Full text of DOI:10.1016/j.poly.2018.08.048

Accepted Manuscript
A new 2D→3D polycatenated Cd(II) coordination polymer: Syntheses, struc-
ture and luminescent sensing
Fei Yuan, Chun-Mei Yuan, Huai-Ming Hu, Yuan-Yuan Liang, Xiaofang Wang,
Chun-Sheng Zhou
PII:
S0277-5387(18)30516-3
https://doi.org/10.1016/j.poly.2018.08.048
POLY 13371
DOI:
Reference:
Polyhedron
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18 August 2018
Please cite this article as: F. Yuan, C-M. Yuan, H-M. Hu, Y-Y. Liang, X. Wang, C-S. Zhou, A new 2D→3D
polycatenated Cd(II) coordination polymer: Syntheses, structure and luminescent sensing, Polyhedron (2018), doi:
https://doi.org/10.1016/j.poly.2018.08.048
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A new 2D→3D polycatenated Cd(II) coordination polymer:
Syntheses, structure and luminescent sensing
Fei Yuana,b, Chun-Mei Yuana, Huai-Ming Hub*, Yuan-Yuan Liangb, Xiaofang Wangb,
Chun-Sheng Zhoua*
aShaanxi Key Laboratory of Comprehensive Utilization of Tailings Resources,
College of Chemical Engineering and Modern Materials, Shangluo University,
Shangluo 726000, China
bKey Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry
of Education, College of Chemistry and Materials Science, Northwest University,
Xi'an 710127, China
*To whom correspondence should be addressed.
Prof. Dr. Huai-Ming Hu
College of Chemistry and Materials Science
Northwest University
Xi’an 710127, China
Tel/Fax: +86-29- 81535025
Email: ChemHu1@NWU.EDU.CN
1

Abstract：A new 3D coordination polymer, [NH2(CH3)2]n[Cd(TCBPA)]n·3nH2O (1)
{H3TCBPA=tris[(4-carboxyl)-phenylduryl]amine}, was constructed under
solvothermal conditions and structurally characterized by elemental analysis, FT-IR
spectroscopy, powder X-ray diffraction (PXPD) and thermogravimetric analysis
(TGA). Single crystal X-ray diffraction indicates that compound 1 displays a uninodal
3-connected 2D→3D polycatenated network with the point symbol of 63. Furthermore,
photoluminescence of 1 was investigated and has been successfully applied in the
detection of Fe3+ ion in DMF solution.
Keywords: Coordination polymer; Carboxylate ligand; Luminescence sensor;
Solvothermal synthesis; Topology
2

1. Introduction
Currently, increasing interest still has been evoked by transition metal
coordination polymers with porous character or well-regulated network in the fields
of crystal engineering owing to their wide potential application as gas storage or gas
separation, catalysis, magnetism, sensor and so on [1-3]. However, the rational design
and synthesis of new porous coordination polymers (CPs) with unique structure and
function remains a great challenge in coordination chemistry [4, 5]. Generally, the
diversity in the self-assembly process of such coordination polymers influenced by
the coordination geometry of metal centers, the coordination ability of organic ligand,
number of coordination donors provided by ligands and the reaction conditions and so
on [6-9]. Especially, the selection of organic ligand with suitable binding groups are
very crucial in the building of coordination polymers with novel structures. Most
bridging semi-rigid ligands usually facilitate interpenetrating MOFs because they can
lead to the formation of nanosized cages, porous frameworks enclosing cavities,
chambers and channels [10]. Therefore, tricarboxylate-based ligands have
successfully been used for the construction of CPs. Meanwhile, we are interested in
the porous and interpenetrating structures constructed from the semi-rigid trigonal
ligands with N,O-donor and d10 transition metal ions.
On the basis of the above considerations, a semi-rigid tricarboxylate ligand,
tris[(4-carboxyl)-phenylduryl]amine (H3TCBPA, Scheme 1) is employed in the realm
of crystal engineering according to the following consideration: (a) H3TCBPA, as a
semi-rigid bridging ligand, can link metal ions via coordination bond to construct high
dimensional and honeycomb porous coordination polymers. (b) It has a large
π-conjugated nonlinear structure with N,O donors that can offer additional hydrogen
bonding and π–π interactions to consolidate the whole framework structures. (c)
Metal ions prefer binding O atoms of three carboxylate groups rather than the N atom
in H3L because of steric effect resulting from phenyl groups around N atom, so this N
atom as a functional site is predicted to recognize metal ions. Herein, we report
synthesis and crystal structure of one new coordination polymer
[NH2(CH3)2]n[Cd(TCBPA)]n·3nH2O (1). Meanwhile, the solid-state luminescence of 1
3

was also examined under ultraviolet irradiation at ambient temperature. Compound 1
show high selectivity and sensitivity for Fe3+ cation due to the quenching effect,
which may be a potential sensor material for detecting Fe3+ cation.
[Scheme 1 is here]
2. Experimental
2.1 Materials and physical measurements
Ligand H3TCBPA was prepared via a Pd-catalyzed Suzuki coupling reaction
between tris(4-bromophenyl)amine and 4-(methoxycarbonyl)phenylboronic acid as
reported previously [10e]. Other chemicals were of reagent grade and used without
further purification. Infrared spectra were obtained from KBr pellets on a Bruker
EQUINOX 55 Fourier transform infrared spectrometer in the 400-4000 cm-1 region.
Elemental analyses (C, H, N) were performed on an elementar Vario EL III elemental
analyzer. Thermal gravimetry analyses (TGA) were carried out with a Universal V2.6
DTA system at a rate of 10℃/min in a nitrogen atmosphere. Photoluminescent spectra
were measured using a Hitachi F-4500 Fluorescence Spectrometer for the solid
powder samples at room temperature. Quantum efficiency was measured using the
integrating sphere on a FluoroMax-4 spectrophotometer.
2.2 Preparation of [NH2(CH3)2]n[Cd(TCBPA)]n·3nH2O (1)
Compound 1 was prepared by solvothermal reaction of CdCl2•2.5H2O (0.0229 g,
0.1 mmol) and H3TCBPA (0.0152 g, 0.025 mmol) in distilled water (7 mL) and
N,N-dimethylacetamide (DMA) (3 mL) and using 0.5 mol.L-1 NaOH aqueous solution
to adjust the pH to 5.0 that was placed in a Teflon-lined stainless steel vessel (25 mL),
heated to 120℃ for 72h and then cooled to room temperature at a rate of 5℃/h. The
crystalline product was obtained, washed with distilled water (5 mL), and dried in air
to give 0.0105 g, yield 51.5% based on H3TCBPA. Elemental anal. calcd for:
C39H24CdNO6 (%): C, 65.51; H, 3.38; N, 1.96. Found (%): C, 60.35; H, 4.64. N, 3.41.
IR (KBr, cm−1): 3422 (s), 1594 (s), 1522 (s), 1403 (s), 1327 (m), 1283 (m), 1187 (m),
4

1108 (w), 1012 (w), 833 (w), 793 (m), 726 (w), 653 (w).
2.3 Single crystal x-ray diffraction
Suitable single crystal of 1 was carefully selected under an optical microscope
and glued to thin glass fibers. Intensity data were collected on a Bruker Smart APEX
II CCD diffractometer with graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å)
at room temperature. Empirical absorption corrections were applied using the
SADABS program. The structure was solved by direct method and refined by the
full-matrix least-square based on F2 using the SHELXTL-97 program. All
non-hydrogen atoms were refined anisotropically and the hydrogen atoms of organic
ligands were generated geometrically. The squeeze option embedded in platon was
used to remove the contribution of all disordered guest molecules. Crystal data and
structural refinement parameters for 1’ are summarized in Table 1. Selected bond
distances and bond angles are listed in Table S1.
3. Results and discussion
3.1 Structural description
X-ray single crystal structural analysis reveals that compound 1 crystallizes in the
orthorhombic system with Ibca space group and is a 3D anionic framework structure
with [H2N(CH3)2]+ counter ions which are located in the channels to balance the
charge. The asymmetric unit of 1 contains one half Cd(II) ion, one half deprotonated
(TCBPA)3- ligand and the disordered guest molecules (including one half protonated
[NH2(CH3)2]+ cation resulting from the hydrolyzation of N,N-dimethylacetamide
(DMA), and one and a half lattice water molecules). The SQUEEZE routine of the
PLATON software suite was used to remove the highly disordered guest molecules.
Guest molecules were estimated from the results of PLATON-SQUEEZE,
thermogravimetric analysis (TGA), and elemental analysis. As shown in Fig. 1, Cd1
center is hexa-coordinated to six oxygen atoms (O1, O2, O1B, O2B, O3C, O3D) from
three different (TCBPA)3- anions. The coordination geometry of Cd1 center can be
described as a distorted CdO6 octahedron, the O2, O1B, O2B and O3D atoms
5

comprise the equatorial plane, and the O1, O3C atoms occupy the axial positions
[O1-Cd1-O3C = 142.7(2)°]. The Cd-O bond lengths lie in 2.278(4) to 2.345(5) Å,
which are comparable to other cadmium (II) compounds reported [11].
In 1, the six phenyl rings of (TCBPA)3- ligand are non-planar, three outer phenyl
groups are twisted with respect to the adjacent one, the dihedral angles between the
outer and adjacent phenyl rings are respectively 39.41°, 42.07°and 42.07°, which
result from the freely rotating phenyl rings combined by intervening C-C bonds.
Notably, (H3TCBPA) ligands are deprotonated to form (TCBPA)3- anions. The
deprotonated (TCBPA)3- anions adopting μ3-η2:η2:η2 coordination mode connected
Cd(II) ions to form a 2D layer which exist hexagon pores (Figs. 2, S1 and S2). These
2D layers are interpenetrated among each other to form a 2D→3D polycatenated
framework (Figs. 3 and S3). In spite of the interpenetration described above, the
resulting 3D network contains one-dimensional channels with a hexagon pore of
22.282 × 21.775 × 21.775 Å based on Cd-Cd distances (Figs. 4 and S4), which is a
typical nano-channel [12] that has rarely been reported in the molecular cycling
fashion of all coordination polymers. The calculations using PLATON [13] suggest
that the void space of 1 after the removal of disordered guest molecules is 34.2%
(8434.5 Å3 per unit) of the total cell volume, which is higher than that of the reported
FIR-5 [10d]. To further understand the structure of 1, topological analysis by
reducing the multidimensional structure to a simple node-and-linker net was
performed. The topological analysis by TOPOS [14] revealed that the structure is a
uninodal 3-connected 2D + 2D→3D polycatenated net (Fig. 3) with the schläfli
symbol of 63 and the vertex symbol of [6.6.6.]. Lately, L.-B. Yuan et al reported a
Cd-MOF with H3TCBPA ligand [15a], which is different from that of our compound
and some comparisons on structural features are shown in Table 2.
[Fig. 1 is here]
[Fig. 2 is here]
6

[Fig. 3 is here]
[Fig. 4 is here]
3.2 Powder X-ray diffraction and IR spectra
Powder X-ray diffraction experiment was carried out for the pristine sample of
compound 1. The observed powder X-ray diffraction (PXRD) pattern is in good
agreement with the simulated on the basis of the single-crystal X-ray diffraction data
(Fig. S5) and indicated the phase purity of the as-synthesized products. Additionally,
IR spectra data of the organic ligand and compound 1 were measured in the range
400-4000 cm-1 (Fig. S6). Compared with the free ligand, the νC=O (-COOH) of 1687
cm-1 disappears in the IR spectra of the compounds, and the characteristic peaks of
νas(COO-) and νs(COO-) are observed at 1595-1522 cm-1 and 1491-1402 cm-1 for 1.
The fact indicate that the carboxylate groups are coordinated to the Cd2+ cation [15b].
3.3 Luminescent properties and luminescent Detecting
The photoluminescence spectra of 1 and H3TCBPA ligand in the solid state at
room temperature were measured, as shown in Fig. 5. H3TCBPA ligand exhibits
strong emission band at 503 nm upon excitation at 360 nm, which may result from the
π*-π or π*-n electronic transitions. The stronger emission band at 489 nm was
observed for 1 under the same excitation condition at room temperature, which is
similar to that of the reported Cd-MOF [15a]. The calculated Commission
Internationale de l’Eclairage (CIE) chromaticity coordinates is approximately (0.16,
0.33), which agrees with the observed bluish-green light (insert of Fig. 5). Compared
to the emission spectra of free H3TCBPA, the emission of 1 displays blue-shift of 14
nm, which may be assigned to the π*→π or π*–n transition of intra-ligand due to
Cd(II) cation (d10 configuration) is difficult to oxidize or reduce [16]. The
enhancement of luminescence may result from ligand coordinate to Cd(II) centers,
which effectively increases the rigidity of the ligand and reduces the loss of energy by
radiationless decay [17]. The absolute emission quantum yield (Φ) was measured for
7

1 at room temperature upon excitation at 360 nm. The Φ value for 1 is 8.46%, which
is lower than that of the reported Cd-MOF [15a]. Furthermore, the corresponding
life-time for 1 is ca. 1.23 ns (Fig. S7), which is slightly shorter than that of the
reported Cd-MOF [15a].
[Fig. 5 is here]
Notably, the uncoordinated N atoms from H3TCBPA ligands as free Lewis base
may be potential active sites for sensing functions and recognizing metal ions, and
this provides opportunities for 1 to become a candidate as luminescent sensor [18].
Therefore, in order to research luminescent responses of 1 to different metal ions,
compound 1 was ground into powder and suspended in DMF solution containing 10-2
M of different nitrate salts (AgNO3，Al(NO3)3，Ca(NO3)2，NaNO3，KNO3，Zn(NO3)2，
Cd(NO3)2， Pb(NO3)2，Cu(NO3)2，Mn(NO3)2，Co(NO3)2，Ni(NO3)2，Fe(NO3)3) for
48h, and then their luminescent spectra are recorded, as shown Fig. 6a. Interestingly,
the Fe3+ ion shows a significant quenching effect on luminescence intensity of 1; in
contrast, luminescence intensity for 1 in other metal ions system are little enhance or
decreased to a degree, indicating highly selective sensing of 1 for Fe3+ ions (Figs. 6b
and 6c).
[Fig. 6 is here]
To gain more insight into the quenching effect resulted from Fe3+, titration
experiments were carried out via changing concentration of Fe3+ cations in solution.
The titration experiments indicated that luminescent intensities at 489 nm were
gradually weakened by increasing the amount of Fe3+ ions and is almost completely
quenched at Fe3+ concentration of 1.339 mM, which is comparable to that reported by
Wang’s group [19a] (Fig. 7). However, the titration experiments of Na+ and Ca2+
cations in solution showed the opposite spectral changes as compared with Fe3+ (Fig.
S8), which may be attributed to effective intramolecular energy transfer from Cd2+ to
H3TCBPA ligand [19b]. Importantly, luminescence intensity of the suspension
8

follows the first-order exponential decay formula I=1980.19×exp(-CV/0.24)+30.51
(insert of Fig. 7), by which Fe3+ could be detected quantitatively (I=luminescence
intensity of 1-Fe(NO3)3@DMF suspensions, CV=Fe3+ volume concentration, R2=0.99),
displaying the diffusion-controlled quenching process for Fe3+ ions [20, 21]. The
excellent result indicates that compound 1 can be used as the excellent luminescent
sensor to detect Fe3+ ions as highly selective luminescent crystalline materials. To
further examine the sensing sensitivity for Fe3+ ion, 1 was immersed in DMF
solutions with gradually decreased Fe3+ concentration in the range of 10-2-10-6 mol/L.
Noteworthy, luminescence intensity of Fe3+@1 is heavily relied on the concentration
of Fe3+ ion. As shown in Fig. 8, luminescence intensity of 1 is almost completely
quenched at a Fe3+ concentration of 10-3 mM. It is remarkable that compound 1
features a highly sensitive sensing for Fe3+ ions in DMF solution.
[Fig. 7 is here]
[Fig. 8 is here]
3.4 Thermogravimetric analysis
In order to reveal the thermal stability of 1, the thermal gravimetric analysis (TGA)
measurement was performed under nitrogen atmosphere with a heating rate of 10°C
min-1 in the range of 30-900 °C (Fig. S9). TGA cure shows that the first weight loss of
6.06% happened in the temperature range of 100 °C-264 °C, which can be attributed
to the loss of three lattice water molecules (calcd 6.62%). After that, the second
weight loss of 5.50% below 330 °C was assigned to the release of [H2N(CH3)2]+
cation (calcd 5.64%). Then the framework is stable to nearly 351 °C, where a
continuous weight loss of 71.08% was observed from 351 °C to 619 °C, which can be
ascribed to decomposition of (TCBPA)3- ligands (calcd 73.87%). The remaining
residuals are cadmium oxide (obsd. 4.13%, cacd. 4.49%). The result indicates that the
structure can be stable up to 350 °C.
9

4. Conclusion
In conclusion, a new 2D→3D polycatenated framework containing nano channel
structure has been hydrothermally synthesized by the reaction of cadmium chloride
with semi-rigid polycarboxylic acid. The results indicate that compound 1 possesses
excellent fluorescence and high thermostability. Most importantly, 1 shows highly
efficient luminescent sensing for Fe3+ ion. This work provides an easy and facile route
to design and yield new luminescent MOFs as promising sensing materials.
Acknowledgements
We thank the Nature Science Foundation of Shanxi Province (No. 2018JQ2039),
the Technology Plan Project of Shangluo (No. SK2016-44), and the Natural Science
Foundation of Shangluo University (No.16SKY019) for financial support. We also
thank the Fund of National Chemical Experimental Teaching Demonstration Center
of Northwest University.
Appendix A. Supplementary material
CCDC No. 1852197 contains the supplementary crystallographic data for
compound 1. This data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retriev-ing.html,
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.
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12

Table 1. Crystallographic data and structural refinement parameters for 1’a
Compound
1’ after squeeze
C39H24CdNO6
714.99
Empirical formula
Formula weight
Crystal system
Orthorhombic
Ibca
Space group
a/Ǻ
12.0107(8)
18.7677(14)
37.418(3)
90
b/Ǻ
c/Ǻ
α/°
β/°
90
γ/°
90
V/Ǻ3
8434.6(10)
8
Z
ρcal (g•cm-3)
F(000)
1.126
2888
Reflections Collected
S on F2
20085
1.058
Rint
0.0325
R1, wR2 [I>2σ(I)]
R1, wR2 (all data)
0.0389，0.1041
0.0454，0.1086
2
2 2 1/2
aR1 = Σ||Fo| – |Fc||/Σ|Fo|, wR2 = [Σw(Fo – Fc2)2/Σw(Fo ) ]
13

Table 2 Comparison of structural features for 1 and the reported Cd-MOF[15a]
Compounds
Formulas
1
FIR-44
[NH2(CH3)2]n[Cd(TCBPA)]n·3nH2O [Cd3(TPA)2(H2O)(DMA)3]·15H2O·12DMA
Space groups
Coordination
numbers
Ibca
six
P-1
six
Coordination
configurations
Coordination
modes
octahedron
μ3-η2:η2:η2
octahedron
μ5-η1:η1:η1:η1:η2 and μ5-η1:η1:η2:η2:η1
[Cd3(TPA)2(H2O)(DMA)3]
Framework
structures
[Cd(TCBPA)]-
Guest molecules
Dimensionality
H2O and [NH2(CH3)2]+
2D→3D
H2O and DMA
2D
14

Figure captions:
Scheme 1. Molecular structure of H3TCBPA ligand
Fig. 1. The coordination environment of 1
Fig. 2. The view of 2D space filling mode of 1
Fig. 3. Perspective (a) and schematic (b) view of 2D→3D polycatenation of 1
Fig. 4. The space filling mode of an interpenetration 2D→3D net in 1
Fig. 5. The emission spectra of H3TCBPA and 1 in solid state at room temperature.
The inset the CIE chromaticity coordinates of the emission spectrum in 1.
Fig. 6. (a) The photoluminescence spectra; (b) the luminescence intensities of various
1- M(NO3)x@DMF suspensions when excited at 360 nm; (c) Visual change
upon the addition of various M(NO3)x.
Fig. 7. Luminescence spectra of 1 in DMF in the presence of different amounts of
Fe3+ (excited at 360 nm) (inset: the plot of intensity versus Fe3+ concentration).
Fig. 8. Luminescence spectra of 1 in DMF solutions with Fe(NO3)3 at different
concentrations.
15

Scheme 1.
Fig. 1.
Fig. 2.
16

Fig. 3.
(a)
(b)
Fig. 4.
17

Fig. 5.
Fig. 6.
(a)
(b)
(c)
18

Fig. 7.
Fig. 8.
19

20

Graphical Abstract
A novel 3D Cd(II) coordination polymer constructed from a semi-rigid tricarboxylate ligand
shows a 2D→3D polycatenated framework containing nano-channel. Meanwhile, its
photoluminescence was investigated and has been successfully applied in the detection
of Fe3+ ion in DMF solutions.
21