Synthesis, crystal structures and photocatalytic properties of four silver(I) coordination polymers based on semirigid bis(pyrazole) and carboxylic acid co-ligands

Article abstract of DOI:10.1007/s11243-016-0071-2

Four Ag(I) coordination polymers, formulated as [Ag(L1)(tpa)_0.5]_n (1), {[Ag(L2)(ndc)_0.5]·0.5H₂ndc}_n (2), [Ag(L3)_0.5(ndc)_0.5]_n (3) and {[Ag(L3)]·H₃bptc}_n (4) (L1?=?4,4′-bis(pyrazole-1-ylmethyl)-biphenyl, L2?=?4,4′-bis(3,5-dimethylpyrazol-1-ylmethyl)-biphenyl, L3?=?1,4-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene, H₂tpa?=?terephthalic acid, H₂ndc?=?2,6-naphthalenedicarboxylic acid, H₄bptc?=?3,3′,4,4′-biphenyltetracarboxylic acid), have been hydrothermally synthesized and structurally characterized. Complex 1 features the rare binodal (4,4)-connected 2D 4,4L10 topological network with a point symbol of {3²·4.6²·7}₂{3²·6²·7²}. Complex 2 has a folded ladder-like chain structure, which is further extended into a 3D supramolecular network via O–H···O hydrogen bonding and π···π stacking interactions. Complexes 3 and 4 both possess 1D zigzag chain structures. Complex 3 is further extended into a binodal (3,4)-connected network with the point symbol of {4.8⁴·10}{6²·8²}₂ by Ag···O weak interactions, while complex 4 is further connected through O–H···O hydrogen bonding and π···π interactions to afford a 2D supramolecular structure. The photoluminescence spectra and photocatalytic properties of these complexes for degradation of methylene blue and methyl orange are reported.

Full text of DOI:10.1007/s11243-016-0071-2

Transition Met Chem
DOI 10.1007/s11243-016-0071-2
Synthesis, crystal structures and photocatalytic properties of four
silver(I) coordination polymers based on semirigid bis(pyrazole)
and carboxylic acid co-ligands
Dian-Heng Huan1 Yan-Qin Zhao1 Gui-Ying Dong1 Fu-Jun Yin2
Sheng-Chun Wang1
•
•
•
•
Received: 10 April 2016 / Accepted: 1 June 2016
Ó Springer International Publishing Switzerland 2016
Abstract Four Ag(I) coordination polymers, formulated
as [Ag(L1)(tpa)0.5 n
(1), {[Ag(L2)(ndc)0.5]Á0.5H2ndc}n
(2), [Ag(L3)0.5(ndc)0.5 n
O–HÁÁÁO hydrogen bonding and pÁÁÁp interactions to afford
a 2D supramolecular structure. The photoluminescence
spectra and photocatalytic properties of these complexes
for degradation of methylene blue and methyl orange are
reported.
]
]
(3) and {[Ag(L3)]ÁH3bptc}n (4)
(L1= 4,40-bis(pyrazole-1-ylmethyl)-biphenyl, L2 = 4,40-
bis(3,5-dimethylpyrazol-1-ylmethyl)-biphenyl, L3 = 1,4-
bis(3,5-dimethylpyrazol-1-ylmethyl)benzene,
H2tpa =
terephthalic acid, H2ndc = 2,6-naphthalenedicarboxylic
acid, H4bptc = 3,30,4,40-biphenyltetracarboxylic acid),
have been hydrothermally synthesized and structurally
characterized. Complex 1 features the rare binodal (4,4)-
connected 2D 4,4L10 topological network with a point
symbol of {32Á4.62Á7}2{32Á62Á72}. Complex 2 has a folded
ladder-like chain structure, which is further extended into a
3D supramolecular network via O–HÁÁÁO hydrogen bonding
and pÁÁÁp stacking interactions. Complexes 3 and 4 both
possess 1D zigzag chain structures. Complex 3 is further
extended into a binodal (3,4)-connected network with the
point symbol of {4.84Á10}{62Á82}2 by AgÁÁÁO weak inter-
actions, while complex 4 is further connected through
Introduction
The crystal engineering of supramolecular architectures
based on metal and mixed organic building blocks has
attracted much attention, owing to their fascinating net-
work topologies, as well as potential applications in various
fields such as catalysis [1], luminescence [2], gas storage
[3], molecular magnetism [4] and ion exchange [5]. In
contrast to other transition metals, Ag(I) has a tendency to
display highly versatile and irregular coordination numbers
and geometries (linear, trigonal, tetrahedral, square planar
and square pyramidal) because of its stable d10 closed-shell
electronic configuration. This in turn results in a wide
variety of sophisticated coordination architectures, includ-
ing grids [6], helicates [7], cyclic helicates [8] and clusters
[9]. In addition, Ag(I) coordination polymers (CPs) often
show AgÁÁÁAg [10], AgÁÁÁp [11], AgÁÁÁN [12] and AgÁÁÁO
[13] interactions, as well as noncovalent intermolecular
interactions such as hydrogen bonding [14] and pÁÁÁp
interactions [15], as well as exhibiting high-dimensional
structures and interesting optoelectronic properties. How-
ever, it is still difficult to control the final supramolecular
architectures because of various parameters such as the
selection of metals with different coordination geometries
[16], the nature of the ligands used [17], the metal–ligand
ratio [18], solvent system [19], pH of the reaction [20] and
temperature [21].
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-016-0071-2) contains supplementary
material, which is available to authorized users.
& Gui-Ying Dong
tsdgying@126.com
& Sheng-Chun Wang
tswlhx@126.com
1
College of Chemical Engineering, Hebei Key Laboratory for
Environment Photocatalytic and Electrocatalytic Materials,
North China University of Science and Technology,
Tangshan 063009, Hebei, People’s Republic of China
2
Jiangsu Marine Resources Development Research Institute,
Huaihai Institute of Technology,
Lianyungang 222005, Jiangsu, People’s Republic of China
123

Transition Met Chem
The synthetic strategy of mixing both N-donor and
polycarboxylate ligands has been proved to be a fruitful
approach for the construction of CPs with intriguing mul-
tidimensional structures. Polycarboxylates such as tereph-
thalic acid (H2tpa), 2,6-naphthalenedicarboxylic acid
(H2ndc) and 3,30,4,40-biphenyltetracarboxylic acid (H4
bptc) are often used as multifunctional organic ligands, not
only because of their various coordination modes, which is
beneficial for the construction of CPs [22], but also because
of their ability to act as hydrogen bond acceptors and
donors in the assembly of supramolecular structures [23].
In recent years, bis(pyrazoles), as an important family of
semirigid N-donor ligands, have attracted great interest
[24, 25]. A rigid phenyl center linking two coordinating
groups via flexible methylene (–CH2–) linkers confers on
these ligands both flexibility and rigidity, leading to dif-
ferent conformations and coordination modes in a variety
of supramolecular coordination complexes. Moreover, the
pyrazole rings and larger conjugated p systems facilitate
both hydrogen bonding and pÁÁÁp stacking interactions. For
example, Shi’s group has synthesized a variety of transition
metal (Cu, Zn, Ag, Cd) CPs based on p-bis[(1-pyra-
zolyl)methyl] benzene ligands [26]. To the best of our
knowledge, however, 4,40-bis(pyrazole-1-ylmethyl)-biphe-
nyl (L1), 4,40-bis(3,5-dimethylpyrazol-1-ylmethyl)-biphe-
nyl (L2) and 1,4-bis(3,5-dimethylpyrazol-1-ylmethyl)
benzene (L3), as semirigid bis(pyrazolyl) ligands, have
been little used to prepare Ag(I) CPs generated from
mixed-ligand systems with interesting structures and
functional properties, in particular photocatalytic proper-
ties. Therefore, in order to further study the structures and
photocatalytic properties of ternary mixed Ag(I) CPs, we
selected these compounds as N-donor co-ligands.
Scheme 1 Three semirigid bis(pyrazole) ligands in this work
were recorded on a Perkin-Elmer automatic analyzer. IR
spectra (KBr pellets) were obtained on a Nicolet IR Avatar
360 spectrophotometer in the range of 4000–400 cm-1
.
Thermogravimetric analyses experiments (TGA) were
performed on a Netzsch TG 209 thermal analyzer under an
N2 atmosphere with a heating rate of 10 °C/min. Powder
X-ray diffraction (PXRD) patterns were recorded with a
D/MAX 2500PC diffractometer at 40 kV, 100 mA with
Herein, we report four silver(I) coordination polymers
derived from semirigid bis(pyrazolyl) ligands: [Ag(L1)
(tpa)0.5]n (1), {[Ag(L2)(ndc)0.5]Á0.5H2ndc}n (2), [Ag(L3)0.5
(ndc)0.5]n (3) and {[Ag(L3)]ÁH3bptc}n (4). All four com-
plexes were characterized by elemental analysis, IR spec-
troscopy, thermogravimetric analyses (TGA) and powder
X-ray diffraction (PXRD). Furthermore, the photolumi-
nescence and photocatalytic properties of these complexes
are presented.
˚
Cu–Ka radiation (k = 1.5418 A). Solid-state fluorescence
spectra were obtained with a Hitachi F-7000 fluorescence
spectrophotometer at room temperature. The solid-state
UV–Vis diffuse reflectance spectra were measured using a
UV–Vis spectrophotometer, and a BaSO4 plate was used as
the reflectance standard.
Synthesis of complex 1
A mixture of AgNO3 (17.0 mg, 0.1 mmol), L1 (31.4 mg,
0.1 mmol), H2tpa (33.2 mg, 0.2 mmol) and distilled water
(10 mL) was stirred for 30 min and then transferred to a
25-mL Teflon-lined container and kept under autogenous
pressure at 120 °C for 3 days. After cooling to room
temperature at a rate of 10 °C/h, colorless block single
crystals of complex 1, [Ag(L1)(tpa)0.5]n, were obtained
with a yield of 61.4 % (based on Ag). Anal. Calcd. for
C24H20AgN4O2 (Fw = 504.31): C, 57.2; H, 4.0; N,
11.1 %. Found: C, 57.3; H, 4.0; N, 11.0 %. IR (KBr,
Experimental
Materials and measurements
The free ligands L1, L2 and L3 (Scheme 1) were synthe-
sized according to the reported methods [27, 28]. All other
chemicals were commercially available and used without
further purification. Elemental analyses for C, H and N
123

Transition Met Chem
cm-1): 1599 s, 1518 m, 1400 s, 1281 m, 1093 m, 1055 m,
758 s, 744 m, 623 w.
addition, control experiments for MB or MO degradation
were performed under the same conditions without any
catalyst. The characteristic peaks for methylene blue
(664 nm) and methyl orange (506 nm) were used to monitor
the photocatalytic decomposition process.
Synthesis of complex 2
The synthesis of complex 2 was analogous to that of
complex 1, except that L2 (37.0 mg, 0.1 mmol) and H2ndc
(21.6 mg, 0.1 mmol) were used instead of L1 and H2tpa.
Colorless block single crystals of complex 2,
{[Ag(L2)(ndc)0.5]Á0.5H2ndc}n, were acquired in 50.2 %
yield based on AgNO3. Calcd. for C36H33AgN4O4
(Fw = 693.53): C, 62.4; H, 4.8; N, 8.1 %. Found: C, 62.3;
H, 4.7; N, 8.2 %. IR (KBr, cm-1): 1696 s, 1604 s, 1566 s,
1542 m, 1492 m, 1385 s, 1351 m, 1281 m, 1193 w,
1038 w, 782 s, 481 w.
X-ray crystallography
Crystallographic data for complexes 1–4 were collected on
an Agilent SuperNova Dual diffractometer equipped with
˚
mirror monochromatic Mo–Ka (k = 0.71073 A) or Cu–Ka
˚
(k = 1.54184 A) radiation by using a x scan mode at
293(2) K, except for complex 2 which was analyzed at
100 K. CrysAlisPRO software was used to collect, index,
scale and apply analytical absorption corrections based on
faces of the crystal [29]. All of the structures were solved
by direct methods and refined on F2 by full-matrix least
squares methods using SHELXL-97 [30]. All non-hydro-
gen atoms were found from the Fourier difference maps
and refined anisotropically. Crystallographic crystal data
and structure processing parameters for the complexes are
summarized in Table 1. Selected bond lengths and angles
are listed in Table 2.
Synthesis of complex 3
The preparation of complex 3 was analogous to that of
complex 2, except that L2 was substituted by L3 (29.4 mg,
0.1 mmol). Colorless block single crystals of complex 3,
[Ag(L3)0.5(ndc)0.5]n, were isolated in 56.2 % yield based
on AgNO3. Calcd. for C15H14AgN2O2 (Fw = 362.15): C,
49.7; H, 3.9; N, 7.7 %. Found: C, 49.7; H, 3.8; N, 7.8 %.
IR (KBr, cm-1): 1615 s, 1568 s, 1401 s, 1341 s, 1290 m,
1183 m, 907 m, 776 s, 568 w, 479 w.
Results and discussion
Synthetic and spectral aspects
Synthesis of complex 4
Silver(I) CPs generated from mixed-ligand systems can
display a wide range of multidimensional structures and
interesting properties [7–10]. In the present work,
hydrothermal synthesis using different ligand combinations
yielded new complexes, whose crystal structures were
determined by X-ray diffraction analysis. The elemental
analyses of the complexes 1–4 are in good agreement with
the theoretical requirements of their compositions, and these
complexes possess different polydimensional frameworks.
All four complexes are air-stable and insoluble in
common solvents. In order to check their phase purities,
their powder X-ray diffraction (PXRD) patterns were
measured at room temperature (Fig. S1). The measured and
simulated powder patterns are in good agreement, con-
firming the phase purities of the bulk materials.
The preparation of complex 4 was analogous to that of
complex 3, except that H2ndc was substituted by H4bptc
(33.0 mg, 0.1 mmol). Colorless block single crystals of
complex 4, {[Ag(L3)]ÁH3bptc}n, were obtained in 50.2 %
yield based on AgNO3. Calcd. for C34H31AgN4O8
(Fw = 731.50): C, 55.8; H, 4.2; N, 7.7 %. Found: C, 55.9;
H, 4.1; N, 7.6 %. IR (KBr, cm-1): 1702 s, 1595 m, 1553 s,
1417 m, 1353 m, 1290 m, 1147 w, 874 w, 760 s, 644 m,
467 w.
Photocatalytic experiments
The photocatalytic performance of each complex for the
decomposition of MB or MO was measured by the following
procedure: A 0.01 mol crystal sample of each title complex
was mixed with 150 mL of MB or MO aqueous solution
(20.0 mg L-1) and then magnetically stirred for about
30 min in the dark to obtain uniform working suspension.
The suspension was then irradiated using a 500 W high-
pressure mercury lamp, while continuously stirring with a
magnetic stirrer. Aliquots (3 mL) of the suspension were
taken out at given intervals, separated through centrifugation
and then analyzed by UV–visible spectrophotometry. In
In the IR spectra of complexes 1–4, the medium inten-
sity bands from 1518 to 1568 cm-1 are assigned to the
m(C=N) stretching modes of the pyrazole rings. The mas
(COOH) bands of the uncoordinated carboxyl groups in
complexes 2 and 4 were observed at 1696 and 1702 cm-1
.
The asymmetric and symmetric stretching vibrations of the
carboxylate groups were observed at 1599 and 1400 cm-1
for 1, 1604 and 1385 cm-1 for 2, 1615 and 1401 cm-1 for
3 and 1595 and 1417 cm-1 for 4. The values of
123

Transition Met Chem
Table 1 Crystallographic data for complexes 1–4
Complex
1
2
3
4
Empirical formula
Formula weight
C24H20AgN4O2
504.31
C36H33AgN4O4
693.53
C15H14AgN2O2
362.15
C34H31AgN4O8
731.50
˚
Wavelength/A
0.71073
Triclinic
P¯ı
0.71073
Triclinic
P¯ı
0.71073
Triclinic
P¯ı
0.71073
Crystal system
Space group
Monoclinic
P2/c
Unit cell dimensions
˚
a/A
8.4155(8)
11.2864(8)
11.9091(13)
82.8370(9)
81.7250(10)
71.1400(10)
1055.56(17)
2
10.6438(3)
11.0943(4)
14.2944(5)
110.907(3)
92.143(3)
97.697(3)
1555.99(9)
2
7.5054(11)
8.6213(12)
12.0214(17)
103.249(2)
91.193(2)
110.792(2)
703.37(17)
2
13.6781(13)
7.3157(7)
15.9658(16)
90
˚
b/A
˚
c/A
a/°
b/°
c/°
96.3110(10)
90
3
˚
V/A
1587.9(3)
2
Z
Dc/g cm-3
1.587
1.480
1.710
1.530
F(000)
510
712
362
748
Crystal size/mm
h Range/°
Reflections collected
Independent reflections
Rint
0.22 9 0.19 9 0.19
2.47–27.57
9811
0.25 9 0.18 9 0.17
3.32–76.03
17,711
0.29 9 0.27 9 0.25
2.61–27.56
6478
0.23 9 0.22 9 0.20
2.57–27.55
14,120
4795
6315
3197
3643
0.0218
0.0321
0.0245
0.0412
Absorption coefficient/mm-1
0.984
5.574
1.435
0.694
T/K
293(2)
100
293(2)
293(2)
Goodness of fit on F
Final R, wR2 [I [ 2r(I)]
1.020
1.106
1.011
1.041
R1 = 0.0306
wR2 = 0.0709
R1 = 0.0370
wR2 = 0.0749
0.558, -0.699
R1 = 0.0337
wR2 = 0.0916
R1 = 0.0376
wR2 = 0.0942
0.593, -1.080
R1 = 0.0370
wR2 = 0.0786
R1 = 0.0565
wR2 = 0.0878
0.526, -0.374
R1 = 0.0414
wR2 = 0.1036
R1 = 0.0709
wR2 = 0.1168
0.661, -0.395
R (all data)
Largest diff. peak and hole
Dt[tas(COO)–ts(COO)] indicate the presence of bridging
(199 cm-1 for 1) and monodentate (219 cm-1 for 2,
214 cm-1 for 3) carboxylate groups [31].
Ag1 atom, forming a distorted square pyramidal geometry
with a s5 value of 0.18 (for perfect square pyramidal
geometry, s5 = 0). Remarkably, the Ag1–Ag1A distance
˚
˚
of 2.8483(5) A is comparable to the value of 2.89 A in
Crystal structure of complex 1
metallic silver and in the range expected for the sum of the
˚
covalent radii of two silver atoms (2.90 A) [32], but sig-
Single-crystal X-ray diffraction analysis revealed that
complex 1 crystallizes in the triclinic P¯ı space group and
exhibits a 2D coordination network. The asymmetric unit
includes an independent Ag(I) center, one L1 ligand and
half of a tpa ligand. As shown in Fig. 1a, each Ag center is
surrounded by atoms O1A and O2 from two tpa ligands
nificantly lower than twice the van der Waals radii of silver
˚
ions (3.44 A) [33], indicating the existence of an argen-
tophilic interaction. This argentophilic interaction is simi-
lar to those found in [Ag6(p-mpspa)6]6- (2.8036(6) A) (H2-
˚
p-mpspa = 3-(4-methoxyphenyl)-2-sulfanylpropenoic acid)
˚
˚
[10], [Sr2Ag4(HL)(H2O)14]Á2H2O (2.840 A and 2.850 A)
(H3L = 5-sulfo-salicylic acid) [34] and (Ag2L2)Á5AgCF3-
˚
(Ag1–O1A 2.276(2), Ag1–O2 2.419(2) A, symmetry code:
˚
A: -x, -y ? 1, -z ? 2), plus atoms N2B and N3 from
˚
two L1 ligands (Ag1–N2B 2.324(2), Ag1–N3 2.375(2) A,
CO2Á5DMSO (2.742(8) A) (H2L2 = 9-(penta-1,4-diyn-3-
ylidene)-9H-fluorene) [35]. The bond angles around Ag(1)
symmetry code: B: -x, -y ? 2, -z ? 1) and the adjacent
range from 71.05(4) to 126.33(7)°.
123

Transition Met Chem
{32Á4.62Á7}2{32Á62Á72} (Fig. 1c). To the best of our
knowledge, although the present topological type has been
theoretically predicted, this is the first example of a CP
with the 4,4L10 topology.
˚
Table 2 Selected bond lengths (A) and angles (°) for complexes 1–4
Parameter
Value
Parameter
Value
1
Ag1–O1A
Ag1–N3
2.276(2)
2.375(2)
2.8483(5)
103.68(7)
137.06(7)
84.14(7)
Ag1–N2B
Ag1–O2
2.324(2)
2.419(2)
Crystal structure of complex 2
Ag1–Ag1A
O1A–Ag1–N3
O1A–Ag1–O2
N3–Ag1–O2
N2B–Ag1–N3
100.65(8)
92.19(7)
126.33(7)
147.94(5)
82.74(5)
X-ray crystallographic analysis revealed that complex 2
crystallizes in the triclinic crystal system and P¯ı space
group. The structure contains one crystallographically
independent Ag(I) center, one L2 ligand, half of a com-
pletely deprotonated ndc ligand as well as half of a lattice
ndc ligand in the asymmetric unit. The tricoordinate Ag1
atoms have a slightly distorted T-shaped geometry
(Fig. 2a), provided by atom O2 of the l2-g1,g1-ndc ligand
O1A–Ag1–N2B
O1A–Ag1–N2B
N3–Ag1–Ag1A
O1A–Ag1–Ag1A
N2B–Ag1–Ag1A 100.28(6)
O2–Ag1–Ag1A
71.05(4)
2
Ag1–N4A
Ag1–O2
2.157(2)
2.576(2)
162.86(9)
Ag1–N1
2.162(2)
99.03(7)
97.70(8)
N1–Ag1–O2
N4A–Ag1–O2
˚
(Ag1–O2 2.576(2) A), plus atoms the N1 and N4A from
N4A–Ag1–N1
two different l2-L2 ligands with Ag1–N1 and Ag1–N4A
3
4
˚
distances of 2.162(2) and 2.157(2) A, respectively. The
Ag1–N2
2.104(3)
Ag1–O2
Ag1–N2
2.113(2)
2.099(3)
values of the Ag–N and Ag–O bond lengths are in good
agreement with those of similar Ag(I) complexes [36, 37].
In complex 2, for each of the trans-L2 ligands, the
dihedral angle between parazole rings is 8.76(10)°. These
bridge adjacent Ag atoms to form an infinite 1D [Ag(L2)]n
zigzag chain with a non-bonding AgÁÁÁAg distance of
N2–Ag1–O2
174.85(10)
Ag1–N2A
2.099(3)
N2A–Ag1–O2
175.94(14)
Symmetry codes: for 1: A : -x, -y ? 1, -z ? 2; B: -x, -y ? 2,
-z ? 1; for 2: A: x, y - 1, z; for 4: A: – x ? 2, y, z ? 3/2
˚
11.0943(5) A (Fig. S3a). The completely deprotonated l2-
g1,g1-ndc ligands link adjacent Ag atoms belonging to
distinct [Ag(L2)]n zigzag chains to form a folded ladder-
like chain (Fig. S3b). The chains are further packed into a
2D supramolecular layer via O–HÁÁÁO hydrogen bonding
interactions between O3 and O1 from free and l2-g1,g1-
ndc ligands (O3ÁÁÁO1 2.484(3)) (Fig. 2b). The adjacent 2D
layers are further connected by two kinds of pÁÁÁp stacking
interactions between parazole rings from distinct L2
In complex 1, each completely deprotonated l4-
g1,g1,g1,g1-tpa ligand coordinates to four Ag(I) atoms
through four carboxyl oxygen atoms, forming a 1D
bimetallic [Ag2(tpa)]n chain (Fig. S2a). Simultaneously,
two carboxylate groups clamp a pair of Ag(I) atoms to
form ligand-supported argentophilic AgÁÁÁAg interactions.
Each trans-L1 ligand, in which the dihedral angle between
the two parazole planes is 82.89(13)°, acts as l2-bridging
linker bridging two Ag atoms to form a dinuclear
[Ag2(L1)2] secondary building unit (SBU) with a non-
ligands with centroid-to-centroid distances of 3.5865(19)
˚
and 3.6144(19) A, respectively, resulting in
supramolecular network (Fig. 2c).
a 3D
˚
bonding AgÁÁÁAg distance of 13.288 A. Interestingly,
Crystal structure of complex 3
adjacent [Ag2(L1)2] SBUs are linked by two closer Ag
atoms with argentophilic AgÁÁÁAg interactions to form
infinite 1D loop-and-chain structures (Fig. S2b). The
interlaced connection of the 1D chains of Ag(I)/tpa and
Ag(I)/L1 units gives rise to a 2D framework showing a
Complex 3 crystallizes in the triclinic space group P¯ı. One
Ag(I) center, half a L3 ligand and half a ndc ligand are located
in the asymmetric unit. As shown in Fig. 3a, the central Ag1 is
coordinated by atom N2 of the l2-L3 ligand (Ag1–N2
˚
large window with dimensions of 11.2864 9 15.3522 A,
˚
2.104(3) A) and atom O2 from the ndc ligand (Ag1–O2
˚
2.113(2) A) plus a weakly coordinated O2C atom from
involving shared Ag atoms (Fig. 1b). A better insight into
the nature of this intricate framework was acquired by
using TOPOS 4.0 software. The L1 ligands can be sim-
plified as linear connectors; the Ag centers are considered
as four-connected nodes, connected by two Ag atoms and
two tpa ligands, while the tpa ligands linking four Ag
atoms are viewed as four-connected nodes. This combi-
nation of nodes and connectors suggests a binodal (4,4)-
connected 4,4L10 network with a point symbol of
˚
anotherndcligand(Ag1–O2C2.733(3) A, symmetrycode:C:
-x ? 1, -y ? 1, -z ? 1). The N2–Ag1–O2 band angle is
174.84(10)°, consistent with a [2 ? 1] T-shaped coordination
˚
geometry. The length of the Ag1–O2C bond 2.733(3) A is
significantly longer than normal, but shorter than the sum of
˚
the van der Waals radii of Ag and O (3.24 A) and so can be
regarded as a AgÁÁÁO interaction [38]. The Ag1–N2 and Ag1–
O2 bond lengths fall in the expected ranges.
123

Transition Met Chem
Fig. 1 a Coordination
environment of Ag(I) center in
complex 1 with 30 % thermal
ellipsoids. Hydrogen atoms are
omitted for clarity (symmetry
code: A: –x, –y ? 1, –z ? 2; B:
–x, –y ? 2, –z ? 1; C: –x, –y,
–z ? 2); b view of 2D
framework of 1; c simplified
view of the 2D binodal (4,4)-
connected 4,4L10 topology of 1
˚
Both the completely deprotonated ndc ligands and the
trans-L3 ligand with two parallel parazole rings bridge
adjacent Ag(I) atoms to give an infinite 1D [Ag2
(L3)(ndc)]n zigzag chain (Fig. S4a), where the nonbonding
AgÁÁÁAg distances across the L and ndc ligands are
10.1264(12) and 13.2111(18) A, respectively. As shown in
Fig. 3b, adjacent 1D zigzag chains are extended to a 2D
supramolecular network showing a large window with
˚
dimensions of 16.6542(14) 9 19.1013(16) A by means of
AgÁÁÁO interactions. As for the topological geometry, the
123

Transition Met Chem
Fig. 2 a Coordination
environment of Ag(I) center in
complex 2 with 30 % thermal
ellipsoids. Hydrogen atoms are
omitted for clarity (symmetry
codes: A: x, y – 1, z; B: –x ? 2,
–y ? 1, –z ? 1); b view of the
2D supramolecular layer formed
by strong O–HÁÁÁO hydrogen
bonding interactions in 2;
c view of the 3D supramolecular
framework formed by pÁÁÁp
stacking and hydrogen bonding
interactions of 2
Ag centers and ndc ligands can be considered as four-
connected nodes and the L3 ligands can be simplified as
linear connectors. The 2D framework can then be simpli-
fied as a new binodal 3,4-connected topology with the point
symbol of {4Á84Á10}{62Á82}2 (Fig. 3c).
Ag1 center is linearly coordinated by atoms N2 and N2A
˚
from two neighboring L3 ligands (Ag1–N2 2.099(3) A,
˚
Ag1–N2A 2.099(3) A, symmetry code: A: –x ? 2, –y ? 1,
–z ? 1). The values of the Ag–N and Ag–O bond lengths
are in good agreement with those observed in similar
Ag(I) complexes.
Crystal structure of complex 4
Each L3 ligand adopts trans-conformation, with two
parallel parazole rings bridging the adjacent Ag(I) atoms
into an infinite 1D [Ag(L3)]n zigzag chain, in which the
nonbonding AgÁÁÁAg distance across two distinct L3
ligands is 8.2160(8) (Fig. S5a). Each lattice bptc ligand
Complex 4 crystallizes in the monoclinic space group P2/c.
One Ag(I) center, one L3 ligand and one lattice bptc ligand
are located in the asymmetric unit. As shown in Fig. 4a, the
123

Transition Met Chem
Fig. 3 a Coordination
environment of Ag(I) center in
complex 3 with 30 % thermal
ellipsoids. Hydrogen atoms are
omitted for clarity; b view of 2D
supramolecular network of 3
formed by AgÁÁÁO interactions;
c simplified view of the 2D
binodal 3,4-connected new
topology of 3
123

Transition Met Chem
Fig. 4 a Coordination
environment of Ag(I) center in
complex 4 with 30 % thermal
ellipsoids. Hydrogen atoms are
omitted for clarity; b view of 2D
supramolecular layer formed by
pÁÁÁp stacking interactions and
hydrogen bonding interactions
of 4
connects another two into a 1D linear chain by O–HÁÁÁO
temperature to 800 °C at a heating rate of 10 °C/min under
a nitrogen atmosphere. As shown in Fig. 5, the TGA
analysis revealed that these complexes were quite stable up
to 200 °C. Complex 1 revealed a two-step weight loss
process. The first step occurred from 226 to 325 °C with a
weight loss of 61.5 %, which can be ascribed to the loss of
L1 ligand (calcd: 62.3 %). The second step was observed
in the range from 371 to 503 °C, corresponding to the
release of tpa ligand and resulting in the complete
decomposition of the complex with 23.7 % residual weight
corresponding to Ag2O (calcd: 23.0 %). In complexes 2–4,
only one weight loss of 82.4 % from 204 to 640 °C (calcd:
83.3 %) for 2, 67.6 % from 216 to 645 °C (calcd: 68.0 %)
for 3 and 84.7 % from 210 to 519 °C (calcd: 84.2 %) for 4
was observed, accompanying the loss of total organic
ligands. The final residues of all the title complexes cor-
respond to Ag2O.
hydrogen bonding interactions between O1 and O1B from
˚
different bptc ligands (O1ÁÁÁO1B 2.449 (3) A) (Fig. S5b).
The two kinds of chains are further connected through pÁÁÁp
interactions between the parazole rings of L3 and benzene
rings of ndc ligands with a centroid-to-centroid distance of
˚
3.6511(19) A, yielding
(Fig. 4b).
a 2D supramolecular layer
Thermal properties
To investigate the thermal stabilities of the complexes,
thermogravimetric analysis (TGA) was performed at room
Photoluminescence properties
Hybrid CPs, especially those with d10 metal centers, have
been widely found to present photoluminescence properties
and may find applications as photoluminescent materials
[39]. The photoluminescence properties of the Ag(I) com-
plexes 1–4 as well as the corresponding free ligands (L1,
L2 and L3) in the solid state have been investigated at
room temperature (Fig. 6). The free ligands L1, L2 and L3
show intense emission bands with maxima at 330, 421 and
288 nm upon excitation at 245, 350 and 250 nm, respec-
tively, which may be attributed to p* ? p or p* ? n
Fig. 5 TGA curves of complexes 1–4
123

Transition Met Chem
Fig. 7 Diffuse reflectance spectra of Kubelka–Munk function versus
energy of complexes 1–4
Fig. 6 Solid-state photoluminescence spectra of complexes 1–4 as
well as the corresponding ligands (L1, L2 and L3)
transitions [40]. The emission peaks of the complexes
occur at 372 nm (kex = 300 nm) for 1, 489 nm
(kex = 250 nm) for 2, 400 nm (kex = 300 nm) for 3 and
380 nm (kex = 275 nm) for 4, which are red-shifted by
42 nm (1), 68 nm (2), 112 nm (3) and 92 nm (4) compared
with the corresponding free ligands. These emissions may
be assigned to ligand-to-metal charge transfer (LMCT)
transitions [41].
Optical and photocatalytic properties
The UV–Vis spectra of the complexes were recorded in the
crystalline state at room temperature. As depicted in
Fig. S6, all spectra show absorption components ascribed
to p ? p* transitions of the ligands, while the main UV
absorption bands at 285, 280, 277 and 292 nm for com-
plexes 1–4, respectively, can be attributed to LMCT tran-
sitions [42]. In order to investigate the semiconductor
properties of the complexes, their diffuse reflectance data
were transformed using the Kubelka–Munk function to
obtain their band gaps (Eg). As shown in Fig. 7, the Eg
values evaluated from the steep absorption edge are
3.23 eV for 1, 3.24 eV for 2, 3.31 eV for 3 and 3.35 eV for
4. These band gap values suggest that complexes 1–4 may
be responsive to UV light and so have potential to mediate
photocatalytic reactions.
Photocatalytic degeneration of organic pollutants has
become one of the most green and efficient technologies
for environmental remediation, and much effort has been
devoted to studying CPs as photocatalysts for the degra-
dation of organic dyes. Methyl orange (MO) and methylene
blue (MB) provide two examples of poorly biodegradable
dyes, as found in wastewater of the textile industry [43].
Therefore, we selected MO and MB as model pollutants in
order to evaluate the photocatalytic activities of complexes
Fig. 8 Absorption spectra of the MB (a) and MO (b) solution during
decomposition reaction under UV irradiation in the presence of
complex 1
123

Transition Met Chem
1–4. As shown in Figs. 8, S7 and S8, little change in the
degradation of MB or MO was observed in the control
experiments. In contrast, the absorption intensities of MB
or MO reduced gradually with increasing irradiation times
when using each of these complexes as a photocatalyst. As
shown in Fig. 9a, the degradation efficiency of MB [9]
increased from 11.1 % (without any catalyst) to 92.8 % for
complex 1, 59.7 % for complex 2, 72.6 % for complex 3
and 72.5 % for complex 4 after 120 min of irradiation.
Similarly, in Fig. 9b, the degradation efficiency of MO
increased from 10.1 % (without any catalyst) to 84.8 % for
complex 1, 56.7 % for complex 2, 77.6 % for complex 3
and 68.6 % for complex 4 after 120 min of irradiation. It is
evident that the photodegradation performances of com-
plex 4 for both MB and MO under UV light are better than
those of complexes 1–3. An additional control experiment
using an equimolar amount of AgNO3 under the same
conditions showed no observable photocatalytic activity.
It is noteworthy that the photocatalytic efficiencies of
the present complexes were higher than those obtained
with other CPs under UV irradiation as reported recently.
For example, Ma’s group has reported three complexes,
which exhibited photodegradation activities for MB under
UV light, with degradation ratios for MB after 150 min of
39, 27 and 58 %, which are lower values than those of
complexes 1–4 [44]. Moreover, the photocatalytic activi-
ties of the present complexes toward MO are higher than
those of complexes reported by Wang’s group, where the
degradation ratios for MO were 27.8, 29.6, 75.8 and
76.6 % [45]. Returning to the present complexes, their
PXRD patterns were measured after the catalytic experi-
ments and found to be nearly identical to those of the
original complexes (Fig. S1), implying good stability in the
photocatalytic degradation experiments.
Although the value of the band gap Eg is an effective
indicator of the photocatalytic properties, the structures of
the complexes are also important [46–48]. Thus, complex 1
is expected to be the most active of the complexes, since it
has the smallest band gap. Besides, the 2D structure of
complex 1 shows a large open channel with dimensions of
˚
15.7945(8) 9 12.1963(8) A, which should be conducive to
the transport of excited holes/electrons to its surface.
Although the band gap of complex 2 is not the largest, it
has the lowest degradation rates for MB and MO, which
may result from its dense 3D supramolecular structure.
Because our photocatalytic reaction is heterogeneous, we
speculate that multihole catalysts with more extended
networks may be beneficial to improve catalyst activity.
Conclusion
In this work, we have assembled four Ag(I) CPs from
carboxylic acid and semirigid bis(pyrazole) ligands under
hydrothermal conditions. The polycarboxylate ligands,
exhibiting rich coordination modes, have great influence on
the structural diversities of these complexes, while the
semirigid bis(pyrazole) ligands with different conforma-
tions and coordination modes help to shape the network
structures of these complexes. Under UV irradiation, these
complexes exhibited high catalytic activities for the pho-
todegradation of MB and MO, implying that they may be
potential catalysts for the photodecomposition of organic
pollutants in industrial wastewater.
Supplementary materials
CCDC 1427868, 1465080, 1465081 and 1465082 con-
tain the supplementary crystallographic data for complexes
1–4. These data can be obtained free of charge via
Fig. 9 Decomposition of MB (a) and MO (b) solution in a
photocatalytic process
123

Transition Met Chem
20. Su Z, Fan J, Okamura TA, Sun WY, Ueyama N (2010) Cryst
Growth Des 10:3515–3521
21. Zheng B, Dong H, Bai JF, Li YZ, Li SH, Scheer M (2008) J Am
Chem Soc 130:7778–7779
22. Hu JM, Blatov VA, Yu B, Hecke KV, Cui GH (2016) Dalton
Trans 45:2426–2429
http://www.ccdc.cam.ac.uk/deposit 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.
´
23. Dias SSP, Andre V, Kłak J, Duarte MT, Kirillov AM (2014)
Cryst Growth Des 14:3398–3407
Acknowledgments The project was supported by the National Nat-
ural Science Foundation of China (51474086), Natural Science
Foundation—Steel and Iron Foundation of Hebei Province
(B2015209299).
24. Christer BA, John D, Meg EF (2006) CrystEngComm 8:586–588
25. Hazel F, Ian ST, Michael DW (2011) CrystEngComm
13:1432–1440
26. Wang XY, Liu SQ, Wei XL, Zhang CY, Song G, Bai FY, Xing
YH, Shi Z (2012) Polyhedron 47:151–164
27. Hoskins BF, Robson R, Slizys DA (1997) J Am Chem Soc
119:2952–2953
References
1. Cui GH, He CH, Jiao CH, Geng JC, Blatov VA (2012) Crys-
tEngComm 14:4210–4216
2. Shustova NB, McCarthy BD, Dinca M (2011) J Am Chem Soc
133:20126–20129
3. Rosi NL, Eckert J, Eddaoudi M, Vodak DT, Kim J, O’Keeffe M,
Yaghi OM (2003) Science 300:1127–1129
28. Hartshorn CM, Steel PJ (1995) Aust J Chem 48:1587–1599
29. Agilent Technologies (2012) CrysAlis PRO Agilent Technolo-
gies, Yarnton, England
30. Sheldrick GM (2008) Acta Crystallogr Sect A: Found Crystallogr
64:112–122
31. Deacon GB, Phillips RJ (1980) Coord Chem Rev 33:227–250
4. Li HH, Shi W, Xu N, Zhang ZJ, Niu Z, Han T, Cheng P (2012)
Cryst Growth Des 12:2602–2612
5. Wang JC, Liu QK, Ma JP, Huang F, Dong YB (2014) Inorg
Chem 53:10791–10793
´
´
´
32. Cordero B, Gomez V, Platero-Prats AE, Reves M, Echeverrıa J,
Cremades E, Alvarez S (2008) Dalton Trans 21:2832–2838
33. Bisht KK, Kathalikkattil AC, Suresh E (2012) RSC Adv
2:8421–8428
6. Jaros SWM, Guedes da Silva MFC, Florek M, Oliveira MC,
Smolenski P, Pombeiro AJ, Kirillov AM (2014) Cryst Growth
Des 14:5408–5417
7. Stephenson A, Ward MD (2012) RSC Adv 2:10844–10853
8. Argent SP, Adams H, Riis-Johannessen T, Jeffery JC, Harding
LP, Mamula O, Ward MD (2006) Inorg Chem 45:3905–3919
9. Hao JM, Yu B, Hecke KV, Cui GH (2015) CrystEngComm
17:2279–2293
34. Li Q, Fu ML, Liu X, Guo GC, Huang JS (2006) Inorg Chem
Commun 9:767–771
35. Hau SC, Mak TC (2013) Polyhedron 64:63–72
36. Marcinkowski D, Wałe˛sa-Chorab M, Patroniak V, Kubicki M,
Ka˛dziołka G, Michalkiewicz B (2014) New J Chem 38:604–610
37. Kole GK, Chin CK, Tan GK, Vittal JJ (2013) Polyhedron
52:1440–1448
38. Yang L, Powell DR, Houser RP (2007) Dalton Trans 9:955–964
39. Sun D, Liu FJ, Huang RB, Zheng LS (2013) CrystEngComm
15:1185–1193
´
10. Barreiro E, Casas JS, Couce MD, Laguna A, Lopez-de-Luzuriaga
JM, Monge M, Lopez EMV (2013) Dalton Trans 42:5916–5923
´
11. Liang MX, Ruan CZ, Sun D, Kong XJ, Ren YP, Long LS, Zheng
LS (2014) Inorg Chem 53:897–902
40. Xu JX, Wang RY, Li YM, Gao ZY, Yao R, Wang S, Wu BL
(2012) Eur J Inorg Chem 20:3349–3360
12. Huan DH, Liu YG, Yu B, Hecke KV, Cui GH (2016) Inorg Chem
Commun 67:17–21
13. Sun D, Wei ZH, Wang DF, Zhang N, Huang RB, Zheng LS
(2011) Cryst Growth Des 11:1427–1430
41. Sarma D, Ramanujachary KV, Lofland SE, Magdaleno T,
Natarajan S (2009) Inorg Chem 48:11660–11676
42. Gong Y, Jiang PG, Wang YX, Wu T, Lin JH (2013) Dalton Trans
42:7196–7203
14. Wang XX, Liu YG, Ge M, Cui GH (2015) Chinese. J Inorg Chem
31:2065–2072
43. Wang SL, Hu FL, Zhou JY, Zhou Y, Huang Q, Lang JP (2015)
Cryst Growth Des 15:4087–4097
15. Salonen LM, Ellermann M, Diederich F (2011) Angew Chem
123:4908–4944
44. Zhang HM, Yang J, Kan WQ, Liu YY, Ma JF (2015) Cryst
Growth Des 16:265–276
16. Liu GZ, Wang JG, Wang LY (2012) CrystEngComm 14:951–960
17. Wang XX, Yu B, Hecke KV, Cui GH (2014) RSC Adv
4:61281–61289
18. Zhao XL, Zhang LL, Ma HQ, Sun D, Wang DX, Feng SY, Sun
DF (2012) RSC Adv 2:5543–5549
45. Wang XL, Gong CH, Zhang JW, Hou LL, Luan J, Liu GC (2014)
CrystEngComm 16:7745–7752
46. Hu Y, Luo F, Dong FF (2011) Chem Commun 47:761–763
47. Kan WQ, Liu B, Yang J, Liu YY, Ma JF (2012) Cryst Growth
Des 12:2288–2298
19. Li CP, Yu Q, Chen J, Du M (2010) Cryst Growth Des
10:2650–2660
48. Liu L, Ding J, Li M, Lv XF, Wu J, Hou HW, Fan YT (2014)
Dalton Trans 43:12790–12799
123