Synthesis, structure, thermal stability and luminescence of six coordination polymers based on 3-(4-hydroxypyridinium-1-yl)phthalic acid and auxiliary dipyridyl ligands

Article abstract of DOI:10.1016/j.ica.2014.03.019

Hydro(solvo)thermal reactions of metal salts and 3-(4-hydroxypyridinium-1- yl)phthalic acid (H₂L) with 4,4′-bipyridine (4,4′-bipy), N,N′-bis(4-pyridylmethyl)piperazine (4-bpmp), and 1,3-bis(4-pyridyl) propane (bpp) auxiliary dipyridyl ligands afforded six new coordination polymers, namely [CdL(H₂O)]_n (1), [CoL(4,4'-bipy) _0.5(H₂O)]_n (2), [ZnL(4-bpmp) _0.5(H₂O)]_n·2nH₂O (3), [ZnL(bpp)]_n·5nH₂O (4), [Zn₂L ₂(bpp)(H₂O)₂]_n·nH ₂O (5) and [Zn₂L₂(bpp)(H₂O)] _n·4nH₂O (6). They were characterized by elemental analysis, IR, PXRD, thermogravimetry and X-ray structural analysis. Complex 1 is a 1D ribbon coordination polymer. Complex 2 is a 2D coordination polymer constructed from L and 4,4′-bipy ligands, which is further extended into a 3D supramolecular framework through strong hydrogen bonds. Complex 3 features a 1D chain polymeric structure formed by [Zn₂L₂] dimer and 4-bpmp linker. Complex 4 exhibits a 1D nano-tubular structure with larger cavities, which are fully occupied by (H₂O)₅ clusters. Complex 5 displays a 1D linear chain structure. Complex 6 is a 2D layered coordination polymer. These complexes exhibit structural diversity originating from four typical coordination modes of 3-(4-hydroxypyridinium-1-yl)phthalate and various dipyridyl spacers. Thermogravimetric analyses demonstrate that the dehydrate complexes are thermally stable to ca. 260-300 °C. Complexes 1 and 3 emit strong blue luminescence originating from ligand-centered emission.

Full text of DOI:10.1016/j.ica.2014.03.019

Inorganica Chimica Acta 416 (2014) 13–21
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, structure, thermal stability and luminescence of six
coordination polymers based on 3-(4-hydroxypyridinium-1-yl)phthalic
acid and auxiliary dipyridyl ligands
a
a
b
a,
Jin-Jin Shen a, Ming-Xing Li a, , Zhao-Xi Wang , Shou-Rong Zhu , Min Shao , Xiang He
⇑
⇑
a Department of Chemistry, College of Sciences, Shanghai University, Shanghai 200444, PR China
b Laboratory for Microstructures, Shanghai University, Shanghai 200444, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Hydro(solvo)thermal reactions of metal salts and 3-(4-hydroxypyridinium-1-yl)phthalic acid (H2L) with
4,40-bipyridine (4,40-bipy), N,N0-bis(4-pyridylmethyl)piperazine (4-bpmp), and 1,3-bis(4-pyridyl)propane
(bpp) auxiliary dipyridyl ligands afforded six new coordination polymers, namely [CdL(H2O)]n (1),
[CoL(4,4’-bipy)0.5(H2O)]n (2), [ZnL(4-bpmp)0.5(H2O)]nꢀ2nH2O (3), [ZnL(bpp)]nꢀ5nH2O (4), [Zn2L2(bpp)-
(H2O)2]nꢀnH2O (5) and [Zn2L2(bpp)(H2O)]nꢀ4nH2O (6). They were characterized by elemental analysis,
IR, PXRD, thermogravimetry and X-ray structural analysis. Complex 1 is a 1D ribbon coordination poly-
mer. Complex 2 is a 2D coordination polymer constructed from L and 4,40-bipy ligands, which is further
extended into a 3D supramolecular framework through strong hydrogen bonds. Complex 3 features a 1D
chain polymeric structure formed by [Zn2L2] dimer and 4-bpmp linker. Complex 4 exhibits a 1D nano-
tubular structure with larger cavities, which are fully occupied by (H2O)5 clusters. Complex 5 displays
a 1D linear chain structure. Complex 6 is a 2D layered coordination polymer. These complexes exhibit
structural diversity originating from four typical coordination modes of 3-(4-hydroxypyridinium-1-
yl)phthalate and various dipyridyl spacers. Thermogravimetric analyses demonstrate that the
dehydrate complexes are thermally stable to ca. 260–300 °C. Complexes 1 and 3 emit strong blue lumi-
nescence originating from ligand-centered emission.
Received 2 January 2014
Received in revised form 6 March 2014
Accepted 11 March 2014
Available online 25 March 2014
Keywords:
3-(4-Hydroxypyridinium-1-yl)phthalic acid
Coordination polymer
Crystal structure
Thermal stability
Luminescence
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
In this work, 3-(4-hydroxypyridinium-1-yl)phthalic acid (H2L,
Scheme 1) is chosen as primary ligand for the following reasons:
The design and self-assembly synthesis of coordination
polymers have attracted great interest due to their fascinating
structural motifs and various functional properties such as lumines-
cence, magnetism, catalysis, ferroelectric, and porous materials
[1–6]. Their coordination frameworks are highly influenced by
diversified factors such as ligand character, metal ion, coligand, sol-
vent system, pH value, reaction temperature, and crystallization
method. The selection of the organic ligand is a key factor for
preparing functional coordination polymers. In particular, the self-
assembly of polycarboxylates with metal ions by hydro(solvo)ther-
mal reactions has become one of the most effective synthesis
strategies [7–9]. It is known that polycarboxylate ligands have been
proved to be excellent structural constructors due to their various
coordination modes [10–12].
(1) this ligand contains two adjacent carboxyl groups that can dis-
play various coordination modes; (2) the functional hydroxyl
group can coordinate to metal center to facilitate the formation
of coordination polymer, and can play a hydrogen bond acceptor
to extend the supramolecular network; (3) the pyridyl ring often
twists a larger dihedral angle with respect to the phenyl ring across
the CꢁN single bond; which can bring versatile binding modes or
configurations, and promote structural diversity. Recently,
five papers concerning 3-(4-hydroxypyridinium-1-yl)phthalate
complexes were published, in which most of reported compounds
are lanthanide complexes [13–17].
In constructing polycarboxylate coordination polymers,
a
number of neutral N-heterocyclic organic compounds play
auxiliary ligands to promote structural diversity. 4,40-Bipyridine
is
a prominent example for playing a bridging ligand in
constructing diverse architectures of coordination networks
[18–20]. Relative to rigid 4,40-bipyridine, flexible N,N0-bis
⇑
Corresponding authors. Tel.: +86 21 66132803; fax: +86 21 66134594.
E-mail addresses: mx_li@mail.shu.edu.cn (M.-X. Li), hxiang@shu.edu.cn (X. He).
http://dx.doi.org/10.1016/j.ica.2014.03.019
0020-1693/Ó 2014 Elsevier B.V. All rights reserved.

14
J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
M
C
M
C
M
C
M
C
M
O
O
O
M
O
O
M O O
M
O
O
O
C
C
O
O
N
O
O
C
O
C
O
M
M
O
N
O
O
N
O
N
I
II
III
IV
Scheme 1. Schematic description of 3-(4-hydroxypyridinium-1-yl)phthalic acid and its coordination modes in 1–6.
(4-pyridylmethyl)piperazine (4-bpmp) and 1,3-bis(4-pyridyl)pro-
pane (bpp) ligands have more advantages [21–24], because their
flexibility and conformational freedom allow them to get con-
form to the coordination environment of the metal ions. In order
to further understand the coordination features of 3-(4-hydrox-
ypyridinium-1-yl)phthalic acid, we selected rigid 4,40-bipyridine,
flexible 4-bpmp and bpp as auxiliary ligands, successfully
synthesized six 1D and 2D coordination polymers. Herein, we
report their synthesis, crystal structure, thermal stability and
luminescence.
2.2.3. [ZnL(4-bpmp)0.5(H2O)]nꢀ2nH2O (3)
A
mixture of Zn(NO3)2ꢀ6H2O (0.2 mmol), H2L (0.1 mmol),
4-bpmp (0.1 mmol), DMA (6 mL) and water (3 mL) was sealed in
a 15 mL Teflon-lined reactor, which was heated at 85 °C for 72 h.
Upon cooling to room temperature at a rate of 10 °C hꢁ1, colourless
crystals of 3 were obtained in 37% yield based on H2L. Anal. Calc. for
C
21H23N3O8Zn (%): C, 49.38; H, 4.54; N, 8.23. Found: C, 49.98; H,
4.07; N, 7.66%. IR (KBr, cmꢁ1): 3420m, 3071w, 2836w, 1634s,
1534s, 1386s, 1196m, 857m, 776m.
2.2.4. [ZnL(bpp)]nꢀ5nH2O (4)
A mixture of Zn(NO3)2ꢀ6H2O (0.2 mmol), H2L (0.1 mmol), bpp
(0.2 mmol), DMF (3 mL) and water (6 mL) was sealed in a 15 mL
Teflon-lined reactor, which was heated at 85 °C for 72 h. Upon
cooling to room temperature at a rate of 10 °C hꢁ1, colourless block
crystals of 4 were obtained in 48% yield based on H2L. Anal. Calc. for
2. Experimental
2.1. Materials and methods
All chemicals were of reagent grade and used without further
purification. 3-(4-Hydroxypyridinium-1-yl)phthalic acid can be
prepared according to the literature procedure [25]. Elemental
analyses (C, H, and N) were performed on a Vario EL III analyzer.
Infrared spectra were recorded with a Nicolet A370 FT-IR spec-
trometer using KBr pellets in 400–4000 cmꢁ1 region. Powder
X-ray diffraction data (PXRD) were recorded at a scanning rate of
5° minꢁ1 in the 2h range of 5–50° on a Rigaku DLMAX-2550 diffrac-
tometer. Thermogravimetric analyses (TG-DSC) were completed on
C
26H31N3O10Zn (%): C, 51.12; H, 5.11; N, 6.88. Found: C, 50.93; H,
5.34; N, 6.75%. IR (KBr, cmꢁ1): 3421m, 3068w, 2949w, 1634s,
1565s, 1381s, 1192m, 857m.
2.2.5. [Zn2L2(bpp)(H2O)2]nꢀnH2O (5)
A mixture of Zn(NO3)2ꢀ6H2O (0.2 mmol), H2L (0.1 mmol), bpp
(0.2 mmol), DMA (3 mL) and water (6 mL) was sealed in a 15 mL
Teflon-lined reactor, which was heated at 120 °C for 72 h. Upon
cooling to room temperature at a rate of 10 °C hꢁ1, colourless block
crystals of 5 were obtained in 64% yield based on H2L. Anal. Calc. for
a
Nerzsch STA 449C thermal analyzer at a heating rate of
10 °C minꢁ1 in air. Luminescent spectra were recorded on a Shima-
C
39H34N4O13Zn2 (%): C, 52.20; H, 3.82; N, 6.24. Found: C, 52.32; H,
dzu RF-5301 spectrophotometer.
3.73; N, 6.15. IR (KBr, cmꢁ1): 3373m, 3072w, 2950w, 1633s, 1561s,
1390s, 1197m, 853m,776m.
2.2. Syntheses of complexes
2.2.1. [CdL(H2O)]n (1)
2.2.6. [Zn2L2(bpp)(H2O)]nꢀ4nH2O (6)
A mixture of Zn(NO3)2ꢀ6H2O (0.2 mmol), H2L (0.1 mmol), bpp
(0.2 mmol), DMF (3 mL) and water (6 mL) was sealed in a 15 mL
Teflon-lined reactor, which was heated at 120 °C for 72 h. Upon
cooling to room temperature at a rate of 10 °C hꢁ1, colourless block
crystals of 6 were obtained in about 3% yield based on H2L. Anal.
Calc. for C39H38N4O15Zn2 (%): C, 50.18; H, 4.10; N, 6.00. Found: C,
50.65; H, 4.13; N, 6.01%. IR (KBr, cmꢁ1): 3430m, 3075w, 2944w,
1635s, 1548s, 1374s, 1196m, 857m, 778m.
A
mixture of Cd(NO3)2ꢀ6H2O (0.2 mmol), H2L (0.1 mmol),
N,N-dimethylacetamide (DMA, 4 mL) and water (4 mL) was sealed
in a 15 mL Teflon-lined reactor, which was heated at 120 °C for
72 h. Upon cooling to room temperature at a rate of 10 °C hꢁ1, col-
ourless crystals of 1 were obtained in 35% yield based on H2L. Anal.
Calc. for C13H9NO6Cd (%): C, 40.28; H, 2.34; N, 3.61. Found: C,
40.60; H, 2.28; N, 3.58%. IR (KBr, cmꢁ1): 3415m, 3088w, 1636s,
1533s, 1392s, 1199s, 855s, 780m, 708m.
2.3. X-ray crystallography
2.2.2. [CoL(4,4’-bipy)0.5(H2O)]n (2)
The well-shaped single crystals of 1–6 were selected for X-ray
diffraction study. Data collections were performed with graphite
monochromatic Mo Ka radiation (k = 0.71073 Å) on a Bruker
A mixture of Co(NO3)2ꢀ6H2O (0.2 mmol), H2L (0.1 mmol), 4,40-
bipy (0.1 mmol), triethylamine (25
l
L) and water (8 mL) was
sealed in a 15 mL Teflon-lined reactor, which was heated at
140 °C for 72 h. Upon cooling to room temperature at a rate of
10 °C hꢁ1, red crystals of 2 was obtained in 37% yield based on
H2L. Anal. Calc. for C18H13N2O6Co (%): C, 52.45; H, 3.18; N, 6.80.
Found: C, 52.53; H, 3.09; N, 6.71%. IR (KBr, cmꢁ1): 3405m,
3067w, 1633s, 1531s, 1382s, 1190m, 860m, 824m, 771m.
Smart Apex-II CCD diffractometer at room temperature. Determi-
nations of the crystal system, orientation matrix and cell dimen-
sions were performed according to the established procedures.
Lorentz polarization and absorption correction were applied. The
structures were solved by direct methods and refined by
full-matrix least-squares based on F2 using the SHELXTL-97 program

J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
15
Table 1
Crystallographic data and structural refinements for 1–6.
Complexes
1
2
3
4
5
6
Formula
C
13H9NO6Cd
C18H13N2O6Co
412.23
C21H23N3O8Zn
510.79
C26H31N3O10Zn
610.91
C39H34N4O13Zn2
897.44
C39H38N4O15Zn2
933.47
monoclinic
C2/c
26.556(1)
18.790(1)
17.493(1)
90
113.397(1)
90
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
387.61
triclinic
P1
triclinic
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
P1
P1
P1
P1
6.549(2)
9.516(3)
10.152(3)
83.987(3)
87.186(3)
87.672(3)
628.1(3)
2
8.934(2)
9.807(2)
10.589(3)
95.546(2)
107.412(2)
107.116(3)
828.5(4)
2
8.534(11)
10.332(13)
13.772(18)
75.897(18)
85.450(16)
66.642(15)
1081(2)
9.113(4)
12.184(6)
15.398(7)
105.448(5)
103.501(5)
106.108(5)
1493.5(12)
2
8.674(8)
11.168(10)
20.267(18)
101.759(10)
102.310(9)
99.121(10)
1836(3)
a
(°)
b (°)
c
(°)
V (Å3)
8010.9(9)
8
1.548
Z
2
2
Dc (g cmꢁ3
)
2.050
1.767
1.652
1.076
1.569
1.191
1.341
0.877
1.624
1.383
l
(mmꢁ1
)
1.274
Reflections
Rint
3912/2775
0.0083
5255/3693
0.0107
4431/3506
0.0187
9259/6563
0.0173
9590/6357
0.0154
24916/9127
0.0305
Data/restraint/param
2775/0/190
1.11
3693/0/249
1.052
3506/0/303
1.016
6563/6/358
1.106
6357/0/539
1.059
9127/0/543
1.032
Goodness-of-fit (GOF) on F2
R1, wR2 [I > 2
r
(I)]
0.0198, 0.0539
0.0205, 0.0544
0.0290, 0.0724
0.0311, 0.0746
0.0350, 0.0948
0.0407, 0.0978
0.0558, 0.1819
0.0671, 0.1929
0.0336, 0.0829
0.0411, 0.0867
0.0559, 0.1412
0.0812, 0.1579
R1, wR2 (all data)
Largest difference in peak and hole (e Åꢁ3
)
0.667 and ꢁ0.688 0.334 and ꢁ0.419 0.411 and ꢁ0.501 1.384 and ꢁ0.383 0.481 and ꢁ0.395 1.289 and ꢁ1.542
[26]. All non-hydrogen atoms were refined anisotropically, and
hydrogen atoms were located and included at their calculated
position. The crystal data and refinement results are summarized
in Table 1. The selected bond distances and angles are presented
in Table 2. Hydrogrn bonds are listed in Table S1 (Supporting
information).
3. Results and discussion
3.1. Description of crystal structures
3.1.1. [CdL(H2O)]n (1)
Single crystal X-ray diffraction study reveals that complex 1 is a
1D ribbon coordination polymer. As shown in Fig. 1a, the asym-
metric unit contains one crystallographically independent Cd(II)
ion, one L ligand and one coordinated water molecule. Cd1 is in a
distorted octahedral geometry, coordinated by two chelating car-
boxyl groups from different L ligands, hydroxyl O6 atom and water
O3 atom. The equatorial plane is formed by the coordination of O2,
O4, O6 and O3 atoms. The axial positions are occupied by O1 and
O5 atoms with a O1–Cd1–O5 bond angle of 141.81(6)°. The Cd–O
bond distances vary from 2.164(2) to 2.529(2) Å. Cd(II) ion often
adopts a six- or senven-coordinated geometry in complexes, such
as a 3D homochiral metal–organic framework [CdL(bix)]nꢀ1.75nH2-
O [13]. The larger Cd1–O2 (2.529(2) Å) and Cd1–O5 (2.434(2) Å)
bond distances still fall in the normal range of Cd–O coordination
bond [27].
Table 2
Selected bond distances (Å) and angles (°) for 1–6.
1
Cd(1)–O(1)
Cd(1)–O(2)
Cd(1)–O(5)
O(1)–Cd(1)–O(5)
O(6)–Cd(1)–O(2)
O(4)–Cd(1)–O(2)
2
2.277(2)
2.529(2)
2.434(2)
141.81(6)
90.35(7)
84.22(7)
Cd(1)–O(3)
Cd(1)–O(4)
Cd(1)–O(6)
O(6)–Cd(1)–O(3)
O(4)–Cd(1)–O(3)
2.295(2)
2.263(2)
2.164(2)
101.74(7)
111.01(8)
Co(1)–O(1)
Co(1)–O(2)
Co(1)–N(1)
O(3W)–Co(1)–N(1)
O(4)–Co(1)–O(2)
3
1.992(1)
2.005(1)
2.149(2)
170.14(5)
118.90(6)
Co(1)–O(4)
Co(1)–O(3W)
2.000(1)
2.080(1)
O(1)–Co(1)–O(2)
O(1)–Co(1)–O(4)
128.49(6)
110.90(6)
Two carboxyl groups of H2L are completely deprotonated. The
dihedral angle between pyridyl ring and phenyl ring is 67.50(2)°.
Zn(1)–O(3)
Zn(1)–N(1)
Zn(1)–O(1)
1.942(3)
2.031(3)
2.407(3)
Zn(1)–O(2)
Zn(1)–O(5W)
2.015(3)
2.039(3)
The L ligand adopts a l5– , ,
g12 g12 g11 pentadentate coordination
mode to connect three Cd(II) ions through two chelating carboxyl
groups and the hydroxyl group oxygen (mode I, Scheme 1). This
results in the formation of a 1D polymeric ribbon structure
(Fig. 1a). The shortest Cdꢀ ꢀ ꢀCd separation across the ribbon is
5.873(1) Å. These 1D ribbons are parallelly stacked. The coordi-
nated water O3 combines with the carboxyl O1 and O4 atoms in
adjacent 1D ribbons by hydrogen bonds (O3–H3Bꢀ ꢀ ꢀO1 = 2.821 Å,
O3–H3Aꢀ ꢀ ꢀO4 = 2.972 Å, Table S1), which further extend the 1D
ribbon structure into a 2D supramolecular network (Fig. 1b). The
packing diagram is shown in Fig. 1c.
O(3)–Zn(1)–O(2)
O(3)–Zn(1)–N(1)
4
113.24(10)
123.19(13)
O(3)–Zn(1)–O(5W)
O(3)–Zn(1)–O(1)
100.00(13)
97.81(11)
Zn(1)–O(1)
1.936(3)
2.021(3)
114.47(12)
115.51(12)
Zn(1)–O(3)
Zn(1)–N(2)
O(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(2)
1.928(3)
2.050(3)
97.92(12)
109.42(12)
Zn(1)–N(1)
O(3)–Zn(1)–O(1)
O(3)–Zn(1)–N(1)
5
Zn(1)–O(3)
Zn(1)–O(5)
1.965(2)
2.038(2)
1.952(2)
1.989(2)
107.54(7)
99.57(8)
101.83(12)
128.60(8)
Zn(1)–O(4)
Zn(1)–N(1)
Zn(2)–O(2)
Zn(2)–N(2)
O(4)–Zn(1)–N(1)
O(3)–Zn(1)–N(1)
O(1)–Zn(2)–O(2)
O(2)–Zn(2)–N(2)
1.964(2)
2.034(2)
2.045(2)
2.054(2)
135.14(8)
107.45(8)
104.40(9)
94.89(8)
Zn(2)–O(1)
Zn(2)–O(6)
O(3)–Zn(1)–O(4)
O(4)–Zn(1)–O(5)
O(1)–Zn(2)–O(6)
O(1)–Zn(2)–N(2)
6
Zn(1)–O(1)
Zn(1)–O(3)
Zn(2)–O(2)
Zn(2)–O(6)
3.1.2. [CoL(4,40-bipy)0.5(H2O)]n (2)
Complex 2 is a 2D coordination polymer. As shown in Fig. 2a,
the asymmetric unit contains one independent Co(II) ion, one L
ligand, half 4,40-bipy ligand, and one coordinated water molecule.
Co1 is five-coordinated by two carboxyl oxygen (O1 and O2) atoms
from different L ligands, one hydroxyl oxygen (O4) atom, one
4,40-bipy nitrogen atom and one water oxygen (O3W) atom. The
Co–O bond distances vary from 1.992(1) to 2.080(1) Å, and the
Co–N1 bond distance is 2.149(2) Å. The distortion of coordination
1.951(3)
1.960(3)
1.946(3)
2.069(5)
99.27(11)
109.16(12)
120.64(13)
Zn(1)–N(1)
Zn(1)–N(2)
Zn(2)–O(4)
Zn(2)–O(5)
O(1)–Zn(1)–N(2)
O(4)–Zn(2)–O(2)
O(2)–Zn(2)–O(6)
2.036(3)
2.023(3)
1.886(3)
1.960(4)
109.46(13)
131.76(17)
97.72(18)
O(1)–Zn(1)–O(3)
O(1)–Zn(1)–N(1)
O(2)–Zn(2)–O(5)

16
J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
Fig. 1. (a) Asymmetric unit and 1D ribbon structure of 1. (b) 2D supramolecular network. (c) Packing diagram.
Fig. 2. (a) Asymmetric unit of 2. (b) 1D Co-L ribbon. (c) 2D polymeric network linked by 4,40-bipy space. (d) Packing diagram.
geometry around Co1 can be expressed in terms of
value of 0 and 1 for an ideal square pyramidal and ideal trigonal
bipyramidal geometry, respectively [28]. In complex 2, the Co1
locates in a distorted trigonal bipyramidal geometry with a
of 0.70. The apical positions are occupied by N1 and O3W atoms
with a N1–Co1–O3W bond angle of 170.14(5)°.
s
, which has a
ligand plays a bidentate linker. The 1D ribbons are further linked
by 4,40-bipy spaces to generate a 2D polymeric network (Fig. 2c).
These 2D networks are held together by hydrogen bond
(O3–H3BꢀꢀꢀO5, 2.790 Å) as shown in packing diagram (Fig. 2d).
Recently, Du et al. reported a [ZnL(4,40-bipy)0.5]n complex, which is
a 3D coordination polymer prepared in basic aqueous solution [14].
s value
Two carboxyl groups of H2L are completely deprotonated. The
pyridyl ring is twisted out of the plane of the phenyl ring, and the
twisted angle between both aromatic moiety is 72.09(2)°. The L
3.1.3. [ZnL(4-bpmp)0.5(H2O)]nꢀ2nH2O (3)
Complex 3 is a 1D chain coordination polymer. As shown in
Fig. 3a, the asymmetric unit contains one independent Zn(II) ion,
one L ligand, half 4-bpmp ligand, and one coordinated water as
well as two lattice water molecules. Zn1 is five-coordinated by
three carboxyl oxygen atoms from two L ligands, one water oxygen
(O5W) atom and one pyridyl nitrogen atom of 4-bpmp, forming a
ligand adopts a l3– , ,
g1 g1 g1 tridentate coordination mode to con-
nect three Co(II) ions through two monodentate carboxyl groups
and hydroxyl oxygen (mode II, Scheme 1). This results in the forma-
tion of a 1D polymeric ribbon as shown in Fig. 2b. The shortest
Coꢀ ꢀ ꢀCo separation across the ribbon is 4.713(1) Å. The 4,40-bipy

J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
17
Fig. 3. (a) Asymmetric unit and 1D polymeric chain structure of 3. (b) 2D supramolecular network.
distorted square pyramidal geometry with a
s
value of 0.44. The
perpendicularly connected by bidentate bpp spaces to form a 1D
nanotubular coordination polymer (Fig. 4c and d). Every two
[Zn2L2] macrocycles and two bpp spaces construct a larger cyclic
cavity with the size of 10.43 ꢂ 13.03 Å2. This new macrocycle runs
almost perpendicular to the [Zn2L2] macrocycle. Viewed along the
a axis (Fig. 4e), these 1D nano-tubes are parallelly stacked. The cav-
ities are fully occupied by (H2O)5 crystal water clusters [31]. As cal-
culated by Platon programs, the potential solvent accessible void
volume is 32%, after the removal of the guest water molecules.
Du et al. reported a [ZnL(bpp)]n complex, which is a 2D coordina-
tion polymer prepared in basic aqueous solution [14].
basal plane is completed by O1, O2, O5W and N1 atoms. Amongst
them, the O1 is weakly coordinated to Zn1 with a larger Zn1–O1
distance of 2.405(3) Å. The apical site is occupied by O3 atom with
a Zn–O3 bond distance of 1.943(2) Å. Although Zn(II) ion often dis-
plays tetrahedral or octahedral coordination geometry, however
square-pyramidal geometry is also observed in reported Zn(II)
complexes [29,30].
Two carboxyl groups of H2L are completely deprotonated. The
pyridyl ring is twisted 64.52(2)° with respect to the phenyl ring.
Two carboxyl groups of L ligand adopt different coordination fash-
ions (mode III, Scheme 1). One carboxyl group adopts a chelating
coordination fashion, while the other one is a monodentate car-
boxyl group. The hydroxyl oxygen is uncoordinated. Two triden-
tate L ligands coordinated with two Zn(II) ions to form a [Zn2L2]
dimer with a Znꢀ ꢀ ꢀZn separation of 5.015(5) Å. These dimers are
further connected by bidentate 4-bpmp linkers to form a 1D
polymeric chain (Fig. 3a). These 1D chains are parallelly arranged
and combined by hydrogen bonds (O5–H5Aꢀ ꢀ ꢀO6 = 2.646 Å, O5–
H5Bꢀ ꢀ ꢀN2 = 2.826 Å), finally forming a 2D supramolecular network
(Fig. 3b).
3.1.5. [Zn2L2(bpp)(H2O)2]nꢀnH2O (5)
Complex 5 is a 1D chain coordination polymer. The asymmetric
unit contains two independent Zn(II) ions, two L ligands, one bpp
ligand, two coordinated water molecules as well as one lattice
water molecule (Fig. 5a). Zn1 adopts a distorted tetrahedral geom-
etry, coordinated by two carboxyl oxygen atoms from different L
ligands, water oxygen (O5) atom and pyridyl nitrogen (N1) atom.
The Zn1–O bond distances vary from 1.965(2) to 2.038(2) Å. The
Zn1–N1 bond distance is 2.034(2) Å. Zn2 also adopts a tetrahedral
geometry, coordinated by two carboxyl oxygen atoms, water O6
atom and pyridyl N2 atom. The bond distances and angles around
Zn2 are somewhat different with those around Zn1. The Zn2–O
bond distances vary from 1.952(2) to 2.045(2) Å, and the Zn2–N2
bond distance is 2.054(2) Å.
3.1.4. [ZnL(bpp)]nꢀ5nH2O (4)
Complex 4 is a 1D nano-tubular coordination polymer. The
asymmetric unit contains one independent Zn(II) ion, one L ligand,
one bpp ligand together with five lattice water molecules (Fig. 4a).
The coordination geometry around Zn1 is best described as a dis-
torted tetrahedron. Zn1 is four-coordinated by two pyridyl nitro-
gen atoms and two carboxyl oxygen atoms from different bpp
and L ligands. The average Zn–N and Zn–O bond distances are
2.035, 1.932 Å, respectively.
Two carboxyl groups of each H2L are completely deprotonated.
For two independent L ligands, their pyridyl rings twist respec-
tively 69.77(2)° or 75.07(2)° with respect to the phenyl rings. Sim-
ilar to complex 4, both L ligands adopt coordination mode IV and
coordinate to two Zn(II) ions via two monodentate carboxyl
groups. Two L ligands link two Zn(II) ions to form a [Zn2L2] dimer.
These dimers are further connected by bidentate bpp linkers to
form a 1D polymeric chain (Fig. 5a). Comparing with the structure
of 4, it can be observed that Zn(II) is coordinated by two pyridyl
nitrogens in 4, but coordinated by one pyridyl nitrogen in 5. More-
over, the [Zn2L2] macrocycles are pillared by two rows of bpp
ligands in 4, however these [Zn2L2] dimers are linearly linked by
one row of bpp ligands. Although the coordination modes of L
Two carboxyl groups of H2L are completely deprotonated. The
pyridyl ring is twisted 73.69(2)° with respect to the phenyl ring.
The L ligand is bidentate and coordinates to two Zn(II) ions via
two monodentate carboxyl groups (mode IV, Scheme 1). The
hydroxyl oxygen does not participate in the coordination with
Zn1. As shown in Fig. 4b, two L ligands link two Zn(II) ions to form
a 14-membered [Zn2L2] macrocycle with a Znꢀ ꢀ ꢀZn separation of
5.167(2) Å. These macrocycles are parallelly arranged and further

18
J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
Fig. 4. (a) Asymmetric unit of 4. (b) 14-Membered [Zn2L2] macrocycle. (c) 1D nanotubular coordination polymer connected by bpp linkers. (d) Nano-tube viewed along the a
axis. (e) Parallelly stacked 1D nano-tubes filled with (H2O)5 clusters.
Fig. 5. (a) Asymmetric unit and 1D polymeric chain structure of 5. (b) Packing diagram with H-bonding network.
ligands are similar, however the structures of 4 and 5 are obviously
different. In addition, there exist three strong hydrogen bonds (O6–
H6Aꢀ ꢀ ꢀO12, 2.657 Å, O5–H5Aꢀ ꢀ ꢀO8, 2.793 Å, O6–H6Bꢀ ꢀ ꢀO12 =
2.694 Å), which combine the 1D chains into a 3D supramolecular
architecture (Fig. 5b).
3.1.6. [Zn2L2(bpp)(H2O)]nꢀ4nH2O (6)
Complex 6 is a 2D coordination polymer. The asymmetric unit
contains two independent Zn(II) ions, two L ligands, one bpp
ligand, one coordinated water molecule as well as four lattice
water molecules (Fig. 6a). Zn1 adopts a distorted tetrahedral

J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
19
geometry, coordinated by two carboxyl oxygen atoms from two L
3.2. Coordination modes of 3-(4-hydroxypyridinium-1-yl)phthalate
and structural comparison
ligands and two pyridyl nitrogen atoms from two bpp
ligands. The average Zn1–O and Zn1–N bond distances are
1.956(2) and 2.030(2) Å. Zn2 also adopts a tetrahedral geome-
try, coordinated by four oxygen atoms. Two carboxyl oxygen atoms
are from two L ligands, the other two oxygens are hydroxyl O5 and
water O6. The Zn2–O bond distances vary from 1.886(3) to
2.069(5) Å.
In above six 1D and 2D coordination polymers, all carboxyl
groups of 3-(4-hydroxypyridinium-1-yl)phthalic acid are com-
pletely deprotonated, and the L ligands display four types of coor-
dination modes. As summarized in Scheme 1, the L ligand adopts
mode I, II, and III in complexes 1, 2, and 3 respectively. Mode IV
can be found in bpp-containing complexes 4, 5, and 6. Meanwhile,
mode II is also observed in complex 6. The terminal hydroxy group
is either monodentate coordination in modes I and II, or free in III
and IV. Two adjacent carboxyl groups of L ligand are both chelating
coordination in mode I, bis-monodentate coordination in modes II
and IV, or mixed coordination containing a chelating carboxyl
group and a monodentate carboxyl group in mode III.
The coordination polymers 1–6 are assembled by [M2L2] dimers
in which L ligand acts as a connector. The pyridyl ring often twists
a larger dihedral angle with respect to the phenyl ring. Two
adjacent carboxyl groups in benzene ring benefit for the formation
of 1D polymeric chain or ribbon, avoiding the 2D and 3D expan-
sion. The various coordination fashions of carboxyl groups and
Both H2L ligands are completely deprotonated and adopt two
kinds of coordination modes to combine Zn(II) ions. One L ligand
connected three Zn centers through two monodentate carboxyl
groups and hydroxy group oxygen (mode II). Another L ligand
adopts a l2– ,
g1 g1 bidentate coordination mode (mode IV) to
bridge Zn1 and Zn2 through two monodentate carboxyl groups.
The pyridyl rings twist 70.75(2)° and 78.36(2)° with respect to
the phenyl rings respectively. As shown in Fig. 6b, the L ligands link
Zn(II) ions to form a 1D linear chain. These 1D chains are further
connected by bidentate bpp linkers into a 2D layered coordination
polymer (Fig. 6c). Viewed along the c axis, the 2D networks are
parallelly stacked. The crystal water clusters (H2O)4 are perched
in the rhombic pore.
Fig. 6. (a) Asymmetric unit of 6. (b) 1D [Zn2L2(H2O)]n linear chain. (c) 2D network. (d) The stacking diagram.

20
J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
the dipyridyl ancillary ligands lead to the formation of the 1D and
2D coordination polymers with varied structures.
The Zn(II) complexes 4, 5 and 6 are constructed with same
ligands 3-(4-hydroxypyridinium-1-yl)phthalate and 1,3-bis(4-pyr-
idyl)propane. All the Zn(II) centers locate at
a tetrahedral
geometry, and the bpp ligands play a bidentate linker. The three
complexes were prepared in same Zn:H2L:bpp molar ratio
(2:1:2). However, the slight difference in reaction temperatures
(85 or 120 °C) and solvents (DMF or DMA) results in three products
with obviously different structures. The Zn1 ions in 4 and 6 are
coordinated by two pyridyl groups to form a 1D nano-tubular poly-
mer and a 2D layered network respectively, while both Zn(II) ions
in 5 are coordinated by one pyridyl group to form a 1D chain
polymer.
3.3. Infrared spectra and PXRD patterns
The IR spectra of 1–6 exhibit characteristic bands of 3-(4-
hydroxypyridinium-1-yl)phthalate and dipyridyl auxiliary ligands
(Fig. S1). The observed strong bands in the range of 1565 to
1531 cmꢁ1 are attributed to the asymmetric stretching vibration
of the carboxylic group, while the strong peaks at ca. 1390 cmꢁ1
are attributed to the symmetric stretching vibration of the carbox-
ylic group [32]. The absence of strong bands near 1700 cmꢁ1 in 1–6
indicates the complete deprotonation of carboxyl groups in 3-(4-
hydroxypyridinium-1-yl)phthalic acid. The strong peaks at ca.
1630 cmꢁ1 are assigned to the stretching vibrations of aromatic
rings [14,15]. The bands near 855 and 780 cmꢁ1 can be designated
Fig. 7. TG curves of complexes 1–5.
11.98%, calcd. 13.50%). Complex 5 lost three water molecules in
100–195 °C (found 5.68%, calcd. 6.02%). The anhydrous compound
was thermally stable until 255 °C. Then successive weight-loss
process was corresponded to the decomposition of bpp and L
ligands to afford ZnO residue at 610 °C (found 10.02%, calcd.
9.07%). Thermogravimetric analyses demonstrate that the dehy-
drate complexes are thermally stable to ca. 260–320 °C and then
continuously decomposed.
to
c(C–H out of plane) bending vibrations of pyridyl and phenyl
groups. The weak peaks near 2860 mꢁ1 are assigned to the
3.5. Luminescence
m
(ꢁCH2) stretching vibration of 4-bpmp and bpp. The broad bands
in the range of 3420 to 3370 cmꢁ1 are associated with the lattice
and coordinated water molecules in 1–6. These IR spectra are in
good agreement with the results of elemental analysis and single
crystal structural analysis.
It is well known that d10 transition metal complexes possess
varied luminescent properties. Organic ligands and their coordina-
tion modes significantly affect emission wavelength and lumines-
cent mechanism. The luminescent behaviors of H2L ligand and
Zn(II)/Cd(II) complexes 1, 3, 4 and 5 were investigated (Fig. 8).
When excited with 322 nm light, free H2L ligand exhibits weak
emission peaks at 467 and 380 nm. Under the similar excitation
condition, complex 1 exhibit an intense emission peak at 425
and one shoulder peak at 381 nm. Complex 3 displays luminescent
behavior with two strong emission peaks at 419 and 382 nm.
In order to check the phase purity of the products, powder X-ray
diffraction (PXRD) experiments have been carried out for com-
plexes 1–5, except 6 (poor yield). As shown in Fig. S2, the peak
positions of the experimental and simulated PXRD patterns are in
good agreement with each other, indicating that the crystal struc-
tures are truly representative of the bulk crystal products. The dif-
ferences in intensity may be owing to the preferred orientation of
the crystal samples.
Complex
4 displays two weak emission peaks at 428 and
379 nm. Complex 5 displays similar luminescent behavior to
complex 4 with two weak emission peaks at 430 and 376 nm.
The similar emission energy between the complexes and H2L
ligand indicates that the luminescent mechanism of complexes 1,
3.4. Thermal stabilities
Thermogravimetric analyses of complexes 1–5 were performed
in the temperature range of 20–800 °C in air. As shown in Fig. 7
(Fig. S3), complex 1 lost one coordinated water molecule in 176–
230 °C (found: 4.30%, calcd: 4.64%). The anhydrous compound
was thermally stable until 318 °C, and then released L ligand con-
tinuously to afford CdO residue at 750 °C (found 33.04%, calcd.
33.04%). Complex 2 lost one coordinated water molecule in 134–
180 °C (found: 4.12%, calcd: 4.37%). The anhydrous compound
was thermally stable until 286 °C, and then decomposed quickly
to release 4,4’-bipy and L ligands. The residue at 500 °C was
Co2O3 (found 20.11%, calcd. 20.12%) [33,34]. Complex 3 released
three water molecules in 30–124 °C (found 10.73%, calcd.
10.57%). The anhydrous compound was thermally stable until
296 °C. Then successive weight-loss process was corresponded to
the decomposition of 4-bpmp and L ligands to afford ZnO residue
at 634 °C (found 13.48%, calcd. 15.93%). Complex 4 lost lattice
water molecules in 30–96 °C (found 13.98%, calcd. 14.43%). The
anhydrous compound was thermally stable until 280 °C. Then suc-
cessive weight-loss process was corresponded to the decomposi-
tion of bpp and L ligands to afford ZnO residue at 500 °C (found
Fig. 8. Emission spectra of H2L and complexes 1, 3, 4 and 5.

J.-J. Shen et al. / Inorganica Chimica Acta 416 (2014) 13–21
21
3, 4 and 5 originates from ligand-centered emission. In addition,
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