Synthesis, structure and luminescent property of a new 3D porous metal-organic framework with rutile topology

Article abstract of DOI:10.1016/j.molstruc.2007.01.064

A new 3D porous metal-organic framework (MOF), Cd(CTC)(HPDA)·(H₂O) (1) (CTC = cis,cis-1,3,5-cyclohexanetricarboxylate and PDA = 1,3-propanediamine) has been synthesized by using an organic amine, PDA, as a template. X-ray crystallography reveals that two cadmium centers are coordinated by six different carboxylate groups to construct a dinuclear octahedral secondary building unit (SBU), and these octahedral SBUs are further interconnected by the cyclohexane rings of CTC to generate a 3D network with quadrangular channel dimensions of ca. 10 × 17 A?². In this structure, the dinuclear octahedral SBU can be defined as a 6-connected node, and CTC ligating with three SBUs can act as a 3-connected node. So the resulting structure of 1 is a binodal (3,6)-connected net with rutile topology. Additionally, polymer 1 exhibits intense fluorescence at 364 nm with the excitation peak at 240 nm in the solid state at room temperature.

Full text of DOI:10.1016/j.molstruc.2007.01.064

Available online at www.sciencedirect.com
Journal of Molecular Structure 871 (2007) 80–84
www.elsevier.com/locate/molstruc
Synthesis, structure and luminescent property of a new 3D
porous metal–organic framework with rutile topology
*
Zhao Jin, Guang-Shan Zhu , Yong-Cun Zou, Qian-Rong Fang, Ming Xue,
*
Zhong-Yue Li, Shi-Lun Qiu
State Key Laboratory of Inorganic Synthesis & Preparative Chemistry, Jilin University, Changchun 130012, China
Received 11 December 2006; received in revised form 24 January 2007; accepted 29 January 2007
Available online 8 February 2007
Abstract
A new 3D porous metal–organic framework (MOF), Cd(CTC)(HPDA)Æ(H2O) (1) (CTC = cis,cis-1,3,5-cyclohexanetricarboxylate and
PDA = 1,3-propanediamine) has been synthesized by using an organic amine, PDA, as a template. X-ray crystallography reveals that
two cadmium centers are coordinated by six different carboxylate groups to construct a dinuclear octahedral secondary building unit
(SBU), and these octahedral SBUs are further interconnected by the cyclohexane rings of CTC to generate a 3D network with quadran-
2
˚
gular channel dimensions of ca. 10 · 17 A . In this structure, the dinuclear octahedral SBU can be defined as a 6-connected node, and
CTC ligating with three SBUs can act as a 3-connected node. So the resulting structure of 1 is a binodal (3,6)-connected net with rutile
topology. Additionally, polymer 1 exhibits intense fluorescence at 364 nm with the excitation peak at 240 nm in the solid state at room
temperature.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Metal–organic framework; Fluorescence; 1,3-Propanediamine; cis,cis-1,3,5-Cyclohexanetricarboxylate; Rutile topology; Template
1. Introduction
framework is mainly dependent on the solvent media and
the strength of organic base [18]. Additionally, Zaworotko
et al. presented two very interesting Zn–BTC compounds by
self-assembly of triangular, square, and tetrahedral molecu-
lar building blocks (MBBs) in the presence of different
solvents, benzene and chlorobenzene [19]. In previous
studies, our group has successfully prepared some novel
MOFs by utilizing various organic bases, and found that
they play different roles in the formation of various types
of structures: an agent to deprotonate O-donor ligands, a
template to construct new architectures, and a ligand to
coordinate to the metal ion [20–23]. As a sequel, we use an
organic amine, PDA (PDA = 1,3-propanediamine), as a
template, and report here the crystal structure and lumines-
cent property of a new 3D porous MOF with rutile topology,
Cd(CTC)(HPDA)Æ(H2O) (1) (CTC = cis,cis-1,3,5-cyclohex-
anetricarboxylate), constructed from 6-connected dinuclear
octahedral cadmium–carboxylate SBUs (SBU = secondary
building unit) and 3-connected CTC ligands.
Metal–organic frameworks (MOFs) have attracted
much attention because of their enormous varieties of
interesting molecular topologies and wide potential appli-
cations as functional materials [1–14]. However, it is still
a challenging task to explore successful synthetic strategies
for the preparation of the MOFs that have expected appli-
cations and intriguing structures, because these prepara-
tions are affected by many factors, such as solvent
system, template, and reaction temperature [15–17].
Recently, Yaghi et al. successfully synthesized a series of
Zn–BTC (BTC = 1,3,5-benzenetricarboxylate) frameworks
by employing different solvents and organic bases, and
found that the dimensionality of the resulting Zn–BTC
*
Corresponding authors. Tel.: +86 4315168887; fax: +86 4315168331.
E-mail addresses: zhugs@mail.jlu.edu.cn (G.-S. Zhu), sqiu@mail.jlu.
edu.cn (S.-L. Qiu).
0022-2860/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.01.064

J. Zhao et al. / Journal of Molecular Structure 871 (2007) 80–84
81
Table 1
2. Experimental
Crystal data for 1
Empirical formula
Fw
C12H20N2O7Cd
416.70
2.1. Materials and measurements
Cryst syst
Monoclinic
P21/c(14)
9.7538(14)
17.423(3)
10.0230(15)
118.697(2)
1494.1(4)
4
298(2)
0.71073
1.853
1.499
0.0245
All reagents and solvents were commercially available
and used as received without further purification. A Per-
kin-Elmer TGA 7 thermogravimetric analyzer and a Per-
kin-Elmer DTA 1700 differential thermal analyzer were
used to obtain thermogravimetric analysis (TGA) and dif-
ferential thermal analysis (DTA) curves in air with a heat-
ing rate of 10 ꢁC minꢀ1. Powder X-ray diffraction (XRD)
data were collected on a Siemens D5005 diffractometer
Space group (No.)
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
T (K)
˚
k (A)
qcalc (g/cm3)
˚
with CuKa radiation (k = 1.5418 A). Analyses for C, H,
l (mmꢀ1
)
and N were carried out on a Perkin-Elmer 2400 element
analyzer, and the inductively coupled plasma (ICP) analy-
sis on a Perkin-Elmer Optima 3300 DV ICP spectrometer.
The infrared (IR) spectra were recorded (400–4000 cmꢀ1
region) on a Nicolet Impact 410 FTIR spectrometer using
KBr pellets. Fluorescence spectroscopy data were recorded
on a LS55 luminescence spectrometer.
a
R1 ðI > 2rðIÞÞ
b
wR2
0.0670
P
P
P
2
2 1=2
aR1 ¼ kF oj ꢀ jF ck=jF oj, bwR2 ¼ ½ wðF o2 ꢀ F c2Þ = wðF 2oÞ ꢁ
.
Table 2
˚
Selected bond lengths (A) and bond angles (ꢁ) for 1
˚
Bond lengths (A)
2.2. Preparation of Cd(CTC)(HPDA)Æ(H2O) (1)
Cd(1)–O(5)#1
Cd(1)–N(1)
Cd(1)–O(3)#2
Cd(1)–O(4)#2
Cd(1)–O(2)
2.252(2)
2.330(3)
2.384(3)
2.449(3)
2.467(3)
2.515(3)
2.527(3)
A
mixture of CdCl2Æ2.5 H2O (0.01 g, 0.05 mmol),
H3CTC (0.02 g, 0.1 mmol), DMF (DMF = N,N-dimethyl-
formamide, 8.0 mL), EG (EG = ethylene glycol, 3.0 mL)
and H2O (2.0 mL) was stirred in air for 2 h, and then a
DMF solution (0.5 mL) of PDA (0.05 mL) was slowly dif-
fused into the above mixture solution at 65 ꢁC for five days.
The resulting colorless block-shaped single crystals of 1
were collected in 62% yield based on cadmium. The com-
plex was insoluble in common organic solvents such as ace-
tone, methanol, ethanol, dichloromethane, acetonitrile,
chloroform, and DMF. Elemental analysis and ICP analy-
sis for C12H22N2O7Cd (418.73): C 34.47, H 5.11, N 6.72,
Cd 26.88% (calcd: C 34.42, H 5.30, N 6.69, Cd 26.85%).
Cd(1)–O(2)#3
Cd(1)–O(1)
Bond angles (ꢁ)
O(5)#1–Cd(1)–N(1)
O(5)#1–Cd(1)–O(3)#2
N(1)–Cd(1)–O(3)#2
O(5)#1–Cd(1)–O(4)#2
N(1)–Cd(1)–O(4)#2
O(3)#2–Cd(1)–O(4)#2
O(5)#1–Cd(1)–O(2)
N(1)–Cd(1)–O(2)
O(3)#2–Cd(1)–O(2)
O(4)#2–Cd(1)–O(2)
O(5)#1–Cd(1)–O(2)#3
N(1)–Cd(1)–O(2)#3
O(3)#2–Cd(1)–O(2)#3
O(4)#2–Cd(1)–O(2)#3
O(2)–Cd(1)–O(2)#3
O(5)#1–Cd(1)–O(1)
N(1)–Cd(1)–O(1)
107.52(10)
141.07(9)
90.90(11)
93.87(9)
83.39(10)
53.60(9)
126.18(9)
101.20(10)
80.91(9)
134.46(8)
79.75(9)
172.21(9)
84.79(10)
99.15(9)
71.74(9)
87.83(9)
ꢀ
FT-IR(KBr): m ¼ 3419ðsÞ, 2937 (w), 2362 (w), 1653 (w),
1558 (s), 1516 (s), 1406 (s), 1352 (m), 1215 (w), 1066 (m),
981 (w), 919 (m), 773 (w), 719 (w), 694 (w), 586 (w), 538
(w) cmꢀ1
.
2.3. X-ray crystallography
82.87(11)
129.17(9)
166.02(10)
51.60(8)
A colorless block-shaped crystal of 1 was selected for
X-ray structural analysis on a Bruker SMART CCD
diffractometer at 298 K. The complex crystallized in the
space group P21/c, monoclinic, dimensions 0.32 · 0.30 ·
0.18 mm3. A total of 7601 reflections were collected in the
range of 2.34 < h < 25.00, of which 2614 were unique.
The final R1(wR2) value 0.0245 (0.0670) for 2283 indepen-
dent reflections [I > 2r(I)]. The structure was solved and
refined by full-matrix least-squares on F2 values (SHEL-
XL-97) [24]. Non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were fixed at calculated positions.
The crystallographic data and selected bond lengths and
angles for polymer 1 are listed in Tables 1 and 2,
respectively.
O(3)#2–Cd(1)–O(1)
O(4)#2–Cd(1)–O(1)
O(2)–Cd(1)–O(1)
O(2)#3–Cd(1)–O(1)
94.81(9)
Symmetry transformations used to generate equivalent atoms: #1 x ꢀ 1, y,
z; #2 ꢀx + 1, y ꢀ 1/2, ꢀz + 1/2; #3 ꢀx + 1, ꢀy, ꢀz + 1.
3. Results and discussion
3.1. Synthesis
Polymer 1 was synthesized under mild conditions in the
presence of an organic amine, PDA. In a typical synthesis,

82
J. Zhao et al. / Journal of Molecular Structure 871 (2007) 80–84
a mixture of CdCl2Æ2.5H2O with H3CTC was prepared with
a mole ratio of 2:1 in DMF/EG/H2O, then a DMF solu-
tion of PDA was allowed to diffuse into the above mixture
at 65 ꢁC to deprotonate the acid and initiate the copoly-
merization process. After keeping the reaction solution
for five days, colorless block shaped crystals of 1 were col-
lected in 62% yield based on cadmium. It is notable that
PDA plays a template role in this structure, because the
control reaction without using PDA or using another base
(such as triethylamine (TEA) or ethylenediamine (EDA))
instead will not result in compound 1 under the same con-
ditions, and only some very little unknown crystals or
white powder which should be cadmium hydroxide have
been obtained. Additionally, the experiments without EG
will also result in white powder of cadmium hydroxide.
3.2. Description of the structure
X-ray crystallography reveals that 1 crystallizes in the
monoclinic system, space group P21/c (No. 14). The basic
building unit of 1 contains two cadmium centers, six
CTC ligands, and two coordinated HPDA. As shown in
Fig. 1, each Cd(II) center is coordinated by six oxygen
atoms from four different carboxylate groups of CTC
and one nitrogen atom from terminal HPDA molecule,
and each CTC ligand coordinates to four cadmium ions
through its three carboxylate groups in the unidentate, che-
lating bidentate and chelating/bridging bidentate coordina-
tion fashions, respectively. In this structure, the distances
˚
˚
of Cd–O (2.252–2.527 A) are similar to normal Cd–OCO
distances (2.251–2.879 A) [25], and the bond angles of
O(N)–Cd–O(N) are from 51.60(8)ꢁ to 172.21(9)ꢁ.
As shown in Fig. 2, two cadmium centers are coordi-
nated by six different carboxylate groups to construct a
dinuclear octahedral SBU, and these octahedral SBUs are
further interconnected by the cyclohexane rings of CTC
Fig. 2. (a) Simplified views of 6- and 3-connected building blocks in 1. The
color code: Cd, green; N, blue; O, red; C, gray. (b) Perspective view of the
framework along the [100] direction. (c) The (3,6)-connected net of 1 with
rutile topology (TiO2). Black lines represent the unit cell of rutile topology.
(For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
to generate a 3D network with quadrangular channel
2
˚
dimensions of ca. 10 · 17 A (measured between opposite
atoms) viewed along the [100] direction. In this structure,
the vacancies of each asymmetric unit are filled with one
coordinated HPDA molecule and one guest H2O which
connects to the framework via hydrogen bonds (O7ꢂ ꢂ ꢂO6
˚
˚
˚
2.657 A, O7ꢂ ꢂ ꢂN2 2.796 A and O7ꢂ ꢂ ꢂO4 3.004 A).
A better insight into the nature of 1 can be achieved by
the application of topological approach [26–29]. As dis-
cussed above, the dinuclear octahedral SBU is defined as
a 6-connected node. Similarly, CTC ligating with three
SBUs can act as a 3-connected node. According to the sim-
plification principle, the resulting structure of 1 is a binodal
Fig. 1. ORTEP drawing (at a 30% probability level) of the coordination
environment of cadmium ions in 1.

J. Zhao et al. / Journal of Molecular Structure 871 (2007) 80–84
83
reflections cannot be observed in the XRD pattern, imply-
ing the mostly decomposition of the structure.
(570 nm)
(364 nm)
3.5. Photoluminescent property
The solid-state excitation–emission spectrum of 1 has
been studied at room temperature (Fig. 3). The strongest
emission peak for the free H3CTC is at 570 nm with the
excitation peak at 396 nm. It is attributed to the p fi n
*
transitions [35]. Compared with the free H3CTC, polymer
1 exhibits a blue-shift emission peak at 364 nm with the
excitation peak at 240 nm. The emission peak of 1 can be
assigned to the emission of ligand-to-metal-charge-transfer
(LMCT) [36]. The strong fluorescent emission of 1 makes it
a potentially useful photoactive material.
300
350
400
450
500
550
600
650
Wavelength (nm)
4. Conclusion
Fig. 3. Fluorescence emission spectra of the free CTC ligand (black line)
and polymer 1 (blue line) in the solid state at room temperature. (For
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
A new 3D porous MOF with rutile topology and
quadrangular channel dimensions of ca. 10 · 17 A ,
2
˚
Cd(CTC)(HPDA)Æ(H2O) (1), has been synthesized by uti-
lizing an organic amine, PDA, as a template. Furthermore,
the polymer 1 possesses an intense luminescent property at
room temperature. We believe that those polymers with
potential properties and charming topologies will be fur-
ther synthesized by using different organic amines as
templates.
(3,6)-connected net, and its Schla¨fli symbol is
(4Æ62)2(42Æ610Æ83) (the first symbol for 3-connected CTC
and the second one for 6-connected dinuclear octahedral
SBU), which is a deformed version of the idealized rutile
structure (Fig. 2c) [30,31].
3.3. IR spectrum
Acknowledgements
The IR spectrum of 1 shows the presence of vibrational
bands at 1585–1519 cmꢀ1, which are characteristic of the
asymmetric stretching of the carboxylic groups of CTC.
The absorptions at 1406 cmꢀ1 are due to the symmetric
vibrations of the carboxylic groups of CTC. The lack of
the characteristic bands of the carboxylic groups of any
protonated forms (1730–1680 cmꢀ1) [32–34] indicates the
complete deprotonation of H3CTC after the reaction.
The broad band at 3419 cmꢀ1 belongs to the typical band
of the guest H2O molecules, and the band at 1066 cmꢀ1
is attributed to the vibration of tC–N of PDA.
We are grateful for the financial support of the State
Basic Research Project (2006CB806100), Outstanding
Young Scientist Foundation of NSFC (20625102), NSFC
(Grant Nos. 20571030, 20531030, and 20371020) and
Graduate Innovation Lab of Jilin University.
Appendix A. Supplementary data
Crystallographic data for the structure reported in this
paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary Publication No.
CCDC-615742. Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road, Cam-
bridge CB21EZ, UK (fax: +44 1223 336 033; e-mail: depos-
it@ccdc.cam.ac.uk). Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.molstruc.2007.01.064.
3.4. Thermogravimetric analysis
The differential thermal analysis (DTA) for 1 has two
endothermic peaks at 131.7 and 419.4 ꢁC, correspondingly,
the thermogravimetric analysis (TGA) curve shows two
stages ranging from 30 to 250 ꢁC, and from 350 to
476 ꢁC. The weight loss of 22.06% between 30 and 250 ꢁC
corresponds to the loss of one guest H2O and one coordi-
nated HPDA of each asymmetric unit (calculated
22.25%). The polymer is stable between 250 and 350 ꢁC,
and the decomposition of 1 began at about 370 ꢁC. The res-
idue was CdO (experimental: 30.67% and calculated:
30.58%). To further study its stability, the polymer is cal-
cined at 100 ꢁC for 1 h. However, the intensity of diffrac-
tion peaks of the polymer become very weak and many
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