Self-assembly of a series of metal–organic frameworks with semi-rigid multicarboxylate 3,4-bis(carboxymethoxy)benzoic acid ligands

Article abstract of DOI:10.1016/j.poly.2017.06.039

Seven new metal–organic frameworks based on 3,4-bis(carboxymethoxy)benzoic acid (H₃bcba), 3,5-bis(4-pyridyl)-1,2,4-triazolyl (Hbpt) or 4,4′-bipyridyl (4,4′-bipy), named [Sr₃(bcba)₂(H₂O)₃]_n (1), [Sr(Hbcba)(H₂O)₃]_n (2), [Zn(Hbcba)(H₂O)₂]_n (3), [Zn₃(bcba)₂(Hbpt)₂(H₂O)₂]_n (4), [Zn₃(bcba)₂(4,4′-bipy)₂]_n·nH₂O (5), [Eu(bcba)(H₂O)]_n·nH₂O (6) and [Nd(bcba)(H₂O)]_n·nH₂O (7), have been successfully synthesized via hydrothermal reaction. Single crystal X-ray diffraction reveals that complexes 1, 3, 4 have one-dimensional (1D) zigzag chains, while the rest are composed of 1D double chains. The 3D network in complex 2 and 3 is formed by hydrogen bonds. Complex 4 constitutes a (3,3,4)-connected network and complex 5 constitutes a (4,5,6)-connected network. Complex 6 and 7 are isomorphous. In addition, the thermogravimetric analyses (TGA) for complexes 1–6 are discussed, and the luminescent properties of complex 3–6 have been also investigated.

Full text of DOI:10.1016/j.poly.2017.06.039

Accepted Manuscript
Self-assembly of a series of metal–organic frameworks with semi-rigid multi-
carboxylate 3,4-bis(carboxymethoxy)benzoic acid ligands
Xiao-Zong Li, Can Zhao, You Zhang, Ting Luo, Yi-Hang Wen, Hai Xu
PII:
S0277-5387(17)30457-6
DOI:
http://dx.doi.org/10.1016/j.poly.2017.06.039
POLY 12720
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
30 May 2017
24 June 2017
Please cite this article as: X-Z. Li, C. Zhao, Y. Zhang, T. Luo, Y-H. Wen, H. Xu, Self-assembly of a series of
metal–organic frameworks with semi-rigid multicarboxylate 3,4-bis(carboxymethoxy)benzoic acid ligands,
Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.06.039
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Self-assembly of a series of metal–organic frameworks with
semi-rigid multicarboxylate 3,4-bis(carboxymethoxy)benzoic acid
ligands
*
Xiao-Zong Lia, Can Zhaoa, You Zhanga, Ting Luob, Yi-Hang Wena & Hai Xub*
aCollege of Cheimistryt and Life Sciences, Zhejiang Normal University, Jinhua, Zhejiang, 321004, P. R.China
b
College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan, 410083, P. R. China
Seven
new
Metal–Organic
Frameworks
based
on
3,4-bis(carboxymethoxy)benzoic
acid
(H3bcba),
3,5-bis(4-pyridyl)-1,2,4-triazolyl (Hbpt) or 4,4’-bipyridyl (4,4’-bipy), named [Sr3(bcba)2(H2O)3]n (1), [Sr(Hbcba)(H2O)3]n (2),
[Zn(Hbcba)(H2O)2]n (3), [Zn3(bcba)2(Hbpt)2(H2O)2]n (4), [Zn3(bcba)2(4,4’-bipy)2]n⋅nH2O (5), [Eu(bcba)(H2O)]n⋅nH2O (6) and
[Nd(bcba)(H2O)]n⋅nH2O (7), have been successfully synthesized via hydrothermal reaction. Single crystal X-ray diffraction
reveals that complexes 1, 3, 4 have one-dimensional (1D) zigzag chains, while the rest are composed of 1D double chains. The
3D network in complex 2 and 3 is formed by hydrogen bonds. Complex 4 constitutes a (3,3,4)-connected network and complex
5 constitutes a (4,5,6)-connected network. Complex 6 and 7 are isomorphous. In addition, the thermogravimetric analyses
(TGA) for complexes 1-6 are discussed, and the luminescent properties of complex 3-6 have been also investigated.
Keywords：metal-organic frameworks, 3,4-bis(carboxymethoxy) benzoic acid, luminescent property, topology
the MOFs possess special luminescent properties [8,9].
Moreover, lanthanide metal ions [10,11], main group metal
irons with s-p electron transfer and a few transition metal
ions containing d-d electron transfer are utilized as the
central metal irons of MOFs in terms of their excellent
luminescent merits. In addition, Metal-to-ligand charge
transfer (MLCT) [12] and Ligand-to-metal charge transfer
(LMCT) [13] also enables MOFs to have luminescent
properties. Moreover, MOFs have also been a hot topic for
their superior functional properties and applications in gas
storage, separation and sensing in the last two decades
[14-21]. Among these functional properties, the guest
species recognition and adsorption properties are typically
due to the existing permanent porosity in MOFs’ structures.
New designs and constructs of metal-organic frameworks
affording novel functions have been widely explored in the
past decade. However, it is still a major challenge to
synthesis desirable architectures with useful properties
owing to many factors may affect the self-assembly of
MOFs, such as solvent, pH value, temperature,
metal-to-ligand ratio, counteranions, etc [22-29]. Besides,
the configurations of ligands, such as the length, rigidity and
flexibility, symmetry and coordination sites, also play the
critical roles in constructing MOFs [30-31].
1. Introduction
Solid state light emitting materials attract much attention
of chemists due to their diverse applications in lighting,
display, sensing and optical devices [1-5]. In the past,
rare-earth ions play a valuable role in traditional inorganic
luminescent materials [2,3]. However, organic luminescent
materials have emerged as very promising light emissive
materials in the evolution of efficient organic light-emitting
diodes (OLEDs) in recent years [4,5]. Therefore,
Metal–organic frameworks (MOFs) with the combination of
metal ions and organic materials are also very promising as
multifunctional luminescent materials, attributing to the
generation of luminescence from the inorganic and the
organic moieties. Their luminescence mechanisms are
generally divided into the following categories. Firstly,
some MOFs generally select organic ligands with
fluorescence properties. The luminescence of organic
ligands is generated by electron π→π* transitions or n→π*
transitions [6,7]. Secondly, it is well known that MOFs can
encapsulate guest molecules into their voids through
exchanging the solvent molecules or other reasonable
methods. The light guest molecules into the cavity makes
Hence, our studies are mainly focused on selecting
suitable organic ligands or mixed ligands to construct MOFs
*Corresponding authors (email: wyh@zjnu.edu.cn; xhisaac@csu.edu.cn)

2
with specified structures and properties. In this work, our
selection of semi-rigid 3,4-bis(carboxymethoxy)benzoic
acid (H3bcba) [32] as the main multifunctional bridging
ligand based on the following considerations: (1) It contains
three carboxylate groups, which make the ligand have more
coordination modes and can construct high-dimensional
structures and new topology; (2) It can act as
hydrogen-bonding acceptor and hydrogen-bonding donor
with the different number of deprotonated carboxyl groups,
which is favorable to stabilize the network; (3) The
conjugated moiety of H3bcba ligand may enhance the
luminescence properties of metal-organic complexes.
Herein, we report the syntheses and crystal structures of
seven new MOFs based on mixed H3bcba and rigid
N-donors 3,5-bis(4-pyridyl)-1,2,4-triazolyl (Hbpt) or
4,4’-bipyridyl (4,4’-bipy) ligands. In these complexes, the
bcba3- ligand exhibits various bridging modes (Scheme 1).
In addition, the TGA for complexes 1-6 and the luminescent
properties of complex 3-6 have been also investigated.
After being cooled to room temperature at the rate of 5 ℃
•h-1, brown crystal blocks were obtained (Yield: 27% based
on Sr). Anal. Calcd. (%) for C11H14SrO11 (409.83): C 32.20,
H 3.41; Found (%): C 31.98, H 3.57. IR data (KBr, cm−1):
3597 (s), 2869 (m), 1627 (s), 1539 (s), 1501 (s), 1363 (s),
1204 (s), 1053 (m), 1011 (m), 816 (s), 732 (s), 602 (s), 533
(m).
Synthesis of [Zn(Hbcba)(H O)2]n (3): Zn(NO3)2·6H2O
(0.1189 g, 0.6 mmol) and H32bcba (0.0543 g, 0.2 mmol)
were dissolved in 5 mL H2O. The mixture was then sealed
in a 25 mL stainless steel reactor and heated to 140℃ for 3
days. After being cooled to room temperature at the rate of
5 ℃•h-1, brown ribbon-shaped crystals were obtained (Yield:
35% based on Zn). Anal. Calcd. (%) for C11H12ZnO10
(369.58): C 35.71, H 3.24; Found (%): C 35.69, H 3.02. IR
data (KBr, cm−1): 3222 (s), 2635 (w), 2366 (w), 1672 (m),
1609 (s), 1521 (s), 1471 (m), 1427 (s), 1346 (m), 1314 (s),
1278 (s), 1215 (s), 1139 (s), 1127 (s), 1071 (m), 1052 (s),
958 (m), 877 (m), 833 (s), 758 (s), 652 (s), 539 (m).
Synthesis of [Zn3(bcba) (Hbpt)2(H2O)2]n (4): Zn(NO3)2·6H2O
(0.1194 g, 0.4 mmol), 2 H3bcba (0.0547 g, 0.2 mmol) and
Hbpt (0.0458 g, 0.2 mmol) were dissolved in the mixture of
4.5 mL H2O and 0.5 mL DMF. The solution was then sealed
in a 25 mL stainless steel reactor and heated to 140 ℃ for
3 days. After being cooled to room temperature at the rate of
5 ℃•h-1, purple needle-like crystals were obtained (Yield:
67% based on Zn). Anal. Calcd. (%) for C46H36N10Zn3O18
(1212.96): C 45.50, H 2.96, N 11.54; Found (%): C 45.42,
H 2.73, N 11.83. IR data (KBr, cm−1): 3397 (m), 3078 (s),
1634 (s), 1528 (s), 3434 (s), 1389 (s), 1346 (m), 1208 (s),
1152 (m), 1064 (m), 1033 (s), 852 (s), 814 (s), 733 (s), 683
(m), 646 (m), 508 (s).
2. Experimental
2.1 Materials and instrumentations
All of the chemical reagents and solvents are commercially
available and used without further purification. The
fluorescence spectra were obtained at room temperature on
a LS50B luminescence spectrometer (Perkin-Elmer, Inc.,
USA). Elemental analyses were carried out on
a
Perkin-Elmer 2400 Series II analyzer. Single-crystal X-ray
diffraction data of all complexes were collected on a Bruker
APEX-II CCD diffractometer. The IR spectra were obtained
with KBr pellets in the range of 400~4000 cm-1 on a Nicolet
NEXUS 670 FT-IR spectrometer. Thermogravimetric
analyses (TGA) were performed on a NETZSCH STA-449C
thermoanalyzer.
Synthesis
of
[Zn3(bcba)2(4,4’-bipy)2]n·nH2O
(5):
Zn(NO3)2·6H2O (0.1194 g, 0.4 mmol), H3bcba(0.0546 g, 0.2
mmol) and 4,4’-bipy(0.0312 g, 0.2 mmol) were dissolved in
the mixture of 4.5 mL H2O and 0.5 mL DMF. The solution
was then sealed in a 25 mL stainless steel reactor and heated
to 140 ℃ for 3 days. After being cooled to room
2.2 Preparation of complexes
temperature at the rate of 5 ℃•h-1, yellow rod-like crystals
were obtained (Yield: 62% based on Zn). Anal. Calcd. (%)
for C42H32N4Zn3O17 (1060.83): C 47.50, H 3.02 N 5.27;
Found (%): C 47.36, H 2.94, N 5.11. IR data (KBr, cm−1):
3584 (m), 3473 (m), 3473 (m), 3072 (m), 2966 (m), 2371
(w), 1953 (w), 1615 (s), 1509 (m), 1421 (s), 1333 (w), 1721
(s), 1215 (s), 1146 (m), 1108 (s), 1052 (s), 933 (m), 889 (m),
814 (s), 777 (s), 726 (s), 633 (s), 457 (s).
Synthesis of [Sr3(bcba)2(H2O)3]n (1): SrCl2·6H2O (0.266 g,
1.0 mmol) and H3bcba (0.135 g, 0.5 mmol) were dissolved
in 17 mL H2O. The pH of the solution was adjusted to 9
with an aqueous NaOH solution (2.0 mol·L−1). The mixture
was then sealed in a 25 mL stainless steel reactor and heated
to 140 ℃ for 3 days. After being cooled to room
temperature at the rate of 5 ℃•h-1, some brown sheet-like
crystals were obtained (Yield: 30% based on Sr). Anal.
Calcd. (%) for C22H20Sr3O19 (851.24): C 31.02, H 2.35;
Found (%): C 30.98, H 2.29. IR data (KBr, cm−1): 3624 (w),
2872 (m), 1610 (s), 1548 (s), 1509 (s), 1382 (s), 1213 (s),
1046 (m), 1021 (m), 805 (s), 745 (s), 657 (s), 521 (m).
Synthesis of [Sr(Hbcba)(H2O)3]n (2): SrCl2·6H2O (0.1622 g,
0.6 mmol) and H3bcba (0.0543 g, 0.2 mmol) were dissolved
in 8 mL H2O. The mixture was then sealed in a 25 mL
stainless steel reactor and heated to 140 ℃ for 3 days.
Synthesis of [Eu(bcba)(H2O)]n·nH2O (6): Eu(NO3)3·6H2O
(0.4463 g, 1.0 mmol), H3bcba (0.133 g, 0.5 mmol) and
NaOH (0.064 g, 1.6 mmol) were dissolved in 17 mL H2O.
The mixture was then sealed in a 25 mL stainless steel
reactor and heated to 140℃ for 3 days. After being cooled
to room temperature at the rate of 5 ℃·h-1, colorless
ribbon-shaped crystals were obtained (Yield: 55% based on
Eu). Anal. Calcd. (%) for C11H11EuO10 (455.16): C 29.00, H
2.42; Found (%): C 29.22, H 2.27. IR data (KBr, cm−1):

2
3654 (s), 3495 (s), 3072 (w), 2928 (w), 2359 (w), 1672 (m),
1609 (s), 1421 (s), 1389 (s), 1340 (s), 1264 (s), 1202 (s),
1115 (s), 1033 (s), 925 (s), 908 (m), 846 (s), 783 (s), 639 (s),
601 (s), 533 (m).
Synthesis of [Nd(bcba)(H2O)]n·nH2O (7): Nd(NO3)3·6H2O
(0.1771 g, 0.4 mmol), H3bcba (0.0498 g, 0.2 mmol) and
NaOH (0.0545 g, 1.25 mmol) were dissolved in 5 mL H2O.
The solution was then sealed in a 25 mL stainless steel
reactor and heated to 140℃ for 3 days. After being cooled
2.3 X-ray crystallography
The single crystal X-ray diffraction data of complexes 1-7
were collected on a Bruker SMART APEX-II CCD
diffractometer with MoKα radiation (λ = 0.71073 Å). All of
the structures were solved by direct method and refined by
full-matrix least-squares on F2 using SHELX-97 program
package [33]. Non-hydrogen atoms were refined
anisotropically. The hydrogen atoms of ligands were
generated theoretically, and then refined isotropically by
riding on their parent carbon atoms. Crystal data for
complexes 1-7 are listed in Table 1 and selected bond
lengths and angles for complexes 1-7 are listed in Table S1.
The hydrogen-bonding parameters for 2 and 3 are listed in
Table S2.
to room temperature at the rate of 5 ℃•h-1, colorless
ribbon-shaped crystals were obtained (Yield: 36% based on
Nd). Anal. Calcd. (%) for C11H11NdO10 (447.44): C 29.50, H
2.46; Found (%): C 30.08, H 2.31. IR data (KBr, cm−1):
3650 (s), 3481 (s), 3055 (w), 2921 (w), 2249 (w), 1632 (m),
1398 (s), 1342 (s), 1253 (s), 1201 (s), 1121 (s), 1029 (s),
949 (s), 903 (m), 842 (s), 773 (s), 622 (s), 609 (s), 521 (m).
Table 1 Crystal data and structure refinement for complex 1-7
Complex
Empirica
l
formula
Formula
Weight
1
2
3
4
5
6
7
C22H20O1
9Sr3
C11H14O1
1Sr
C11H12O1
0Zn
C46H36N1
0O18Zn3
C42H32N4
O17Zn3
C11H11Eu
O10
C11H11N
dO10
851.24
409.83
369.58
1212.96
1060.83
455.16
447.44
Monocli
nic
Monocli
nic
Monocli
nic
Orthorho
mbic
Monocli
nic
Monocli
nic
Monocli
nic
Crystal Syst
em
space gr
oup
P21/c
P21/c
P21/n
Pnn2
P21/c
C2/c
C2/c
Colour
Colorless
7.8456
(4)
15.9412
(8)
Colorless
15.8144
(4)
6.80360
(10)
Brown
5.1919
(3)
22.7617
(12)
Purple
13.8883
(8)
35.194
(2)
Pink
9.1423
(4)
18.1241
(7)
Colorless
21.3444
(16)
6.1687
(5)
Colorless
21.5603
(3)
6.21040
(10)
a (Å)
b (Å)
21.7950
(13)
90
102.123
(3)
13.7353
(3)
90
104.687
(10)
11.4542
(7)
90
102.109
(3)
5.3727
(3)
90
13.2248
(5)
90
111.598
(3)
20.9035
(16)
90
110.072
(3)
20.9891
(3)
90
110.6010
(10)
c (Å)
α (°)
β (°)
90
90
2665.1
(2)
90
1429.56
(5)
90
1323.50
(13)
90
2626.1
(3)
90
2037.44
(14)
90
2585.1
(3)
90
2630.68
(7)
γ (°)
V (Å3)
T/K
Z
296(2)
4
296(2)
4
296(2)
4
296(2)
2
296(2)
2
296(2)
8
296(2)
8
Dc (g/c
m3)
2.122
1.900
1.855
1.534
1.729
2.339
2.259
µ (mm-1)
F (000)
Θmin/θmax
(°)
6.076
1672
1.60/25.0
0
3.831
824
2.66/27.6
9
1.910
752
1.79/27.5
6
1.440
1232
2.74/27.6
2
1.837
1076
2.00/27.5
4
4.908
1760
2.03/27.5
5
4.002
1736
2.02/27.5
7
-17≦h≦
18, -45≦k
≦45,-6≦l
≦6
-9≦h≦
-20≦h≦
-6≦h≦
-11≦h≦
-27≦h≦
27≦h≦
Limiting
Indices
9,-18≦k≦1 20, -8≦k≦ 6,-29≦k≦2
7,-23≦l≦2 8,-17≦l≦1 9,-14≦l≦1
11,-23≦k≦ 27,-8≦k≦ 28, -8≦k≦
23,-17≦l≦ 8,-27≦l≦2 8, -27≦l≦
5
7
4
17
7
26
Reflectio
ns collected
19522
46648
25665
27278
39820
19552
25184
3049（0.
0475）
Uniques
(Rint)
4683(0.0
487)
3327(0.0
543)
3032(0.0
516)
6042(0.0
469)
4688(0.0
332)
2979(0.0
443)
Paramete
rs
403
212
202
354
304
205
205
Goodnes
1.034
1.100
1.097
1.137
1.043
1.075
1.058

2
s-of-fit on
F2
Final R
Indices [I>
2σ (I)]
0.0333/0.
0663
0.0350/0.
0841
0.0409/0.
0800
0.0459/0.
1535
0.0355/0.
0913
0.0279/0.
0835
0.0389/0.
0813
R indice
s (all data)
∆ρmax,∆ρ
min/(e.Å-3)
0.0553/0.
0708
0.569,-0.
560
0.0450/0.
0899
0.996,-1.
132
0.0557/0.
0843
0.529,-0.
528
0.0546/0.
1604
1.275,-0.
399
0.0435/0.
0960
0.745,-0.
408
0.0287/0.
0842
1.473,-1.
127
0.0469/0.
0843
1.349，-
1.695
M
O
M
M
M
O
(a)
(b)
O
O
M
O
O
O
O
M
O
O
M
O
O
O
O
M
O
O
M
M
M
M
O
O
O
(c)
(d)
(e)
M
M
O
O
O
M
O
M
O
O
O
M
O
O
M
O
M
O
O
O
HO
O
M
O
O
O
O
O
O
Scheme 1 Coordination modes of the bcba3- ligand
from flexible –COO- of three bcba3- ligand with the Sr(II)-O
distances of 2.540(3)—2.647(3) Å, including one O atom
(O14) as a cap. The Sr(III) ion is in a dodecahedron
geometry, coordinated by five O atom from three flexible
–COO- of three bcba3- ligands with the Sr(III)-O distances
of 2.493(3)—2.761(3) Å, two O atoms from rigid –COO- of
two bcba3- ligands with the Sr(III)-O distances of 2.533(3)
and 2.619(3) Å, and one O atoms from one coordinated
water molecules. The bcba3- ligand adopts two different
coordination modes (Scheme 1(a) and (b)).The SBUs
([Sr3CO5]) (Figure 1(b)) including three Sr atoms and five O
atoms from carboxylate groups, connects the bcba3- ligands
through carboxylate groups to form the 1D zigzag chain
(Figure 1(c)). The 1D zigzag chains are connected through
the bcba3- ligand to form a 3D framework (Figure 1(d)).
3. Results and discussion
3.1 Crystal structure of the complexes
3.1.1 Crystal structure of [Sr3(bcba)2(H2O)3]n (1)
X-ray crystallography shows that complex 1 crystallizes
in monoclinic system with P21/c space group. As shown in
Figure 1(a), the asymmetric unit is composed of three
crystallographically independent Sr2+ cations, namely Sr(I),
Sr(II) and Sr(III), two fully deprotonated bcba3- anion and
three coordinated water molecules. The Sr(I) ion is in a
dodecahedron geometry, coordinated by five O atoms from
three flexible –OCH2COO- of two bcba3- ligands with the
Sr(I)-O distances of 2.448(3)—2.737(3) Å, and three O
atoms from rigid –COO- of two bcba3- ligands with the
Sr(I)-O distances of 2.453(3)—2.778(3) Å. The Sr(II) ion is
in a capped octahedral geometry, coordinated by one O
atom from rigid –COO- of one bcba3- ligand, two O atoms
from two coordinated water molecules with the Sr(II)-O
distances of 2.663(3) and 2.723(3) Å, and four O atoms

2
three coordinated water molecules with the Sr(I)-O
distances of 2.636(3)—2.739(3) Å. In this complex, the
rigid carboxyl is not deprotonated, while flexible
carboxylate is protonated. The Hbcba2- ligand adopts two
different coordination modes, respectively bridging and
tetradentate chelating (Scheme 1(c)). The binuclear SBUs is
formed by two Sr, three O atoms from the flexible –OCOO-
(O7,O7#3,O8) and C11. The connected SBUs forms the 1D
double-chain (Figure 2(b)), and these connected 1D
double-chains via the hydrogen-bonding interactions (table
s2) form the layered structure (Figure 2(c)).
Figure 1 (a) Coordination environment of Sr2+ ions in 1 (Omitting all H
atoms). Symmetry codes: #1 x-1, -y-1/2, z-1/2; #2 -x, -y-1, -z-1; #3 -x, -y-1,
-z; #4 x, -y-1/2, z+1/2; #5 x+1, -y-3/2, z+1/2; #6 -x, y-1/2, -z-1/2; #7 -x+1,
y-1/2, -z+1/2; (b) the [Sr3CO5] SBUs; (c) view of the 1D zigzag chain; (d)
view of the 3D network.
Figure 2 (a) coordination environment of Sr2+ ions in 2 (Omitting all H
atoms) Symmetry codes: #1 -x+1, y-1/2, -z+1/2; #2 x, y-1, z; #3 -x+1,
y+1/2, -z+1/2; #4 x, y+1, z; (b) view of the 1D zigzag chain; (c) view of
the layered structure.
3.1.3 Crystal structure of [Zn(Hbcba)(H2O)2]n (3)
X-ray crystallography shows that complex
3
3.1.2 Crystal structure of [Sr(Hbcba)(H2O)3]n (2)
crystallizes in monoclinic system with P21/n space group.
As shown in Figure 3(a), the asymmetric unit is composed
of one crystallographically independent Zn2+ cation, namely
Zn(I), one partially deprotonated Hbcba2- anion and two
coordinated water molecules. The Zn(I) ion is in a trigonal
bipyramid geometry, coordinated by three O atoms from the
semi-rigid Hbcba2- ligand with the Zn(I)-O distances of
1.947(2)—2.006(2) Å, and two O atoms from two
coordinated water molecules with the Zn(I)-O distances of
1.9518(19) and 2.005(2) Å. Two O atoms from the
X-ray crystallography shows that complex
2
crystallizes in monoclinic system with P21/c space group.
As shown in Figure 2(a), the asymmetric unit is composed
of one crystallographically independent Sr2+ cations, namely
Sr(I), one partially deprotonated bcba3- anion and three
coordinated water molecules. The Sr(I) ion is in a tricapped
trigonal prism geometry, coordinated by six O atoms from
three partially deprotonated bcba3- ligands with the Sr(I)-O
distances of 2.539(2)—2.754(2) Å, and three O atoms from

2
semi-rigid Hbcba2- adopt chelating bidentate modes
(Scheme 1(d)). Other O atoms adopt monodentate bridging
modes (Scheme 1(d)). The 1D zigzag chains (Figure 3(b))
are formed by connecting the partially deprotonated Hbcba2-
ligands to the adjacent Zn(I) ion. The free water molecules
connect O atoms from Hbcba2- ligands through the hydrogen
bonds (Table S2). The connected adjacent 1D zigzag chains
atom from the semi-rigid carboxylate coordinated to Zn(I)
through a monodentate bridging pattern (Scheme 1(e)) with
the Zn(I)-O distances of 1.959(4) Å, one N atoms from the
Hbpt ligand through monodentate bridging pattern with the
Zn(I)-N distances of 2.062(4) Å and one O atom from one
coordinated water molecules with the Zn(I)-O distances of
1.994(4) Å. The Zn(II) ion is in a tetrahedral geometry,
coordinated by two N atoms from Hbpt ligand with the
Zn(II)-N distances of 2.062(4) and 2.047(4) Å, and two O
atoms from the semi-rigid carboxylate with the Zn(II)-O
distances of 1.949(4)—2.374(4) Å. The adjacent Zn(I)
atoms were linked through the rigid carboxylate and the
semi-rigid carboxylate from the same bcba3- ligand to form a
1D zigzag chain (Figure 4(b)). These adjacent 1D zigzag
chains were linked through another set of semi-rigid
–OCOO- to form a 3D network (Figure 4(c)). In the
complex 4, those Hbpt ligands play a vital role to hold the
framework.
−π
through hydrogen-bonding and π interactions form a 3D
network (Figure 3(c)).
In the structure, every bcba3- ligand connected by three
Zn atoms is regarded as µ3-η1:η1:η1-bridged ligand. Every
Hbpt is looked as µ2-η1:η1-bridged ligand. The Zn atoms
have two kinds of linking modes. The Zn(I) connects two
bcba3- ligands and one Hbpt ligand, so it can be looked as
three-connected nodes. While the Zn(II) connects two bcba3-
ligands and two Hbpt ligands, so it can be looked as
four-connected nodes. Thus, the topology of the structure
could be simplified as a (3,3,4)-network (Figure 4(d)).
Figure 3 In complex 3 (a) coordination environment of Zn2+ ions
(Omitting all H atoms) Symmetry codes: #1 x+3/2, -y+1/2, z+1/2; #2 x-3/2,
-y+1/2, z-1/2; #3 x+1/2, -y+1/2, z+1/2; #4 –x+2, -y, -z; #5 x+2, y, z+1; (b)
view of the 1D zigzag chain; (c) view of the 3D network with the
hydrogen-bonding interactions.
3.1.4 Crystal structure of [Zn3(bcba)2(Hbpt)2(H2O)2]n(4)
X-ray crystallography shows that complex
4
crystallizes in orthorhombic system with Pnn2 space group.
As shown in Figure 4(a), the asymmetric unit is composed
of one and a half crystallographically independent Zn2+
cations, namely Zn(I) and Zn(II), one fully deprotonated
bcba3- anion, one Hbpt ligand and one coordinated water
molecules. The Zn(I) ion is in a trigonal bipyramid
geometry with the O1, O1W, O8#1 locating in equatorial
positions and N5, O7#1 locating in axial positions. These
two O atoms from a rigid carboxylate coordinated to Zn(I)
through a bidentate chelating pattern (Scheme 1(e)) with the
Zn(I)-O distances of 2.372(4) and 2.017(4) Å. The other O

2
bcba3- ligands and one 4,4’-bipy ligand, so it can be looked
as four-connected nodes. While the Zn(II) connects four
bcba3- ligands and two 4,4’-bipy ligands, so it can be looked
as six-connected nodes. Thus, the topology of this structure
could be simplified as a (4,5,6)-network (Figure 5(e)).
Figure 4 In complex 4 (a) coordination environment of Zn2+ ions (Omitting
all H atoms) Symmetry codes: #1 x-1/2, -y+3/2, z+1/2; #2 -x+3/2, y-1/2,
z-5/2; #3 x+1/2, -y+3/2, z-5/2; #4 -x+2, -y+1, z; #5 x-1/2, -y+3/2, z+5/2;
#6 x+1/2, -y+3/2, z-1/2; (b) view of the 1D zigzag chain; (c) view of the
3D network; (d)view of the (3,3,4)-connected trinodal topology net.
3.1.5 Crystal structure of [Zn3(bcba)2(4,4’-bipy)2]n•nH2O(5)
X-ray crystallography shows that complex
5
crystallizes in monoclinic system with P21/c space group.
As shown in Figure 5(a), the asymmetric unit is composed
of one and a half crystallographically independent Zn2+
cations, namely Zn(I) and Zn(II), one fully deprotonated
bcba3- anion, one 4,4’-bipy ligand and half free water
molecules. The Zn(I) ion is in an distorted octahedron
geometry, coordinated by a N atom from 4,4’-bipy ligand,
four O atoms from two semi-rigid bcba3- ligands through
chelating bidentate modes, and another O atom from
semi-rigid carboxylate of bcba3- ligand. The Zn(II) ion is in
a octahedron geometry, coordinated by two N atoms from
4,4’-bipy ligands locating in axial position, four O atoms
from four semi-rigid carboxylates of bcba3- ligands locating
in equatorial plane. The Zn-O distances are in
1.972(2)—2.373(3) Å, and the Zn-N distances are 2.092(2)
and 2.119(2) Å. Four Zn atoms connected to the partial
atoms of the bcba3- ligands form the SBUs (Figure 5(b))
with a twenty four-number ring. The connected adjacent
SBUs forms the 1D double-chain (Figure 5(c)), then the 1D
double-chain connected through the bcba3- to build the 3D
network (Figure 5(d)). In complex 5, the 4,4’-bipy ligand
also plays a vital role to hold the framework and strengthen
the stability of framework.
In the structure, every bcba3- ligand connected by five Zn
atoms is regarded as µ5-η1:η1:η1:η1:η2-bridged ligand. Every
4,4’-bipy is looked as µ2-η1:η1-bridged ligand. The Zn atoms
have two kinds of linking modes. The Zn(I) connects three
Figure 5 (a) Coordination environment of Zn2+ ions in 5(Omitting all H
atoms). Symmetry codes: #1 x+1, y, z; #2 -x, y+1/2, -z+1/2; #3 -x-1, -y, -z;
#4 x-2, y, z-1; #5 -x+1,-y,-z+1;#6 x,-y-1/2,z-1/2; #7 -x-1, y+1/2, -z+1/2. (b)
view of the [Zn4C12O8] SBUs; (c) view of the 1D double-chain; (d) view of

2
the 3D supermolecular network; (e) the (4,5,6)-connected trinodal topology
net.
3.1.6 Crystal structure of [Eu(bcba)(H2O)]n·nH2O (6)
X-ray crystallography shows that complex 6 and 7 are
isomorphous, and crystallize in monoclinic system with
C2/c space group. Only the structure of 6 is described in
details. As shown in Figure 6(a), the asymmetric unit is
composed of one crystallographically independent Eu3+
cations, namely Eu(I), one fully deprotonated bcba3- anion,
one coordinated water molecule and one free water
molecule. The Eu(I) ion is in a tricapped trigonal prism
geometry, coordinated by eight O atoms from the bcba3-
ligands, one O atom from coordinated water molecule. The
Eu-O distances are in 2.341(3)—2.653(3) Å.
In complex 6, the twelve-numbered ring of trinuclear
SBUs (Eu3C3O6) including three Eu3+ atoms, three C atoms
and six O atoms through bond linkage of Eu atom forms the
1D double-chain (Figure 6(b)). The adjacent binuclear
SBUs (Eu2C2O4) linked through the semi-rigid carboxylates
of bcba3- ligands forms the 1D channel (Figure 6(c)).
Two-dimensional network structure (Figure 6(d)) is formed
by one-dimensional channel and one-dimensional double
chain staggered connection, then it was connected to bcba3-
ligand to build a 3D supramolecular network (Figure 6(e))
through hydrogen-bonding interactions (Figure 6(f)).
Figure 6 In complex 6: (a) coordination environment of Eu3+ ions; (b) view

2
of the 1D double-chain building with the trinuclear cluster; (c) the 1D
channel building with the binuclear blocks; (d) view of the 2D network; (e)
view of the 3D network (Omitting all coordination H2O); (f) view of the 3D
supramolecular network with hydrogen-bonding interactions.
20.03%). As shown in Figure 7(c), for 5, the weight loss in
the range of 303–305 °C corresponds to the release of lattice
water molecules (obsd 3.02%, calcd 1.69%). The next
weight loss in the temperature range of 305–494 °C is
attributed to the release of bcba3- ligand and 4,4’-bipy (obsd
75.08%, calcd 79.75%), leading to the formation of ZnO as
the residue (obsd 21.14%, calcd 22.90%). As shown in
Figure 7(d), for 6, the weight loss in the range of 25–166 °C
corresponds to the release of lattice water molecules (obsd
5.52%, calcd 3.95%). The next weight loss in the
temperature range of 166–304 °C is attributed to the release
of coordinated water molecules (obsd 4.72%, calcd 3.95%).
The last weight loss in the temperature range of 304–670 °C
is attributed to the release of bcba3- ligand (obsd 55.17%,
calcd 58.66%), leading to the formation of Eu2O3 as the
residue (obsd. 41.54%, calcd. 38.66%).
To confirm whether the crystal structures are truly
representative of the bulk materials, PXRD experiments
were carried out for 1–6. The PXRD experimental and
computer-simulated patterns of the corresponding
complexes are shown in the picture (Figure 8). It is shown
that the synthesized bulk materials 1 and 2 maybe have
impurity, while complexes 3, 4, 5, 6 are pure phase
materials.
3.2 Thermal analysis and PXRD patterns
To characterize the complexes more carefully in terms
of thermal stability, the thermal behaviors of 3–6 were
examined by thermogravimetric analysis (TGA). As shown
in the Figure 7(a), for 3, the weight loss corresponding to
the release of two coordinated water molecules is observed
from 122 to 226 °C (obsd 9.86%, calcd 9.74%). The next
weight loss in the temperature range of 258–423 °C is
attributed to the release of bcba3- ligand (obsd 69.86%, calcd
72.24%), and the decomposition of the residual composition
occurred from 258 to 423 °C, leading to the formation of
ZnO as the residue (obsd 23.40%, calcd 21.91%). As shown
in the Figure 7(b), for 4, the weight loss in the range of
270–502 °C corresponds to the release of bcba3- ligand,
Hbpt ligand and coordinated water molecules (obsd 80.41%,
calcd 83.59%). When the temperature reaches 502 ℃, the
complex has completely decomposed, leading to the
formation of ZnO as the residue (obsd 18.92%, calcd
Figure 7 The TGA curves of the complex 3-6.

2
Figure 8 Power X-ray diffraction patterns of complex 1-6(1:simulated and 2:experimental).
the emission peak appears at around 447 nm (λex=417 nm)
3.3 Luminescent properties
and is red-shifted by 75 nm with respect to the free H3bcba
ligand, while it is blue-shifted by 21 nm with respect to the
free Hbpt. It is noteworthy that the emission bands of
complexes 4 and 5 are broader than those observed for
complex 3. For 6 (Figure 10(d)), the emission spectra
centered at 550, 576, 639, 612, and 709 nm can be seen,
Luminescent properties of complexes with d10 and
lanthanide metal centers have attracted intense interests due
to their potential applications in fluorescent chemical sensor
and electroluminescent displays [34-38]. In this work, the
photoluminescent properties of H3bcba, Hbpt and 4,4’-bipy
ligands and complex 3–6 were investigated in the solid state
at room temperature. As shown in Figure 9, the main
emission peaks of H3bcba, Hbpt and 4,4’-bipy are at 372 nm
(λex=350 nm), 468 nm (λex=340 nm), and 496 nm
(λex=412 nm), respectively, which can be attributed to the
n→π* or π*→π transitions. The emission peak of 3 is at 323
nm (λex=300 nm), which is blue-shifted by 49 nm with
respect to the free H3bcba ligand (Figure 10(a)). As shown
in Figure 10(c), complex 5 shows an emission peak at 510
nm (λex=389 nm), which is red-shifted by 121 nm relative
to the H3bcba ligand and by 12 nm relative to the 4,4’-bipy.
Therefore, the emissions of 3 and 5 can probably be
attributed to their ligands. As shown in Figure 10(b), for 4,
5
7
→4)
which correspond to D0→ Fn (n=0
transitions of Eu3+
ions, respectively. The weakest emission peaks around 576
5
nm is attributed to the magnetic dipolar D0→7F1 transition;
the medium-strong emission around 550 nm, 639 nm and
709 nm is attributed to the magnetic dipolar 5D0→7F0
transition, 5D0→7F3 transition and 5D0→7F4 transition,
respectively. The strongest emission peak around 612 nm is
5
ascribed to the electric-dipolar D0→7F2 transition. Because
the ratio of the strongest emission peak around 612 nm and
the weakest emission peaks around 576 nm is 2, 4, so the
Eu(III) has lower symmetry.
Because metal ions with d10 configurations are especially
difficult to be oxidized or reduced, the emission of complex

2
[39-42]. Thus, comparing to the free ligand, the
fluorescence quenching of complex 3, 4, 5 can be attributed
to the deprotonated effect of ligand, the pH value, the
solvent and the coordination interaction of the organic
ligand to Zn2+ ion.
3, 4, 5 cannot be assigned as metal-to-ligand charge transfer
(MLCT) or ligand-to-metal charge transfer (LMCT) in
nature. It can probably be based on the photoluminescence
of intraligand and ligand-to-ligand charge transition (LLCT),
and appears to be substantially influenced by the
conformational and accumulational changes of the ligand
Figure 9 Solid-state emission spectra of free ligands: (a) for Hbpt and (b) for H3bcba and 4,4’-bipy.
Figure 10 Solid-state emission spectra of (a) 3 and free H3bcba ligand; (b) 4 and free ligand; (c) 5 and free ligands; (d) complex 6
by the Eu3+ center. It is believed that the prime research of
this work will supply further access to the rational design
and synthesis of the novel functional coordination
complexes based on semi-rigid carboxylate ligands.
4. Conclusions
In summary, seven complexes based on different metal
carboxylate clusters have been synthesized with semi-rigid
carboxylate connecter H3bcba under hydrothermal
conditions. The ligand H3bcba adopts flexible coordination
modes and can meet various requirements of different
metals, building new complexes with intriguing
constructions. Complex 4 is (3,3,4)-connected network with
the 1D zigzag chain containing tetranuclear secondary
building. Complex 5 possesses (4,5,6)-connected network
with the 1D double-chain. Complex 2, 6, 7 are the 3D
structural frameworks with the 1D double-chain, and 6, 7
have a trinuclear secondary building units (SBUs). Complex
3 possesses a 3D network with the hydrogen-bonding
interactions within the 1D zigzag chain. In addition, the
luminescence of complex 3, 4 and 5 all is affected by the
ligand, while the luminescence of the complex 6 is affected
Acknowledgments This work was supported financially by the Open
Research Fund of Top Key Discipline of Chemistry in Zhejiang Provincial
Colleges and the Key Laboratory of the Ministry of Education for
Advanced Catalysis Materials (ZJHX201515).
Appendix A. Supplementary data CCDC 1548266-1548272 contains the
supplementary crystallographic data for these complexes. These data can
be obtained free of charge via × × × , or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in the online
version, at×××.
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2

2
A series of metal–organic frameworks based
on designed 3,4-bis(carboxymethoxy)benzoic
acid ligands were synthesized, structurally
characterized, and the luminescent properties
of some complexes have been also investigated.