Synthesis and crystal structures of ZnCl2 and CdCl2 containing helical coordination polymers derived from a flexible bis(pyridylurea) ligand

Article abstract of DOI:10.1016/j.ica.2018.01.028

A flexible bis(pyridylurea) ligand, 1,1′-[oxybis(2,1-phenylene)] bis(3-pyridin-3-ylurea) (L), has been synthesized and characterized. The interaction of L with ZnCl₂ and CdCl₂ has been investigated. In the structure of {[ZnLCl₂]·2DMF}_n (1), the flexible ligands bridge the Zn^II centers to form 1D helical chains with a pitch of 9.743 ?. The P and M helical chains are arranged equally, and the whole complex 1 is racemic. In the structure of [CdLCl₂(DMF)]_n (2), the flexible ligands bridge Cd^II centers to form one-dimensional P and M helical chain structures in a similar manner. Then the chlorine atoms act as bridges in bidentate modes linking the P helical chain with M helical chain to form a 1D looped chain coordination polymer.

Full text of DOI:10.1016/j.ica.2018.01.028

Inorganica Chimica Acta 476 (2018) 123–128
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Synthesis and crystal structures of ZnCl and CdCl containing helical
2
2
coordination polymers derived from a flexible bis(pyridylurea) ligand
⇑
Chao Huang, Xian-Mei Yi, Dong-Mei Chen, Bi-Xue Zhu
Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang 550025, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
0
Article history:
A flexible bis(pyridylurea) ligand, 1,1 -[oxybis(2,1-phenylene)] bis(3-pyridin-3-ylurea) (L), has been syn-
thesized and characterized. The interaction of L with ZnCl and CdCl has been investigated. In the struc-
ture of {[ZnLCl (1), the flexible ligands bridge the Zn centers to form 1D helical chains with a
]ꢀ2DMF}
pitch of 9.743 Å. The P and M helical chains are arranged equally, and the whole complex 1 is racemic. In
Received 1 September 2017
Received in revised form 22 January 2018
Accepted 26 January 2018
2
2
II
2
n
II
2 n
the structure of [CdLCl (DMF)] (2), the flexible ligands bridge Cd centers to form one-dimensional P and
M helical chain structures in a similar manner. Then the chlorine atoms act as bridges in bidentate modes
linking the P helical chain with M helical chain to form a 1D looped chain coordination polymer.
Ó 2018 Elsevier B.V. All rights reserved.
Keywords:
Pyridylurea
Bidentate
Coordination polymer
Helical chain
Racemic
1
. Introduction
{[ZnLCl
CdLCl
2
]ꢀ2DMF}
n
(1) and 1D looped chain coordination polymer
[
2
(DMF)] (2).
n
The synthesis of coordination polymers has attracted much
2
. Experimental
interest in recent years not only because of their intriguing struc-
tures, but also for their potential applications in functional solid
materials, ion exchange, catalysis, and gas adsorption [1–6], etc.
The design strategy for novel self-assembled structures is based
on the presence of suitable metal-ligand interactions and
2.1. Materials and physical measurements
All commercially available chemicals were of reagent grade and
used without further purification. All solvents were purified by
conventional methods before use. Elemental analysis was obtained
from a Vario EL III elemental analyzer. H NMR spectra was
recorded in DMSO-d
ter. IR spectra was measured as KBr pellets on a Bio-Rad FTIR
instrument at the range of 4000–400 cm . The crystal structure
was determined by Bruker Smart Apex Ⅱ CCD and SHELXL crystal-
lographic software of molecular structure.
supramolecular contacts (hydrogen bonding and
p p stacking
ꢀ ꢀ ꢀ
interactions) [7–11]. The flexible ligands could adopt different
coordination modes by adjusting their conformation, length, or
inherent angle of the terminal coordinative groups, thus leading
to fascinating structures of the metal organic frameworks (MOFs)
1
6
using a JEOL ECX 400 MHz NMR spectrome-
ꢁ
1
[
12–14]. The pyridyl moiety has been proved to be the most pop-
ular building block for the construction of metal–organic networks
due to its strong coordination ability to metal ions. Among them,
the bis(pyridylurea) ligands with both rigid and flexible bridges
are ideal units for the construction of various coordination
polymers, such as metallomacrocycles, helical chains, and layered
networks [15–23].
2
2
.2. Synthesis
.2.1. Synthesis of 1,1 -[oxybis(2,1-phenylene)] bis(3-pyridin-3-
0
0
ylurea) (L)
L. Nicotinic acid acyl azide and bis(2-aminophenyl) ether were
synthesized according to previous literatures [24–26], respectively.
A solution of nicotinic acid acyl azide (1.04 g, 7.0 mmol) in toluene
In this work, the flexible ligand 1,1 -[oxybis(2,1-phenylene)]
bis(3-pyridin-3-ylurea) (L) was synthesized by the reaction of
3
-isocyanato-pyridine and bis(2-aminophenyl) ether (Scheme 1).
Reaction of with ZnCl or CdCl in DMF/MeOH solution
resulted in the formation of 1D helical chain coordination polymer
L
2
2
(
30 mL) was refluxed under nitrogen for 1.5 h, and bis(2-amino-
phenyl) ether (0.60 g, 3.0 mmol) in acetonitrile (30 mL) was added
dropwise. The mixture was stirred for another 1.5 h and cooled
to room temperature. The precipitate that formed was
collected by filtration and purified by recrystallization from
⇑
Corresponding author.
E-mail address: bxzhu@gzu.edu.cn (B.-X. Zhu).
https://doi.org/10.1016/j.ica.2018.01.028
020-1693/Ó 2018 Elsevier B.V. All rights reserved.
0

1
24
C. Huang et al. / Inorganica Chimica Acta 476 (2018) 123–128
Scheme 1. Synthesis of the bis(pyridylurea) ligand.
Table 1
Crystal data and structure refinement for the ligand, complexes 1 and 2.
Compound
L
Complex 1
34Cl
722.92
Monoclinic
P2 /n
10.832(3)
9.743(3)
32.396(10)
93.993(5)
3410.6(17)
4
Complex 2
27Cl
696.85
Monoclinic
P2 /c
10.100(16)
9.139(14)
42.820(7)
92.038(3)
3950.1(11)
4
Empirical formula
Formula weight
Crystal system
Space group
a/(Å)
C
24
H
20
6
N O
3
C
30
H
N
2 8
O
5
Zn
C
27
H
2 7 4
N O Cd
440.46
Monoclinic
P2 /c
10.899(4)
14.206(5)
14.242(5)
105.238(8)
2127.7(13)
4
1
1
1
b/(Å)
c/(Å)
b/(°)3
V/(Å )
Z
D
/(gꢀcmꢁ3)
1.375
1.408
1.172
c
h range/(°)
1.94 ꢂ 25.00
1.26 ꢂ 26.00
0.95 ꢂ 27.83
ꢁ
1
Absorption coefficient/mm
0.095
0.927
0.722
F(0 0 0)
920
1496
1408
Reflections collected
Independent reflections
10,650
3732
29,034
6683
36,172
9305
Observed reflections (I > 2
Number of parameters
Goodness-of-fit on F2
r(I))
2273
298
1.078
4933
415
1.078
6527
372
1.030
Final R indices (I > 2
r
(I))
R
R
1
= 0.0590, wR
= 0.1029, wR
2
= 0.1705
= 0.1898
R
R
1
= 0.0548, wR
= 0.0763, wR
2
2
= 0.1593
= 0.1702
R
R
1
= 0.0461, wR
= 0.0688, wR
2
= 0.1230
= 0.1388
R indices (all data)
1
2
1
1
2
Largest diff. Peak and hole (e Åꢁ3)
0.496 and ꢁ0.209
0.894 and ꢁ0.489
0.461 and ꢁ0.529
CH
3
OH/DMF(V: V = 2:1) to give a white solid. Yield: 1.07 g, 81%;
(%) for C27
46.60, H 3.96, N 14.01. FT-IR (KBr pellet,
1714 (s, CO), 1606 (s, NH).
H
27Cl
2
N
7
O
4
Cd: C 46.54, H 3.91, N 14.07; found(%): C
1
ꢁ1
mp: 285 ꢂ 286 °C. H NMR (DMSO-d
6
, 400 MHz): d 6.84 (d, 2H,
m
/cm ): 3354 (m, NH),
J = 7.6 Hz, Ar-H), 7.02 (t, 2H, J = 5.2 Hz, Ar-H), 7.18 (t, 2H, J = 5.6
Hz, Ar-H), 7.36 (dd, 2H, J = 2.8 Hz, Ar-H), 7.99 (m, 2H, Py-H), 8.23
2.3. Crystallographic data collection and structure determination
(
d, J = 2.8 Hz, 2H, Py-H), 8.35 (d, J = 6.8 Hz, 2H, Py-H), 8.61 (s, 2H,
13
Py-H), 8.75 (s, 2H, CONH), 9.52 (s, 2H, CONH). C NMR (DMSO-
, 400 MHz): d 152.98, 145.76, 143.53, 140.33, 136.81, 131.60,
25.47, 124.64, 124.15, 123.20, 120.23, 118.38. Anal. Calcd(%) for
: C 65.45, H 4.58, N 19.08; found(%): C 65.49, H 4.62,
The single-crystal X-ray diffraction was performed on a Bruker
Smart Apex Ⅱ CCD diffractometer. Intensities of reflections were
measured using Mo K monochromatized radiation (k = 0.71 073
Å) at 293(2) K. Data reductions and absorption corrections were
performed using the SAINT and SADABS software packages, respec-
tively. The structures were solved by direct methods and refined by
d
6
1
C
a
24
20 6 3
H N O
ꢁ1
N 19.03. FT-IR (KBr pellet, m/cm ): 3344 (m, NH), 1715 (s, CO),
+
+
1
599 (s, NH). ESI-MS: m/z = 441 [M+H] , 463 [M+Na] .
2
full-matrix least-squares methods on F using the SHELXS-97 and
2.2.2. Synthesis of Zn(II) and Cd(II) complexes
SHELXL-97 [27] programs. Anisotropic thermal factors were
assigned to all the non-hydrogen atoms. Crystal data and structure
refinement parameters are listed in Table 1. Selected bond lengths
and angles for the two complexes are listed in Table 4.
{
[ZnLCl (1). ZnCl (136 mg, 1 mmol) in methanol (20
2
]ꢀ2DMF}
n
2
mL) was added dropwise with stirring to L (440 mg, 1 mmol) in
DMF (20 mL) and stirring was continued at room temperature for
3
h. The initial white precipitate that formed was filtered off. The
filtrate was allowed to evaporate slowly at room temperature to
yield colorless single crystals that proved suitable for X-ray analy-
sis. The crystalline product was washed and dried under vacuum
3. Results and discussion
before analysis. Yield, 42%. Anal. Calcd. (%) for C30
H34Cl
2
N
8
O
5
Zn:
3.1. X-ray structures
C 49.84, H 4.74, N 15.50; found (%): C 49.88, H 4.69, N 15.56. FT-
ꢁ
1
IR (KBr pellet,
m
/cm ): 3335 (m, NH), 1711 (s, CO), 1598 (s, NH).
(2). CdCl O (228 mg, 1 mmol) in metha-
ꢀ2.5H
3.1.1. Crystal structure of the ligand
Suitable single crystals of free ligand were obtained from
MeOH/DMF(1:1 v/v) solution via slow evaporation. The crystal
[
CdLCl (DMF)]
2
n
2
2
nol (30 mL) was added dropwise with stirring to L (440 mg, 1
mmol) in DMF (20 mL) and stirring was continued at room temper-
ature for 2 h. The solution was filtered off and left for slow evapo-
ration at room temperature. X-ray quality block-shaped colorless
crystals were obtained after 5 days. The crystals were collected
by filtration, washed with methanol, and dried at room tempera-
ture to give complex 2 as a white solid in 38% yield. Anal. Calcd.
1
belongs to the centrosymmetric monoclinic space group P2 /c
and its asymmetric unit is comprised of a fully occupied ligand
(Fig. 1a). The dihedral angle between the two aromatic rings is
88.05°. The dihedral angles between the central aromatic rings
and the neighboring urea moieties are found to be 11.84 and
1.47°, and between urea moieties and the terminal pyridyl rings

C. Huang et al. / Inorganica Chimica Acta 476 (2018) 123–128
125
Fig. 1. (a) Molecular structure of the ligand; (b) The hydrogen bonds and p–p stacking interaction in the ligand. Non-urea hydrogen atoms are omitted for clarity; (c) Layered
structure in the ab plane formed by NAHꢀ ꢀ ꢀN bonds and
p–
p
stacking interaction.
Table 2
Hydrogen bonding distances (Å) and angles (°) for the ligand.
D–Hꢀ ꢀ ꢀA
D–H(Å)
Hꢀ ꢀ ꢀA(Å)
Dꢀ ꢀ ꢀA(Å)
\DHA
Symmetry code
#
#
1
1
N2–H2Aꢀ ꢀ ꢀN6
N3–H3Aꢀ ꢀ ꢀO2
N3–H3Aꢀ ꢀ ꢀN6
N4–H4ꢀ ꢀ ꢀO2
0.8600
0.8603
0.8603
0.8603
0.8603
0.8596
0.9298
0.9303
0.9295
0.9297
0.9307
2.0787
2.1930
2.3234
2.2664
2.3167
2.1178
2.2982
2.3481
2.4125
2.3573
2.2943
2.919(3)
2.620(3)
3.124(3)
2.661(3)
3.125(4)
2.959(4)
2.914(4)
2.941(5)
3.313(4)
2.932(4)
2.908(4)
165.48
110.40
2 ꢁ x, ꢁ1/2 + y, 1/2 ꢁ z
0
155.00
107.95
156.58
165.80
123.32
121.34
163.27
119.76
123.03
2 ꢁ x, ꢁ1/2 + y, 1/2 ꢁ z
#
2
N4–H4ꢀ ꢀ ꢀN1
1 ꢁ x, 1 ꢁ y, ꢁz
1 ꢁ x, 1 ꢁ y, ꢁz
#
2
N5–H5Aꢀ ꢀ ꢀN1
C5–H5ꢀ ꢀ ꢀO1
C8–H8ꢀ ꢀ ꢀO1
#
3
C11–H11ꢀ ꢀ ꢀO3
C17–H17ꢀ ꢀ ꢀO3
C21–H21ꢀ ꢀ ꢀO3
2 ꢁ x, 1 ꢁ y, 1 ꢁ z
are 9.90 and 1.59°. Each ligand molecule is found to be associated
with three neighboring ligand molecules via NAHꢀ ꢀ ꢀN hydrogen
bonding between the pyridyl N atoms and the urea N atoms. Fur-
and two nitrogen donors from pyridine rings belonging to different
ligands. The Zn1–N6 and Zn1–N1a bond lengths are 2.059(3) and
2.078(3) Å. The Zn1–Cl1 and Zn1–Cl2 bond lengths are 2.2092
(12) and 2.2215(12) Å. The N–Zn–Cl bond angles are in the range
of 104.25(9)–114.63(9), which are distorted from the ideal tetrahe-
dral geometry as a consequence of the opening of the two chloro
ligands. The bond angles for Cl1–Zn–Cl2 and N6–Zn–N1a are
123.99(5) and 95.69(12), respectively, which are consistent with
those found in similar complexes. The two DMF solvents are
bonded to the urea nitrogen atoms via four NAHꢀ ꢀ ꢀO hydrogen
bonding (Nꢀ ꢀ ꢀO@2.7603–3.2391 Å) (Fig. 2b). The flexible ligand in
thermore,
dyl ring and the aromatic ring with the face-to-face distance of ca.
.69 and 3.82 Å (Fig. 1b). Through these NAHꢀ ꢀ ꢀN hydrogen bond-
ings and stacking interactions, the structure is linked into a
two-dimensional sheet in the ab plane (Fig. 1c) (Table 2).
p–p stacking interactions are formed between the pyri-
3
p–p
3.1.2. Crystal structure of complex 1
Slow evaporation of a solution of ZnCl
2
and L in MeOH–DMF
]ꢀ2DMF} (1). Complex
/n. The asymmetric
II
afforded colorless block crystals of {[ZnLCl
2
n
complex 1 bridges the Zn centers to form 1D helical chains run-
1
crystallizes in the monoclinic space group P2
1
ning along the b axis with a pitch of 9.743 Å (Fig. 2c). The P and
M helical chains are equally arranged, and each helical chain shows
the opposite helicity to the neighboring chain so that the whole
complex 1 is racemic. In the extended structure of 1, each helical
II
unit comprises a independent Zn center, two chlorine ions, a
ligand L, and two solvent DMF molecules (Fig. 2a). In the crystal
structure, the zinc centers are each bound to two chlorine ions
Fig. 2. (a) Coordination environments of the Zn atom in complex 1. H atoms and lattice DMF molecules are omitted for clarity; (b) NAHꢀ ꢀ ꢀO hydrogen bonds between the urea
N atoms and DMF molecules; (c) Racemic helical chains in complex 1; (d) Racemic helices viewed along the b axis in complex 1. Symmetry codes: a) 2 ꢁ x, 1 ꢁ y, 1 ꢁ z.

1
26
C. Huang et al. / Inorganica Chimica Acta 476 (2018) 123–128
Fig. 3. (a) Coordination environments of the Cd atom in complex 2. H atoms are omitted for clarity; (b) 1D looped chain structure of complex 2 containing both P and M
helical chains; (c) top view along the b axis in complex 2. Symmetry codes: a) x, 2 + y, z; b) 2 ꢁ x, 2 ꢁ y, 1 ꢁ z.
chain forms CAHꢀ ꢀ ꢀCl and CAHꢀ ꢀ ꢀO hydrogen bonds with the
3.2. Powder X-ray diffraction (PXRD)
neighboring chains (Fig. 2d).
In order to check the phase purity of the two complexes, the
powder X-ray diffraction (PXRD) patterns of complex 1 and 2 were
measured at room temperature. As shown in Fig. 4, the peak posi-
tions of the simulated and as-synthesized PXRD patterns are in
agreement with each other, demonstrating a good phase purity
of the two complexes. The difference in reflection intensities
between the simulated and experimental patterns was due to the
variation in crystal orientation [31,32] or particle size for the pow-
der sample.
3
.1.3. Crystal structure of complex 2
The reaction of L and CdCl in MeOH–DMF (v/v 2:1) gave the
complex [CdLCl (DMF)]n (2) as colorless block crystals. Complex
crystallizes in the monoclinic space group P2 /c. The asymmetric
2
2
2
1
unit of 2 consists of one Cd(II) atom, two chlorine anions, one inde-
pendent ligand, and one coordinated DMF molecule (Fig. 3a). The
cadmium atom is six-coordinated by two nitrogen atoms from
two pyridine ring of two different pyridylurea ligands, an oxygen
atom from a DMF molecule, two bridged chlorine atom (Cl2,
Cl2a) and a terminal chlorine atom (Cl1) in a slightly distorted
octahedral geometry. Atoms N(1), N(6b), Cl(2) and Cl(2a) consti-
tute the basal plane of the octahedron, and atoms O(4) and Cl(1)
are located at the axial positions [28–30]. All the ligands act as
bis(monodentate) bridging ligand linking the Cd(II) ions to form
a one-dimensional P and M helical chain structure alternatively.
Then the chlorine atoms act as bridges in bidentate modes linking
the P helical chain with the M helical chain to form a 1D looped
chain coordination polymer (Fig. 3b). The coordination polymer
can be considered as a PM type double chain, and each chain shows
the same helicity to neighboring double chains. The Cd–Cd dis-
tance from one Cd atom to its nearest neighbor through the pyridy-
3.3. TG analyses of the complexes
In order to examine the thermal stability of two complexes, TGA
experiments for the two complexes were performed between
30 and 800 °C in the N
2
atmosphere at the heating rate of
ꢁ
1
10 °Cꢀmin (Fig. 5). The TG analyses of complex 1 showed a slight
weight loss from room temperature to 295 °C corresponding to the
release of DMF molecules (observed weight loss 18.1%, calculated
20.1%), as well as a major weight loss occurring at above 300 °C
due to the decomposition of the organic ligand. The TGA curve
showed complex 2 is stable below 260 °C. Upon further heating,
an obvious weight loss (84%) occurs in the temperature range of
260–320 °C, which is corresponding to the loss of coordinated
DMF molecules and the decomposition of the organic framework.
TGA experiments suggest that complex 2 is more stable than
lurea ligand in the [CdLCl(DMF)]
distance between the two Cd atoms bridged by chloride atoms is
.900 Å (Table 3).
n
chain is 9.139 Å, while the
3
Table 3
Hydrogen bonding distances (Å) and angles (°) for complex 1.
D–Hꢀ ꢀ ꢀA
D–H(Å)
Hꢀ ꢀ ꢀA(Å)
Dꢀ ꢀ ꢀA(Å)
\DHA
Symmetry code
#
#
4
4
N2–H2ꢀ ꢀ ꢀO4
N3–H3ꢀ ꢀ ꢀO2
N3–H3ꢀ ꢀ ꢀO4
N4–H4ꢀ ꢀ ꢀO2
N4–H4ꢀ ꢀ ꢀO5
N5–H5ꢀ ꢀ ꢀO5
0.8599
0.8599
0.8599
0.8599
0.8599
0.8601
0.9300
0.9300
0.9300
0.9300
0.9301
0.9301
0.9299
0.9599
1.9132
2.2635
2.3228
2.1787
2.4870
1.9817
2.7457
2.3669
2.3382
2.5407
2.3390
2.4102
2.4169
2.7658
2.7603
2.6680
3.0981
2.6045
3.2391
2.8277
3.6219
2.9217
2.9199
3.4521
2.9213
2.9340
3.3318
3.7128
168.07
108.81
150.10
110.26
146.52
167.60
157.40
118.03
120.29
166.57
120.35
115.56
167.88
169.10
ꢁ1 + x, y, z
ꢁ1 + x, y, z
#
5
C2–H2Aꢀ ꢀ ꢀCl2
C3–H3Aꢀ ꢀ ꢀO1
C8–H8ꢀ ꢀ ꢀO1
1/2 ꢁ x, ꢁ1/2 + y, 1/2 ꢁ z
ꢁx, 2 ꢁ y, ꢁz
#6
C11–H11ꢀ ꢀ ꢀO3
C17–H17ꢀ ꢀ ꢀO3
C21–H21ꢀ ꢀ ꢀO3
C22–H22ꢀ ꢀ ꢀO1
#7
ꢁ1 + x, 1 + y, z
#8
C29–H29Bꢀ ꢀ ꢀCl2
1/2 ꢁ x, 1/2 + y, 1/2 ꢁ z

C. Huang et al. / Inorganica Chimica Acta 476 (2018) 123–128
127
Table 4
Selected bond distances (Å) and angles (°) for complexes 1 and 2.
Complex 1
N6–Zn1
2.059(3)
Cl2–Zn1
2.2215(12)
Zn1–N1a
2.078(3)
Cl1–Zn1
2.2092(12)
95.69(12)
104.92(9)
N6–Zn1ꢁN1a
N6–Zn1ꢁCl2
Complex 2
Cd1–Cl2a
N6–Zn1ꢁCl1
N1a–Zn1ꢁCl2
114.63(9)
109.67(9)
N1a–Zn1ꢁCl1
Cl1–Zn1ꢁCl2
104.25(9)
123.99(5)
2.6560(10)
2.323(3)
84.27(3)
89.80(7)
79.64(10)
172.42(8)
90.95(7)
Cd1–Cl2
Cd1–N6b
2.6041(9)
2.441(3)
102.37(3)
93.42(7)
82.86(10)
90.71(8)
85.73(8)
Cd1–Cl1
Cd1–N1
2.5425(11)
2.404(3)
96.69(3)
164.86(7)
92.61(8)
171.00(8)
91.19(10)
Cd1–O4
Cl2–Cd1ꢁCl2a
O4–Cd1ꢁCl2
O4–Cd1ꢁN6b
N6b–Cd1ꢁCl2a
N1–Cd1ꢁCl2a
Cl1–Cd1ꢁCl2
O4–Cd1ꢁCl2
O4–Cd1ꢁN1
N6b–Cd1ꢁCl1
N1–Cd1ꢁCl1
Cl1–Cd1ꢁCl2a
O4–Cd1ꢁCl1
N6b–Cd1ꢁCl2
N1–Cd1ꢁCl2
N1–Cd1ꢁN6b
Fig. 4. Powder X-ray diffraction patterns: as-synthesized (red) and simulated from the single-crystal diffraction data (black): (a) 1; (b) 2.
4
. Conclusion
In summary, A flexible bis(pyridylurea) ligand, 1,1 -[oxybis(2,1-
0
phenylene)] bis(3-pyridin-3-ylurea) (L), has been synthesized and
characterized. The interaction of L with Zn(II) ions and Cd(II) ions
has been investigated. In the structure of {[ZnLCl
the flexible ligands bridge the Zn centers to form 1D helical chains
with a pitch of 9.743 Å. The P and M helical chains are arranged
2
]ꢀ2DMF}
n
(1),
II
equally, and the whole complex 1 is racemic. In the structure of
II
[
CdLCl
2
(DMF)]
n
(2), the flexible ligands bridge Cd centers to form
one-dimensional P and M helical chain structures in a similar man-
ner. Then the chlorine atoms act as bridges in bidentate modes
linking the P helical chain with M helical chain to form a looped-
chain 1D coordination polymer.
Acknowledgments
Fig. 5. TGA curves of complexes 1 and 2.
This research was supported by the ‘‘Chun-Hui” Fund of Chinese
Ministry of Education (No. Z2016009), and Student’s Platform for
Innovation and Entrepreneurship Training Program (No.
201510657050).
complex 1 below 260 °C, which is mainly due to the structural dif-
ferences of their helicoidal chains.

1
28
C. Huang et al. / Inorganica Chimica Acta 476 (2018) 123–128
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at https://doi.org/10.1016/j.ica.2018.01.028.
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