Structures and properties of four coordination polymers constructed from 1,3-bis-(4-pyridyl)-propane and aromatic dicarboxylic acids

Article abstract of DOI:10.1039/c4ra00163j

Four coordination polymers associated with 1,3-bis-(4-pyridyl) propane (bpp) and 5-methylisophthalic acid (H₂mip) or 5-nitroisophthalic acid (H₂nip) formulated as [Zn(bpp)(mip)]_n (1), [Co(bpp)(mip)]_n (2), [Zn₂(bpp)₂(nip) ₂]_n (3) and [Co(bpp)(nip)(H₂O)]_n (4) have been synthesized under hydrothermal conditions. Single crystal analyses reveal that complex 1 presents a four-fold interpenetrating framework based on three-dimensional (3D) subunits with dia topology. Compound 2 has a 1D binuclear chain structure. Complex 3 shows 2D 4⁴-sql layer structure packing in ABAB mode. Complex 4 exhibits a two-fold interpenetrating framework based on three-dimensional (3D) subunits with dia topology. These compounds have been characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis and powder X-ray diffraction. In addition, the photoluminescence of 1 and 3 and magnetic properties of 2 and 4 were investigated.

Full text of DOI:10.1039/c4ra00163j

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PAPER
Structures and properties of four coordination
polymers constructed from 1,3-bis-(4-pyridyl)-
propane and aromatic dicarboxylic acids†
Cite this: RSC Adv., 2014, 4, 13919
*
*
Bo Xu, Qing-Shan Liang, Lian-Tao Liu, Qi-Sheng Liu and Cun-Cheng Li
Four coordination polymers associated with 1,3-bis-(4-pyridyl) propane (bpp) and 5-methylisophthalic acid
(H2mip) or 5-nitroisophthalic acid (H2nip) formulated as [Zn(bpp)(mip)]n (1), [Co(bpp)(mip)]n (2),
[Zn2(bpp)2(nip)2]n (3) and [Co(bpp)(nip)(H2O)]n (4) have been synthesized under hydrothermal conditions.
Single crystal analyses reveal that complex 1 presents a four-fold interpenetrating framework based on
three-dimensional (3D) subunits with dia topology. Compound 2 has a 1D binuclear chain structure.
Complex 3 shows 2D 44-sql layer structure packing in ABAB mode. Complex 4 exhibits a two-fold
interpenetrating framework based on three-dimensional (3D) subunits with dia topology. These
compounds have been characterized by infrared spectroscopy, elemental analysis, thermogravimetric
analysis and powder X-ray diffraction. In addition, the photoluminescence of 1 and 3 and magnetic
properties of 2 and 4 were investigated.
Received 8th January 2014
Accepted 4th March 2014
DOI: 10.1039/c4ra00163j
www.rsc.org/advances
between the two pyridyl groups.8 The rigidity and steric
hindrance effect of the piperazine ring make it less exible than
Introduction
the other exible bipyridyl ligand as 1,3-bis-(4-pyridyl)-propane.
As known, exibility of the bipyridyl ligand has important
inuence on the resulting structures of the nal products.
Products with different topological structures may be obtained
by rational design and tuning of the length and the exibility of
the bipyridyl ligands. Thus, based on our previous work, we now
expand our research to the synthesis of CPs with mixed 1,3-bis-
(4-pyridyl)-propane (bpp) ligand and aromatic dicarboxylic
Coordination polymers (CPs) are a class of hybrid material
constructed from metal ions linked by organic ligands through
coordination bonds. The rational design and construction of
coordination polymers (CPs) have been receiving considerable
attention over the past two decades not only because of the
variety of their topological structures but also due to their
excellent properties in many elds such as molecular separa-
tion, optics, catalysis and so on.1–4 A large number of CPs with
novel structures and fascinating properties have been obtained
through different synthesis approach. But it is still a great
challenge for us to effective control the construction of CPs with
expected structure and property because too many factors as
temperature, solvent system, counter ion and so on play
important role on the assemble process.5–7
Design and speculation of the structure and property of CPs
constructed from exible ligands is much more difficult as
exible ligands usually show different conguration and
various coordination modes when reaction with metal ions. We
have long been focusing on the research of construction of CPs
based on a exible bipyridyl ligand N,N0-bis-(4-pyridyl-methyl)
piperazine (bpmp) with a long spacer –CH2(C4H8N2)CH2–
acids. 1,3-Bis-(4-pyridyl)-propane with
a
longer linker
–CH2CH2CH2– between two pyridyl groups is more exible and
may show different conguration when coordinated to metal
ions. But coordination mode of the bpp ligand is sole as it
almost always holds the bidentate bridging mode. So two
aromatic dicarboxylic acids including 5-nitroisophthalic acid
and 5-methylisophthalic acid are involved as auxiliary ligands.
These aromatic dicarboxylic acids are chosen as the auxiliary
ligands mainly because of their various coordination modes on
one hand. One the other hand, aromatic dicarboxylic acids
usually deprotoned and act as anions when coordinating to
metal cations and thus achieve charge balance without other
anions as Clꢀ or NO3ꢀ get involved in the structure. Both of
these two features may increase the opportunity for novel
structures and interesting properties to some extent. This is also
a current research focus and a large number of coordination
compounds based on mixed N-coordinated ligand and poly-
carboxylate ligand system have been explored.9–11 In this paper,
we give a report of four compounds based on mixed 1,3-bis-(4-
pyridyl)-propane (bpp) and different aromatic dicarboxylic acids
including 5-methylisophthalic acid (H2mip) and 5-
Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong (University
of Jinan), School of Chemistry and Chemical Engineering, University of Jinan, Jinan,
Shandong, 250022, China. E-mail: chm_xub@ujn.edu.cn; chm_licc@ujn.edu.cn
† Electronic supplementary information (ESI) available: Figures showing PXRD
patterns, TG curves and table showing selected bond lengths. CCDC
980158–980161 for the complexes 1–4. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c4ra00163j
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nitroisophthalic acid (H2nip), formulated as [Zn(bpp)(mip)]n temperature during 12 hours. Colorless block crystals were
(1), [Co(bpp)(mip)]n (2), [Zn2(bpp)2(nip)2]n (3) and [Co(bpp)(ni- recovered by ltration, washed by distilled water, and dried in
p)(H2O)]n (4). We herein report the syntheses, structures, char- air at ambient temperature. Yield: 67% (based on Zn). Calcd for
acterization and luminescent or magnetic properties of these
compounds.
C22H20N2O4Zn (441.77): C 59.81, H 4.56, N 6.34; found: C 59.70,
H 4.49, N 6.30. IR (KBr, cmꢀ1): 3434 (m, br), 3070 (w), 2927 (w),
1624 (vs), 1509 (m), 1430 (m), 1334 (s), 1236 (m), 1031 (m), 1022
(w), 829 (m), 773 (m), 730 (m).
Experimental details
Materials and general methods
[Co(bpp)(mip)]n 2. Compound 2 was prepared in the same
way as that for 1 but using Co(NO3)2$6H2O (58.2 mg, 0.2 mmol)
instead of Zn(NO3)2$6H2O. Purple block crystals were recovered
by ltration, washed by distilled water, and dried in air at
ambient temperature. Yield: 63% (based on Co). Calcd for
All commercially available reagents and starting materials were
of reagent-grade quality and used without further purication.
Elemental analyses (C, H, N) were carried out on an Elementar
Vario EL III analyzer. Infrared (IR) spectra were recorded on
Perkin-Elmer Spectrum One as KBr pellets in the range 4000–
400 cmꢀ1. UV-visible absorption spectra were collected in
Hitachi U-4100. Thermogravimetric analysis was recorded with
a Perkin-Elmer Diamond TG/DTA instrument at a heating rate
of 10 ꢁC minꢀ1 under nitrogen atmosphere. X-ray Powered
diffraction (XRPD) patterns of the samples were recorded by an
X-ray diffractometer (Rigaku D/Max 2200PC) with a graphite
monochromator and CuKa radiation at room temperature
while the voltage and electric current are held at 40 kV and 20
mA. Solid-state emission and excitation spectra are carried out
on an Edinburgh FLS920 phosphorimeter equipped with a
continuous Xe-900 xenon lamp and an nF900 ns ash lamp.
Temperature-dependent magnetic measurements were carried
out on a SQUID-MPMS-XL-7 magnetometer.
C
22H20N2O4Co (435.33): C 60.70, H 4.63, N 6.43; found: C 60.54,
H 4.56, N 6.48. IR (KBr, cmꢀ1): 3369 (s, br), 2974 (w), 1616 (s),
1547 (m), 1427 (m), 1389 (s), 1224 (w), 1050 (m), 878 (w), 777 (w),
725 (m).
[Zn2(bpp)2(nip)2]n 3. Compound 3 was prepared in the same
way as that for 1 but using H2nip (42.2 mg, 0.2 mmol) instead of
H2mip. Colorless block crystals were recovered by ltration,
washed by distilled water, and dried in air at ambient temper-
ature. Yield: 61% (based on Zn). Calcd for C42H34N6O12Zn2
(945.49): C 53.35, H 3.62, N 8.89; found: C 53.24, H 3.53, N 8.77.
IR (KBr, cmꢀ1): 3428 (w, br), 3100 (w), 2943 (w), 1643 (s), 1526
(m), 1434 (m), 1337 (s), 1236 (w), 1073 (m), 889 (w), 782 (w), 725
(m).
[Co(bpp)(nip)(H2O)]n 4. Compound 4 was prepared in the
same way as that for 3 but using Co(NO3)2$6H2O (58.2 mg, 0.2
mmol) instead of Zn(NO3)2$6H2O. Red block crystals were
recovered by ltration, washed by distilled water, and dried in
air at ambient temperature. Yield: 65% (based on Co). Calcd for
Synthesis of complexes 1–4
C
21H19N3O7Co (484.33): C 52.08, H 3.95, N 8.68; found: C 52.21,
[Zn(bpp)(mip)]n 1. A mixture of Zn(NO3)2$6H2O (59.4 mg, 0.2
mmol), bpp (39.6 mg, 0.2 mmol), H2mip (35.6 mg, 0.2 mmol)
and NaOH (16.0 mg 0.4 mmol) in deionized water (10 mL),
sealed in a 25 mL Teon-lined stainless steel autoclave, and
heated at 150 ꢁC for 84 hours, then slowly cooled to room
H 3.90, N 8.62. IR (KBr, cmꢀ1): 3410 (s, br), 3098 (m), 2955 (m),
1630 (s), 1534 (m), 1429 (m), 1367 (s), 1226 (w), 1072 (m), 820
(w), 786 (m), 732 (m).
Table 1 Crystal data and structure refinement parameters for compounds 1–4
Complex
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
C
22H20N2O4Zn
C22H20N2O4Co
435.33
Triclinic
ꢀ
P1
8.9484(6)
10.1378(6)
11.8315(6)
68.413(5)
84.359(5)
78.184(5)
976.58(10)
2
C42H34N6O12Zn2
945.49
Triclinic
ꢀ
P1
9.5955(3)
14.7243(14)
14.8584(14)
67.778(9)
85.961(5)
85.587(5)
1935.7(3)
2
C21H19N3O7Co
484.33
Monoclinic
C2/c
14.4137(15)
18.2182(15)
16.6210(16)
90
102.434(11)
90
441.77
Monoclinic
P21/n
11.0364(11)
11.3292(8)
15.9216(16)
90
103.696(9)
90
1934.1(3)
4
˚
a (A)
˚
b (A)
˚
c (A)
a (deg.)
b (deg.)
g (deg.)
3
˚
V (A )
4262.2(7)
8
1.510
Z
Dcalc (g cmꢀ3
F(000)
)
1.517
912
1.480
450
1.622
968
1992
Rens collected/unique
10 107/3940
1.302
1.155
0.0687
0.1987
10 135/3996
0.910
1.070
0.0386
0.1024
17 261/7657
1.315
1.035
0.0943
0.2589
13 006/4359
0.854
0.944
0.0768
0.1844
m (mmꢀ1
)
GOF on F2
R1,a (I > 2s(I))
wR2b (all data)
P
P
P
P
a
2
R ¼ ||Fo| ꢀ |Fc||/ |Fo|. b wR(F2) ¼ [ w(Fo ꢀ Fc2)2/ w(Fo2)2]1/2
.
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Crystallographic details
Suitable single crystal with a approximate dimensions were
mounted on a Xcalibur Eos Gemini diffractometer with
˚
graphite-monochromated Mo Ka (l) 0.71073 A radiation at
room temperature. Data reduction was performed with the
CrysAlisPro program.12 Empirical absorption corrections were
applied to the data using the SADABS program.13 The structures
were solved by direct methods and rened by the full-matrix
least-squares on F2 using the SHELXTL-97 program.14 All non-
hydrogen atoms were rened with anisotropic displacement
parameters. The positions of hydrogen atoms attached to
carbon atoms were generated geometrically and rened with
isotropic thermal parameters. Crystallographic data and struc-
ture determination summaries are listed in Table 1, and the
selected bond lengths and angles for the complexes are listed in
Table S1.† The topological analysis and some diagrams were
produced using TOPOS program.15
Results and discussion
Crystal structure of 1
X-ray crystallographic analysis reveals that compound 1 crys-
tallizes in the monoclinic space group P21/n. There are one Zn(II)
ion, one mip2ꢀ ligand and one bpp ligand in the asymmetric
unit of complex 1. The view of the local coordination environ-
ment of the Zn(II) center in 1 is illustrated in Fig. 1a. Each Zn(II)
ion is tetrahedrally coordinated to two bpp ligands via the
˚
˚
pyridyl N atoms (Zn1–N1 ¼ 2.051(4) A, Zn1–N2A ¼ 2.046(4) A),
two mip2ꢀ ligands via the carboxyl O atoms (Zn1–O1 ¼ 1.961(3)
˚
˚
A, Zn1–O4A ¼ 1.959(3) A). Further insight into the structure of 1
found that the mip2ꢀ ligand holds the h1–h1 bridging coordi-
nation mode as shown in Scheme 1a, while the bpp ligand acts
as bidentate ligand with the dihedral angle between the two
pyridyl groups is ca. 75.76ꢁ linking the Zn(II) ions to a 3D
network. Topological analysis of 1 were carried out using the
TOPOS program, and the result shows that complex 1 is a
typically 3D fourfold interpenetrating diamond framework
containing adamantanoid cages as shown in Fig. 1b. As known,
large void in MOFs is usually occupied by guest molecules or
lled through interpenetrating with other motifs. The capa-
cious space of the adamantanoid cages in 1 causes four-fold
interpenetration occurring and the nal 3D fourfold inter-
penetrating diamond network is shown in Fig. 1c.
Crystal structure of 2
X-ray single crystal structure analysis reveals that the asym-
metric unit of 2 consists of one crystallographically indepen-
dent Co(II), one mip2ꢀ anion, and one bpp ligand. As shown in
Fig. 2a, the central Co(II) ion is six-coordinated by four oxygen
atoms from two mip2ꢀ anions and two nitrogen atoms from two
bpp molecules. The coordination geometry of the Co(II) ion is a
slightly distorted octahedron with the four oxygen atoms from
two mip2ꢀ anions dene the equatorial positions and two
Fig. 1 (a) The coordination environment of Zn(II) ion in 1; (b) view of
the 3D dia network and (c) schematic illustration of the four-fold
interpenetrating network in 1.
nitrogen atoms from two bpp molecules occupied the axial groups adopts chelating coordination mode while the other one
positions. The mip2ꢀ anion acts in a h2m2–h2 coordination acts in a bidentate bridging mode linking two Co(II) ions to form
mode as shown in Scheme 1b with one of the two carboxylate binuclear structure. Meanwhile, the two Co(II) ions in the
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binuclear node are further bridged by two bpp ligands with the
two pyridyl groups almost parallel to each other (dihedral angle
between the two pyridyl groups is ca. 16.43ꢁ). These binuclear
subunits are further linked by mip2ꢀ anion to form one-
dimensional chain structure (Fig. 2b). Packing of these chains
results in a 3D supramolecular structure as shown in Fig. 2c.
The dihedral angle in 2 is much smaller than that in 1 due to the
two exible C–C single bonds between the two pyridyl groups.
This long distance makes it much more exible so as to show
different congurations and resulting different structures.
Crystal structure of 3
Single crystal X-ray diffraction reveals that complex 3 crystallize
ꢀ
in P1 space group of the triclinic system. The asymmetric unit of
3 consists of two Zn(II) ions, two bpp ligands and two fully
deprotonated nip2ꢀ ligands. Both the local coordination envi-
ronments around Zn1 and Zn2 can be described as slightly
distorted tetrahedron geometry with two carboxylate oxygen
atoms from two nip2ꢀ ligands and two pyridyl nitrogen atoms
Scheme 1 Coordination modes of the aromatic dicarboxylic acids in
1–4.
Fig. 2 (a) The coordination environment of Co(II) ion in 2; (b) view of a
single chain and (c) packing of the 1D chains in complex 2.
Fig. 3 (a) The coordination environment of Zn(II) ion in 3; (b) a view of
the 2D 44-sql layer and (c) packing of the 2D layers in ABAB mode.
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from two bpp molecules as shown in Fig. 3a. The Zn–N bond
˚
distance ranges from 2.046(4) to 2.051(4) A while the Zn–O bond
˚
length ranges from 1.959(3) to 1.961(3) A, respectively, which
are well-matched to those observed in other zinc–nitrogen and
zinc–oxygen donor compounds.16,17 The nip2ꢀ ligands show h1–
h1 coordination mode as shown in Scheme 1c linking the
central Zn(II) ions into chain structure, which are further
bridged by the bpp ligand into 2D corrugated layer structure
with 44-sql topology as shown in Fig. 3b and c. Packing of such
layers in ABAB mode form the whole structure of compound 3
(Fig. 3c). These layers are further stabilized by p/p interactions
between the layers to form a 3D supramolecular structure.
Crystal structure of 4
Complex 4 crystallizes in a monoclinic space group C2/c. Its
asymmetric unit contains one independent Co(II) cation, one
bpp molecules and one nip2ꢀ anion. As shown in Fig. 1a, the
coordination number of Co(II) ion is six and each Co(II) is linked
to three oxygen atoms from two nip2ꢀ anion with the Co–O
˚
˚
bond distance range from 2.031(4) A to 2.247(4) A, two nitrogen
atoms from two bpp ligands with bond length of Co1–N1 ¼
˚
˚
2.143(5) A, Co1–N2A ¼ 2.122(5) A and one ligated water mole-
˚
cule with the Co1–O1W bond length of 2.102(5) A. These values
are comparable to those in reported Co compounds.18,19 The
nip2ꢀ anion acts in a h2–h1 coordination mode as shown in
Scheme 1d with one of the two carboxylate groups adopts
chelating coordination mode while the other one acts in a
monodentate bridging mode. The bpp ligand exhibits a dihe-
dral angle of 81.77ꢁ between the two pyridyl planes in complex
4. This means that the two pyridyl planes of a bpp ligand are
almost perpendicular to each other, which is further validated
as the ligand link the Co(II) ions into 1D zigzag chains. Mean-
while, the Co(II) ions are also linked by the H2nip ligand into 1D
chains and the two kinds of chains intersect with each other to
give up a 3D diamond network (Fig. 4b). Then the ada-
mantanoid cage also shows a large cavity as that in compound
1, which is interpenetrated by another independent framework
to form a 3D doubly interpenetrating structure as shown in
Fig. 4c.
Fig. 4 (a) The coordination environment of Co(II) ion in 4; (b) view of
the 3D dia network and (c) schematic illustration of the two-fold
interpenetrating network in 4.
Structure discussion
Coordination modes of the two aromatic dicarboxylic acids are
shown in Scheme 1 and dihedral angles between the two pyridyl
groups of the bpp ligand in complexes 1–4 are listed in Table 2. coordination modes of ligands can signicantly inuence the
The different coordination modes and dihedral angles indicate topological networks of coordination complexes. On the other
that mixed N-coordinated ligand and polycarboxylate ligand hand, the two C–C single bands between the two pyridyl groups
systems can surely provide various possibilities for the in the bpp ligand give it sufficient exibility to show different
construction of coordination polymers with distinct structure congurations with various dihedral angles when coordination
features. As shown in Table 2, for the two Zn(II)-based in different environment as in complexes 1–4. Synthesis of
complexes 1 and 3, H2mip and H2nip hold the same h1–h1 coordination complexes with interesting structures and novel
coordination mode with all the carboxylate group acting in a properties based on mixed N-coordinated ligand and poly-
monodentate bridging mode. While for the two Co(II)-based carboxylate ligand system is now a current research focus for
complexes 2 and 4, H2mip and H2nip hold similar bidentate chemists. Some other interesting networks assemble from 1,3-
linking mode. That is to say it's the central metal cations that bis-(4-pyridyl)-propane and aromatic acids have also been
greatly affect the coordination mode of the aromatic dicarbox- reported.20 For example, Liu and co-workers reported a novel 3D
ylic acids in our system. Undoubtedly, such different coordination polymer with (10,3)-d topology le/right-handed
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Table 2 The ligand conformations and the corresponding angles for
1–4
Dihedral Coordination
Metal
angles
modes of
Complexes centers of bpp
carboxylic acids Structures
1
Zn
75.76ꢁ
h1–h1
Fourfold dia
interpenetration
44-sql layer
Chain
Twofold dia
interpenetration
3
2
4
Zn
Co
Co
88.10ꢁ
16.43ꢁ
81.77ꢁ
h1–h1
h2m2–h2
h2–h1
helical channels based on mixed ligands of 5-sulfoisophthalate
and bpp.20a Li and co-workers reported a complex with 3-fold
interpenetrating dia network and interesting nonlinear-optic
property assemble from 2-amino-1,4-benzene dicarboxylic acid
and bpp.20b Among these structures, two-fold interpenetrating
frameworks are most common while those four-fold inter-
penetrating networks are relative rare and somewhat
uncommon.
Fig. 5 Luminescent spectra of compounds 1 and 3.
UV-vis absorbance properties and photoluminescent
properties
The solid-state UV-vis spectra of compounds 1–4 are measured
and the results are shown in Fig. S4.† Compounds 1–4 show
similar weak absorption band with maximum at about 330 nm,
which is probably owing to n / p* transitions of the aromatic
rings. Considering the excellent luminescence of coordination
polymers constructed from d10 metal ions, the solid-state
luminescent properties of compounds 1 and 3 have been
investigated at room temperature. As depicted in Fig. 5,
Complexes 1 and 3 exhibit broad emission bands with
maximum at 502 and 510 nm upon excitation at 330 nm
respectively. Luminescent spectra of the bpp, H2mip and H2nip
have also been investigated but no emission band has been
observed in the range of 450 to 600 nm upon excitation at
330 nm. The H2mip ligand display a emission peak at 357 nm
upon excitation at 315 nm according to literature.22 These
results indicate that the emissions of compounds 1 and 3 can be
probably ascribed to metal-to-ligand charge transfer (MLCT)
transition between Zn(II) ions and the aromatic ligands.23,24 As
for complexes 2 and 4, Co2+ ion has unsaturated electron
conguration d7, the interaction between Co2+ ion and ligand
leads to strong quenching effect and therefore the two
compounds don't exhibit the emission nature.
Thermal analysis and PXRD results
Thermogravimetric analysis (TGA) studies were performed to
characterize the thermal stability of complexes 1–4 under an
nitrogen atmosphere. The TGA curves of complexes 1–3
(Fig. S2†) show no weight loss below 300 ꢁC as there is no water
or other solvent molecule in the structure. One obvious weight
loss began at about 315 ꢁC indicating the decomposition of the
framework. Complex 4 exhibits two signicant weight losses.
The rst weight loss of 3.79% occurs between 120 ꢁC and
177 ꢁC corresponds to the removal of the one coordinated
water molecule (calcd: 3.72%). And then begin to decompose
from 245 ꢁC upon further heating. Additionally, to conrm
whether the crystal structures of 1–4 are truly representative
of the bulk materials, powder X-ray diffraction has been
performed with the as-synthesized polycrystalline samples
under room temperature. The results shown in Fig. S1†
indicate that the X-ray powder diffraction data are in agree-
ment with that calculated on the basis of the single crystal
structural datas, that is, 1–4 have been obtained successfully
as pure crystalline phases.
Magnetic property
The variable-temperature magnetic susceptibility study of
complex 2 and 4 were carried out at an applied eld of 1000 Oe
in the temperature range of 2–300 K, as shown in Fig. 6. For
FT-IR spectra
The FT-IR spectra of complexes 1–4 were determined in the complex 2, the cmT value at 300 K is ca. 3.87 cm3 K molꢀ1, which
frequency range of 500–4000 cmꢀ1, as shown in Fig. S3.† The is slightly higher than that of the spin-only value of 3.75 cm3 K
strong peaks around 1624 and 1430 cmꢀ1 for 1, 1616 and 1427 molꢀ1 for two Co(II) ions with S ¼ 3/2 and g ¼ 2 owing to the
cmꢀ1 for 2, 1643 and 1434 cmꢀ1 for 3 and 1630 and 1429 cmꢀ1 signicant orbital contribution of Co(II) in an octahedral envi-
for 4 are associated with the asymmetric and symmetric ronment.25,26 The cmT value decreases gradually upon lowering
stretching vibrations of carboxylate groups.15 The bands around the temperature and goes down to a minimum of 1.80 cm3 K
1334 and 1031 cmꢀ1 for 1, 1389 and 1050 cmꢀ1 for 2, 1337 and molꢀ1 at 2 K. The temperature dependence of the reciprocal
1073 cmꢀ1 for 3 and 1367 and 1072 cmꢀ1 for 4 are characteristic susceptibility above 35 K obeys the Curie–Weiss law with a
of the stretching vibrations of C–N bond, suggesting the pres- Weiss constant, q ¼ ꢀ16.12 K and a Curie constant, Cm ¼ 4.04
ence of the pyridyl ring.21
cm3 molꢀ1 K. The high value of C and negative q value may be
13924 | RSC Adv., 2014, 4, 13919–13926
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exibility and conguration of the bpp ligand and the different
coordination modes of the H2mip or H2nip ligands, the four
complexes show different structures: fourfold 3D inter-
penetrating framework with dia topology for 1, 3D supramo-
lecular structure assembled from binuclear chains for 2, 3D
supramolecular structure based on 2D sql layers packing of
ABAB mode for 3 and 3D doubly interpenetrating diamond
network for 4. The results indicate that the exibility and the
conguration of ligands play a crucial role in determining the
topological structure of the resulting coordination polymers.
The photoluminescent properties of 1 and 3 were investigated,
which were assigned to MLCT transitions. The magnetic prop-
erty studies of 2 and 4 indicating antiferromagnetic coupling
interactions exist between Co(II) ions.
Acknowledgements
This work was nancially supported by The Shandong Provin-
cial Natural Science Foundation of China (grant no.
ZR2012BQ004) and Doctor's Foundation of University of Jinan
(XBS1208), C. Li, as a Taishan Scholar Endowed Professor,
acknowledges the support from Shandong Province and UJN.
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˚
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28
˚
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