A series of flexible bis(imidazole)-based coordination polymers tuned by central metal ions and dicarboxylates: Diverse structures and properties

Article abstract of DOI:10.1016/j.ica.2013.12.024

Seven new coordination polymers, namely, [Ni(L)_1.5(2-CMSN) (H₂O)]·2H₂O 1, [Co₂(L) ₂(2-CMSN)₂(H₂O)]·H₂O 2, [Cd(L)(2-CMSN)(H₂O)] 3 [Zn(L)(2-CMSN)]·2H₂O 4, [Cd(ADTZ)(H₂O)] 5, [Cd(L)(ADTZ)(H₂O)] 6, and [Zn(L)(ADTZ)]·H₂O 7 [where 2-H₂CMSN = 2-carboxymethylsulfanyl nicotinic acid, H₂ADTZ = 2,5-(s-acetic acid) dimercapto-1,3,4-thiadiazole, L = 1,4-bis(imidazol-1-ylmethyl)benzene] have been synthesized under hydrothermal conditions. The complexes were structurally characterized by single crystal X-ray diffraction analyses, infrared spectroscopy (IR), elemental analyses, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Complex 1 features a 1D ladder-like double chain. Complexes 2 and 3 exhibit the similar 2D networks based on six-nuclear metallic rings. Complex 4 is a 2D sheet. Complex 5 exhibits a 3D (4,6)-connected (4³·5³)(4⁵·5³· 6⁷) topology. Complex 6 shows a 2D undulated network with the Schla?fli symbol of (3·5²)(3²·5 ³·6⁴·7). Complex 7 is a 3D 4-fold interpenetrated dia network. Structural comparison of these polymers suggests that different central metals and dicarboxylates play important roles in the construction of 1-7. The luminescent properties of complexes 3, 4, 6, 7 and the electrochemical properties of complexes 1, 2 have been investigated. Furthermore, the complexes 2-4, 6 and 7 exhibit photocatalytic activities for dye methylene blue degradation under UV light and show good stability toward photocatalysis.

Full text of DOI:10.1016/j.ica.2013.12.024

Accepted Manuscript
A series of flexible bis(imidazole)-based coordination polymers tuned by central
metal ions and dicarboxylates: diverse structures and properties
Xiu-Li Wang, Yun Qu, Guo-Cheng Liu, Jian Luan, Hong-Yan Lin, Xiao-Min
Kan
PII:
S0020-1693(13)00677-4
http://dx.doi.org/10.1016/j.ica.2013.12.024
ICA 15784
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Revised Date:
Accepted Date:
18 November 2013
23 December 2013
24 December 2013
Please cite this article as: X-L. Wang, Y. Qu, G-C. Liu, J. Luan, H-Y. Lin, X-M. Kan, A series of flexible
bis(imidazole)-based coordination polymers tuned by central metal ions and dicarboxylates: diverse structures and
properties, Inorganica Chimica Acta (2014), doi: http://dx.doi.org/10.1016/j.ica.2013.12.024
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A series of flexible bis(imidazole)-based coordination
polymers tuned by central metal ions and
dicarboxylates: diverse structures and properties
Xiu-Li Wang∗, Yun Qu, Guo-Cheng Liu, Jian Luan, Hong-Yan Lin and
Xiao-Min Kan
Department of Chemistry, Bohai University, Liaoning Province Silicon Materials
Engineering Technology Research Center, Jinzhou 121000, P.R. China
Abstract
Seven new coordination polymers, namely, [Ni(L)1.5(2-CMSN)(H2O)]·2H2O 1,
[Co2(L)2(2-CMSN)2(H2O)]·H2O
2,
[Cd(L)(2-CMSN)(H2O)]
3
[Zn(L)(2-CMSN)]·2H2O 4, [Cd(ADTZ)(H2O)] 5, [Cd(L)(ADTZ)(H2O)] 6, and
[Zn(L)(ADTZ)]·H2O 7 [where 2-H2CMSN = 2-carboxymethylsulfanyl nicotinic acid,
H2ADTZ
=
2,5-(s-acetic
acid)
dimercapto-1,3,4-thiadiazole,
L
=
1,4-bis(imidazol-1-ylmethyl)benzene] have been synthesized under hydrothermal
conditions. The complexes were structurally characterized by single crystal X-ray
diffraction analyses, infrared spectroscopy (IR), elemental analyses, powder X-ray
diffraction (PXRD) and thermogravimetric analyses (TGA). Complex 1 features 1D
ladder-like double chains. Complexes 2 and 3 exhibit the similar 2D networks based
on six-nuclear metallic rings. Complex 4 is a 2D sheet. Complex 5 exhibits a 3D
(4,6)-connected (43·53)(45·53·67) topology. Complex 6 shows a 2D undulated network
with the Schläfli symbol of (3·52)(32·53·64·7). Complex 7 is a 3D 4-fold
interpenetrated dia network. Structural comparison of these polymers suggests that
different central metals and dicarboxylates play important roles in the construction of
1–7. The luminescent properties of complexes 3, 4, 6, 7 and the electrochemical
properties of complexes 1, 2 have been investigated. Furthermore, the complexes 2–4,
6 and 7 exhibit photocatalytic activities for dye methylene blue degradation under UV
∗ Corresponding author. Tel.: +86-416-3400158
E-mail address: wangxiuli@bhu.edu.cn (X.-L. Wang)
1

light and show good stability toward photocatalysis.
Keywords: bis(imidazole)-based ligand; N/S-containing dicarboxylate; coordination
polymer; crystal structure; fluorescent property; photocatalytic property
1. Introduction
The design and construction of coordination polymers have attracted increasing
attention in the field of crystal engineering due to their novel diverse structures and
topologies [1–3], as well as their potential applications in many areas such as catalysis
[4, 5], gas adsorption [6–8], fluorescence [9, 10] and ion exchange [11, 12]. It is
well-known that the construction of coordination polymers is dependent on many
factors, such as coordination geometry of the central metal ions [13], solvents [14],
pH values [15–17], reaction temperatures [18, 19], organic ligands [20–22]. Among
these factors, the N-donor organic ligand, as a kind of excellent building units, is one
of the most important factors, because their various flexibility, length, steric effects
and angle of coordination atoms will result in diverse structures [23, 24]. The
multicarboxylate ligands are also excellent building blocks, which can serve as good
candidates for building highly connected, self-penetrating, or helical coordination
frameworks due to their bent backbones and versatile bridging fashions [25, 26]. So
far, multicarboxylate ligands have been widely used in the construction of
coordination polymers [27, 28]. However, to our knowledge, the coordination
chemistry of N-heterocycle-S-containing dicarboxylates have received relatively less
attention [29].
As a continuous effort of our previous work [30], here we selected a flexible
N-donor ligand 1,4-bis(imidazol-1-ylmethyl)benzene (L) and two flexible
N/S-containing dicarboxylic acids 2-carboxymethylsulfanyl nicotinic acid
(2-H2CMSN) and 2,5-(s- acetic acid) dimercapto-1,3,4-thiadiazole (H2ADTZ)
(Scheme 1) as the mixed ligands to construct diverse coordination polymers based
on the following considerations: (i) The flexible L ligand can rotate to meet the
requirement of coordination geometries of metal ions in the assembly process [31]. (ii)
2-H2CMSN is an interesting flexible ligand due to its potential versatile coordinate
behavior, which possesses a pyridyl ring, a rigid carboxyl group (–COOH) and a
2

flexible S-containing carboxyl group (–SCH2COOH) [32]. H2ADTZ contains two
flexible –SCH2COOH groups and a thiadiazole ring. These two carboxylate ligands
have different bending and rotating ability, versatile coordination orientation, may
construct various architectures [33]. (iii) In addition, the nitrogen atoms of pyridyl or
thiadiazole rings and the sulfur atoms from flexible –SCH2COOH groups have
potential coordinate ability, which may also enrich the coordination modes of the
N/S-containing ligands and induce excellent structures.
As is known, central metals with different coordination environments can also
influence the final structures and topologies of the coordination polymers to some
extent [34]. In order to investigate the effect of transition metal ions on the structural
varieties of the coordination polymers, in this work, we employed different transition
metals, including Cu2+, Co2+, Ni2+, Cd2+, Zn2+ and Ag+, to react with L ligand and
2-H2CMSN or H2ADTZ under similar reaction conditions. However, we failed in the
construction of Cu2+ and Ag+ complexes, and successfully synthesized seven
coordination
polymers,
namely,
2,
[Ni(L)1.5(2-CMSN)(H2O)]·2H2O
[Cd(L)(2-CMSN)(H2O)]
1,
3,
[Co2(L)2(2-CMSN)2(H2O)]·H2O
[Zn(L)(2-CMSN)]·2H2O 4, [Cd(ADTZ)(H2O)] 5, [Cd(L)(ADTZ)(H2O)] 6, and
[Zn(L)(ADTZ)]·H2O 7. The luminescent properties of the complexes 3, 4, 6 and 7
have been investigated in the solid state. The electrochemical properties of complexes
1 and 2 have also been studied. Furthermore, complexes 2–4, 6 and 7 exhibit good
photocatalysis activity for photodegradation of MB under UV irradiation and good
stability towards UV photocatalysis.
Insert Scheme 1
2. Experimental
2.1. Materials and measurements
All chemicals purchased were of reagent grade, and used without further
purification. The 2-H2CMSN, H2ADTZ and L ligands were synthesized by the
method of the literatures [35–37]. Elemental analyses were performed on a
Perkin-Elmer 240C element analyzer. FT-IR spectra were taken on a Varian FT-IR 640
spectrometer (KBr pellets). Powder X-ray diffraction (PXRD) investigations were
3

carried out with a Ultima IV with D/teX Ultra diffractometer at 40 kV, 40 mA with Cu
Kα (λ = 1.5406 Å) radiation. Thermogravimetric data for the complexes 1–7 were
carried out on a Pyris Diamond thermal analyzer. Fluorescence spectra were recorded
at room temperature on
a
Hitachi F-4500 fluorescence/phosphorescence
spectrophotometer. A CHI 440 electrochemical workstation connected to a
Digital-586 personal computer was used for control of the electrochemical
measurements and for data collection. A conventional three-electrode system was
used with an SCE as reference electrode, a platinum wire as auxiliary electrode and
the modified electrodes as the working electrodes, respectively. UV-Vis absorption
spectra were obtained using a SP-1900 UV-Vis spectrophotometer.
2.2. Preparation of the complexes
2.2.1. [Ni(L)1.5(2-CMSN)(H2O)]·2H2O 1
A mixture of Ni(NO3)2·6H2O (0.058 g, 0.20 mmol), L (0.024 g, 0.10 mmol),
2-H2CMSN (0.022 g, 0.10 mmol) and H2O (8 mL) was placed in a 25 mL Teflon
reactor and the pH value was adjusted around 6 by addition of 0.1 M NaOH solution.
o
The mixture was heated at 100 C for 3 days, and then the autoclave was gradually
cooled to room temperature. Green block-shaped crystals of 1 were obtained in 34%
yield (based on Ni). Elemental anal.(%) Anal. Calc. for C29H32NiN7O7S: C 51.12, H
4.73, N 14.39. Found: C 51.03, H 4.65, N 14.31. IR (KBr, cm-1): 3130w, 3035w,
2932w, 2361m, 1591s, 1443m, 1373 s, 1286w, 1238m, 1157w, 1090m, 1030m, 941w,
835w, 735m, 662w.
2.2.2. [Co2(L)2(2-CMSN)2(H2O)]·H2O 2
The same synthetic method as that for 1 was used except that Ni(NO3)2·6H2O was
replaced by Co(NO3)2·6H2O (0.058 g, 0.20 mmol). Pink block-shaped crystals of 2
were obtained. Yield: 32% (based on Co). Elemental anal.(%) Anal. Calc. for
C44H42Co2N10O10S2: C 50.19, H 4.02, N 13.30. Found: C 50.03, H 4.15, N 13.35. IR
(KBr, cm-1): 3125w, 2932w, 2361m, 1595s, 1543m, 1381s, 1271w, 1232m, 1157w,
1109m, 1088m, 941w, 858w, 725m, 660w.
2.2.3. [Cd(L)(2-CMSN)(H2O)] 3
4

The same synthetic method as that for 1 was used except that Cd(NO3)2·4H2O
(0.062 g, 0.20 mmol) was used instead of Ni(NO3)2·6H2O. Yellow block-shaped
crystals of 3 were obtained. Yield: 40% (based on Cd). Elemental anal.(%) Anal. Calc.
for C22H21CdN5O5S: C 45.57, H 3.65, N 12.08. Found: C 45.33, H 3.69, N 12.15. IR
(KBr, cm-1): 3126w, 3030w, 2934w, 2361m, 1582s, 1545m, 1377s, 1297w, 1232m,
1155w, 1101m, 1076m, 937w, 832w, 737m, 656w.
2.2.4. [Zn(L)(2-CMSN)]·2H2O 4
The same synthetic method as that for 1 was used except that Ni(NO3)2·6H2O was
replaced by Zn(NO3)2·6H2O (0.059 g, 0.20 mmol). Yellow block-shaped crystals of 4
were obtained. Yield: 21% (based on Zn). Elemental anal.(%) Anal. Calc. for
C22H23ZnN5O6S: C 47.96, H 4.21, N 12.71. Found: C 47.83, H 4.29, N 12.65. IR (KBr,
cm-1): 3130w, 3052w, 2363m, 1604s, 1530 m, 1443m, 1383s, 1291w, 1240m, 1153w,
1101m, 1033m, 950w, 849w, 724m, 657w.
2.2.5. [Cd(ADTZ)(H2O)] 5
A mixture containing Cd(NO3)2·4H2O (0.062 g, 0.20 mmol), H2ADTZ (0.027 g,
0.10 mmol) and H2O (8 mL) was placed in a 25 mL Teflon reactor and the pH value
was adjusted around 6 by addition of 0.1 M NaOH solution. The mixture was heated
at 100 oC for 3 days, and then the autoclave was gradually cooled to room temperature.
Yellow block-shaped crystals of 5 were obtained in 23% yield (based on Cd).
Elemental anal.(%) Anal. Calc. for C6H5CdN2O5S3: C 18.30, H 1.28, N 7.12. Found:
C 18.38, H 1.33, N 7.05. IR (KBr, cm-1): 3494m, 2938w, 2345w, 1579s, 1410s, 1387s,
1214m, 1616w, 1053m, 930w, 904m, 776m, 682w, 618w, 542m.
2.2.6. [Cd(L)(ADTZ)(H2O)] 6
The preparation of 6 was similar to that of 5 except that L (0.024 g, 0.10 mmol)
was added to the reaction system of 5. Yellow block-shaped crystals of 6 were
obtained in 39% yield (based on Cd). Elemental anal.(%) Anal. Calc. for
C20H20CdN6O5S3: C 37.95, H 3.18, N 13.28. Found: C 37.86, H 3.26, N 13.15. IR
(KBr, cm-1): 3423w, 3117w, 2347m, 1578s, 1448m, 1380s, 1277w, 1239m, 1114m,
1038m, 955w, 860w, 712m, 618w.
2.2.7. [Zn(L)(ADTZ)]·H2O 7
5

The same synthetic method as that for 6 was used except that Cd(NO3)2·4H2O was
replaced by Zn(NO3)2·6H2O (0.059 g, 0.20 mmol). Yellow block-shaped crystals of 7
were obtained. Yield: 19% (based on Zn). Elemental anal.(%) Anal. Calc. for
C20H20ZnN6O5S3: C 40.99, H 3.44, N 14.34. Found: C 40.87, H 3.49, N 14.25. IR
(KBr, cm-1): 3431w, 3126w, 2928w, 2190m, 1595s, 1524m, 1387s, 1237m, 1089w,
1055m, 952w, 859w, 750m, 658w.
2.3. Preparation of complexes 1 and 2 bulk-modified carbon paste electrodes (CPEs)
The complexes 1 and 2 bulk-modified CPEs (1-CPE, 2-CPE) were fabricated by
mixing 0.50 g graphite powder and 0.030 g complexes 1 or 2 in an agate mortar for
approximately 30 min to achieve a uniform mixture; then 0.16 mL paraffin oil was
added and stirred with a glass rod [38]. The homogenized mixture was packed into a 3
mm inner diameter glass tube and the tube surface was wiped with weighing paper.
The electrical contact was established with the copper wire through the back of the
electrode. The bare CPE was prepared by similar process without complexes 1 and 2.
2.4. X-ray crystallographic study
Diffraction intensities for complexes 1–7 were collected using a Bruker APEX–II
CCD diffractometer equipped with graphite-monochromated Mo-Kα radiation with
radiation wavelength 0.71073 Å by using the φ−ω scan technique at 296(2) K. The
structures were solved by the direct method and refined by the Full-matrix
least-squares on F2 using the SHELXL software [39]. Non-hydrogen atoms were
refined with anisotropic temperature parameters. The hydrogen atoms of organic
ligands were generated geometrically and refined isotropically. The detailed crystal
data and structures refinement for 1–7 are summarized in Table 1. Selected bond
lengths and angles are given in Table S1–S7. Hydrogen bonding geometries of
complexes 1–4 and 6 are summarized in Table S8. CCDC 932694, 932695, 932697,
940612, 940617, 932698, and 932699 for complexes 1–7 contain the supplementary
crystallographic data in this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Insert Table 1
3. Results and discussion
6

3.1. Description of crystal structures
3.1.1. [Ni(L)1.5(2-CMSN)(H2O)]·2H2O 1
Single crystal X-ray crystallography reveals that complex 1 features 1D double
chain structure. It crystallizes in triclinic crystal system with P–1 space group. The
asymmetric unit of 1 contains one crystallographically independent Ni2+ ion, one and
a half L ligands, one 2-CMSN anion, one coordinated water molecule, and two
crystalline water molecules. As illustrated in Fig. 1a, the coordination environment
around the Ni2+ ion is composed of three nitrogen atoms (N1, N2, N6#1) from three L
ligands, one oxygen atom and one sulfur atom (O1, S1) from one 2-CMSN anion and
one coordinating water molecule (O1W). The Ni–O bond distances are 2.070(6) Å
[Ni(1)–O(1)] and 2.057(5) Å [Ni(1)–O(1W)], the Ni–N bond distances are in the
range of 2.060(6)–2.094(6) Å, and the Ni–S bond distance is 2.554(2) Å (Table S1).
Each L ligand bridges two Ni2+ ions to form a 1D ladder-like double chain with the
Ni1···Ni1A distance of 14.156(21) Å and Ni1···Ni1B distance of 13.8410(18) Å (Fig.
1b). The 2-CMSN anions are attached to both sides of the 1D ladder-like double chain
as the chelating ligands. There are O1W–H1WA···O5 intermolecular
hydrogen-bonding interactions (Table S8) in 1, which link the 1D double chains into a
2D supramolecular network (Fig. S1). Finally, the 2D supramolecular layers are
linked by π–π stacking interactions between the pyridyl rings of 2-CMSN anions to
generate a 3D supramolecular architecture [Cg–Cg 3.7119(4) Å] (Fig. S2).
Feng’s
[Ni2(2-CMSN)2(bpp)2(H2O)4]·1.5H2O
[Ni(2-CMSN)(4,4′-bipy)1.5(H2O)]·0.75H2O (bpp
group
have
reported
two
2D
and
3D
complexes
and
=
1,3-bi(4-pyridyl)-propane,
4,4′-bipy = 4,4′-bipyridine)] [32]. In the two complexes, the sulfur atoms of 2-CMSN
ligands are non-coordinated. However, in this work, we choose the same Ni2+ ion and
dicarboxylate 2-CMSN, with L as N-donor ligand instead of bpp or 4,4′-bipy, a
different 1D double chain structure was obtained, in which the sulfur atoms of
2-CMSN anions coordinated with Ni2+ ion. The different coordination geometry of
2-CMSN and diverse structures of these complexes may be attributed to N-donor
ligands with different coordination groups and different steric hindrance (changing
7

pyridyl group to imidazole group).
Insert Fig. 1
3.1.2. [Co2(L)2(2-CMSN)2(H2O)]·H2O 2 and [Cd(L)(2-CMSN)(H2O)] 3
When Co2+ and Cd2+ ion were used instead of the Ni2+ ion of 1, the similar 2D
networks based on six-nuclear metallic ring of 2 and 3 were obtained. Thus, complex
2 is employed as a representative structure to be described in detail. Single crystal
X-ray diffraction analysis reveals that complex 2 crystallizes in the triclinic space
group P–1. The asymmetric unit of 2 consists of two Co2+ ions, two L ligands, two
2-CMSN anions, one coordinated water molecule and one lattice water molecule.
Both Co1 and Co2 are six coordinate, exhibiting distorted octahedral coordination
geometries (Fig. 2a). The Co1 atom is coordinated by two oxygen atoms (O1, O2) and
one sulfur atom (S2) from two 2-CMSN anions, two nitrogen atoms (N1, N2) from
two L ligands and one coordinating water molecule (O1W). The Co2 atom is
surrounded by three oxygen atoms (O3, O8#3, O6#3) and one sulfur atom (S1#3)
from two different 2-CMSN anions and two nitrogen atoms (N3, N4) from two L
ligands. The Co–O bond distances are in the range of 1.9879(16)–2.2113(16) Å, while
the Co–N bond distances are from 2.0796(18) to 2.1228(19) Å. The Co–S bond
distances are 2.6991(6) Å [Co(1)–S(2)] and 2.6773(6) Å [Co(2)–S(1)] (Table S2). The
L ligands connect two adjacent Co2+ atoms to form a 1D wave-like [Co-L]n chain. The
2-CMSN anions adopt two types of coordination modes (Scheme 2): a
monodentate-chelating bridging mode and a bis(chelating) bridging mode. A couple
of 2-CMSN anions connected the adjacent 1D chains to generate a 2D layer structure
(Fig. 2b). From a topological viewpoint, each Co center can be treated as 3-connected
node, a couple of 2-CMSN anions and the L ligands are simplified as linkers, the
structure of 2 can be described as a 2D network based on six-nuclear metallic ring
(Fig. 2c). The extension of the 2D layer into a 3D supramolecular network is
accomplished by hydrogen-bonding interactions between the coordinated water
molecule (O1W) and the oxygen atom [O(5)] of carboxyl groups with the distance of
2.69 Å [O1W–H1WB···O5] (Fig. S3 and Table S8). The structure of complex 3 is
shown in Fig. S4.
8

Zhang and coworkers have obtained a 3D complex {[Co(bcpb)(L)]·xH2O}n
[H2bcpb = 3,5-bis(3-carboxyphenyl)pyridine] [40], in which the 3-connected bcpb
ligands linked the Co2+ ions to form a polymeric (4·82) [Co(bcpb)]n 2D net. Two
adjacent 2D sheets are linked by the L ligands in a trans fashion to generate a 3D
framework. In complex 2 based on the same metal ion and N-donor ligand, a flexible
2-CMSN ligand was used instead of the rigid bcpb ligand, a different 2D layer
structure was obtained. The structural difference may be due to the different flexibility
of carboxylate co-ligands.
Insert Fig. 2
3.1.3. [Zn(L)(2-CMSN)]·2H2O 4
Complex 4 crystallizes in the monoclinic space group C2/c. The asymmetric unit of
4 contains one crystallographically independent Zn2+ ion, one L ligand, one 2-CMSN
anion, and two crystalline water molecules. Zn2+ ion is four coordinated by two
imidazole nitrogen atoms (N1, N2#1) of two L ligands, two oxygen atoms (O1, O4)
from the monodentate carboxyl groups of two 2-CMSN anions, showing a distorted
tetrahedron geometry (Fig. 3a). The Zn–N bond distances are 2.026(5) Å [Zn(1)–N(1)]
and 2.027(5) Å [Zn(1)–N(2)#1], while the Zn–O bond distances are 1.956(4) Å
[Zn(1)–O(1)] and 1.988(8) Å [Zn(1)–O(4)] (Table S4), respectively. The nitrogen
atoms from two imidazole rings of L ligands connect the adjacent Zn2+ atoms to build
1D [Zn-L]n ‘Ω’-like chain, with the Zn···Zn distance of 14.010(14) Å. The 2-CMSN
anions adopt bis(monodentate) bridging mode. The neighboring [Zn-L]n ‘Ω’-like
chains are linked by pairs of 2-CMSN anions to form a 2D layer, as shown in Fig. 3b.
Each Zn2+ ion can be considered as a 3-connected node, whilst L ligands and a couple
of 2-CMSN anions are regarded as linkers, and the final structure of 4 is a
3-connected network (Fig. 3c). In addition, there exist C14–H14A···O2 intermolecular
hydrogen bonding interactions, which further extend the 2D layers into a 3D
supramolecular architecture (Fig. S5 and Table S8).
Insert Fig. 3
3.1.4. [Cd(ADTZ)(H2O)] 5
X-ray crystallography reveals that complex 5 crystallizes in the orthorhombic
9

system with space group P212121. There is one Cd2+ ion, one ADTZ anion and one
coordinated water molecule in the asymmetric unit of 5. The Cd1 ion is
six-coordinated by one nitrogen atom (N2) from one ADTZ anion, three oxygen
atoms (O1, O3, O4#1) from three ADTZ anions and two oxygen atoms (O1W,
O1W#3) from two H2O molecules in a distorted octahedral coordination geometry
(Fig. 4a). The Cd–N bond length is 2.352(3) Å [Cd(1)–N(2)#2], and the Cd–O bond
lengths are in the range of 2.230(3)–2.401(3) Å (Table S5). Two equivalent water
molecules (O1W and O1W#3) serve as double bridges linking Cd2+ ions to form
left-handed helical chains, in which the Cd···Cd distance is 4.3235(4) Å and the
Cd–O–Cd angle is 128.18(12)° (Fig. 4b). Each ADTZ anion connects four Cd2+ ions
to generate a 3D framework (Fig. 4c), in which the two carboxyl groups of ADTZ
anion adopt bis(monodentate) and monodentate bridging modes connecting three Cd2+
ions and the thiadiazole nitrogen atom also coordinates with a Cd2+ ion. The
coordination water molecules as bridging ligands consolidate the 3D framework.
Topologically, the ADTZ anions can be considered as a four-connected nodes and
Cd2+ ions can be regarded as six-connected nodes, and the H2O can be regarded as
linear linkers, the whole structure of 5 can be simplified as a 3D 4,6-connected
framework with the Schläfli symbol of (43·53)(45·53·67) (Fig. 4d).
In our previous work, we have reported a 2D (4,4) network [Cd(dpq)(ADTZ)] (dpq
= dipyrido[3,2-d:2′3′-f]quinoxaline) [33]. The carboxyl groups of each ADTZ anion
adopt bidentate bridging and chelate coordination modes to link three Cd2+ ions to
generate a 2D sheet. The dpq ligand acts as a typical terminal chelating ligand inlay
the grid of the layer. However, in complex 5, neutral N-containing ligands have not
been introduced. The ADTZ anions connect four Cd2+ ions to generate a 3D
framework. It is noted that, in 5, the nitrogen atoms of thiadiazole rings coordinated
with Cd2+ ions, which is not common in coordination polymers.
Insert Fig. 4
3.1.5. [Cd(L)(ADTZ)(H2O)] 6
X-ray structural analysis reveals that complex 6 is a 2D undulated network in
monoclinic crystal system with P21/c space group. The asymmetric unit of 6 contains
10

one Cd2+ ion, one L ligand, one ADTZ anion and one coordinated water molecule. As
illustrated in Fig. 5a, the Cd1 center is six-coordinated by two nitrogen atoms (N1, N2)
from two L ligands, three oxygen atoms (O1, O2#1, O3#2) from three different ADTZ
anions and one coordinated water molecule (O1W) in a distorted octahedral
environment. The Cd–N bond distances are 2.324(3) Å (Cd1–N1) and 2.260(3)
(Cd2–N2) Å, and the Cd–O bond distances are in the range of 2.279(2)–2.488(2) Å
(Table S6). The two carboxylic groups of ADTZ anion adopt two kinds of
coordination modes: monodentate and bidentate bridging coordination mode. Each
ADTZ anion connects three cadmium ions to form a 2D undulated network (Fig. 5b).
The L ligands link the Cd2+ atoms in trans-conformation to form a 1D right-handed
helical chain with the Cd···Cd distance of 13.544(10) Å (Fig. 5c). The dihedral angle
between the two imidazole rings of the L ligand is 77.6°. It is noted that the 1D
right-handed helical chains are inlayed in 2D undulated layer, which consolidate the
2D network. From a topological perspective, the Cd2+ atoms can be defined as
5-connected nodes, the ADTZ anions can be considered as 3-connected nodes, and the
L ligands can be regarded as connectors. The topology of 6 can be described as a
(3,5)-connected net with the Schläfli symbol of (3·52)(32·53·64·7) (Fig. 5d). Moreover,
the 3D supramolecular architecture of 6 is stabilized by C12–H12A···O1W
hydrogen-bonding interactions (Fig. S6 and Table S8).
Insert Fig. 5
3.1.6. [Zn(L)(ADTZ)]·H2O 7
Single crystal X-ray diffraction analysis reveals that 7 is in monoclinic crystal
system with P21/c space group. The fundamental building unit of 7 contains one Zn2+
atom, one ADTZ anion, one L ligand and one lattice water molecule. The Zn2+ center
is coordinated by two nitrogen atoms (N1, N3) from two L ligands and two oxygen
atoms (O1, O3#1) from the carboxyl groups of two ADTZ anions, showing a distorted
tetrahedral coordination geometry (Fig. 6a). The Zn–N bond lengths are 2.011(3) Å
[Zn(1)–N(1)] and 2.017(3) Å [Zn(1)–N(3)], and the Zn–O bond lengths are 1.955(3)
Å [Zn(1)–O(1)] and 2.005(3) Å [Zn(1)–O(3)#1] (Table S7). Zn2+ ions are connected
by L ligands to generate an infinite 1D meso-helical chain [Zn-(L)]n with the Zn···Zn
11

distances of 14.250(16) Å and 15.123(19) Å (Fig. 6b). The ADTZ anions also adopt
bis(monodentate) bridging coordination mode connecting the center metals to form a
1D meso-helical chain [Zn-(ADTZ)]n with the Zn···Zn distance of 11.3114(15) Å (Fig.
6c). Finally, the 1D meso-helical [Zn-(L)]n chain are further connected by ADTZ
anions toward different directions to generate a 3D structure (Fig. 6d). Considering
the Zn2+ atom as a 4-connected node and the L, ADTZ ligands as linkers, the overall
structure of 7 is a diamond framework (dia net) (Fig. 6e). Four identical frameworks
interpenetrate each other, giving a 4-fold interpenetrating framework (Fig. 6f).
The complex [Zn(L)(D-ca)]n (D-H2ca=D-camphoric acid) was obtained by Zuo and
co-workers [41]. The D-ca ligands connect Zn2+ atoms into a 1D [Zn(D-ca)]n chain.
These chains are further linked by the L ligands to afford a 2D network with (4,4)
topology. In this work, we used the H2ADTZ instead of D-H2ca, and obtained a
completely different structure 7. Compared with D-H2ca, H2ADTZ have two flexible
S-containing carboxyl group (–SCH2COOH) and one thiadiazole ring. The stronger
bending ability and the smaller steric hindrance may result in high-dimensional
structures.
Insert Fig. 6
3.1.7 Effect of the central metals on the structures of the complexes
It is well established that the central metal ions have remarkable effects on the
formation of the final frameworks [13, 30, 42]. In complexes 1–4, the same organic
dicarboxylate (2-CMSN) and flexible N-donor ligand (L) were used to combine with
different metal ions [Ni2+ in 1, Co2+ in 2, Cd2+ in 3 and Zn2+ in 4]. In 1, the six
coordinate Ni2+ ions are connected by L ligands to afford a 1D double chain. The
2-CMSN anions have no effect on extending the dimension, which only act as
terminal ligands. In 2 and 3, six coordinate Co2+ and Cd2+ ions are bridged by
2-CMSN anions and L ligands to form 2D networks. Although the layers of 2 and 3
are similar, some subtle differences exist between them. In 2, there exist two
crystallographically independent Co2+ ions. The 2-CMSN anions adopt two types of
coordination modes (Scheme 2). In 3, there is only one crystallographically
independent Cd2+ ion. The 2-CMSN anions adopt one coordination mode (Scheme 2).
12

The Ni2+/Co2+/Cd2+ ions in complexes 1–3 display the coordination number of 6.
However, the Zn2+ ions in complex 4 exhibit the coordination number of 4. The four
coordinate Zn2+ ions are connected by 2-CMSN anions and L ligands to generate a 2D
net. In 1–3, the sulfur atoms of 2-CMSN ligands coordinated with the metal ions.
However, in 4, the sulfur atoms of 2-CMSN ligands are non-coordinated. On the other
hand, in complexes 6 and 7, Cd2+ and Zn2+ ions also display different coordination
numbers: 6 for Cd2+ in 6 and 4 for Zn2+ in 7. In 6, the six coordinate Cd2+ ions are
bridged by L ligands and ADTZ anions to form a 2D undulated network. The four
coordinate Zn2+ ions are linked by ADTZ anions and L ligands to generate a 3D 4-fold
interpenetrated dia network in 7. The structural discrepancy can be attributed to
various coordination number and modes of different metal ions. Furthermore, the
coordination number of the Zn2+ ions is lower than those of the Ni2+, Co2+ and Cd2+
ions, which may be attributed to the smaller radii of the Zn2+ ions [43]. The structural
discrepancies between these complexes may be attributed to the different coordination
characters of the central metals, which indicate that the central metals show obvious
effect on the structures of the title complexes.
Insert Scheme 2
3.1.8 Effects of the dicarboxylate anions and N-donor ligand on the structures of the
complexes
Comparing complex 3 with 6, as well as 4 with 7, which contain the same L ligands
and central metal atoms, the completely different structures can be attributed to the
different dicarboxylate anions. In 3, the 2-CMSN anion coordinates with Cd2+ centers
in a monodentate-chelating bridging mode (Scheme 2), resulting in a bimetallic
Cd2(2-CMSN)2 loops, which are linked by L ligands to give a 2D sheet. In 6, the
ADTZ anion adopting a bis(monodentate) bridging mode (Scheme 2) connects the
adjacent Cd2+ ions to construct a 2D undulated network. The L ligands only
consolidated the 2D network by linking the Cd2+ ions in the same 2D layer. In
complex 4, a pair of 2-CMSN anions adopt a bis(monodentate) bridging mode
connecting Zn2+ ions to form a bimetallic Zn2(2-CMSN)2 loops, which are linked by L
ligands to give a 2D network. While in 7, the ADTZ anions also adopt the
13

bis(monodentate) bridging mode linking Zn2+ ions to generate a 1D meso-helical
chain [Zn-(ADTZ)]n, which are further linked by L ligands to from a 3D 4-fold
interpenetrating diamond framework. The various structures indicate that the
polycarboxylate anions have a remarkable effect on the final structures, which can be
explained in terms of their differences in the positions and flexibility of the carboxyl
groups. The above results suggest that the polycarboxylates play important roles in
the assembly and structures of coordination polymers. In addition, the N-donor ligand
also shows significant effect on the structures of the complexes. In the absence of the
N-donor ligand, complex [Cd(ADTZ)(H2O)] (5) displays a 3D framework. Both the
carboxyl oxygen atoms and the nitrogen atoms of thiadiazole rings of the ADTZ
anions are coordinated with Cd2+ ions (Scheme 2). However, when the N-donor ligand
(L) was introduced into the reaction system, a structurally different complex 6 was
obtained. The nitrogen atoms of ADTZ ligands are non-coordinated.
3.2. Properties
3.2.1. PXRD measurement and thermogravimetric analyses of the title complexes
In order to confirm whether the crystal structures are truly representative of the
bulk materials, the PXRD patterns of complexes 1–7 were recorded. The experimental
PXRD patterns are in good agreement with the corresponding simulated ones,
implying that the synthesized bulk materials and the measured single crystals are the
same (Fig. S8).
Thermal gravimetric analyses (TGA) of complexes 1–7 were performed to
investigate their thermal stabilities (Fig. 7). For complex 1, the weight loss
corresponding to the release of one coordinated water molecule and two lattice water
molecules are observed from 98 to 135 °C (obsd 7.1%, calcd 7.93%). The weight loss
from 283 to 600 °C is attributed to the collapse of the architecture of 1. The remaining
residue corresponds to the formation of NiO (obsd 11.18%, calcd 10.96%). For 2, the
weight loss of 3.2% in the temperature range 133–170 °C is consistent with the
removal of one coordinated water molecule and one lattice water molecule (calcd
3.42 %). The weight loss corresponding to the release of organic ligands is observed
from 245 to 776 °C. The remaining residue is assigned to CoO (obsd 7.51%, calcd.
14

7.12 %). Complex 3 loses its one coordinated water molecule from 187 to 215 °C
(obsd 2.78%, calcd 3.11%), and the decomposition of the residual composition occurs
from 240 to 775 °C, leading to the formation of CdO as the residue (obsd 22.5%,
calcd 22.14%). For 4, the weight loss of 6.08% from 78 to 170 °C is attributed to the
loss of two lattice water molecules (calcd 6.54 %). In the temperature range of
244–568 °C, the organic components start to decompose. The weight of the remaining
residue corresponding to the formation of ZnO is 14.5% (calcd 14.77 %). For 5, the
organic components decompose from 240 to 521 °C. The remaining residue
corresponds to the formation of CdO (obsd 32.2%, calcd 32.53 %). Complex 6 loses
its coordinated water molecule in the temperature range of 217–269 °C (obsd 2.6%,
calcd 2.85 %), and the residual components decompose from 320 to 443 °C. The
weight of the remaining residue is 20.5% and corresponds to the formation of CdO
(calcd 20.29%). For 7, the weight loss in the temperature range of 91–184 °C can be
attributed to the removal of a coordinated water molecule (obsd 3.3%, calcd 3.07%).
The decomposition of the organic components occurs in the temperature range of
254–609 °C. The remaining weight corresponds to the formation of ZnO (obsd 13.8%,
calcd 13.89%).
Insert Fig. 7
3.2.2. Photoluminescent properties
Luminescent properties of Zn2+/Cd2+ complexes have attracted intense interest due
to their potential applications in photochemistry, chemical sensors, and
electroluminescent display [44–46]. Therefore, in this paper, the photoluminescent
properties of L ligand and complexes 3, 4, 6 and 7 have been investigated in the solid
state at room temperature (Fig. 8). The L ligand exhibits emission band with a
maximum at 390 nm upon excitation at 340 nm. The emission band are probably
attributable to the π*→π transition [47]. The emission peaks of Cd2+-complexes occur
at 423 nm (λex = 300 nm) for 3, 460 nm (λex = 320 nm) for 6. The emission peaks of
Zn2+-complexes occur at 438 nm (λex = 320 nm) for 4, 475 nm (λex = 340 nm) for 7. It
is well known that the Zn2+ and Cd2+ ions are difficult to oxidize or reduce because of
the d10 configuration [48, 49]. Therefore, the emissions of complexes are neither
15

metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT)
in nature [50]. The emissions of these complexes may be attributed to intraligand
transitions [51]. Compared with the most of luminescent Zn2+/Cd2+ coordination
polymers, complexes 3, 4, 6 and 7 have similar luminescent properties [52, 53].
Insert Fig. 8
3.2.3. Electrochemical behaviors
Redox properties of 1 and 2 were investigated with 1 or 2 bulk-modified carbon
paste electrodes (1-CPE, 2-CPE) in 0.01 M H2SO4–0.5 M Na2SO4 aqueous solution.
Fig. S9 show the cyclic voltammograms of 1-CPE and 2-CPE in 0.01 M H2SO4–0.5
M Na2SO4 aqueous solution. It can be seen clearly that in the potential range of + 800
to 0 mV, a redox couple is observed at the 1-CPE and 2-CPE, respectively. The mean
peak potential E1/2=(Epa + Epc)/2 is 342 mV for 1, 411 mV for 2 (100 mV·s-1), which
could be attributed to the redox of Ni(III)/Ni(II) and Co(III)/Co(II) [54, 55]. The
effects of scan rates on the electrochemical behaviors of 1-CPE and 2-CPE are shown
in Fig. S10 and Fig. 9. The peak potentials of cyclic voltammograms change gradually
following the scan rates from 20 to 200 mV⋅s–1: the cathodic peak potentials shift
toward the negative direction and the corresponding anodic peak potentials to the
positive direction with increasing scan rates. The peak currents are proportional to the
scan rates up to 200 mV⋅s–1 (inset of Fig. 9 and Fig. S10), which indicate that the
redox process of the 1–, 2–CPEs are surface-confined.
Insert Fig. 9
3.2.4. Photocatalytic Properties
Photocatalysts have attracted much attention due to their potential applications in
purifying water and air by decomposing organic molecules [56, 57]. Herein,
methylene blue (MB), as a model dye contaminant, was selected to evaluate the
photocatalytic effectiveness in the purification of wastewater. In this work, the
photocatalytic performances of complexes 1–7 for the photodegradation of MB under
UV irradiation were investigated. The experiments were carried out in typical
processes: 50 mg powder of the title complexes was dispersed in the 200 mL MB
solution (10.0 mg·L–1), magnetically stirred in the dark for 0.5 h to ensure the
16

equilibrium of the working solution. Then the solution was exposed to UV irradiation
from an Hg lamp, kept continuously stirring. A sample was taken out every 30 min for
analysis. The simple photocatalysis experiments of the aqueous MB solution were
also performed under the same conditions without any catalyst (Fig. S11).
The photocatalytic property of the title complexes are shown in Fig. 10 and Fig.
S11. It can be seen that the absorption peak of MB decreased obviously along with the
reaction time for the complexes 2–4, 6 and 7. However, the absorption peaks
decreased much slowly in the presence of complexes 1 and 5. The concentrations of
MB (C) against reaction time (t) for the title complexes were plotted. The calculation
results show that approximately 64% of MB had been decomposed after 180 min for 2
as photocatalyst, 37% for 3, 54% for 4, 72% for 6 and 62% for 7. The approximately
20% of MB had been decomposed after 180 min for 1 as photocatalyst, 9% for 5 and
the dissociation of MB was no more than 7% without any catalyst (Fig. 11). In
addition, the photocatalytic performance of 6 was better than that of the complex
[Cd(ADTZ)(biim-4)1.5]·5H2O [biim-4 = 1,1′-(1,4-butanediyl)bis(imidazole)] for the
decomposition of MB under UV irradiation [30]. For complex 6, approximately 72%
of MB was decomposed after 180 min, whereas 49% of MB was degraded after 180
min for [Cd(ADTZ)(biim-4)1.5]·5H2O. The differences of photocatalytic activities
may be attributed to the different extent of the conjugation of organic ligands and
central metals, as well as the final structures of the complexes [57, 58–60]. During the
photocatalytic process, UV-Vis light induces L ligand and 2-CMSN/ADTZ anions to
produce O and/or N-metal charge transfer promoting electrons from the highest
occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital
(LUMO). In order to return to its stable state for HOMO, one electron was captured
from water molecules, which was oxygenated to generate the •OH radicals [61, 62].
Therefore, the •OH active species could decompose the dye effectively to complete
the photocatalytic process.
In order to investigate the stability of title complexes as photocatalyst, we repeated
the PXRD of the complexes after the photocatalytic experiment, and the PXRD
patterns are nearly identical to those of the original complexes (Fig. S8). The result
17

indicates that the catalysts may be recycled after the catalytic experiments [63].
Insert Fig. 10 and Fig. 11
4. Conclusion
Seven new coordination polymers exhibiting diverse structures have been
synthesized under hydrothermal conditions by reacting 2-H2CMSN/H2ADTZ and
N-donor ligand (L) with different metal ions. The diverse architectures and other
interesting features of these complexes have been identified, such as different
dimensional frameworks, molecular topology, interpenetration, and weak interactions
(hydrogen-bonding and π–π stacking interactions, etc.). The structural diversities of
the complexes indicate that the coordination characters of the central metal ions and
the dicarboxylates with different coordination sites and flexibilities have significant
effects on the formation and dimensions of the final structures. The photoluminescent
emissions indicate that complexes 3, 4, 6 and 7 may be potential candidates for optical
materials. Complexes 1 and 2 possess good electrochemical properties. Moreover, the
photocatalytic behaviors of complexes 2–4, 6 and 7 imply that they may be effective
and stable photocatalysts for the photodegradation of MB under ultraviolet-light
irradiation.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of
China (No. 21171025), Program of New Century Excellent Talents in University
(NCET-09-0853), and Program of Innovative Research Team in University of
Liaoning Province (LT2012020).
Appendix A. Supplementary material
CCDC 932694, 932695, 932697, 940612, 940617, 932698, and 932699 contain the
supplementary crystallographic data for 1–7. These data can be obtained free of
charge
from
The
Cambridge
Crystallographic
Data
the
Centre
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or from
Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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22

Figures
Scheme 1 Structures of N-donor ligand (L) and 2-H2CMSN/H2ADTZ used in this
work.
Scheme 2 Coordination modes of the dicarboxylates and metal ions in complexes
1–7.
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Fig. 1 (a) Coordination environment of the Ni2+ ion in 1 (30% probability
displacement ellipsoids). Symmetry code: #1 x + 1, y – 1, z; (b) View of the 1D
ladder-like double chain structure of 1.
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Fig. 2 (a) Coordination environment of the Co2+ ions in 2 (30% probability
displacement ellipsoids). Symmetry code: #3 x – 1, y, z + 1; (b) View of the 2D layer
of 2; (c) View of the schematic representation of the 2D layer.
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Fig. 3 Coordination environment of the Zn2+ ion in 4 (30% probability displacement
ellipsoids). Symmetry code: #1 x, –y + 2, z – 1/2; (b) View of the 2D layer of 4; (c)
View of the schematic representation of 2D layer.
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Fig. 4 (a) Coordination environment of the Cd2+ ion in 5 (30% probability
displacement ellipsoids). Symmetry code: #1 x + 1, y, z; #2 –x, y – 1/2, –z + 3/2; #3 x
– 1/2, –y + 1/2, –z + 2; #7 x + 1/2, –y + 1/2, –z + 2; (b) The left-handed helical chain
constructed by μ2-H2O molecules and Cd2+ ions; (c) The 3D framework of 5; (d)
Schematic representation of the 3D framework with the Schläfli symbol of
(43·53)(45·53·67).
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Fig. 5 (a) Coordination environment of the Cd2+ ion in 6 (30% probability
displacement ellipsoids). Symmetry code: #1 x + 1, y, z; #2 –x + 1, y + 1/2, –z + 2/3;
(b) View of the 2D undulated network of 6; (c) The 1D right-handed helical chain
constructed by Cd2+ ions and L ligands; (d) View of the schematic representation of
2D network with the (3·52)(32·53·64·7) topology.
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Fig. 6 (a) Coordination environment of the Zn2+ ion in 7 (30% probability
displacement ellipsoids) Symmetry code: #1 x + 1, –y + 1/2, z + 1/2; (b) The 1D
meso-helical chain constructed by Zn2+ ions and L ligands; (c) The 1D meso-helical
chain constructed by Zn2+ ions and ADTZ anions; (d) The 3D framework of 7; (e)
Schematic representation of the 3D framework of 7; (f) Schematic representation of
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