Syntheses, structural diversities and characterization of a series of coordination polymers with two isomeric oxadiazol-pyridine ligands

Article abstract of DOI:10.1039/c6ra28153b

In this work two positional-isomeric oxadiazol-pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L₁) and 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L₂) have been designed and synthesized. A series of novel coordination polymers, namely [Cd₂(μ₂-L₁)₂(μ₂-NCS)₄]_n (1), {[Cd(L₁)(μ₂-dca)₂(H₂O)]·H₂O}_n (2), {[Cu(μ₂-L₁)₂(NCS)₂]·0.5H₂O}_n (3), {[Ag₂(μ₂-L₁)(μ₃-L₁)₂]·2PF₆}_n (4), {[Ag₃(μ₂-L₁)₄(μ₂-CF₃SO₃)(CF₃SO₃)]·CF₃SO₃} (5), {[Cd(L₂)₂(μ₂-NCS)₂]}_n (6), [Ag(μ₂-L₂)(μ₂-CF₃SO₃)]_n (7) and {[Ag(μ₂-L₂)]·BF₄}_n (8) have been isolated. Both 1 and 2 are 2D Cd^II coordination polymers containing infinite {Cd-NCS-Cd} chains (for 1) or infinite {Cd-dca-Cd} layers (for 2), respectively. 3 is a 2D Cu^II coordination polymer, in which central metal ions are bridged via a bidentate bridging L₁ ligand. While when different Ag^I salts were introduced into the reaction system, 1D Ag^I coordination polymers 4 and 5 with diverse coordination modes can be isolated. Furthermore, when the isomeric oxadiazol-pyridine L₂ is used to replace L₁ in the reaction system, 6-8 can be isolated. 6 is a 2D Cd^II coordination polymer containing {Cd-NCS-Cd} layers. 7 is a 2D neutral Ag^I coordination polymer while 8 is a 2D cationic Ag^I coordination polymer. Variable temperature magnetic susceptibility measurements (2-300 K) reveal anti-ferromagnetic interactions between central copper(ii) ions for 3. Solid-state luminescent properties of 1, 2 and 4-8 have been investigated indicating strong fluorescent emissions. Additionally, luminescent measurements illustrate that complex 8 exhibits highly sensitive luminescence sensing for Cr₂O₇^2? ions in aqueous solutions with high quenching efficiency K_sv = 2.08 × 10⁴ L mol^?1 and low detection limit (0.19 μM (S/N = 3)). 8 also represents the first report of a coordination polymer based on oxadiazol-pyridine derivatives with a luminescence response to Cr₂O₇^2? anion pollutants in aqueous solutions.

Full text of DOI:10.1039/c6ra28153b

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PAPER
Syntheses, structural diversities and
characterization of a series of coordination
polymers with two isomeric oxadiazol-pyridine
ligands†
Cite this: RSC Adv., 2017, 7, 9704
Bin Ding,*ab Jie Wu, Xiang Xia Wu, Jian Zhong Huo, Zhao Zhou Zhu,
ab
ab
ab
ab
ab
ab
Yuan Yuan Liu and Fang Xue Shi
In this work two positional-isomeric oxadiazol-pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine
) and 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L ) have been designed and synthesized. A series of
novel coordination polymers, namely [Cd (m -L
[Cu(m -L (NCS) ]$0.5H O} (3), {[Ag (m -L )(m -L
CF SO } (5), {[Cd(L (m -NCS) ]} (6), [Ag(m -L )(m -CF
(L
1
2
2
2
1
)
2
(m
]$2PF
SO
2
-NCS)
4
]
n
(1), {[Cd(L
(4), {[Ag (m
(7) and {[Ag(m
1
)(m
-L
-L
2
-dca)
(m -CF
)]$BF
2
(H
2
O)]$H
2
O}
n
(2),
)]$
{
2
1
)
2
2
2
n
2
2
1
3
1
)
2
6
}
n
3
2
1
)
4
2
3
SO )(CF
3
3
SO
3
3
3
2
)
2
2
2
n
II
2
2
2
3
)]
3 n
2
2
4
}
n
(8) have been
isolated. Both 1 and 2 are 2D Cd coordination polymers containing infinite {Cd–NCS–Cd} chains (for 1)
II
or infinite {Cd–dca–Cd} layers (for 2), respectively. 3 is a 2D Cu coordination polymer, in which central
I
metal ions are bridged via a bidentate bridging L
1
ligand. While when different Ag salts were introduced
I
into the reaction system, 1D Ag coordination polymers 4 and 5 with diverse coordination modes can be
2 1
isolated. Furthermore, when the isomeric oxadiazol-pyridine L is used to replace L in the reaction
II
system, 6–8 can be isolated. 6 is a 2D Cd coordination polymer containing {Cd–NCS–Cd} layers. 7 is
I
I
a 2D neutral Ag coordination polymer while 8 is a 2D cationic Ag coordination polymer. Variable
temperature magnetic susceptibility measurements (2–300 K) reveal anti-ferromagnetic interactions
between central copper(II) ions for 3. Solid-state luminescent properties of 1, 2 and 4–8 have been
investigated indicating strong fluorescent emissions. Additionally, luminescent measurements illustrate
Received 13th December 2016
Accepted 27th January 2017
72ꢀ
that complex 8 exhibits highly sensitive luminescence sensing for Cr
2
O
ions in aqueous solutions with
4
ꢀ1
high quenching efficiency Ksv ¼ 2.08 ꢁ 10 L mol and low detection limit (0.19 mM (S/N ¼ 3)). 8 also
represents the first report of a coordination polymer based on oxadiazol-pyridine derivatives with
DOI: 10.1039/c6ra28153b
2ꢀ
rsc.li/rsc-advances
a luminescence response to Cr
O
2 7
anion pollutants in aqueous solutions.
be applied in the selective and sensitive detection of environ-
mental pollutants, which can further protect human health and
In the past several decades, metal organic coordination poly- the environment from harm by these pollutants. Their tunable
mers have attracted much interest due to their promising channel size, good structural stability, and large surface area of
applications for gas storage/separation, catalysis, lumines- luminescent coordination polymers make these coordination
cence, drug delivery, sensors and magnetic materials. Among materials more competitive over other luminescent materials
these coordination materials, luminescent metal organic coor- because more analytes can effectively interact with the channel
dination polymers have received great interest because they can surface areas of the coordination polymers, which can ulti-
mately improve the rate of luminescence response, decreasing
Introduction
10
1–9
a
the uorescence detection limit and improving the detection
sensitivity.
Key Laboratory of Inorganic–Organic Hybrid Functional Material Chemistry (Tianjin
11
Normal University), Ministry of Education, Tianjin Key Laboratory of Structure and
Performance for Functional Molecule, College of Chemistry, Tianjin Normal
University, 393 Binshui West Road, Tianjin 300387, PR China. E-mail: hxxydb@
mail.tjnu.edu.cn
In the crystal engineering of functional coordination poly-
mers, the variable selection of metal ions and organic ligands
provides endless possible outcomes of the nal products.
Although these porous coordination polymers with targeted
secondary building units (SBUs) and topologies can be synthe-
sized by careful selection of the metal ions and organic ligands,
b
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education),
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin),
College of Chemistry, Nankai University, Tianjin 300071, China
†
1
1
Electronic supplementary information (ESI) available. CCDC 1486502 (1),
518712 (2), 1486501 (3), 1486507 (4), 1486509 (5), 1486505 (6), 1486508 (7), and the nal structures of the products are still highly inuenced by
487692 (8). For ESI and crystallographic data in CIF or other electronic format
several factors including metal–ligand ratio, pH, solvent,
see DOI: 10.1039/c6ra28153b
9704 | RSC Adv., 2017, 7, 9704–9718
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temperature, and soon. In particular, judicious selection of spectrometer. Variable-temperature magnetic susceptibilities
ligands is important for deliberate structural changes and were measured using a MPMS-7 SQUID magnetometer.
12
functional properties of coordination polymers. Therefore Diamagnetic corrections were made with Pascal's constants for
many new exible or rigid ligands have been explored and all constituent atoms. Photoluminescence spectra were
assembled into metal–organic polymers via coordination bonds measured by MPF-4 uorescence spectrophotometer with
or supramolecular interactions such as hydrogen bonds, p–p a xenon arc lamp as the light source.
13–16
stacking, and host–guest ionic interactions et al.
1
Synthesis of 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L ).
1,3,4-Oxidazoles can be employed as one kind of efficient 35 mmol of the nicotinohydrazide were suspended in 95 mmol
bridging ligands and offer a range of charge-balance require- (2.7 eq.) triethyl orthoacetate. The reaction mixture was heated
ments, alternative linking modes and different orientations of under reux for 12 hours. Aer cooling to ambient temperature
1
7,18
donor groups.
atives have gained more interest as ligands to bridge different diethylether and dried in air. Yield: 70% of theory. H-NMR (400
metal ions to form functional coordination polymers because of MHz, DMSO-d ); 7.88–7.90 (m, 2H,
): d ¼ 2.61 ppm (s, 3H, CH
Currently oxidazole-pyridine and their deriv- the formed solid was ltered off, washed twice with 15 mL of
1
6
3
13
19
their intriguing bridging fashions. It is noted that investiga- arom. C–H); 8.80–8.82 (m, 2H, arom. C–H). C-NMR (100 MHz,
tion of the substituent position isomerization inuence of DMSO-d ); 119.9 (s, 2C, arom. C–H);
): d ¼ 10.7 ppm (s, 1C, CH
oxidazole-pyridine ligands on the formation of coordination 130.5 (s, 1C, C ); 150.9 (s, 2C, arom. C–H); 162.4 (s, 1C, C ]N);
polymers is still scarcely reported. Especially, to the best of our 165.0 (s, 1C, C ]N). FT-IR (cm , KBr): 1565(m), 1549(w),
knowledge, 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L ) and 4- 1465(m), 1430(m), 1349(w), 1247(w), 1131(m), 1086(m),
6
3
q
q
ꢀ1
q
1
(
5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L ) are never reported in 1044(m), 1014(m), 823(m), 705(m).
2
the coordination chemistry. The development of new ligand
Synthesis of 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L2).
systems is continuously an important aspect for the chemistry 35 mmol of the 4-pyridinecarboxylic hydrazide were suspended
of metal–organic coordination polymer. Previously we also re- in 95 mmol (2.7 eq.) triethyl orthoacetate. The reaction mixture
ported a series of functional coordination polymers using was heated under reux for 12 hours. Aer cooling to ambient
20
versatile N-containing ligands. In this work two position- temperature the formed solid was ltered off, washed twice with
1
isomeric oxadiazol-pyridine ligands L
1 2
and L have been 15 mL of diethylether and dried in air. Yield: 55% of theory. H-
employed, a series of novel coordination polymers, namely NMR (400 MHz, DMSO-d ): d ¼ 2.60 ppm (s, 3H, CH ); 7.61–7.64
6
3
[
{
(
(
Cd (m -L ) (m -NCS) ] (1), {[Cd(L )(m -dca) (H O)]$H O} (2), (m, 1H, arom. C–H); 8.32–8.34 (m, 1H, arom. C–H); 8.78–8.79
2 2 1 2 2 4 n 1 2 2 2 2 n
1
3
1
[Cu(m -L ) (NCS) ]$0.5H O} (3), {[Ag (m -L )(m -L ) ]$2PF }
(m, 1H, arom. C–H); 9.13 (s, 1H, arom. N]C–H). C{ H}-NMR
(100 MHz, DMSO-d ); 120.0 (s, 1C, C );
): d ¼ 10.6 ppm (s, 1C, CH
)]$ 124.3 (s, 1C, C ); 133.9 (s, 1C, arom. C–H); 146.9 (s, 1C, arom. C–
(8) have been isolated. Variable temperature magnetic H); 152.2 (s, 1C, arom. C–H); 164.4 (s, 1C, arom. C–H); 162.1 (s,
2
1 2
2
2
n
2
2
1
3
1 2
6 n
4), {[Ag
-NCS)
3
(m
]}
2
-L
1
)
4
(m
2
-CF
3
SO
-L
3
)(CF
3
SO
3
)]$CF
3
SO
3
} (5), {[Cd(L
-L
2
)
2
6
3
q
m
2
2
n
(6), [Ag(m
2
2
)(m
2
-CF
3
SO
3
)]
n
(7) and {[Ag(m
2
2
q
BF
susceptibility measurements (2–300 K) reveal anti- 1C, C
ferromagnetic interactions between central copper(II) ions for 1430(m), 1354(w), 1271(m), 1142(m), 1033(m), 834(m), 770(m).
. Solid-state luminescent properties of 1, 2 and 4–8 have been
4
}
n
ꢀ
1
q
]N). FT-IR (cm , KBr): 1585(m), 1538(w), 1413(m),
3
investigated indicating strong uorescent emissions. Addi-
tionally, luminescent measurements illustrate that 8 exhibits
Preparation of compounds 1–8
2
ꢀ
highly sensitive luminescence sensing for Cr
2
O
7
in aqueous
[Cd (m -L ) (m -NCS) ] (1). A mixture of CdCl (18.33 mg,
2
2
1 2
2
4 n
2
4
solutions with high quenching efficiency Ksv ¼ 2.08 ꢁ 10 L 0.10 mmol), L (17.71 mg, 0.10 mmol), NH NCS (15.23 mg, 0.20
1
4
ꢀ
1
mol and low detection limit (0.19 mM (S/N ¼ 3)), which make mmol) and water (20 mL) was reuxed and stirred for 12 h, then
2
ꢀ
it a promising candidate for sensing Cr
2
O
7
ions in practical. the resulting solutions were ltered. The ltrate was kept in
desiccator. Aer a few days suitable colorless single
rst report of coordination polymers based on oxadiazol-pyridine crystals were obtained for X-ray diffraction study, yield 55%.
Luminescent measurements illustrate that 8 also represents the a CaCl
2

2
ꢀ
derivatives as luminescent response to Cr O
ions in the water Elemental analysis calcd (%) for C H Cd N O S : C 30.82%,
20 14 2 10 2 4
2
7
solutions. Different coordination modes of L and L are also H 1.81%, N 17.97%; found: C 30.97%, H 1.93%, N 18.16%. FT-IR
1
2
ꢀ1
briey discussed, which indicates these isomeric oxadiazol- (cm , KBr): 2090(s), 1572(m), 1558(w), 1465(m), 1263(w),
pyridine building blocks have great potential in the construc- 1131(m), 1098(m), 1033(m), 1014(m), 814(m), 719(m).
tion of these unique metal organic coordination polymers.
{[Cd(m -L )(m -dca) (H O)]$H O} (2). A mixture of CdCl2
2 1 2 2 2 2 n
(18.33 mg, 0.10 mmol), L
1
(17.71 mg, 0.10 mmol), Nadca
(
17.81 mg, 0.20 mmol) and water (20 mL) was reuxed and
Experimental section
General methods
stirred for 12 h, then the resulting solutions were ltered. The
ltrate was kept in a CaCl desiccator. Aer a few days suitable
1 2
Ligands L and L were prepared by literature methods. All the colorless single crystals were obtained for X-ray diffraction

2
21
other reagents were purchased commercially and used without study, yield 57%. Elemental analysis calcd (%) for
further purication. Deionized water was used as solvent in this C H CdN O : C 45.88%, H 2.02%, N 22.93%; found: C
2
1
11
9 3
ꢀ
1
work. C, H, and N microanalyses were carried out with a Perkin- 46.15%, H 2.16%, N 23.12%. FT-IR (cm , KBr): 3500(m),
Elmer 240 elemental analyzer. FT-IR spectra were recorded from 2170(s), 1570(m), 1550(w), 1352(m), 1260(w), 1129(m), 1080(m),
KBr pellets in the range 4000–400 cm on a Bio-Rad FTS 135 1035(m), 1015(m), 815(m), 720(m).
ꢀ
1
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˚
{
[Cu(m
2
-L
1
)
2
(NCS)
2
]$0.5H
2
O}
n
(3).
A
mixture of CuCl
2
monochromated Mo-Ka radiation (l ¼ 0.71073 A) by using
(
(
17.05 mg, 0.10 mmol), L
1
(17.71 mg, 0.10 mmol), NH
4
NCS the u–4 scan technique. Lorentz polarization and MULTI-
15.23 mg, 0.20 mmol) and water (20 mL) was reuxed and SCAN absorption corrections were applied. The structures
stirred for 12 h, then the resulting solutions were ltered. The were solved by direct methods and rened with the full-matrix
ltrate was kept in a CaCl
desiccator. Aer a few days suitable least-squares technique using the SHELXS-97 and SHELXL-97
green single crystals were obtained for X-ray diffraction study, programs.
yield 37%. Elemental analysis calcd (%) for C H CuN O S : to all non-hydrogen atoms. The positions of hydrogen atoms

2
2
2,23
Anisotropic thermal parameters were assigned
1
8
14.5
8 2.5 2
C 42.35%, H 2.86%, N 21.95%; found: C 42.46%, H 2.97%, N of the water molecules were located from difference maps and
ꢀ
1
2
1
2.13%. FT-IR (cm , KBr): 3410(m), 2090(s), 1557(m), 1420(m), rened with isotropic temperature factors. The positions of
359(w), 1268(m), 1093(m), 816(m), 719(m).
other hydrogen atoms were generated geometrically. Analyt-
{[Ag
2
(m
2
-L
1
)
3
]$2PF
6
}
n
(4). A mixture of AgPF
6
(25.29 mg, 0.10 ical expressions of neutral-atom scattering factors were
mmol), L
1
(17.71 mg, 0.10 mmol) and water (20 mL) was employed, and anomalous dispersion corrections were
reuxed and stirred for 12 h, then the resulting solutions were incorporated. The crystallographic data and details of rene-
ltered. The ltrate was kept in a CaCl desiccator. Aer a few ments for compounds 1–8 are summarized in Table 1.

2
days colorless suitable single crystals were obtained for X-ray Selected bond lengths and angles are listed in Table 2. Cor-
diffraction study, yield 59%. Elemental analysis calcd (%) for responding hydrogen bonds lengths and angles for 1–8 are
C H21Ag F N O P
24 2 12 9 3 2
: C 29.14%, H 2.14%, N 12.74%; found: C listed in Table S1.†
ꢀ
1
2
1
9.34%, H 2.38%, N 12.97%. FT-IR (cm , KBr): 1589(m),
420(m), 1270(m), 1110(m), 838(s), 704(m).
Results and discussion
3 3 n
SO } (5). A mixture of
{[Ag
3
(m
2
-L )]$CF
1
(25.69 mg, 0.10 mmol), L (17.71 mg, 0.10 mmol) and
1
)
4
(m
2
-CF
3
SO
3
)(CF
3
SO
3
AgCF SO
3
3
The crystal samples of complexes 1–8 can retain their crystalline
integrity at room temperature for two weeks. As shown in
Schemes 1 and 2, only nitrogen atoms of oxadiazole and pyri-
dine rings can participate in coordination and the steric effect
prevents oxadiazole oxygen atoms from metal coordination.
There are ve different coordination modes in 1–8: for 1, 3 and
water (20 mL) was reuxed and stirred for 12 h, then the resulting
solutions were ltered. The ltrate was kept in a CaCl desiccator.
Aer a few days suitable single crystals were obtained for X-ray
diffraction study, yield 39%. Elemental analysis calcd (%) for
2
35 3 9 12 13 3
C H28Ag F N O S : C 29.70%, H 1.99%, N 11.87%; found: C
ꢀ
1
2
1
9.96%, H 2.06%, N 11.96%. FT-IR (cm , KBr): 1589(m),
410(m), 1275(m), 1168(m), 820(m), 1031(bm), 827(m), 720(m).
5
, these L
bridging coordination modes a. For 2, these L
mono-dentate coordination mode b, while in 4 two different
coordination (bidentate bridging mode and tridenate
1
ligands in these coordination polymers contain
1
ligands contain
{
2 2 2 2 n
[Cd(L ) (m -NCS) ]} (6). 6 was prepared through the similar
synthetic method of 3 only using L (17.71 mg, 0.10 mmol) to
replace L (17.71 mg, 0.10 mmol) in the reaction system. Aer
a few days suitable colorless single crystals were obtained for X-
2
a
1
bridging mode c) for L can be observed. For 6, mono-dentate
1
coordination mode d for L can be observed while for 7–8 bi-
2
ray diffraction study, yield 41%. Elemental analysis calcd (%) for
dentate bridging coordination mode for L can be observed.
2
18 8 2 2
C H14CdN O S : C 39.24%, H 2.56%, N 20.34%; found: C
These various different coordination modes also draw the self-
assembly of coordination polymers to form different coordina-
tion polymers.
ꢀ
1
3
1
9.57%, H 2.79%, N 20.59%. FT-IR (cm , KBr): 2100 (s),
617(m), 1567(m), 1251(m), 728(m).
[
2 2 2 3 3 n
Ag(m -L )$(m -CF SO )] (7). 7 was prepared through the
similar synthetic method of 5 only using L (17.71 mg, 0.10
mmol) to replace L1 (17.71 mg, 0.10 mmol) in the reaction
2
2 2 1 2 2 4 n
Structure of [Cd (m -L ) (m -NCS) ] (1)
system. Aer a few days suitable colorless single crystals were As shown in Fig. 1, the asymmetric structural unit of [Cd
2
(m
2
-
II
obtained for X-ray diffraction study, yield 36%. Elemental anal-
ysis calcd (%) for C Ag
S: C 20.55%, H 1.34%, N 7.99%; two m
found: C 20.76%, H 1.57%, N 8.16%. FT-IR (cm , KBr): 1616(m), The central Cd atom is six-coordinated by two nitrogen atoms
L
1
)
2
(m
2
-NCS)
-bridging L
4 n
] (1) contains two central Cd ions (Cd1 and Cd2),
ꢀ
H
9 7
F N O
2 3 3 4
2
1 2
ligands and two m -bridging SCN groups.
ꢀ1
II
ꢀ
ꢀ
1
565(m), 1418(m), 1272(m), 1142(m), 1033(m), 834(m), 707(m). from L
[Ag(m -L )]$BF (8). A mixture of AgBF (0.10 mmol), L
forming CdN
0.10 mmol) and water (20 mL) was reuxed and stirred for 12 h, 2.302(4) to 2.431(2) A, Cd–S distances are 2.7140(15) A, all the N–
1
, two SCN sulfur atoms and two SCN nitrogen atoms
{
2
2
4
}
n
4
2
4 2
S
donor set. The Cd–N distances vary from
˚
˚
(
then the resulting solutions were ltered. The ltrate was kept in Cd–N and N–Cd–S angles fall in the range of 83.24(12)–
ꢂ
a CaCl desiccator. Aer a few days suitable single crystals were 94.27(9) , such coordination mode is in line with an octahe-
2
II
obtained for X-ray diffraction study, yield 46%. Elemental anal- drally coordinated Cd center.
ysis calcd (%) for C16
1
1
H
14AgBF
4
N
6
O
2
: C 37.17%, H 2.73%, N
As shown in Fig. 2, these thiocyanate ligands adopt bidentate
6.26%; found: C 37.34%, H 2.97%, N 16.46%. FT-IR (cm , KBr): bridging coordination mode, which link these neighboring Cd
ꢀ
1
II
616(m), 1566(m), 1416(m), 1266(m), 1051(bm), 836(m), 725(m). centers forming {Cd–NCS–Cd} chains. The shortest Cd/Cd
˚
distance within the {Cd–NCS–Cd} chains is 5.714(20) A. On the
other hand, as listed in Scheme 2(a), these L ligands in 1 adopt
1
X-ray crystallography
m2-bridging coordination mode. These {Cd–NCS–Cd} chains are
Diffraction intensities for complexes 1–8 were collected on further interlinked via bi-dentate L ligands forming the 2D
a Bruker SMART 1000 CCD diffractometer with graphite- coordination polymer. These L carbon atoms (C(4) and C(8))
1
1
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ꢂ
a
Table 2 Selected bond lengths ( A˚ ) and angles ( ) for 1–8
1
Cd(1)–N(4A)
Cd(1)–N(3A)
Cd(1)–S(2A)
Cd(2)–N(5)
N(4A)–Cd(1)–N(4)
N(4)–Cd(1)–N(3A)
N(4)–Cd(1)–N(3)
2.302(4)
2.431(3)
Cd(1)–N(4)
Cd(1)–N(3)
Cd(1)–S(2)
N(4)–Cd(1)–S(2A)
N(4A)–Cd(1)–N(3A)
N(4A)–Cd(1)–N(3)
N(3A)–Cd(1)–N(3)
2.302(4)
2.431(3)
Cd(2)–N(1)
Cd(2)–N(1A)
Cd(2)–N(5B)
N(3A)–Cd(1)–S(2A)
N(4A)–Cd(1)–S(2)
N(3A)–Cd(1)–S(2)
S(2A)–Cd(1)–S(2)
2.402(3)
2.402(3)
2.291(4)
81.44(9)
93.69(10)
94.27(9)
173.86(6)
2.7140(15)
2.291(4)
102.64(18)
83.24(12)
170.09(13)
2.7140(15)
93.70(10)
170.09(13)
83.24(12)
92.13(16)
2
Cd(1)–N(4)
2.261(3)
Cd(1)–N(6A)
2.264(4)
Cd(1)–N(1)
2.358(3)
Cd(1)–N(7)
2.326(4)
Cd(1)–N(9A)
2.326(3)
Cd(1)–O(2)
2.363(2)
N(4)–Cd(1)–N(6A)
N(6A)–Cd(1)–N(7)
N(6A)–Cd(1)–N(9A)
N(6)–Cd(1)–N(1)
N(9A)–Cd(1)–N(1)
98.40(13)
91.66(17)
93.34(14)
93.57(14)
89.37(13)
N(4)–Cd(1)–N(7)
N(4)–Cd(1)–N(9A)
N(7)–Cd(1)–N(9A)
N(7)–Cd(1)–O(2)
N(1)–Cd(1)–O(2)
92.38(14)
168.22(14)
86.39(16)
86.59(13)
88.01(9)
N(4)–Cd(1)–N(1)
N(7)–Cd(1)–N(1)
N(4)–Cd(1)–O(2)
N(6A)–Cd(1)–O(2)
N(9A)–Cd(1)–O(2)
90.76(11)
173.45(13)
84.10(11)
177.01(13)
84.13(12)
3
Cu(1)–N(4)
Cu(1)–N(1)
N(4)–Cu(1)–N(4A)
N(4A)–Cu(1)–N(1)
1.974(2)
2.0578(19)
180.0
Cu(1)–N(4A)
1.974(2)
88.99(8)
88.99(8)
91.01(8)
Cu(1)–N(1A)
N(1)–Cu(1)–N(1A)
N(4)–Cu(1)–N(1A)
2.0578(19)
180.0
91.01(8)
N(4A)–Cu(1)–N(1A)
N(4)–Cu(1)–N(1)
N(4)–Cu(1)–N(1A)
91.01(8)
4
Ag(1)–N(2)
Ag(1)–N(8)
Ag(2)–N(6)
N(2)–Ag(1)–N(4A)
N(4A)–Ag(1)–N(8)
2.277(4)
2.309(4)
2.225(4)
124.79(16)
109.87(16)
Ag(1)–N(4A)
Ag(1)–N(3)
Ag(2)–N(9A)
N(2)–Ag(1)–N(8)
N(2)–Ag(1)–N(3)
2.307(4)
2.406(4)
2.231(4)
111.05(14)
102.49(14)
Ag(2)–N(7)
Ag(2)–N(1)
N(4A)–Ag(1)–N(3)
N(6)–Ag(2)–N(9A)
N(8)–Ag(1)–N(3)
2.421(4)
2.554(4)
98.30(17)
152.34(16)
108.07(14)
5
Ag(1)–N(4)
Ag(1)–N(1)
Ag(2)–N(3)
N(4)–Ag(1)–N(1)
N(7)–Ag(2)–N(3)
N(3)–Ag(2)–N(6)
2.209(4)
2.458(4)
2.297(4)
103.68(13)
143.19(14)
104.96(13)
Ag(1)–N(12A)
Ag(2)–N(7)
Ag(2)–N(6)
N(12A)–Ag(1)–N(1)
N(7)–Ag(2)–N(6)
N(7)–Ag(2)–O(5)
2.211(4)
2.284(3)
2.352(4)
104.13(14)
109.20(13)
94.06(14)
Ag(3)–N(10)
Ag(3)–N(9)
Ag(2)–O(5)
N(3)–Ag(2)–O(5)
N(9)–Ag(3)–N(10)
N(6)–Ag(2)–O(5)
2.154(3)
2.152(3)
2.591(4)
77.79(13)
175.45(15)
123.73(15)
6
Cd(1)–N(4)
Cd(1)–N(1)
N(4)–Cd(1)–N(4A)
N(4A)#1–Cd(1)–N(1)
2.325(3)
2.364(2)
180.00(15)
89.49(9)
Cd(1)–N(4A)
Cd(1)–N(1A)
N(4)–Cd(1)–N(1)
N(1)–Cd(1)–S(1B)
2.325(3)
2.364(2)
90.51(9)
90.37(6)
Cd(1)–S(1A)
Cd(1)–S(1B)
N(4)–Cd(1)–S(1A)
N(1)–Cd(1)–S(1A)
2.7253(9)
2.7253(9)
91.75(8)
89.63(6)
7
Ag(1)–N(1)
Ag(1)–O(4)
N(1)–Ag(1)–O(2A)
2.165(2)
2.710(2)
99.27(1)
Ag(1)–N(3A)
N(1)–Ag(1)–N(3A)
N(3A)–Ag(1)–O(4)
2.184(2)
164.72(9)
83.54(1)
Ag(1)–O(2A)
N(1)–Ag(1)–O(4)
2.623(2)
94.19(1)
8
Ag(1)–N(1)
Ag(1)–N(3B)
N(1)–Ag(1)–N(1)
N(1)–Ag(1)–N(3)
2.282(3)
2.349(3)
121.29(18)
94.85(12)
Ag(1)–N(1)
N(1)–Ag(1)–N(3A)
N(1)–Ag(1)–N(3)
2.282(3)
125.45(12)
125.45(12)
Ag(1)–N(3A)#1
N(3A)–Ag(1)–N(3B)
N(1)–Ag(1)–N(3)
2.349(3)
94.65(17)
94.85(12)
a
Symmetry transformations used to generate equivalent atoms: for 1: (A) ꢀx, y, ꢀz + 1/2; (B) x + 1, y, z. For 2: (A) x, y, z ꢀ 1. For 3: (A) ꢀx, ꢀy + 1, ꢀz +
. For 4: (A) x + 1, y, z. For 5: (A) x + 2, y ꢀ 1, z + 1. For 6: (A) ꢀx + 2, ꢀy + 1, ꢀz; (B) x, ꢀy + 1/2, z ꢀ 1/2. For 7: (A) x ꢀ 1, ꢀy + 3/2, z + 1/2. For 8: (A) 3/2 ꢀ x,
1
y, 2 ꢀ z; (B) 1 ꢀ x, 1/2 + y, 3/2 ꢀ z.
ꢀ
and SCN nitrogen and sulfur atoms (N(4) and S(1)) generate Structure of {[Cd(L )(m -dca) (H O)]$H O} (2)
1
2
2
2
2
n
these non-classical hydrogen bonds (C(4)–H(4)/N(4), 3.448(6)
The asymmetric structural unit of {[Cd(m -L )(m -dca) (H O)]$
2
1
2
2
2
˚
˚
A; C(8)–H(8B)/S(1), 3.652(5) A), which further stabilize the 2D
II
H O} (2) contains one central Cd ion (Cd1), one m -bridging L
1
2
n
2
24,25
coordination polymer 1.
ꢀ
ligand, two m
2
-bridging dca groups and one coordinated water
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Scheme 1 Two isomeric oxadiazol-pyridine ligands 3-(5-methyl-
1
1
,3,4-oxadiazol-2-yl)pyridine (L ) and 3-(5-methyl-1,3,4-oxadiazol-2-
yl)pyridine (L ).
2
2 2 1 2 2 4 n
Fig. 2 2D coordination polymer [Cd (m -L ) (m -NCS) ] (1) containing
infinite {Cd–NCS–Cd} chains.
Fig. 3 The fundamental structural unit of {[Cd(L
O} (2).
1 2 2 2
)(m -dca) (H O)]$
1 2
Scheme 2 Five different coordination modes of L and L in 1–8 (color
code: cyan, metal; blue, N; light grey, C).
H
2
n
ꢀ
As shown in Fig. 4, these bidentate bridging dca ligands
II
connect these neighboring Cd centers forming {Cd–dca–Cd}
layers. The shortest Cd/Cd distances within the {Cd–dca–Cd}
˚
˚
layers are 7.819(1) A and 8.575(4) A. On the other hand, as listed
in Scheme 2(b), these L ligands in 2 adopt mono-dentate
coordination mode. Therefore these {Cd–NCS–Cd} layers are
further decorated via these mono-dentate L ligands. These
1
1
coordinated aqua molecules (O(2)), lattice aqua molecules
ꢀ
(O(3)), L
1
nitrogen atoms (N(3)) and dca nitrogen atoms (N(8))
generate these classical hydrogen bonds (O(2)–H(2A)/O(3),
˚
˚
2
2
.740(4) A; O(2)–H(2B)/N(3), 2.854(4) A; O(3)–H(3A)/O(2),
˚
˚
.965(4) A; O(3)–H(3B)/N(8), 2.970(6) A), which further stabi-
lize the 2D coordination polymer 2.
2 2 1 2 2 4 n
Fig. 1 The fundamental structural unit of [Cd (m -L ) (m -NCS) ] (1).
Structure of {[Cu(m
2 1 2 2 2 n
-L ) (NCS) ]$0.5H O} (3)
molecule (O2) and one lattice aqua molecule (O3) (Fig. 3). The
II
central Cd atom is six-coordinated by one nitrogen atom (N1) As shown in Fig. 5, the asymmetric structural unit of 3 contains
ꢀ
II
from one L
1
, four dca nitrogen atoms (N4, N7, N6A and N9A) one central Cu ion (Cu1), one m
2
-bridging L
1
ligand and two
ꢀ
II
and one terminal aqua molecule (O2) forming CdN O donor set. terminal bridging SCN groups. The central Cu atom is six-
5
˚
The Cd–N distances are 2.261(3)–2.326(4) A, Cd–O distances are coordinated by four nitrogen atoms (N1, N1A, N3A and N3B)
˚
2
.363(2) A. All the N–Cd–N and N–Cd–O angles fall in the range from four L , two thiocyanate nitrogen atoms (N4 and N4A)
1
ꢂ
of 84.10(11)–98.40(13) , such coordination mode is in accor- forming the CuN
dance with an octahedrally coordinated Cd center.
6
donor set. The Cu–N distances are 1.974(2)–
II
˚
2.0578(19) A, all the N–Cu–N angles fall in the range of 88.99(8)–
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nitrogen atoms (N(2)) generate these non-classical hydrogen bonds
˚
(
C(1)–H(1)/N(2), 3.304(3) A), which also further extend 3 into a 3D
supramolecular architecture. Such weak intermolecular interac-
tions are key for the stabilization of the 2D coordination polymer 3.
2 2 1 3 1 2 6 n
Structure of {[Ag (m -L )(m -L ) ]$2PF } (4)
When AgBF are used, 1D Ag(I) coordination polymers, {[Ag (m -
4
2
3
L
1
)
2
(m
2
-L
1
)]$2PF
6
}
n
(4), can be isolated. For 4, the coordination
ꢀ
polymer crystallizes in triclinic P1 space group with one formula
unit in the asymmetric unit. The asymmetric unit contains two
I
Ag atoms (Ag1 and Ag2), two tri-dentate bridging L
1
, one bi-
ꢀ
dentate bridging L
central Ag atom (Ag1) is four-coordinated by four nitrogen
atoms (N2, N4, N3A and N4A) from four L forming AgN donor
1
and two free PF
6
anions (Fig. 7). The
I
1 2 2 2
Fig. 4 Side view of 2D coordination polymer {[Cd(L )(m -dca) (H O)]$
H O}
2 n
(2) containing infinite {Cd–dca–Cd} layers.
1
4
I
set. The other central Ag atom (Ag2) is also four-coordinated by
four nitrogen atoms (N1, N6, N7 and N9A) from four L
AgN
the N–Ag–N angles are in the range of 98.30(17)–152.34(16) ,
1
forming
˚
4
donor set. The Ag–N distances are 2.225(4)–2.554(4) A, all
ꢂ
such coordination mode is in accord with a tetrahedrally coor-
I
dinated Ag center.
As shown in Fig. 8, Ag1 and Ag2 are inter-linked via oxadia-
zole nitrogen atoms forming di-nuclear Ag(I) clusters, neigh-
boring Ag/Ag distances within di-nuclear Ag(I) clusters are
I
˚
3
.845(6) A. These bridging L
1
ligands connect adjacent Ag ions
forming a cluster-based 1D double chain coordination polymer,
which is shown along the crystallographic a-axis. These non-
classical hydrogen bonds (C(8)–H(8B)/F(12), 3.341(9) A˚ ;
˚
˚
C(17)–H(17)/F(7), 3.190(10) A; C(17)–H(17)/F(8), 3.347(10) A;
Fig.
.5H
5
The fundamental structural unit of {[Cu(m
(3).
-L
2 1
2 2
) (NCS) ]$
˚
C(21)–H(21)/N(5), 3.504(8) A) also can be observed, which
0
2
O}
n
further extend 4 into a 3D supramolecular architecture. Such
weak intermolecular interactions are important for the stabili-
I
ꢂ
1.01(8) , such coordination mode is in accordance with an
zation of the 1D cluster-based Ag coordination polymer 4.
9
II
octahedrally coordinated Cu center.
As shown in Fig. 6 and Scheme 2(a), these L
adopt m -bridging coordination mode. These L ligands connect
ligands in 3 also Structure of {[Ag
3
(m
is used, 1D Ag(I) coordination polymer,
SO )(CF SO )]$CF SO } (5), can be isolated.
2 1 4 2 3 3 3 3 3 3
-L ) (m -CF SO )(CF SO )]$CF SO } (5)
1
2
1
When AgCF
3
SO
3
II
neighboring Cu centers forming the 2D coordination polymer 3.
{
[Ag (m -L (m
3
2
1
)
4
2
-CF
3
3
3
3
3
3
The corresponding Cu/Cu distance within the 2D coordination
˚
polymer is 9.997(5) A. These L
1
carbon molecules (C(1)) and L
1
2 2 1 3 1 2 6 n
Fig. 7 The fundamental structural unit of {[Ag (m -L )(m -L ) ]$2PF }
2 1 2 2 2 n
Fig. 6 2D coordination polymer {[Cu(m -L ) (NCS) ]$0.5H O} (3).
(4).
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I
2 2 1 3 1 2 6 n
Fig. 8 1D Ag coordination polymer {[Ag (m -L )(m -L ) ]$2PF } (4).
ꢀ
For 5, the coordination polymer also crystallizes in triclinic P1 which further extend 5 into a 3D supramolecular architecture.
space group with one formula unit in the asymmetric unit. The Such weak intermolecular interactions are key for the stabiliza-
I
I
asymmetric unit contains three Ag atoms (Ag1, Ag2 and Ag3), tion of 1D Ag double chain coordination polymer 5.
ꢀ
four bi-dentate bridging L
1
, two terminal CF
one free CF SO anion (Fig. 9). The central Ag atom (Ag1) is
three-coordinated by four nitrogen atoms (N4, N1 and N12A)
3
SO
3
anions and
ꢀ
I
3
3
Structure of {[Cd(L ) (m -NCS) ]} (6)
2
2
2
2 n
I
from three L
1
forming AgN
donor set. The central Ag atom As shown in Fig. 11, the asymmetric structural unit of
3
II
{
[Cd(L ) (m -NCS) ]} (6) contains one central Cd ions (Cd1),
2 2 2 2 n
two terminal coordinated L ligands and two m -bridging NCS
groups. The central Cd atom is six-coordinated by two nitrogen
(
Ag2) is four-coordinated by three nitrogen atoms (N3, N6 and
ꢀ
ꢀ
N7) from three L
1
and one CF
3
SO
3
oxygen atom (O5) forming
1
2
I
II
3
AgN O donor set. The central Ag atom (Ag3) is three-
atoms (N1 and N1A) from two L
N4A) and two sulfur atoms (S1A and S1B) form four NCS
2
, two nitrogen atoms (N4 and
coordinated by two nitrogen atoms (N9 and N10) from two L
1
ꢀ
ꢀ
and one CF
3
SO
3
2
oxygen atom (O9) forming AgN O donor set.
˚
˚
groups forming CdN4S donor set. The Cd–N distances vary
from 2.325(3) to 2.364(2) A˚ , Cd–S distances are 2.7253(9) A˚ . All
The Ag–N distances vary from 2.209(4) A to 2.458(4) A, Ag–O
2
˚
distances are 2.591(4) A, all the N–Ag–N and N–Ag–O angles fall
in the range of 77.79(13)–143.19(14) , All the bond distances the N–Cd–N and N–Cd–O angles are in the range of 89.63(6)–
and bond angles all fall into the normal range.
As shown in Fig. 10, L adopt bi-dentate bridging coordination
mode, which connect neighboring Ag1, Ag2 and Ag3, forming 1D
ꢂ
ꢂ
9
1.75(8) , such coordination mode is in accordance with an
II
octahedrally coordinated Cd center.
As shown in Fig. 12, these bidentate bridging NCS ligands
connect neighboring Cd centers forming the {Cd–NCS–Cd}
1
ꢀ
II
double chain coordination polymer 5. The shortest neighboring
layers. The shortest distances of Cd/Cd within the {Cd–NCS–
Cd} layers are 6.280(1) and 7.570(1) A˚ . On the other hand, as
Ag/Ag distances within 1D double chain are 4.478(2) and
˚
4
.858(8) A. These non-classical hydrogen bonds (C(1)–H(1A)/
˚
˚
listed in Scheme 2(b), these L ligands in 6 adopt mono-dentate
O(13), 3.348(7) A; C(4)–H(4)/N(2), 3.259(6) A; C(12)–H(12)/N(5),
2
˚
˚
coordination mode. Therefore these {Cd–NCS–Cd} layers are
3
.241(6) A; C(15)–H(15)/O(11), 3.393(7) A) also can be observed,
3 2 1 4 3 3 2
Fig. 9 The fundamental structural unit of {[Ag (m -L ) (CF SO ) ]$
CF SO }(5).
3
3
2 2 2 2 2 n
Fig. 11 The fundamental structural unit of {[Cd(m -L ) (m -NCS) ]} (6).
I
3 2 1 4 2 3 3 3 3 3 3
Fig. 10 1D Ag coordination polymer {[Ag (m -L ) (m -CF SO )(CF SO )]$CF SO }(5).
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2 2 2 2 2 n
Fig. 12 2D coordination polymer {[Cd(m -L ) (m -NCS) ]} (6) containing infinite {Cd–NCS–Cd} layers.
2 2
further decorated via these mono-dentate L ligands. These L
carbon atoms (C(1)) and nitrogen atoms (N(3)) generate non-
˚
classical hydrogen bonds (C(1)–H(1)/N(3), 3.528(4) A), which
further stabilize the 2D coordination polymer 6.
Structure of [Ag(m -L )$(m -CF SO )] (7)
2
2
2
3
3 n
As shown in Fig. 13, the asymmetric structural unit of [Ag(m -
2
I
L )$(m -CF SO )] (7) contains one central Ag ions (Ag1), one m -
2
2
3
3
n
2
2 2 2 3 3 n
Fig. 14 2D coordination polymer [Ag(m -L )(m -CF SO )] (7).
ꢀ
bridging L ligand, one m -bridging CF SO group. For 7, the
2
2
3
3
1
coordination polymer crystallizes in monoclinic P2 /n space
group with one formula unit in the asymmetric unit. The central
˚
I
hydrogen bonds (C(2)–H(2C)/F(1), 3.338(5) A; C(6)–H(6)/O(4),
Ag atom (Ag1) is four-coordinated by two nitrogen atoms (N1
˚
ꢀ
3.308 A), which further extend 7 into a 3D supramolecular
architecture. Such weak intermolecular interactions are
important for the stabilization of the 1D cluster-based Ag
and N3A) from two L
1
and two CF
3
SO
3
oxygen atoms (O2A and
O4) forming AgN
2
O
2
donor set. Ag–N distances are 2.165(2)–
I
˚
˚
2
.184(2) A, Ag–O distances are 2.623(2)–2.710(2) A, all the N–Ag–
coordination polymer 7.
ꢂ
N and N–Ag–O angles are in the range of 83.54(1)–94.19(1) ,
such coordination mode is in accord with a tetrahedrally coor-
I
2 2 4 n
Structure of {[Ag(m -L )]$BF } (8)
dinated Ag center.
3
3ꢀ
As shown in Fig. 14, these CF
bridging coordination modes via its two oxygen atoms (O2 and
O4). On the other hand, these L
2 4
ligands also adopt bridging bridging L ligand, one free BF
SO anions adopt bi-dentate As shown in Fig. 15, the fundamental structural unit of {[Ag(m
2
2
-
-
I
L
2
)]$BF
4
}
n
(9) contains one central Ag ions (Ag1), one m
ꢀ
group. For 8, the coordination
/a space group with one
2
coordination mode as listed in Scheme 2(e). These bridging polymer crystallizes in monoclinic I
2
ꢀ
I
CF SO3 anions and L ligands link these neighboring Ag(I) formula unit in the asymmetric unit. The central Ag atom (Ag1)
3
2
centers, which ultimately forming the 2D coordination polymer is four-coordinated by four nitrogen atoms (N1, N3A, N1A and
ꢀ
7
. These L carbon atoms (C(2) and C(6)) and CF SO oxygen N3B) from four L
2
forming AgN donor set. The Ag–N distances
˚
ꢂ
4
2
3
3
and uoride atoms (O(4) and F(1)) generate these non-classical are 2.282(3)–2.349(3) A, all the N–Ag–N angles are in the range of
94.65(17)–125.45(12) , such coordination mode is in accord
I
with a tetrahedrally coordinated Ag center.
As shown in Fig. 16, these L ligands also adopt bridging
coordination mode as listed in Scheme 2(e). These bridging L
2
2
2 2 2 3 3 n 2 2 4 n
Fig. 13 The fundamental structural unit of [Ag(m -L )(m -CF SO )] (7). Fig. 15 The fundamental structural unit of {[Ag(m -L )]$BF } (8).
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minimum values at 2 K. Fitting the magnetic susceptibility data
with the Curie–Weiss law cM ¼ C/(T ꢀ q), where C and q
represent the Curie constant and the Weiss temperature, it can
give q values of ꢀ1.05 K. These q values reveal anti-
II
ferromagnetic interactions between central Cu ions. The
result of weak anti-ferromagnetic interactions can be attributed
to can be attributed to very weak antiferromagnetic interactions
as indicated by large metal–metal distances or the presence of
26
zero-eld splitting or both in 3.
Luminescence properties
Coordination polymers have been investigated for potential
applications as luminescent materials, such as light-emitting
27
diodes (LEDs). Owing to the ability of affecting the emission
wavelength and strength of organic materials, syntheses of
coordination polymers by judicious choice of conjugated
organic spacers and transition metal centers can be an efficient
method for obtaining new types of luminescent materials,
I
2 2 4 n
Fig. 16 2D cationic Ag coordination polymer {[Ag(m -L )]$BF } (8).
ligands link these neighboring Ag(I) centers, which ultimately
forming the 2D grid-like cationic coordination polymer. These
non-classical hydrogen bonds (C(4)–H(4)/F(2), 3.085(9) A) also
can be observed, which further extend 8 into a 3D supramo-
lecular architecture. Such weak intermolecular interactions are
10
10 10
28
especially for d or d –d systems. In the present work, we
have explored the luminescent properties of L , L ligands and
1
2
˚
organic/inorganic coordination polymers 1, 2 and 4–8 based on
the ligands in the solid state.
As shown in Fig. 18, at room temperature, free L and L
1 2
ligands in the solid state are luminescent, which show the broad
I
important for the stabilization of the 2D Ag coordination
polymer.
emission maximum centered at 360 nm (lex ¼ 280 nm) and
3
61 nm (l ¼ 280 nm), respectively. For the free L and L ligands,
ex
1
2
the chromophores are aromatic pyridine and oxadiazol rings, the
Magnetic properties of 3
observed emission is due to p–p* transition. In comparison with
Variable temperature dc magnetic susceptibility data were that of free ligand, upon excitation of solid samples of 1, 2, 6 and 8
collected on a microcrystalline powder sample of 3 in a 1000 Oe show emission bands with maximum at ca. 360 nm (for 1), ca.

eld in the temperature range 1.8–300 K. The temperature- 361 nm (for 2), ca. 363 nm (for 6) and ca. 362 nm (for 8) respec-
dependent magnetic susceptibility data of complexes 3 have tively. The emissions of 1, 2, 6 and 8 should be assigned to
29
been measured in the temperature range of 2–300 K. The intraligand p–p* transitions. The slight shis of the emission
diamagnetic correction was evaluated by using Pascal's bands relative to free L and L ligands can be attributed to the
1
2
3
30
constants. As shown in Fig. 17, The c T values are ca. 0.416 cm
kmol (for 3) at room temperature, which are expected spin-
coordination action of ligand to central metal ions.
On the other hand, for these 1D or 2D cluster-based Ag
only values for an isolated Cu(II) ion. When the temperature is coordination polymers 4, 5 and 7, it is noted that red-shi of
lowered, c T values remain constants and then smoothly
m
ꢀ
1
I
M
decrease and drop rapidly below ca. 20 K reaching the
1 2
Fig. 17 Variable-temperature magnetic susceptibility data for 3 in the Fig. 18 Solid-state fluorescence spectra of 1–2, 4–8 and L , L ligand
2–300 K temperature range.
molecules.
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luminescent emissions can be observed (emission bands with a negligible effect on the luminescence intensity for other
2
ꢀ
maximum centered at 395 nm for 4 (l ¼ 300 nm), 403 nm for 5 anions. PXRD pattern of 8-Cr O
was measured and remains
ex
2 7
(l
¼ 300 nm) and 372 nm for 7 (l ¼ 300 nm)). The photo- well consistent with the simulated one of 8, indicating that 8
ex
ex
luminescence origin of the emission bands should be attributed still remains stable. The result indicates the high selectivity of 8
2
ꢀ
to metal-to-ligand charge transfer (MLCT) as discussed in the for the detection and specic recognition of Cr
2
O
7
anions in
1
previous literature. Because 5 and 6 contain similar 1D struc- aqueous solutions. Therefore 8 may be chosen as a candidate
2
ꢀ
tural motifs, different band shapes in the luminescent emis- for the selective sensing of Cr
2
O
7
.
ꢀ
ꢀ
sions of 5 and 6 can be ascribed to different guest PF
6
/CF
3
SO
3
Generally, waste water contains more than one type of
anions, which can greatly affect luminescence emission pollutant anions, and therefore, it is essential to investigate the
3
1
I
bands.
These cluster-based Ag coordination polymers inuence of mixed anions on the luminescence of 8. The
ꢀ
4
increase the ligand conformational rigidity, thereby reducing detailed experiments are as follows: 0.4 mL of Na Cr O (10
2
2 7
ꢀ4
the non-radiative decay of the intraligand (p–p*) excited state. M) and 0.4 mL of other anion solutions (10 M) were slowly
The syntheses of new Cd(II) and Ag(I) complexes with these dropped into a 3.2 mL suspension of 8, respectively. The
isomeric oxadiazol-pyridine ligands can be an efficient method luminescence measurements of resultant solutions, containing
32,33
2ꢀ
for obtaining new types of luminescent materials.
Cr
2
O
7
and other anions, were carried out at once. It is also
noted that there was only a negligible effect on the lumines-
2
ꢀ
cence intensity for Cr
2
O
7
anions. This selective detection of
2
ꢀ
Luminescent sensing properties of Cr
for 8
2
O
7
anion pollutants
2ꢀ
Cr O
anions has no interfering effects from other anions
such as SiF , CO , HCO , BF4 , NO3 , SCN , Ac , SO
2
7
2ꢀ
2ꢀ
2ꢀ
ꢀ
42ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
,
6
3
3
4
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
3ꢀ
2ꢀ
3ꢀ
In general, water pollutions are a global environmental issue, Br , Cl , F , I , BrO
, IO , CrO , HPO
and PO
, sug-
3
4
4
2
ꢀ
and considerable research attention has been paid to the gesting that 8 can selectively detect Cr O
2 7
anions among the
removal of pollutants from waste water. With the development above anions.
2
ꢀ
of modern industry, Cr O
anions have been widely used in
Moreover, to explore the detection limit of 8 as a luminescent
2
7
2
ꢀ
the eld of chromium plating, metallurgy, pigment probe for detecting Cr
2
ꢀ
O
7
, as shown in Fig. 19(b), a series
(5 mM to 100 mM) were prepared by
2
manufacturing, leather tanning, and wood preservation. These suspension of 8-Cr
anion pollutants have been a focus of concern because they dropping different concentrations of Cr
cause serious damage to human health and the environment. suspension of 8. The luminescence intensity of 8 gradually
O
2 7
2
ꢀ
O
solutions into the
2
7
2
7
ꢀ
Therefore, the exploration of new materials for the efficient decreases with increasing the concentration of Cr
O
. As
2
34
detection of these anion pollutants is highly important.
In this work, the product of 8 as the luminescent probes was decreases with the concentration of Cr
carefully explored for sensing diverse ions, owing to its strong mM to 70 mM. The detection limit of 8 as a luminescent probe for
shown in Fig. 19(c) and (d), the luminescence intensity linearly
2
ꢀ
2
O
7
ranging from 0.5
2
ꢀ
visible blue light when excited by ultraviolet light. The photo- detecting Cr
2
O
7
is supported by the calculated results based
luminescence emission bands of 8 in aqueous solutions are on the equation: detection limit ¼ 3s/k (s is the standard
centered at around 360 nm. These emission bands should be deviation of blank measurement; k is the slope between the
2
ꢀ
more likely to be due to intra-ligand transitions because similar luminescence intensity vs. log[Cr
photo-luminescent bands can be observed for free L
ligands in relationship between the quenching effect and Cr
aqueous solutions. On the other hand, water stability of 8 was concentration, the linear luminescence intensity vs. Cr
also investigated, the solid state samples were suspended in concentration plot was made, which can be tted into I
O
]). To further explore the
2
7
2
ꢀ
ꢀ
O
O
2
2
2
7
7
2
0
/I ¼ 1 +
2
ꢀ
aqueous solutions for 12 h, then water solutions were ltrated
and solid state samples were dried by the vacuum oven. Then before and aer adding Cr
solid state samples were characterized by PXRD patterns. As sents the concentration of Cr
shown in Fig. S1,† PXRD patterns of solid state samples sus- quenching rate constant). The Ksv value is calculated to be 2.08
K
sv[Cr
2
O
7
] (I and I represent the luminescence intensity of 8
0
2
ꢀ
2ꢀ
7
2
O
7
, respectively; [Cr
2
O
] repre-
2
ꢀ
O
2 7
, and Ksv represents the
4
ꢀ1
pended in the water solutions and these calculated patterns ꢁ 10 L mol , indicating the high quenching efficiency of
2
ꢀ
35–37
deduced from single-crystal X-ray data are in good agreement. Cr
O
7
in the emission of 8.
The high quenching efficiency
2
The result indicates that the coordination polymer structure is and low detection limit 0.19 mM (S/N ¼ 3) also reveal that 8 can
unchangeable and can retain stable in aqueous solutions.
In order to study the luminescent responses to different Cr
anions, the products of 8 were ground into powder and sus-
act as luminescent probes for discrimination and detection of
2
ꢀ
2
O
7
.
4ꢀ
8 is a cationic coordination polymer, in which free BF
pended in the water solution containing different salt solutions anions are located between these 2D cationic layers, while in
ꢀ
4
2ꢀ
ꢀ
2ꢀ
2ꢀ
3ꢀ
I
of the same concentration (10 M) of SiF
6
, CO
3
, HCO
3
,
,
other Ag coordination polymers these anions are tightly linked
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
BF
CrO
4
, NO
3
, SCN , Ac , SO
4
, Br , Cl , F , I , BrO
3
, IO
to main frameworks through coordination bonds. As illustrated
. Aqueous solutions of in the previous literature, these cationic coordination polymers
2
ꢀ
2ꢀ
3ꢀ
2ꢀ
4
2
, HPO
4
2ꢀ
and PO
4
and Cr
, NO
2
O
7
ꢀ
2ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
ꢀ
2ꢀ
SiF
6
, CO
3
ꢀ
, HCO
3
, BF
4
3
, SCN , Ac , SO
4
, Br , can effectively capture Cr
2
O
7
anions through anion exchange
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
2ꢀ
3ꢀ
38
Cl , F , I , BrO , IO3 , CrO4 , HPO4
and PO4
and process, which may effectively lead to the uorescent
3
2
ꢀ
Cr O
were prepared from these corresponding potassium quenching of 8. On the other hand, in comparison with other
2
7
2
ꢀ
2ꢀ
salts, respectively. As shown in Fig. 19(a), Cr
2
O
7
gave signi- anions, only Cr
2
O
7
exhibits two wide absorption bands from
39
cant uorescence quenching effect, while there was only 230 to 413 nm. The bands almost cover the whole ranges of
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ꢀ4
Fig. 19 (a) Comparison of the luminescence intensity of 8 at 360 nm incorporating aqua solutions (10 M) upon the addition of various anions;
2
ꢀ
(
8
b) liquid luminescence spectra of 8 under different concentrations of Cr
O
2 7
aqueous solution; (c) comparison of the luminescence intensity of
2ꢀ
2ꢀ
under different concentrations of Cr
2
O
7
anion pollutants aqueous solution. (d) The linear luminescence intensity vs. Cr
2
O
7
anion pollutants
concentration plot.
absorption bands that arise from 8. Thus, the luminescence
quenching mechanism also further causes by the competition 2PF } (4), {[Ag (m -L ) (m -CF SO )(CF SO )]$CF SO } (5), {[Cd(L )
2 2
2 n 2 1 2 2 2 n 2 2 1 3 1 2
H O} (2), {[Cu(m -L ) (NCS) ]$0.5H O} (3), {[Ag (m -L )(m -L ) ]$
6
n
3
2
1 4
2
3
3
3
3
3
3
2
ꢀ
of excitation energy between Cr O
anions and 8. Upon illu- (m -NCS) ]} (6), [Ag(m -L )(m -CF SO )] (7) and {[Ag(m -L )]$
2 2 n 2 2 2 3 3 n 2 2
ions for excitation energy BF } (8) have been isolated. Both 1 and 2 are 2D Cd coordi-
4 n
2
7
2
ꢀ
II
mination, the adsorption of Cr O
2
7
hinders the UV/vis absorption of the target coordination poly- nation polymers containing innite {Cd–NCS–Cd} chains (for 1)
II
mer, thus resulting in a decrease, or even full quenching, of the or innite {Cd–dca–Cd} layers (for 2). 3 is a 2D Cu coordination
luminescence intensities. This luminescent sensing mecha- polymer, in which central metal ions are bridged via bidentate
2
ꢀ
I
nism for Cr
2
O
7
is consistent with those previously proposed bridging L
1
ligand. While when different Ag salts were intro-
40,41
I
by previous literature.
To the best of our knowledge, work on duced into the reaction system, 1D cluster-based Ag coordina-
these metal–organic polymers as luminescent probes for tion polymers 4 and 5 with diverse coordination modes can be
2
ꢀ
discrimination and detection of Cr O
is important and still isolated. Further when the isomeric oxadiazol-pyridine L2 is
2
7
42
limited. 8 also represents the rst report of coordination used to replace L in the reaction system, 6–8 can be isolated. 6
polymers based on oxadiazol-pyridine derivatives as lumines- is a 2D Cd coordination polymer containing 2D {Cd–NCS–Cd}
1
II
2
ꢀ
I
cent response to Cr
2
O
7
in the water solutions.
layers. 7 is a 2D neutral Ag coordination polymer while 8 is a 2D
I
cationic Ag coordination polymer. Variable temperature
magnetic susceptibility measurements (2–300 K) reveal anti-
ferromagnetic interactions between central copper(II) ions for
Conclusions and perspectives
In conclusion, in this work two position-isomeric oxadiazol- 3. Solid-state luminescent properties of 1, 2 and 4–8 have been
pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L1) investigated indicating strong uorescent emissions. Addi-
and 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L ) have been tionally, luminescent measurements illustrate that complex 8
2
2ꢀ
designed and synthesized. A series of novel coordination poly- also exhibits highly sensitive luminescence sensing for Cr
2
O
7
mers, namely [Cd (m -L ) (m -NCS) ]
2 2 1 2 2 4 n
1 2 2 2
(1), {[Cd(L )(m -dca) (H O)]$ anion pollutants in aqueous solutions with high quenching
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4
ꢀ1
efficiency Ksv ¼ 2.08 ꢁ 10 L mol and low detection limit (0.19
mM (S/N ¼ 3)). 8 also represents the rst report of coordination
polymers based on oxadiazol-pyridine derivatives as lumines-
5 (a) J. R. Li, R. J. Kuppler and H. C. Zhou, Chem. Soc. Rev.,
2009, 38, 1477; (b) R. Vaidhyanathan, S. S. Iremonger,
G. K. H. Shimizu, P. G. Boyd, S. Alavi and T. K. Woo,
Science, 2010, 330, 650; (c) P. Nugent, Y. Belmabkhout,
S. D. Burd, A. J. Cairns, R. Luebke, K. Forrest, T. Pham,
S. Ma, B. Space, L. Wojtas, M. Eddaoudi and
M. J. Zaworotko, Nature, 2013, 495, 80; (d) H. Yin, J. Wang,
Z. Xie, J. Yang, J. Bai, J. Lu, Y. Zhang, D. Yin and
J. Y. S. Lin, Chem. Commun., 2014, 50, 3699.
2
ꢀ
cent response to Cr O
anion pollutants in the water solu-
2
7
tions. On the basis of this work, further syntheses, structures
and properties studies of these coordination polymers using
these isomeric oxadiazol-pyridine derivatives as basic building
blocks are also under way in our laboratory.
6
(a) R. Kitaura, K. Fujimoto, S. Noro, M. Kondo and
S. Kitagawa, Angew. Chem., Int. Ed., 2002, 41, 133; (b)
R. Kitaura, G. Onoyama, H. Sakamoto, R. Matsuda, S. Noro
and S. Kitagawa, Angew. Chem., Int. Ed., 2004, 43, 2684; (c)
B. Chen, F. R. Fronczek and A. W. Maverick, Inorg. Chem.,
Acknowledgements
This work was supported nancially by the Open Project of Key
Lab Adv Energy Mat Chem (Nankai Univ), Tianjin Educational
Committee (20120508), Natural Science Foundation of Tianjin
2004, 43, 8209; (d) P. A. Maggard, B. Yan and J. Luo, Angew.
(
2
(
Grant no. 14JCQNJC05900), Young Scientist Fund (Grant no.
1301128), National Natural Science Foundation of China
Grant No. 21375095) and the Program for Innovative Research
Chem., Int. Ed., 2005, 44, 2; (e) R. Custelcean and
M. G. Gorbunova, J. Am. Chem. Soc., 2005, 127, 16362; (f)
Y. Yoshida, K. Inoue and M. Kurmoo, Inorg. Chem., 2009,
Team in University of Tianjin (TD12-5038).
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2010, 2, 780; (h) M. J. Manos, E. J. Kyprianidou,
G. S. Papaefstathiou and A. J. Tasiopoulos, Inorg. Chem.,
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