Effect of auxiliary ligands on cobalt(II) coordination polymers with 5-(imidazol-1-ylmethyl)isophthalate

Article abstract of DOI:10.1016/j.poly.2012.06.020

The reactions of cobalt(II) salt with 5-(imidazol-1-ylmethyl)isophthalic acid (H₂L) as a main ligand and 1,10-phenanthroline (phen), 2-(pyridin-2-yl)-1H-benzo[d]imidazole (pybim) or 1,2-di(pyridin-4-yl)ethylene (dpe) as auxiliary ligand by hydrothermal method lead to the formation of four new complexes [Co(L)(phen)]·2H₂O (1), [Co(L)(pybim)(H ₂O)]·2H₂O (2), [Co(L)(pybim)]·H₂O (3) and [Co(L)(dpe)_0.5] (4), among them 2 and 3 were obtained by changing the metal-to-ligand ratio. While in the absence of any auxiliary ligand, complex [Co(L)] (5) was obtained. The complexes 1-5 have been characterized by single crystal and powder X-ray diffractions, IR, elemental and thermogravimetric analyses. Complexes 1 and 2 have double- and single-chain structures, while 2 and 3 are 3-connected uninodal and (3,6)-connected binodal 2D networks with (6³) and [(6³)(6⁶)] topology, respectively. All the complexes 1-4 show 3D supramolecular structures through hydrogen bonding/π-π interactions. Complex 5 shows a (5,5)-connected binodal 3D net with [(4⁵)(6⁵)] topology. The results imply that the auxiliary ligand as well as the metal-to-ligand ratio has great impact on the structure of the complexes.

Full text of DOI:10.1016/j.poly.2012.06.020

Polyhedron 52 (2013) 1268–1275
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Effect of auxiliary ligands on cobalt(II) coordination polymers
with 5-(imidazol-1-ylmethyl)isophthalate
⇑
Hai-Wei Kuai, Chao Hou, Wei-Yin Sun
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering,
Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 18 June 2012
The reactions of cobalt(II) salt with 5-(imidazol-1-ylmethyl)isophthalic acid (H2L) as a main ligand and
1,10-phenanthroline (phen), 2-(pyridin-2-yl)-1H-benzo[d]imidazole (pybim) or 1,2-di(pyridin-4-yl)eth-
ylene (dpe) as auxiliary ligand by hydrothermal method lead to the formation of four new complexes
[Co(L)(phen)]ꢀ2H2O (1), [Co(L)(pybim)(H2O)]ꢀ2H2O (2), [Co(L)(pybim)]ꢀH2O (3) and [Co(L)(dpe)0.5] (4),
among them 2 and 3 were obtained by changing the metal-to-ligand ratio. While in the absence of
any auxiliary ligand, complex [Co(L)] (5) was obtained. The complexes 1–5 have been characterized by
single crystal and powder X-ray diffractions, IR, elemental and thermogravimetric analyses. Complexes
1 and 2 have double- and single-chain structures, while 2 and 3 are 3-connected uninodal and (3,6)-con-
nected binodal 2D networks with (63) and [(63)(66)] topology, respectively. All the complexes 1–4 show
Dedicated to Alfred Werner on the 100th
Anniversary of his Nobel prize in Chemistry
in 1913.
Keywords:
Imidazole and carboxylate-containing
ligand
Crystal structure
Cobalt(II) complex
Auxiliary ligand
3D supramolecular structures through hydrogen bonding/p–p interactions. Complex 5 shows a (5,5)-con-
nected binodal 3D net with [(45)(65)] topology. The results imply that the auxiliary ligand as well as the
metal-to-ligand ratio has great impact on the structure of the complexes.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
moieties to assembly coordination polymers in the presence of
different auxiliary ligands. This is based mostly on the following
During the past decades, considerable development and pro-
gress of synthesis and characterization of metal–organic frame-
works (MOFs) have been achieved in coordination, materials
and supramolecular chemistry, reflected by the fact that a grow-
ing interests of chemists were directed towards the field and a
great number of MOFs with fascinating structures and interest-
ing properties were prepared and reported [1–6]. The aim of
crystal engineering is mainly to exploit new crystalline materials
with intriguing architectures and potential applications in mag-
netism, heterogeneous catalysis, ion-recognition, nonlinear optics
and adsorption [7,8]. Therefore, it becomes important to assem-
ble coordination compounds with abundant structures for the
exploration of crystalline materials. It is known that many fac-
tors can subtly influence on the assembly and structure of the
complexes [9,10]. Among the factors, the option of organic li-
gands undoubtedly plays decisive role in the assembly of resul-
tant coordination polymers [11]. Therefore, the structures and
properties of MOFs may be adjustable through the alteration of
organic ligands [12,13].
considerations: (1) H2L is an aromatic dicarboxylate-containing li-
gand, and may perform well in the assembly of coordination poly-
mers with various structures for the well coordinating capacity of
carboxylate group and its mutable coordination modes such as
l1- :g - :g - :g
g1 0-monodentate, l1 g1 1-chelating, and l2 g1 1-bridging
[14,15]. (2) H2L can adopt different conformations in the self-
assembly for the existence of a flexible imidazol-1-ylmethyl arm
[16,17]. Therefore, the variable coordination modes and confor-
mations of H2L provide the feasibility to assemble polymers with
various architectures by the adjustments of reaction conditions
including the presence of different auxiliary ligands. In this contri-
bution, three kinds of N-donor auxiliary ligands were introduced
into the reactions, and four new coordination polymers [Co(L)(-
phen)]ꢀ2H2O (1), [Co(L)(pybim)(H2O)]ꢀ2H2O (2), [Co(L)(py-
bim)]ꢀH2O (3), and [Co(L)(dpe)0.5
] (4) have been obtained
under the hydrothermal conditions with the employment of aux-
iliary ligands, 1,10-phenanthroline (phen), 2-(pyridin-2-yl)-1H-
benzo[d]imidazole (pybim), and 1,2-di(pyridin-4-yl)ethylene
(dpe). Complex [Co(L)] (5) was obtained in the absence of any
auxiliary ligands. Complexes 1–5 have been characterized by sin-
gle-crystal X-ray structure determination, IR, elemental analysis,
powder X-ray diffraction, and thermogravimetric analyses. In
With such background in mind, recently we select 5-(imidazol-
1-ylmethyl)isophthalic acid (H2L) as the main organic bridging
addition, preliminary magnetic property of
investigated.
5 has also been
⇑
Corresponding author. Tel.: +86 25 83593485; fax: +86 25 83314502.
E-mail address: sunwy@nju.edu.cn (W.-Y. Sun).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.06.020

H.-W. Kuai et al. / Polyhedron 52 (2013) 1268–1275
1269
Table 1
Crystal data and structure refinements for complexes 1–5.
Compound
1
2
3
4
5
Formula
C
24H20N4O6Co
C24H23N5O7Co
552.40
monoclinic
P21/c
13.353(2)
11.0086(17)
16.140(3)
90.00
93.408(7)
90.00
293(2)
2368.4(7)
4
1.549
0.781
C24H19N5O5Co
516.37
C18H13N3O4Co
394.24
monoclinic
P21/n
10.985(5)
10.132(5)
14.190(5)
90.00
93.051(5)
90.00
293(2)
1577.1(12)
4
1.660
1.119
C12H8N2O4Co
327.59
monoclinic
P21/c
8.7187(12)
16.490(2)
7.7481(11)
90.00
100.451(2)
90.00
293(2)
1095.5(3)
4
1.838
1.578
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
519.37
triclinic
P1
triclinic
ꢀ
ꢀ
P1
10.154(10)
10.188(10)
13.595(13)
80.837(10)
71.365(15)
60.11
293(2)
1155.4(19)
2
9.7385(19)
9.8487(18)
14.1656(14)
87.555(2)
79.562(3)
64.531(2)
293(2)
1205.4(3)
2
1.423
a
(°)
b (°)
(°)
c
T (K)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.493
0.791
l
(mmꢁ1
)
0.756
F(000)
534
1140
530
804
612
h for data collection (°)
Reflections collected
Unique reflections
1.58–28.00
8019
5502
1.073
0.0608, 0.1744
0.0720, 0.1820
3.03–27.62
24561
5476
1.095
0.0689, 0.1738
0.0731, 0.1773
1.46–26.00
10161
4678
1.163
0.0593, 0.1383
0.0793, 0.1443
2.29–28.00
9612
3764
1.061
0.0372, 0.0858
0.0511, 0.0922
2.38–26.60
6055
2275
1.358
0.0938, 0.1687
0.0958, 0.1695
Goodness-of-fit (GOF) on F2
b
R1a, wR2 [I > 2
r(I)]
R1, wR2 (all data)
P
P
a
R1
=
||Fo| ꢁ |Fc||/ |Fo|.
P
P
2
2
2
wR2 ¼ j wðjFoj2 ꢁ jFcj Þj= jwðFoÞ j1=2, where w ¼ 1=½r2ðF2oÞ þ ðaPÞ þ bPꢂ; P ¼ ðFo2 þ 2F2c Þ=3.
b
2 were collected by filtration and after washed by water and etha-
nol several times in 59% yield based on H2L. Anal. Calc. for
C24H23N5O7Co: C, 52.18; H, 4.20; N, 12.68. Found: C, 52.46; H,
3.96; N, 12.42%. IR (KBr pellet, cmꢁ1): 3373 (m, br), 1609 (s),
1560 (s), 1449 (s), 1371 (s), 1310 (s), 1236 (m), 1191 (w), 1134
(w), 1109 (w), 1089 (m), 1027 (w), 945 (w), 835 (m), 802 (w),
774 (s), 753 (s), 720 (s), 659 (m), 634 (w), 532 (w).
2. Experimental
2.1. Materials and measurements
All commercially available chemicals and solvents are of re-
agent grade and were used as received without further purifica-
tion. The ligand H2L was prepared according to the previously
reported method [18]. Elemental analyses of C, H, and N were ta-
ken on a Perkin–Elmer 240C elemental analyzer at the analysis
center of Nanjing University. Infrared spectra (IR) were recorded
on a Bruker Vector22 FT-IR spectrophotometer by using KBr pel-
lets. Thermogravimetric analyses (TGA) were performed on a
simultaneous SDT 2960 thermal analyzer under nitrogen atmo-
sphere with a heating rate of 10 °C minꢁ1. Powder X-ray diffraction
(PXRD) patterns were measured on a Shimadzu XRD-6000 X-ray
2.4. Preparation of [Co(L)(pybim)]ꢀH2O (3)
Complex 3 was obtained by an analogous hydrothermal proce-
dure as that used for synthesis of 2 except that pybim (19.5 mg,
0.1 mmol) was used, namely the metal-to-ligand ratio of Co(N-
O3)2ꢀ6H2O:pybim was changed from 1:2 to 1:1. Pale red block crys-
tals of 3 were isolated by filtration and washed by water and
ethanol several times in 72% yield. Anal. Calc. for C24H19N5O5Co:
C, 55.82; H, 3.71; N, 13.56. Found: C, 55.59; H, 3.93; N, 13.29%. IR
(KBr pellet, cmꢁ1): 3417 (m, br), 1619 (s), 1563 (s), 1521 (m),
1481 (m), 1443 (s), 1419 (m), 1366 (s), 1325 (m), 1288 (m), 1235
(w), 1161 (w), 1100 (m), 1046 (w), 1026 (w), 981 (w), 940 (w),
842 (w), 784 (m), 748 (s), 723 (m), 694 (m), 661 (m), 633 (m),
571 (w).
diffractometer with Cu K
a (k = 1.5418 Å) radiation at room tem-
perature. The magnetic measurement in the temperature range
of 1.8–300 K was carried out on a Quantum Design MPMS7 SQUID
magnetometer in a field of 2000 Oe. Diamagnetic corrections were
made with Pascal’s constants.
2.2. Preparation of [Co(L)(phen)]ꢀ2H2O (1)
Reaction mixture of Co(NO3)2ꢀ6H2O (29.1 mg, 0.1 mmol), H2L
(24.6 mg, 0.1 mmol), phen (18.0 mg, 0.1 mmol), and KOH
(11.2 mg, 0.2 mmol) in 10 mL H2O was sealed in a 16 mL Teflon-
lined stainless steel container and heated at 160 °C for 3 days. After
cooling to the room temperature, red block crystals of 1 were col-
lected by filtration and washed by water and ethanol for several
times with a yield of 62%. Anal. Calc. for C24H20N4O6Co: C, 55.50;
H, 3.88; N, 10.79. Found: C, 55.21; H, 4.16; N, 10.52%. IR (KBr pellet,
cmꢁ1): 3443 (m, br), 1617 (s), 1577 (s), 1552 (s), 1516 (m), 1450
(s), 1421 (m), 1376 (s), 1290 (w), 1240 (w), 1220 (w), 1114 (m),
1090 (m), 938 (w), 852 (m), 782 (m), 745 (m), 729 (s), 663 (w).
2.5. Preparation of [Co(L)(dpe)0.5] (4)
Complex 4 was obtained by an analogous hydrothermal proce-
dure as that used for synthesis of 1 except that dpe (18.2 mg,
0.1 mmol) was used instead of phen. Dark purple block crystals
of 4 were collected by filtration and after washed by water and eth-
anol several times in 65% yield based on H2L. Anal. Calc. for
C
18H13N3O4Co: C, 54.84; H, 3.32; N, 10.66. Found: C, 54.59; H,
3.48; N, 10.39%. IR (KBr pellet, cmꢁ1): 1623 (s), 1579 (s), 1513
(w), 1431 (w), 1345 (s), 1304 (w), 1284 (w), 1222 (w), 1112 (w),
1088 (w), 1063 (w), 1030 (w), 964 (w), 834 (m), 780 (m), 727
(m), 649 (w), 559 (w).
2.3. Preparation of [Co(L)(pybim)(H2O)]ꢀ2H2O (2)
2.6. Preparation of [Co(L)] (5)
Complex 2 was obtained by an analogous hydrothermal proce-
dure as that used for synthesis of 1 except that pybim (39.0 mg,
0.2 mmol) was used instead of phen. Dark red needle crystals of
Complex 5 was obtained by an analogous hydrothermal proce-
dure as that used for synthesis of 1 except that no auxiliary ligand

1270
H.-W. Kuai et al. / Polyhedron 52 (2013) 1268–1275
Table 2
Selected bond lengths (Å) and bond angles (°) for complexes 1–5.
1
Co(1)–O(3)
Co(1)–N(2)
Co(1)–O(2)#1
2.084(3)
2.155(3)
2.315(3)
Co(1)–N(1)
Co(1)–O(1)#1
Co(1)–N(12)#2
2.144(3)
2.156(3)
2.115(3)
O(3)–Co(1)–N(1)
O(1)#1–Co(1)–O(3)
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(12)#2
N(2)–Co(1)–N(12)#2
119.37(12) O(3)–Co(1)–N(2)
89.32(12)
90.99(12)
146.85(10)
91.99(12)
91.73(12)
78.21(11)
97.09(11)
O(3)–Co(1)–N(12)#2
O(1)#1–Co(1)–N(1)
O(1)#1–Co(1)–N(2)
174.74(10) O(1)#1–Co(1)–N(12)#2 93.25(12)
2
Co(1)–O(5)
Co(1)–N(2)
Co(1)–O(1)#1
2.033(3)
2.070(3)
2.191(3)
85.60(12)
88.55(11)
155.24(11) N(1)–Co(1)–N(2)
170.55(11) O(1)#1–Co(1)–N(1)
97.18(11)
Co(1)–N(1)
Co(1)–N(11)
Co(1)–O(2)#1
O(5)–Co(1)–N(2)
O(1)#1–Co(1)–O(5)
2.254(3)
2.111(3)
2.152(2)
108.36(12)
95.22(11)
76.58(12)
87.88(11)
98.31(11)
96.18(11)
91.24(11)
O(5)–Co(1)–N(1)
O(5)–Co(1)–N(11)
O(2)#1–Co(1)–O(5)
N(1)–Co(1)–N(11)
O(2)#1–Co(1)–N(1)
O(1)#1–Co(1)–N(2)
O(1)#1–Co(1)–N(11)
O(1)#1–Co(1)–O(2)#1
N(2)–Co(1)–N(11)
150.33(11) O(2)#1–Co(1)–N(2)
100.06(11)
60.44(9)
O(2)#1–Co(1)–N(11)
3
Co(1)–N(1)
Co(1)–N(11)
2.200(3)
2.077(3)
2.018(3)
75.80(13)
91.31(12)
96.03(13)
Co(1)–N(2)
Co(1)–O(1)#1
2.072(3)
2.089(3)
Co(1)–O(3)#2
N(1)–Co(1)–N(2)
O(1)#1–Co(1)–N(1)
N(2)–Co(1)–N(11)
O(3)#2–Co(1)–N(2)
O(3)#2–Co(1)–N(11)
N(1)–Co(1)–N(11)
O(3)#2–Co(1)–N(1)
O(1)#1–Co(1)–N(2)
171.47(12)
89.40(12)
99.78(12)
87.62(13)
135.19(11)
123.66(13) O(1)#1–Co(1)–N(11)
97.33(12) O(1)#1–Co(1)–O(3)#2
4
Co(1)–O(1)
1.9903(17) Co(1)–N(21)
2.0358(19)
2.048(2)
96.66(7)
129.77(7)
105.76(7)
Co(1)–O(3)#1
O(1)–Co(1)–N(21)
O(1)–Co(1)–N(1)#2
N(1)#2–Co(1)–N(21)
2.0082(17)
111.56(7)
109.11(7)
102.99(8)
Co(1)–N(1)#2
O(1)–Co(1)–O(3)#1
O(3)#1–Co(1)–N(21)
O(3)#1–Co(1)–N(1)#2
Fig. 1. (a) The coordination environment of Co(II) in 1 with the ellipsoids drawn at
the 30% probability level. The hydrogen atoms and lattice water molecules are
omitted for clarity. (b) The 1D double chain of 1.
5
Co(1)–O(1)
2.106(5)
1.9650(18) Co(1)–O(2)#3
2.085(6)
89.2(2)
91.6(2)
145.4(2)
Co(1)–O(3)#1
2.015(5)
1.992(5)
Co(1)–O(4) #2
Co(1)–N(1)#4
O(1)–Co(1)–O(3)#1
O(1)–Co(1)–O(2)#3
O(3)#1–Co(1)–O(4)#2
O(1)–Co(1)–O(4)#2
O(1)–Co(1)–N(1)#4
O(2)#3–Co(1)–O(3)#1
O(2)#3–Co(1)–O(4)#2
O(2)#3–Co(1)–N(1)#4
85.6(2)
165.1(2)
95.0(2)
119.3(2)
103.2(2)
O(3)#1–Co(1)–N(1)#4 87.4(2)
O(4)#2–Co(1)–N(1)#4 89.0(2)
Symmetry transformations used to generate equivalent atoms:
For 1, #1 ꢁ1 + x, 1 + y, z; #2 2 ꢁ x, 2 ꢁ y, 1 ꢁ z; for 2, #1 x, 1 + y, z; for 3, #1 ꢁ1 + x,
1 + y, z; #2 x, 1 + y, z; for 4, #1 x, 1 + y, z; #2 ꢁ1/2 + x, 3/2 ꢁ y, ꢁ1/2 + z; for 5, #1
1 ꢁ x, 1/2 + y, 5/2 ꢁ z; #2 1 ꢁ x, ꢁy, 2 ꢁ z; #3 x, 1/2 ꢁ y, ꢁ1/2 + z; #4 1 + x, 1/2 ꢁ y, 1/
2 + z.
was added. Dark purple block crystals of 5 were obtained in 72%
yield. Anal. Calc. for C12H8N2O4Co: C, 47.55; H, 2.66; N, 9.24. Found:
C, 47.82; H, 2.92; N, 9.09%. IR (KBr pellet, cmꢁ1): 1632 (s), 1612 (s),
1571 (s), 1546 (m), 1513 (m), 1456 (m), 1435 (m), 1378 (s), 1333
(m), 1284 (m), 1243 (w), 1218 (w), 1108 (m), 1088 (m), 1030
(w), 944 (w), 834 (w), 780 (m).
2.7. X-ray crystallography
Scheme 1. Coordination modes of the L2ꢁ ligand in complexes 1–5.
The crystallographic data collections for complexes 1 and 3–5
were carried out on a Bruker SMART APEX CCD area-detector diffrac-
tometer using graphite-monochromated Mo
K
a
radiation
(k = 0.71075 Å). The structures of 1–5 were solved by direct meth-
ods and all non-hydrogen atoms were refined anisotropically on F2
by the full-matrix least-squares technique using the SHELXL-97 crys-
tallographic software package [21]. In 1–5, all hydrogen atoms at-
tached to C atoms were generated geometrically. The hydrogen
atoms of free water molecules of O6 in 1 and O7 in 3 could not
(k = 0.71073 Å) at 293(2) K. The diffraction data were integrated
by using the SAINT program [19], which was also used for the inten-
sity corrections for the Lorentz and polarization effects. Semi-
empirical absorption correction was applied using the SADABS pro-
gram [20]. The crystallographic data for 2 were collected on a Rig-
aku XtaLABmini diffractometer at 293 K with Mo K
a radiation

H.-W. Kuai et al. / Polyhedron 52 (2013) 1268–1275
1271
Fig. 2. (a) The coordination environment of Co(II) in 2 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms and lattice water molecules are omitted for
clarity. (b) 1D chain of 2.
be located and thus were not included in the refinement, while the
ones of other water molecules in 1–3 and the ones of NH in 2 and 3
were found at reasonable positions in the difference Fourier maps
and fixed there. The details of crystal parameters, data collection,
and refinements for the complexes are summarized in Table 1; se-
lected bond lengths and angles are listed in Table 2. The hydrogen
bonding data for 1, 2, and 4 are listed in Table S1.
3.2. Crystal structure description of [Co(L)(pybim)(H2O)]ꢀ2H2O (2)
Complex 2 crystallizes in monoclinic crystal system with P21/c
space group (Table 1). The asymmetric unit of 2 consists of one
Co(II), one L2ꢁ ligand, one pybim, one coordinated and two lattice
water molecules. Each Co(II) is six-coordinated with distorted octa-
hedral coordination geometry by two carboxylate oxygen atoms
from one L2ꢁ, one oxygen atom from the coordinated water mole-
cule, one nitrogen atom from imidazolyl group of L2ꢁ, and two
nitrogen atoms from the pybim molecule (Fig. 2a). It is noteworthy
that only one of two carboxylate groups of L2ꢁ coordinates with
3. Results and discussion
3.1. Crystal structure description of [Co(L)(phen)]ꢀ2H2O (1)
Co(II) in l2
one is free of coordination, which is different from those in 1. Thus
the L2ꢁ ligand in 2 just acts as a
2-connector, linking Co(II) atoms
to form a 1D chain (Fig. 2b). In addition to the coordination inter-
actions, there are hydrogen bonds (Table S1) and stacking
- :g
g1 1-chelating coordination mode, while the other
The single-crystal X-ray structure analysis revealed that com-
plex 1 is composed of one-dimensional (1D) double-chains based
on Co(II), L2ꢁ and phen ligands and free water molecules. There
are one Co(II), one L2ꢁ ligand, one phen molecule, and two lattice
water molecules in the asymmetric unit of complex 1. As shown
in Fig. 1a, each Co(II) is six-coordinated by one nitrogen atom from
imidazolyl group, two nitrogen ones from phen molecule, and
three carboxylate oxygen atoms from two different L2ꢁ ligands to
furnish a distorted octahedral coordination geometry. The carbox-
l
p–p
interactions in 2 which further link the lD chains into a 2D network
(Fig. S2a). More interestingly, the coordinated pybim molecules are
arranged at the same side of 1D chain and there are
p–p interac-
tions with centroid–centroid distance 3.808(6) Å between the py-
bim molecules from two adjacent chains (Fig. S2b). Finally, a
sandwich-like 2D double-deck network is formed as illustrated in
Fig. S2c.
ylate groups in the L2ꢁ ligand exhibit l1
- :g -
g1 1-chelating and l1
g1
:g
0-monodentate mode, respectively (Scheme 1). Each L2ꢁ ligand
connects three Co(II) atoms to form a 1D polymeric ladder struc-
ture with the nearest intrachain Coꢀ ꢀ ꢀCo distance of 10.100(4) Å
(Fig. 1b). As depicted in Fig. S1a, the adjacent chains form a two-
3.3. Crystal structure description of [Co(L)(pybim)]ꢀH2O (3)
dimensional (2D) network through the strong offset
p
–
p
stacking
Complex 3 was obtained by a similar procedure used for prep-
aration of 2, except that the ratio of metal-to-ligand was changed.
Single-crystal X-ray diffraction analysis reveals that complex 3 is in
interactions with the centroid–centroid distance between the cen-
tral benzene rings of 3.592(3) Å. The 2D networks are further
linked together by weak C–Hꢀ ꢀ ꢀO interactions to give a three-
dimensional (3D) supramolecular framework (Fig. S1b). The hydro-
gen bonding data are summarized in Table S1.
ꢀ
triclinic crystal system with P1 space group. The asymmetric unit
of 3 contains one Co(II), one L2ꢁ ligand, one pybim molecule, and
one lattice water molecule. Each Co(II) is five-coordinated with

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H.-W. Kuai et al. / Polyhedron 52 (2013) 1268–1275
3.4. Crystal structure description of [Co(L)(dpe)0.5] (4)
When 1,2-di(pyridin-4-yl)ethylene (dpe) was introduced into
the reaction system as auxiliary ligand, complex 4 was obtained.
Crystallographic analysis revealed that complex 4 crystallizes in
monoclinic system with P21/n space group. There are one Co(II),
one L2ꢁ ligand, and half molecule of dpe in the asymmetric unit
of 4. As shown in Fig. 4a, each Co(II) is four-coordinated by one
imidazolyl nitrogen atom of L2ꢁ, one pyridyl nitrogen atom of
dpe, two carboxylate oxygen atoms from two different L2ꢁ ligands
to furnish distorted tetrahedral coordination geometry. Both car-
boxylate groups of L2ꢁ in 4 adopt l1 g1 0-monodentate coordina-
- :g
tion mode (Scheme 1). Thus, in 4 each L2ꢁ ligand links three
different Co(II) atoms as a 3-connector and in turn each Co(II) is
coordinated by three different L2ꢁ ligands. Such kind of connec-
tions proceeds infinitely to form 2D network, which is pillared by
l2-bridge dpe to form a new 2D layer (Fig. 4b). The topological
analysis was carried out to get insight of the structure of 4. As men-
tioned above, each L2ꢁ ligand is neighbored by three Co(II) ions
which can be viewed as a 3-connector, each dpe ligand could be
considered as a 2-connector, while each Co(II) can be regarded as
a 4-connected node. Thus, the resulting structure of 4 is a (3,4)-
connected binodal 2D net with Point (Schläfli) symbol of (63)(66)
(Fig. 4c). If weak C–Hꢀ ꢀ ꢀO interactions is considered, a 3D supramo-
lecular framework is formed through interesting 2D + 2D ? 3D
parallel interpenetration (Fig. 4d).
3.5. Crystal structure description of [Co(L)] (5)
Complex 5 is in monoclinic crystal system with P21/c space
group. As shown in Fig. 5a, the asymmetric unit of complex 5 con-
tains one Co(II) and one L2ꢁ ligand. Each Co(II) is five-coordinated
by four carboxylate oxygen atoms from four different L2ꢁ ligands
and one imidazolyl nitrogen atom from L2ꢁ ligand to furnish
distorted trigonal bipyramidal coordination geometry. Both of
two carboxylate groups of L2ꢁ ligand in 5 adopt l2 g1 1-bridging
- :g
coordination mode (Scheme 1). Thus in complex 5 each L2ꢁ ligand
bridges five different Co(II) atoms and each Co(II) is coordinated by
five different L2ꢁ ligands. Such kind of linkage infinitely expands to
give a 3D architecture (Fig. 5c), where 2D layer structure can be
isolated if the coordination of imidazolyl group is ignored
(Fig. 5b). Within the 2D structure there are [Co2(OCO)2] subunits
and 1D Co(II)-carboxylate chains formed through the connections
of carboxylate groups and Co(II) atoms with the nearest Coꢀ ꢀ ꢀCo
distance of 4.081(3) Å. In 5, both L2ꢁ ligands and metal ions act
as 5-connected nodes, and thus 5 can be described as a (5,5)-con-
nected binodal 3D net with the Point (Schläfli) symbol of (45)(65)
(Fig. 5d).
Fig. 3. (a) The coordination environment of Co(II) in 3 with the ellipsoids drawn at
the 30% probability level. The hydrogen atoms and lattice water molecules are
omitted for clarity. (b) 2D network of 3. (c) Schematic representation of 2D network
with (63) topology: green, L2ꢁ ligand; red, Co(II). (Color online.)
3.6. Preparation and structural comparison of complexes 1–5
distorted trigonal bipyramidal coordination geometry by two car-
boxylate oxygen atoms from two different L2ꢁ ligands, two nitro-
gen ones from coordinated pybim molecule, and one nitrogen
from the imidazolyl group of L2ꢁ (Fig. 3a). The equatorial plane is
defined by two carboxylate oxygen atoms and one nitrogen atom
from the pybim molecule, while the other two nitrogen atoms oc-
cupy the axial positions. Both carboxylate groups of L2ꢁ in 3 adopt
Complexes 1–5 were readily prepared by reactions of H2L ligand
with cobalt(II) salt in the presence or absence of the N-donor aux-
iliary ligand under hydrothermal conditions and characterized by
single-crystal X-ray structure determination, elemental analysis,
and IR as described above. The pure phase of the synthesized 1–5
was confirmed by powder X-ray diffraction (PXRD) measurements.
As shown in Fig. S3, each PXRD pattern of the as-synthesized sam-
ple is consistent with the simulated one.
The results of structural analyses indicate that complexes 1–5
have diverse architectures from 1D chain to 3D frameworks with
different topologies. The structural diversity of 1–5 is closely re-
lated with auxiliary ligands introduced into the reaction system.
Complexes 1, 2 and 4 with different auxiliary ligands exhibit differ-
ent structures. Complex 5 is structurally different from the other
l1- :g
g1 0-monodentate coordination mode (Scheme 1). In 3 each
L2ꢁ ligand bridges three different Co(II) atoms and in turn each
Co(II) is coordinated by three different L2ꢁ ligands. Such kind of
connections extends infinitely to form a 2D network (Fig. 3b). Both
of L2ꢁ and Co(II) in 3 can be regarded as 3-connectors, thus the
network of 3 can be simplified into a uninodal 3-connected 2D
network with Point (Schläfli) symbol of (63) (Fig. 3c), calculated
by TOPOS [22].

H.-W. Kuai et al. / Polyhedron 52 (2013) 1268–1275
1273
Fig. 4. (a) The coordination environment of Co(II) in 4 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity. (b) 2D pillared-
network of 4. (c) Schematic representation of the binodal (3,4)-connected 2D net of 4 with (63)(66) topology: the big spheres, Co(II); the small spheres, L2ꢁ ligand. (d) The 3D
framework of 4 constructed by hydrogen bonding interactions.
four in the absence of any auxiliary ligand. Moreover, complexes 2
and 3 display different architectures with the same auxiliary li-
gand, which may be ascribed to the different metal-to-ligand ratio.
In addition, it is noteworthy that the metal centers show different
coordination number and geometry in these complexes, namely,
six-coordinated with distorted octahedral coordination geometry
in 1 and 2; five-coordinated with distorted trigonal bipyramidal
geometry in 3 and 5, and four-coordinated with tetrahedral coordi-
nation geometry in 4. The results imply that the auxiliary ligand as
well as the metal-to-ligand ratio has great impact on the structure
of the resultant complexes.
(Calc. 6.93%), and from 366 to 553 °C, there is a steep weight loss
which could be assigned to the decomposition of the framework.
The total weight loss in the temperature range 30–660 °C is
85.8%, which is in agreement with the weight loss calculated for
the loss of ligands and water molecules leading to the formation
of CoO as final residuals above 560 °C (85.6%). For 2, a weight loss
of 9.52% in the temperature range of 92–166 °C corresponds to the
liberation of coordinated and lattice water molecules (Calc. 9.78%).
Then the decomposition of the framework started at 353 °C. For 3,
a weight loss of 3.76% within the temperature range of 136–210 °C
is assigned to the release of lattice water molecules (Calc. 3.48%),
and the decomposition of the residue can be observed at 346 °C.
No obvious weight loss could be observed before the decomposi-
tion of the frameworks occurred at about 400 °C for 4 and 5.
3.7. Thermal stability of complexes 1–5
Complexes 1–5 were subjected to thermogravimetric analysis
(TGA) to ascertain their thermal stability, and the TGA curves of
1–5 are shown in Fig. S4. In the TGA curve of complex 1 there is
a weight loss of 7.18% within the temperature range of 96–
128 °C, corresponding to the release of two lattice water molecules
3.8. Magnetic property of complex 5
The Co(II) atoms are bridged by carboxylate groups to form 1D
Co(II)-carboxylate chains in 5, which may mediate magnetic inter-

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H.-W. Kuai et al. / Polyhedron 52 (2013) 1268–1275
Fig. 5. (a) The coordination environment of Co(II) in 5 with the ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity. (b) The 2D network
in 5. (c) The 3D structure of 5 with different 2D layers shown in different color. (d) The schematic representations of the binodal (5,5)-connected 3D net of 5 with (45)(65)
topology: green, L2ꢁ ligand; red, Co(II). (Color online.)
the neighboring Co(II) centers [24]. In order to estimate the
strength of the magnetic interactions in 5, the following was used
[25]:
vMT ¼ AexpðꢁE1=kTÞ þ BexpðꢁE2=kTÞ
ð1Þ
Here, A + B equals the curie constant (C), and E1, E2 represent the
‘activation energies’ corresponding to the spin–orbit coupling and
the antiferromagnetic exchange interaction, respectively. The ob-
tained values of A + B = 2.89 emu K molꢁ1 and E1/k = 33.94 K agree
with those given in a previous report [25]. The value of ꢁE2/
k = ꢁ0.94 K, corresponding to J = ꢁ1.88 K, further proved that the
antiferromagnetic interactions exist between neighboring Co(II)
atoms in 5 [26].
4. Conclusion
Fig. 6. Temperature dependences of magnetic susceptibility of vM and
vMT for 5.
The solid line represents the fitted curve.
Five new Co(II) coordination polymers have been synthesized
through the hydrothermal reactions. The structures of the resul-
tant complexes varied from 1D chain to 3D framework with differ-
ent topologies. The structural diversity of the complexes is
achieved by the presence of auxiliary ligands and the alteration
of metal-to-ligand ratio.
actions while in 1–4, the Co(II) atoms are linked by L ligands and
no magnetic interactions can be expected [23]. The temperature
dependence of magnetic susceptibility of 5 was investigated from
300 to 1.8 K with an applied magnetic field of 2000 Oe. The mag-
netic behaviors of 5 in the forms of vM and
vMT versus T are de-
picted in Fig. 6. The vꢁM1 value (above 50 K) obeys the Curie–
Weiss law well with a Weiss constant (h) of ꢁ10.09 K and a Curie
constant (C) of 2.87 emu K molꢁ1 (Fig. S5).
Acknowledgements
The negative value of h and the shape of the
suggests there may exist antiferromagnetic interactions between
vMT versus T curve
This work was financially supported by the National Natural
Science Foundation of China (Grant Nos. 91122001 and

H.-W. Kuai et al. / Polyhedron 52 (2013) 1268–1275
1275
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[19] SAINT, Program for Data Extraction and Reduction, Bruker AXS, Inc., Madison,
WI, 2001.
CCDC 877980–877984 contain the supplementary crystallo-
graphic data for 1–5. 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, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
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