Topological modulation of metal-thiadiazole dicarboxylate coordination polymers through auxiliary ligand alteration

Article abstract of DOI:10.1039/c5ce00649j

Five new Co^II/Zn^II coordination polymers (CPs), namely [Co(tdzdc)(4,4′-bipy)(H₂O)]_n (1), {[Co(tdzdc)(bpp)(H₂O)]·3H₂O}_n (2), {[Zn₂(tdzdc)₂(4,4′-bipy)(H₂O)₂]·3H₂O}_n (3), [Zn₂(tdzdc)₂(obpy)(H₂O)₂]_n (4) and [Zn(tdzdc)(tmb)]_n (5), have been synthesized based on the primary ligand 1,2,5-thiadiazole-3,4-dicarboxylic acid (H₂tdzdc) together with four selected N/O-donor auxiliary ligands, i.e., 4,4′-bipy: 4,4′-bipyridine, bpp: 1,3-bi(pyridin-4-yl)propane, obpy: [4,4′-bipyridine]-N,N′-dioxide, and tmb: 1,4-bis((1H-1,2,4-triazol-1-yl)methyl)benzene. Single-crystal structural analyses unveil different topologies and interpenetration degrees of 1-5, associated with four different kinds of coordination modes of H₂tdzdc that depend on the auxiliary ligands used. CPs 1-4 are all constructed by extending the one-dimensional metal-ligand chain through the respective auxiliary ligands. Among them, the linear rigid auxiliary ligands (i.e., bipy and obpy) generate two-dimensional planes of 1, 3 and 4, which exhibit different interpenetration degrees of 0, 2 and 3, respectively, while the flexible bpp auxiliary ligand forms a three-dimensional net of 2. In contrast, CP 5 has a basic structural unit comprising dinuclear metal clusters that facilitate the formation of a 3-fold interpenetrated two-dimensional net extended through the tmb auxiliary ligand. Furthermore, magnetic investigations of the two Co^II-based CPs reveal that despite being mediated by syn-anti bridging of the carboxylate, both 1 and 2 display antiferromagnetic and canted antiferromagnetic behaviors, respectively.

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Topological modulation of metal–thiadiazole
dicarboxylate coordination polymers through
Cite this: DOI: 10.1039/c5ce00649j
auxiliary ligand alteration†
b
b
b
b
Zhen-Xin Zhao,ab Yun-Wu Li, Sui-Jun Liu, Li-Fu Wang, Ze Chang, Jian Xu b and
*
b
*
Ying-Hui Zhang
Five new CoII/ZnII coordination polymers (CPs), namely ijCoIJtdzdc)IJ4,4′-bipy)IJH2O)]n (1), {[CoIJtdzdc)IJbpp)IJH2O)]
·3H2O}n (2), {[Zn2IJtdzdc)2IJ4,4′-bipy)IJH2O)2]·3H2O}n (3), ijZn2IJtdzdc)2IJobpy)IJH2O)2]n (4) and ijZnIJtdzdc)IJtmb)]n (5),
have been synthesized based on the primary ligand 1,2,5-thiadiazole-3,4-dicarboxylic acid (H2tdzdc)
together with four selected N/O-donor auxiliary ligands, i.e., 4,4′-bipy: 4,4′-bipyridine, bpp: 1,3-
biIJpyridin-4-yl)propane, obpy: ij4,4′-bipyridine]-N,N′-dioxide, and tmb: 1,4-bisIJ(1H-1,2,4-triazol-1-
yl)methyl)benzene. Single-crystal structural analyses unveil different topologies and interpenetration
degrees of 1–5, associated with four different kinds of coordination modes of H2tdzdc that depend on
the auxiliary ligands used. CPs 1–4 are all constructed by extending the one-dimensional metal–ligand
chain through the respective auxiliary ligands. Among them, the linear rigid auxiliary ligands (i.e., bipy and
obpy) generate two-dimensional planes of 1, 3 and 4, which exhibit different interpenetration degrees of
0, 2 and 3, respectively, while the flexible bpp auxiliary ligand forms a three-dimensional net of 2. In con-
trast, CP 5 has a basic structural unit comprising dinuclear metal clusters that facilitate the formation of a
3-fold interpenetrated two-dimensional net extended through the tmb auxiliary ligand. Furthermore,
magnetic investigations of the two CoII-based CPs reveal that despite being mediated by syn–anti bridg-
ing of the carboxylate, both 1 and 2 display antiferromagnetic and canted antiferromagnetic behaviors,
respectively.
Received 2nd April 2015,
Accepted 27th April 2015
DOI: 10.1039/c5ce00649j
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ligands can be considered as one of the most effective
methods to achieve the targeted assembly structures and
Introduction
Coordination polymers (CPs) have been of growing interest in
chemistry and materials science during the past two decades
not only because of their fascinating structures but also due
to their versatile properties, exhibiting potential applications
in gas capture and storage, magnetism, luminescence, cataly-
sis, and so on.1,2 Based on diverse starting ligands, a wide
variety of CPs with distinctive topological networks and differ-
ent degrees of entanglement3,4 have been obtained,
manifesting the important role of organic ligands in coordi-
nation assembly. Thus, sophisticated selection of appropriate
properties of CPs.5 In this context, the involved coordination
groups play a key role in determining the coordination behav-
iors of ligands that consequently impact the coordination
geometries and properties of CPs. For example, azole and car-
boxylate groups have been widely used to design novel
ligands, due to their unusual coordination modes.6 Besides
that, the backbone and even the non-coordinating hetero-
atoms also influence the coordination behaviors of ligands.
Recently, the use of auxiliary ligands has been proven to
be capable of providing greater flexibility in tuning the geom-
etries and properties of CPs via the synergistic coordination
effect between primary and auxiliary ligands.7 As a result,
both the structural traits and coordination modes of the
involved auxiliary ligands can greatly impact the topological
structures and even the dimensions of the resulting CPs. For
example, 4,4′-bipyridine (4,4′-bipy), a typical linear N-donor
ligand, has been extensively used as an auxiliary organic
linker to promote the dimensions of CPs.8 On the other
hand, central metal ions play a vital role in the functionalization
of CPs, since their characteristic electronic properties domi-
nantly determine, in some cases, the physical and chemical
a School of Chemistry and Materials Engineering, Henan University of Urban
Construction, Pingdingshan 467036, Henan Province, PR China
b Department of Chemistry, TKL of Metal- and Molecule-Based Material Chemistry
and Collaborative Innovation Center of Chemical Science and Engineering (Tianjin),
Nankai University, Tianjin 300071, PR China. E-mail: jxu@nankai.edu.cn,
zhangyhi@nankai.edu.cn; Fax: +86 22 23502458; Tel: +86 22 23502458
† Electronic supplementary information (ESI) available: X-ray crystallographic
data file in CIF format for CCDC 987500 (1), 987506 (2), 987504 (3), 987511 (4)
and 987512 (5), supplementary tables, and additional characterization. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c5ce00649j
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properties of polymers, for example, a variety of CoII-based
magnetic complexes as well as luminescent materials based
on ZnII.9
background corrections by experimental measurements on
sample holders.
In our previous studies, the multidentate organic ligand
1,2,5-thiadiazole-3,4-dicarboxylate (tdzdc2−), obtained via an
in situ solvothermal reaction of 3,4-dicyano-1,2,5-thiadiazole
with MCl2 (MII = CoII, NiII) and NaOH, exhibits unique advan-
tages in the fabrication of highly connected coordination
topologies.10 Thus, in this work, we extend our study to the
primitive H2tdzdc ligand, which is less explored and could
serve as a good model ligand, and systematically investigate
the reactions of this primary ligand with CoII and ZnII cations
in the presence of different auxiliary ligands. Herein, four
representative N/O-donor auxiliary ligands with different
sizes and flexibilities are selected (Scheme 1), i.e., 4,4′-bipy,
1,3-biIJpyridin-4-yl)propane (bpp), ij4,4′-bipyridine]-N,N′-dioxide
(obpy), and 1,4-bisIJ(1H-1,2,4-triazol-1-yl)methyl)benzene (tmb),
which consequently form five new CoII/ZnII CPs, including
ijCoIJtdzdc)IJ4,4′-bipy)IJH2O)]n (1), {[CoIJtdzdc)IJbpp)IJH2O)]·3H2O}n (2),
{[Zn2IJtdzdc)2IJ4,4′-bipy)IJH2O)2]·3H2O}n (3), ijZn2IJtdzdc)2IJobpy)IJH2O)2]n
(4), and ijZnIJtdzdc)IJtmb)]n (5). Structural analyses demon-
strate that the different auxiliary ligands bring about distinct
topological structures and degrees of interpenetration of the
resulting CPs, suggesting an in-depth exploration of the rela-
tionship between complex frameworks and auxiliary ligands.
Furthermore, the magnetic properties of the two CoII-based
CPs (1 and 2) are also studied.
Synthesis of H2tdzdc, tmb, obpy and complexes 1–5
H2tdzdc was synthesized in two steps according to the
literature10 with minor modifications (see Scheme 2).
3,4-Dicyano-1,2,5-thiadiazole. Diaminomaleonitrile (10.8 g,
0.1 mol) and 22 mL of SOCl2 (approximately 35.7 g, 0.3 mol)
were placed in a dried 100 mL round-bottomed flask. The
reaction mixture was heated to 50 °C for 1 h and then heated
to reflux (65 °C) for 3 h. After being cooled to room tempera-
ture, the product mixture was evaporated under reduced pres-
sure to remove unreacted SOCl2. The dark brown liquid resi-
due was then poured into CH2Cl2 (500 mL) and filtered to
give a brown filtrate. Finally, the filtrate was evaporated in
vacuum to give a brown solid IJ3,4-dicyano-1,2,5-thiadiazole).
H2tdzdc. 3,4-Dicyano-1,2,5-thiadiazole (13.6 g, 0.1 mol),
850 mL of H2O and NaOH (70 g, 1.75 mol) were placed in a
dried 1000 mL round-bottomed flask. The reaction mixture
was heated to reflux for 24 h. After being cooled to room tem-
perature, the mixture was filtered to remove the insoluble
component. Adjusting the pH value of the filtrate to 1 by
adding aqueous HCl resulted in a black precipitate that was
removed through filtration. The filtrate was collected and
evaporated under reduced pressure to give a gray solid. This
solid was washed five times with diethyl ether (300 mL) and
the ether solution was collected and evaporated under
reduced pressure to give a pale yellow solid (H2tdzdc). The
total yield was 35% based on diaminomaleonitrile. Anal.
calcd for C4H2N2O4S: C, 27.59; H, 1.15; N, 16.09. Found: C,
27.76; H, 1.20; N, 16.19. IR (KBr, cm−1) for C4H2N2O4S (4000–
400 cm−1): 1622 IJνIJCO)), 1599 IJνIJCN)), 1308 IJνIJC–C)), 828
IJνIJN–S)), 816 IJνIJC–S)). 13C NMR for C4H2N2O4S (300 MHz,
D2O (TMS)) (ppm): 161.84 (s), 152.51 (s).
Experimental
Materials and general methods
All chemicals except H2tdzdc, obpy and tmb were of reagent
grade and were used without further purification. Elemental
analyses (C, H and N) were performed on a Perkin-Elmer
240C analyzer (Perkin-Elmer, USA). Powder X-ray diffraction
(PXRD) patterns were recorded on a Rigaku D/Max-2500 dif-
fractometer at 60 kV and 300 mA with a Cu-target tube and a
graphite monochromator. Simulation of the PXRD patterns
based on single crystal data was carried out by using the
diffraction-crystal module of the Mercury (Hg) program. IR
spectra were measured in the range of 400–4000 cm−1 on a
Tensor 27 OPUS FT-IR spectrometer using KBr pellets
(Bruker, Germany). Magnetic data were measured with a
Quantum Design MPMS XL-7 SQUID magnetometer. Diamag-
netic corrections were estimated using Pascal's constants and
obpy. This ligand was synthesized according to the litera-
ture11 with minor modifications (Scheme 2). 4,4′-Bipy (15.6 g,
0.1 mol), glacial acetic acid (80 mL) and 35% H2O2 (40 mL)
were placed in a dried 250 mL round-bottomed flask. The
reaction mixture was heated to 70–80 °C for 4 h, then 35%
H2O2 (30 mL) was added and the reaction mixture was heated
for another 12 h. The product mixture was cooled to room
temperature and the unreacted acetic acid and H2O2 were
evaporated under reduced pressure. Water (40 mL) was
Scheme 1 Auxiliary ligands used in the preparation of 1–5.
Scheme 2 The synthetic routes for H2tdzdc, obpy and tmb.
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added to the residue and the mixture was evaporated under
reduced pressure to give an oily organic product. Adding 200 mL
of acetone to the oily organic residue produces a pale yellow
precipitate that was collected and washed with acetone sev-
eral times. Finally, the white target product (obpy) was
obtained through recrystallization of the pale yellow solid.
tmb. This ligand was synthesized according to the litera-
ture12 with minor modifications (Scheme 2). 1,2,4-Triazole
(1.38 g, 0.02 mol), K2CO3 (5 g), KI (0.5 g), 30 mL of acetone
and 2 g of polyethylene glycol 400 were placed in a dried 100
mL round-bottomed flask, and the reaction mixture was
stirred for 1 h. Then, 1,4-bisIJchloromethyl)benzene (1.75 g,
0.01 mol) was added and the reaction mixture was heated to
reflux for 24 h. After being cooled to room temperature, the
mixture was filtered to give a solid crude product, which was
purified by recrystallization to give a pale yellow microcrystal-
line powder (tmb).
ijCoIJtdzdc)IJ4,4′-bipy)IJH2O)]n (1). A mixture of H2tdzdc (87
mg, 0.5 mmol), 4,4′-bipy (78 mg, 0.5 mmol) and CoIJOAc)2
·4H2O (124.4 mg, 0.5 mmol) in 10 mL of H2O was stirred for
about 10 min. Then, the reaction mixture was sealed in a 23
mL Teflon-lined autoclave and heated to 160 °C for 4 days.
After the autoclave was cooled to room temperature in 12 h,
red crystals were collected with a ~20% yield based on CoII.
Anal. calcd for C14H10N4SCoO5 (%): C, 41.49; H, 2.49; N,
13.83. Found (%): C, 41.05; H, 2.99; N, 13.61. IR (KBr, cm−1)
(4000–400 cm−1): 3267 (br), 2381 (vs), 1603 (vs), 1507 (vs), 1467
(s), 1329 (s), 1264 (m), 1083 (w), 810 (s), 605 (m), 554 (m).
{[CoIJtdzdc)IJbpp)IJH2O)]·3H2O}n (2). A mixture of H2tdzdc
(52.2 mg, 0.3 mmol), bpp (111.8 mg, 0.6 mmol) and CoIJOAc)2
·4H2O (74.7 mg, 0.3 mmol) in 10 mL of H2O was stirred for
about 10 min, which was then sealed in a 23 mL Teflon-lined
autoclave and heated to 160 °C for 4 days. After the autoclave
was cooled to room temperature in 12 h, scarlet crystals were
collected with a ~50% yield based on CoII. Anal. calcd for
C17H20N4SCoO8 (%): C, 40.80; H, 4.00; N, 11.20. Found (%):
C, 40.73; H, 4.36; N, 11.12. IR (KBr, cm−1) (4000–400 cm−1):
3363 (br), 2395 (vs), 1605 (s), 1425 (s), 1388 (m), 1307 (s),
1192 (m), 797 (s), 565 (m).
with
a
~45% yield based on ZnII. Anal. calcd for
C9H6N3SZnO6 (%): C, 30.92; H, 1.73; N, 12.02. Found (%): C,
30.59; H, 1.95; N, 11.75. IR (KBr, cm−1) (4000–400 cm–1): 3278
(w), 3086 (br), 2391 (vs), 1601 (vs), 1452 (s), 1400 (m), 1208
(m), 817 (s), 596 (m).
ijZnIJtdzdc)IJtmb)]n (5). A mixture of H2tdzdc (34.8 mg, 0.2
mmol), tmb (48 mg, 0.2 mmol) and ZnIJOAc)2 (43.9 mg, 0.2
mmol) in 5 mL of H2O was stirred for about 10 min. The mix-
ture was sealed in a 6 mL glass bottle and heated to 90 °C for
3 days. After the bottle was cooled to room temperature, col-
orless crystals were collected with a ~40% yield based on ZnII.
Anal. calcd for C16H12N8SZnO4 (%): C, 40.22; H, 2.53; N,
23.45. Found (%): C, 40.16; H, 3.12; N, 23.0. IR (KBr, cm−1)
(4000–400 cm−1): 3429 (w), 3114 (vs), 1612 (vs), 1537 (vs),
1388 (m), 1274 (m), 800 (s), 712 (m), 666 (m), 552 (m).
Crystallographic data and structure refinements. The
single-crystal X-ray diffraction data of 1–5 were collected on a
Rigaku SCX-mini diffractometer at 293(2) K with Mo-Kα radi-
ation (λ = 0.71073 Å) in ω scan mode. The program
CrystalClear13 was used to integrate the diffraction profiles.
The structures were solved by direct methods using the
SHELXS program of the SHELXTL package and refined by
full-matrix least-squares methods with SHELXL (semi-empiri-
cal absorption corrections were applied by using the SADABS
program).14 Non-hydrogen atoms were located by successive
difference Fourier syntheses and refined with anisotropic
thermal parameters on F2. All hydrogen atoms of the ligands
were generated theoretically at specific atoms and refined iso-
tropically with fixed thermal factors. The hydrogen atoms of
water in 1, 2 and 4 were added using the difference Fourier
maps and refined with suitable restraints. The hydrogen
atoms of water in 3, which were directly included in the final
molecular formula, were not assigned due to the limited crys-
tal quality. A summary of crystallographic data, data collec-
tion and refinement parameters for 1–5 is provided in
Table 1.
Results and discussion
Structural analysis
{[Zn2IJtdzdc)2IJ4,4′-bipy)IJH2O)2]·3H2O}n (3). A mixture of
H2tdzdc (69.6 mg, 0.4 mmol), 4,4′-bipy (62.4 mg, 0.4 mmol)
and ZnIJOAc)2 (87.8 mg, 0.4 mmol) in 12 mL of H2O was
stirred for about 10 min, and then the mixture was sealed in
a 23 mL Teflon-lined autoclave and heated to 160 °C for 4
days. After the autoclave was cooled to room temperature,
colorless crystals were collected with a ~50% yield based on
ZnII. Anal. calcd for C18H18N6S2Zn2O13 (%): C, 29.97; H, 2.52;
N, 11.65. Found (%): C, 30.59; H, 3.17; N, 11.75. IR (KBr,
cm−1) (4000–400 cm−1): 3219 (w), 2384 (vs), 1608 (vs), 1442
(s), 1392 (m), 1303 (m), 815 (s), 606 (m), 512 (m), 452 (m).
ijZn2IJtdzdc)2IJobpy)IJH2O)2]n (4). A mixture of H2tdzdc (104.4
mg, 0.6 mmol), obpy (112.8 mg, 0.6 mmol) and ZnIJOAc)2
(131.7 mg, 0.6 mmol) in 10 mL of H2O was stirred for about
10 min. The mixture was sealed in a 23 mL Teflon-lined auto-
clave and heated to 160 °C for 4 days. After the autoclave was
cooled to room temperature, colorless crystals were collected
Structure of ijCoIJtdzdc)IJ4,4′-bipy)IJH2O)]n (1). Complex 1
crystallizes in the monoclinic space group P21/n with Z = 4.
Its asymmetric unit consists of one CoII ion, one tdzdc2−
anion, one 4,4′-bipy molecule and one coordinated water
molecule. As shown in Fig. 1a, each CoII ion shows an octahe-
dral geometry completed by four equatorial O atoms from
three carboxylate groups and one coordinated water mole-
cule, as well as two axial N atoms from two individual 4,4′-
bipy ligands. The tdzdc2− anions link two adjacent CoII ions
by the carboxylate groups in a μ2-κO,O′:κO″ mode (Scheme 3a)
to form a zigzag chain (–M–O–C–O–M–). Further, each two
neighboring zigzag chains is bridged by 4,4′-bipy to produce a
two-dimensional (2D) layer structure (Fig. 1b). Herein, if each
CoII ion is simplified as a 4-connected node, 1 can be topolog-
ically classified as a 2D network with sql topology by TOPOS
4.0,15 represented by a Schläfli symbol of {44·62} (Fig. 1c).
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Table 1 Crystal data and structure refinements for 1–5
1
2
3
4
5
Formula
Mr
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C14H10N4SCoO5
405.25
Monoclinic
P21/n
11.455(2)
8.5195(17)
16.698(3)
90
C17H20N4SCoO8
499.36
Monoclinic
Cc
14.944(3)
16.940(3)
10.384(2)
90
C18H18N6S2Zn2O13
721.30
Monoclinic
C2/c
34.618(7)
10.056(2)
7.5334(15)
90
C9H6N3SZnO6
349.63
Monoclinic
P21/c
14.550(3)
10.115(2)
7.4802(15)
90
C16H12N8SZnO4
477.77
Orthorhombic
Pbca
10.772(2)
18.039(4)
18.646(4)
90
β [°]
103.81(3)
90
1582.5(5)
1.701
123.74(3)
90
2186.0(11)
1.517
100.66(3)
90
2577.3(9)
1.859
95.76(3)
90
95.76(3)
2.120
90
90
γ [°]
V [Å3]
3623.2(13)
1.752
8
ρ [g cm−3
Z
]
4
4
4
4
FIJ000)
820
1.251
1028
0.931
1456
2.102
700
2.466
1936
1.517
μ [mm−1
]
Collected reflections
Unique reflections
Rint
13 288
2782
0.0255
0.0374
0.0840
1.091
9473
3858
0.0341
0.0323
0.0750
1.002
10 843
2266
0.0630
0.0946
0.2250
1.133
9108
1928
0.0797
0.0722
0.1820
1.153
29 161
3189
0.0943
0.0582
0.1145
1.126
a
R1 [I > 2σIJI)]
wR2 [all data]
b
GOF on F2
P
P
P
P
a
2
R1 = ‖Fo| − |Fc‖/ |Fo|. b wR2 = { ijwIJFo − Fc2)2]/ wIJFo2)2}1/2
.
Structure of {[CoIJtdzdc)IJbpp)IJH2O)]·3H2O}n (2). Complex 2
It is notable that in 2, only one carboxylate group of tdzdc2−
coordinates to the CoII ion, along with one thiadiazole-N atom
from the same tdzdc2− anion, while the other carboxylate
group is free of coordination, resulting in a μ2-κO:κO′,N mode
of tdzdc2− (Scheme 3b). In other words, two neighboring CoII
ions are connected by one carboxylate group from one tdzdc2−
anion in a syn–anti mode to generate a one-dimensional (1D)
chain. Further, each 1D chain is linked to four neighboring
chains by bpp to form a 3D structure (Fig. 2c). Simplifying CoII
ions as 4-connected nodes, the complex would produce a 3D
cds-type net with a Schläfli symbol of {65·8} (Fig. 2d). Evi-
dently, the distinct coordination configurations and struc-
tural topologies of 1 and 2 should be attributed to the intro-
duction of different auxiliary ligands, or specifically the
distinct flexibilities and molecular lengths of 4,4′-bipy and
bpp. The rigid 4,4′-bipy ligands in 1 acting as linear linkers
make the 1D structure nearly planar and consequently pro-
duce a 2D network, while the curved flexible bpp ligands in 2
are capable of extending the 1D chains along three directions
to form a 3D network. This indicates that the structural traits
of auxiliary ligands can significantly affect the linkage between
block units and thereby the resulting geometry of CPs.
crystallizes in the monoclinic space group Cc with an asym-
metric unit containing one CoII ion, one tdzdc2− anion, one
bpp molecule, and one coordinated and three lattice H2O
molecules. As shown in Fig. 2a, each CoII ion is surrounded
by three N atoms from two different bpp ligands and one
tdzdc2− ligand, as well as three O atoms from two individual
tdzdc2− anions and one coordinated water molecule,
exhibiting a six-coordinated octahedral geometry. In contrast
to the coordination environment of 1, in which two 4,4′-bipy
ligands coordinate to one CoII ion from opposite directions,
giving rise to a N–Co–N angle of 174.423IJ91)°, the two bpp
ligands in 2 coordinate to one CoII in a neighboring arrange-
ment with a N–Co–N angle of 89.92IJ11)°.
Structure of {[Zn2IJtdzdc)2IJ4,4′-bipy)IJH2O)2]·3H2O}n (3).
Complex 3 crystallizes in the monoclinic space group C2/c
with an asymmetric unit consisting of one ZnII ion, one
Fig. 1 Views of (a) the coordination environment of CoII ions, (b) the
2D layer structure, and (c) the sql topological net of 1.
Scheme 3 Four coordination modes of the H2tdzdc ligands in CPs
1–5: (a) for 1, (b) for 2, (c) for 3 and 4, and (d) for 5.
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Structure of ijZn2IJtdzdc)2IJobpy)IJH2O)2]n (4). Complex 4
crystallizes in the monoclinic space group P21/c. Its asymmet-
ric unit comprises one ZnII ion, one tdzdc2− anion, as well as
one half obpy molecule and one coordinated H2O molecule.
As shown in Fig. 4a, each ZnII ion is six-coordinated to one N
atom from one tdzdc2− anion and five O atoms from two indi-
vidual tdzdc2− anions, one obpy molecule and one water mol-
ecule. Herein, the involved ZnII ion has a similar octahedral
coordination environment as in 3, except that the N atom of
4,4′-bipy is replaced with obpy-O. Two neighboring ZnII ions
are linked by one tdzdc2− in a μ2-κO,O′:κO″,N mode (Scheme 3c)
to form a zigzag chain, which is further connected by obpy to
generate a 2D layer structure. By this coordination, a three-fold
interpenetrated hcb net with a Schläfli symbol of {63} is formed.
Despite several similarities, such as the coordination envi-
ronment of involved ZnII ions, the coordination mode of
tdzdc2− anions and also the 2D net architecture, 3 and 4 sig-
nificantly exhibit distinct topological structures along with
different degrees of interpenetration. This can be rationalized
in terms of the different sizes and coordination geometries of
the auxiliary ligands. In detail, the longer backbone length of
obpy, compared to that of 4,4′-bipy, leads reasonably to a
higher degree of interpenetration. On the other hand, the
inclining orientation of obpy in 4 relative to the plane com-
prising equatorial O atoms of the ZnII octahedron differs
from the pseudo-normal orientation of 4,4′-bipy in 3, which
results in different topological structures of 3 and 4.
Fig. 2 Views of (a) the coordination environment of CoII and linkage
modes of the ligands, (b) the 1D chain of CoII linked by tdzdc2−, (c) the
3D structure composed of 1D chains and (d) the 3D cds-type
topological net of 2.
tdzdc2− anion, one half 4,4′-bipy molecule, as well as one
coordinated and one and a half lattice H2O molecules. As
shown in Fig. 3a, each ZnII ion is six-coordinated to four equa-
torial O atoms from three carboxylate groups and one coordi-
nated water, as well as two axial N atoms from one 4,4′-bipy
and one thiadiazole ring. Furthermore, two neighboring ZnII
ions are bridged by one tdzdc2− in a μ2-κO,O′:κO″,N mode
(Scheme 3c), forming a zigzag chain which is further linked by
4,4′-bipy to give a 2D layer. For 3, either two involved 2D layers
interpenetrate with each other to generate a two-fold inter-
penetrated hcb net with a Schläfli symbol of {63}.
Furthermore, in the asymmetric units of 1 and 2, both the
two bipyridine-N donors coordinate to one metal ion, while
in the asymmetric units of 3 and 4, there exists only one
bipyridine-N donor (or obpy-O) together with one thiadiazole-
N donor instead, showing very different coordination proper-
ties of CoII and ZnII ions.
Structure of ijZnIJtdzdc)IJtmb)]n (5). Complex 5 crystallizes
in the orthorhombic space group Pbca and its asymmetric
Fig. 3 Views of (a) the coordination environment of ZnII, (b) the 2D
two-fold interpenetrated structure and (c) the topological packing
arrangement of 3.
Fig. 4 Views of (a) the coordination environment of ZnII and linkage
modes of the ligands, (b) the 2D layer structure composed of 1D
chains, and (c) the three-fold interpenetrated hcb net of 4.
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unit consists of one ZnII ion, one tdzdc2− anion and one tmb
molecule. As shown in Fig. 5a, each ZnII ion is surrounded by
two N atoms from two individual tmb molecules as well as
four carboxylate O atoms from two tdzdc2− ligands, noting
that the N atoms of tdzdc2− anions do not take part in coordi-
nation bonding. The basic block unit of 5 is the dinuclear
{Zn2} cluster that is formed through double linking of two
adjacent ZnII ions with two tdzdc2− anions, both of which
present the same μ2-κO,O′:κO″,O‴ mode (Scheme 3d). Fur-
thermore, each {Zn2} cluster links with four neighboring
{Zn2} clusters by four tmb ligands through monodentate
coordination of tmb-N to form a three-fold interpenetrated
2D layer structure, which should be attributed to the high
degree of structural flexibility of tmb. From a topological
point of view, 5 exhibits an sql net with a Schläfli symbol of
{44·62} (Fig. 5c).
range at 1 kOe fields. Before measurement, the crystallo-
graphic phase purity of crushed crystalline samples was con-
firmed by PXRD patterns (see Fig. S1 in the ESI†). Magnetic
investigations reveal the antiferromagnetic (AF) properties of
1 and canted antiferromagnetic behaviors of 2, as discussed
in detail as follows.
As shown in Fig. 6, the χMT values for 1 and 2 at room
temperature are 3.97 and 3.29 emu mol−1 K, respectively,
which are much larger than the known spin-only value (1.875
emu mol−1 K) for one magnetically isolated CoII ion (S = 3/2,
g = 2) and therefore indicative of strong spin–orbit coupling
in both 1 and 2. In addition, for 1, as the temperature
decreases, the value of χMT decreases slowly down to a mini-
mum value of 0.40 emu mol−1 K at 2 K, which indicates AF
coupling between the CoII ions. For 2, the χMT value initially
decreases slowly down to a minimum value of 2.03 emu
mol−1 K at 4.5 K, which is slightly larger than the value (1.875
emu mol−1 K) for one spin-only CoII ion, indicating weak fer-
romagnetic (F) or canted AF coupling between the CoII ions.
In summary, all tdzdc2− anions in 1–5 were found to coor-
dinate to the two metal ions, but in four different coordina-
tion modes (Scheme 3). For 1–4, the basic secondary struc-
tural unit is made up of 1D chains constructed by linking the
metal ions with the carboxylate groups of tdzdc2− anions,
while in 5, the primary secondary unit is the dinuclear ZnII
cluster {Zn2} which is constructed through chelating coordi-
nation of four carboxylate groups from two tdzdc− anions, in
which the thiadiazole ring is free of coordination. In addi-
tion, all the involved N atoms participate in coordination
bonding in imidazoledicarboxylate ligands,6e however, it is
not observed here for tdzdc anions,2 which might be ascribed
to the influence of the S atoms.
Magnetic properties
The magnetic properties of 1 and 2 were investigated using
solid state magnetic susceptibility measurements in a 2–300 K
Fig. 5 Views of (a) the coordination environment of ZnII and linkage
modes of the ligands, (b) the 2D layer structure and (c) the three-fold
interpenetrated sql net of 5.
Fig. 6 Plots of χMT vs. T (red part for the Curie–Weiss fitting) and χM
−1
vs. T (solid line shows the best fit at high temperature) for (a) 1 and
(b) 2. Inset in (b): the M vs. H plot at 2 K.
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Upon further cooling to 2 K, an abrupt increase of χMT to
2.16 emu mol−1 K subsequently occurs. The Curie–Weiss
fitting [χM = C/IJT − θ)] of the magnetic data in the tempera-
ture range of 2–300 K for 1 and 100–300 K for 2 gives C =
4.25 emu mol−1 K, θ = −22.69 K for 1 and C = 3.51 emu mol−1
K, θ = −21.75 K for 2, respectively. As known, the magnetic
behavior of high-spin CoII ions is fairly complicated and diffi-
cult to explain. Therefore, we suggest that the decrease of
χMT values at high temperatures should be attributed mainly
to the strong spin–orbital coupling of a single CoII ion, which
also contributes to the negative θ values.
Key Scientific Research Project of Colleges and Universities in
Henan Province (15A150032) and Pingdingshan Key Scientific
Research Project (2013066).
Notes and references
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coupling of the CoII ions was estimated using eqn (1).16
χMT = A exp(−E1/kT) + B exp(−E2/kT)
(1)
In eqn (1), the sum of parameters A and B equals to the
Curie constant, while E1 and E2 refer to the spin–orbit cou-
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+ B = 4.30 emu mol−1 K, −E1/k = −45.59 K and −E2/k = −4.44 K
for 1, and A + B = 3.48 emu mol−1 K, −E1/k = −51.87 K and
−E2/k = −0.18 K for 2. The negative value of −E2/k for both 1
and 2 further indicates the dominant AF interactions in 1
and weak canted AF interactions in 2.
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CoII ions of 2, isothermal field-dependent magnetization
MIJH) has also been investigated (see the inset of Fig. 6b).
Upon increasing the field strength, magnetization increases
fast at low fields and slowly at high fields, and ultimately
approximates to 2.38 Nβ at 50 kOe, which strongly supports
the canted antiferromagnetism in 2.
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Conclusions
Five CoII/ZnII CPs have been prepared based on H2tdzdc and
four N/O-donor auxiliary ligands. Structural analyses reveal a
significant dependence of the assembly structure on auxiliary
ligands. The distinct topological networks as well as the differ-
ent interpenetration degrees are observed in these CPs, which
can be interpreted reasonably in terms of the different sizes
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Acknowledgements
This work was supported by the NSFC (21421001, 21403116,
and 21403102), MOE Innovation Team (IRT13022) of China,
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