PH modulated assembly in the mixed-ligand system Cd(ii)-dpstc-phen: Structural diversity and luminescent properties

Article abstract of DOI:10.1039/c3ce27108k

Hydrothermal reaction of cadmium salt, 3,3′,4,4′- diphenylsulfonetetracarboxylic acid (H₄dpstc) and 1,10-phenanthroline (phen) under different pH conditions have afforded four novel supramolecular complexes, in which the pH value of the reaction solution plays a crucial structure-directing role. [Cd(H₂dpstc)(phen)]_n (1) formed in a neutral reaction environment exhibits a 1D infinite chain structure containing partially deprotonated H₂dpstc^2- as the H-bond donors and acceptors. Whereas [Cd₂(dpstc)(phen)₂] _n·4.5nH₂O (2), [Cd₂(dpstc)(phen) ₂]_n·nH₂O (3) and [Cd₂(dpstc) (phen)₄(H₂O)₂]·6H₂O (4) contain fully deprotonated dpstc^4- ligands due to the alkaline reaction conditions. Complex 2 possesses a unique 2D layered structure with 1D channels. The most striking feature of 2 is that its 2D holed (4,4)-water-net is constructed from hexameric water clusters and two types of dimeric water clusters. Surprisingly, the water net and the metal-organic skeleton are interpenetrated to form a fascinating 3D metal-organic-water supramolecular architecture. A further increase of the pH value leads to another 2D layered framework of 3 containing dumbbell-shaped rings as subunits. Reaction at a strongly alkaline solution leads to a discrete molecule of 4. Meanwhile solid-state properties such as thermal stability and the photoluminescence properties at room temperature for these complexes have also been systematically investigated.

Full text of DOI:10.1039/c3ce27108k

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pH modulated assembly in the mixed-ligand system
Cd(II)–dpstc–phen: structural diversity and luminescent
properties3
Cite this: CrystEngComm, 2013, 15,
3992
Shu-Quan Zhang, Fei-Long Jiang, Ming-Yan Wu, Lian Chen, Jun-Hua Luo and Mao-
Chun Hong*
Hydrothermal reaction of cadmium salt, 3,39,4,49-diphenylsulfonetetracarboxylic acid (H4dpstc) and 1,10-
phenanthroline (phen) under different pH conditions have afforded four novel supramolecular complexes,
in which the pH value of the reaction solution plays a crucial structure-directing role. [Cd(H2dpstc)(phen)]n
(1) formed in a neutral reaction environment exhibits a 1D infinite chain structure containing partially
deprotonated H2dpstc22 as the H-bond donors and acceptors. Whereas [Cd2(dpstc)(phen)2]n?4.5nH2O (2),
[Cd2(dpstc)(phen)2]n?nH2O (3) and [Cd2(dpstc)(phen)4(H2O)2]?6H2O (4) contain fully deprotonated dpstc42
ligands due to the alkaline reaction conditions. Complex 2 possesses a unique 2D layered structure with 1D
channels. The most striking feature of 2 is that its 2D holed (4,4)-water-net is constructed from hexameric
water clusters and two types of dimeric water clusters. Surprisingly, the water net and the metal–organic
skeleton are interpenetrated to form a fascinating 3D metal–organic–water supramolecular architecture. A
further increase of the pH value leads to another 2D layered framework of 3 containing dumbbell-shaped
rings as subunits. Reaction at a strongly alkaline solution leads to a discrete molecule of 4. Meanwhile
solid-state properties such as thermal stability and the photoluminescence properties at room temperature
for these complexes have also been systematically investigated.
Received 29th December 2012,
Accepted 15th March 2013
DOI: 10.1039/c3ce27108k
www.rsc.org/crystengcomm
case is provided by Zhou and coworkers where a series of
metal–organic polyhedra were obtained by assembling various
V-shaped dicarboxylate ligands as linkers with square four-
connected [Mo2(CO2)4] as nodes.2e,f,k
Introduction
The past decades have seen significant growth of interest in
the rational design and assembly of coordination polymers
(CPs) with predictable structures and desirable properties,
because it plays a key role in the exploration of the functional
materials with industrial applications.1 Many efforts have been
made to achieve this goal, among which the approach of the
appropriate choice of well-designed organic ligands contain-
ing modifiable backbones and connectivity information as
linkers, together with metal ions or polymetallic clusters
(secondary building units) as nodes, has been proved to be an
effective route to construct metal–organic frameworks (MOFs)
with predictable topologies.2 In this area, Yaghi and coworkers
provide excellent examples where they used different linear
dicarboxylate ligands and Zn4O clusters to afford a series of
IRMOFs with the same structural topology (pcu net) and
predetermined cavity size and functionalization.2a,b Another
Although some progress has been made in the rational
design of MOFs, it is still a great challenge to prepare CPs with
predictable structures and valuable properties because many
subtle variables, such as temperature, solvent, pH value, and
the ratio between metal salts and ligands, have non-ignorable
influences on the crystallization processes.3 Systematic studies
on the role of simple variables such as pH value of the reaction
solution need to be investigated, although such studies are
still relatively rare. To our knowledge, the pH value of the
reaction mostly affects the deprotonation extent of ligands and
the generation of an OH2 ligand in aqueous solution.3b,4 In
recent years, some interesting influences of pH value have
been discovered, such as its effects on controlling the helicity
of helical chains, the morphology of the grown crystals and the
in situ formation of ligands.5 And even in a high pH solution
Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, State Key
Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of
Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, China.
E-mail: hmc@fjirsm.ac.cn; Fax: +86-591-83794946; Tel: +86-591-83792460
22
(pH = 9), the CO2 in air can be captured to generate CO3
anions, as reported by Sun and coworkers.6 Our interest is to
investigate the influence of pH value on the structural diversity
of CPs and even on their properties. Our approach is to
perform a series of reactions under similar conditions with
only one factor varied. In such a case, the diversity in assembly
Electronic supplementary information (ESI) available: Crystallographic
3
information, supplementary figures and XRD patterns of complexes 1–4. CCDC
894377–894380. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3ce27108k
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1168 (m), 1140 (m), 1092 (w), 846 (m), 760 (m), 728 (m), 670
(m), 624 (w), 488 (w).
and functionality of CPs can be ascribed exclusively to the
change of the factor.
In our previous work, we have preliminarily discussed the
pH effects on the structures of a series of zinc(II)–4-(4-
carboxyphenoxy)phthalate complexes.7 As part of our ongoing
interest in understanding the ability of pH value to direct the
assembly of metal–organic systems, in this work we investigate
the formation of four new cadmium(II) coordination polymers,
[Cd(H2dpstc)(phen)]n (1), [Cd2(dpstc)(phen)2]n?4.5nH2O (2),
Synthesis of [Cd2(dpstc)(phen)2]n?nH2O (3)
The preparation of 3 was similar to that of 1 except that the pH
value was adjusted to 10.0 by addition of 1 M NaOH solution.
After cooling to room temperature, brown block-shaped
crystals of complex 3 were obtained by filtration in 70% yield
based on phen. Anal. calcd for C40O11N4SH24Cd2 (Mr = 993.49):
C, 48.36%; H, 2.43%; N, 5.64%. Found: C, 48.21%; H, 2.44%;
N, 5.59%. Selected IR data (KBr pellet, cm21): 3408 (m), 3058
(w), 1590 (s), 1412 (s), 1330 (m), 1170 (m), 1150 (m), 1094 (m),
1072 (w), 852 (m), 728 (m), 670 (m), 642 (m), 558 (w), 482 (w).
[Cd2(dpstc)(phen)2]n?nH2O
(3)
and
[Cd2(dpstc)(phen)4(H2O)2]?6H2O (4) (H4dpstc = 3,39,4,49-diphe-
nylsulfonetetracarboxylic acid, phen = 1,10-phenanthroline),
under hydrothermal conditions.8 Their structures range from
discrete molecules to 2D layered architectures, revealing that
the pH value of the reaction plays an essential role in
structural control during self-assembly processes.
Synthesis of [Cd2(dpstc)(phen)4(H2O)2]?6H2O (4)
A mixture of CdSO4?8/3H2O (0.4 mmol, 103 mg), H4dpstc (0.1
mmol, 40 mg), phen (0.1 mmol, 20 mg) NaOH (0.75 mmol, 30
mg) and H2O (5 mL) was placed in a Teflon lined steel
autoclave (23 mL). This mixture solution was strongly alkaline
(pH . 12.0). The autoclave was sealed, heated to 160 uC and
held at the temperature for 72 hours. The autoclave was
allowed to cool to 30 uC for 24 h. Big brown block-shaped
crystals of complex 4 (with the dimension about 0.5–1 mm)
can be in concomitance with some white powders. After
picking out the crystals and washing with water, the yield
based on phen is about 21%. Anal. calcd for C64O18N8SH54Cd2
(Mr = 1480.01): C, 51.94%; H, 3.67%; N, 7.57%. Found: C,
52.04%; H, 3.65%; N, 7.52%. Selected IR data (KBr pellet,
cm21): 3416 (m), 1585 (s), 1435 (s), 1330 (m), 1168 (m), 1093
(m), 1068 (w), 851 (m), 728 (m), 645 (m), 618 (m), 490 (w).
Experimental section
Materials and methods
All reactants were reagent grade and used as purchased
without further purification. Elemental analyses for C, H, N
were carried out on a German Elementary Vario EL III
instrument. The FT-IR spectra were performed on a Nicolet
Magna 750 FT-IR spectrometer using KBr pellets in the range
of 4000–400 cm21. Thermogravimetric analyses were recorded
on a NETZSCH STA 449C unit at a heating rate of 10 uC min21
under nitrogen atmosphere. The powder X-ray diffraction
(XRD) patterns were collected by a Rigaku DMAX2500 X-ray
X-ray crystallography
diffractometer using Cu Ka radiation (l
= 0.154 nm).
All the structural data of complexes 1–4 were collected on a
Rigaku Mercury CCD diffractometer equipped with a graphite-
monochromated Mo Ka radiation (l = 0.71073 Å) at room
temperature. All of the structures were resolved by the direct
method and refined by full-matrix least-squares fitting on F2 by
SHELX-97.9 All non-hydrogen atoms were refined with
anisotropic thermal parameters. The hydrogen atoms of the
water molecules and carboxylic groups were found in the
electron density map and refined by riding. The other
hydrogen atoms were located at geometrically calculated
positions and refined by riding. Crystallographic data and
structure refinement parameters for complexes 1–4 are
summarized in Table 1. Selected bond lengths and bond
Fluorescent analysis of the complexes was performed on an
Edinburgh Instruments FLS920 spectrofluorimeter equipped
with both continuous (450 W) and pulse xenon lamps.
Synthesis of [Cd(H2dpstc)(phen)]n (1)
A mixture of CdSO4?8/3H2O (0.4 mmol, 103 mg), H4dpstc (0.1
mmol, 40 mg), phen (0.1 mmol, 20 mg) and H2O (5 mL) was
placed in a Teflon lined steel autoclave (23 mL). The pH of this
mixture solution was about 7.0. The autoclave was sealed,
heated to 160 uC and held at the temperature for 72 hours. The
autoclave was allowed to cool to 30 uC for 24 h. Brown block-
shaped crystals of complex 1 were collected in 88% yield based
on phen. Anal. calcd for C28O10N2SH16Cd (Mr = 684.89): C,
49.10%; H, 2.35%; N, 4.09%. Found: C, 48.96%; H, 2.33%; N,
4.08%. Selected IR data (KBr pellet, cm21): 3256 (m), 3078 (w),
1744 (s), 1704 (s), 1540 (s), 1429 (s), 1387 (s), 1210 (s), 1168 (s),
1094 (m), 1066 (m), 854 (m), 728 (m), 646 (m), 616 (m), 548 (w),
493 (w).
angles are listed in the ESI (Table S1). More details on the
3
crystallographic studies as well as atomic displacement
parameters are given in the ESI
as CIF files.
3
Crystallographic data for the structures reported in this paper
have been deposited in the Cambridge Crystallographic Data
Center with CCDC reference numbers 894377–894380 for
complexes 1–4.
Synthesis of [Cd2(dpstc)(phen)2]n?4.5nH2O (2)
The preparation of 2 was similar to that of 1 except that the pH
value was adjusted to 8.0 by addition of 0.2 M NaOH solution.
After cooling to room temperature, colorless lamellar crystals
were obtained by filtration in 73% yield based on phen. Anal.
calcd for C40O14.5N4SH31Cd2 (Mr = 1056.55): C, 45.47%; H,
2.96%; N, 5.30%. Found: C, 45.30%; H, 3.02%; N, 5.22%.
Selected IR data (KBr pellet, cm21): 3402 (m), 1578 (s), 1388 (s),
Result and discussion
The coordination modes of the H4dpstc ligand are shown in
Scheme 1. The following structure discussion is based on CIF
files of complexes 1–4. Final formulas of complexes 1–4 are
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Table 1 Crystallographic data for 1–4
Complexes
1
2
3
4
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C28H16CdN2O10
684.92
S
C40H31Cd2N4O14.5
1056.55
S
C40H24Cd2N4O11
993.49
Monoclinic
P21/n
11.8489(7)
16.7123(6)
18.8636(11)
90
105.170(4)
90
3605.2(3)
4
S
C64H54Cd2N8O18
1480.01
S
Triclinic
Triclinic
Triclinic
¯
¯
¯
P1
P1
P1
7.4706(18)
10.994(2)
16.357(4)
71.743(7)
86.791(7)
76.869(7)
1242.3(5)
2
10.905(5)
13.194(7)
14.970(8)
110.429(7)
95.307(6)
91.644(6)
2005.5(17)
2
9.885(3)
14.331(4)
21.418(7)
85.964(5)
89.432(6)
86.079(6)
3019.6(16)
2
a (u)
b (u)
c (u)
V (Å3)
Z
T (K)
293(2)
1.831
1.032
293(2)
1.750
1.189
1054
293(2)
1.830
1.310
1968
293(2)
1.628
0.822
1500
Dc (g cm23
)
m (mm21
F (000)
)
684
h range (u)
2.7–27.5
13 465
5660
379
1.051
0.0229
0.0544
2.3–27.5
15 581
9042
559
1.084
0.0523
0.1464
2.2–27.5
27 780
8229
523
1.077
0.0394
0.0973
2.3–27.5
22 597
13 092
838
1.040
0.0474
0.1438
Collected reflections
Unique reflections
Parameters
Gof on F2
a
R1 (I . 2s(I))
b
wR2 (all data)
a
b
2
R1 = S||Fo| 2 |Fc||/S|Fo|. wR2 = [Sw(Fo 2 Fc2)2/Sw(Fo)2]1/2
.
m3-k1:k2:k2 mode (Scheme 1a), linking adjacent cadmium
binuclear clusters to form a one-dimensional (1D) chain
(Fig. 1b). As shown in Fig. 1c, these chains are decorated with
phen ligands at both sides, which are arranged parallel with
the centroid distance of 6.702 Å.
Some interesting supramolecular contacts are observed in
the solid-state structure of 1. Besides strong intermolecular
hydrogen bonds between the carboxyl oxygen atoms of
further determined by elemental analyses and thermogravi-
metric studies.
Structural description of [Cd(H2dpstc)(phen)]n (1)
Complex 1 was hydrothermally synthesized in a neutral
reaction environment with pH = 7.0. X-Ray crystallographic
analysis reveals that the asymmetric unit of 1 consists of one
Cd(II) ion, one partly deprotonated H2dpstc22 ligand and one
chelating phen ligand as shown in Fig. 1a. The Cd2+ center is
seven-coordinated by two nitrogen atoms of phen ligand and
five oxygen atoms from three carboxyl groups belonging to
three different H2dpstc22 ligands, respectively. Therefore the
Cd2+ center adopts distorted monocapped octahedral coordi-
nation geometry. Two Cd2+ centers aggregate to cadmium
binuclear clusters through connections of chelating–bridging
carboxyl groups (O3–C8–O4). The H2dpstc22 ligands adopt the
i
H2dpstc22 ligands in the neighboring chains (O6 O4
=
…
ii
…
2.585 (2) Å and O8 O5 = 2.726 (2) Å, i = 1 2 x, 1 2 y, 2 2
z, ii = 2x, 2y, 2 2 z), obvious p–p stacking interactions
provided by the nearly parallel aromatic rings belonging to the
adjacent phen ligands (the centroid distances range from
3.4618 to 3.8070 Å) (Table S2, ESI, Fig. 1e) link together the 1D
3
chains into a three-dimensional (3D) supramolecular frame-
work (Fig. 1d).
Structural description of [Cd2(dpstc)(phen)2]n?4.5nH2O (2)
Compared to 1, complex 2 was obtained by adjusting pH value
of the same reaction mixture to 8.0. Complex 2 crystallizes in
¯
the triclinic space group P1, and its structure features a two-
dimensional layered framework with 1D channels. As shown
in Fig. 2a, the asymmetric unit contains two Cd(II) ions, one
dpstc42 ligand, two phen ligands and four and a half lattice
water molecules. Each Cd(II) ion adopts distorted octahedral
coordination geometry, completed by two nitrogen atoms of
chelating phen ligand and the other four carboxyl oxygen
atoms from three different dpstc42 ligands. In complex 2, the
carboxyl groups of ligand dpstc42 are all deprotonated, which
can be classified into two types. One type of carboxyl groups
(O3–C3–O4, O5–C9–O6 and O7–C11–O8) coordinates to two
Cd(II) ions through syn–anti bidentate mode, and the other
Scheme 1 The coordination modes of H4dpstc ligands in complexes 1–4.
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Fig. 1 (a) The coordination environments of Cd(II) atoms in complex 1 (hydrogen atoms are omitted for clarity). Symmetry transformations used to generate
equivalent atoms: A = x 2 1, y, z, B = 1 2 x, 2y, 1 2 z. (b) The 1D chain of 1 in ac plane (phen ligands are omitted for clarity). (c) The 1D chain of 1, viewed along the [1
0 0] direction. (d) The 3D supramolecular framework of complex 1 viewed along the [1 0 0] direction (violet dashed lines represent the hydrogen bonds between the
carboxyl groups). (e) The illustration of p–p interactions in complex 1.
carboxyl group (O1–C1–O2) serves as a bridge to connect two
Cd(II) ions by m-O2 atom. The Cd1 and Cd2 centers are
connected by these two types of carboxyl groups to form an
dimers of O13 atoms along the crystallographic a axis through
hydrogen-bonds. All of the dimeric water clusters act as
bridges to connect the adjacent hexamers. Therefore, a (4,4)-
net containing the fused hexamers and dimers is formed
through abundant hydrogen-bonding interactions in the ac
plane (Fig. 3c). In addition, the water sheets stack along the a
axis forming one-dimensional rectangular channels with the
windows of effective dimensions 7.3 6 12.2 Å, taking into
account the van der Waals radii of the oxygen atoms (Fig. 4).
This 32-menbered water rectangle contains four hexamers as
the vertices and four dimers including two dimers of O12
atoms and two dimers of O13 atoms as the edges (Fig. 3b). The
information of the hydrogen-bonding interactions in 2 is listed
infinite Cd(II)–carboxylate chain (Fig. S1a, ESI ). As depicted in
3
Fig. 2c, the 1D chains are further bridged by dpstc42 ligands to
fabricate a 2D layered network. The bridging dpstc42 ligands
between the adjacent chains are arranged alternately and the
vertices (–SO2 groups) of neighboring V-shaped ligands are
directed in opposite orientations (Fig. 2b and S1b, ESI ).
3
Therefore, 1D channels with approximately square windows in
the 2D layer are generated from the alternant arrangement of
the V-shaped ligands. The lattice water molecules are filled in
the channels (Fig. 2b). Similar to 1, there are strong p–p
interactions between the nearly parallel phen ligands in
…
in Table 2, and the average O O separation of 2.81 Å among
complex 2 (Fig. 2e, Table S2, ESI ) with the distances between
the water molecules in the layer is between the corresponding
value of 2.76 Å in ice Ih and 2.85 Å in liquid water.10
Interestingly, the 2D holed water network is interpenetrated
with the metal–organic skeleton, where the dpstc42 ligands
pass through the holes of water sheet while the water chains
composed of hexamers and dimers of two O12 atoms are filled
in the channels of 2D metal–organic skeleton (Fig. 4 and S3a,
3
planes of phen from 3.408 to 3.536 Å. The 2D layers in 2 are
stacked in AAAA fashion to a 3D supramolecular assembly
which is stabilized by these intense supramolecular interac-
tions (Fig. 2d).
The most attractive feature for 2 is the hydrogen-bonding
two-dimensional water sheets. As depicted in Fig. 3a, the water
network consists of three types of water clusters including a
hexamer of twofold O11, O14 and O15 atoms, a dimer of two
O12 atoms and another dimer of two O13 water molecules.
Each hexamer serves as a four-connected node linking two
dimers of O12 atoms along the crystallographic c axis and two
ESI ). The planes of the water polymers and the metal–organic
3
layered frameworks meet each other at an angle of 86.57u (Fig.
S2, ESI ). There is a unique class of connection between both
3
polymers. Two carboxyl oxygen atoms of each dpstc42 ligand
…
are hydrogen-bonded to the water network (O6 O11 = 2.821(8)
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Fig. 2 (a) The coordination environments of Cd(II) atoms in complex 2 (hydrogen atoms are omitted for clarity). Symmetry transformations used to generate
equivalent atoms: A = 2x, 2y, 1 2 z, B = x, y 2 1, z, C = 2x, 1 2 y, 2 2 z. (b) The 2D layer with 1D channels in 2, water molecules are filled in the channels, viewed
along the [0 0 1] direction. (c) The 2D layer of 2 in the bc plane (phen ligands are omitted for clarity). (d) The 3D supramolecular framework of complex 2 viewed
along the [0 0 1] direction. (e) The illustration of p–p interactions in complex 2.
…
Å, O1 O12 = 2.75(1) Å) (Fig. S3b, ESI ). Consequently, the
four carboxyl oxygen atoms and two nitrogen atoms of
chelating phen ligand but located in different coordination
environments, where Cd1 is surrounded by a distorted
octahedra and Cd2 is in a triangular prism. The two types of
Cd(II) centers aggregate to cadmium binuclear clusters
through sharing the vertex of O6 atoms. As illustrated in
Fig. 5b, every four binuclear units are linked by four dpstc42
ligands resulting in a dumbbell-shaped ring. Each fully
deprotonated dpstc42 ligand in 3 adopts m5-k1:k1:k2:k2:k2
mode (Scheme 1c) to connect five Cd(II) ions which belong
to three different cadmium binuclear clusters. The two
phthalic groups (named phthalic group A and B) of the
dpstc42 ligand exhibit different connectivity. Phthalic group A
binds to one binuclear unit, whereas phthalic group B bridges
two binuclear clusters. As depicted in Fig. 5c, the dumbbell-
3
overall structure of 2 can be considered as a fascinating 3D
metal–organic–water supramolecular architecture (Fig. 4 and
S2, ESI ). To our knowledge, the examples of the interlocked
3
structures between water networks and metal–organic frame-
works are still limited.11
Structural description of [Cd2(dpstc)(phen)2]n?nH2O (3)
When the pH value of the reaction mixture was adjusted to
10.0, a two-dimensional layered structure of 3 was obtained.
Single-crystal X-ray analysis has revealed that 3 crystallizes in a
P21/n space group. As shown in Fig. 5a, there are two
crystallographically independent cadmium atoms, one dpstc42
ligand, two phen molecules and one free water molecule in an
asymmetric unit. Two Cd(II) ions are both six-coordinated with
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Fig. 3 (a) A perspective view of the hexameric water cluster and two types of dimeric water clusters in complex 2. (b) Large (H2O)32 water rectangle in the water layer.
(c) The 2D water net in 2 containing large windows in the ac plane.
shaped rings, acting as the subunits, assemble into a 2D
herringbone-like net by connecting the binuclear units of
neighboring rings through the phthalic groups B. In addition,
the phen ligands are decorated in and out of the plane of the
2D layer of 3.
molecule with two Cd2+ ions, one m-bridging fully deproto-
nated dpstc42 ligand, four chelating phen ligands, two aqua
ligands and six lattice water molecules in its asymmetry unit
(Fig. 6a). Both Cd2+ ions lie in similar octahedral {N4O2}
environments. All of the nitrogen atoms come from two
chelating phen ligands and the other two oxygen atoms are
from a monodentate carboxyl group of dpstc42 ligands and
one coordinated water molecule, respectively. Although all of
the carboxyl groups of the dpstc42 ligand are deprotonated,
only 3- and 39-carboxyl groups coordinate to the Cd(II) ions in
the syn-coordination mode (Scheme 1d). Therefore, the
dpstc42 ligand can be viewed as a bridge to aggregate the
two Cd(II) centers to a binuclear molecule and the distance
between the two Cd2+ ions is 10.329(3) Å.
Structural description of [Cd2(dpstc)(phen)4(H2O)2]?6H2O (4)
¯
Complex 4 crystallizes in the triclinic space group P1. The
discrete Cd(II) complex within 4 is a neutral binuclear
Table 2 Selected hydrogen-bond lengths (Å) and angles (u) for 2a
…
…
…
D–H A
D–H
H
A
D
A
…
O11–H11A O6
0.93
0.93
0.86
0.94
0.86
0.88
0.90
0.90
0.88
1.97
2.04
2.17
2.28
2.26
1.99
2.02
1.97
1.83
2.824(9)
2.96(3)
2.760(12)
2.96(2)
2.64(3)
2.81(2)
2.705(16)
2.84(3)
2.63(3)
152.2
174.3
125.7
129.0
106.8
155.4
132.2
163.1
149.0
…
O11–H11B O15
…
O12–H12A O1
i
…
O12–H12B O12
ii
…
O13–H13A O13
…
O13–H13B O14
…
O14–H14A O11
…
O15–H15A O12
iii
…
Fig. 4 Partial structure of 2 exhibits the interpenetration between the metal–
organic network and the water 2D polymers, viewed along the [0 1 0] direction.
One of the 2D metal–organic networks is highlighted in light blue, 2D water
layers are represented in space-filling mode.
O15–H15B O14
a
Symmetry codes: (i) 2x, 1 2 y, 1 2 z; (ii) 21 2 x, 1 2 y, 2 2 z; (iii)
2x, 1 2 y, 2 2 z.
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Fig. 5 (a) The coordination environments of Cd(II) atoms in complex 3 (hydrogen atoms are omitted for clarity). Symmetry transformations used to generate
equivalent atoms: A = 1/2 2 x, 1/2 + y, 1/2 2 z, B = 2x, 1 2 y, 2z. (b) A dumbbell-shaped ring in 3. (c) The two-dimensional net of complex 3 (phen ligands are
omitted for clarity). (d) The 2D layer of 3, viewed along the [0 1 0] direction.
Some interesting supramolecular contacts are observed in
the solid-state structure of 4. In this complex, half of the
carboxyl groups of the dpstc42 ligands remain uncoordinated;
therefore, they can act as excellent hydrogen bond acceptors.
deprotonated phthalic motifs. Nevertheless, at the alkaline
condition (the higher pH value of 8, 10 and more than 12), all
of the products of complexes 2–4 own completely deproto-
nated ligand dpstc42. To understand how pH controls the
extent of deprotonation, we estimate the acidity of each
carboxylic group on the H4dpstc. By considering the electron-
withdrawing and electron-donating effects of the substituent
groups (sulphone group and carboxylic group itself), the
4-carboxylic group seems to be the most acidic, and the
49-carboxylic group is the second most one, and then the 3-
and 39-carboxylic groups are relatively weaker. To confirm this
deduction, the MarvinSketch software12 is used to calculate
the pKa values of carboxylic groups through some approximate
treatments. And if the ligand is viewed as a monoprotic acid,
the pKa value of 4-COOH (pKa = 2.55) is smaller than that of
3-COOH (pKa = 2.75, and two phthalic groups are equally).
Further considering the ligand as a diacid, we suppose that the
4-COOH is deprotonated to evaluate the pKa values of the
remaining three carboxylic groups, respectively. The result
tells us that the pKa value of 49-COOH shows slightly smaller
than that of 39-COOH, and the pKa value of 3-COOH is
significantly larger than those of former ones. From compar-
ing the pKa values of these carboxylic groups, obviously,
4-COOH is the most acidic and the 49-COOH may be the
second most. The description of the deduction, the model
used to calculate pKa values and the detailed result of the
As shown in Fig. S4, ESI, abundant and strong hydrogen
3
bonding interactions can be found among carboxyl groups,
lattice water molecules and aqua ligands which hold together
the discrete binuclear coordination molecules into a 3D
supramolecular structure (Fig. 6c, Table S4, ESI ).
3
Furthermore, the 3D supramolecule is stabilized by p–p
stacking interactions between almost parallel phen ligands
…
and the C–H p interactions (or so called edge-to-face aromatic
interactions) between nearly perpendicular phen aromatic
rings (Fig. S6b, Tables S2 and S3, ESI ).
3
The effects of pH value of the reaction on the final structures
of the complexes
As the pH value is the only difference in the syntheses of
complexes 1–4, it is clear that the assembly process of this type
of crystalline products is pH-dependent. By comparison of
complexes 1–4, the changes in pH value of the initial solution
can lead to different protonated extent and therefore the
connectivity of the polycarboxylate ligands. At a neutral
reaction condition (pH = 7), complex 1 was isolated, where
the H4dpstc ligands are partially deprotonated to H2dpstc22
anions which include both protonated phthalic groups and
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Fig. 6 (a) The coordination environments of Cd(II) atoms in complex 4 (hydrogen atoms are omitted for clarity). (b) Illustration of supramolecular interactions in 4
…
(cyan dashed lines represent the p–p stacking interactions and violet dashed lines represent the C–H p interactions). (c) The 3D stacking mode of dinuclear molecules
in 4, viewed along the [1 0 0] direction.
calculation can be seen in ESI. In addition, we calculated the
distribution of partial and fully deprotonated ligand species in
Therefore, two higher dimensional and more complicated 2D
networks including one 2D layered architecture with 1D
channels and a 2D herringbone-like network are formed,
respectively. When we further elevate the pH value of reaction
solution (strongly alkaline), a new structure of 4 was obtained,
where the dpstc42 ligands are fully deprotonated. However,
the discrete molecule 4 shows a low dimensional structure.
This is probably because the metal salt converts to the
precipitate of M(OH)2 when meeting a strongly alkaline
solution. This assumption can be confirmed by the PXRD
pattern of the precipitate of reaction, which matches the
3
aqueous solution with various pH values (Fig. S7 and S8, ESI ).
3
In complex 1, the deprotonated phthalic groups serve as
bridges to ligate the metal ions to 1D chains, and the
protonated ones act as the hydrogen bond donors and
acceptors to extend the 1D chains to a 3D supramolecule
structures. As depicted in Fig. S7 and S8, ESI, this type of
3
deprotonated ligands can hardly be generated, because the
3-COOH exhibits weaker acidity than the both 39- and
49-COOH. This phenomenon may be caused by some other
factors in the crystallization process. One probable reason we
guessed is that the coordination of 3- and 4-COOH to metal
ions might trend to congregate the metal ions to clusters,
b-Cd(OH) (ref. 13) well (Fig. S9, ESI ). Because the precipitates
3
2
of metal hydroxide are hard to participate in self-assembly
process, increasing the pH value may reduce the concentration
of the metal ion which coincides with the low product yield.
Meanwhile, because of the satisfactory water-solubility of phen
at high temperature, the high pH value of the reaction solution
will result in a high ratio of phen vs. metal ion. As a result,
more phen ligands chelate to the metal centers (two phen per
Cd(II) center in 4 and one phen per Cd(II) center in 1–3). The
increase of the steric hindrance and the decrease of the
coordination sites on Cd2+ ions confine the dpstc42 ligands
coordinating to metal centers in a low connectivity mode and
finally lead to a simple 0D molecular structure of 4.
which make the system more stable. And from Fig. S7, ESI, we
3
can see that at a higher pH value than 8.0, the ligand exists in
aqueous solution as the form of dpstc42 completely, which is
in accord with the situation of complexes 2–4. Because of the
different deprotonated extent, the connectivity of the ligand
may be different. In complex 1, the partially deprotonated
H2dpstc22 ligand only connects three Cd(II) ions leading to a
relatively low dimensional structure. And in structures of 2 and
3, the dpstc42 ligands manifest various coordination abilities
(linking six and five cadmium ions per ligand respectively).
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220 uC corresponds to the departure of one lattice water
molecule (calculated: 1.81%, found: 1.90%) and then the
framework undergoes decomposition after 280 uC. As to 4, a
weight loss of 9.39% is observed in the temperature range of
30–145 uC, which corresponds to the release of six lattice water
molecules and two coordinated aqua molecules (calcd 9.76%),
and then the framework is found to decompose at about 200
uC.
Photoluminescence properties
Metal–organic coordination polymers, especially those con-
taining d10 metal ions, exhibit excellent photoluminescence
properties and have potential on the field of light emitting
devices, chemical or biological sensors and so on.14 As a series
of d10 metal–organic hybrid coordination polymers, the solid
state emission spectra of complexes 1–4 together with the
ligands H4dpstc and phen have been investigated at room
temperature (Fig. 8). The free ligand H4dpstc displays
photoluminescence with emission maximum at 434 nm upon
excitation at 365 nm, and the free phen ligand shows tri-
centers emission with three split peaks centered at 380 nm,
415 nm and 440 nm (lex = 350 nm), respectively. It can be
presumed that these bands originated from the p A p* or n A
p* transitions. The emission spectra of complexes 1–4 are
shown in Fig. 8b. Excitation at 330 nm leads to an intense blue
fluorescent emission with maximum and shoulder bands at
431 and 450 nm for 1, which possibly originates from the
intraligand transitions of H2dpstc22 and phen ligands,
respectively. Irradiation of complex 2 at 350 nm results in a
blue fluorescent emission band at 436 nm, which closely
matches to those of the fluorophore ligand H4dpstc indicating
the metal-perturbed intraligand charge transfer. While com-
plex 3 shows intense UV/violet luminescent emissions under
UV irradiation, and its solid state emission spectrum contains
two peaks at 370 and 390 nm and a weak shoulder bands 413
nm (lex = 330 nm), respectively. In comparison to the metal
free ligand phen, these bands of 3 can be assigned to intra-
Fig. 7 TGA curves for complexes 1–4.
The above-mentioned results show that the reaction pH
value has an important influence on the structures of the
assembly process since it determines the deprotonation extent
and then indirectly influences the connectivity of the
polycarboxylate ligand. And in the extreme alkaline pH value,
the decrease of concentration of the metal ion derived from
generation of precipitate of metal hydroxide must also be
taken into account in the assembly process.
Thermal analyses
To investigate the thermal stability of these complexes, the
thermogravimetric analysis (TGA) experiments are carried out
in the temperature range of 30–900 uC under a flow of nitrogen
with heating rate of 10 uC min21 (Fig. 7). There is no obvious
weight loss before 250 uC for complex 1 and then it
decomposes rapidly on further heating. A total loss of 7.82%
is observed for 2 in the temperature range of 30–120 uC, which
can be attributed to the loss of lattice water molecules (calcd
7.67%), and the decomposition of the residue is observed at
about 300 uC. For complex 3, the weigh loss in the range of 30–
ligand (p A p*) fluorescent emissions (Table S2, ESI ). The
3
Fig. 8 Emission spectra of (a) ligand H4dpstc, phen and (b) complexes 1–4 in the solid state at room temperature.
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N. Yanai and S. Kitagawa, Chem. Soc. Rev., 2009, 38, 1228;
(i) H. Xu, Z.-F. Xu, Z.-Y. Yue, P.-F. Yan, B. Wang, L.-W. Jia,
G.-M. Li, W.-B. Sun and J.-W. Zhang, J. Phys. Chem. C, 2008,
112, 15517; (j) O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H.
K. Chae, M. Eddaoudi and J. Kim, Nature, 2003, 423, 705.
2 (a) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter,
M. O’Keeffe and O. M. Yaghi, Science, 2002, 295, 469; (b)
M. Eddaoudi, D. B. Moler, H.-L. Li, B.-L. Chen, T.
M. Reineke, M. O’Keeffe and O. M. Yaghi, Acc. Chem.
Res., 2001, 34, 319; (c) M. Fujita, K. Umemoto,
M. Yoshizawa, N. Fujita, T. Kusukawa and K. Biradha,
Chem. Commun., 2001, 509; (d) H. Furukawa, J. Kim, N.
W. Ockwig, M. O’Keeffe and O. M. Yaghi, J. Am. Chem. Soc.,
2008, 130, 11650; (e) J.-R. Li, A. A. Yakovenko, W.-G. Lu, D.
J. Timmons, W.-J. Zhuang, D.-Q. Yuan and H.-C. Zhou, J.
Am. Chem. Soc., 2010, 132, 17599; (f) J.-R. Li and H.-C. Zhou,
Nat. Chem., 2010, 2, 893; (g) M. O’Keeffe, Chem. Soc. Rev.,
2009, 38, 1215; (h) J. J. Perry, J. A. Perman and M.
J. Zaworotko, Chem. Soc. Rev., 2009, 38, 1400; (i) N. Stock
and S. Biswas, Chem. Rev., 2012, 112, 933; (j) D.
J. Tranchemontagne, J. L. Mendoza-Cortes, M. O’Keeffe
and O. M. Yaghi, Chem. Soc. Rev., 2009, 38, 1257; (k)
D. Zhao, D.-J. Timmons, D.-Q. Yuan and H.-C. Zhou, Acc.
Chem. Res., 2011, 44, 123.
3 (a) H.-X. Deng, C. J. Doonan, H. Furukawa, R. B. Ferreira,
J. Towne, C. B. Knobler, B. Wang and O. M. Yaghi, Science,
2010, 327, 846; (b) J.-Z. Gu, Z.-Q. Gao and Y. Tang, Cryst.
Growth Des., 2012, 12, 3312; (c) L.-N. Li, S.-Y. Wang, J.-
X. Ma, T.-L. Chen, Z.-H. Sun, J.-H. Luo and M.-C. Hong,
Cryst. Growth Des., 2012, 12, 4109; (d) L.-F. Ma, L.-Y. Wang,
D.-H. Lu, S. R. Batten and J.-G. Wang, Cryst. Growth Des.,
2009, 9, 1741; (e) P. Mahata, M. Prabu and S. Natarajan,
Inorg. Chem., 2008, 47, 8451; (f) J.-J. Zhang, L. Wojtas, R.
W. Larsen, M. Eddaoudi and M. J. Zaworotko, J. Am. Chem.
Soc., 2009, 131, 17040; (g) W.-H. Zhang, Y.-Y. Wang, E.
K. Lermontova, G.-P. Yang, B. Liu, J.-C. Jin, Z. Dong and Q.-
Z. Shi, Cryst. Growth Des., 2010, 10, 76.
spectrum of complex 4 shows a broad emission band centered
at 458 nm, which can probably be assigned to the intraligand
(p–p*) fluorescent emission of both dpstc42 and phen.
Compared to the free ligands (H4dpstc and phen), the
emission spectra of complexes 1, 2 and 4 show slight red-
shifts. It may tentatively be ascribed to the strong p-stacking
interactions in these solid-state compounds (Table S2, ESI ),
3
which are expected to play an essential role in decreasing the
HOMO–LUMO gaps.15 The slight blue-shift observed in the
emission spectrum of 3 may due to the weaker p-stacking
interaction in 3 than that in the crystalline phen ligand.
Conclusions
The dependence of simple variables such as the reaction pH
value under hydrothermal conditions has been investigated
during the preparation of Cd–dpstc/phen mixed ligands
systems. The structural variation of the four compounds from
0D binuclear molecule to 1D chain and two types of 2D layers
indicates that the pH value has great influence on the
structures of the products. Through comparison of the
structures of 1–4, we have found that the effect of the pH
value can modulate the structures of complexes through
affecting the deprotonation extent and then the connectivity of
the polycarboxylate ligands as well as the existent states of the
metal ions in the reaction solution. At the same time, we have
also investigated the thermal stability and the luminescent
properties of these compounds, and discovered that the
properties can be adjusted indirectly by pH value through
their influence on the structures. It is believed that the
initiatory researches of this work will provide a valuable
approach for the construction of other coordination polymers
with diverse structures under different reaction conditions.
4 (a) L. Chen, G.-J. Xu, K.-Z. Shao, Y.-H. Zhao, G.-S. Yang, Y.-
Q. Lan, X.-L. Wang, H.-B. Xu and Z.-M. Su, CrystEngComm,
2010, 12, 2157; (b) M. Chen, S.-S. Chen, T. A. Okamura,
Z. Su, M.-S. Chen, Y. Zhao, W.-Y. Sun and N. Ueyama, Cryst.
Growth Des., 2011, 11, 1901; (c) Y.-N. Chi, F.-Y. Cui, A.-R. Jia,
X.-Y. Ma and C.-W. Hu, CrystEngComm, 2012, 14, 3183; (d)
A. B. Lago, R. Carballo, E. Garcia-Martinez and E.
M. Vazquez-Lopez, Cryst. Growth Des., 2011, 11, 59; (e)
L. Pan, T. Frydel, M. B. Sander, X.-Y. Huang and J. Li, Inorg.
Chem., 2001, 40, 1271; (f) H.-X. Yang, S.-Y. Gao, J. Lu, B. Xu,
J.-X. Lin and R. Cao, Inorg. Chem., 2010, 49, 736; (g) J.-
X. Yang, X. Zhang, J.-K. Cheng, J. Zhang and Y.-G. Yao,
Cryst. Growth Des., 2012, 12, 333; (h) B. Zheng, J.-F. Bai and
Z.-X. Zhang, CrystEngComm, 2010, 12, 49; (i) C.-P. Li, Q. Yu,
J. Chen and M. Du, Cryst. Growth Des., 2010, 10, 2650.
5 (a) G.-C. Ou, X.-L. Feng and T.-B. Lu, Cryst. Growth Des.,
2011, 11, 851; (b) D. Sun, Z.-H. Wei, C.-F. Yang, D.-F. Wang,
N. Zhang, R.-B. Huang and L.-S. Zheng, CrystEngComm,
2011, 13, 1591; (c) J.-A. Zhang, M. R. Langille and C.
A. Mirkin, J. Am. Chem. Soc., 2010, 132, 12502.
Acknowledgements
We thank 973 Program (2011CBA00507; 2011CB932504),
National Natural Science Foundation of China (21131006)
and the Natural Science Foundation of Fujian Province for
funding this research.
Notes and references
1 (a) A. U. Czaja, N. Trukhan and U. Muller, Chem. Soc. Rev.,
2009, 38, 1284; (b) P. Horcajada, R. Gref, T. Baati, P.
K. Allan, G. Maurin, P. Couvreur, G. Ferey, R. E. Morris and
C. Serre, Chem. Rev., 2012, 112, 1232; (c) L. E. Kreno,
K. Leong, O. K. Farha, M. Allendorf, R. P. Van Duyne and J.
T. Hupp, Chem. Rev., 2012, 112, 1105; (d) J. Lee, O. K. Farha,
J. Roberts, K. A. Scheidt, S. T. Nguyen and J. T. Hupp, Chem.
Soc. Rev., 2009, 38, 1450; (e) Z.-J. Lin, T.-F. Liu, X.-L. Zhao,
J. Lu and R. Cao, Cryst. Growth Des., 2011, 11, 4284; (f) N.
W. Ockwig, O. Delgado-Friedrichs, M. O’Keeffe and O.
M. Yaghi, Acc. Chem. Res., 2005, 38, 176; (g) R. Robson, J.
Chem. Soc., Dalton Trans., 2000, 3735; (h) T. Uemura,
6 L.-Y. Kong, H.-F. Zhu, Y.-Q. Huang, T. A. Okamura, X.-
H. Lu, Y. Song, G.-X. Liu, W.-Y. Sun and N. Ueyama, Inorg.
Chem., 2006, 45, 8098.
This journal is ß The Royal Society of Chemistry 2013
CrystEngComm, 2013, 15, 3992–4002 | 4001

View Article Online
Paper
CrystEngComm
7 S.-Q. Zhang, F.-L. Jiang, M.-Y. Wu, J. Ma, Y. Bu and M.-
C. Hong, Cryst. Growth Des., 2012, 12, 1452.
12 The pKa value was calculated using the Calculator Plugins in
MarvinSketch, which can be download freely from https://
www.chemaxon.com/products/marvin/marvinsketch/.
13 L. Hemmingsen, R. Bauer, M. J. Bjerrum, K. Schwarz,
P. Blaha and P. Andersen, Inorg. Chem., 1999, 38, 2860.
14 (a) Y.-J. Cui, Y.-F. Yue, G.-D. Qian and B.-L. Chen, Chem.
Rev., 2012, 112, 1126; (b) L. E. Kreno, K. Leong, O. K. Farha,
M. Allendorf, R. P. Van Duyne and J. T. Hupp, Chem. Rev.,
2012, 112, 1105; (c) M. D. Allendorf, C. A. Bauer, R.
K. Bhakta and R. J. T. Houk, Chem. Soc. Rev., 2009, 38,
1330; (d) R. J. Kuppler, D. J. Timmons, Q.-R. Fang, J.-R. Li,
T. A. Makal, M. D. Young, D.-Q. Yuan, D. Zhao, W.-
J. Zhuang and H.-C. Zhou, Coord. Chem. Rev., 2009, 253,
3042.
15 (a) S.-L. Zheng, J.-H. Yang, X.-L. Yu, X.-M. Chen and W.-
T. Wong, Inorg. Chem., 2004, 43, 830; (b) N. K. Al-Rasbi,
C. Sabatini, F. Barigelletti and M. D. Ward, Dalton Trans.,
2006, 4769; (c) B. V. Bukvetskii, E. V. Fedorenko, A.
G. Mirochnik and V. E. Karasev, J. Struct. Chem., 2007,
48, 1148; (d) H.-J. Liu, X.-T. Tao, J.-X. Yang, Y.-X. Yan,
Y. Ren, H.-P. Zhao, Q. Xin, W.-T. Yu and M.-H. Jiang, Cryst.
Growth Des., 2008, 8, 259; (e) A. Hori, S. Takatani, T.
K. Miyamoto and M. Hasegawa, CrystEngComm, 2009, 11,
567.
8 (a) F. Fu, D.-S. Li, S.-H. Deng, B.-F. Zhu and D. Guo, Inorg.
Chem. Commun., 2011, 14, 1386; (b) F. Fu, D.-S. Li, Y.-P. Wu,
X.-M. Gao, M. Du, L. Tang, X.-N. Zhang and C.-X. Meng,
CrystEngComm, 2010, 12, 1227; (c) X.-M. Gao, D.-S. Li, J.-
J. Wang, F. Fu, Y.-P. Wu, H.-M. Hu and J.-W. Wang,
CrystEngComm, 2008, 10, 479; (d) G.-X. Liu, R.-Y. Huang, L.-
F. Huang, X.-J. Kong and X.-M. Ren, CrystEngComm, 2009,
11, 643; (e) G.-X. Liu, K. Zhu, H.-M. Xu, S. Nishihara, R.-
Y. Huang and X.-M. Ren, CrystEngComm, 2010, 12, 1175; (f)
R.-T. Liu, L. Hou, B. Liu, Y.-N. Zhang, Y.-Y. Wang and Q.-
Z. Shi, Inorg. Chim. Acta, 2011, 366, 53; (g) D.-F. Sun, R. Cao,
Y.-Q. Sun, W.-H. Bi, X.-J. Li, Y.-Q. Wang, Q. Shi and X. Li,
Inorg. Chem., 2003, 42, 7512.
9 G. M. Sheldrick, SHELXS-97. Program for the Solution of
¨
Crystal Structures, University of Gottingen, Germany, 1997.
10 (a) J. K. Gregory, D. C. Clary, K. Liu, M. G. Brown and R.
J. Saykally, Science, 1997, 275, 814; (b) M. Matsumoto,
S. Saito and I. Ohmine, Nature, 2002, 416, 409.
11 (a) Y.-G. Huang, Y.-Q. Gong, F.-L. Jiang, D.-Q. Yuan, M.-
Y. Wu, Q. Gao, W. Wei and M.-C. Hong, Cryst. Growth Des.,
2007, 7, 1385; (b) W.-T. Xu, F.-L. Jiang, Y.-F. Zhou, K.-
C. Xiong, L. Chen, M. Yang, R. Feng and M.-C. Hong,
Dalton Trans., 2012, 41, 7737.
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