1D chain Cd(II) and Co(II) coordination polymers: Synthesis, crystal structures and luminescence properties

Article abstract of DOI:10.1016/j.molstruc.2007.03.019

Two novel 1D infinite chain coordination polymers, [CdL(NO₃)₂]_n and [CoL(NO₃)₂]_n (L = 4,4′-bis[2-(2-pyridyl)ethenyl]biphenyl) have been prepared by reacting Cd(NO₃)₂ a

Full text of DOI:10.1016/j.molstruc.2007.03.019

Available online at www.sciencedirect.com
Journal of Molecular Structure 873 (2008) 73–78
www.elsevier.com/locate/molstruc
1D chain Cd(II) and Co(II) coordination polymers: Synthesis,
crystal structures and luminescence properties
a
a,
a
a
Mei Sun a,b, Peng Wang , Hongping Zhou *, Jiaxiang Yang , Jieying Wu ,
a,c,d,
c
c
Yupeng Tian
*, Xutang Tao , Minhua Jiang
a
Department of Chemistry, Anhui University, Hefei 230039, PR China
Department of Material and Chemistry, Anhui Institute of Architecture & Industry, Hefei 230022, PR China
b
c
State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, PR China
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
d
Received 6 February 2007; received in revised form 4 March 2007; accepted 4 March 2007
Available online 16 March 2007
Abstract
Two novel 1D infinite chain coordination polymers, [CdL(NO3)2]n and [CoL(NO3)2]n (L = 4,40-bis[2-(2-pyridyl)ethenyl]biphenyl)
have been prepared by reacting Cd(NO3)2 and Co(NO3)2 with the novel ligand L. Complexes 1 and 2 have been characterized by
elemental analysis, IR and single crystal X-ray diffraction determination. The metal ions in the polymers have six coordinate pseudo
octahedral structures with two pyridyl nitrogen atoms of L and four oxygen atoms of nitrate. The ligand coordinates to metal ions form-
ing bridges in different geometries (cis and trans coordination modes). The results of TGA determination show that the coordination
polymers are quite thermally stable. The complexes exhibit a strong emission band with the maximum intensity at 524 and 545 nm in
solid-state, respectively, upon excitation at 350ꢀ450 nm.
ꢀ 2008 Published by Elsevier B.V.
Keywords: Bipyridyl ligand; Coordination polymer; Crystal structure; Fluorescence
1. Introduction
ganic/organic coordination complexes can offer the advan-
tages of high thermal stability and solvent resistance
compared to all-organic materials.
Organic/inorganic hybrid materials are currently receiv-
ing considerable attention [1–3] owing to their potential
properties in magnetism, spectroscopy, catalysis, and non-
linear optical owing to their potential properties in magne-
tism, spectroscopy, catalysis, and nonlinear optical activity
[4–7]. The hybrid materials combine the advantageous
properties characteristic of crystalline inorganic solids with
those of organic molecules within a molecular-scale com-
posite. The organic compounds have low melting points
or low decomposition temperatures, inhibiting their appli-
cations. The functionalized organic molecule (addition of
donor atoms, e.g. N or O) allowed to incorporate into inor-
Two components are necessary in every synthetic
approach leading to extended supramolecular multimetal-
lic assemblies: the ligand (the organic tecton) and the metal
ion. In the language of supramolecular chemistry, the
ligand is a programmed species, whose information is read
by the metal ions according to their coordination algo-
rithm. This is often achieved by employing bifunctional
N, N0-donor ligands such as 4,40-bipyridine or 2,20-bipyri-
dine and their derivatives [8–12] as linkers between adja-
cent metal ions. However, some organic ligands with
special functionality for supramolecular architectures and
functional compounds, because of synthetic difficulties,
have been reported rarely to date.
*
Corresponding authors. Tel.: +86 551 5108151; fax: +86 551 5107342.
On the other hand, metal ion is a key factor in determin-
ing the dimensionality of the resulting systems. A 1:1
E-mail addresses: zhpzhp@263.net (H.-P. Zhou), yptian@ahu.edu.cn
(Y.-P. Tian).
0022-2860/$ - see front matter ꢀ 2008 Published by Elsevier B.V.
doi:10.1016/j.molstruc.2007.03.019

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M. Sun et al. / Journal of Molecular Structure 873 (2008) 73–78
ligand-to-metal ratio leads to either linear or zig-zag
chains. Metal ions also display a range of coordination
geometries allowing for greater flexibility in constructing
materials with specific topologies. For example, Cd(II)
and Co(II)-containing coordination polymers have
attracted considerable recent interest owing to the change-
ability to form bonds with different donors, the large radius
and various coordination modes [8,9].
Taking account of the above considerations, we have
designed and synthesized a novel functional bipyridyl
ligand 4,40-bis[2-(2-pyridyl)ethenyl]biphenyl for assembling
with Cd(II) and Co(II) cation. Here two novel 1D infinite
chain coordination polymers, [CdL(NO3)2]n and [CoL(-
NO3)2]n (L = 4,40-bis[2-(2-pyridyl)ethenyl]biphenyl) have
been prepared and structurally characterized. The com-
pounds were characterized by single crystal X-ray
crystallography.
7.39 (d, J = 16.07 Hz, 2 H), 7.26–7.28 (m, 2 H) (Fig. 1).
UV–Vis ( kmax) /nm: 354 (p–p*).
2.2.2. Preparation of [CdL(NO3)2]n (1)
Crystals were obtained by using a fritted U-tube. L
(0.360 g, 1 mmol) in CHCl3 solution was placed on the side
of the U-tube, and on the other side of the U-tube
Cd(NO3)2 (0.948 g, 4 mmol) in ethanol was added followed
by enough ethanol to equalize hydrostatic pressures on
both sides. After two weeks, well-formed yellow crystals
(1) were obtained within the solutions of both sides. Yield:
70%. Anal. Calc. for C26H20CdN4O6: C, 52.10; H, 3.35; N,
9.39. Found C, 52.06; H, 3.38; N, 9.42 %. IR (KBr, cmꢀ1):
821 (s), 1385 (s), 1591 (s), 3521 (s).
2.2.3. Preparation of [CoL(NO3)2]n (2)
The complex was synthesized by the same procedure
above, but from Co(NO3)2. Yield: 73%. Anal. Calc. for
C26H20CoN4O6: C, 57.42; H, 3.68; N, 10.31. Found C,
57.45; H, 3.70; N, 10.28%. IR (KBr, cmꢀ1): 814 (s), 1278
(s), 1495 (s), 1599 (s), 3421 (s).
2. Experimental
All chemicals used were of analytical grade. The solvents
were purified by conventional methods.
2.3. X-ray crystallography and structure solution
2.1. Physical measurements
The relevant crystal data and structural parameters are
summarized in Table 1. Selected bond distances and angles
are shown in Table 2, respectively. Data collections
[1.77ꢁ 6 h 6 25.03o] were performed using a Siemens
SMART CCD area detector diffractometer with Mo Ka
Elemental analysis data were obtained using a Perkin-
Elmer 240 analyzer. Infrared spectra were recorded from
KBr discs in the range 4000ꢀ400 cmꢀ1 on a Nicolet FT
1
IR-170SX instrument. H NMR spectrum was performed
˚
radiation with an x-scan mode [k = 0.7103 A]. The struc-
on Bruker 500 MHz Ultrashield spectrometer and was
reported as parts per million (ppm) from TMS (d). Elec-
tronic absorption spectra were obtained on a UV-265 spec-
trophotometer in DMF solution (1.0 · 10ꢀ5 mol dmꢀ3).
The luminescent spectra were measured on single crystals
at room temperature using a model Perkin-Elmer LS55
fluorescence spectrophotometer. The excitation slit was
10 nm, the emission slit was 10 nm also, and the response
time was 2 s. TGA of the compounds were carried out
using a Perkin-Elmer Pris-1 DMDA-V1 analyzer in a
ture was solved with direct methods using the program
SHELXTL (Sheldrick, 1997) [13] and refined anisotropi-
cally with SHELXTL using full-matrix least squares proce-
dure giving for (1) a final R1 value of 0.0347 for 168
parameters, and 2110 unique reflections with I P 2r (I)
and wR2 of 0.0617 for all 6003 reflections, and for (2), a
final R1 value of 0.0476 for 168 parameters, and 2132
unique reflections with I P 2r (I) and wR2 of 0.0875 for
all 6284 reflections. All the non-hydrogen atoms were
located from the trial structure and then refined anisotrop-
ically with SHELXTL using full-matrix least-squares pro-
cedure. The hydrogen atom positions were geometrically
idealized and allowed to ride on their parent atom and
fixed displacement paraments.
atmosphere of N2 at a heating rate of 20 K minꢀ1
.
2.2. Synthesis
2.2.1. Preparation of the ligand (L)
4,40-bis[2-(2-pyridyl)ethenyl] biphenyl) (L) was prepared
by solid-state reaction. The mixture of biphenyl bisphos-
phonates (0.364 g, 1 mmol), pyridine carboxaldehyde
(0.32 g, 3 mmol) and potassium t-butoxide was forcibly
milled for 5 min. Yellow powder was collected by filtration,
washed with water and ethanol and dried under vacuum.
Yield: 90%. Anal. Calc. for C26H20N2: C, 86.64; H, 5.59;
N, 7.77. Found: C, 86.61; H, 5.63; N, 7.76%. IR (KBr,
cmꢀ1): 3049 (m), 1592 (w), 1484 (w), 1435 (m), 1187 (s),
3. Results and discussion
3.1. Syntheses
In this report, the novel ligand was first successfully syn-
thesized by the solid-state reactions of the condensation
between phosphonate ester and aldehyde derivative at
room temperature. Conventionally, the reactions of the
condensation between phosphonate ester and aldehyde
derivatives are all prepared in a solution with a rigorous
experimental condition for long reaction time in nitrogen
gas and separation with column chromatography [14–17].
1
1118 (s), 997 (w), 721 (s), 541 (s). H NMR (500 MHz,
CDCl3) d 8.59 (d, J = 4.25 Hz, 2 H), 7.77–7.82 (m, 10 H),
7.73 (d, J = 16.10 Hz, 2 H), 7.58 (d, J = 7.78 Hz, 2 H),

M. Sun et al. / Journal of Molecular Structure 873 (2008) 73–78
75
Fig. 1. 1H NMR spectrum of the ligand.
Table 1
Table 2
Selected bond lengths (A) and angles (ꢁ) for 1 and 2
˚
Crystallographic data for 1 and 2
Complex
1
2
1
Cd(1)–N(1)
2.227(3)
2.227(3)
2.305(3)
2.444(2)
N(1)–Cd(1)ꢀN(1A)
N(1)–Cd(1)ꢀO(1)
N(1)–Cd(1)ꢀO(2)
O(2)–Cd(1)ꢀO(1)
O(3)–N(2)ꢀO(1)
122.98(15)
89.36(9)
122.05(9)
53.72(9)
121.7(4)
Empirical formula
Formula mass
Crystal color
C
596.86
26H20CdN4O6
C26H20CoN4O6
543.39
Mauve
Cd(1)–N(1A)
Cd(1)–O(2)
Cd(1)–O(1)
Yellow
0.45 · 0.21 · 0.13
Monoclinic
P2/c
7.580(4)
6.859(4)
23.290(12)
98.041(7)
1199.0(10)
2
Crystal dimensions
Crystal system
Space group
0.22 · 0.13 · 0.11
Monoclinic
C2/c
14.530(5)
13.372(5)
14.267(5)
119.440(5)
2413.9(14)
4
2
˚
a [A]
Co(1)–N(1)
Co(1)–N(1A)
Co(1)–O(1)
Co(1)–O(2)
2.065(3)
2.065(3)
2.065(3)
2.264(3)
N(1)–Co(1)ꢀO(1)
N(1)–Co(1)ꢀO(2)
O(1)–Co(1)ꢀO(2)
O(3)–N(2)ꢀO(2)
N(1)–Co(1)ꢀN(1A)
106.09(12)
87.98(12)
58.02(12)
123.4(5)
˚
b [A]
˚
c [A]
b [ꢁ]
3
˚
V [A ]
100.62(19)
Z
Dcalcd.[g cmꢀ3
]
1.653
1.495
Tot. no. data
No. unique data
R1
6003
2110
0.0347
6284
2132
0.0476
solvent, which agrees with the principles of ‘green
chemistry’.
wR2
GOF
0.0617
0.910
0.0875
0.785
3.2. Infrared spectra
While in our approach the reactants were simply forcibly
milled in open mortar at room temperature for several min-
utes. The method of dealing with the product is facility in
washing by water and ethanol. During synthesis and deal-
ing process, the product was obtained without any organic
Based on IR spectra, we can deliberately diagnose the
coordination mode of the nitrate group in complexes 1
and 2. Specifically, asymmetric stretching vibrations
vas(N–O) appear near 1591 cmꢀ1 for 1 and 1599 cmꢀ1 for
2, and the symmetric stretching vibrations vs(NꢀO) are

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M. Sun et al. / Journal of Molecular Structure 873 (2008) 73–78
observed near 1385 cmꢀ1 for 1 and between 1495 and
1278 cmꢀ1 for 2. The separations [vas(NꢀO)–vs(NꢀO)] of
complexes 1 and 2 (206 and 321 cmꢀ1) are much larger
than the value of 180 cmꢀ1 for the free nitrate group, indi-
cating that the coordinated nitrate group is in a bidentate
bridging or chelating mode, which can be proved by their
crystal structural determination. While in 2, the absorption
peaks around ms(NꢀO) bands split and made the spectrum
become more complicated. The dN–O (out-of-plane bending
vibration) bands appeared at 821 and 814 cmꢀ1 for 1 and 2.
This fact may be explained by the behavior of the N atom
in the pyridine ring as a metal binding site.
nitrate coordination is quite common for cadmium com-
plexes [18,19] and previously characterized cadmium com-
plexes exhibit essentially identical Cd–O bond lengths for
the bidentate nitrate group. But in complex 1 the two oxy-
gen atoms of the bidentate nitrate group bind to Cd
unsymmetrically with CdꢀO distances of 2.444(2) and
˚
2.305(3) A, respectively. The two identical Cd–N distances
˚
of 2.227(3) A are comparable to those of known cadmium
pyridine complexes [19]. Contrasting to the free ligand, the
ligand is still highly planar and conjugated, leading to a p-
bridge for the charge transfer, which can be proved by its
luminescent properties.
The chain polymer is composed of [CdL(NO3)2]n mono-
mer. A compact single stranded 1-D zig-zag chain is
formed by self assembly of [CdL(NO3)2]n via coordination
of metal-related peripheral pyridine-N of this unit to the
neighbouring Cd(II) center running along a crystallo-
graphic axis in the c direction. The adjacent chains are
linked by the C–HÆÆÆO to form plane. The bond length of
3.3. Crystal structure of (1) and (2)
Single crystal X-ray diffraction analysis reveals that the
structure of the complex 1 presents an 1-D zig-zag infinite
chain as depicted in Fig. 3. The coordination geometry
around the Cd(II) center in (1) is shown in Fig. 2. Cd(1)
resides on a crystallographic two-fold axis and the metal
centers all adopt six coordination modes. Each Cd center
is coordinated by two nitrogen atoms of the two bipyridyl
ligands and to four oxygen atoms of nitrate in a bidentate
fashion. The overall geometry around the Cd center can be
described as a pseudo octahedral. The polyhedron contains
oxygen and nitrogen atoms with a maximum deviation of
˚
C–HÆÆÆO is 2.437 A and the angle of C–HÆÆÆO is 131.36ꢁ.
˚
The planes are similarly separated by 3.646 A, suggesting
p–p stacking interactions (Fig. 4).
In the complex 2, the Co centers also adopt six-coordina-
tion modes in Fig. 5, but they present different architectures
from Cd centers, indicating that the nature of the cation
plays an important role in the coordination polymer. Each
Co center coordinates to two pyridyl nitrogen atoms of the
two bipyridyl ligands and to two nitrate groups in a bidentate
fashion. But the equatorially coordinating oxygen atoms are
˚
0.2990 A from the idealized plane defined by the Cd and
oxygen atoms. The axially coordinated in
configuration with two bipyridyl ligand nitrogen atoms
a trans
˚
not planar with a maximum deviation of 0.9217 A from the
form a N(1)ꢀCd(1)ꢀN(1A) angle of 122.98ꢁ. Bidentate
idealized plane defined by the Co and four oxygen atoms.
The dihedral angle between the two nitrate groups is 87ꢁ
and it is too small for the ligand to coordinates to Co ion
from the front of the dihedral angle. In order to minimize ste-
ric hindrance between the bulky ligands and two nitrate
groups, both the ligands coordinate to Co from the back of
the nitrate groups forming a N(1)ꢀCo(1)ꢀN(1A) angle of
100.62ꢁ, such that the ligands coordinate to Co ion center
in a cis configuration. The nitrate groups coordinate very
unsymmetrically to Co in a bidentate fashion with CoꢀO
˚
distances of 2.065(3) and 2.264(3) A; one CoꢀO distances
are smaller to those of other known cobalt complexes con-
˚
taining bidentate nitrate groups (2.12–2.15 A) [20–22]. The
˚
Fig. 2. Molecular structure and atom numbering of 1.
Co–N bond length of 2.065(3) A is comparable to those of
Fig. 3. 1-D zig-zag infinite chain structure of 1 (H atoms have been omitted for clarity. Red: O; blue: N; green: Cd and white C). (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)

M. Sun et al. / Journal of Molecular Structure 873 (2008) 73–78
77
Fig. 4. Packing diagram for 1.
3.4. UV-vis spectra
The electronic absorption spectra of the free ligand,
complex 1 and 2 (c = 10ꢀ5 mol Lꢀ1) were measured in
DMF solutions. All the compounds (L, 1 and 2) exhibit
essentially the same absorption profile: an intense and
low-lying (near UV region) absorption band at 354 nm.
Their electronic origins are proposed to be similar because
of the comparable absorption coefficients. The large molar
absorption coefficients (e = 2.1 · 105 L molꢀ1 cmꢀ1) are
indicative of highly p-conjugated systems.
Fig. 5. Molecular structure and atom numbering of 2.
related cobalt complexes containing pyridyl ligands. The
bond angle between Co and two nitrogen atoms (N(1)–
Co(1)–N(1A)) is 101ꢁ.
The cyclic units share further Co atoms forming an infi-
nite 1D chain along a crystallographic axis in the a direc-
tion, as shown in Fig. 6. In the chain all nitrate groups
are on the same side of the chain and the ligands are all
on the other side, which is different from the zig-zag chain
of complex 1. The adjacent chains are linked by the C–
HÆÆÆO to form plane. The bond length of C–HÆÆÆO is
˚
2.369 A and the angle of C–HÆÆÆO is 158.61ꢁ. The planes
of the adjacent molecules are similarly separated by
˚
3.654 A, suggesting p–p stacking interactions (Fig. 7), as
Fig. 7. Packing diagram for 2.
complex 1.
Fig. 6. 1-D infinite chain structure of 2 (H atoms have been omitted for clarity. Red: O; blue: Cd and white C). (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)

78
M. Sun et al. / Journal of Molecular Structure 873 (2008) 73–78
the Ministry of Education of China, Education Committee
of Anhui Province (2006KJ032A, 2006KJ135B), Person
with Ability Foundation of Anhui Province 2002Z021,
The Team for Scientific Innovation Foundation of Anhui
Province (2006KJ007TD), key Laboratory of Opto-Elec-
tronic Information Acquisition and Manipulation (Anhui
University), Ministry of Education, person with Ability
Foundation of Anhui University.
Appendix A. Supplementary data
Crystallographic data have been deposited with the
CCDC (12 Union Road, Cambridge CB21EZ, UK, Fax:
+44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk; www:
http://www.ccdc.cam.ac.uk) and are available on request
quoting the deposition number CCDC227580 for 1;
CCDC227583 for 2. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.molstruc.2007.03.019.
Fig. 8. Fluorescent spectrum of complex 1 and 2 in the solid state at room
temperature.
3.5. Photoluminescence
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bands with the maximum intensity at 524 and 545 nm, upon
excitation at 350–450 nm and are red-shifted 48 and 73 nm
compared to the emission wavelength of the free ligand,
respectively. Generally, the intraligand and fluorescence
emission wavelength is determined by the energy gap
between p and p* molecular orbitals of the free ligand, which
is simply related to the extent of p conjugation in the system
[23]. This large red shift reveals stronger interactions than
that of the ligands between molecules and is the result of sig-
nificant p–p* stacking of the aromatic rings [24]. The lumi-
nescent properties of the free ligand and its metal complexes
were investigated in solid state at room temperature (Fig. 8).
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3.6. Thermal stability
To study the thermal stability of the free ligand and
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This work was supported by a grant for the National
Natural Science Foundation of China (50532030,
50325311,50335050), Doctoral Program Foundation of