Five heterometallic SrII-MII (M = Co, Ni, Zn, Cu) 3-D coordination polymers: Synthesis, structures and magnetic properties

Article abstract of DOI:10.1016/j.poly.2013.12.042

Five heterometallic coordination polymers based on pyridine 2,3-dicarboxylic acid (H₂pydc), namely [MSr(pydc)₂(H ₂O)₂]_n (M = Co (1), Ni (2)), [MSr ₂(pydc)₃(H₂O)_4<

Full text of DOI:10.1016/j.poly.2013.12.042

Polyhedron 71 (2014) 91–98
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Five heterometallic SrII–MII (M = Co, Ni, Zn, Cu) 3-D coordination
polymers: Synthesis, structures and magnetic properties
a
b
Yanmei Chen a,b, Qian Gao a, Haifeng Zhang a, Dandan Gao b, Yahong Li a,c, , Wei Liu , Wu Li
⇑
a Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
b Key Laboratory of Salt Lake Resources and Chemistry, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China
c State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Five heterometallic coordination polymers based on pyridine 2,3-dicarboxylic acid (H2pydc), namely
[MSr(pydc)2(H2O)2]n (M = Co (1), Ni (2)), [MSr2(pydc)3(H2O)4]nꢀ2nH2O (M = Ni (3), Zn (4)) and
[CuSr(pydc)2(H2O)3]nꢀ2nH2O (5), have been synthesized via rationally choosing the appropriate metal
salts and dexterously adjusting the pH values of the reaction system. X-ray crystallographic analyses
reveal that the polymers display three varieties of 3-D framework structures. The magnetic properties
of complexes 1 and 2 were investigated, and antiferromagnetic MIIꢀꢀꢀMII interactions were found for both
complexes.
Received 7 November 2013
Accepted 28 December 2013
Available online 11 January 2014
Keywords:
Pyridine-2,3-dicarboxylic acid
Heterometallic complexes
Alkaline earth metal
Magnetic properties
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
In our previous work, we have reported two series of heterome-
tallic coordination polymers, SrII–CuII [6] and SrII–LnIII [20,21],
Heterometallic coordination polymers containing both transi-
tion metals and alkaline earth metals are currently being widely
investigated due to the pleasing architectures that many such com-
plexes possess and their potential applications in the fields of
catalysis, material science and biochemistry [1–5]. However, the
involvement of alkaline earth metals in heterometallic complexes
is challengeable, and chemists are often frustrated by obtaining
homometallic coordination polymers instead of heterometallic
ones. The most important reasons are as follows [6]: (i) the transi-
tion metal ions have a strong tendency to coordinate both nitrogen
and oxygen atoms, whereas the alkaline earth metals prefer oxy-
gen donors to nitrogen donors. They will compete for oxygen
atoms; (ii) the broad span of coordination numbers of alkaline
earth metals makes the topologies of the coordination polymers
uncontrollable. Hence, it is of high demand to discover an efficient
approach to incorporate both transition metals and alkaline earth
metals into one coordination system. Recent advances have re-
vealed that N-heterocyclic carboxylates are useful to combine alka-
line earth metals with transition metals [7–9]. Alkaline earth
metals are firstly coordinated by the oxygen atoms to form ‘‘com-
plex-ligands’’, then the ‘‘complex-ligands’’ bind with transition
metal ions to generate heterometallic coordination polymers
[5,9–19].
based on N-heterocyclic carboxylate ligands. They were all
constructed by employing ‘complex-ligands’ of SrII ions. As a
continuation of our previous studies, we have investigated the
synthetic chemistry of heterometallic SrII–MII (M = Co, Ni, Zn, Cu)
coordination polymers by employing pyridine 2,3-dicarboxylic
acid (H2pydc) as a ligand. Pyridine 2,3-dicarboxylic acid can
coordinate with either transition metals or alkaline earth metals
to form coordination complexes [22–33]. However, other than
two heterometallic complexes (Co–Ca, Co–Ba) reported by the
Lazarescu group [22], no heterometallic complexes containing
both strontium and transition metals and supported by pyridine
2,3-dicarboxylic acid have been reported.
Herein, we present the synthesis and characterization of the
first series of MII–SrII heterometallic complexes, [MSr(pydc)2
(H2O)2]n (M = Co (1), Ni (2)), [MSr2(pydc)3(H2O)4]nꢀ2nH2O (M = Ni
(3), Zn (4)) and [CuSr(pydc)2(H2O)3]nꢀ2nH2O (5), based on pyri-
dine-2,3-dicarboxylic acid. These complexes display three varieties
of 3-D framework structures. The magnetic properties of com-
plexes 1 and 2 were also investigated.
2. Experimental
2.1. General procedures
⇑
Corresponding author at: Key Laboratory of Organic Synthesis of Jiangsu
Province, College of Chemistry, Chemical Engineering and Materials Science,
Soochow University, Suzhou 215123, China.
All manipulations were performed under aerobic and solvother-
mal conditions. The reagents and solvents were purchased from
commercial suppliers and used without further purification. The
E-mail address: liyahong@suda.edu.cn (Y. Li).
http://dx.doi.org/10.1016/j.poly.2013.12.042
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

92
Y. Chen et al. / Polyhedron 71 (2014) 91–98
C, H and N microanalyses were carried out with a Carlo-Erba
EA1110 CHNO-S elemental analyzer. FT-IR spectra were recorded
resultant solution to room temperature gave crystals of the prod-
uct. The yields of 1 and 2 are 0.0330 g (65%, based on Co) and
0.0283 g (55%, based on Ni), respectively. Anal. Calc. for CoSrC14
H10N2O10 (1, orange rod crystals): C, 32.86; H, 1.77; N, 5.47. Found:
C, 32.65; H, 1.99; N, 5.45%. Selected IR data (KBr, cmꢁ1): 3472(w),
3078(s), 1613(s), 1573(s), 1462(s), 1413(s), 1385(s), 1108(s),
850(s), 779(s), 733(s), 711(s), 672(s). Anal. Calc. for NiSrC14H10
N2O10 (2, light-blue acicular crystals): C, 32.81; H, 1.97; N, 5.47.
Found: C, 32.62; H, 2.29; N, 5.46%. Selected IR data (KBr, cmꢁ1):
3474(w), 3081(s), 1615(s), 1574(s), 1456(s), 1413(s), 1387(s),
1111(s), 852(s), 840(s), 736(s), 711(s), 677(s).
from KBr pellets in the range 400–4000 cmꢁ1 on
a Nicolet
Magna-IR 500 spectrometer. Powder X-ray diffraction (PXRD) data
were recorded on a Rigaku D/Max-2500 diffractometer at 40 kV
and 100 mA with a Cu-target tube and a graphite monochromator.
Thermal gravimetric analysis (TGA) was conducted on a NETZSCH
STA 449F3 instrument in flowing N2 with a heating rate of
5 °C/min. Magnetic susceptibility measurements were performed
in the temperature range 2–300 K, using a Quantum Design MPMS
XL-7 SQUID magnetometer.
2.2. Crystal structure refinement
2.3.2. Synthesis of [MSr2(pydc)3(H2O)4]nꢀ2nH2O (M = Ni (3), M = Zn
(4))
Data were collected at room temperature on a Bruker Smart
ApexII diffractometer equipped with a graphite monochromator
A mixture of H2pydc (0.0333 g, 0.2 mmol), SrCl2ꢀ6H2O (0.0266 g,
0.1 mmol), Ni(CH3COO)2ꢀ4H2O (0.0251 g, 0.1 mmol) [or Zn(CH3
utilizing Mo K
a
radiation (k = 0.71073 Å); the
x
and
u
scan tech-
COO)2ꢀ2H2O
(0.0219 g,
0.1 mmol)],
imidazole
(0.0319 g,
nique was applied. The structures were solved by direct methods
using SHELXS-97 [34] and refined on F2 using full-matrix least-
squares with SHELXL-97 [35,36]. Hydrogen atoms of water molecules
were localized from a difference Fourier map and the positions of
the remaining H atoms were located in geometrically calculated
positions. It should be noted that the hydrogen atoms of the water
molecules (O13) in 3 and 4 were not located and thus some B-type
errors related to the CIF-check files may be observed. Crystallo-
graphic data together with refinement details for 1–5 are summa-
rized in Table 1. See CIF files for further details.
0.469 mmol) and H2O/C2H5OH (2 mL, v/v = 2:1) was sealed in a
6 mL Pyrex-tube and heated at 120 °C for 1 day under autogenous
pressure. Cooling of the mixture to room temperature gave crystals
of the product. The yields of 3 and 4 are 0.0235 g (56%, based on Sr)
and 0.0254 g (60%, based on Sr), respectively. Anal. Calc. for NiSr2
C21H21N3O18 (3, blue platy crystals): C, 30.12; H, 2.53; N, 5.02.
Found: C, 29.67; H, 2.74; N, 5.08%. Selected IR data (KBr, cmꢁ1):
3448(w), 1613(s), 1569(s), 1400(s), 1112(s), 843(s), 7101(s),
675(s). Anal. Calc. for ZnSr2C21H21N3O18 (4, colorless platy crys-
tals): C, 29.88; H, 2.51; N, 4.98. Found: C, 29.51; H, 2.72; N,
4.81%. Selected IR data (KBr, cmꢁ1): 3453(w), 1614(s), 1572(s),
1446(s), 1382(s), 1275(s), 1238(s), 1113(s), 881(s), 843(s), 787(s),
710(s).
2.3. Preparations
2.3.1. Synthesis of [MSr(pydc)2(H2O)2]n (M = Co (1), Ni(2))
A
mixture of H2pydc (0.0333 g, 0.2 mmol), Sr(OH)2ꢀ8H2O
2.3.3. Synthesis of [CuSr(pydc)2(H2O)3]nꢀ2nH2O (5)
(0.0266 g, 0.1 mmol), Co(CH3COO)2ꢀ4H2O (0.0247 g, 0.1 mmol) [or
Ni(CH3COO)2ꢀ4H2O (0.0256 g, 0.1 mmol)], H2O/C2H5OH (2 mL,
v/v = 2:1) was sealed in a 6 mL Pyrex-tube. The tube was heated
at 120 °C for 1 day under autogenous pressure. Cooling of the
Complex 5 was prepared by the same procedure as that of 3,
using CuCl2ꢀ2H2O (0.0171 g, 0.1 mmol) instead of Ni(CH3COO)2ꢀ4
H2O as the starting material. Blue bar crystals of 5 were obtained.
The crystals were collected by filtration, washed with H2O (3 mL)
Table 1
Crystallographic data and structure refinement for complexes 1–5.
1
2
3
4
5
a
Formula
CoSrC14H10N2O10
512.79
569(2)
0.71073
orthorhombic
Pnma
NiSrC14H10N2O10
512.57
569(2)
0.71073
orthorhombic
Pnma
NiSr2C21H21N3O18
837.36
569(2)
0.71073
triclinic
ZnSr2C21H21N3O18
844.02
569(2)
0.71073
triclinic
SrCuC14H16N2O13
571.46
569(2)
0.71073
triclinic
M (g molꢁ1
T (K)
)
a
k (Å)b
Crystal system
Space group
a (Å)
ꢀ
ꢀ
ꢀ
P1
P1
P1
7.891(3)
16.554(7)
12.826(5)
90.00
90.00
90.00
1675.5(12)
4
2.033
7.8101(13)
16.489(3)
12.635(2)
90.00
90.00
90.00
1627.2(5)
4
2.092
7.834(5)
13.782(9)
13.798(9)
107.577(10)
97.328(10)
97.034(10)
1388.0(16)
2
7.875(7)
13.898(13)
13.910(13)
107.624(12)
97.416(14)
97.310(13)
1416(2)
2
6.593(4)
10.723(7)
14.033(9)
94.269(12)
101.964(12)
92.428(11)
966.1(11)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
q
l
(mg mmꢁ3
(mmꢁ1
)
2.004
4.592
1.979
4.682
1.964
3.936
)
4.236
4.499
F(000)
1012
1016
832
836
570
2h range (°)
Measured/independent
4.02–54
9910/1892
0.0387
0.0279
0.0916
4.06–49.98
8319/1488
0.0409
0.0335
0.0932
3.66–49.98
16017/4881
0.0368
0.0921
0.2473
5.08–50
15530/4973
0.0377
0.1068
0.2769
5.04–48.48
4832/3032
0.0382
0.0980
0.3049
Rint reflections
c
R1
d,e
wR2
GOF on F2
1.069
1.063
1.033
1.077
1.099
a
b
c
Including solvate molecules.
Mo K
a
radiation.
P
P
R1
=
(|Fo| ꢁ |Fc|)/ (|Fo|) for observed reflections.
2
w ¼ 1=½r2ðFo2Þ þ ðaPÞ þ bPꢂ and P ¼ ½maxðFo2; 0Þ þ 2F2c ꢂ=3.
d
e
1=2
P
P
wR2
¼
½wðFo2 ꢁ Fc2Þ2ꢂ= ½wðF2oÞ2ꢂ
for all data.

Y. Chen et al. / Polyhedron 71 (2014) 91–98
93
and dried in air. Yield: 0.0198 g (35%, based on Cu). Anal. Calc. for
C
14H12CuN2O11Sr: C, 29.43; H, 2.82; N, 4.90. Found: C, 29.61; H,
2.72; N, 4.96%. Selected IR data (KBr, cmꢁ1): 3439(m), 1619(s),
1586(s), 1377(s), 1118(s), 881(s), 837(s), 728(s), 704(s), 475(s).
3. Results and discussion
3.1. Synthesis
It is known that numerous factors, including the pH values of
the systems, metal sources and solvents, influence the formation
of the heterometallic coordination polymers. Sr(OH)2ꢀ8H2O is a
better metal source than SrCl2ꢀ6H2O in the preparation of 1. It is
believed that Sr(OH)2ꢀ8H2O is used not only as the metal source
but also as an alkaline to adjust the pH value of the reaction system
of 1.
For the preparation of 4 and 5, we found that imidazole is a bet-
ter base than Sr(OH)2ꢀ8H2O for adjusting the pH value of the sys-
tems. The yields of 4 and 5 using SrCl2ꢀ6H2O and imidazole as
the metal source and alkaline, respectively, are much higher than
those employing Sr(OH)2ꢀ8H2O as the metal source. However, it
is interesting to note that two distinct complexes, 2 and 3, were
generated on employing Sr(OH)2ꢀ8H2O or SrCl2ꢀ6H2O and imidaz-
ole as the reagents. This strategy for the rational assembly of het-
erometallic coordination polymers via dexterously choosing the
appropriate reagents as metal sources as well as alkaline has rarely
been reported [6], reflecting the synthetic novelty of this work.
It is intriguing that no crystals were obtained when copper
acetate was used as the starting material. However, the reaction
of H2pydc, SrCl2ꢀ6H2O, imidazole and CuCl2ꢀ2H2O led to the
isolation of 5 as blue crystals.
EtOH plays a vital role in the crystal growth process. In the ab-
sence of EtOH, powder forms of the coordination polymers were
obtained. EtOH may hinder the diffusion of crystallization nutri-
ents in the reaction system and make the crystal growth slower
and more homogeneous [37].
The methods for the synthesis of 1–5 were summarized in
Scheme 1.
3.2. Description of structures
3.2.1. Structure of [MSr(pydc)2(H2O)2]n (M = Co (1), M = Ni (2))
The crystal structure determination reveals that complexes 1
and 2 are isostructural. The structure of 1 will be discussed here
in detail. Complex 1 exhibits a 3-D framework structure (Fig. 1).
The CoII ion is six-coordinated by four oxygen atoms (O1, O1E,
O4C, O4F) and two nitrogen atoms (N1, N1E) of four pydc2ꢁ anions
(Fig. 1a). Each CoII ion is connected to eight SrII ions by four carbox-
ylic groups (O1–C6–O2, O1E–C6E–O2E, O4C–C7C–O3C, O4F–C7F–
O3F) of four pydc2ꢁ ligands (in coordination mode A of Scheme 2).
The Sr1 ion is eight-coordinated by six carboxylate oxygen atoms
(O2, O2A, O2B, O2C, O3, O3A) of four pydc2ꢁ ligands and two ter-
minal water molecules (O5, O6) in a slightly distorted dodecahe-
dral geometry (Fig. 1b). Each SrII ion is connected to two
Fig. 1. (a) Coordination environments of the Co1 ions in 1. (b) Coordination
environments of the Sr1 ions in 1 (A: x, ꢁy + 3/2, z; B: x + 1/2, ꢁy + 3/2, ꢁz + 3/2; C:
x + 1/2, y, ꢁz + 3/2; D: x ꢁ 1/2, y, ꢁz + 3/2; E: ꢁx + 1, ꢁy + 1, ꢁz + 2; F: ꢁx + 1/2,
ꢁy + 1, z + 1/2). (c) The polyhedron structure of the 3-D framework of 1 viewed
along the a-axis and schematic representation of the 3-nodal topology net with the
topological notation (42.82.102)(43.62.8)2(44.62) in the bc plane. Hydrogen atoms are
omitted for clarity. Color codes: lavender, Sr; violet, Co; red, O; blue, N; green, C.
(Colour online.)
neighboring SrII ions by two
l2-O atoms to form a 1-D [Sr(O)2Sr]n
chain structure viewed along the a-axis (Fig. 1c). The 1-D
[Sr(pydc)2]n2nꢁ chains are connected by CoII ions through pydc2ꢁ li-
gands to form a 3-D framework structure (Fig. 1c). The intramolec-
ular hydrogen bonds between coordinated water molecules as the
hydrogen donors and carboxylate oxygen atoms as hydrogen
acceptors enhance the stability of the framework structure
(Fig. S1).
Sr(OH) 8H O
·
2
2
[CoSr(pydc)2(H2O)2]n
[NiSr(pydc)2(H2O)2]n
(1)
(2)
Co(OAC)2 4H2O
·
O
H2
2 8
)
H
O
(
r
S
O
Ni(OAC) 4H O
·
2
2
S
r
OH
O
C
l
+
2 6
[NiSr2(pydc)3(H2O)4]n 2nH2O (3)
H
2O
·
+
i
m
N
The pydc2ꢁ ligand acts as a 4-bridge, linking two CoII ions and
l
OH
SrCl 6H O+im
·
2
2
Zn(OAC)2 2H2O
·
[ZnSr2(pydc)3(H2O)4]n 2nH2O (4)
two SrII ions. To better understand the 3-D framework structure, a
topological approach has been applied. The pydc2ꢁ ligand can be
simplified to a 4-connected node, as shown in Fig. 1c, and the CoII
and SrII ions can also be simplified to a 4-connected node. The
·
SrCl 6H O+im
·
2
2
CuCl2 2H2O
[CuSr(pydc)2(H2O)3]n 2nH2O (5)
·
·
Scheme 1. Synthesis of complexes 1–5.

94
Y. Chen et al. / Polyhedron 71 (2014) 91–98
is eight-coordinated by five carboxylate oxygen atoms (O2, O3,
Co
O
O
O
O
Sr
O
O6, O7, O7A) of three pydc2ꢁ ligands and three terminal water
molecules (O9, O10, O11) in a slightly distorted dodecahedral
geometry. Two SrII ions are bridged by two carboxylate oxygen
Sr
O
O
Sr
O
O
O
O
Sr
Sr
Sr
N
N
N
atoms (l2-O7, l
2-O7A) to form a [Sr2(pydc)4]4ꢁ unit. Each SrII ion
is connected to one Cu1 ion by the carboxylic group O2–C6–O1,
and linked to two Cu2 ions by the carboxylate groups
O6–C13–O5 and O7–C14–O8.
The Cu1 ion is six-coordinated by four carboxylate oxygen
atoms (O1, O1F, O4E, O4G) and two nitrogen atoms (N1, N1F) of
four pydc2ꢁ ligands in a distorted octahedral geometry (Fig. 3b).
The Cu1–O1 and Cu1–N1 distances are 1.954(10) and
1.969(12) Å, respectively. The Cu1–O4E and Cu1–O4G distances
are 2.529(11) Å, and this bond length difference may be caused
by the Jahn–Teller effect [40,41]. Each Cu1 ion is connected to four
SrII ions and other two Cu1 ions by four pydc2ꢁ ligands (in coordi-
nation mode D).
O
Co
Ni
Ni
A
B
C
Cu
Cu
Sr
Sr
O
O
O
O
O
O
O
O
Sr
N
N
Cu
Cu
D
E
Scheme 2. Coordination modes of the pydc2ꢁ anions in 1–5 (dotted line represents
The Cu2 ion is six-coordinated (Fig. 3c). It is chelated by two
pydc2ꢁ ligands with four atoms (N2, O5, N2B, O5B), and is coordi-
nated by two oxygen atoms (O8C, O8D), showing the Jahn–Teller
effect [40,41]. The Cu2–N2, Cu2–O5 and Cu2–O8C distances are
1.967(11), 1.962(11) and 2.485(9) Å, respectively. Each Cu2 ion is
connected to eight SrII ions and two Cu2 ions through the pydc2ꢁ
ligands (in coordination mode E). The [Sr2(pydc)4]4ꢁ units are con-
nected by Cu1 ions to form a 2-D network in the ac plane (Fig. 3d).
The 2-D networks are connected by Cu2 ions to form a 3-D frame-
work structure (Fig. 3e). In addition, hydrogen bonds between lat-
tice water molecules (or coordination water molecules) as
hydrogen donors and carboxylate oxygen atoms of pydc2ꢁ ligands
as acceptors are observed (Fig. S3).
the longer bond lengths originated from the John–Teller effect).
overall structure of 1 can be simplified to a new 3-nodal 4,4,4-c net
with a Schläfli symbol of (42.82.102)(43.62.8)2(44.62) [38,39].
3.2.2. Structure of [MSr2(pydc)3(H2O)4]nꢀ2nH2O (M = Ni (3), M = Zn
(4))
X-ray crystallography analyses reveal that complexes 3 and 4
are isostructural. Complex 3 is taken here as a representative
example to depict the structure in detail. The asymmetric unit of
3 consists of one NiII ion, three pydc2ꢁ anions, two SrII ions, four
coordinated water molecules and two lattice water molecules. As
shown in Fig. 2a, the Ni1 center is six-coordinated by three oxygen
atoms (O1, O5D, O9) and three nitrogen atoms (N1, N2D, N3) from
three pydc2ꢁ anions (two are in coordination mode B and one is in
The pydc2ꢁ ligands display two kinds of coordination modes (D
and E). To better understand the 3-D network of the structure, a
topological approach has been applied. As shown in Fig. 3f, each
two neighboring SrII ions can be simplified to a 4-connected node
with the point symbol 86. Each pydc2ꢁ ligand can be simplified
to a 3-connected node with point symbol 4.82, and each CuII ion
can be simplified to a 4-connected node with point symbol
42.82.102. The nature of the 3-D framework structure of 5 can be
simplified to a 3-nodal 3,4,4-c net with a Schläfli symbol of
(4.82)4(42.82.102)2(86) [39]. The topological type is sqc945.
Complexes 1–5 join a very small family of MII–AEII (M = Co;
AE = Ca and Ba) [22] coordination polymers supported by pyridine
2,3-dicarboxylic acid, whereas the structures of 1–5 are totally dif-
ferent from those of the reported complexes. Complexes 1–5 all ex-
hibit 3-D framework structures, however, the topological
architectures are totally different, revealing the structure diversity
of the MII–AEII coordination polymers.
coordination mode C) to form
a
[Ni(pydc)3]4ꢁ unit. Each
[Ni(pydc)3]4ꢁ moiety is connected to six SrII ions through the car-
boxylic groups of the pydc2ꢁ ligands.
The coordination numbers of Sr1 and Sr2 ions are seven and
nine, respectively. The Sr1 ion (Fig. 2b) is coordinated by four car-
boxylate oxygen atoms (l2-O7B, l2-O8, l2-O11A, l2-O4) from four
pydc2ꢁ ligands and three terminal water molecules (O13, O14,
O16). The Sr2 ion (Fig. 2c) is coordinated by eight oxygen atoms
(O3, l2-O4, l2-O6, l2-O8, l2-O11A, O12A, l2-O6E, l2-O7E) of four
pydc2ꢁ ligands and one terminal water molecule (O15).
The Ni1F and Ni1K ions are connected to Sr2 ions through car-
boxylic groups O6–C13–O5 and O6E–C13E–O5E, respectively
(Fig. 2d). The Sr1 ions and Sr2 ions are bridged by
l2-O atoms or
carboxylic groups to form a 1-D chain structure along the a-axis.
The chains are bridged by [Ni(pydc)3]4ꢁ units to form a 3-D frame-
work structure (Fig. 2e). Moreover, intramolecular hydrogen bonds
between coordination water molecules as hydrogen donors and
carboxylate oxygen atoms as hydrogen acceptors are observed
(Fig. S2).
3.3. XRD patterns and thermal properties
In order to check the phase purity of the complexes, the powder
X-ray diffractions (PXRD) of 1–5 have been measured and com-
pared with those simulated from the single-crystal structures.
The measured PXRD patterns of 1–5 are in good agreement with
the patterns generated from their single crystal data (Fig. S9), indi-
cating the phase purity of the samples. The differences in intensity
are due to the preferred orientation of the powder samples.
The thermogravimetric analyses were performed under an N2
atmosphere in the temperature range 30–1250 °C. The results reveal
that complexes 1–5 possess two obvious steps of weight loss (Fig. 4).
The first weight loss occurs in the range 30–220 °C, with a weight
loss of 7.36%, 8.61%, 14.17%, 13.86% and 15.99%, respectively, which
corresponds to the loss of all coordinated and lattice water mole-
cules (Calc. 7.03%, 7.02%, 12.90%, 12.80% and 15.75%, respectively).
Above 300 °C, the frameworks begin to collapse and these com-
pounds are gradually decomposed to complicated oxides. The
The pydc2ꢁ ligands display coordination modes B and C in
Scheme 2. All of the pydc2ꢁ ligands act as a
l3-bridge, linking
one NiII ion and two SrII ions. A topological approach has been ap-
plied to simplify the nature of the 3-D framework. Each NiII ion can
be considered as a 3-connected node, every four neighboring SrII
ions (two Sr1 and two Sr2 ions) can be considered as an 8-con-
nected node and each pydc2ꢁ ligand, serving as a linear linker, con-
nects adjacent 3-connected and 8-connected nodes (Fig. 3f). The
whole structure can be simplified to a 2-nodal 3,8-c topology net
with a Schläfli symbol of (43)2(46.618.84) [39]. The topological type
is tfz-d.
3.2.3. Structure of [CuSr(pydc)2(H2O)3]nꢀ2nH2O (5)
X-ray single-crystal diffraction analysis reveals that complex 5
exhibits a 3-D network structure. As shown in Fig. 3a, the Sr1 ion

Y. Chen et al. / Polyhedron 71 (2014) 91–98
95
Fig. 2. (a) Coordination environments of the Ni1 ions in 3. (b) Coordination environments of the Sr1 ions in 3. (c) Coordination environments of the Sr2 ions in 3. (d) The
connection modes of the Sr1, Sr2 and Ni1 ions in 3 (A: ꢁx + 2, ꢁy + 2, ꢁz + 1; B: ꢁx + 1, ꢁy + 1, ꢁz; C: x ꢁ 1, y, z; D: x, y, z + 1; E: ꢁx + 2, ꢁy + 1, ꢁz; F: x, y, z ꢁ 1; G: x + 1, y, z; K:
ꢁx + 2, ꢁy + 1, ꢁz + 1). (e) The 3-D polyhedral structure of 3 viewed along the a-axis. (f) Schematic representation of the 2-nodal topology net with the topological notation
(43)2(46.618.84) in the bc plane. Hydrogen atoms and lattice water molecules are omitted for clarity. Color codes: lavender, Sr; bright-green, Ni; red, O; blue, N; green, C.
(Colour online.)
compositions of the oxides were further determined by X-ray pow-
der diffraction. The results indicate that complex 1 is decomposed to
SrCoOx (Fig. S16). Both complexes 2 and 3 are decomposed to a mix-
ture of SrCO3 and NiO (Figs. S17 and S18). The composition of the res-
idue of TGA analysis of complex 4 is SrCO3 and ZnO (Fig. S19).
Complex 5 is broken up into SrCO3 and CuO (Fig. S20).
2 K. Such behavior is characteristic for CoII complexes and it is pro-
posed that three factors contribute to the decrease of the magnetic
susceptibility with the lowering temperature [46]: (a) an intramo-
lecular antiferromagnetic coupling between two CoII centers, (b) an
intermolecular antiferromagnetic coupling along the chains, and
(c) the contribution of the orbital momentum. This behavior is
indicative of the presence of antiferromagnetic exchange interac-
tions between the metal ions. We attempted to evaluate the mag-
netic interactions by fitting the experimental susceptibility using
3.4. Magnetic properties
Ng2
b
2SðSþ1Þ
1þu
the equation XM
¼
for the Co(II) chain complex [47].
Variable-temperature dc magnetic susceptibility data were re-
corded for polycrystalline samples of 1 and 2 at an applied mag-
netic field of 1000 Oe in the temperature range 2–300 K. The
3kT
1ꢁu
However, the results were not satisfactory. The reciprocal mag-
netic susceptibilities in the temperature range 2–300 K follow
MT value of 1 at 300 K is 2.93 cm3 K molꢁ1 (Fig. 5), which is obvi-
the Curie–Weiss Law of 1/
v
M = (T ꢁ h)/C with a Curie constant
v
C = 2.97 cm3 K molꢁ1 and Weiss constant h = ꢁ5.82 K, which con-
firms the existence of the weak antiferromagnetic CoIIꢀꢀꢀCoII
interactions.
ously larger than the spin-only value of 1.88 cm3 K molꢁ1 expected
for one S = 3/2 uncoupled spin, possibly due to the orbital contribu-
tions of the metal ions [42–45]. The
vMT value decreases gradually
The value of
v
MT for 2 is 1.41 cm3 K molꢁ1 at 300 K (Fig. 6),
from 2.93 to 2.53 cm3 K molꢁ1 from 300 to 50 K, and then at lower
temperatures decreases more steeply to reach 1.68 cm3 K molꢁ1 at
which is larger than the expected value (1.00 cm3 K molꢁ1
,

96
Y. Chen et al. / Polyhedron 71 (2014) 91–98
Fig. 3. (a) Coordination environments of the Sr1 ions in 5. (b) Coordination environments of the Cu1 ions in 5. (c) Coordination environments of the Cu2 ions in 5 (A: #1
ꢁx ꢁ 1, ꢁy + 1, ꢁz + 2; B: ꢁx, ꢁy, ꢁz + 2; C: ꢁx ꢁ 1, ꢁy, ꢁz + 2; D: x + 1, y, z; E: x ꢁ 1, y, z; F: ꢁx ꢁ 2, ꢁy + 1, ꢁz + 1; G: ꢁx ꢁ 1, ꢁy + 1, ꢁz + 1). (d) The connection of Cu1 ions and
[Sr2(pydc)4]4ꢁ units in the ac plane. (e) The 3-D polyhedron framework structure of 5 viewed along the a-axis. (f) Schematic representation of the 5-nodal topology net with
the topological notation (4.82)4(42.82.102)2(86) in the bc plane. Hydrogen atoms and lattice water molecules are omitted for clarity. Color codes: lavender, Sr; turquoise, Cu;
red, O; blue, N; green, C. (Colour online.)

Y. Chen et al. / Polyhedron 71 (2014) 91–98
97
g = 2.0, S = 3/2) for one NiII ion. As the temperature is lowered, the
MT value first decreases smoothly and then decreases abruptly to
1
2
3
4
5
100
90
80
70
60
50
40
30
v
a minimum value of 0.42 cm3 K molꢁ1 at 2 K. We endeavored to fit
the experimental susceptibility using various models for the Ni(II)
chain complex [48,49], but none of the results were well-pleasing.
Fitting the data in the temperature range 2–300 K to the Curie–
Weiss law gives a C value of 1.39 cm3 K molꢁ1 and a h value of
ꢁ5.58 K. The negative value of h indicates weak antiferromagnetic
couplings between the NiII ions.
4. Conclusion
Five heteronuclear coordination polymers MII–SrII (M = Co, Ni,
Zn, Cu) based on pyridine 2,3-dicarboxylic acid (H2pydc) have been
synthesized for the first time. These complexes display three vari-
eties of 3-D topological structures. The magnetic properties of
complexes 1 and 2 have been determined and both of them show
antiferromagnetic exchange interactions between the metal
centers.
0
200
400
600
800
1000
1200
Temperature (oC)
Fig. 4. The TGA curves of complexes 1–5.
1.0
Acknowledgements
3.0
2.5
2.0
1.5
The authors appreciate the financial support from the Natural
Science Foundation of China (21272167 and 21201127), A project
funded by the Priority Academic Program Development of Jiangsu
Higher Education Institution, Graduate Education Innovation
Project in Jiangsu Province (CXZZ12_0808), Qinghai Science &
Technology Department of China (2011-G-208 and 2011-Z-722),
and KLSLRC (KLSLRC-KF-13-HX-1).
0.8
0.6
0.4
0.2
0.0
120
100
80
χ
60
40
χ
20
χ
0
Appendix A. Supplementary data
0
50
100
150
200
250
300
T / K
CCDC 948529, 948485, 948484, 948483 and 948528 contain the
supplementary crystallographic data for complexes 1–5, respec-
tively. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
For tables of selected bond lengths and angles, additional figures
of these complexes and other electronic formats see supporting
information. Supplementary data associated with this article can
be found, in the online version, at http://dx.doi.org/10.1016/
j.poly.2013.12.042.
0
50
100
150
T/ K
200
250
300
Fig. 5. Temperature dependence of the magnetic susceptibilities in the form of
v
MT
vs. T and vM vs. T for 1 at 1 kOe. Inset: Temperature dependence of the magnetic
susceptibilities in the form of vMꢁ1v T for 1 at 1 kOe. The solid line corresponds to
the best fit from 300 to 2 K.
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