Synthesis and characterization of d10 metal complexes with mixed 1,3-di(1H-imidazol-4-yl)benzene and multicarboxylate ligands

Article abstract of DOI:10.1016/j.jssc.2013.03.042

Seven new coordination polymers [Zn(H₂L)(mbdc)] (1), [Zn(H ₃L)(btc)] (2), [Zn(H₂L)(Hbtc)] (3), [Zn(H ₂L)(Hbtc)]·H₂O (4), [Zn₂(H ₂L)(btc)(μ₂-OH)] (5), [Cd(H₂L)(mbdc)] (6) and [Cd₃(H₂L)₂(btc)₂(H ₂O)]·5H₂O (7) were synthesized by reactions of the corresponding metal salt with rigid ligand 1,3-di(1H-imidazol-4-yl)benzene (H₂L) and different carboxylic acids of 1,3-benzenedicarboxylic acid (H₂mbdc) and benzene-1,3,5-tricarboxylic acid (H₃btc), respectively. The results of X-ray crystallographic analysis indicate that complex 1 is 1D chain while 2 is a (3,3)-connected 2D network with Point (Schlaefli) symbol of (4,8²). Complexes 3 and 6 are 2D networks, 4 is a 3-fold interpenetrating 3D framework with Point (Schlaefli) symbol of (6⁵,8) and 5 is a (3,8)-connected 2D network with Point (Schlaefli) symbol of (3,4²)₂(3⁴,4 ⁶,5⁶,6⁸,7³,8), while 7 is a (3,10)-connected 3D net with Schlaefli symbol of (3,4,5)₂(3 ⁴,4⁸,5¹⁸,6¹²,7²,8). The thermal stability and photoluminescence of the complexes were investigated. Furthermore, DFT calculations were performed for 2-4 to discuss the temperature controlled self-assembly of the complexes.

Full text of DOI:10.1016/j.jssc.2013.03.042

Journal of Solid State Chemistry 202 (2013) 215–226
Contents lists available at SciVerse ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Synthesis and characterization of d10 metal complexes with mixed
1,3-di(1H-imidazol-4-yl)benzene and multicarboxylate ligands
n
Zhi-Hao Chen, Yue Zhao, Shui-Sheng Chen, Peng Wang, Wei-Yin Sun
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures,
Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Seven new coordination polymers [Zn(H2L)(mbdc)] (1), [Zn(H3L)(btc)] (2), [Zn(H2L)(Hbtc)] (3), [Zn(H2L)
(Hbtc)] ꢀ H2O (4), [Zn2(H2L)(btc)(μ2-OH)] (5), [Cd(H2L)(mbdc)] (6) and [Cd3(H2L)2(btc)2(H2O)] ꢀ 5H2O (7)
were synthesized by reactions of the corresponding metal salt with rigid ligand 1,3-di(1H-imidazol-4-yl)
benzene (H2L) and different carboxylic acids of 1,3-benzenedicarboxylic acid (H2mbdc) and benzene-
1,3,5-tricarboxylic acid (H3btc), respectively. The results of X-ray crystallographic analysis indicate that
complex 1 is 1D chain while 2 is a (3,3)-connected 2D network with Point (Schläfli) symbol of (4,82).
Complexes 3 and 6 are 2D networks, 4 is a 3-fold interpenetrating 3D framework with Point (Schläfli)
symbol of (65,8) and 5 is a (3,8)-connected 2D network with Point (Schläfli) symbol of (3,42)2
Received 9 November 2012
Received in revised form
16 March 2013
Accepted 17 March 2013
Available online 26 March 2013
Keywords:
Crystal structure
Photoluminescence
Zinc(II) complex
Cadmium(II) complex
DFT calculations
(34,46,56,68,73,8), while 7 is a (3,10)-connected 3D net with Schläfli symbol of (3,4,5)2(34,48,518
,
612,72,8). The thermal stability and photoluminescence of the complexes were investigated. Furthermore,
DFT calculations were performed for 2–4 to discuss the temperature controlled self-assembly of the
complexes.
& 2013 Elsevier Inc. All rights reserved.
1. Introduction
studied organic ligands in the construction of MOFs with varied
coordination modes of the carboxylate group.
Metal-organic frameworks (MOFs) which consist of metal ions
or clusters and organic linkers have attracted great interest from
chemists in recent years [1], due to their potential application in
gas storage/separation, ion exchange, magnetism, catalysis, photo-
active material and so on [2–6]. In the assembly reactions of MOFs,
the primary considerations are the coordination preference of
ligands and the coordination geometry of metal centers, however,
other factors can also play important roles in the formation of the
structures, such as the choice of auxiliary ligand, pH value,
template and reaction temperature [7–11]. The multidentate
organic ligands with N and/or O donors as coordination sites are
widely used as building blocks in the construction of MOFs.
Particularly, the ditopic and tripodal imidazole-containing ligands
e.g. 1,4-di(1-imidazolyl)benzene, 1,4-di(1H-imidazol-4-yl)benzene,
1,3,5-tri(imidazole-1-ylmethyl)-2,4,6-trimethyl-benzene, 1,3,5-tri
(1-imidazolyl)benzene, 1,3,5-tri(1H-imidazol-4-yl)benzene, have
been widely used in our studies, and the results have shown that
such ligands can react with varied metal salts leading to the
formation of MOFs with different structures and properties [12].
On the other hand, multicarboxylate compounds, such as benze-
nedicarboxylate and benzenetricarboxylate, are the most widely
In this work, we focused our attention on reactions of 1,3-di
(1H-imidazol-4-yl)benzene (H2L) together with different carbox-
ylate ligands and d10 metal salts, and made systematic investiga-
tion on the impact of carboxylate ligands on the construction of
frameworks. In addition, the effect of temperature and base on the
assembly of MOFs was also studied. Herein, we report the synth-
esis, crystal structure and property of seven new coordination
polymers [Zn(H2L)(mbdc)] (1), [Zn(H3L)(btc)] (2), [Zn(H2L)(Hbtc)]
(3), [Zn(H2L)(Hbtc)] ꢀ H2O (4), [Zn2(H2L)(btc)(μ2-OH)] (5), [Cd(H2L)
(mbdc)] (6) and [Cd3(H2L)2(btc)2(H2O)] ꢀ 5H2O (7) obtained by
reactions of H2L and different carboxylic acids of benzene-1,3,5-
tricarboxylic acid (H3btc) and 1,3-benzenedicarboxylic acid
(H2mbdc) with corresponding metal salt under hydrothermal
conditions. DFT calculations for 2–4 were performed to discuss
the temperature controlled self-assembly of MOFs. The thermal
stability and photoluminescence of the complexes in the solid
state were investigated.
2. Experimental section
2.1. Materials and measurements
n
All commercially available chemicals and solvents are of reagent
grade and were used as received without further purification. The
Corresponding author. Fax: þ86 25 8331 4502.
E-mail addresses: sunwy@nju.edu.cn, sweiyin@yahoo.com (W.-Y. Sun).
0022-4596/$ - see front matter & 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.jssc.2013.03.042

216
Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
ligand H2L was prepared according to the literature [13]. Elemental
analyses of C, H, and N were performed on a Perkin–Elmer 240C
elemental analyzer at the analysis center of Nanjing University.
Infrared spectra (IR) were recorded on a Bruker Vector22 FT-IR
spectrophotometer by using KBr pellets. Thermogravimetric analyses
(TGA) were carried out on a simultaneous SDT 2960 thermal analyzer
under nitrogen at a heating rate of 10 1C min−1. The luminescence
spectra for the powdered solid samples were measured on an
Aminco Bowman Series 2 spectrofluorometer with a xenon arc lamp
as the light source. In the measurements of emission and excitation
spectra the pass width is 5 nm, and all the measurements were
carried out under the same experimental conditions. Powder X-ray
diffraction (PXRD) measurements were performed on a Bruker D8
Advance X-ray diffractometer using Cu-Kα radiation (λ¼1.5418 Å), in
which the X-ray tube was operated at 40 kV and 40 mA at room
temperature.
(8.0 mg, 0.2 mmol) in 10 mL of H2O was sealed in a 16 mL Teflon
lined stainless steel container and heated at 180 1C for 3 d. After
the reaction mixture was cooled to room temperature, colorless
block crystals of 1 were collected with a yield of 67% by filtration
and washed with water and ethanol several times. Anal. Calcd for
C
20H14N4O4Zn: C, 54.63, H, 3.21, N, 12.74%. Found: C, 54.32, H, 3.41,
N, 12.57%. IR (KBr pellet, cm−1): 3426 (w, br), 3091–2874 (m), 1607
(s), 1567 (s), 1479 (s), 1437 (m), 1398 (s), 1371 (s), 1221 (w), 1128
(w), 1076 (m), 973 (w), 900 (w), 849 (w), 820 (m), 782 (w), 748
(m), 719 (m), 653 (w), 626 (w).
2.2.2. [Zn(H3L)(btc)] (2)
A
mixture of H2L (21.0 mg, 0.1 mmol), Zn(NO3)2 ꢀ 6 H2O
(29.7 mg, 0.1 mmol), H3btc (21.0 mg, 0.1 mmol) and NaOH
(8.0 mg, 0.2 mmol) in 10 mL of H2O was sealed in a 16 mL Teflon
lined stainless steel container and heated at 160 1C for 3 d. After
cooling to the room temperature, yellow block crystals of 2 were
collected by filtration and washed with water and ethanol several
times with a yield of 71%. Anal. Calcd for C21H14N4O6Zn: C, 52.14,
H, 2.92, N, 11.58%. Found: C, 52.44, H, 2.81, N, 11.66%. IR (KBr pellet,
cm−1): 3444 (w, br), 3122–2855 (m), 1618 (s), 1574 (s), 1533 (s),
2.2. Syntheses
2.2.1. [Zn(H2L)(mbdc)] (1)
A
mixture of H2L (21.0 mg, 0.1 mmol), Zn(NO3)2 ꢀ 6H2O
(29.7 mg, 0.1 mmol), H2mbdc (16.6 mg, 0.1 mmol) and NaOH
Table 1
Crystallographic data for complexes 1–7.
4
1
2
3
C20H14N4O4Zn
439.72
293(2)
Triclinic
P-1
C21H14N4O6Zn
483.73
293(2)
Monoclinic
P21/c
C21H14N4O6Zn
483.73
293(2)
Triclinic
P-1
C21H16N4O7Zn
501.75
293(2)
Orthorhombic
Pna21
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
8.8319(10)
9.7098(10)
11.5626(13)
106.277(2)
92.356(2)
111.188(2)
876.17(17)
2
15.185(3)
7.5341(16)
19.632(3)
90
126.563(10)
90
1804.0(6)
4
1.781
9.1439(3)
9.2915(3)
12.0125(4)
110.1260(10)
90.0200(10)
99.3210(10)
943.88(5)
2
8.4321(14)
15.064(3)
15.064(3)
90
90
90
1913.4(6)
4
1.742
a/Å
b/Å
c/Å
a/1
β/1
γ/1
V (Å3)
Z
Dc/(g cm−3
F(0 0 0)
)
1.667
448
1.702
492
984
1024
1.86–25.10
6312
3072
1.039
0.0380
1.67–25.01
9428
3168
0.943
0.0372
0.0660
2.26–25.01
9438
3297
1.096
0.0245
1.91–25.04
9037
2958
1.033
0.0306
0.0787
θ range/1
Reflections collected
Independent reflections
Goodness-of-fit on F2
R1 [I42s (I)]a
wR2 [I42s (I)]b
0.0874
0.0642
6
7
5
C21H14N4O7Zn2
565.18
293(2)
C20H14N4O4Cd
486.75
293(2)
C42H38N8O18Cd3
1,280.03
293(2)
Empirical formula
Formula weight
Temperature/K
Triclinic
P-1
Triclinic
P-1
Monoclinic
P21/c
Crystal system
Space group
9.8679(8)
10.2786(7)
10.6037(8)
90.5100(10)
108.4710(10)
106.379(3)
972.99(13)
2
8.3451(9)
10.1109(10)
11.2679(11)
100.743(2)
90.027(2)
112.287(2)
861.65(15)
2
16.6011(12)
16.2848(12)
19.7529(10)
90
118.741(4)
90
4,682.2(5)
4
1.816
a/Å
b/Å
c/Å
a/1
β/1
γ/1
V (Å3)
Z
Dc/(g cm−3
F(0 0 0)
)
1.929
568
1.876
484
2,536
2.04–25.10
4967
3417
1.023
0.0328
1.85–25.00
4312
2982
1.223
0.0350
1.72–25.01
22,935
8,247
1.343
0.1257
θ range/1
Reflections collected
Independent reflections
Goodness-of-fit on F2
R1 [I42s (I)]a
wR2 [I42s (I)]b
0.0914
0.0813
0.2447
a
R1 ¼Σ||Fo|−|Fc||/Σ|Fo|.
b
2
wR2¼|Σw(|Fo|2−|Fc|2)|/Σ|w(Fo)2|1/2, where w¼1/[s2(Fo2) þ(aP)2þbP]. P¼(Fo þ2Fc2)/3.

Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
217
1436 (s), 1349 (s), 1145 (w), 1114 (w), 971 (w), 845 (w), 819 (m),
762 (m), 729 (m), 713 (m), 646 (w), 620 (w), 543 (w).
SADABS program [15]. The structures of 1–7 were solved by
direct methods and all non-hydrogen atoms were refined anisotropi-
cally on F2 by the full-matrix least-squares technique using the
2.2.3. [Zn(H2L)(Hbtc)] (3)
Table 2
Complex 3 was synthesized by the same procedure as that used
for preparation of 2, except that the reaction mixture was heated
at 65 1C. After cooling to the room temperature, colorless block
crystals of 3, which were picked out from the mixture of 2 and 3,
were washed with water and ethanol several times with a yield of
30%. Anal. Calcd for C21H14N4O6Zn: C, 52.14, H, 2.92, N, 11.58%.
Found: C, 51.99, H, 2.98, N, 11.43%. IR (KBr pellet, cm−1): 3420 (w,
br), 3121–2852 (m), 1681 (s), 1536 (s), 1484 (w), 1437 (s), 1348(s),
1232(w), 1176 (w), 820 (m), 763 (m), 730 (m), 714 (m), 647 (w),
620 (w), 500 (w).
a
Selected bond lengths (Å) and bond angles (1) for complexes 1–7
.
1
Zn(1)–O(4)
1.946(2)
2.005(2)
116.1(1)
118.7(1)
101.8(1)
Zn(1)–O(2)#1
1.960(2)
2.055(3)
99.4(1)
113.3(1)
107.9(1)
Zn(1)–N(4)
Zn(1)–N(1)#2
O(4)–Zn(1)–O(2)#1
O(2)#1–Zn(1)–N(4)
O(2)#1–Zn(1)–N(1)#2
2
O(4)–Zn(1)–N(4)
O(4)–Zn(1)–N(1)#2
N(4)–Zn(1)–N(1)#2
Zn(1)–O(6)#1
Zn(1)–O(3)#2
O(6)#1–Zn(1)–N(4)
N(4)–Zn(1)–O(3)#2
N(4)–Zn(1)–O(4)
3
Zn(1)–O(2)#1
Zn(1)–N(2)#2
O(2)#1–Zn(1)–O(4)
O(4)–Zn(1)–N(2)#2
O(4)–Zn(1)–N(4)
4
1.922(2)
1.973(2)
131.2(1)
104.9(1)
110.2(1)
Zn(1)–N(4)
Zn(1)–O(4)
O(6)#1–Zn(1)–O(3)#2
O(6)#1–Zn(1)–O(4)
O(3)#2–Zn(1)–O(4)
1.955(3)
1.981(3)
105.9(1)
103.6(1)
95.3(1)
1.941(1)
1.993(2)
113.85(6)
121.05(6)
95.90(6)
Zn(1)–O(4)
Zn(1)–N(4)
O(2)#1–Zn(1)–N(2)#2
O(2)#1–Zn(1)–N(4)
N(2)#2–Zn(1)–N(4)
1.969(1)
2.007(2)
97.39(6)
114.36(7)
115.51(6)
2.2.4. [Zn(H2L)(Hbtc)] ꢀ H2O (4)
A trace amount of complex 4 was found in the synthesis of 2 at
180 1C. The yellow block crystals of 4 were difficultly separated
from 2 and the yield of 4 was very poor, so only the crystal
structure of 4 was obtained.
Zn(1)–O(4)
Zn(1)–N(4)
1.916(2)
1.955(2)
101.1(1)
112.2(1)
95.8(1)
Zn(1)–O(1)#1
Zn(1)–N(2)#2
O(4)–Zn(1)–N(4)
O(4)–Zn(1)–N(2)#2
N(4)–Zn(1)–N(2)#2
1.950(2)
1.999(2)
127.5(1)
112.3(1)
103.7(1)
O(4)–Zn(1)–O(1)#1
O(1)#1–Zn(1)–N(4)
O(1)#1–Zn(1)–N(2)#2
5
2.2.5. [Zn2(H2L)(btc)(μ2-OH)] (5)
A
mixture of H2L (21.0 mg, 0.1 mmol), Zn(NO3)2 ꢀ 6H2O
Zn(2)–O(7)
1.912(2)
1.946(2)
1.948(2)
1.948(2)
104.0(1)
112.1(1)
118.0(1)
107.8(1)
106.2(1)
108.1(1)
Zn(1)–O(7)
1.919(2)
1.976(2)
1.993(2)
2.002(2)
110.9(1)
108.7(1)
112.2(1)
110.5(1)
117.4(1)
96.1(1)
Zn(2)–O(6)#1
Zn(1)–N(4)
(29.7 mg, 0.1 mmol), H3btc (21.0 mg, 0.1 mmol) and NaOH
(16.0 mg, 0.4 mmol) in 10 mL of H2O was sealed in a 16 mL Teflon
lined stainless steel container and heated at 180 1C for 3 d. After
the reaction mixture was cooled to room temperature, colorless
block crystals of 5 were collected by filtration and washed with
water and ethanol several times in 48% yield. Anal. Calcd for
Zn(2)–O(3)#2
Zn(1)–O(4)
Zn(2)–O(1)#3
Zn(1)–N(2)#4
O(7)–Zn(2)–O(6)#1
O(7)–Zn(2)–O(3)#2
O(6)#1–Zn(2)–O(3)#2
O(7)–Zn(2)–O(1)#3
O(6)#1–Zn(2)–O(1)#3
O(3)#2–Zn(2)–O(1)#3
6
O(7)–Zn(1)–N(4)
O(7)–Zn(1)–O(4)
N(4)–Zn(1)–O(4)
O(7)–Zn(1)–N(2)#4
N(4)–Zn(1)–N(2)#4
O(4)–Zn(1)–N(2)#4
C
21H14N4O7Zn2: C, 44.63, H, 2.50, N, 9.91%. Found: C, 44.84, H, 2.66,
Cd(1)–O(4)
Cd(1)–N(4)
Cd(1)–O(1)#1
2.228(3)
2.231(3)
2.363(3)
138.8(1)
87.3(1)
133.8(1)
93.5(1)
96.3(1)
81.8(1)
Cd(1)–N(1)#2
2.372(3)
2.451(3)
2.590(3)
54.2(1)
115.4(1)
80.2(1)
83.8(1)
105.3(1)
170.2(1)
74.4(1)
N, 10.06%. IR (KBr pellet, cm−1): 3428 (w), 3141–2855 (m), 1614 (s),
1573 (s), 1435 (s), 1370 (s), 1132 (w), 816 (w), 766 (m), 730 (m), 715
(m), 644 (w), 554 (w).
Cd(1)–O(2)#1
Cd(1)–O(2)#3
O(4)–Cd(1)–N(4)
O(4)–Cd(1)–O(1)#1
N(4)–Cd(1)–O(1)#1
O(4)–Cd(1)–N(1)#2
N(4)–Cd(1)–N(1)#2
O(1)#1–Cd(1)–N(1)#2
O(4)–Cd(1)–O(2)#1
N(4)–Cd(1)–O(2)#1
7
O(1)#1–Cd(1)–O(2)#1
N(1)#2–Cd(1)–O(2)#1
O(4)–Cd(1)–O(2)#3
N(4)–Cd(1)–O(2)#3
O(1)#1–Cd(1)–O(2)#3
N(1)#2–Cd(1)–O(2)#3
O(2)#1–Cd(1)–O(2)#3
2.2.6. [Cd(H2L)(mbdc)] (6)
Complex 6 was synthesized by the same procedure as that used
for preparation of 1, except that Cd(NO3)2 ꢀ 4H2O (30.8 mg,
0.1 mmol) was used instead of Zn(NO3)2 ꢀ 6H2O. After cooling to
the room temperature, colorless block crystals of 6 were collected
by filtration and washed with water and ethanol several times in
65% yield. Anal. Calcd for C20H14N4O4Cd: C, 49.35, H, 2.90, N,
11.51%. Found: C, 49.43, H, 2.75, N, 11.42%. IR (KBr pellet, cm−1):
3120–2865 (m), 1599 (s), 1547 (s), 1476 (m), 1457 (m), 1387 (s),
1114 (m), 1071 (w), 822 (w), 786 (w), 752 (m), 723 (m), 701 (w),
650 (w), 626 (w).
123.9(1)
87.1(1)
Cd(1)–N(2)#1
2.20(1)
2.20(1)
2.28(1)
2.33(1)
2.35(1)
2.41(1)
2.16(1)
2.20(1)
2.35(1)
175.0(4)
88.4(4)
87.1(4)
98.8(3)
85.8(4)
171.5(3)
85.7(3)
96.5(3)
89.9(3)
86.3(3)
90.1(4)
87.5(4)
86.5(3)
97.8(3)
174.5(4)
109.9(4)
96.7(4)
147.4(4)
96.0(4)
110.9(4)
83.6(3)
100.3(3)
101.2(3)
Cd(2)–O(1)#3
2.35(1)
2.40(1)
2.50(1)
2.21(1)
2.22(1)
2.27(1)
2.31(1)
2.38(1)
2.49(1)
54.5(3)
136.3(3)
149.4(3)
85.6(4)
80.1(3)
53.4(3)
102.2(3)
140.6(4)
100.6(3)
93.7(4)
88.9(4)
127.9(4)
90.3(3)
92.9(4)
97.5(4)
142.8(3)
55.2(3)
86.9(4)
53.7(4)
112.8(3)
156.9(3)
102.3(3)
Cd(1)–N(4)
Cd(2)–O(10)
Cd(1)–O(7)#2
Cd(2)–O(2)#3
Cd(1)–O(10)
Cd(3)–N(6)#4
Cd(1)–O(4)
Cd(3)–O(5)
Cd(1)–O(1W)
Cd(3)-O(2)#5
Cd(2)–O(3)
Cd(3)–O(12)#6
Cd(2)–N(8)
Cd(3)–O(11)#6
Cd(2)–O(9)
Cd(3)–O(6)
N(2)#1–Cd(1)–N(4)
N(2)#1–Cd(1)–O(7)#2
N(4)–Cd(1)–O(7)#2
N(2)#1–Cd(1)–O(10)
N(4)–Cd(1)–O(10)
O(7)#2–Cd(1)–O(10)
N(2)#1–Cd(1)–O(4)
N(4)–Cd(1)–O(4)
O(7)#2–Cd(1)–O(4)
O(10)–Cd(1)–O(4)
N(2)#1–Cd(1)–O(1W)
N(4)–Cd(1)–O(1W)
O(7)#2–Cd(1)–O(1W)
O(10)–Cd(1)–O(1W)
O(4)–Cd(1)–O(1W)
O(3)–Cd(2)–N(8)
O(3)–Cd(2)–O(9)
N(8)–Cd(2)–O(9)
O(3)–Cd(2)–O(1)#3
N(8)–Cd(2)–O(1)#3
O(9)–Cd(2)–O(1)#3
O(3)–Cd(2)–O(10)
N(8)–Cd(2)–O(10)
O(9)–Cd(2)–O(10)
O(1)#3–Cd(2)–O(10)
O(3)–Cd(2)–O(2)#3
N(8)–Cd(2)–O(2)#3
O(9)–Cd(2)–O(2)#3
O(1)#3–Cd(2)–O(2)#3
O(10)–Cd(2)–O(2)#3
N(6)#4–Cd(3)–O(5)
N(6)#4–Cd(3)–O(2)#5
O(5)–Cd(3)–O(2)#5
N(6)#4–Cd(3)–O(12)#6
O(5)–Cd(3)–O(12)#6
O(2)#5–Cd(3)–O(12)#6
N(6)#4–Cd(3)–O(11)#6
O(5)–Cd(3)–O(11)#6
O(2)#5–Cd(3)–O(11)#6
O(12)#6–Cd(3)–O(11)#6
N(6)#4–Cd(3)–O(6)
O(5)–Cd(3)–O(6)
2.2.7. [Cd3(H2L)2(btc)2(H2O)] ꢀ 5H2O (7)
Complex 7 was synthesized by the same procedure as that used
for preparation of 5, except that Cd(NO3)2 ꢀ 4H2O (46.2 mg,
0.15 mmol) was used instead of Zn(NO3)2 ꢀ 6H2O. After the reaction
mixture was cooled to room temperature, colorless block crystals
of 7 were collected by filtration and washed with water and
ethanol several times with a yield of 32%. Anal. Calcd for
C
42H38N8O18Cd3: C, 39.41, H, 2.99, N, 8.75%. Found: C, 39.56, H,
2.78, N, 8.52%. IR (KBr pellet, cm−1): 3420–3150 (m), 1615 (s), 1546
(s), 1436 (s), 1364 (s), 1136 (m), 1077 (w), 943 (w), 829 (w), 769
(m), 733 (m), 642 (w).
O(2)#5–Cd(3)–O(6)
O(12)#6–Cd(3)–O(6)
O(11)#6–Cd(3)–O(6)
2.3. Crystal structure determination
a
Symmetry transformations used to generate equivalent atoms: For 1: #1 x, yþ1, z,
#2 −xþ1, −yþ1, −z. For 2: #1 −xþ1, −yþ2, −zþ1, #2 −xþ1, y þ1/2, −zþ1/2. For 3:
#1 x, y−1, z, #2 x, y, z þ1. For 4: #1 −xþ2, −y, zþ1/2, #2 −xþ1/2, y−1/2, z−1/2. For 5:
#1 −xþ2, −yþ1, −zþ1, #2 −xþ1, −yþ1, −zþ1, #3 x, y þ1, z, #4 x þ1, y þ1, z. For 6: #1
x, yþ1, z, #2 −xþ1, −yþ1, −zþ1, #3 −xþ2, −y, −zþ1. For 7: #1 x, −yþ3/2, z−1/2, #2
x, −yþ3/2, zþ1/2, #3 −xþ1, y þ1/2, −zþ1/2, #4 x, y−1, z, #5 −xþ1, −yþ1, −zþ1, #6
−x, y−1/2, −zþ1/2.
The data collections for 1–7 were carried out on a Bruker Smart
Apex CCD area-detector diffractometer using graphite-
monochromated Mo Kα radiation (λ¼0.71073 Å) at 20(2) 1C. The
diffraction data was integrated by using the SAINT program [14].
Semi-empirical absorption corrections were applied using the

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Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
SHELXL-97 crystallographic software package [16]. The hydrogen
atoms on the nitrogen atom of imidazole groups in 2, the ones of
non-deprotonated carboxylic acid (–COOH) in 3 and 4, the ones of
coordinated water molecule in 7, and the one of hydroxyl (–OH) in 5
were found directly from the differential Fourier map. All the other
hydrogen atoms were generated geometrically except that the hydro-
gen atoms of free water molecules were not identified. The details of
the crystal parameters, data collection, and refinements for the
complexes are summarized in Table 1, selected bond lengths and
angles with their estimated standard deviations are listed in Table 2.
2.4. DFT calculations
In order to understand the relation between structure and energy,
calculations were performed for the compounds based upon the
crystallographic data of [Zn(H3L)(btc)] (2), [Zn(H2L)(Hbtc)] (3),
Fig. 1. (a) The coordination environment of Zn(II) in 1 with the ellipsoids drawn at the 50% probability level. The hydrogen atoms except those on the nitrogen atom of
imidazole groups are omitted for clarity. Symmetry Code: a 1−x, 1−y, −z, b x, 1þy, z. (b) The 1D chain of 1. (c) 2D network of 1 linked by hydrogen bonds indicated by
dashed line.
Scheme 1. Coordination modes of mbdc2−, Hbtc2− and btc3− ligands appeared in 1–7.

Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
219
[Zn(H2L)(Hbtc)] ꢀ H2O (4) by using the total-energy code CASTEP,
which employs pseudopotentials to describe electron interactions
and represents electronic wave functions using a plane-wave basis
set [17]. The total energy was calculated by density functional
theory (DFT) within the framework of nonlocal gradient-corrected
approximations [Perdew–Burke–Ernzerhof (PBE)]. Under the per-
iodic boundary condition (PBC) [18], different unit cells were
treated by using the kinetic energy cutoff from 300 eV for plane-
waves, employing also the ultrasoft pseudopotential (USP) method
for the Local Density Approximations (LDA). The following orbital
electrons are treated as valence electrons: C 2s22p2, H 1s1, N
2s22p3, O 2s22p4, and Zn 3d104s2.
3. Results and discussion
3.1. Crystal structure of [Zn(H2L)(mbdc)] (1)
Structural analysis revealed that the asymmetric unit of 1
consists of one Zn(II) atom, one H2L and one mbdc2−. Fig. 1a shows
Fig. 2. (a) The coordination environment of Zn(II) in 2 with the ellipsoids drawn at the 50% probability level. The hydrogen atoms except those on the nitrogen atom of
imidazole groups are omitted for clarity. Symmetry Code: a 1−x, 0.5þy, 0.5−z, b 1−x, 2−y, 1−z. (b) The 2D layer of Zn(II)-btc3−. (c) The 2D network of 2. (d) Schematic
representation of the (4,82) topology. (e) 3D framework of 2 linked by hydrogen bonds indicated by dashed line.

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Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
that each Zn(II) atom is four-coordinated with distorted tetrahe-
dral coordination geometry by two N (N1a, N4) atoms of two
different H2L and two O (O2b, O4) atoms from two distinct mbdc2−
ligands. The Zn–N bond distances are 2.055(3) and 2.005(2) Å
while the Zn–O ones are 1.960(2) and 1.946(2) Å, and the coordi-
nation angles around the Zn1 are in the range of 99.37(10)–118.72
(10)1 (Table 2). The mbdc2− ligand acts as a m2-bridge using its two
carboxylate groups with m1−η1:η0-monodentate mode (Type I,
Scheme 1) and connects Zn(II) atoms to form an infinite one-
dimensional (1D) chain. Furthermore, the H2L ligands bridge the
adjacent 1D chains to give a double chain (Fig. 1b). Then, the
double chains are further linked together by N–H ꢀ ꢀ ꢀ O hydrogen
bonds to generate a two-dimensional (2D) network (Fig. 1c). The
hydrogen bonding data are summarized in Table S1.
Scheme 1). The Zn(II) atoms and btc3− ligands form a 2D network
via coordination interactions as shown in Fig. 2b. The H3Lþ
coordinates with Zn(II) as terminal ligand (Fig. 2c). Because the
terminal coordinated H3Lþ ligands bring about no change to the
topology of the Zn(II)-btc3− 2D network, according to the simpli-
fication principle, the resulting structure of 2 is a binodal (3,3)-
connected network with (4,82) topology (Fig. 2d). The adjacent 2D
layers are further connected together by N–H ꢀ ꢀ ꢀ O hydrogen
bonds between the protonated imidazole and non-coordinated
carboxylate groups to form a 3D framework (Fig. 2e, Table S1).
3.3. Crystal structure of [Zn(H2L)(Hbtc)] (3)
When the reaction was carried out at 65 1C, complex 3 was
obtained. The structure of 3 is different from that of 2 prepared by
the reaction at 160 1C, implying the impact of the reaction
temperature on the complexes [19]. As shown in Fig. 3a, the Zn
(II) atom is four-coordinated by two N and two O atoms which is
the same as that in 1. In 3, each Hbtc2− uses its two carboxylate
groups in m1−η1:η0-monodentate coordination mode to link two Zn
(II) atoms to form a chain, while the non-deprotonated carboxylic
group is free of coordination (Type III, Scheme 1). However, the
H2L ligands bridge the adjacent chains to form a 2D network of 3
(Fig. 3b), rather than the double chain of 1 (Fig. 1b). From the view
of topology, the Zn(II) atom is considered as a 4-connected
node, H2L and Hbtc2− ligands are regarded as linear linkers,
thus, the structure of 3 can be defined as a network with (4,4)
3.2. Crystal structure of [Zn(H3L)(btc)] (2)
When H3btc, instead of H2mbdc, was used to react with H2L
and Zn(NO3)2 ꢀ 6H2O in the presence of NaOH, complex 2 was
obtained. It is interesting that H3btc completely deprotonated to
give btc3−, while one of the two imidazole of H2L is protonated to
form H3Lþ. The Zn(II) atom in 2 has distorted tetrahedral coordi-
nation environment with three O atoms from three distinct btc3−
ligands and one N atom from one H3Lþ ligand (Fig. 2a). Each btc3−
ligand connects three Zn(II) atoms using its two of three carbox-
ylate groups in m1−η1:η0-monodentate, m2−η1:η1-bismonodentate
modes, while the third one is free of coordination (Type II,
Fig. 3. (a) The coordination environment of Zn(II) in 3 with the ellipsoids drawn at the 50% probability level. The hydrogen atoms except those on the nitrogen atom of
imidazole groups are omitted for clarity. Symmetry Code: a x, y, 1þz, b x, −1þy, z. (b) The 2D layer of 3. (c) 2D (4,4) network of 3 based on the binuclear subunits. (d) 3D
framework of 3 linked by hydrogen bonds indicated by dashed line.

Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
221
topology (Fig. 3c). Moreover, the 3D structure is generated and
consolidated from the 2D networks by N–H ꢀ ꢀ ꢀ O hydrogen bonds
(Fig. 3d, Table S1).
Schläfli symbol of the topology is (65,8) since the Zn(II) is 4-
connected node, and H2L and Hbtc2− ligands are linear linkers.
3.5. Crystal structure of [Zn2(H2L)(btc)(μ2-OH)] (5)
3.4. Crystal structure of [Zn(H2L)(Hbtc)] ꢀ H2O (4)
Increasing the amount of NaOH in the preparation reaction
[21], complex 5 was isolated. The results of crystallographic
analysis revealed that the asymmetric unit of 5 consists of two
crystallographically independent Zn(II) atoms bridged by one OH-
group, one btc3- and one H2L (Fig. 5a). In addition to the hydroxyl
bridge, Zn1 is coordinated by three carboxylate O atoms from
different btc3− ligands and Zn2 is coordinated by two N atoms
from two different H2L ligands and one carboxylate O atom, hence,
both Zn1 and Zn2 are four coordinated with distorted tetrahedral
geometry. The btc3− in 5 acts as a m4-bridge to link four zinc atoms,
one carboxylate group adopts a m2−η1:η1 bridging coordination
mode connecting two zinc atoms, and the other two carboxylate
groups adopt monodentate mode coordinating to one zinc atom
(Type V, Scheme 1). Two [Zn2(OH)] units are bridged by carbox-
ylate groups to form a tetranuclear subunit (Fig. 5b, highlighted by
pink circle), which is further linked through the btc3− ligands to
generate a 2D network (Fig. 5b). Meanwhile, H2L ligands act as
Complex 4 was synthesized by the reaction at 180 1C, and it
was found that 4 has similar composition with 3 except the
existence of free water molecule in 4, however, they have different
structures. As shown in Fig. 4a, Zn1 atom in 4 is in a distorted
tetrahedral coordination environment with N2O2 donor set, and
two carboxylate groups of Hbtc2− in 4 adopt m1−η1:η0-monoden-
tate coordination mode and the non-deprotonated one is free of
coordination (Type IV, Scheme 1), which are similar with those in
3. In 4, two kinds of zigzag chains are formed by the Zn(II) with
H2L and Zn(II) with Hbtc2−, respectively. And such two kinds of
zigzag chains connect each other to generate a 3D structure of 4
(Fig. 4b), with large channels (Fig. 4c), rather than the 2D network
of 3 (Fig. 3b). The large voids allow to form interpenetrated
framework to stabilize the overall structure [20], accordingly, 4
is a 3-fold interpenetrating 3D architecture (Fig. 4d), and the
Fig. 4. (a) The coordination environment of Zn(II) in 4 with the ellipsoids drawn at the 50% probability level. The hydrogen atoms except those on the nitrogen atom of
imidazole groups and water molecule are omitted for clarity. Symmetry Code: a 0.5−x, −0.5þy, −0.5þz, b 2−x, −y, 0.5þz. (b) The 3D framework of 3. (c) The large rectangle
channels in 4. (d) Schematic representation of the 3-fold interpenetrated adamantanoid units of 4.

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Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
Fig. 5. (a) The coordination environment of Zn(II) in 5 with the ellipsoids drawn at the 50% probability level. The hydrogen atoms except those on the nitrogen atom of
imidazole groups are omitted for clarity. Symmetry Code: a 1þx, 1þy, z, b x, 1þy, z, c 1−x, 1−y, 1−z, d 2−x, 1−y, 1−z. (b) The 2D layer of Zn(II)-btc3−. (c) The 2D network of 5.
(d) Schematic representation of the (3,42)2(34,46,56,68,73,8) topology. (e) 3D framework of 5 linked by hydrogen bonds indicated by dashed line.
hinges to connect adjacent zinc atoms of the Zn(II)-btc3− network
from two sides, yet forming the final 2D network of 5 constructed
by H2L and btc3- ligands (Fig. 5c). From topological view, the center
of the tetranuclear unit acts as eight-connected nodes to link each
other through 3-connectors of btc3− into a 2D network with a
Schläfli symbol (3,42)2(34,46,56,68,73,8) topology (Fig. 5d). Further-
more, adjacent layers in an—ABAB—arrangement are linked
together by π–π and N–H ꢀ ꢀ ꢀ O hydrogen bonding interactions to
generate a 3D structure (Fig. 5e, Table S1). The distance between
the nearly parallel imidazole ring planes of two adjacent H2L
ligands is 3.73 Å [22].
tion modes (Type VI, Scheme 1). The Cd(II) atoms and
mbdc2− ligands connect each other to form a 1D chain. Meanwhile,
each pair of H2L ligands bridges two Cd(II) atoms in two
adjacent chains to construct a 2D network (Fig. 6b). In addition
to the coordination, there are face-to-face π–π interactions
between the nearly parallel imidazole ring planes of two adjacent
H2L ligands from two different layers with a centroid-centroid
distance of 3.52 Å. There also exists N–H ꢀ ꢀ ꢀ O hydrogen bonds
between the adjacent layers, therefore, the π–π and hydrogen
bonding interactions link the 2D layers to a 3D framework of 6
(Fig. 6c).
3.6. Crystal structure of [Cd(H2L)(mbdc)] (6)
3.7. Crystal structure of [Cd3(H2L)2(btc)2(H2O)] ꢀ 5H2O (7)
The Cd(II) atom in 6 is six-coordinated by two N (N1a, N4)
atoms of two different H2L ligands and four O (O1b, O2b, O2c,
O4) atoms of three different mbdc2− (Fig. 6a). In 6, each
mbdc2- ligand connects three Cd(II) atoms with its carboxylate
groups in m1−η1:η1-chelating and m2−η2:η1-bridging coordina-
As show in Fig. 7a, three Cd(II) atoms in 7 are all six-
coordinated with distorted octahedral geometry. Cd1 is coordi-
nated by two N atoms from two H2L, three O atoms from three
btc3− ligands and one O atom from a coordinated water molecule,
Cd2 and Cd3 are both coordinated by one N atom from one H2L and

Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
223
Fig. 6. (a) The coordination environment of Cd(II) in 6 with the ellipsoids drawn at the 50% probability level. The hydrogen atoms except those on the nitrogen atom of
imidazole groups are omitted for clarity. Symmetry Code: a 1−x, 1−y, 1−z, b x, 1þy, z, c 2−x, −y, 1−z. (b) The 2D layer of 6. (c) 3D framework of 6 linked by hydrogen bonds
indicated by dashed line.
five O atoms from three different btc3− ligands. In 7, there are two
kinds of btc3− with different conformations and coordination
modes of the carboxylate groups: m1−η1:η0-monodentate, m1−η1:
η1-chelating, m2−η2:η1-bridging, μ2−η1:η1-bismonodentate (Types
VII and VIII, Scheme 1). If the coordination of btc3− is ignored, H2L
and Cd1 constitute a zigzag chain, while the H2L ligands and Cd2,
Cd 3 only form a Cd2(H2L) unit (Fig. 7b). These zigzag chains and
Cd2(H2L) units further connected by btc3− ligands to form a 3D
framework (Fig. 7c).
network and 3D net for 5 and 7, respectively. On the other hand,
H2L serves as a neutral ligand to link two metal centers in 1 and 3–
7, while in 2, H2L is partially protonated to generate a H3Lþ as
terminal ligand. The auxiliary carboxylate ligands also have
different coordination modes: mbdc2−, Hbtc2− and btc3− ligands
act as 2-, 3-, 4- and 5-connectors in 1–7 as illustrated in Scheme 1.
In addition, the remarkable difference between the structures of 2
and 5 implies the great influence of the amount of NaOH used in
the reaction [24].
Topological analysis has been proved to be a useful and simple
method to analyze the extended frameworks, especially for the
complicated 3D frameworks [23]. The Cd1, Cd2 and Cd3 atoms are
bridged by carboxylate groups of btc3− ligands to form a trinuclear
subunit (Fig. 7c, highlighted in pink cycle), which can be treated as
a 10-connected node, while btc3− and H2L ligands are 3- and
2-connectors, respectively. Therefore, the 3D structure of 7 is a
It is interesting to note that there are three different complexes 2–
4 synthesized by changing the reaction temperature, implying the
hydrothermal reaction temperature has great influence on the
structures of the complexes [25]. Changing the reaction temperature
from 180 to 65 1C leads to increasing the amount of 3 and decreasing
the amount of 2. When the reaction temperature was between 65
and 85 1C, a mixture of 2 and 3 was obtained (Fig. S1). Pure 2 can be
synthesized between 100 and 160 1C, while the reaction temperature
is high at 180 1C, a trace of 4 can be found in 2. Table 3 shows the
summary of the complexes synthesized at different temperatures. In
order to get more detailed information on this, we performed
periodic DFT calculations. The results are shown in Table S2. It is
clear that the relative energy of the dehydrated frameworks per zinc
in the order of 3o2o4 (Fig. 8). The calculations therefore show that
the transformation of 3 to 2 or 4 is endothermic, indicating that 3 is
the most stable among three of them. In this work, the most
energetically favorable structure of 3 was obtained at lower tem-
perature while the framework 4 with high energy can only be
obtained with very low yield at higher temperature. The results
indicate that thermodynamic factor is primary in dictating the
formation of the complexes.
(3,10)-connected net with a Schläfli symbol (3,4,5)2(34,48,518,612
,
72,8) topology (Fig. 7d).
3.8. Synthesis of the complexes and comparison of the structures
Seven Zn(II) and Cd(II) coordination polymers were successfully
synthesized and structurally characterized using rigid ditopic
ligand H2L and multicarboxylic acids. Among these complexes,
Zn(II) and Cd(II) atoms are four- and six-coordinated, respectively.
Different coordination number and geometry of the metal centers
lead to the structure diversity of the complexes. For example, 1
and 6 as well as 5 and 7 were prepared under the same reaction
conditions except for the different metal salt, the framework
structures are 1D chain and 2D network for 1 and 6, and 2D

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Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
Fig. 7. (a) The coordination environment of Cd(II) in 7 with the ellipsoids drawn at the 50% probability level. The hydrogen atoms except those on the nitrogen atom of
imidazole groups and free water molecules are omitted for clarity. Symmetry Code: a x, 1.5−y, −0.5þz, b x, 1.5−y, −0.5þz, c 1−x, 0.5þy, 0.5−z, d x, −1þy, z, e 1−x, 1−y, 1−z, f
−x, −0.5þy, 0.5−z. (b) The layer of Cd(II)–H2L. (c) The 3D framework of 7. (d) Schematic representation of the (3,4,5)2(34,48,518,612,72,8) topology.
3.10. Photoluminescence property
Table 3
Summary of the complexes synthesized at different temperatures.
Inorganic–organic hybrid coordination polymers have been
Reaction temperature
Products
65–85 1C
2 and 3
100–160 1C
180 1C
reported to have ability to adjust the emission wavelength of organic
materials through incorporation of metal centers, especially for the d10
metal centers [27]. The solid-state photoluminescent properties of
complexes 1–3 and 5–7, together with the free H2L, H2mbdc and
H3btc, have been investigated at room temperature under the same
conditions. The emission spectra of the complexes and ligands are
depicted in Fig. 9. It can be seen that all of the emission bands of
complexes and ligands were, respectively, observed at 413 nm
2
2 and a trace of 4
3.9. Thermal stabilities and powder X-ray diffraction of the
complexes
(λex ¼315 nm) for 1, 411 nm (λex¼336 nm) for 2, 419 nm (λex
¼
338 nm) for 3, 454 nm (λex¼378 nm) for 5, 433 nm (λex ¼367 nm)
for 6, 458 nm (λex ¼411 nm) for 7, while weak emissions at 427 nm
(λex ¼307 nm) for H2L, 398 nm (λex ¼349 nm) for H2mbdc and 416 nm
(λex ¼359 nm) for H3btc. The fluorescent emissions observed in the
complexes may be tentatively assigned to the intraligand fluorescence
since the free ligands (H2L, H2mbdc and H3btc) exhibit similar
emissions under the same conditions [28]. The red- and blue-shifted
emissions of 1–3 and 5–7 are caused by the coordination of the
ligands to the metal centers [28,29]. The enhanced emissions of the
complexes may mainly originate from the coordination interactions
between the metal atom and the ligand [30]. Specifically, the
coordination interactions enhanced the conformational rigidity of
the complexes and decreased the non-radiative energy loss [31].
Complexes 1–3 and 5–7 were subjected to thermogravimetric
analysis (TGA) to ascertain the stability of the frameworks (Fig. S2)
[26]. Only complex 7 shows a weight loss of 8.51% around 210 1C
for the release of the free and coordinated water molecules
(calc. 8.40%) and when temperature reach 360 1C, the residue of
7 was decomposed. For the other five complexes, no obviously
weight losses were found before the decomposition of the struc-
ture occurred at about 420–460 1C, which are in agreement
with the crystal structures. The pure phase of the complexes was
confirmed by the PXRD, where the patterns of as-synthesized 1–3
and 5–7 are consistent with the corresponding simulated ones
(Fig. S3).

Z.-H. Chen et al. / Journal of Solid State Chemistry 202 (2013) 215–226
225
Absolute
energy
[Zn(H2L)(Hbtc)] (4)
2.01 eV
[Zn(H3L)(btc)] (2
1.10 eV
[Zn(H2L)(Hbtc)] (3)
0.00 eV
Temp
Fig. 8. Comparison of the absolute energy of the structures based upon per zinc(II) as a function of temperature.
Appendix A. Supporting information
1
2
Supplementary data associated with this article can be found in
the online version at http://dx.doi.org/10.1016/j.jssc.2013.03.042.
3
5
6
7
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H2mbdc
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