Cd(II) coordination polymers constructed from flexible disulfide ligand: Solvothermal syntheses, structures and luminescent properties

Article abstract of DOI:10.1016/j.ica.2011.06.020

Four novel coordination polymers, [Cd(Hdtbb)(dtbb)_0.5(DMF)] _n (1), {[Cd(dtbb)(2,2′-bpy)(H₂O)]·2DMA} _n (2), {[Cd₂(dtbb)₂(1,4-bix) ₂]·3DMF}_n (3) and [Cd(dtbb)(1,4-btx)]_n (4) [H₂dtbb = 2,2-dithiobisbenzoic acid, 2,2′-bpy = 2,2′-bipyridine, 1,4-bix = 1,4-bis(imidazol-1-ylmethyl)benzene, 1,4-btx = 1,4-bis(triazol-1-ylmethyl)benzene] have been synthesized and structurally characterized. Complexes 1 and 2 possess one-dimensional (1D) infinite structures. The structures of complexes 3 and 4 exhibit two dimensional (2D) frameworks, which mainly due to the differences in the bridging modes of dtbb^2- ligand and the effect of the N-donor auxiliary ligands. The infrared spectra, thermogravimetric and luminescent properties were also investigated for these compounds.

Full text of DOI:10.1016/j.ica.2011.06.020

Inorganica Chimica Acta 376 (2011) 222–229
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Cd(II) coordination polymers constructed from flexible disulfide ligand:
Solvothermal syntheses, structures and luminescent properties
Jianghua Yu a, Rong Yao a, Limin Yuan a, Bin Xu a, Botao Qu a, Wenlong Liu a,b,
⇑
a College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China
b State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Four novel coordination polymers, [Cd(Hdtbb)(dtbb)0.5(DMF)]n (1), {[Cd(dtbb)(2,20-bpy)(H2O)]ꢀ2DMA}n
(2), {[Cd2(dtbb)2(1,4-bix)2]ꢀ3DMF}n (3) and [Cd(dtbb)(1,4-btx)]n (4) [H2dtbb = 2,2-dithiobisbenzoic acid,
2,20-bpy = 2,20-bipyridine, 1,4-bix = 1,4-bis(imidazol-1-ylmethyl)benzene, 1,4-btx = 1,4-bis(triazol-1-yl-
methyl)benzene] have been synthesized and structurally characterized. Complexes 1 and 2 possess
one-dimensional (1D) infinite structures. The structures of complexes 3 and 4 exhibit two dimensional
(2D) frameworks, which mainly due to the differences in the bridging modes of dtbb2ꢁ ligand and the
effect of the N-donor auxiliary ligands. The infrared spectra, thermogravimetric and luminescent proper-
ties were also investigated for these compounds.
Article history:
Received 10 November 2010
Received in revised form 8 June 2011
Accepted 9 June 2011
Available online 13 July 2011
Keywords:
Coordination polymers
2,2-Dithiobisbenzoic acid
Auxiliary ligands
Luminescence
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
requirements when they react with different metal salts, the
flexible and multifunctional coordination sites provide a high
In the past decades, the realm of crystal engineering has
achieved significant success in developing a variety of coordination
networks [1–21]. The interest arise not only from their versatile
fascinating architectures but also from their promising applica-
tions as functional materials [22–24,3,25–30]. Many works have
been devoted to the selection or design of suitable ligands contain-
ing certain features. Among the reported studies, organic ligands
with carboxylate groups are of especial interest because they can
adopt a variety of coordination modes and result in diverse
multidimensional frameworks [31–38]. To date, a number of rigid
ligands, such as benzenedicarboxylate isomers [39–42], 1,3,5-
benzenetricarboxylate [43–45], 1,2,4,5-benzenetetracarboxylate
[46,47] and pyridinedicarboxylate isomers [48–50], have been suc-
cessfully employed and well documented in the preparation of
various carboxylato-containing metal–organic coordination com-
plexes with useful properties. However, there is an unfavorable
investigation on the MOFs containing flexible bridging carboxylate
ligands [51–55]. Compared with the rigid ligands, the skew and
versatile coordination orientation of the flexible bridging ligands
is favorable for constructing novel structures [56–59].
likelihood for build novel coordination frameworks with high
dimensions. Whereas, there have been few reports of studies on
flexible disulfide derivatives of carboxylates [60–64]. Considering
the points mentioned above, to further explore the coordination
characteristics of flexible disulfide bridging aromatic dicarboxylate
ligand, we chose 2,2-dithiobisbenzoic acid (H2dtbb, Scheme 1(a))
as primary ligand to construct Cd(II) photoluminescent coordina-
tion polymers by taking advantage of its multicarboxylate bridging
coordination ability together with the flexibility of its C–S–S–C
bonds, incorporating the auxiliary ligands 2,20-bipyridine (2,20-
bpy, Scheme 1(b)) for 2, 1,4-bis(imidazol-1-ylmethyl)benzene
(1,4-bix, Scheme 1(c)) for 3, and 1,4-bis(triazol-1-ylmethyl)-
benzene (1,4-btx, Scheme 1(d)) for 4. Herein, we report the synthe-
ses, crystal structures and photoluminescent properties of four
Cd(II) complexes with these ligands: [Cd(Hdtbb)(dtbb)0.5(DMF)]n
(1), {[Cd(dtbb)(2,20-bpy)(H2O)]ꢀ2DMA}n (2), {[Cd2(dtbb)2(1,4-
bix)2]ꢀ3DMF}n (3) and [Cd(dtbb)(1,4-btx)]n (4).
2. Experimental
Disulfide bridging phenyl carboxylate ligands possess flexibility
owing to the presence of –S–S– spacers between the phenyl rings
and can adopt various conformations according to geometric
2.1. Materials and methods
The ligand 1,4-bix and 1,4-btx were synthesized according to
literatures [65,66]. All other reagents and solvents employed were
commercially available and used as received without further
purification. Elemental analyses for C, H, and N were carried out
⇑
Corresponding author at: College of Chemistry and Chemical Engineering,
Yangzhou University, Yangzhou 225002, China. Tel./fax: +86 514 87975244.
E-mail address: liuwl@yzu.edu.cn (W. Liu).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.06.020

J. Yu et al. / Inorganica Chimica Acta 376 (2011) 222–229
223
2.18. Found: C, 44.76; H, 3.21; N, 2.14%. IR data (KBr pellet,
[cmꢁ1]): 3420(m), 2941(w), 2489(w), 1664(s), 1575(m), 1374(s),
m
1229(m), 1134(w), 1032(w), 932(w), 833(w), 725(m).
2.2.2. {[Cd(dtbb)(2,20-bpy)(H2O)]ꢀ2DMA}n (2)
A
mixture of CdO (0.02 g, 0.20 mmol), H2dtbb (0.06 g,
0.20 mmol), 2,20-bpy (0.02 g, 0.10 mmol), DMA (3 ml), H2O (2 ml)
was sealed in a 25 ml Teflon-lined stainless steel vessel and heated
at 80 °C for 2d. After the mixture had been slowly cooled to room
temperature over 24 h, yellow block crystals of 2 were obtained
with 56% yield on cadmium basis. Elemental analysis, Aanl. Calc.
for C32H36CdN4O7S2 (Mr. 765.17): C, 50.23; H, 4.74; N, 7.32. Found:
C, 50.27; H, 4.71; N, 7.28%. IR data (KBr pellet, m
[cmꢁ1]): 3438(m),
2923(m), 1588(s), 1544(s), 1374(s), 1248(s), 1008(m), 839(w),
744(m), 634(m).
Scheme 1. Chemical structures of H2dtbb (a) and auxiliary ligand 2,20-bpy (b), 1,4-
bix (c) and 1,4-btx (d).
2.2.3. {[Cd2(dtbb)2(1,4-bix)2]ꢀ3DMF}n (3)
A
mixture of CdO (0.03 g, 0.20 mmol), H2dtbb (0.09 g,
0.30 mmol), 1,4-bix (0.03 g, 0.10 mmol), DMF (5 ml) was sealed
in a 25 ml Teflon-lined stainless steel vessel and heated at 80 °C
for 48 h, and then cooled to room temperature over 1d. Yellow
block crystals of 3 suitable for X-ray diffraction were obtained with
75% yield on cadmium basis. Elemental analysis, Anal. Calc. for
using a Perkin–Elmer 240 elemental analyzer. The IR spectra were
obtained as KBr pellets on a Bruker VECTOR 22 spectrometer in the
4000–400 cmꢁ1 region. Thermogravimetric analyses were per-
formed on a TGAV5.1A Dupont 2100 instrument from room tem-
perature to 600 or 800 °C with a heating rate of 10 °C minꢁ1 in
nitrogen environment. Luminescence spectra for the solid
C
65H63Cd2N11O11S4 (Mr. 1527.30): C, 51.12; H, 4.16; N, 10.09.
Found: C, 51.20; H, 4.13; N, 10.12%. IR data (KBr pellet,
m
[cmꢁ1]):
3445(m), 2815(w), 2513(w), 1683(s), 1621(s), 1367(m), 1254(s),
1115(m), 1041(w), 913(w), 801(w), 732(m), 669(w), 536(w).
samples were recorded using
spectrophotometer.
a Hitachi 850 fluorescence
2.2.4. [Cd(dtbb)(1,4-btx)]n (4)
2.2. Synthesis of the complexes
A
mixture of CdO (0.04 g, 0.30 mmol), H2dtbb(0.09 g,
0.30 mmol), 1,4-btx (0.02 g, 0.10 mmol), DMF (2 ml) , H2O (3 ml)
was heated at 80 °C for 2d in a sealed Teflon-lined stainless steel
vessel (25 ml) under autogenous pressure. Slow cooling of the
reaction mixture to room temperature gave yellow block crystals
with 56% yield on cadmium basis. Elemental analysis, Anal. Calc.
for C26H20CdN6O4S2 (Mr. 657.00): C, 47.53; H, 3.07; N, 12.79.
2.2.1. [Cd(Hdtbb)(dtbb)0.5(DMF)]n (1)
mixture of CdCO3 (0.03 g, 0.20 mmol), H2dtbb (0.09 g,
A
0.30 mmol), DMF (2 ml) , H2O (1 ml) and NaOH (0.1 mol/L, 2 ml),
was placed in a 25 ml Teflon-lined stainless steel vessel, which
was sealed and heated at 80 °C for 2d. After the mixture had been
slowly cooled to room temperature, yellow plate crystals of 1 were
obtained with 65% yield on cadmium basis. Elemental analysis,
Anal. Calc. for C24H20CdNO7S3 (Mr. 643.03): C, 44.83; H, 3.14; N,
Found: C, 47.23; H, 3.22; N, 12.2%. IR data (KBr pellet, m
[cmꢁ1]):
3398(m), 3103(m), 1587(s), 1533(s), 1380(s), 1272(s), 1133(m),
966(m), 861(m), 752(m).
Table 1
Crystal data and structure refinements for compounds 1–4.
1
2
3
4
Empirical formula
Formula mass
Crystal system
Space group
a (Å)
C
24H20CdNO7S3
C32H36CdN4O7 S2
765.17
monoclinic
P21/c
11.803(6)
26.668(14)
10.907(6)
90
107.330(7)
90
C65H63Cd2N11O11S4
1527.30
monoclinic
C2/c
31.263(3)
12.0748(10)
18.9417(16)
90
105.9230(10)
90
C26H20CdN6O4 S2
657.00
642.99
monoclinic
C2/c
30.351(3)
8.8251(8)
21.869(2)
90
122.0180(10)
90
triclinic
ꢀ
P1
10.7370(17)
11.2552(17)
11.7481(18)
73.996(2)
88.977(2)
76.188(2)
2
1323.5(4)
1.649
1.028
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Z
8
4
4
V (Å3)
4966.5(8)
1.720
1.178
3277(3)
1.551
0.847
6876.0(10)
1.474
0.806
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
F(0 0 0)
2584
1568
3116
660
Crystal size (mm)
h Range (°)
Reflections collected
0.40 ꢂ 0.30 ꢂ 0.10
1.58–27.65
21084
0.38 ꢂ 0.20 ꢂ 0.18
2.10–25.50
23978
0.34 ꢂ 0.25 ꢂ 0.20
1.82–25.00°
24355
0.34 ꢂ 0.28 ꢂ 0.20
1.81–27.60
11599
Unique reflections
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
5776[Rint = 0.0212]
5776/0/328
1.049
6069 [Rint = 0.075]
6069/0/427
1.072
6056 [Rint = 0.0375]
6056/83/409
1.118
5970 [Rint = 0.0309]
5970/0/352
1.121
R1, wR2 [I > 2
r
(I)]
0.0218, 0.0619
0.0219, 0.0678
0.344 and ꢁ0.288
0.0471, 0.1176
0.0621, 0.1260
1.24 and ꢁ1.01
0.0411, 0.1119
0.0660, 0.1250
0.923 and ꢁ0.745
0.0421, 0.1109
0.0691, 0.1600
0.644 and ꢁ1.185
R1, wR2 (all data)
Largest difference in peak and hole (e Åꢁ3
)
R1
=
R
||Fo| ꢁ |Fc|/
R
|Fo|, wR2 = |
R
R .
w(|Fo|2 ꢁ |Fc|2)|/ |w(F2o )2|1/2

224
J. Yu et al. / Inorganica Chimica Acta 376 (2011) 222–229
Table 2
Selected bond lengths (Å) and angles (°) for complexes 1a, 2b, 3c and 4d.
1
Cd1–O2
Cd1–O6
2.1796(14)
2.2945(15)
113.14(5)
143.28(5)
102.82(5)
54.96(5)
Cd1–O7
Cd1–O5
2.2418(15)
2.4676(13)
105.68(5)
91.71(6)
143.83(5)
78.45(5)
Cd1–O1#1
Cd1–O3#2
2.2539(14)
2.5022(14)
87.25(6)
101.95(5)
86.75(5)
O2–Cd1–O7
O2–Cd1–O6
O2–Cd1–O5
O6–Cd1–O5
O1#1–Cd1–O3#2
O2–Cd1–O1#1
O7–Cd1–O6
O7–Cd1–O5
O2–Cd1–O3#2
O6–Cd1–O3#2
O7–Cd1–O1#1
O1#1–Cd1–O6
O1#1–Cd1–O5
O7–Cd1–O3#2
O5–Cd1–O3#2
82.33(6)
101.80(5)
169.58(5)
78.67(5)
2
Cd1–O1
Cd1–N1
2.309(3)
2.354(3)
Cd1–O3#1
Cd1–O5
2.332(3)
2.379(3)
Cd1–N2
Cd1–O2
2.347(3)
2.456(3)
Cd1–O4#1
O1–Cd1–O3#1
O1–Cd1–N1
O1–Cd1–O5
N1–Cd1–O5
N2–Cd1–O2
O1–Cd1–O4#1
N1–Cd1–O4#1
2.555(3)
98.12(12)
146.41(11)
81.91(13)
81.89(12)
85.10(10)
84.71(9)
O1–Cd1–N2
140.25(11)
96.78(11)
177.39(11)
55.26(9)
151.76(10)
53.69(9)
O3#1–Cd1–N2
N2–Cd1–N1
N2–Cd1–O5
O3#1–Cd1–O2
O5–Cd1–O2
N2–Cd1–O4#1
O2–Cd1–O4#1
87.60(12)
70.19(11)
94.04(12)
95.56(10)
86.61(11)
127.72(10)
127.11(10)
O3#1–Cd1–N1
O3#1–Cd1–O5
O1–Cd1–O2
N1–Cd1–O2
O3#1–Cd1–O4#1
O5–Cd1–O4#1
80.21(11)
123.77(11)
3
Cd1–N1
2.227(3)
Cd1–O2
2.442(3)
Cd1–N3
2.262(3)
Cd1–O3#1
N1–Cd1–N3
N1–Cd1–O3#1
N3–Cd1–O3#1
N1–Cd1–O1
N3–Cd1–O1
2.265(3)
Cd1–O4#1
2.522(3)
Cd1–O1
2.313(3)
101.07(13)
134.85(12)
92.11(12)
102.07(12)
131.98(13)
O3#1–Cd1–O1
N1–Cd1–O2
N3–Cd1–O2
O3#1–Cd1–O2
O1–Cd1–O2
100.28(11)
95.85(13)
81.76(12)
128.91(12)
54.52(11)
N1–Cd1–O4#1
N3–Cd1–O4#1
O3#1–Cd1–O4#1
O1–Cd1–O4#1
O2–Cd1–O4#1
87.54(11)
133.30(12)
54.06(10)
89.20(11)
143.52(11)
4
Cd1–O1#1
Cd1–O2#2
O1#1–Cd1–N1
O1#1–Cd1–O3
O1#1–Cd1–O4
O3–Cd1–O4
N1–Cd1–N6#3
2.232(4)
2.333(3)
Cd1–O3
Cd1–O4
2.349(3)
2.374(4)
Cd1–N1
Cd1–N6#3
2.291(4)
2.382(4)
112.75(16)
94.37(14)
146.11(14)
55.53(13)
93.58(16)
O1#1–Cd1–O2#2
N1–Cd1–O3
N1–Cd1–O4
O4–Cd)–N6#3
O2#2–Cd1–N6#3
99.95(15)
151.52(16)
99.92(16)
86.05(16)
176.12(15)
N1–Cd1–O2#2
O2#2–Cd1–O3
O2#2–Cd1–O4
O1#1–Cd1–N6#3
O3–Cd1–N6#3
83.17(15)
83.75(13)
92.39(15)
83.25(15)
98.25(15)
a
b
c
Symmetry codes: #1 ꢁx + 2, ꢁy + 2, ꢁz #2 x, ꢁy + 2, z ꢁ 1/2 #3 x, ꢁy + 2, z + 1/2 #4 ꢁx + 2, y, ꢁz ꢁ 1/2.
Symmetry codes: #1 x + 1, y, z #2 x ꢁ 1, y, z.
Symmetry codes: #1 x, y + 1, z #2 x, y ꢁ 1, z #3 ꢁx + 1, ꢁy + 2, ꢁz + 2 #4 ꢁx + 3/2, ꢁy + 1/2, ꢁz + 2 #5 ꢁx + 1, y, ꢁz + 3/2.
Symmetry codes: #1 x, y, z ꢁ 1 #2 ꢁx + 2, ꢁy, ꢁz + 2 #3 ꢁx + 2, ꢁy + 1, ꢁz #4 x, y, z + 1.
d
2.3. X-ray crystallography
The six Cd–O distances range from 2.1796(14) to 2.5022(14) Å.
The dtbb2ꢁ ligand adopts l4 g1 coordination mode, and
-
g1 g1 g1
: : :
Single crystal X-ray diffraction analyses of 1–4 were carried out
on a Bruker SMART APEX II CCD diffractometer with graphite-
two carboxylate groups of ligand link to two Cd(II) ions in the
bidentate bridging mode, while the partly deprotonated Hdtbbꢁ
monochromated Mo K
a
radiation (k = 0.71073 Å) at 296(2) K.
anion employs l2- : :g
g1 g1 1 coordination mode and two carboxylate
Empirical absorption corrections were applied by using the SADABS
program [67]. The structures were solved by direct methods and
refined by the full matrix least-squares based on F2 using SHELXTL
programe package [68]. All nonhydrogen atoms were refined
anisotropically. The hydrogen atoms except for those of water mol-
ecules were generated geometrically and refined using a riding
model. Crystal data and details of the structure determination for
complexes 1–4 are listed in Table 1. Selected bond lengths and an-
gles are given in Table 2.
groups coordinate to two Cd(II) ions in the bidentate chelate and
monodentate modes, respectively. The two aromatic rings of
Hdtbb- ligands form dihedral angle and torsion angle (C3/S1/
S1#4/C3#4) of 72.53(67)° and 89.63(92)°, the dihedral angle be-
tween the two phenyl rings of dtbb2ꢁ ligands and torsion angle
(C14/S2/S3/C21) are 82.40(76)° and 88.42(99)°. Two Cd1 atoms
are joined by carboxylate groups of two dtbb2ꢁ ligands construct
a dimeric unit with Cd–Cd distance to be 3.654 Å. These dimeric
units are further organized into an infinite one dimensional chain
through bidentate bridging mode dtbb2ꢁ ligands (Fig. 1b). While
the other Hdtbb- anion connects this chain forming a one-dimen-
sional triple chain structure (Fig. 1c). The O–HꢀꢀꢀO hydrogen bon-
dings (O4ꢀꢀꢀO6, 2.626(2) Å) stabilize the 1D chain structure.
Further, such chains showing a parallel arrangement are connected
by interchains C–HꢀꢀꢀO H-bonds between phenyl rings and carbox-
ylic groups (Table S1, supporting information), forming a 3-D
supramolecular network (Fig. S1).
3. Results and discussion
3.1. Crystal structure of complex 1
The crystallographic analysis reveals that 1 is a one dimensional
chain coordination polymer. Complex 1 crystallizes in the mono-
clinic system, C2/c space group. The asymmetric unit of 1 contains
one crystallographically nonequivalent Cd(II) ion (Cd1), one
Hdtbbꢁ ligand, half dtbb2ꢁ ligand and one DMF molecule. Cd1 is
six-coordinated by three oxygen atoms from two carboxylic groups
of two dtbb2ꢁ ligands, two oxygen atoms from two carboxylic
groups of two Hdtbbꢁ ligands and one oxygen atom from DMF
molecule, exhibiting the distorted octahedral geometry (Fig. 1a).
3.2. Crystal structure of complex 2
X-ray crystallographic analysis reveals that 2 crystallizes in a
monoclinic space group P21/c and there are one Cd(II) ion (Cd1),
one dtbb2ꢁ ligand, one 2,20-bpy ligand, one H2O molecule and

J. Yu et al. / Inorganica Chimica Acta 376 (2011) 222–229
225
Fig. 1. (a) Molecular structure of 1. Thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity. Symmetry code: #1 ꢁx + 2, ꢁy + 2, ꢁz #2 x,
ꢁy + 2, z ꢁ 1/2 #3 x, ꢁy + 2, z + 1/2 #4 ꢁx + 2, y, ꢁz ꢁ 1/2. (b) A view of the 1D chain in 1. (c) A view of the 1D triple chain structure along the b-axis in 1. DMF molecules are
omitted for clarity.
Fig. 2. (a) Molecular structure of 2. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms and free DMA molecules are omitted for clarity. Symmetry code : #1
x + 1, y, z #2 x ꢁ 1, y, z. (b) A view of the 1D chain structure in 2.

226
J. Yu et al. / Inorganica Chimica Acta 376 (2011) 222–229
two free DMA molecules in the asymmetric unit. The Cd(II) ion is
seven-coordinated by four oxygen atoms from two carboxylic
groups of two different dtbb2ꢁ ligands, two nitrogen atoms from
one 2,20-bpy molecule and one O atom from water molecule in a
pentagonal bipyramid geometry (Fig. 2a). The five Cd–O distances
range from 2.309(3) to 2.555(3) Å and the Cd–N bond lengths are
2.354(3) Å and 2.347(3) Å. The dtbb2ꢁ ligand is tetradentate, two
carboxyl groups adopt bidentate chelating fashions. The pair of
phenyl rings of dtbb2ꢁ employs a bended conformation, and the
dihedral angle between the two phenyl rings and torsion angle
(C7/S2/S1/C8) are 77.56 (11)°and 93.07(19)°. The Cd centers are
linked together by the bis-chelating dtbb2ꢁ ligands to form a 1D
chain (Fig. 2b). The 2,20-bpy molecule coordinate to a Cd center
in chelate mode. Interestingly, the DMA molecules is hydrogen
bonded to coordinated H2O molecules and 2,20-bpy phenyl rings,
leading to the formation of a 3D supramolecular network (Table
S1, Fig. S2).
nitrogen atoms from two 1,4-bix molecules, resulting in a slightly
distorted octahedral geometry. The four Cd–O distances fall in the
range of 2.262(3)–2.522(3) Å and the Cd–N bond lengths are
2.227(3) Å and 2.262(3) Å. Each dtbb2ꢁ anion links two Cd(II) ions
with its two carboxylate groups in bidentate chelating modes. The
pair of phenyl rings of the ligand employs a bended conformation,
the dihedral angle between the two phenyl rings and torsion angle
(C7/S1/S2/C8) are 79.76(16)° and 88.65(20)°. Two crystallographi-
cally independent 1,4-bix ligands adopting trans conformations
connect Cd1 atoms, alternately, to form a rare one dimensional
meso-helical chain with a pitch of 23.925 Å (Fig. 3b), which are fur-
ther extended by the dtbb2ꢁ ligands to afford a 2D 4-connected
staircase-like net (Fig. 3c and d). The adjacent 2D structure are
linked together through both Cphenyl–HꢀꢀꢀOcarboxylic and Cimidazol
–
HꢀꢀꢀOcarboxylic hydrogen bonds (Table S1) to afford a 3D supramolec-
ular network (Fig. S3).
3.4. Crystal structure of complex 4
3.3. Crystal structure of complex 3
ꢀ
Compound 4 crystallizes in the triclinic system, P1 space group.
Utilizing the bridging N,N0-donor ligand 1,4-bix, instead of the
chelating ligand 2,20-bipy, the 2D complex 3 is obtained. Complex
3 crystallizes in C2/c space group and the asymmetric unit contains
one crystallographically nonequivalent Cd(II) ion (Cd1), one dtbb2ꢁ
ligand, two half 1,4-bix molecules, one and a half DMF molecules
(Fig. 3a). Each Cd(II) ion is coordinated by four oxygen atoms from
two carboxylic groups of two different dtbb2ꢁ ligands and two
It contains one crystallographically Cd(II) ion (Cd1), one dtbb2ꢁ li-
gand and one 1,4-btx ligand in the asymmetric unit. The coordina-
tion geometry for the six-coordinate Cd1 atom can be described as
a distorted octahedral geometry (Fig. 4a). The Cd1 atom is coordi-
nated by four oxygen atoms from three different dtbb2ꢁ ligands
and two nitrogen atoms from two 1,4-btx molecules. The Cd–O dis-
tances range from 2.232(4) to 2.374(4) Å and the Cd–N bond
Fig. 3. (a) Molecular structure of 3. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms and free DMF molecules are omitted for clarity. Symmetry code: #1 x,
y + 1, z #2 x, y ꢁ 1, z #3 ꢁx + 1, ꢁy + 2, ꢁz + 2 #4 ꢁx + 3/2, ꢁy + 1/2, ꢁz + 2 #5 ꢁx + 1, y, ꢁz + 3/2. (b) 1D meso-helical chain along the a-axis in 3. (c) Perspective view of the 2D
structure in 3. (Hydrogen atoms are omitted for clarity). (d) Schematic representation of 2D (4,4)-connected structure of complex 3 (dtbb2ꢁ ligands are show as yellow linkers
and 1,4-bix ligands are show as purple links). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

J. Yu et al. / Inorganica Chimica Acta 376 (2011) 222–229
227
Fig. 4. (a) Molecular structure of 4. Thermal ellipsoids are drawn at 50% probability and hydrogen atoms are omitted for clarity. Symmetry code: #1 x, y, z ꢁ 1 #2 ꢁx + 2, ꢁy,
ꢁz + 2 #3 ꢁx + 2, ꢁy + 1, ꢁz #4 x, y, z + 1. (b) 1D double chain along the b-axis in 4. (c) Perspective view of the 2D structure in 4. (Hydrogen atoms are omitted for clarity). (d)
The 2D 44-sql layer formed in compound 4 (blue spheres represent the bisnuclear Cd(II) units, two dtbb2ꢁ ligands are show as blue linkers and two 1,4-btx ligands are show as
purple links). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
lengths are 2.291(4) Å and 2.382(4) Å. The two carboxylate groups
of dtbb2ꢁ ligand adopt different coordination modes, namely
bidentate bridging and chelating bidentate. The two aromatic rings
of dtbb2ꢁ ligands form dihedral angle and torsion angle (C18/S1/
S2/C19) of 84.80(22)° and 90.09(25)°. Cd1 atoms are connected
by two carboxylate groups of two dtbb2ꢁ ligands construct a di-
meric unit with Cd–Cd distance to be 4.407 Å. Each Cd(II) dimeric
unit connects with the other two neighboring ones by the dtbb2ꢁ
ligands leading to an infinite one dimensional double chain
(Fig. 4b). The cis-1,4-btx ligands linking one dimensional double
chain further generate an infinite 2D framework (Fig. 4c). Binuclear
Cd(II) units as 4-connected joints are bridged by two kinds of 2-
connected struts: dtbb2ꢁ and 1,4-btx ligand, so the 2D net can be
simplified to be a 44-sql net (Fig. 4d). The adjacent 2D nets pack
to form the supramolecular network through intersheets C–HꢀꢀꢀO
the above structural descriptions of our example compounds, four
kinds of coordination modes for the dtbb2ꢁ ligand are found as
shown in Scheme 2. In complexes 1–4, all the carboxylate groups
of dtbb2ꢁ employ monodentate, bidentate chelating and bidentate
bridging coordination modes. In 1, two carboxylate groups of
dtbb2ꢁ ligand both adopt l2 g1 g1 bridging mode links to two
- :
Cd(II) ions, while those of another Hdbb- ligand coordinate to
H-bonds (Table S1), C–Hꢀꢀꢀ
p
triazol and C–Hꢀꢀꢀ
pphenyl interactions (Ta-
ble S2, Fig. S4).
3.5. The coordination modes of the multi-carboxylate dtbb2ꢁ ligands
and effect of N-donor ligands
It is known that multi-carboxylate ligands are good candidates
for the construction of supramolecular frameworks with specific
structure due to their varied coordination modes. According to
Scheme 2. The coordination modes of Hdtbbꢁ and dtbb2ꢁ ligands observed within
compounds 1–4.

228
J. Yu et al. / Inorganica Chimica Acta 376 (2011) 222–229
two Cd(II) ions in l1
-
g1
:
g
0 and l1
-
g1
:
g
1 modes (Scheme 2a and b).
main emission peak of H2dtbb is at 465 nm (kex = 389 nm), which
may be attributed to p⁄
transition. The compounds 1–4 show
Two carboxylate groups in 2 and 3 both show chelating mode (l1
1) (Scheme 2c). Two carboxylate groups of dtbb2ꢁ ligand coor-
dinated to Cd(II) ions in l1
g1 and l2 1modes in the com-
-
? p
g1
:g
emissions at about 455 nm (kex = 396 nm), 468 nm (kex = 395 nm),
453 nm (kex = 403 nm) and 452 nm (kex = 385 nm), respectively. It
should be pointed out that the emissions of compounds 1–4 are
neither metal-to-ligand charge transfer (MLCT) nor ligand-to-
metal charge transfer (LMCT) in nature since the Cd2+ ions are
difficult to oxidize or to reduce due to their d10 configuration,
which are mainly based on the luminescence of ligands. They can
-
g1
:
- :g
g1
plex 4 (Scheme 2d). The results described above show that the
bridging fashions of the dtbb2ꢁ ligand play an important role in
the construction of supramolecular frameworks. In addition, the
conformation of dtbb2ꢁ ligands impacts on the structures of
coordination polymers. The S–S bond lengths, the C–S–S–C torsion
angles, and the dihedral angle between two phenyl rings in dtbb2ꢁ
ligands are listed in Table S3. The considerably larger dihedral
angles, torsion angles and thus less repulsion between the two
benzoate groups are believed to partially contribute to their
thermodynamically and kinetically favored formation.
A comparison of the crystal structures of 1–4 clearly indicates
that the auxiliary N-donor ligands also have a significant influence
on structural assembly of coordination architectures. When no
auxiliary ligand or rigid chelating 2,20-bpy is introduced, the ex-
pected low-dimensional species 1(1D) and 2 (1D) are obtained.
However, when the semi-rigid bridging ligands 1,4-bix or 1,4-btx
are introduced into the systems, the resulting complexes 3 and 4
show 2D coordination frameworks.
probably be assigned to the intraligand p⁄
? p transitions of
dtbb2ꢁ ligand. Different intensity emission bands of 1–4 are
probably due to the variation of the metal ions and the coordina-
tion environment around them because the photoluminescence
behavior is closely associated with the metal ions and the ligands
coordinated around them [69,70].
4. Conclusion
In summary, four novel Cd(II) coordination polymers have been
synthesized based on 2,2-dithiobisbenzoic acid and different aux-
iliary N-donor ligands, which display various 1D and 2D topologi-
cal networks. Our research results not only demonstrate that the
coordination modes and conformations of the flexible dtbb2ꢁ li-
gand have a significant influence on the final supramolecular archi-
tectures of complexes 1–4, but also illustrate that the structural
diversity in MOFs that can be achieved by adjustments of the aux-
iliary ligands in the present system. In addition, the photolumines-
cence investigation shows that all the coordination polymers 1–4
appear potentially applied as new luminescent materials.
3.6. Thermal properties
To examine the thermal stability of compounds 1–4, thermal
gravimetric (TG) analyses were carried out (Fig. S5). Complex 1
gives a gradual weight loss of 11.24% in the range of 25–296 °C,
which corresponds to the loss of the DMF molecule (calculated
11.36%). The framework starts to decompose at 296 °C. For com-
plex 2, the weight loss between 95 and 218 °C corresponds to the
release of isolated DMA and coordinated H2O molecules (calcd
25.12%, obsd 25.55%), followed by losing the 2,20-bpy molecules
between 297 and 345 °C (calcd 20.41%, obsd 20.96%), and then be-
gan to decompose upon further heating. For 3, the first weight loss
of 13.86% (calcd 14.16%) in the range of 96–271 °C reveals the
exclusion of DMF molecule and immediately followed by the struc-
ture decomposition. In the case of 4, the 2D framework was stable
up to 261 °C, then a sharp weight loss occurs from 261 to
365 °C(46.06%), and is attributed to the loss of the coordinated
dtbb2ꢁ ligands (46.48%).
Acknowledgments
We gratefully acknowledge the financial support by the Na-
tional Natural Science Foundation of China (20972132), the SRF
for ROCS, SEM and the Foundation of Key Laboratory of Environ-
mental Material and Environmental Engineering of Jiangsu Prov-
ince. We also acknowledge the support from Yangzhou University.
Appendix A. Supplementary material
CCDC 798109, 798110, 798111 and 798112 contain the supple-
mentary crystallographic data for complexes 1, 2, 3 and 4, respec-
tively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2011.
06.020.
3.7. Photoluminescent Properties
The solid-state emission spectra of the free H2dtsa ligand and
complexes 1–4 were measured at room temperature (Fig. 5). The
References
[1] C. Janiak, Dalton Trans. (2003) 2781.
[2] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T. Reineke, M. O’Keeffe, O.M. Yaghi, Acc.
Chem. Res. 34 (2001) 319.
[3] S.L. James, Chem. Soc. Rev. 32 (2003) 276.
[4] A.Y. Robin, K.M. Fromm, Coord. Chem. Rev. 250 (2006) 2127.
[5] M. Kawano, M. Fujita, Coord. Chem. Rev. 251 (2007) 2592.
[6] J. Vittal, Coord. Chem. Rev. 251 (2007) 1781.
[7] J.P. Zhang, X.C. Huang, X.M. Chen, Chem. Soc. Rev. 38 (2009) 2385.
[8] S.Y. Gao, D.Q. Yuan, J. Lu, T.H. Li, R. Cao, Chem. Commun. (2007) 1813.
[9] S.S. Zhang, S.Z. Zhan, M. Li, R. Peng, D. Li, Inorg. Chem. 46 (2007) 4365.
[10] H.X. Yang, J.X. Lin, J.T. Chen, X.D. Zhu, S.Y. Gao, R. Cao, Cryst. Growth Des. 8
(2008) 2623.
[11] Q.R. Fang, G.S. Zhu, Z. Jin, Y.Y. Ji, J.W. Ye, M. Xue, H. Yang, Y. Wang, S.L. Qiu,
Angew. Chem., Int. Ed. 46 (2007) 6638.
[12] X.L. Li, K. Chen, Y. Liu, Z.X. Wang, T.W. Wang, J.L. Zuo, Y.Z. Li, Y. Wang, J.S. Zhu,
J.M. Liu, Y. Song, X.Z. You, Angew. Chem., Int. Ed. 46 (2007) 6820.
[13] H.Q. Hao, W.T. Liu, W. Tan, Z.J. Lin, M.L. Tong, Cryst. Growth Des. 9 (2009) 457.
[14] J. Zhang, S.M. Chen, R.A. Nieto, T. Wu, P.Y. Feng, X.H. Bu, Angew. Chem., Int. Ed.
49 (2010) 1267.
Fig. 5. Fluorescent emission spectra for solid H2dtbb and compounds 1–4 at 298 K.
[15] J.P. Zhang, X.M. Chen, J. Am. Chem. Soc. 130 (2008) 6010.

J. Yu et al. / Inorganica Chimica Acta 376 (2011) 222–229
229
[16] Z. Duan, Y. Zhang, B. Zhang, F.L. Pratt, Inorg. Chem. 48 (2009) 2140.
[17] R.Q. Zou, H. Sakurai, S. Han, R.Q. Zhong, Q.J. Xu, Am. Chem. Soc. 129 (2007)
8402.
[18] X.Y. Wang, Z.M. Wang, S. Gao, Chem. Commun. (2008) 281.
[19] A.J. Lan, K.H. Li, H.H. Wu, L.Z. Kong, N. Nijem, D.H. Olson, T.J. Emge, Y.J. Chabal,
D.C. Langreth, M.C. Hong, J. Li, Inorg. Chem. 48 (2009) 7165.
[20] M.S. Wang, G.C. Guo, W.Q. Zou, W.W. Zhou, Z.J. Zhang, G. Xu, J.S. Huang,
Angew. Chem., Int. Ed. 47 (2008) 3565.
[45] H.J. Choi, M.P. Suh, J. Am. Chem. Soc. 126 (2004) 15844.
[46] A. Majumder, V. Gramlich, G.M. Rosair, S.R. Batten, J.D. Masuda, M.S. Fallah, J.
Ribas, J.P. Sutter, C. Desplanches, S. Mitra, Cryst. Growth Des. 6 (2006) 2355.
[47] S.K. Ghosh, P.K. Bharadwaj, Inorg. Chem. 43 (2004) 5180.
[48] H.L. Gao, L. Yi, B. Zhao, X.Q. Zhao, P. Cheng, D.Z. Liao, S.P. Yan, Inorg. Chem. 45
(2006) 5980.
[49] B. Zhao, P. Cheng, Y. Dai, C. Cheng, D.Z. Liao, S.P. Yan, Z. H. Jiang, G.L. Wang,
Angew. Chem., Int. Ed. 42 (2003) 934.
[21] S. Ma, D. Yuan, X.S. Wang, H.C. Zhou, Inorg. Chem. 48 (2009) 2072.
[22] S.R. Batten, R. Robson, Angew. Chem., Int. Ed. 37 (1998) 1460.
[23] B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629.
[24] O.R. Evans, W. Lin, Acc. Chem. Res. 35 (2002) 511.
[25] N.W. Ockwig, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 38 (2005) 176.
[26] R.G. Xiong, J.L. Zuo, X.Z. You, Chem. Commun. (2000) 2061.
[27] X.B. Zhao, B. Xiao, A.J. Fletcher, K.M. Thomas, D. Bradshaw, M. Rosseinsky, J. Sci.
306 (2004) 1012.
[28] C.D. Wu, A.G. Hu, L. Zhang, W.B. Lin, J. Am. Chem. Soc. 127 (2005) 8940.
[29] S.Q. Zang, Y. Su, Y.Z. Li, Z.P. Ni, Q.J. Meng, Inorg. Chem. 45 (2006) 174.
[30] P.K. Thallapally, J. Tian, M.R. Kishan, C.A. Fernandez, S.J. Dalgarno, P.B. McGrail,
J.E. Warren, J. Am. Chem. Soc. 130 (2008) 16842.
[31] Q. Chu, G.X. Liu, Y.Q. Huang, X.F. Wang, W.Y. Sun, Dalton Trans. (2007) 4302.
[32] S.Q. Zang, Y. Su, C.Y. Duan, Y.Z. Li, H.Z. Zhu, Q.J. Meng, Chem. Commun. (2006)
4997.
[33] L.L. Wen, Z.D. Lu, X.M. Ren, C.Y. Duan, Q.J. Meng, S. Gao, Cryst. Growth Des. 9
(2009) 227.
[50] B. Zhao, P. Cheng, X.Y. Chen, C. Cheng, W. Shi, D.Z. Liao, S.P. Yan, Z.H. Jiang, J.
Am. Chem. Soc. 126 (2004) 3012.
[51] D.R. Xiao, E.B. Wang, H.Y. An, Y.G. Li, Z.M. Su, C.Y. Sun, Chem. Eur. J. 12 (2006)
6528.
[52] S.Q. Zang, Y. Su, Y.Z. Li, H.Z. Zhu, Q.J. Meng, Inorg. Chem. 45 (2006) 2972.
[53] D.R. Xiao, E.B. Wang, H.Y. An, Y.G. Li, L. Xu, Cryst. Growth Des. 7 (2007) 506.
[54] S.M. Hawxwell, G.M. Espallargas, D. Bradshaw, M.J. Rosseinsky, T.J. Prior, A.J.
Florence, J. van de Streeke, L. Brammer, Chem. Commun. (2007) 1532.
[55] S.L. Li, Y.Q. Lan, J.F. Ma, J. Yang, G.H. Wei, L.P. Zhang, Z.M. Su, Cryst. Growth Des.
8 (2008) 675.
[56] L. Han, M.C. Hong, Inorg. Chem. Commun. 8 (2005) 406.
[57] H.W. Hou, Y.L. Wei, Y.L. Song, Y.L. Fan, Y. Zhu, Inorg. Chem. 43 (2004) 1323.
[58] C.Y. Su, M.D. Smith, H.C. zur Loye, Angew. Chem., Int. Ed. 42 (2003) 4085.
[59] A.V. Davis, K.N. Raymond, J. Am. Chem. Soc. 127 (2005) 7912.
[60] J.L. Du, T.L. Hu, J.R. Li, S.M. Zhang, X.H. Bu, Eur. J. Inorg. Chem. (2008) 1059.
[61] S.Y. Cai, G.X. Jin, Organometallics 26 (2007) 5442.
[62] K.M. Fromm, J.L. Sagué Doimeadios, A.Y. Robin, Chem. Commun. (2005) 4548.
[63] B.C. Tzeng, B.S. Chen, S.Y. Lee, W.H. Liu, G.H. Lee, S.M. Peng, New J. Chem. 29
(2005) 1254.
[34] W.G. Lu, L. Jiang, X.L. Feng, T.B. Lu, Cryst. Growth Des. 8 (2008) 986.
[35] X.L. Wang, C. Qin, E.B. Wang, L. Xu, Eur. J. Inorg. Chem. (2005) 3418.
[36] Q.R. Fang, G.S. Zhu, M. Xue, J.Y. Sun, F.X. Sun, S.L. Qiu, Inorg. Chem. 45 (2006)
3582.
[37] R.H. Wang, L. Han, F.L. Jiang, Y.F. Zhou, D.Q. Yuan, M.C. Hong, Cryst. Growth
Des. 5 (2005) 129.
[64] L. Hou, D. Li, Inorg. Chem. Commun. 8 (2005) 190.
[65] B.F. Hoskins, R. Robson, D.A. Slizys, J. Am. Chem. Soc. 119 (1997) 2952.
[66] X.R. Meng, Y.L. Song, H.W. Hou, H.Y. Han, B. Xiao, Y.T. Fan, Y. Zhu, Inorg. Chem.
43 (2004) 3528.
[38] C.Y. Sun, S. Gao, L.P. Jin, Eur. J. Inorg. Chem. (2006) 2411.
[39] T.L. Hu, R.Q. Zou, J.R. Li, X.H. Bu, Dalton Trans. (2008) 1302.
[40] Y. Qi, Y. Che, F. Luo, S.R. Batten, Y. Liu, J. Zheng, Cryst. Growth Des. 8 (2008)
1654.
[67] G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction of Area
Detector Data, University of Göttingen, Germany, 2002.
[68] G.M. Sheldrick, SHELXTL, Version 6.10 Reference Manual, Bruker-AXS, 5465 E.
Cheryl, Parkway, Madison, WI 53711-5373, USA, 2000.
[41] L. Xu, S.H. Yan, E.Y. Choi, J.Y. Lee, Y.U. Kwon, Chem. Commun. (2009) 3431.
[42] H. Chun, J. Am. Chem. Soc. 130 (2008) 800.
[69] Z.Y. Fu, X.T. Wu, J.C. Dai, S.M. Hu, W.X. Du, H.H. Zhang, R.Q. Sun, Eur. J. Inorg.
Chem. (2002) 2730.
[43] O.M. Yaghi, H. Li, T.L. Groy, J. Am. Chem. Soc. 118 (1996) 9096.
[44] M. Du, X.J. Jiang, X.J. Zhao, Inorg. Chem. 45 (2006) 3998.
[70] X. Wang, C. Qin, E. Wang, Y. Li, N. Hao, C. Hu, L. Xu, Inorg. Chem. 46 (2004)
1850.