Syntheses, crystal structures and magnetic properties of 1D and 2D cobaltous coordination polymers with mixed ligands

Article abstract of DOI:10.1016/j.ica.2010.05.041

Two new Co(II) coordination polymers with mixed ligands, {[Co(BTA) _0.5(DBI)₂]·DBI·H₂O}_n (1) and [Co(PDA)(DBI)(H₂O)]_n (2) (H₄BTA = benzene-1,2,4,5-tetracarboxylic acid; H₂PDA = 2,2′-(1,2- phenylene)diacetic acid; DBI = 5,6-dimethyl-1H-benzoimidazole) have been synthesized under hydrothermal conditions, respectively. Both of them are characterized by elemental analyses, powder X-ray diffraction, thermogravimetric analysis, single-crystal X-ray diffraction, and magnetic susceptibilities. In 1, the Co(II) ions are four-coordinated and lie in distorted tetrahedron coordination environment. 1D ladder-like chain structure is formed by the bridging BTA^4- ligand. In 2, the Co(II) ions are in slightly distorted octahedral coordination geometry, and linked by PDA^2- ligand exhibiting a 2D layer structure. Temperature-dependent magnetic susceptibility measurements of 1 and 2 revealed that there are antiferromagnetic interactions between Co(II) ions.

Full text of DOI:10.1016/j.ica.2010.05.041

Inorganica Chimica Acta 363 (2010) 3784–3789
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Syntheses, crystal structures and magnetic properties of 1D and 2D cobaltous
coordination polymers with mixed ligands
Shi-Yuan Zhang a, Zhen-Jie Zhang a, Wei Shi a,b, , Bin Zhao a,b, Peng Cheng a
*
a Department of Chemistry, Nankai University, Tianjin 300071, PR China
b State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new Co(II) coordination polymers with mixed ligands, {[Co(BTA)0.5(DBI)2]ꢀDBIꢀH2O}n (1) and [Co(P-
DA)(DBI)(H2O)]n (2) (H4BTA = benzene-1,2,4,5-tetracarboxylic acid; H2PDA = 2,20-(1,2-phenylene)diacetic
acid; DBI = 5,6-dimethyl-1H-benzoimidazole) have been synthesized under hydrothermal conditions,
respectively. Both of them are characterized by elemental analyses, powder X-ray diffraction, thermo-
gravimetric analysis, single-crystal X-ray diffraction, and magnetic susceptibilities. In 1, the Co(II) ions
are four-coordinated and lie in distorted tetrahedron coordination environment. 1D ladder-like chain
structure is formed by the bridging BTA4ꢁ ligand. In 2, the Co(II) ions are in slightly distorted octahedral
coordination geometry, and linked by PDA2ꢁ ligand exhibiting a 2D layer structure. Temperature-depen-
dent magnetic susceptibility measurements of 1 and 2 revealed that there are antiferromagnetic interac-
tions between Co(II) ions.
Received 25 December 2009
Received in revised form 15 May 2010
Accepted 19 May 2010
Available online 26 May 2010
Keywords:
Coordination polymers
Co(II) complexes
Crystal structures
Magnetic properties
Hydrothermal synthesis
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
numerous organic ligands, aromatic acids were given special inter-
est for the abundant coordination modes and appropriate abilities
The fields of crystal engineering have been developed rapidly
[1–4], because of the intriguing structural motifs and potential
applications [5–11]. Recently, much attention has been given to
the construction of coordination polymers (CPs) with interesting
magnetic properties. To obtain such CPs, Co(II) ions are widely cho-
sen as node to expand the structure for not only the variable geo-
metric conformations including square-planar, tetrahedral,
trigonal-bipyramid, octahedral and square-pyramidal among the
first-row transition metal ions, but also the unquenched orbital
contribution to magnetic moment with anisotropy [12–16]. Vari-
ous Co(II) magnetic units containing monomers, dimers, polymers,
chains, ladders, layers and 3D-networks have been synthesized and
characterized due to their interesting magnetic properties such as
ferromagnetic interactions, single molecule magnets or single
chain magnets behaviors, etc [17–19]. On the other hand, it is
important to select appropriate ligands to synthesize new coordi-
nation polymers for the study of magneto-structural relationship
because: (i) Deliberately change of the interactions between metal
ions and ligands can dramatically result in different magnetic
properties [20–22]. (ii) Intermolecular interactions such as hydro-
to transfer ferro/antiferromagnetic interactions. Meanwhile, the
use of neutral auxiliary ligands such as N-donor ligands to the syn-
thetic system of aromatic acids with metal ions is helpful to con-
struct specific structures with interesting properties. In this
contribution, two new coordination polymers with mixed ligands
{[Co(BTA)0.5(DBI)2]ꢀDBIꢀH2O}n (1) and [Co(PDA)(DBI)(H2O)]n (2)
(H4BTA = benzene-1,2,4,5-tetracarboxylic acid; H2PDA = 2,20-(1,2-
phenylene)diacetic acid; DBI = 5,6-dimethyl-1H-benzoimidazole)
were synthesized under hydrothermal conditions and character-
ized by elemental analyses, PXRD, TGA, single-crystal X-ray diffrac-
tion, and magnetic susceptibilities. Magnetic studies of 1 and 2
revealed that there are antiferromagnetic interactions between
Co(II) ions.
2. Experimental
2.1. General remarks
All reagents and solvents employed were commercially avail-
able and used as received without further purification.
gen bonds, p–p stacking, host–guest ionic interactions can signifi-
cantly affect the magnetic interactions [23,24]. Among the
Elemental analyses for C, H and N were carried out by using a
Perkin–Elmer 240 CHN Elemental Analyzer. Infrared spectra were
recorded on a TENOR 27 spectrophotometer as KBr pellets in the
range 4000–400 cmꢁ1
. Magnetic susceptibility measurements
* Corresponding author at: Department of Chemistry, Nankai University, Tianjin
300071, PR China. Tel.: +86 22 23503059; fax: +86 22 23502458.
E-mail address: shiwei@nankai.edu.cn (W. Shi).
were performed in the range of 2–300 K with an applied dc field
of 1000 Oe on a Quantum Design MPMS XL-7 SQUID system. The
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.05.041

S.-Y. Zhang et al. / Inorganica Chimica Acta 363 (2010) 3784–3789
3785
powder X-ray diffraction (PXRD) data were collected on a Rigaku
D/max-250 diffractometer with Cu Ka radiation, and the recording
speed was 0.2°/min over the 2h range of 3–80° at room tempera-
ture. The thermogravimetric analyses were measured by a DSC-
TG-DMA system from room temperature to 800 °C.
parameters and structural refinement for 1 and 2 are summarized
in Table 1. Selected bond lengths and angles are listed in Table 2.
3. Results and discussion
3.1. Synthesis
2.2. Preparations of the coordination polymers
The preparation of 1 can be achieved via the 4:1:1 reaction of
Co(II) nitrate hexahydrate, DBI and H4BTA in aqueous solution by
using hydrothermal method. In the same manner 2 was obtained
using H2PDA instead of H4BTA. The crystal structures show great
differences (1D ladder-like chain versus 2D layer), which may be
caused by both the flexibility of the aromatic acid and the coordi-
nated mode of the carboxylate groups [27,28].
A
mixture of Co(NO3)2ꢀ6H2O (0.4 mmol, 0.1164 g), DBI
(0.1 mmol, 0.0146 g), H4BTA (0.1 mmol, 0.0254 g) and water
(10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel
and heated at 150 °C for 2 days, and then cooled to room temper-
ature at a rate of 10 °C/h. Red block-shaped crystals of 1 were col-
lected, washed with distilled water, and dried in air. Yield: 56%
based on Co(NO3)2ꢀ6H2O. Elemental analysis (%) Anal Calc. for 1:
C, 66.08; H, 5.72; N, 14.45. Found: C, 65.83; H, 5.13; N, 14.19%. IR
data (KBr pellets, cmꢁ1): 3417m, 3132m, 1591s, 1476m, 1418m,
1401m, 1351s, 1309m, 1269m, 1136w, 1086w, 1004w, 973w,
820m, 613w, 518w.
2 was prepared by a procedure similar to that of 1 using H2PDA
(0.1 mmol, 0.0146 g) instead of H4BTA. Yield: 61% based on Co(N-
O3)2ꢀ6H2O. Elemental analysis (%) Anal Calc. for 2: C, 64.22; H,
5.39; N, 7.88. Found: C, 64.75; H, 5.06; N, 7.86%. IR data (KBr pel-
lets, cmꢁ1): 3191s, 2362w, 1542s, 1506m, 1427m, 1399s, 1166w,
842w, 727m, 615m, 426w.
3.2. Crystal structure of {[Co(BTA)0.5(DBI)2]ꢀ(DBI)ꢀ(H2O)}n (1)
ꢀ
1 crystallizes in the triclinic P1 space group, each Co(II) ion is
four-coordinated via two N atoms of DBI and two O atoms of
two carboxylate groups from BTA4ꢁ to form a distorted tetrahe-
dron geometry as shown in Fig. 1(a). The Co–O bond lengths are
1.968(4) and 2.011(4) Å, while the lengths of Co–N are 2.004(5)
and 2.041(5) Å, respectively. Each BTA4ꢁ anion acts as a four-do-
nated linker that connects four Co(II) ions, where two carboxylate
Table 2
Selected bond lengths (Å) and angles (°) for 1 and 2.
2.3. X-ray crystallography
1
Co(1)–
O(1)
Co(1)–
N(3)
1.971(3)
2.045(3)
Co(1)–
N(1)
O(1)–
Co(1)–
N(1)
2.002(3) Co(1)–
O(3)#1
116.07(14) O(1)–
Co(1)–
O(3)#1
111.85(13) O(1)–
Co(1)–
2.009(3)
Single-crystal analyses were performed on Oxford Supernova
CCD diffractometer for 1 and Rigaku Saturn 007 CCD diffractometer
for 2 with Mo Ka radiation (k = 0.71073 Å) by the x–u scan tech-
100.94(12)
nique. All data were collected for absorption by semiempirical
method. The structures were solved primarily by direct method
and secondly by Fourier difference techniques and refined by the
full-matrix least-squares method. The computations were per-
formed with the SHELXL-97 program [25,26]. All non-hydrogen atoms
were refined anisotropically. The hydrogen atoms of organic ligands
were set in calculated positions and refined as riding atoms with a
common fixed isotropic thermal parameter. Crystallographic
N(1)–
Co(1)–
O(3)#1
120.41(14)
N(3)
N(1)–
Co(1)–
N(3)
O(3)#1–
Co(1)–
N(3)
107.36(14)
98.43(13)
2
Table 1
Co(1)–
O(2)#1
2.065(2)
Co(1)–
O(1)
Co(1)–
N(1)
Crystallographic data for 1 and 2.
2.082(2)
1
2
2.104(2)
Co(1)–
O(5)
O(2)#1–
Co(1)–
O(1)
O(2)#1–
Co(1)–
O(5)
O(2)#1–
Co(1)–
Formula
Formula weight
T (K)
C
32H33CoN6O5
C19H19CoN2O5
414.29
293(2)
0.71073
monoclinic
C2/c
33.406(7)
7.3968(15)
14.920(3)
90
2.107(2)
94.47(8)
Co(1)–
O(4)#2
O(2)#1–
Co(1)–
N(1)
O(1)–
Co(1)–
O(5)
2.157(2) Co(1)–
O(3)#2
2.226(2)
87.86(9)
640.57
293(2)
0.71073
triclinic
94.40(9)
O(1)–
Co(1)–
N(1)
k (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢀ
P1
88.22(8)
O(4)#2
95.29(8)
N(1)–
Co(1)–
O(5)
175.75(9)
9.5713(6)
11.1182(7)
14.4993(10)
76.926(5)
85.764(5)
82.410(5)
1488.24(16)
2
98.31(8)
O(1)–
N(1)–
a
b (°)
(°)
Co(1)–
O(4)#2
167.20(8)
156.99(8)
82.54(8)
Co(1)–
O(4)#2
108.53(3)
90
3495.7(12)
8
c
(°)
V (Å3)
90.39(9)
O(5)–
Z
O(4)#2
O(3)#2
85.91(8)
93.80(8)
O(2)#1–
Co(1)–
O(3)#2
O(1)–
Co(1)–
O(3)#2
Dcalc (g cmꢁ3
F(0 0 0)
)
1.429
668
9925
5260 (0.0451)
2.53–25.10
1.047
0.0644, 0.1484
0.0857, 0.1555
1.574
1712
14542
4149 (0.0506)
2.57–27.86
1.116
0.0562, 0.1298
0.0679, 0.1372
Co(1)–
Reflections collected
Unique reflections (Rint
h Range (°)
)
107.30(8)
N(1)–
Co(1)–
O(5)–
Co(1)–
O(3)#2
O(4)#2–
Co(1)–
O(3)#2
Goodness-of-fit (GOF) on F2
b
Ra, Rw [I > 2
r
(I)]
b
Ra, Rw (all data)
60.16(7)
P
P
a
R1
=
||Fo| ꢁ |Fc||/ |Fo|.
b
wR2 = [w(|Fo2| ꢁ |Fc2|)2/w|Fo2|2]1/2. w = 1/[
r
2(Fo)2 + 0.0297P2 + 27.5680P], where
Symmetry transformations used to generate equivalent atoms: for 1: #1 ꢁx + 1, ꢁy,
ꢁz + 1; For 2: #1 ꢁx + 1/2, y + 1/2, ꢁz + 1/2 #2 ꢁx + 1/2, ꢁy + 3/2, ꢁz.
P = (Fo2 + 2 Fc2)/3.

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S.-Y. Zhang et al. / Inorganica Chimica Acta 363 (2010) 3784–3789
Fig. 1. (a) The coordination environment of Co(II) ions in 1. (b) The 1D ladder-like chain of 1. (c) p–p interactions between two adjacent chains shown as green lines. (d)
Hydrogen bonding interactions formed around the free water molecule shown as green dashed lines. Co, cyan or polyhedrons; O, red; N, blue; C, black; H, gray. (For
interpretation of the references in color in this figure legend, the reader is referred to the web version of this article.)

S.-Y. Zhang et al. / Inorganica Chimica Acta 363 (2010) 3784–3789
3787
groups adopt l1
ate groups adopt l1
ladder shape extended along the b axis with the adjacent Co–Co
distance of 5.657 Å (Fig. 1(b)). In the lattice, interactions and
hydrogen bonding interactions are simultaneously observed be-
tween interchain to generate a 3D structure. The interactions
-
g1
:
-
g
1 chelating mode and another two carboxyl-
:g
g1 0 mode, forming a 1D polymeric chain of
ions is 5.282 Å. All PDA2ꢁ ligands adopt the same mode linking
three Co(II) ions to give a 2D layer structure (Fig. 2(b)). The nearest
distance of neighboring Co(II) ions from the alternating chains is
5.724 Å. Hydrogen bonds were also found in O(5)–H(5A)ꢀꢀꢀO(1)
p–p
(2.679 Å) and O(5)–H(5B)ꢀꢀꢀO(3) (2.691 Å). The
p–p interactions
p
–p
of the DBI ligands from adjacent 2D layers were found and further
of the DBI ligands (3.725 and 3.807 Å) connect the nearest alternat-
ing chain along c axis (Fig. 1(c)), and then hydrogen bonding inter-
actions of O(5)–H(5A)ꢀꢀꢀO(4) (2.829 Å), O(5)–H(5B)ꢀꢀꢀO(3) (2.842 Å),
N(4)–H(4)ꢀꢀꢀO(5) (2.889 Å) and N(5)–H(5)ꢀꢀꢀO(5) (2.770 Å) further
connect the 2D layer along b axis to form a 3D supramolecular
framework (Fig. 1(d)).
connected the layers to 3D structure (Fig. 2(c)).
3.4. Magnetic properties of 1 and 2
The temperature-dependent magnetic susceptibilities of 1 and 2
were measured at 1 kOe in the temperature range of 2–300 K. The
3.3. Crystal structure of [Co(PDA)(DBI)ꢀ(H2O)]n (2)
v K
mT value at 300 K is 2.57 cm3 molꢁ1 K for 1 and 3.28 cm3 molꢁ1
for 2, which are both higher than the spin-only value of
1.87 cm3 molꢁ1 K expected for one uncoupled tetrahedral and octa-
hedral high-spin Co(II) ions (S = 3/2, g = 2) [32]. As T decreasing, the
2 crystallizes in monoclinic space group C2/c. Co(II) ion is sur-
rounded by four oxygen atoms from three individual PDA2ꢁ li-
gands, one nitrogen atom from DBI and one oxygen atom from
one water molecule in a slightly distorted octahedral coordination
geometry, as shown in Fig. 2(a). The bond distance of Co(1)–N(1) is
2.104(2) Å and Co–O bond lengths are in the range of 2.065(2) and
2.226(2) Å which are a little longer than those of 1. These bonds are
comparable to reported values [29–31]. The O–Co–O and O–Co–N
angles range from 60.16° to 175.75°. One carboxylate group adopts
v
mT values continuously decreases to 1.36 cm3 molꢁ1 K for 1 and
1.16 cm3 molꢁ1 K for 2. The magnetic susceptibilities of the two
coordination polymers both obey the Curie–Weiss law in the range
of 50–300 K with C = 2.64 cm3 molꢁ1 K, h = ꢁ7.74 K for 1 and C =
3.63 cm3 molꢁ1 K, h = ꢁ30.35 K for 2 (Fig. S3). The moderate nega-
tive h values may come from the existence of antiferromagnetic ex-
change interactions and/or spin-orbital coupling.
the l1
mode in a syn-anti fashion. The
ions to form a 1D zig–zag chain. The distance of neighboring Co(II)
-
g1
:
g1 chelating mode and the other l2
–
g1
:
g1 bridging
The C and h values are observed for other Co(II) coordination
polymers with different geometric conformations. A similar result
was obtained for octahedral system in Co2(2,5-diphenylterephtha-
l
2-carboxylates linked two Co(II)
Fig. 2. (a) The coordination environment of Co(II) ions in 2. (b) The 2D layer structure of 2. DBI ligands are omitted for clarity. (c) Intrachain hydrogen bonding interactions
and interactions between two adjacent layers. Co, polyhedrons; O, red; N, blue; C, black. (For interpretation of the references in color in this figure legend, the reader is
referred to the web version of this article.)
p–p

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S.-Y. Zhang et al. / Inorganica Chimica Acta 363 (2010) 3784–3789
late)2(H2O)2 [33]. The susceptibility (C = 3.12 cm3 K molꢁ1 and
h = ꢁ28.2 K) suggests weak antiferromagnetic coupling within the
chain. Another similar conclusion was reported for {[Co(d-
pyo)(1,4-bdc)(H2O)2][Co(H2O)6](1,4-bdc)ꢀH2O}, dpyo = 4,40-bipyri-
dyl N,N0-oxide [34]. However, when the environment of Co(II) ion
is heavily distorted from an octahedron these values can show
The best fit (as shown in Fig. 3(a)) using a least-squares analy-
sis led to D = ꢁ0.47 cmꢁ1
,
g = 2.30, zJ0 = ꢁ0.48 cmꢁ1 and R =
1.6 ꢂ 10ꢁ4. The negative zJ0 value indicates weak antiferromagnetic
interactions between Co(II) ions.
A similar attempt was also performed to the data of 2, but the
result is not satisfactory. The magnetic data of 2 were fitted by
using a simple phenomenological Eq. (2) [36–38],
major deviations. For
a tetrahedral Co(II) ion, as found in
Co2(2,20-bpdc)2(dpa)2, where bpdc is biphenyldicarboxylate, C =
2.47 cm3 K molꢁ1 and h = ꢁ1.2(2) K [35]. From the comparison of
these simple cases that for tetrahedral system we usually find
the expected values while for octahedral systems the absolute val-
ues are much higher, especially h values.
Since the environment of the high-spin Co(II) ion for 1 is tetra-
hedral, zero field splitting of the 4A2 ground state may play a major
effect with the quenched orbital momentum. The magnetic suscep-
tibility data were first treated by a mononuclear Co(II) mode in the
crystal field, then magnetic interactions between the Co(II) ions are
further considered as a molecular field approximation. The total
equation is
vMT ¼ A expðꢁE1=kTÞ þ B expðꢁE2=kTÞ
ð2Þ
Here, A + B equals the Curie constant, and E1, E2 represent the
‘activation energies’ corresponding to the spin–orbit coupling and
the magnetic exchange interaction, respectively. The fitting of the
experimental data using this model (as shown in Fig. 3(b)) gives
A + B = 3.42 cm3 molꢁ1 K, ꢁE1/k = ꢁ103.75 K, ꢁE2/k = ꢁ1.6 K with
R = 8.1 ꢂ 10ꢁ5. The A + B, ꢁE1/k and ꢁE2/k values of the complex
are of the same magnitude as those values in previously reported
cobalt complexes [36–39]. The ꢁE2/k value of ꢁ1.6 K is corre-
sponding to J = ꢁ3.2 K according to the Ising chain approximation,
which indicates antiferromagnetic interactions of Co(II) ions in 2.
The magnetic interactions of Co(II) ions in 2 is much stronger than
1, which is consistent with the different bridge ligands (the bridge
of 2 is CoꢀꢀꢀO–C–OꢀꢀꢀCo, and that of 1 is CoꢀꢀꢀO–(C)4or5–OꢀꢀꢀCo).
Nb2g2z 1 þ 9expðꢁ2D=kTÞ
vll
¼
¼
ꢂ
4kT
1 þ expðꢁ2D=kTÞ
Nb2g2x
kT
4
1 þ ð3 xÞ½1 ꢁ expðꢁ2xÞꢃ
v?
ꢂ
ðx ¼ D=kTÞ
1 þ expðꢁ2xÞ
4. Conclusion
vco ¼ ðvll þ 2v?Þ=3
Co=½1 ꢁ vCoð2zJ0=Ng2b2Þꢃ
ð1Þ
Two new Co(II) coordination polymers with 5,6-dimethyl-1H-
benzoimidazole and aromatic carboxylic acid were synthesized
and characterized. 1 exhibits 1D ladder-like chain linked by BTA4ꢁ
ions, which further assemble into 3D supermolecular structure
vM
¼
v
through
p–p interactions and hydrogen bond interactions, while
2 shows a 2D layer linked by carboxylate groups. The magnetic
studies revealed the presence of antiferromegnetic interactions be-
tween the adjacent Co(II) ions.
Acknowledgement
This work was support by the National Natural Science
Foundation of China (No. 20801028), the NSF of Tianjin (Nos.
09JCYBJC04000 and 08ZCGHHZ01100), MOE (No. 20070055046)
of China, and the National Innovation Projects for the Undergradu-
ates of China.
Appendix A. Supplementary material
CCDC 743079 and 743080 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.05.041.
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