O(10)
Cd(1)–O(9)
Cd(1)–O(3)
2.287(2)
2.372(3)
Cd(1)–O(4)
In addition, two distinct structures, namely a one-
dimensional polymer 1 and two-dimensional polymer 2,
were obtained at 160 ꢁC for 72 h and 120 ꢁC for 96 h,
respectively. It may be concluded that reactions at relatively
low temperature with long reaction times favor this outcome.
Cd(1)–O(10)#1
2.383(3)
O(7)–Cd(1)–
O(10)
96.05(10) O(7)–Cd(1)–O(4)
89.22(10) O(7)–Cd(1)–O(9)
141.10(10) O(4)–Cd(1)–O(9)
148.31(10)
O(10)–Cd(1)–
O(4)
100.41(11)
94.64(12)
71.93(10)
69.96(10)
O(10)–Cd(1)–
O(9)
Crystal structures of polymers 1 and 2
O(7)–Cd(1)–
O(10)#1
126.83(9)
O(10)–Cd(1)–
O(10)#1
A single-crystal X-ray diffraction analysis reveals that
polymer 1 belongs to the orthorhombic system with space
group P2(1)2(1)2(1), and polymer 2 possesses a two-
dimensional structure crystallizing in the monoclinic space
group P2(1)/n.
O(4)–Cd(1)–
O(10)#1
84.51(10) O(9)–Cd(1)–
O(10)#1
O(7)–Cd(1)–O(3)
O(4)–Cd(1)–O(3)
78.78(9)
O(10)–Cd(1)–O(3) 121.59(10)
71.95(10) O(9)–Cd(1)–O(3)
151.84(9)
96.20(11)
O(10)#1–Cd(1)–
O(3)
As shown in Fig. 2a, the asymmetric unit contains one Cu
-
center, two anionic HOCH2CO2 ligands, and one water
ligand. The Cu2? center exhibits a distorted octahedral
Symmetry transformations used to generate equivalent atoms for 3:
#1: -x ? 1, -y, -z ? 2
CuO6 coordination environment. The glycolate ligands
123

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Transition Met Chem (2013) 38:503–509
µ2- HOCH2CO2
η2-HOCH2CO2
µ2- HOCH2CO2
-
-
-
a
b
c
-
Fig. 1 Coordination modes of HOCH2CO2 anions in polymers 1–3
Fig. 2 a View of coordination
arrangement of Cu center in 1.
b Ball-and-stick representation
of the 1-D zigzag chain (H
atoms omitted for clarity)
present two different coordination modes: l2-g1:g1:g1
(Fig. 1a) and g2 (Fig. 1b). The bonded oxygen atoms, O3,
O4 and O5, O6 from two bidentate glycolate ligands,
comprise an approximate plane through the Cu center (the
dihedral angle between planes O3–Cu1–O4 and O5–Cu1–
bonds. The hydrogen bond distances are in the range of
˚
2.7–3.5 A and weak hydrogen-bonding interactions exist
˚
between two reverse chiral layers (O6–O1#1water = 3.5 A,
symmetry code: #1 x ? 1, y, z).
For polymer 2, the Cu(II) center is coordinated by six
-
oxygen atoms from anionic HOCH2CO2 ligands, which
˚
O6 is 4.7ꢁ) and the Cu–O distances range from 1.9 to 2.0 A.
The bond lengths of Cu1–O7B and Cu1–O1water are 2.7 and
all adopt one kind of coordination, l2-g1:g1:g1 (Fig. 1a).
Compared with the [CuO6] unit in polymer 1, the octahe-
dral unit of 2 shown in Fig. 3a is slightly distorted. The
dihedral angle between planes O5–Cu1–O7 and O4–Cu1–
O8 is 3.6ꢁ, and the four bond distances vary from 1.9 to
˚
2.4 A, respectively, and the angle O1–Cu1–O7B is 171.5ꢁ.
-
A zigzag chain results from the linkage of l2-HOCH2CO2
anions, and the uninvolved g2-HOCH2CO2- anions occupy
alternate sites beside the chain. As depicted in Fig. 2b, the
distance between the intrachain neighboring metal centers is
˚
2.0 A. The bond lengths of Cu–O along the vertical axis
˚
˚
are 2.6 and 2.8 A, corresponding to O10B–Cu1 and O9C–
5.3 A and the Cu–Cu–Cu angle is 58.6ꢁ. Hydrogen-bonding
interactions play an important role in the packing of the
solid-state architecture (Fig. S1, Supplementary Data). The
three-dimensional network is made up of right-handed and
left-handed layers connected by intermolecular hydrogen
Cu1, respectively. The surrounding bond angles of O–Cu–
O0 (where O and O0 are adjacent atoms) are in the range of
80.5–95.3ꢁ. As displayed in Fig. 3b, the chain is close to a
straight line with the angle formed by Cu–Cu–Cu being
123

Transition Met Chem (2013) 38:503–509
507
Fig. 3 a The coordination
environment of Cu center in 2.
b Zigzag chain
[Cu(HOCH2CO2)]n (H atoms
omitted for clarity). c 2-D layer
extended in ab plane composed
of the parallel 1-D chains
-
connected by l2-HOCH2CO2
171.4ꢁ. The neighboring metal centers present two dis-
layer, with only a coordination mode for the l2-
HOCH2CO2 ligands. Both polymers are stabilized by
-
˚
tances of 5.5 and 5.2 A, which may account for the linkage
of HOCH2CO2- ligands that are alternatively placed on the
hydrogen-bonding interactions and constructed from the
R-handed and L-handed chiral layers.
two sides.
Distinct from the 1-D polymer 1, polymer 2 incorporates
a two-dimensional sheet (Fig. 3c). The layer shown in the
ab plane contains infinite rhombus grids (the lengths of the
Crystal structure of polymer 3
˚
side being 5.5 or 5.2 A), which results in a 3-D solid-state
The single-crystal X-ray diffraction analysis reveals that
polymer 3 crystallizes in the monoclinic system with space
group P2(1)/c. Similar to polymer 2, the asymmetric unit
contains two anionic ligands binding the Cd2? center
(Fig. 4a): two bidentate glycolate ligands and another two
monodentate glycolates. Besides the mode l2-g1:g1:g1
(Fig. 1a), one HOCH2CO2 ligand displays another coor-
dination mode, namely l2-g1:g2:g0 (Fig. 1c). O4 and O9
come from two hydroxyl groups, with the bond lengths to
framework with the help of intermolecular hydrogen
bonds. Three kinds of H-bonds exist in the polymer: O(5)–
H(5)…O(7)#1, O(5)–H(5)…O(7)#2, O(8)–H(8)…O(10)#3
(symmetry codes: #1: x, y ? 1, z; #2: -x ? 1/2, y ? 1/2,
-z ? 1/2; #3: x ? 1/2, -y-1/2, z ? 1/2), of which the
last group, as shown in Fig. S2, bridges the neighboring
R-handed and L-handed chiral layers to stabilize the crystal
-
˚
architecture (the donor…acceptor distance being 3.2 A).
Polymer 2 is obtained by substituting one HOCH2CO2
-
˚
Cd(II) being 2.3 and 2.4 A, respectively, and the O4–Cd1–
ligand for a water molecule from polymer 1. Both the
distortions may derive from the electron configuration of
the Cu2? cation, d9, due to the Jahn–Teller effect, and the
octahedron is stretched [30, 31]. The asymmetrically
coordinated oxygen atoms also contribute to the distortion
in polymer 1. Meanwhile, the substitution of the water
ligand should favor the formation of a two-dimensional
O9 angle is 94.6ꢁ. Another four carboxylato oxygen atoms
complete the distorted octahedron, with the distances of
˚
Cd–O varying from 2.2 to 2.4 A which are in the expected
range [32]. As shown in Fig. 4b, c, the 2-D layer is con-
structed from infinite chains of l2-g1:g1:g1-HOCH2CO2
ligands. The selected 1-D chain shown in Fig. 4b could be
-
-
described as—{(HOCH2CO2 )1a{[Cd2(HOCH2CO2 )1c]2}
-
123

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Transition Met Chem (2013) 38:503–509
Fig. 4 a The coordination
environment of Cd in 3. b The
straight chain
[Cd(HOCH2CO2)]n (H atoms
omitted for clarity). c 2-D layer
extended in bc plane composed
of infinite 1-D chains bridged by
-
l2-HOCH2CO2
-
(HOCH2CO2 )1a}n—, in which the subunits [Cd2(HOCH2-
-
CO2 )1c]2 arrange in horizontal and vertical axes, one after
˚
another, with the Cd…Cd distance being 3.8 A. Figure S3
exhibits the solid-state three-dimensional architecture along
the b-axis. The parallel layers are linked by intermolecular
hydrogen bonds, comparable with those observed in poly-
˚
mers 1 and 2 (O(4)–H(4)…O(1)#4: 2.9 A; O(9)–H(9)…O(1)
˚
#4: 3.2 A symmetry code: #4 -x, -y, -z ? 2).
Thermogravimetric analyses
Thermogravimetric analyses were carried out in order to
investigate the thermal stabilities of polymers 1–3 within
the range of 30–850 ꢁC in air (Fig. 5). The TG curve of
polymer 1 presents an initial weight loss of 8 % from 125
to 228 ꢁC, which is ascribed to the release of one water
ligand (calculated 7.8 %). Then, the decomposition of the
glycolate ligands begins, and the remaining CuO residue
accounts for 34.6 % (calculated 34.8 %). Polymers 2 and 3
show similar thermal behavior owing to their similar
structures. Polymer 2 is thermally stable until 93 ꢁC. Then,
Fig. 5 The TG curves for polymers 1–3
the degradation process starts with a large weight loss on
the TG curve in one step. The thermal decay is finished at
403 ꢁC, leaving a solid residue of CuO (found 34.9 %,
calculated 37.7 %). The polymer 3 is thermally stable up to
228 ꢁC, then the whole framework begins to collapse upon
123

Transition Met Chem (2013) 38:503–509
509
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charge on application to CCDC, 12 Union Road, Cam-
bridge CB2 IEZ, UK (Fax: ?44 1223 336 033; E-mail:
deposit@ccdc.cam.ac.uk).
¨
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Acknowledgments We gratefully acknowledge the financial sup-
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Autonomous Region (NJ10245).
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