Four new silver-based complexes constructed from 3-nitrophthalic acid and pyrazine-like ligands: Syntheses, crystal structures and photodegradation activities

Article abstract of DOI:10.1016/j.poly.2017.06.028

Four Ag-based coordination polymers, Ag₄(H₂O)₂(npth)₂ (1), Ag₄(epyz)₂(npth)₂ (2), [Ag(pyz)(Hnpth)]·H₂O (3) and Ag(epyz)_0.5(Hnpth) (4) (H₂npth?=?3-nitrophthalic acid, pyz?=?pyrazine, epyz?=?2,3,5,6-tetramethylpyrazine), have been synthesized by ultrasonic or hydrothermal reactions of Ag(I) salts with H₂npth and various pyrazine derivatives ligands. Compound 1 presents a 2D 4⁴-sql network with Ag₄ units, and compound 2 features novel cage-like Ag₈ SBUs (secondary building unit), which are linked by epyz ligands to form a 3D framework. Compound 3 shows a 1D chain and compound 4 exhibits a 2D coordination polymer construction. The photocatalytic properties for the degradation of organic dye molecules have been examined, and the experiments show that compound 3 has a good degradation effect to Rhodamine B.

Full text of DOI:10.1016/j.poly.2017.06.028

Accepted Manuscript
Four new silver-based complexes constructed from 3-nitrophthalic acid and
pyrazine-like ligands: syntheses, crystal structures and photodegradation activ-
ities
Yuan-Yuan Yang, Lin-Xia Zhou, Yue-Qing Zheng, Hong-Lin Zhu
PII:
S0277-5387(17)30446-1
DOI:
http://dx.doi.org/10.1016/j.poly.2017.06.028
POLY 12709
Reference:
Polyhedron
To appear in:
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Revised Date:
Accepted Date:
2 May 2017
1 June 2017
2 June 2017
Please cite this article as: Y-Y. Yang, L-X. Zhou, Y-Q. Zheng, H-L. Zhu, Four new silver-based complexes
constructed from 3-nitrophthalic acid and pyrazine-like ligands: syntheses, crystal structures and photodegradation
activities, Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.06.028
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Four new silver-based complexes constructed
from 3-nitrophthalic acid and pyrazine-like
ligands: syntheses, crystal structures and
photodegradation activities
Yuan–Yuan Yang, Lin-Xia Zhou, Yue–Qing Zheng*, Hong-Lin Zhu
Joint Laboratory for Environmental Test and Photocatalytic Research of Ningbo
University-Zhejiang Zhonghao Applied Engineering Technology Institute Co., Ltd.
Research Center of Applied Solid State Chemistry, Chemistry Institute for Synthesis and
Green Application, Ningbo University, Ningbo 315211, P.R. China
* Correspondence author:
Prof. Dr. Yue-Qing Zheng
Telefax: Int. +86-0574-87600792
E-mail: zhengyueqing@nbu.edu.cn

Abstract. Four Ag-based coordination polymers, Ag4(H2O)2(npth)2 (1), Ag4(epyz)2(npth)2
(2), [Ag(pyz)(Hnpth)]·H2O (3) and Ag(epyz)0.5(Hnpth) (4) (H2npth = 3-nitrophthalic acid, pyz
= pyrazine, epyz = 2,3,5,6-tetramethylpyrazine), have been synthesized by ultrasonic or
hydrothermal reactions of Ag(I) salts with H2npth and various pyrazine derivatives ligands.
Compound 1 presents a 2D 44-sql network with Ag4 units, and compound 2 features novel
cage-like Ag8 SBUs (secondary building unit), which are linked by epyz ligands to form a 3D
framework. Compound 3 shows a 1D chain and compound 4 exhibits a 2D coordination
polymer construction. The photocatalytic properties for the degradation of organic dye
molecules have been examined, and the experiments show that compound 3 has a good
degradation effect to Rhodamine B.
Keywords: Silver(I); Ag∙∙∙Ag interaction; Coordination polymers; Luminescence; Degradation

1. Introduction
The rational design and construction of metal-organic coordination polymers is attracting
considerable attention in the fields of crystal engineering and supramolecular chemistry [1],
due to their enormous variety of intriguing structures, topological architectures and their
potential applications in various fields, including gas storage [2], luminescence [3],
magnetism [4], antitumor/antibacterial activity [5], degradation of organic pollutants [6] and
so on. As we known, it is still a huge challenge to control the final structures of desired
crystalline products, since many factors affect the self-assembly process, such as the solvent
system, metal-ligand ratio [7], temperature, counter ions [8], pH, template and so on [9].
Hence, we can change those conditions to obtain coordination polymers with novel structures.
Among these polymers, Ag(I)-based coordination polymers have attracted great interest
[10]. The silver(I) ion has a very flexible coordination sphere, the coordination numbers of
Ag(I) ions can vary greatly from two to six, forming diverse Ag(I) aggregates, such as
T-shaped [11], trigonal [12], trigonal bipyramidal, tetragonal [13], square pyramidal,
octahedral and so on. On the other hand, Ag(I) ions tend to form silver-silver bonds, so-called
argentophilicity [14], which play an important role in the construction of multi-nuclear silver
clusters, and further form diverse structures and fascinating topologies. From a synthetic point
of view, carboxylate ligands have been shown to be good building blocks in preparing
coordination polymers with desired topologies [15]. In this paper, we chose 3-nitrophthalic
acid (H2npth) [14d,16] as the ligand, which contains two carboxylate groups and exhibits a
great diversity of coordinate modes through complete or partial deprotonation. Besides, the
carboxylate groups show a strong ability to act as hydrogen bonding acceptors and donors.

This results in it often being chosen as an important organic ligand. To date, a total of 12
complexes of Ag-H2npth have been reported, exhibiting rich coordination modes (Scheme 1)
[14c,14d,15,16a-16c]. On the basis of these articles, we hoped that we could design more
novel multinuclear silver architectural complexes. Moreover, according to the HSAB (hard
soft acid-base) concept [17], the silver(I) ion can be classified as a soft acid, which can
coordinate to soft bases, such as ligands containing N donor ligands. Therefore, pyrazine and
its derivatives can be a kind of excellent organic ligand, which has attracted great interest in
the construction of coordination polymers [18].
On the basis of the above consideration, In this paper, the self-assembly of Ag(I) ions
with H2npth and pyrazine-like ligands is reported and four coordination polymers,
Ag4(H2O)2(npth)2 (1), Ag4(epyz)2(npth)2 (2), [Ag(pyz)(Hnpth)]·H2O (3) and
Ag(epyz)0.5(Hnpth) (4), have been synthesized using different pyrazine derivatives and
synthesis conditions. What is more, the luminescence properties of complexes 1-4 are also
presented. Compound 3 display photocatalytic properties in the degradation of organic dyes
under UV and simulated daylight irradiation.
2. Experimental
2.1. Materials. All chemicals of reagent grade were commercially available and used without
further purification.
2.2. Physical Methods. Powder X-ray diffraction measurements were carried out with a
Bruker D8 Focus X-ray diffractometer to check the phase purity. The C, N and H micro
analyses were performed with a Perkin Elmer 2400II elemental analyzer. The FT-IR spectra
were recorded from KBr pellets in the range 4000-400cm–1 on a Shimadzu FTIR–8900

spectrometer. Thermogravimetric measurement was performed under a flow of nitrogen gas
from room temperature to 900 C at a heating rate of 10 C/min using a Seiko Exstar 6000
TG/DTA 6300 apparatus. Single crystal X-ray diffraction data were collected by a Rigaku
R-Axis Rapid X-ray diffractometer. Photoluminescence properties were investigated in the
solid state at room temperature with an F-7000 FL spectrophotometer. Photocatalytic tests
were performed with a Bilon BL-GHX-V photochemical reaction instrument.
2.3. Synthesis of the complexes
2.3.1. Synthesis of complex 1
A mixture of AgNO3 (33.4 mg, 0.2 mmol), pyrazine (pyz) (16.0 mg, 0.2 mmol) and
3-nitrophthalic acid (H2npth) (42.2 mg, 0.2 mmol) were dissolved in methanol-H2O-DMF
(N,N-dimethylformamide) solvents (6 ml, v/v/v = 1:1:1) in the presence of ammonia (0.5 mL,
14 M) under ultrasonic treatment (160 W, 40 kHz, 30 min) at 40 C. The resultant colorless
solution was allowed to evaporate slowly at room temperature in the dark. Colorless crystals
of compound 1 were obtained after several days. The crystals were isolated by filtration,
washed with deionized water and dried in air. Yield based on silver is 58.71%. Elemental
analysis, anal. calc. (found) for Ag4C16H10N4O14: C, 21.64 (21.67); H, 1.14 (1.12); N, 3.20
(3.16) %. IR (KBr, cm-1): 3355 (m), 3099 (w), 1591 (vs), 1519 (m), 1461 (m), 1399 (s), 1343
(m), 1157 (w), 924 (w), 826 (w), 753 (m), 717 (m).
2.3.2. Synthesis of complex 2
The synthesis of 2 was similar to that of 1, but with 2,3,5,6-tetramethylpyrazine(epyz)
(27.2 mg, 0.2 mmol) in place of pyz. The resultant solution was allowed to evaporate slowly
in the dark at room temperature for several days to give colorless crystals of 2. Yield based on

silver is 68.87%. Elemental analysis, anal. calc. (found) for Ag4C32H29N6O12: C, 34.19 (34.26);
H, 2.54 (2.58); N, 7.51 (7.49) %. IR (KBr, cm-1): 3361 (m), 3097 (w), 2943 (w), 2861 (w),
1643 (m), 1596 (vs), 1534 (s), 1460 (m), 1405 (s), 1343 (s), 1161 (w), 924 (w), 760 (m), 717
(m).
2.3.3. Synthesis of complex 3
A mixture of AgNO3 (33.4 mg, 0.2 mmol), H2npth (42.2 mg, 0.2 mmol), pyz (16 mg, 0.2
mmol) and H2O (10 mL) was stirred for a few minutes, then sealed in a 25 mL Teflon-lined
stainless steel autoclave and heated at 100 °C for 72 h. After cooling to room temperature,
pale yellow crystals were obtained in a yield of 51.91% based on Ag. Elemental analysis, anal.
calc. (found) for AgC12H10N3O7: C, 34.63 (34.61); H, 2.41 (2.40); N, 10.09 (10.10) %. IR
(KBr, cm-1): 3443 (w), 3092 (w), 1720 (m), 1653 (s), 1630 (m), 1540 (vs), 1384 (s), 1348 (vs),
1151 (m), 784 (m), 707 (m).
2.3.4. Synthesis of complex 4
The synthesis of 4 was similar to that of 3, but with epyz (27.2 mg, 0.2 mmol) in place of
pyz. After cooling to room temperature, pale yellow crystals were obtained. Yield based on
silver is 62.03%. Elemental analysis, anal. calc. (found) for AgC12H10N2O6: C, 37.28 (37.30);
H, 2.59 (2.60); N, 7.25 (7.25) %. IR (KBr, cm-1): 3430 (m), 3069 (w), 2924 (w), 2852 (w),
1685 (s), 1556 (m), 1534 (vs), 1419 (m), 1353 (s), 1274 (m), 921 (w), 806 (m), 703 (m).
2.4. X-ray crystallography
Suitable single crystals were selected under a polarizing microscope and fixed with
epoxy cement on fine glass fibers, which were then mounted on a Rigaku R-Axis Rapid
diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) for cell

determination and subsequent data collection. The reflection intensities in the suitable θ
ranges were collected at 293 K using the scan technique. The employed single crystals exhibit
no detectable decay during the data collection. The data were corrected for Lp and absorption
effects. The direct method employing SHELXS-97 [19] gave the initial positions for some
non-hydrogen atoms, and the subsequent difference Fourier syntheses using SHELXL-97 [20]
program resulted in the initial positions for the remaining non-hydrogen atoms. The hydrogen
atoms on the organic ligands were geometrically generated, while the remaining hydrogen
atoms were located from successive difference Fourier syntheses. Finally, the full-matrix
least-squares technique was applied for refinement of positions and anisotropic displacement
parameters of all the non-hydrogen atoms, and positions of the hydrogens were refined using
a riding mode by fixing the initial distances to the associated heavier atoms with isotropic
displacement parameters set to 1.5 times the values of the associated atoms. The crystal
structure of 2 contains solvent-accessible voids of 875 Å, but showed no residual electron
density in the voids. This might indicate that the crystal lost its solvent of crystallization
without collapse of the structure. Detailed information about the crystal data and structure
determination is summarized in Table 1. Selected interatomic distances and bond angles are
given in Tables S1-S4.
2.5 Photocatalytic activity measurements
The photocatalytic activities of the as-prepared samples were evaluated by the
degradation of Rhodamine B (RhB), Methyl orange (MO) and Methylene blue (MB) under
different light sources: (1) UV light using a 300W Hg lamp, (2) visible light irradiation using
a 300 W Xe lamp. 50 mg of the compounds was mixed together with 50 mL of 10 mg/L RhB

solution in a quartz beaker, then magnetically stirred in the dark for about 30 min to ensure
the establishment of an adsorption/desorption equilibrium. After that, the mixtures were
stirred and continuously exposed to light irradiation from different lamphouses. 5 ml of the
sample were continually taken from the reaction beaker and collected by centrifugation with
30 min or 1 h intervals during the irradiation. The suspensions were centrifuged with a
HC-3518 high speed centrifuge at 9000 rpm for 5 min to remove the compound, which was
then analyzed using a Shimadzu UV-vis 2501PC recording spectrophotometer.
3. Results and discussion
3.1. Description of the ccrystal structures
3.1.1. Structure of complex 1
X-ray crystallography of 1 revealed that it crystallizes in the space group P21/c. In the
asymmetric unit, four crystallographically independent Ag(I) ions, two npth ligands (that
containing the O1 atom is named npth1 and that containing the O7 atom is named npth2) and
two coordinated water molecules were identified. The coordination environments of 1 are
depicted in Fig. 1a, where all the Ag1, Ag2, Ag3, and Ag4 atoms are located in a distorted
T-shaped geometry. The coordination environments of the Ag1 and Ag3 atoms are completed
by three O atoms belonging to two different npth ligands and one H2O molecule, and that of
the Ag2 and Ag4 atoms are completed by three O atoms from three different npth ligands. The
Ag–O bond lengths fall in the range 2.116(4)-2.618(3) Å. The largest bond angles around the
Ag1, Ag2, Ag3 and Ag4 atoms are 167.90(17), 168.25(13), 168.25(18) and 167.99(13) ˚. Each
npth ligand adopts the same bridging mode to link five silver atoms in the 5–η2:η1:η1:η1
fashion. The 1-position carboxylate bridged two Ag atoms in a syn/syn fashion, and the

2-position carboxylate groups links to two metal atoms in a 32 bridging/mondentate
bridging fashion.
The O1 atom of the 1-position carboxylate group in npth1 and the O7 atom from the
2-position of carboxylate in npth2 are coordinated with the Ag1 atom, in addition the O4 atom
from the 2-position carboxyl group in npth1 and the O9 atom of the 1-position carboxylate
group in npth2 are coordinated with Ag3, which together form the 14-membered ring unit.
Notably, the carboxylate oxygen atom O10 of the resultant 14-membered rings unit are
coordinate to the Ag4 atom, extending into a 1D chain along the b axis (Ag4–O8#6 = 2.162(4)
Ag4–O10 = 2.190(4) Ag4–O4#6 = 2.618(3) Å). The 1D chains are assembled into a 2D sheet
parallel to ab plane via coordination of distorted T-shaped geometry Ag2 atoms, as observed
in Fig. 1b (Ag2–O2#2 = 2.195(3), Ag2–O3 = 2.162(4) and Ag2–O7 = 2.610(4) Å). The
resulting sheets are held together by interlayer hydrogen bonds between the carbon atoms of
npth ligands and aqua ligands, leading to a 3D supramolecular architecture
(C14–H14A∙∙∙O12#7 = 3.335 Å), as described in Table S1.
There are five kinds of Ag∙∙∙Ag interactions in complex 1 that form the Ag4 unit
[Ag1–Ag2#3 = 2.967(1) Ag1–Ag4#4 = 3.332(1) Ag2–Ag3#3 = 3.355(1) Ag3–Ag4 = 2.962(1)
and Ag4–Ag2#2 = 3.271(1) Å]. The distances of the Ag∙∙∙Ag interactions are between 2.962(1)
and 3.355(1) Å, which are shorter than twice the van der Waals radius of silver ions (3.44 Å),
indicating the presence of argentophilic interactions. All the npth ligands adopt the
5–η2:η1:η1:η1 bridging mode to link rhombic Ag4 units, giving a 2D network. To better
understand the structure of 1, topological analysis was used. According to Wells, it is a
platonic uniform net and can be represented by the symbol (n, p), where n is the size of the

shortest circuit and p is the connectivity of the nodes. All the Ag4 units could be simplified to
a 4-connected node, so this 2D sheet can be simplified to a 44-sql net.
3.1.2. Structure of complex 2
The X-ray diffraction study reveals that the asymmetric unit of 2 consists of four Ag(I)
ions, two epyz ligands (the epyz ligand containing the N1 atom is named epyz1 and that
containing the N3 atom is named epyz2), two npth anions (the npth ligand containing the O1
atom is named npth1, and that containing the O3 atom is named npth2). As shown in Fig. 2a,
there are three kinds of Ag(I) centers in compound 2. Each Ag1 center is five coordinated by
one epyz1 nitrogen atom [Ag1−N1 = 2.270(2) Å] and four oxygen atoms from two individual
npth ligands with Ag–O distances ranging from 2.364(6) to 2.509(4) Å. The Ag2 center is
seven coordinated by one epyz1 nitrogen atom [Ag2−N2#5= 2.284(3) Å] and six oxygen
atoms from two individual npth ligands. The Ag–O bond distances are in the range
2.379(7)-2.560(8) Å. The Ag3 atom is located in a distorted tetrahedral geometry and is
coordinated by one N3 atom from an epyz2 ligand and three O atoms from three different
npth ligands, with Ag–O distances ranging from 2.303(8) to 2.496(9) Å. The epyz ligands
take a bidentate bridging mode, while the two different npth anions take a 4–η3:η1:η3:η1 and a
6–η2:η2:η2:η2 bridging mode.
As shown in Fig. 2a, the npth1 and npth2 ligands bridge four Ag(I) centers (the Ag1, Ag2
and two Ag3 atoms) to form a Ag4(epyz)2(npth)2 unit. Then cage-like Ag8 SBU (secondary
building unit) can be regarded as two centrosymmetric Ag4(epyz)2(npth)2 units connected to
each other by the Ag1–O3 (2.509(4) Å), Ag1–O3#4 (2.509(4) Å), Ag3–O1 (2.303(8) Å),
Ag3–O2#3 (2.350(6) Å) and Ag3–O3#3 (2.496(9) Å) interactions, and is reinforced by an

Ag∙∙∙Ag interaction (Ag3∙∙∙Ag3#3 = 3.1702 (6) Å). The resulting
SBU is a new cage-like
Ag8
unit, which is different from that previously reported in the literature [21]. Each Ag8 SBU is
connected to four adjacent such clusters through epyz1 ligands to form a 2D grid-like layer
parallel to the ab plane (Fig.2b). Simultaneously, the 2D layers are assembled into a 3D
network structure through interlayer epyz2 ligands (Fig. 2c). From a topological point of view,
each Ag8 SBU serves as a six-connected node, while the epyz ligands can act as bridging
ligands (Fig. 2d). Consequently, on the basis of this simplification, the 3D frameworks present
a NaCl topological net with the point symbol (412·63).
3.1.3. Structure of complex 3
Complex 3 is a 2D supermolecular structure, which crystallizes in the monoclinic space
group P21/c. As shown in Fig. 3a, the asymmetric unit of 3 consists of one Ag(I) ion, one pyz
ligand, one half of a completely deprotonated Hnpth anion and one uncoordinated water
molecule. The Ag(I) ions, in a distorted T-shaped coordination geometry, are coordinated by
the two nitrogen atoms from two different pyz ligands (Ag–N1 = 2.185(2) and Ag–N2#3 =
2.183(2) Å; N1–Ag–N2#3 = 161.90(10) ˚) and one oxygen atom from one Hnpth anion
(Ag–O1 = 2.480(2) Å).
The Ag(I) ions are bridged by pyz ligands via the 2-N:N' coordination mode to form a
1D infinite chain structure and the terminal Hnpth ligands decorate alternately on the two
sides of the chains. A weak Ag∙∙∙Ag interaction (Ag∙∙∙Ag#1 = 3.196(1) Å) extends the 1D chain
into a 2D sheet parallel to the bc plane (Fig. 3c), which is reinforced by the uncoordinated
water molecule via inter-chain hydrogen-bonding interactions (O6–H6∙∙∙O7#3 = 2.616,
O7–H72∙∙∙O2#1 = 2.832, O7–H71∙∙∙O1#4 = 2.758 Å). These neighboring 2D sheets are

interconnected to form the 3D supramolecular architecture by C–H⋯O hydrogen bonds.
3.1.4. Structure of complex 4
The asymmetric unit of 4 consists of one Ag(I) ion, one Hnpth anion and half an epyz
ligand in the monoclinic space group P21/c. As shown in Fig. 4a, the half completely
deprotonated Hnpth ligand adopts the 3η4 bridging mode to link three silver atoms with the
2-position carboxylate group chelating one silver ion and simultaneously acting as a
monodentate donor to another Ag atom. Ag(I) shows a five-coordinated distorted
square-pyramidal coordination environment, being bonded to four O atoms from three
different Hnpth ligands and one N atom from one epyz ligand (Ag–O1 = 2.424(2), Ag–O3#1 =
2.443(2), Ag–O2#4 = 2.642(2), Ag–O2 = 2.705(3) and Ag–N2 = 2.257(2) Å). The structural
distortion index tau (τ), as an index of the degree of distortion, is calculated as 0.61 (τ = (α –
β)/60, where α and β correspond to the two largest angles between the donor atoms forming
the basal plane in the square-pyramidal geometry). The value of τ indicates that the Ag center
exhibits a configuration between distorted square pyramidal and trigonal bipyramid (for ideal
square pyramidal geometry, τ = 0) [22].
Two Ag atoms are interlinked by the oxygen O2 atoms of the 2-position carboxylate
group to form a centrosymmetric binuclear unit; such units are connected to one another to
build a 1D chain via bridging Hnpth ligands along the [100] direction (Fig. 4b). The resulting
chains are further interlinked via the 2–N: N' coordination mode of the epyz ligand into 2D
layers parallel to the (010) plane (Fig. 4c). The layers are held together by interlayer hydrogen
bonds (C6–H6A∙∙∙O6#3), leading to a 3D supramolecular architecture.
3.2. Effect of different pyrazine derivatives and synthesis conditions on the assembly of Ag(I)

complexes with H2npth
As is shown in the description above, four Ag(I) complexes, 1-4, with the npth/Hnpth
anion and different pyrazine derivatives were successfully synthesized and characterized.
Complexes 1 and 2 are obtained by ultrasonic treatment with the addition of ammonia
solution, and complexes 3 and 4 are synthesized via a hydrothermal method at 100 °C for 72 h.
To gain an insight into the influence of the pyz ligand in 1, a similar method was followed by
absenting the pyz ligand, affording an amorphous precipitate, thus indicating the pyz ligand
plays a major role in the synthesis of complex 2. By way of a review of the characteristic
structures, complex 1 exhibits a 2D structure which presents tetranuclear units, complex 2
contains a cage-like Ag8 SBU to build up a 3D framework, complex 3 displays a 1D infinite
chain and complex 4 encompasses binuclear units which form a 2D layer. From a
methodological point of view, the method of ultrasonic irradiation synthesis is more likely to
obtain multinuclear complexes or high-dimensional compounds. It is superior to the
traditional mixing, heating and other thermodynamic methods, and ultrasonic irradiation
synthesis has become a convenient, rapid, effective, safe synthetic technology for the
synthesis of complexes.
The H2npth ligand contains two protons, and thus could be deprotonated to the Hnpth-
and npth2- anions. According to the reference reported, there are 12 silver-H2npth complexes

in presence of ancillary ligands. It can be seen from the Table 2, we successfully synthesized
2D and 3D polymers of complexes with novel structures. In our work, the npth/Hnpth ligands
show five different coordination fashions in the four compounds. For 1, each fully
deprotonated npth ligand adopts the μ5–η2:η1:η1:η1 bridging mode to link five silver atoms to
form a 2D network structure (Scheme 1f). 2 is a 3D net structure in which the carboxylate
groups show two coordination modes ( 4–η3:η1:η3:η1 and 6–η2:η2:η2:η2) (Scheme 1m and 1n).
These two coordination modes have not been reported previously, suggestng that the silver
complexes have various modes of coordination. The four npth ligands link eight Ag(I) ions to
form the Ag8 SBU, while the epyz ligands coordinate the Ag ions to form a 3D network. It is
worth noting that the Ag8 SBU in 2 is a new cage-like unit, which has never been reported in
previous Ag-H2npth literature. The Hnpth ligands in 3 and 4 act as terminal (Scheme 1a) and
3–η2:η1:η1 (Scheme 1d) bridging ligands.
3.3. Luminescent properties
The photoluminescence properties of the coordination polymers have been investigated
extensively because of the potential applications in chemical sensors, photochemistry and
electroluminescence. At room temperature, the solid-state excitation and emission spectra of
complexes 1-4 and the corresponding original ligand H2npth were measured (Fig. 5). The
emission spectra were recorded with the light of λ= 300 nm as the excitation source. The free
ligand H2npth displays photoluminescence with two shoulder peaks centered at 425 and 466
nm. Complexes 1-4 show emission spectra with two peaks at 423 and 466 nm for 1, 421 and
467 nm for 2, 420 and 467 nm for 3 and 421 and 468 nm for 4. The emission spectra of 1-4
are similar to that of the H2npth ligand, indicating that the ligand-centered (n–π* or π–π*)

transitions play a leading role.
3.4. Photodegradation activities
Photocatalysts have attracted much attention due to their potential applications in
purifying water and air by decomposing organic molecules [23]. As we know, TiO2 has been
studied extensively as a semiconductor photocatalyst [24]. More recently, there have been a
few contributions about new photocatalytic materials based on coordination polymers that are
successfully accomplished, which indicate that this area is a new application for coordination
polymer materials [25]. Rhodamine B (RhB) is commonly used as a representative of
widespread organic dyes that are very difficult to decompose in waste streams. Thus, we
choose rhodamine B as a model model dye pollutant and the photocatalytic activity of the
as-prepared complexes 1-4 was tested under simulated UV light by a 300W Hg lamp. For
comparison, the photodegradation of RhB without any photocatalyst was also studied under
the same conditions and no RhB degradation was observed.
The experimental results show that compound 3 can degrade 81.8% of rhodamine B in
3.5 h under UV light irradiation. Unfortunately, RhB solutions with complexes 1, 2 and 4
showed no obvious degradation effects (Fig.S4-S6). Additionally, we also carried out
experiments to degrade other dyes (MO and MB) with complex 3. In Fig.6, MB, MO and
RhB were analyzed by UV/Vis absorption at 664, 464 and 554 nm respectively. In the
presence of complex 3, the degradation rate of MB, MO and RhB is 33.2, 44.2 and 81.8%
after 3.5 h with 30 minutes intervals under UV irradiation, respectively, indicating that RhB
shows the best effect for degradation. In addition, we tested the RhB degradation of 3 under
the condition of simulated visible light using a 300W Xe lamp (Fig. 7.), and the degradation

ratio of RhB reached 44.2% after 7 h. The experimental results demonstrate that complex 3 is
a potential candidate for the photo-degradation organic dyes in visible irradiation.
It is well known that many factors affect the complexes for the degradation of organic
pollutants. A variety of conditions from external factors will influence the degradation effect,
such as, PH value, temperature and light source in the catalytic system, the concentrations of
the dye and so on. From the catalyst itself, its catalytic effect not only relates to the specific
surface area of the catalyst, but also to the structure of the catalyst itself. From the
characteristic structures of silver clusters, a total of 20 cases of silver complexes have been
investigated, as shown in Table 3 [26], there are 13 cases of mononuclear silver complexes, 4
cases of binuclear complexes, 2 cases of Ag4 clusters and the last one is an Ag7 cluster. It is
easily to see that mononuclear silver complexes have more advantages in the photocatalytic
degradation of organic pollutants. It is known to all that the recombination of electrons (e-)
and holes (h+) have a great influence on the efficiency of complexes on the degradation of
dyes [27]. The Ag centers in multinuclear silver clusters are mostly connected via O and N
atoms mostly, hence, electron transfer between silver atoms is through O and N atom,
However, in mononuclear silver complexes, electronic transfer may need to proceed through
organic ligands, so it is more difficult compared with multi-core silver clusters. Therefore, we
speculate that electron transfer between Ag atoms is much easier in most multi-core silver
clusters, with an easy recombination between the electrons (e-) and holes (h+). At the same
time, it also can reduce the effect of photocatalysis.
4. Conclusions
In this manuscript, four related coordination polymers based on silver nitrate,

3-nitrophthalic acid and pyrazine-like ligands are synthesized and characterized. Compound 1
presents Ag4 units, and compound 2 features a cage-like Ag8 SBU (secondary building unit),
which is the first time such a multinuclear polymer has been reported. Furthermore, the
3-nitrophthalic acid exhibits three new coordination modes, which also have never been
reported by others. In addition, the methods of ultrasonic synthesis are more likely to obtain
multi-nuclear complexes or high-dimensional compounds. Furthermore, we have tested the
photochemical properties of complexes 1-4 and we found the mononuclear silver complexes
may have more advantages for the degradation of organic pollutants.
Supporting Information Available
Crystallographic data for compounds 1-4 are deposited with the Cambridge Crystallographic
Data Center, 1498925-1498928 [CCDC, 12 Union Road, Cambridge CB2 1EZ, United
Kingdom.
Fax:
(44)1223-336-033.
E-mail:
deposit@ccdc.cam.ac.uk.
Website:
http://www.ccdc.cam.ac.uk]. Experimental and simulated PXRD patterns of 1-4; IR spectra of
1-4; TG curves of 1-4; Selected inter-atomic distances and bond angles for 1-4.
Disclosure statement
No potential conflict of interest is reported by the authors.
Funding
This project was supported by the Public Projects of Zhejiang Province (2017C33008).
Honest thanks are also extended to K.C. Wong Magna Fund in Ningbo University.

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Figure captions
Fig. 1. (a) The coordination environment of Ag(I) ions and npth ligands in 1 with thermal ellipsoids at the
40% probability level. We marked the 14-membered ring unit with a green line. (b) Ball-and-stick view of
the 2D sheet in compound 1 and the 44-sql network incorporating rhombic Ag4 units. (Symmetry codes: #1
= x, y+1, z; #2 = -x+2, y+1/2, -z+1/2; #3 = -x+2, y-1/2, -z+1/2; #4 = x, y-1, z; #5 = -x+1, y-1/2, -z+1/2; #6
= -x+1, y+1/2, -z+1/2)
Fig. 2. (a) The coordination environment of Ag(I) ions and npth ligands in 2 with thermal ellipsoids at the
40% probability level. The cage-like Ag8 unit is marked by a blue line. (b) Ball-and-stick view of the 2D
sheet in compound 2 along the c axis. The phenyl rings of all npth ligands and hydrogen atoms are omitted
for clarity. (c) 3D framework of complex 2. (d) A schematic view of the (412·63) topological net of 2. The
purplish red balls represent 6-connecting Ag8 SBUs, each blue line represents epyz ligands. (Symmetry
codes: #1 = -x+1, -y, -z+1; #2 = x-1/2, -y+1/2, -z+1; #3 = -x+1, -y, z; #4 = x, y, -z+1; #5 = x+1/2, -y+1/2,
-z+1; #6 = x, y, -z.)
Fig. 3. (a) The coordination environment of Ag(I) ions and npth ligands in 3 with thermal ellipsoids at the
40% probability level. (b) View of the structure of complex 3 showing the 1D sheet of Ag(I) ions with
Hnpth anions and pyz ligands along the c axis. (c) Ball-and-stick view of the 2D sheet in the bc plane. All
H and oxygen atoms of the nitro group are omitted for clarity. (Symmetry codes: #1 = -x+1, -y, -z, #2 =
-x+1, y+1/2, -z+1/2, #3 = -x+1, y-1/2, -z+1/2)
Fig. 4. (a) The coordination environment of the Ag(I) ions and npth ligands in 4 with thermal ellipsoids at
the 40% probability level. (b) Presentation of 1D infinite [Ag2(Hnpth)2]n units. (c) Ball-and-stick view of
the 2D sheet in compound 4. All hydrogen atoms are omitted for clarity. (Symmetry codes: #1 = -x-1, -y+1,
-z+1, #2 = -x-1, -y+1, -z+1, #3 = x+1, 1/2+y, 1/2+z, #4 = -x, -y+1, -z+1, #5 = -x+1, -y+1, -z+2.)
Fig. 5. Emission spectra of 1-4 and H2npth in the solid state at room temperature.
Fig. 6. Photocatalytic decomposition of RhB, MB and MO solutions with the change in Ct/C0 of 3 under
UV light.
Fig. 7. Absorption spectra of RhB solutions during the decomposition reaction with the use of complex 3
under a Xe lamp. Insert: photocatalytic decomposition of the RhB solution with the change in Ct/C0 (%).
`

Scheme 1 Coordination modes of 3-nitrophthalic acid with Ag(I) ions.
Scheme 2 Different pyrazine derivatives and synthesis conditions for the controlled structures.