Reactant ratio-modulated entangled Cd(ii) coordination polymers based on rigid tripodal imidazole ligand and tetrabromoterephthalic acid: Interpenetration, interdigitation and self-penetration

Article abstract of DOI:10.1039/c3ce40273h

By adjusting the molar ratio of the reactant metal salt and ligands, three new entangled coordination polymers, [Cd(tib)(tbta)(H₂O)]_n (1) and [Cd(Htib)(tbta)·Htbta·2CH₃OH]_n (2) and [Cd₂(tib)₂(tbta)₂(H₂O) ·10H₂O]_n (3) (tib = 1,3,5-tris(1-imidazolyl)benzene and H₂tbta = tetrabromoterephthalic acid), have been prepared and structurally characterized by X-ray diffraction analyses. Complex 1 is a 2-fold interpenetrated three-dimensional (3D) 8-connected uninodal net with rare hex topology. Complex 2 presents a 2D 6³-hcb network, which is interdigitated with each other to form the 3D supramolecular framework stabilized hydrogen bonds and halogen bonds. Interestingly, an unprecedented hydrogen-bonded [(Htbta)₂(CH₃OH)₄] cluster was unmasked in the void of 2. Complex 3 is a complicated 3D self-penetrated framework with a point symbol of {4·6·8}{4·6 ⁵·8⁴}{6⁶}, which can be seen as a pair of 2-fold interpenetrated networks by breaking bidentate-bridging tib ligand. The comparative study revealed that 1-3 are particularly sensitive to the metal-ligand ratio in this system. The thermal stabilities and photoluminescence behaviors of 1 and 2 were also discussed. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ce40273h

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PAPER
Reactant ratio-modulated entangled Cd(II) coordination
polymers based on rigid tripodal imidazole ligand and
tetrabromoterephthalic acid: interpenetration,
interdigitation and self-penetration3
Cite this: CrystEngComm, 2013, 15,
5552
Lei Wang,* Zhi-Hao Yan, Zhenyu Xiao, Dong Guo, Wenqiang Wang and Yu Yang
By adjusting the molar ratio of the reactant metal salt and ligands, three new entangled coordination
polymers,
[Cd(tib)(tbta)(H2O)]n
(1)
and
[Cd(Htib)(tbta)?Htbta?2CH3OH]n
(2)
and
[Cd2(tib)2(tbta)2(H2O)?10H2O]n (3) (tib = 1,3,5-tris(1-imidazolyl)benzene and H2tbta = tetrabromoter-
ephthalic acid), have been prepared and structurally characterized by X-ray diffraction analyses. Complex 1
is a 2-fold interpenetrated three-dimensional (3D) 8-connected uninodal net with rare hex topology.
Complex 2 presents a 2D 63-hcb network, which is interdigitated with each other to form the 3D
supramolecular framework stabilized hydrogen bonds and halogen bonds. Interestingly, an unprece-
dented hydrogen-bonded [(Htbta)2(CH3OH)4] cluster was unmasked in the void of 2. Complex 3 is a
complicated 3D self-penetrated framework with a point symbol of {4?6?8}{4?65?84}{66}, which can be seen
as a pair of 2-fold interpenetrated networks by breaking bidentate-bridging tib ligand. The comparative
study revealed that 1–3 are particularly sensitive to the metal–ligand ratio in this system. The thermal
stabilities and photoluminescence behaviors of 1 and 2 were also discussed.
Received 10th February 2013,
Accepted 6th May 2013
DOI: 10.1039/c3ce40273h
www.rsc.org/crystengcomm
same time, so many parameters also create obstacles to the
exploration of the suitable reaction conditions and prediction
of resulting structures.
Introduction
Recently, remarkable progress has been witnessed in the study
of polymeric coordination networks, or named coordination
polymers (CPs), not only due to their aesthetic topology and
intriguing structures but also owing to their interesting
physical and chemical properties, such as photoluminescence,
magnetism, ferroelectricity, gas storage, ion exchange, cata-
lysis, etc.1 It is well known that the construction of CPs mainly
depends on the nature of organic spacer and metal ion. In
order to obtain novel structures and expected functionality,
many crystal engineers have studied the design and synthesis
of novel organic ligands, such as multidentated pyridyl,
imidazolyl and various carboxylate ligands.2 However, other
factors, such as solvent,3 temperature,4 counterion5 and the
molar ratio of reactants6 also can induce the formation of
diverse CPs, which are rarely subjected to systematic investiga-
tion, although some sporadic reports have appeared. These
variable synthetic parameters give us both opportunities and
challenges, that is, more and more novel structures may be
obtained through changing the synthetic conditions, at the
Although many investigations have been devoted to the
above-mentioned fields, the influence of molar ratios on the
self-assembly process has been subjected to rare attention.7
Different reactant ratios may perturb the delicate coordination
equilibrium preventing the crystal formation or resulting in a
different CPs with respect to the original or expected
structure.8 An enhanced understanding about any potential
correlations between reactant ratio and resulting structures of
CPs is highly desirable because it may be useful in the
synthetic design and the functionalization of new crystalline
materials.
On the other hand, both 1,3,5-tris(1-imidazolyl)benzene
(tib)9 and tetrabromoterephthalate (tbta)10 are rigid organic
building blocks with triangular and linear geometries,
respectively, which have been proved as versatile linkers to
connect metal ions into higher dimensional structures
through various coordination modes as well as secondary
interactions such as hydrogen bond and halogen bond.
Although
a search in the CSD (Cambridge Structure
College of Chemistry and Molecular Engineering, Qingdao University of Science and
Technology, Qingdao 266042, P. R. China. E-mail: inorchemwl@126.com; Fax: +86
532-840-22681
Database) survey with the help of ConQuest version 1.311
shows 48 and 15 hits based on the tib and tbta ligands,
respectively, the study of a combination of them in one CP has
not been done yet. In order to further study mixed two kinds of
Electronic supplementary information (ESI) available: XRD, IR. CCDC 908378–
3
908380. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3ce40273h
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heated at 120 uC for 4300 min. After the mixture was cooled to
room temperature at a rate of 9 uC h21. The resulting pale
yellow block crystals were collected in 89% yield. Elemental
analysis: anal. calc. for C23H14Br4CdN6O5: C 31.16, H 1.59, N
9.48%. Found: C 31.55, H 1.02, N 9.75%. IR (KBr): v(cm21) =
3433 (s), 1613 (s), 1504 (m), 1404 (m), 1331 (m), 1240 (w), 1113
(w), 1072 (w), 1013 (w), 649 (w), 562 (w).
[Cd(Htib)(tbtpa)?Htbtpa?2CH3OH]n (2). Synthesis of 2 was
similar to that of 1, but the ratio of Cd(NO3)2?4H2O/tib/H2tbtpa
is 1 : 1 : 2. Pale-yellow crystals of 2 were obtained in 92% yield.
Elemental analysis: anal. calc. for C33H22Br8CdN6O10: C 28.03,
H 1.57, N 5.94%. Found: C 28.79, H. 1.21, N 6.28%. Selected IR
peaks (cm21): 3441 (s), 1615 (s), 1585 (s), 1506 (m), 1382 (s),
1334 (w), 1243 (w), 1073 (w), 1012 (w), 819 (w), 562 (w).
[Cd2(tib)2(tbta)2(H2O)?10H2O]n (3). Synthesis of
3 was
similar to that of 1, but the ratio of Cd(NO3)2?4H2O/tib/
H2tbtpa is 1 : 1 : 3. Few yellow crystals of 3 were picked up
from a large quantity of unidentified white precipitates with a
very low yield (below 5%). Due to the extremely low yield, only
structure determination was carried out for this complex.
Scheme 1 The three reactant ratio-modulated entangled complexes.
X-ray crystallography
ligands based CPs and investigate the influence of reactant
molar ratio on the coordination connectivity and related
network, we designed the reactions of them with Cd(II) salt in
congener but three different reactant ratios. The fine distinc-
tions of ratio led to three entirely different structures. In this
paper, we report three entangled mixed-ligand CPs,
[Cd(tib)(tbta)(H2O)]n (1), [Cd(Htib)(tbta)?Htbta?2CH3OH]n (2)
and [Cd2(tib)2(tbta)2(H2O)?10H2O]n (3) (tib = 1,3,5-tris(1-imida-
zolyl)benzene and H2tbta = tetrabromoterephthalic acid),
which range from 2-fold interpenetrated hex network to 3D
self-penetrated framework (Scheme 1).
Single crystals of the complexes 1–3 with appropriate dimen-
sions were chosen under an optical microscope and quickly
coated with high vacuum grease (Dow Corning Corporation)
before being mounted on a glass fiber for data collection. Data
were collected on a Bruker Apex II CCD diffractometer with
graphite-monochromated Mo Ka radiation source (l
=
0.71073 Å). The crystal was positioned at 60 mm from the
CCD. A preliminary orientation matrix and unit cell para-
meters were determined from 3 runs of 12 frames each, each
frame corresponds to a 0.5u scan in 5 s, followed by spot
integration and least-squares refinement. For 1–3, data were
measured using v scans of 0.5u per frame for 10 s until a
complete hemisphere had been collected. Cell parameters
were retrieved using SMART software and refined with SAINT
on all observed reflections.12 Data reduction was performed
with the SAINT software and corrected for Lorentz and
polarization effects. Absorption corrections were applied with
the program SADABS.12 In all cases, the highest possible space
group was chosen. All structures were solved by direct
methods using SHELXS-9713 and refined on F2 by full-matrix
least-squares procedures with SHELXL-97.14 Atoms were
located from iterative examination of difference F-maps
following least squares refinements of the earlier models.
Hydrogen atoms were placed in calculated positions and
included as riding atoms with isotropic displacement para-
meters 1.2–1.5 times Ueq of the attached C atoms. Part of tbta
ligand in complex 3 is split over two sites with a total
occupancy of 1. There are also some solvent accessible void
volumes in the crystals of 3 which are occupied by highly
disordered water molecules. No satisfactory disorder model
could be achieved, and therefore the SQUEEZE program
implemented in PLATON15 was used to remove these electron
densities. All structures were examined using the Addsym
subroutine of PLATON to assure that no additional symmetry
could be applied to the models. Pertinent crystallographic data
collection and refinement parameters are collated in Table 1.
Selected bond lengths and angles are collated in Table 2.
Experimental section
General materials and methods
Chemicals and solvents used in the syntheses were of
analytical grade and used without further purification. IR
spectra were measured on a Nicolet 330 FTIR Spectrometer at
the range of 4000–400 cm21. Elemental analyses were carried
out on a CE instruments EA 1110 elemental analyzer.
Photoluminescence spectra were measured on a Hitachi
F-7000 Fluorescence Spectrophotometer (slit width: 5 nm;
sensitivity: high). X-ray powder diffractions were measured on
a Panalytical X-Pert pro diffractometer with Cu Ka radiation.
Thermogravimetric analyses were performed on a NETZSCH
TG 209 F1 Iris1 Thermogravimetric Analyser from 30 to 800
uC at a heating rate 10 uC min21 under the N2 atmosphere (20
mL min21).
Syntheses of the complexes 1–3
[Cd(tib)(tbtpa)(H2O)]n (1). A mixture of Cd(NO3)2?4H2O
(123.4 mg, 0.4 mmol), tib (110.4 mg, 0.4 mmol) and H2tbtpa
(192.7 mg, 0.4 mmol), KOH (1.2 mg, 0.02 mmol) were
dissolved in 10 mL methanol–H2O (v:v = 1 : 1) in a 25 mL
Teflon-lined stainless steel vessel. The mixture was sealed and
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Table 1 Crystal data for 1 and 2
1
2
3
Empirical formula
Formula weight
C23H14Br4CdN6O5
886.44
C33H22Br8CdN6O10
1414.25
C46H46Br8Cd2N12O19
1934.98
Temperature/K
Crystal system
Space group
298(2)
Triclinic
¯
P1
298(2)
Triclinic
¯
P1
298(2)
Triclinic
¯
P1
a/Å
b/Å
c/Å
10.7437(14)
11.9023(15)
12.0615(16)
90.789(2)
108.826(2)
110.710(2)
1351.2(3)
12.5908(13)
12.7757(14)
13.7370(15)
86.559(2)
80.567(2)
72.878(2)
2083.0(4)
13.5703(10)
14.4080(11)
19.4879(15)
93.9370(10)
109.8560(10)
93.5050(10)
3560.8(5)
a/u
b/u
c/u
Volume/Å3
Z
2
2
2
rcalc/mg mm23
2.179
6.769
2.255
8.259
1.637
5.136
m/mm21
F(000)
844.0
6503
4686
0.0196
1340.0
10 148
7161
0.0280
1668.0
17 054
12 129
0.0380
Reflections collected
Independent reflections
Rint
Data/parameters
Goodness-of-fit on F2
R indexes [I . 2s(I)]
R indexes [all data]
4686/353
1.003
R1 = 0.0332, wR2 = 0.0697
R1 = 0.0483, wR2 = 0.0756
7161/528
0.995
R1 = 0.0382, wR2 = 0.0792
R1 = 0.0674, wR2 = 0.0889
12 129/747
0.959
R1 = 0.0597, wR2 = 0.1568
R1 = 0.0920, wR2 = 0.1715
molecule. As depicted in Fig. 1a, the Cd1 center is six-
coordinated by three atoms from three distinct tib
Result and discussion
N
Synthesis and general characterization
molecules (Cd–N: 2.274(4)–2.359(4) Å), two carboxyl oxygen
atoms from two tbta ligands (Cd–O: 2.296(3) and 2.313(3) Å)
and one coordinated water (Cd–Owater: 2.402(3) Å) to give a
slightly distorted CdN3O3 octahedral geometry. Both Cd–N and
Cd–O bond lengths are well-matched to those observed in
similar complexes.16 Each tib ligand coordinates to three Cd(II)
atoms with a non-planar geometry. The three imidazole rings
of tib ligand in 1 are inclined to the central benzene ring at
dihedral angles of 39.4u, 63.1u and 23.3u, respectively. Due to
the steric hindrance of Br atoms, two carboxyl groups of tbta
ligand are approximately perpendicular to the central phenyl
ring with two small dihedral angles 85.6u and 81.5u,
respectively.
The tridentate tib and bidentate tbta link the Cd centers to
form a regular 3D porous framework as illustrated in Fig. 1c. It
is noteworthy that there are open channels with dimension of
ca. 11.9 6 10.7 Å in the single 3D net of 1 along the c direction,
which allows another identical net to penetrate, namely, the
entire structure of 2 is a 2-fold interpenetrated 3D framework
(Fig. 1e and 1f). A better insight into the nature of this 3D
framework can be obtained using the program package
TOPOS.17 Each Cd center connects other eight neighboring
Cd centers through three tib and two tbta ligands; hence, each
Cd can be regarded as a 8-connected node (Fig. 1b). According
to this simplification principle, this 3D network could be
simplified to a 8-connected uninodal network with hex
Complexes 1–3 were synthesized by using a mixture of
Cd(NO3)2?4H2O, tib and H2tbta but with different reactant
ratios. The Cd/tib/H2tbta ratios are 1 : 1 : 1, 1 : 1 : 2 and
1 : 1 : 3 for 1–3, respectively. Other molar ratios of Cd/tib/
H2tbta were also attempted and did not give satisfactory single
crystals or give the single crystals in such a poor yield that they
were hard to isolate. We have changed solvents and ratios to
improve the yield of 3, unfortunately, no improvement could
be obtained. The single crystals of 1–3 were grown in Teflon-
lined stainless steel vessel with programmed warming and
cooling process.
Powder X-ray diffraction (PXRD) has been used to check the
phase purity of the bulk samples in the solid state. For
complexes 1 and 2, the measured PXRD patterns closely match
the simulated patterns generated from the results of single-
crystal diffraction data (Fig. S1, ESI ), indicative of pure
products. In the IR spectra (Fig. S2, ESI ) of complexes 1 and 2,
3
3
the broad peaks at ca. 3400 cm21 indicate the presence of
water molecules. The IR spectra also show characteristic
absorption bands mainly attributed to the asymmetric (nas: ca.
1600 cm21) and symmetric (ns: ca. 1385 cm21) stretching
vibrations of the carboxylic groups. No band in the region
1690–1730 cm21, indicates complete deprotonation of the
carboxylic groups,20 which is consistent with the result of the
X-ray diffraction analysis.
¨
topology (Fig. 1d) and the short Schlafli symbol for this net
Structure descriptions
is {36?418?53?6}. An analysis of the topology of the interpene-
tration according to a recent classification18 reveals that 1
belongs to class IIa, that is, two interpenetrated nets are
generated only by symmetry element (here is inversion center)
from the single net. As we know, the 8-connected networks are
still in their infancy because the construction of such networks
[Cd(tib)(tbta)(H2O)]n (1). X-ray single-crystal diffraction
analysis reveals that 1 is a unique 2-fold interpenetrated hex
network. It crystallizes in the triclinic crystal system with space
¯
group of P1. The asymmetric unit consists of one Cd(II) ion,
one tib ligand, one tbta ligand and one coordinated water
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Table 2 Selected bond lengths (Å) and angles (u) for 1–3
Complex 1
Cd1–N4i
2.274(4)
Cd1–N6iii
2.326(4)
2.359(4)
Cd1–O3ii
2.296(3)
Cd1–N1
Cd1–O2
2.313(3)
Cd1–O1W
2.402(3)
N4i–Cd1–O3ii
N4i–Cd1–O2
O3ii–Cd1–O2
N4i–Cd1–N6iii
O3ii–Cd1–N6iii
O2–Cd1–N6iii
N4i–Cd1–N1
O3ii–Cd1–N1
91.52(13)
90.15(13)
177.22(12)
167.22(13)
86.85(12)
91.03(13)
101.82(14)
103.73(12)
O2–Cd1–N1
N6iii–Cd1–N1
N4i–Cd1–O1W
O3ii–Cd1–O1W
O2–Cd1–O1W
N6iii–Cd1–O1W
N1–Cd1–O1W
78.09(12)
90.87(13)
84.82(14)
91.06(11)
86.88(11)
82.55(13)
163.50(12)
Symmetry codes: (i) x, y, z 2 1; (ii) x, y + 1, z; (iii) x + 1, y, z.
Complex 2
Cd1–O3
2.153(4)
2.198(5)
111.28(17)
108.50(18)
107.23(19)
Cd1–N1
Cd1–O1
O3–Cd1–O1
N5i–Cd1–O1
N1–Cd1–O1
2.220(5)
2.239(4)
125.60(16)
100.52(18)
102.23(17)
Cd1–N5i
O3–Cd1–N5i
O3–Cd1–N1
N5i–Cd1–N1
Symmetry code: (i) 2x + 1, 2y, 2z + 2.
Complex 3
Cd1–N1
2.314(6)
2.328(6)
2.365(5)
2.403(7)
2.407(8)
2.531(7)
173.0(2)
88.5(2)
87.1(2)
90.2(2)
92.0(2)
159.7(2)
101.7(3)
85.2(2)
116.4(3)
83.7(3)
85.9(3)
88.1(2)
82.9(2)
Cd2–N12
Cd2–O7ii
Cd2–O5
2.292(7)
2.306(6)
2.318(6)
2.320(6)
2.383(13)
Cd1–N10i
Cd1–O1
Cd1–N7
Cd1–O3
Cd1–O1W
Cd2–N6iii
Cd2–O8Biv
N1–Cd1–N10i
N1–Cd1–O1
N10i–Cd1–O1
N1–Cd1–N7
N10i–Cd1–N7
O1–Cd1–N7
N1–Cd1–O3
N10i–Cd1–O3
O1–Cd1–O3
N7–Cd1–O3
N1–Cd1–O1W
N10i–Cd1–O1W
O1–Cd1–O1W
N7–Cd1–O1W
O3–Cd1–O1W
N12–Cd2–O7ii
N12–Cd2–O5
76.8(2)
159.1(3)
95.6(3)
174.3(2)
87.2(2)
92.2(2)
106.2(2)
91.7(2)
84.8(3)
92.9(3)
90.1(3)
160.9(3)
O7ii–Cd2–O5
Fig. 1 (a) The coordination environment of Cd(II) ion in 1. (b) The linking of the
8-connected Cd(II) center in 1. (c) Ball-and-stick presentation of single 3D
framework. (d) Schematic representation of the 8-connected single 3D network
with hex topology. (e) 2-Fold interpenetrated 3D framework. (f) 2-Fold
interpenetrated hex network. (Symmetry codes: (i) x, y, z 2 1; (ii) x, y + 1, z; (iii) x
+ 1, y, z.)
N12–Cd2–N6iii
O7ii–Cd2–N6iii
O5–Cd2–N6iii
N12–Cd2–O8Biv
O7ii–Cd2–O8Biv
O5–Cd2–O8Biv
N6iii–Cd2–O8Biv
Symmetry codes: (i) 2x + 2, 2y + 1, 2z + 1; (ii) 2x + 1, 2y + 1, 2z +
1; (iii) 2x + 1, 2y + 2, 2z + 1; (iv) x, y + 1, z.
lattice methanol molecules. As shown in Fig. 2a, the Cd1 is
located in a rare tetrahedral geometry, completed by two N
atoms belonging to two different Htib ligands and two O
atoms of two tbta ligands. The average Cd–O and Cd–N
distances are 2.196(4) and 2.209(5) Å. The bond angles around
Cd1 range from 100.52(18) to 125.60(16)u. The distortion of the
tetrahedron can be indicated by the calculated value of the t4
parameter introduced by Houser25 to describe the geometry of
a four-coordinate metal system, which is 0.87 (for ideal
tetrahedron t4 = 1). As we know, the most encountered
coordination geometry for Cd(II) is six-coordinated octahe-
dron, while the four-coordinated tetrahedral geometry is very
rare.26 The search in the CSD survey shows 4992 hits for six-
coordinated Cd(II) complexes, but only 1256 hits (25%) for
four-coordinated Cd(II) complexes. It is noteworthy that the
Htib ligand coordinates with two, rather than three like in 1,
Cd(II) atoms using two of its three imidazole groups, and the
third one with N4 was protonated and did not participate in
the coordination, which has been observed previously.27 The
average dihedral angle formed between central phenyl ring
and three terminal imidazole groups is 29.1u.
is rigorously hampered both by the number of available
coordination sites and by the sterically demanding nature of
the rigid ligands.19 For 8-connected networks, the 8-connected
nodes often are highly coordinated rare earth ions20 or
polynuclear metal building blocks,21 however, using single
metal center as node to construct the 8-connected network is
still rare. Moreover, the most commonly encountered 8-con-
nected network is bcu-type (CsCl) net,22 but the hex network,
especially the interpenetrated example is relatively scarce.23
Recently, Ma and Batten reported a pair of interesting
supramolecular isomers, and one of them is the first 3-fold
interpenetrated hex network based on dinuclear Co(II) build-
ing blocks.24
[Cd(Htib)(tbta)?Htbta?2CH3OH]n (2). Structural analysis of
complex 2 indicates an interesting 2D A 3D interdigitated
network based on 2D 63-hcb net. Complex 2 also crystallizes in
¯
the triclinic P1 space group. The asymmetric unit of 2 is
composed of one crystallographically independent Cd(II) ion,
one Htib ligand, two half coordinated tbta ligands lying about
inversion centres, one whole guest Htbta molecule and two
The bidentate Htib and tbta ligands link the tetrahedral
Cd(II) centers to form an infinite 2D network with typical 63-
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Fig. 2 (a) The coordination environment of Cd(II) ion in 2. (b) Ball-and-stick
presentation of the 2D 63-hcb net. (c) Space-filling view of the 2D A 3D
interdigitated motif of 2. (Symmetry codes: (i) x, y, z 2 1; (ii) x, y + 1, z; (iii) x + 1,
y, z.)
hcb net which contains large windows with the pore size of
22.2 6 24.5 Å (Fig. 2b). The phenyl and one of three imidazole
groups are out of the plane defined by the 63-hcb net, causing
the large aperture, which allowed the protuberant groups to
embed, forming the resulting 2D A 3D interdigitated network
(Fig. 2c). There are still large voids in spite of interdigitation.
Fig. 4 (a) The coordination environment of Cd(II) ion in 3. (b) View of 3D
framework with 3-nodal 3,4,5-connected topology (purple: 5-connected Cd
node; green: 4-connected Cd node; blue: 3-connected tib node). (c) The 2-fold
interpenetrated 3,3,4-connected network by breaking bidentate-bridging tib
ligand. (d) View of the details of self-interpenetration by the bidentate tib ligand
highlighted by yellow. (e) Formation of the interpenetration by omitting the
bidentate tib ligand. (Symmetry codes: (i) 2x + 2, 2y + 1, 2z + 1; (ii) 2x + 1, 2y +
1, 2z + 1; (iii) 2x + 1, 2y + 2, 2z + 1; (iv) x, y + 1, z.)
Interestingly,
an
unprecedented
hydrogen-bonded
[(Htbta)2(CH3OH)4] cluster (Fig. 3a) was unmasked in the
…
remaining voids and consolidated through type-I C–O Br
halogen bond28 with Br2 O7, Br6 O1 and Br7 O4 contacts
of 2.980(5), 2.864(5) and 2.967(5) Å, respectively, which are ca.
12% shorter than the sum of Br and O van der Waals radii
(3.37 Å) (Fig. 3b).29
…
…
…
[Cd2(tib)2(tbta)2(H2O)?10H2O]n (3). Complex 3 is an intricate
3D self-penetrated network. As shown in Fig. 4a, the
asymmetric unit of 3 contains two crystallographically unique
Cd(II) ion, two tib ligands, one whole tbta ligand and two half
tbta ligands lying about inversion centres, one coordinated
water molecules and lattice water molecules in a severely
disordered fashion. Two Cd(II) centers are in different
coordination geometries. The Cd1 locates in a distorted
octahedral geometry, completed by three imidazole N atoms,
two carboxyl O atoms and one water molecule. The Cd2 is
coordinated by two tib and three tbta ligands, giving a
distorted square-pyramidal geometry. The distortion of the
CdO5 square-pyramid is indicated by the calculated value of
the t5 factor,30 which is 0.22 for Cd2 (for ideal square-
pyramidal geometry, t5 = 0). Both Cd–N and Cd–O bond
lengths are in the normal ranges. The imidazole ring planes
deviate from the benzene ring planes with dihedral angles
ranging from 9.1 to 36.8u. Two crystallographically unique tib
Fig. 3 (a) The hydrogen-bonded [(Htbta)2(CH3OH)4] cluster in 2. (b) The
halogen bonding between 2D network and [(Htbta)2(CH3OH)4] cluster.
(Halogen bond and hydrogen bond are highlighted by red and green dashed
lines.)
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ligands show bidentate and tridentate coordination modes,
respectively.
different infinite motifs ranging from 2-fold interpenetrated
hex network, 2D A 3D interdigitated network, to 3D self-
penetrated framework were observed. Therefore, the diversity
of coordination modes of tib plays a central role in the final
structures of 1–3, when changing metal–ligand ratios.
The Cd(II) ions are bridged by tib and tatb ligands to form a
complicated 3D framework. The most striking structural
feature of 3 is a self-penetrating net. The topology may be
described in terms of two kinds of mononuclear Cd(II) centers
as 4- and 5-connected nodes and the tridentate tib ligand as a
3-connected node. Notably, the 2-connected tib and tbta
ligands are not ascribed to any node. So the overall 3D
framework belongs to a new 3-nodal 3,4,5-connected network
Thermal analysis
The thermogravimetric (TG) measurements were performed in
N2 atmosphere on polycrystalline samples of complexes 1 and
2 and the TG curves are shown in Fig. 5. The TGA curve of 1
displays a weight loss of 2.87% (calcd: 2.04%) at 110–161 uC,
corresponding to the loss of coordinated water molecules. The
framework is stable up to 286 uC. Then, the framework starts
to collapse, accompanying the release of ligands. Complex 2
shows a first weight loss of 3.61% at 93–155 uC, corresponding
to the loss of lattice methanol molecules (calcd: 4.53%). The
second weight loss of 35.12% corresponds to the decomposi-
tion of uncoordinated Htbta molecule (calcd: 33.99%). And
then the framework begins to collapse, accompanying the
release of organic ligands.
5
4
6
¨
with short Schlafli symbol being {4?6?8}{4?6 ?8 }{6 } (Fig. 4b).
To further understand this complicated structure of 3, we
deleted the bidentate tib ligand which bridges a pair of
adjacent networks, generating a 2-fold interpenetrated net-
work (Fig. 4c). Due to the reduction of the coordination
number of the Cd(II) center, the topology of the 2-fold
interpenetrated network becomes a 3-nodal 3,3,4-connected
3
2
¨
network with short Schlafli symbol of {4?6?8 ?10}{4?6?8}{6?8 }.
Therefore, the framework of 3 is clearly a self-penetrating net
and can be considered as derived from cross-linking of 2-fold
interpenetrated nets via bidentate tib ligand (Fig. 4d and 4e).
An analysis of the interpenetrated topology with the TOPOS
program suggests that this network belongs to class Ia, that is,
both the interpenetrated nets are generated only by translation
and the translating vector is the crystallographic b axis
(14.4080(11) Å).
Photoluminescence properties
The photoluminescence spectra of complexes 1 and 2 are
shown in Fig. 6. The free ligand tib displays photolumines-
cence with emission maxima at 405 nm (lex = 360 nm).31 It
can be presumed that this peak originate from the p* A n or
p* A p transitions. Upon complexation of these ligands with
Cd(II) ion, intense emissions are observed at 410 and 423 nm
(lex = 330 nm) for 1 and 2, respectively. The resemblance
between the emissions of 1 and 2 and those of the free tib
indicates that the emissions of 1 and 2 are probably due to
the intraligand (IL) p A p* transitions modified by metal
coordination.32 And the observed small red shift of the
emission maximum between the complexes and the ligand
was attributed the influence of the coordination of the ligand
to the metal atom.
Comparison of the structures of 1–3: reactant molar ratio
effect
A comparison of three CPs demonstrates that the reactant
molar ratio remarkably affects the resulting motifs in this
system. When the Cd/tib/H2tbta ratios are changed from
1 : 1 : 1 to 1 : 1 : 3, we obtained three different infinite motifs
varying from 2-fold interpenetrated hex network, 2D A 3D
interdigitated 63-hcb network to 3D self-penetrated frame-
work. Although the tbta ligand shows the identical m2-g1:g1
coordination fashion in 1–3, but the coordination modes of tib
ligand have important variations, these are tridentate, biden-
tate, and tridentate + bidentate modes for 1–3, respectively.
Due to the different bridging effects of tib ligand, three
Fig. 5 TGA curves for CPs 1 and 2.
Fig. 6 Photoluminescence spectra of complexes 1 and 2.
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L. Renouf, C. Richardson and A. J. Stevenson, Chem.
Commun., 2010, 46, 5067; (e) X. Zhao, H. He, F. Dai, D. Sun
and Y. Ke, Inorg. Chem., 2010, 49, 8650; (f) Y. Yao, H. Lin,
X. Sun, H. Kou, Q. Cai, H. Li, R. Yu and D. Wang, Transition
Met. Chem., 2005, 30, 294; (g) J. Sun, F. N. Dai, W. B. Yuan,
W. H. Bi, X. L. Zhao, W. M. Sun and D. F. Sun, Angew.
Chem., Int. Ed., 2011, 50, 7061; (h) D. Sun, L.-L. Han,
S. Yuan, Y.-K. Deng, M.-Z. Xu and D.-F. Sun, Cryst. Growth
Des., 2013, 13, 377; (i) J. P. Zhang and X. M. Chen, Chem.
Commun., 2006, 1689; (j) D. Sun, Z.-H. Yan, Y.-K. Deng,
S. Yuan, L. Wang and D.-F. Sun, CrystEngComm, 2012, 14,
7856; (k) D. Sun, Z.-H. Yan, M. Liu, H. Xie, S. Yuan, H. Lu,
S. Feng and D. Sun, Cryst. Growth Des., 2012, 12, 2902; (l)
D. Wang, R. Yu, H. Wang, X. Li and X. Xing, Microporous
Mesoporous Mater., 2007, 101, 66; (m) R. Yu, X. Xing,
T. Saito, M. Azuma, M. Takano, D. Wang, Y. Chen,
N. Kumada and N. Kinomura, Solid State Sci., 2005, 7, 221.
3 (a) C.-P. Li and M. Du, Chem. Commun., 2011, 47, 5958; (b)
D. Sun, Y.-H. Li, H.-J. Hao, F.-J. Liu, Y.-M. Wen, R.-B. Huang
and L.-S. Zheng, Cryst. Growth Des., 2011, 11, 3323; (c)
D. Sun, Z.-H. Wei, D.-F. Wang, N. Zhang, R.-B. Huang and
L.-S. Zheng, Cryst. Growth Des., 2011, 11, 1427.
Conclusions
In conclusion, we have fabricated three new entangled Cd(II)
CPs using a mixed-ligand strategy. By adjusting the molar ratio
of the reactants metal salt and ligands from 1 : 1 : 1 to
1 : 1 : 3, the entangled CPs evolved from a rare 2-fold
interpenetrated hex framework, 2D A 3D interdigitated 63-
hcb network to 3D self-penetrated framework. Furthermore,
the thermal stabilities and photoluminescence behaviors of 1
and 2 were also discussed.
Acknowledgements
This work was supported by the NSFC (Grant No. 20701023
and 21203106), and the Foundation of Shandong Province,
China (No. BS2010CL013 and ZR2011BL015).
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