Synthesis, crystal structure and magnetic properties of two coordination polymers with 4-(4-carboxyphenyl)-4,2′:6′,4″-terpyridine ligand

Article abstract of DOI:10.1016/j.inoche.2014.01.017

Mn^II and Co^II salts reacting with 4-(4-carboxyphenyl)-4,2′:6′,4″-terpyridine (4-Hcptpy) in DMF/H₂O afford two complexes, [Mn(4-cptpy)(DMF)(H₂O) ₂]_n·n(4-cptpy)·nDMF (1) and [Co(4-cptpy)₂(H₂O)₂]_n (2). Complex 1 is a 1D ribbon coordination polymer assembled by Mn₂ dimer and tridentate 4-cptpy ligand. The guest 4-cptpy anion is embedded in 3D supramolecular architecture with strong hydrogen bonds. Complex 2 is a 1D linear chain coordination polymer with quadrangled pores. The complex 1 releases H₂O and DMF in 87-150 C, and the anhydrous [Mn(4-cptpy)] _n·n(4-cptpy) remains thermally stable until 403 C. Variable temperature magnetic susceptibility study in 2-300 K proves that a weak antiferromagnetic interaction exists in the (μ-O₂CR) ₂Mn₂ core.

Full text of DOI:10.1016/j.inoche.2014.01.017

Inorganic Chemistry Communications 42 (2014) 38–41
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, crystal structure and magnetic properties of two coordination
polymers with 4-(4-carboxyphenyl)-4,2′:6′,4″-terpyridine ligand
a
a,
a
b
a,
Meng-Si Wang , Ming-Xing Li ⁎, Xiang He , Min Shao , Zhao-Xi Wang ⁎
a
Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, PR China
Laboratory for Microstructures, Shanghai University, Shanghai 200444, PR China
b
a r t i c l e i n f o
a b s t r a c t
II
II
Article history:
2
Mn and Co salts reacting with 4-(4-carboxyphenyl)-4,2′:6′,4″-terpyridine (4-Hcptpy) in DMF/H O afford two
Received 15 November 2013
Accepted 19 January 2014
Available online 28 January 2014
complexes, [Mn(4-cptpy)(DMF)(H
D ribbon coordination polymer assembled by Mn
anion is embedded in 3D supramolecular architecture with strong hydrogen bonds. Complex 2 is a 1D linear
chain coordination polymer with quadrangled pores. The complex 1 releases H O and DMF in 87–150 °C, and
the anhydrous [Mn(4-cptpy)] ·n(4-cptpy) remains thermally stable until 403 °C. Variable temperature magnetic
susceptibility study in 2–300 K proves that a weak antiferromagnetic interaction exists in the (μ-O CR) Mn core.
2
O)
2
]
n
·n(4-cptpy)·nDMF (1) and [Co(4-cptpy)
2 2 2 n
(H O) ] (2). Complex 1 is a
1
2
dimer and tridentate 4-cptpy ligand. The guest 4-cptpy
2
Keywords:
Coordination polymer
n
4-(4-carboxyphenyl)-4,2′:6′,4″-terpyridine
2
2
2
Crystal structure
Thermal stability
Magnetism
© 2014 Elsevier B.V. All rights reserved.
The molecular self-assembly, crystal engineering and functional
properties of coordination polymers have attracted great interest
owing to their intriguing structural motifs and potential applications
as functional materials [1–3]. The structural diversity and topology of
coordination polymers are attributed to the selection of metal centers,
organic ligands and reaction pathways. Much effort has been focused
on the purposeful design and controllable synthesis of coordination
polymers employing multidentate ligands such as polycarboxylate and
N-heterocyclic ligands [4–7]. In contrast to the cohesive terpyridyl moiety
of 2-Hcptpy that often acts as a chelating group to assemble mono-
nuclear complexes with obvious luminescent properties [8–10], 4-
was heated at 100 °C for 72 h. A clear solution without any solid was
afforded. Colorless crystals of complex 1 were grown from the solution
after one week in 30% yield based on 4-Hcptpy. Anal. Calcd. for
50 8 8
C H46MnN O (%): C, 63.76; H, 4.92; N, 11.90. Found: C, 63.31; H,
−
1
4.72; N, 11.32. IR (KBr, cm ): 3417 m, 3074w, 2934w, 1657s, 1595s,
1548s, 1390s, 827s, 788s, 632m. The experimental and simulated
PXRD patterns of 1 are in good agreement with each other (Fig. S1,
3 2 2
ESI). A mixture of Co(NO ) ·6H O (0.2 mmol), 4-Hcptpy (0.1 mmol),
1,2,4,5-benzenetetracarboxylic acid (0.1 mmol), 2 mL DMF and 6 mL
water was sealed in a 10 mL Teflon-lined reactor. The reactor was heated
at 120 °C for 72 h, and then cooled to room temperature at a rate of 10 °C
−
1
−1
(
4-carboxyphenyl)-2,2′:6′,2″-terpyridine (4-Hcptpy, Scheme 1)
h
. Several red crystals of complex 2 were obtained. IR (KBr, cm ):
contains two side exo-pyridyl groups and trends to construct extended
coordination polymers and metal-organic frameworks. The rigid trigonal
3394m, 3068w, 1596s, 1528s, 1391s, 1018m, 842s, 829m, 784s, 694m,
632m. The complex 2 can be prepared with a similar procedure except
that 1,2,3,4,5,6-cyclohexanehexacarboxylic acid was used instead of
1,2,4,5-benzenetetracarboxylic acid, but the yield is still poor. It was
failed to prepare 2 without the addition of benzenetetracarboxylic acid
or cyclohexanehexacarboxylic acid. This indicates that the preparation
of 2 may be highly influenced by pH value.
4
-Hcptpy bifunctional ligand possesses three pyridyl groups and one
carboxylic group, which is a valuable multidentate ligand in constructing
coordination polymers. However, very few efforts were devoted to 4-
Hcptpy complexes to date. In the course of our investigation for coordi-
nation polymers and MOFs [11–13], two new one-dimensional coordina-
tion polymers, [Mn(4-cptpy)(DMF)(H
2
O)
2
]
n
·n(4-cptpy)·nDMF (1) and
The infrared spectra exhibit characteristic 4-cptpy vibration bands in
both complexes (Fig. S2). The bands near 3070, 1600, and 1550 cm−
are respectively assigned to the stretching vibrations of C\H, C_C
1
[
Co(4-cptpy) (H O) (2), were prepared and structurally character-
2
2
2 n
]
ized. Herein, we report their synthesis, crystal structures, and thermal
and magnetic properties.
−
1
and C_N bonds of 4-cptpy. The bands near 825 and 785 cm are des-
ignated to the δ(C\H) bending vibrations of pyridyl and phenyl rings.
Both complexes were prepared by hydro(solvo)thermal reactions. A
−
1
2 2
mixture of MnCl ·4H O (0.1 mmol), 4-Hcptpy (0.05 mmol), 5 mL DMF
The characteristic absorption band at about 1595 cm corresponds to
and 1 mL water was sealed in a 10 mL Teflon-lined reactor. The reactor
the asymmetric stretching vibration νas(COO), whereas the band at
−
1
about 1390 cm is attributable to the symmetric stretching vibration
(COO). In addition, the ν(O\H) bands of coordinated water occur at
ν
s
−
1
−1
3417 cm for 1 and 3394 cm for 2. In the IR spectrum of 1, the strong
⁎
Corresponding authors. Tel.: +86 21 66132803; fax: +86 21 66134594.
−
1
E-mail addresses: mx_li@mail.shu.edu.cn (M.-X. Li), zxwang@shu.edu.cn (Z.-X. Wang).
absorption band at 1657 cm is ascribed to the stretching vibration of
1387-7003/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2014.01.017

M.-S. Wang et al. / Inorganic Chemistry Communications 42 (2014) 38–41
39
X-ray structural analysis [14] revealed that [Mn(4-cptpy)
DMF)(H O) ·n(4-cptpy)·nDMF (1) is a 1D ribbon coordination
polymer. As shown in Fig. 1a, the asymmetry unit contains an indepen-
(
2
2 n
]
II
2
dent Mn ion, a 4-cptpy ligand, a DMF and two coordinated H O mole-
cules together with a guest 4-cptpy anion and a lattice DMF molecule.
Mn1 is six-coordinated with a slight distorted octahedral geometry.
Four coordination sites on equatorial plane are occupied by N1, O1,
O2, O4 atoms. The axial positions are occupied by water O3 and DMF
O5 with a O3\Mn1\O5 bond angle of 175.04(8)°. The Mn1\O bond
distances vary from 2.121(2) to 2.249(2) Å (Table S1, ESI). The
Mn\N1 distance is 2.319(2) Å.
The carboxyl group of both 4-Hcptpy is deprotonated. One 4-cptpy
acts as a tridentate ligand, while the other 4-cptpy is a guest anion.
II
The tridentate 4-cptpy ligand bonds to three Mn ions via the bridging
carboxyl group and an outer pyridyl group (N1). Another outer pyridyl
group and the central pyridyl group are uncoordinated. Mn1 and Mn1A
are bridged by two carboxyl groups to form a Mn
separation of 5.081(1) Å (Fig. 1b). The binuclear Mn
2
dimer with a Mn⋯Mn
2
units are
interlinked via 4-cptpy spacers to form an extended 1D polymeric ribbon.
These 1D ribbons are parallelly arranged to form a 2D supramolecular
layer (Fig. 1c). Between adjacent 1D ribbons, there exist face-to-face
π–π interactions between central pyridyl rings with a centroid-to-
centroid distance of 3.631 Å.
Scheme 1. Schematic description of 4-Hcptpy ligand.
carbonyl group (C_O) in DMF. The absence of characteristic ν(COOH)
band near 1720 cm indicates that the carboxyl group is deprotonated
for 4-cptpy ligand and guest anion.
The 2D supramolecular layers formed by the 1D ribbons are further
stacked parallelly, which results in a 3D supramolecular architecture as
depicted in Fig. 1d. The uncoordinated 4-cptpy anions are sandwiched
−
1
Fig. 1. (a) The asymmetric unit of 1. (b) The 1D polymeric ribbon. (c) The 2D supramolecular network forming by parallel 1D ribbons. (d) Perspective view of 3D supramolecular network
yellow: lattice DMF, green: 4-cptpy guest anion).
(

40
M.-S. Wang et al. / Inorganic Chemistry Communications 42 (2014) 38–41
between the 2D supramolecular layers as guest. The guest 4-cptpy links
the coordinated water O3 and O4 through four strong hydrogen
bonds. The hydrogen bond distances of O(3)\H(3B)…O(6)#1, O(3)\
H(3A)…O(6)#4, O(4)\H(4A)…N(4)#5 and O(4)\H(4)…O(7)#4 are
2
.703(3), 2.703(3), 2.823(3), 2.600(3) Å, respectively (Table S2, ESI).
To date, ten 4-cptpy complexes have been structurally characterized
16–19]. This is the first example that 4-cptpy acts as a guest in supra-
[
molecular system. Calculated by the Platon program, there exists larger
3
solvent-accessible void space (304.9 Å , equal to 13.3% of the cell
volume). Within these void spaces, the lattice DMF molecules are
perched.
2 2 2 n
The complex [Co(4-cptpy) (H O) ] (2) is a 1D chain coordination
polymer. As shown in Fig. 2a, the asymmetric unit contains an indepen-
dent Co(II) ion, two 4-cptpy ligands and two coordinated water mole-
cules. Co1 is located in a centrosymmetric trans octahedral coordination
sphere, coordinated by two carboxyl oxygens and two water oxygens
on the equatorial plane, and two pyridyl nitrogens at the axial sites. The
bond distances of Co1\N1, Co1\O2 and Co1\O1W are 2.148(9),
2
.074(4), 2.152(1) Å, respectively. The bond angles of N1\Co\N1A,
O2\Co\O2A and O1W\Co\O1WA are exactly equal to 180°.
Fig. 3. Thermogravimetric curves of 1 (red) and 2 (green).
The 4-cptpy serves as a bidentate bridging ligand that coordinates to
Co1 and Co1A via a monodentate carboxyl group and an out pyridyl
group. Another outer pyridyl group and the central pyridyl group are
free (Fig. 2b). The terpyridine piece is nearly coplanar, and twists with
respect to the phenyl ring (59.1° dihedral angle). Every two 4-cptpy
ligands link two cobalt ions to form a quadrangled pore with the size
binding effect, the 1D chains are parallelly arranged to form a 2D supra-
molecular layer (Fig. 2c).
Thermogravimetric analyses were performed in 20–800 °C range at
−
1
a heating rate of 10 °C min in air. From the TG–DSC curves of 1 (Figs. 3
and S3), it can be observed that a weight-loss process occurs in
87–150 °C with an endothermic peak at 126 °C, which can be assigned
2
of 14.17 × 7.53 Å . On the basis of the mutual connection between
4
-cptpy ligands and cobalt ions, a 1D linear chain structure is built up.
Similar to the packing structure of 1, the central pyridyl groups be-
tween adjacent 1D chains of 2 display face-to-face π–π interaction
with a centroid-to-centroid distance of 3.776 Å. Utilizing this weak
to the release of two coordinated H
19.2%; calcd, 19.34%). The anhydrous [Mn(4-cptpy)]
remains thermally stable until heated to 403 °C, then exhibits a rapid
2
O and two DMF molecules (found,
n
·n(4-cptpy)
Fig. 2. (a) The asymmetric unit of 2. (b) The 1D linear chain structure. (c) Perspective view of 2D supramolecular network stacking via π–π interaction.

M.-S. Wang et al. / Inorganic Chemistry Communications 42 (2014) 38–41
41
2
ing from Mn dimer and tridentate 4-cptpy ligand. The guest 4-cptpy
anion is embedded in the 3D supramolecular architecture. Variable tem-
perature magnetic susceptibility study proves that a weak antiferromag-
2 2 2
netic interaction exists in the (μ-O CR) Mn core.
Acknowledgment
Financially supported by the National Natural Science Foundation of
China (21171115, 21203117), and the innovation program (12ZZ089)
of Shanghai Municipal Education Commission.
Appendix A. Supplementary material
Crystallographic data for 1, 2 have been deposited at the Cambridge
Crystallographic Data Center, CCDC–971224 for 1 and −943679 for 2.
These data can be obtained from the Cambridge Crystallographic Data
Center, 12, Union Road, Cambridge CB21EZ, UK. Supplementary data
related to this article can be found online at http://dx.doi.org/10.1016/
j.inoche.2014.01.017.
M
Fig. 4. The plots of χ T vs T for 1. The solid red line represents the best theoretical fit.
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calcd, 39.01%), which further decomposes in 500–730 °C. The final resi-
due is MnO (found, 7.69%; calcd, 9.23%). Complex 2 shows a weight
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[
[
The temperature dependence of magnetic susceptibilities of the
Mn(II) complex 1 was measured in 2–300 K range on a crystalline sam-
ple with a Quantum Design PPMS-9 magnetometer in a magnetic field
[
[
M M
of 1000 Oe. A plot of χ T vs T is shown in Fig. 4. The χ T value of
II
3
−1
carboxyl-bridging Mn
lower than the only-spin value of Mn
Upon cooling the sample, the values of χ
2
dimer at 300 K is 7.74 cm ·K·mol , which is
II
3
−1
2
unit (8.35 cm ·K·mol ).
T keep smoothly decreasing,
[14] Crystal data for 1: C50
H
46MnN
8
O
8
, Mr = 941.89, triclinic, space group P-1, a =
1
9
0
0.819(2), b = 14.098(3), c = 15.868(4) Å, α = 105.950(3), β = 96.694(3), γ =
M
3
−3
3.262(3)°, V = 2301.2(9) Å , Z = 2, Dc = 1.359 g cm , μ (Mo-Kα) =
which indicate an overall antiferromagnetic coupling in 1. Considering
that the Mn dimer is isolated by larger 4-cptpy ligand and 4-cptpy
guest anion, the appropriate magnetic exchange pathway is in the
−1
1 2
.351 mm , F(000) = 982, R = 0.0553, wR = 0.1250 for 10206 unique reflec-
2
6 6
tions and 620 parameters, S = 1.014. Crystal data for 2: C44H32CoN O , Mr =
7
99.69, triclinic, space group P-1, a = 7.123(1), b = 10.787(2), c = 13.232(2) Å,
3
α = 66.423(2), β = 82.408(2), γ = 75.213(2)°, V = 900.4(2) Å , Z = 1, Dc =
1
(
μ-O
Due to the magnetic couple that is located at Mn
/2), a theoretical susceptibility equation based on the spin Hamiltonian
·S ) is employed to evaluate the magnetic exchange con-
stant by fitting the magnetic susceptibility data [20]. This gives the
2
CR)
2
Mn
2
core through the bidentate carboxyl bridges.
−3
−1
1 2
.475 g cm , μ (Mo-Kα) = 0.538 mm , F(000) = 413, R = 0.0458, wR =
2
dimer (S
1
= S
2
=
0.1088 for 3984 unique reflections and 259 parameters, S = 1.009. Data were col-
5
lected on a Bruker Smart Apex-II CCD diffractometer. The structures were solved
2
by direct method and refined on F by full-matrix least squares technique with
(H = −2J S
1
2
SHELXTL program [15]. All non-hydrogen atoms were refined anisotropically, and
hydrogen atoms were located and included at their calculated positions.
−
1
singlet–triplet energy separation value J = −1.08 cm and g =1.91.
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2
The agreement factor R, defined here as R = ∑(χobsd − χ′cacld
) /
[
[
2
−3
∑
(χobsd) , is equal to 5.46 × 10 . This result proves that a weak anti-
ferromagnetic interaction exists in the (μ-O CR) Mn core.
2
2
2
[
[
19] Y.L. Gai, F.L. Jiang, L. Chen, Y. Bu, M.Y. Wu, K. Zhou, J. Pan, M.C. Hong, Dalton Trans. 42
In conclusion, two coordination polymers were assembled by 4-
(2013) 9954.
(
4-carboxyphenyl)-4,2′:6′,4″-terpyridine ligand. [Mn(4-cptpy)(DMF)
20] O. Kahn, Molecular Magnetism, VCH Publishers Inc., 1993. 114.
2 2 n
(H O) ] ·n(4-cptpy)·nDMF (1) exhibits a 1D ribbon structure construct-