Syntheses, crystal structures and characterization of two new Pb(II) and Cu(II) coordination polymers based on 2-(4-fluorophenyl)-1H-imidazo[4,5-f][1,10] phenanthroline and benzenedicarboxylate ligands

Article abstract of DOI:10.1515/znb-2011-0906

Two new coordination polymers, [Pb(L)(1,3-bdc)] 2.5H₂O (1) and [Cu(L)(1,4-bdc)] (2) (L = 2-(4-fluorophenyl)-1H-imidazo[4,5-f][1,10] phenanthroline; 1,3-bdc, 1,4-bdc = 1,3-and 1,4-benzenedicarboxylate), have been hydrothermally synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. Crystal data for 1: C₅₄H ₄₀F₂N₈O₁₃Pb₂, triclinic, space group P1, a = 9.3468(19), b = 9.4607(14), c = 15.581(3) A, α = 90.44(4), β = 101.13(3), γ = 113.97(3)°, V = 1229.6(4) A³, Z = 1. Crystal data for 2: C₂₇H₁₅CuFN ₄O₄, triclinic, space group P 1, a = 9.640(6), b = 10.941(8), c = 11.865(5) A, α = 62.694(4), β = 69.776(3), γ= 79.915(5)°, V = 1043.2(11) A³, Z = 2. In 1, the Pb(II) atoms are bridged by the 1,3-bdc ligands to yield a chain structure. The ligands L are only located on one side of the chain, where π...π interactions among neighboring chains result in a supramolecular ladder, and the O-H... O hydrogen bonding interactions further stabilize this structure. Compound 2 shows a layer structure, with stacking by π-π interactions to give a three-dimensional (3D) supramolecular architecture. N-H...O hydrogen bonding further stabilizes the structure of 2.

Full text of DOI:10.1515/znb-2011-0906

Syntheses, Crystal Structures and Characterization of Two New Pb(II)
and Cu(II) Coordination Polymers Based on 2-(4-Fluorophenyl)-1H-
imidazo[4,5-f][1,10]phenanthroline and Benzenedicarboxylate Ligands
Zhan-Lin Xu, Yu He, and Hui-Lian Wang
Key Laboratory of Preparation and Applications of Environmentally Friendly Materials,
Ministry of Education, Department of Chemistry, Jilin Normal University, Siping 136000, China
Reprint requests to Prof. Zhan-Lin Xu. E-mail: xuzljl@yahoo.com.cn
Z. Naturforsch. 2011, 66b, 899 – 904; received April 12, 2011
Two new coordination polymers, [Pb(L)(1,3-bdc)] ·2.5H2O (1) and [Cu(L)(1,4-bdc)] (2) (L = 2-
(4-fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline; 1,3-bdc, 1,4-bdc = 1,3- and 1,4-benzene-
dicarboxylate), have been hydrothermally synthesized and characterized by elemental analysis, IR
spectra and single-crystal X-ray diffraction. Crystal data for 1: C54H40F2N8O13Pb2, triclinic, space
¯
˚
group P1, a = 9.3468(19), b = 9.4607(14), c = 15.581(3) A, α = 90.44(4), β = 101.13(3), γ =
◦
3
˚
113.97(3) , V = 1229.6(4) A , Z = 1. Crystal data for 2: C27H15CuFN4O4, triclinic, space group
◦
¯
˚
P1, a = 9.640(6), b = 10.941(8), c = 11.865(5) A, α = 62.694(4), β = 69.776(3), γ = 79.915(5) ,
3
˚
V = 1043.2(11) A , Z = 2. In 1, the Pb(II) atoms are bridged by the 1,3-bdc ligands to yield a
chain structure. The ligands L are only located on one side of the chain, where π ···π interactions
among neighboring chains result in a supramolecular ladder, and the O–H···O hydrogen bonding
interactions further stabilize this structure. Compound 2 shows a layer structure, with stacking by
π-π interactions to give a three-dimensional (3D) supramolecular architecture. N–H···O hydrogen
bonding further stabilizes the structure of 2.
Key words: Coordination Polymer, Crystal Structure, 1,3-Benzenedicarboxylate,
2-(4-Fluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline
Introduction
benzenedicarboxylate (1,3-bdc), have been well in-
vestigated by Yaghi et al. [5]. However, coordina-
tion polymers constructed by both benzenedicarboxy-
late and 1,10-phenanthroline-like (phen-like) ligands
have not been well investigated [6 – 8]. Among the
phen-like ligands, 2-(4-fluorophenyl)-1H-imidazo[4,5-
f][1,10]phenanthroline (L) is a good candidate for N-
donor ligands, which has excellent coordinating abil-
ity and a large conjugated system that can easily form
π-π interactions [9 – 13]. In this work, we report two
new coordination polymers, [Pb(L)(1,3-bdc)] ·2.5H2O
(1) and [Cu(L)(1,4-bdc)] (2).
Coordination polymers are of current interest not
only for their potential applications in microelectron-
ics, nonlinear optics, zeolite-like materials for molec-
ular selection, ion exchange, and catalysis but also
for their intriguing variety of architectures and topolo-
gies [1, 2]. So far, large numbers of coordination poly-
mers with one- (1D), two- (2D), and three- (3D) di-
mensional structures have been synthesized by hy-
drothermal methods. It is well known that the con-
struction of the coordination polymers can be influ-
enced by several factors, such as pH value of so-
lution, temperature, geometric requirements of metal
atoms, and the organic ligands [3]. In particular, the
choice of the organic ligand is a key factor that may
be utilized in determining the framework topology. Or-
Results and Discussion
Structure description of 1
Selected bond lengths and angles for [Pb(L)-
ganic ligands with aromatic polycarboxylate groups (1,3-bdc)] ·2.5H2O (1) and [Cu(L)(1,4-bdc)] (2) are
are especially attractive because carboxylate groups listed in Table 1. As shown in Fig. 1, there are one
can bridge two or more metal centers to produce Pb(II) atom, one 1,3-bdc anion, and two and a half wa-
polymers with versatile structural motifs [4]. Ben- ter molecules in the asymmetric unit of 1. The Pb(II)
zenedicarboxylates, such as 1,4- (1,4-bdc) and 1,3- atom is coordinated by two nitrogen atoms from one
c
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Z.-L. Xu et al. · Pb(II) and Cu(II) Coordination Polymers
Fig. 1 (color online). The coordination
environment of the Pb(II) center in 1.
Fig. 2 (color online). View of the chain
structure of 1.
˚
Table 1. Selected bond lengths (A) and angles (deg) for 1
chelating coordination mode and bridge two neighbor-
ing Pb(II) atoms to yield a chain structure (Fig. 2). In
the chain, the Pb···Pb distance bridged by the 1,3-bdc
and 2 with estimated standard deviations in parenthesesa.
Compound 1
Pb1–O2
Pb1–N2
Pb1–O3i
2.398(4)
2.507(4)
2.646(4)
Pb1–O4i
Pb1–N1
Pb1–O1
2.475(4)
2.629(4)
2.669(4)
˚
anion is about 10.248 A. The ligands L play an im-
portant role in the formation of the chain structure.
They only decorate one side of the chain and the
L ligands from adjacent chains furnish strong π-pi
O2–Pb1–O4i
O4i–Pb1–N2
O4i–Pb1–N1
O2–Pb1–O3i
N2–Pb1–O3i
O2–Pb1–O1
N2–Pb1–O1
O3i–Pb1–O1
79.30(12)
77.23(14)
131.05(13)
127.35(12)
74.63(14)
51.40(12)
90.71(14)
164.63(13)
O2–Pb1–N2
O2–Pb1–N1
N2–Pb1–N1
O4i–Pb1–O3i
N1–Pb1–O3i
O4i–Pb1–O1
N1–Pb1–O1
78.16(14)
117.14(14)
63.60(14)
51.28(12)
89.18(14)
130.69(12)
79.99(14)
˚
interactions (centroid-to-centroid distance 3.47 A and
˚
face-to-face distance 3.30 A), which extend the chains
into supramolecular ladders (Fig. 3). Moreover, O–
H···O hydrogen bonding interactions further stabilize
the structure of 1.
Compound 2
Cu1–O2
It is well known that the geometries of Pb(II) com-
plexes can be classified as holo- and hemidirected [14].
Holodirected refers to Pb(II) complexes in which the
bonds to the ligand atoms are located throughout the
surface of an encompassing sphere, whereas hemidi-
rected refers to those cases in which the bonds to the
ligand atoms are directed through only part of an en-
compassing sphere [13]. In compound 1, the arrange-
ment of O and N atoms for Pb(II) suggests a gap or
hole in the coordination geometry around this atom,
and its coordination sphere is, thus, hemi-directed.
1.979(2)
2.450(2)
2.029(3)
Cu1–O3
Cu1–N1
1.953(2)
2.014(3)
Cu1–O3i
Cu1–N2
O3–Cu1–O2
O2–Cu1–O3i
O2–Cu1–N1
O2–Cu1–N2
N1–Cu1–O3i
89.93(10)
95.54(10)
90.91(10)
162.14(10)
88.39(9)
O3–Cu1–O3i
O3–Cu1–N1
O3–Cu1–N2
N1–Cu1–N2
N2–Cu1–O3i
80.87(9)
169.25(10)
100.70(10)
81.33(10)
100.27(10)
a Symmetry transformations used to generate equivalent atoms for 1:
(i) x−1, y−1, z; for 2: (i) −x+1, −y, −z+2.
L ligand (Pb(1)–N(1) = 2.629(4) and Pb(1)–N(2) =
2.507(4) A) and four carboxylate oxygen atoms from
˚
Structure description of 2
two different 1,3-bdc anions (Pb(1)–O(1) = 2.669(4),
Pb(1)–O(2) = 2.398(4), Pb(1)–O(4)i = 2.475 (4) and
As shown in Fig. 4, the asymmetric unit of 2 con-
tains one Cu(II) cation, one L molecule, and two half
1,4-bdc anions. The 1,4-bdc ligand resides around
a crystallographic center of inversion. Each Cu(II)
ii
˚
Pb(1)–O(3) = 2.646(4) A; symmetry operations of
equivalent atoms: (i) x − 1, y − 1, z; (ii) −x + 1, −y,
−z+2). The two carboxylate groups are in a bidentate
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Z.-L. Xu et al. · Pb(II) and Cu(II) Coordination Polymers
901
Fig. 3 (color online). View of the
supramolecular ladder constructed by π-
π interactions in 1.
Fig. 4 (color online). The coordination
environment of the Cu(II) center in 2.
Fig. 5 (color online). A view of the layer structure of com-
plex 2.
Fig. 6 (color online). A view of the 3D architecture of 2 con-
structed by π-π interactions.
atom is five-coordinated by two N atoms from one L,
and three O atoms from three different 1,4-bdc lig-
ands in a distorted square pyramidal environment. It is 3.367(4) A. The dinuclear units are bridged by the
is interesting to note that the two 1,4-bdc ligands backbones of the 1,4-bdc2 ligands to form a chain
˚
structure (Fig. 5). The chains are further linked by
show different coordination modes (Fig. 4). For con-
venience, the 1,4-bdc anions containing the oxygen the 1,4-bdc1 ligands in bis-modentate modes to gen-
atoms labeled O1 and O3 are designated 1,4-bdc1 and erate a layer (Fig. 5). The ligands L are attached to
1,4-bdc2, respectively. Each 1,4-bdc1 coordinates to both sides of the layers, allowing the formation of π-
π stacking interactions (centroid-to-centroid distance
two Cu(II) centers in a bis-monodentate mode. Each
˚
˚
carboxylate group of the 1,4-bdc2 anion connects two of 3.57 A and face-to-face distance of 3.35 A), and
Cu(II) centers in a bis-bridging mode to form a dimer. connect the adjacent layers to a 3D supramolecular ar-
The distance between the Cu(II) centers in the dimer chitecture (Fig. 6). Obviously, the strong π-π stack-
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902
Z.-L. Xu et al. · Pb(II) and Cu(II) Coordination Polymers
ing interactions play an important role in stabilizing
the supramolecular architecture of 2. Moreover, the
N–H···O hydrogen bonding further support the struc-
ture of 2.
It is noteworthy that the skilful combination of
bridging carboxylate anions, phen-like chelating lig-
ands and metal cations has generated a number of
interesting coordination compounds so far. Unfortu-
nately, owing to the termination effect of chelating
phen-like ligands, such coordination polymers are usu-
ally only one- or two-dimensional [6 – 9]. As far as
we know, high-dimensional complexes based on di-
carboxylate and phen-like ligands have rarely been re-
ported [10 – 13]. Therefore, the structure 2 is a rare ex-
ample for layers based on dicarboxylate and aromatic
N-chelating ligands.
IR spectra
The broad band at 3431 cm−1 is attributed to the
O–H stretching frequency of the free water molecules
of compound 1. In the IR spectra of compounds 1
and 2, the special peaks at about 1659 and 1658 cm−1
are attributed to the protonated carboxylate groups
of 1,3-bdc and 1,4-bdc ligands. Peaks at about 1456
and 1450 cm−1 could be assigned to ν(C=N) stretch-
ing vibration of the ligand L.
Thermogravimetric analyses (TGA)
To characterize the compounds 1 and 2 more fully
in terms of thermal stability, their thermal behav-
ior was examined by TGA (Fig. 7). The experiments
were performed on samples consisting of numerous
single crystals under N2 atmosphere with a heating
Fig. 7. TG curves of compounds 1 (a) and 2 (b).
◦
rate of 10 C/min. For 1, the weight loss correspond-
ing to the release of water molecules is observed
◦
from 70 to 140 C (obsd. 6.9 %, calcd. 6.2 %). The
decomposition of the remainder occurred from 250
◦
to 530 C, leading to the formation of PbO as the
residue (obsd. 29.7%, calcd. 30.6%). From the TGA
curve of 2, no weight loss was observed below 235 ◦C,
indicating that there are no small molecules of solvent.
The host framework starts to decompose in the range
from 235 to 575 ◦C. The remaining weight corresponds
to the formation of CuO (obsd. 14.2%, calcd. 14.7%).
UV/Vis absorption spectra
The UV/Vis absorption spectrum of compound 2
was registered from the crystalline state at r. t. (Fig. 8).
The weak band from 550 to 670 nm can be assigned as
Fig. 8. UV/Vis absorption spectrum of compound 2.
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Z.-L. Xu et al. · Pb(II) and Cu(II) Coordination Polymers
903
Table 2. Crystal structure data for 1 and 2.
Compound
Formula
1
2
C54H40F2N8O13Pb2
1461.02
C27H15CuFN4O4
541.97
Mr
Crystal size, mm3
Crystal system
Space group
0.20×0.17×0.13
0.24×0.21×0.18
triclinic
triclinic
¯
¯
P1
P1
˚
a, A
9.3468(19)
9.4607(14)
15.581(3)
90.44(4)
101.13(3)
113.97(3)
1229.6(4)
1
1.97
6.9
706
−8 ≤ h ≤ 11
−11 ≤ k ≤ 11
−16 ≤ l ≤ 18
2.37 – 25.03
6173
9.640(6)
10.941(8)
11.865(5)
62.694(4)
69.776(3)
79.915(5)
1043.2(11)
2
˚
b, A
˚
c, A
α, deg
β, deg
γ, deg
3
˚
V, A
Z
Dcalcd, g cm−3
µ(MoKα ), mm−1
F(000), e
hkl range
1.73
1.1
550
Fig. 9. Plots of the temperature dependence of χmT (squares)
−1
and χm (triangles) for compound 2.
−12 ≤ h ≤ 12
−14 ≤ k ≤ 13
−15 ≤ l ≤ 15
d-d transitions, while the band from 200 to 400 nm is
considered to be due to intraligand transitions [14].
˙
θ range, deg
Refl. collect.
unique
3.05 –27.48
10329
3691
Magnetic properties
3796
Rint
0.0192
0.0431
The temperature-dependent magnetic susceptibility
data of compound 2 have been measured from poly-
crystalline samples at an applied magnetic field of
1000 Oe in the temperature range of 2 – 300 K (Fig. 9).
According to the structure, 2 can be approximately re-
garded as a dicopper(II) complex [15]. Upon cooling,
the values of χmT keep smoothly decreasing in the
300– 8 K range, and then exhibit a maximum value of
Data / ref. parameters 4239 / 379
4729 / 334
0.0459 / 0.1220
0.0639 / 0.1311
1.120
R1 / wR2[I ≥ 2σ(I)]
R1 / wR2 (all data)
GoF (F2)
0.0297 / 0.0684
0.0356 / 0.0706
1.071
1.17 / −0.57
−3
˚
∆ρmax/min, e A
0.55 / −0.67
Syntheses of compounds 1 and 2
A
mixture of Pb(NO3)2 (0.5 mmol), 1,3-H2bdc
0.6406 cm3 mol−1 K at 5 K before going down quickly (0.5 mmol) and L (0.5 mmol) was dissolved in 12 mL dis-
to a minimum value of 0.3001 cm3 mol−1 K at 2 K.
tilled water. The pH value of the system was adjusted to
between 5 and 6 by using triethylamine. The resulting
solution was stirred for about 0.5 h at r. t., sealed in a
23-mL Teflon-lined stainless-steel autoclave and heated
at 464 K for 3 d under autogeneous pressure. The reaction
system was slowly cooled to r. t. Pale-yellow crystals of 1
suitable for single-crystal X-ray diffraction analysis were
collected by filtration, washed several times with distilled
water and dried in air at ambient temperature. Yield: 37 %
based on Pb(II). – Anal. for C54H40F2N8O13Pb2 (1461.02):
calcd. C 44.38, H 2.76, N 7.67; found C 44.70, H 2.26,
N 7.84. – IR (KBr, cm−1): ν = 3431m, 2169m, 1659s,
1613m, 1456s, 1400w, 1221w, 1161m, 841w, 781w,
591w.
This behavior is indicative of antiferromagnetic cou-
pling [16]. The inflexion at 5 – 8 K may be due to a
small canting of the sub-lattice [16].
Experimental Section
General
All materials were of analytical grade and used as received
without further purification. The IR spectra were obtained on
a Perkin-Elmer 2400LSII spectrometer. Elemental analysis
was carried out with a Perkin-Elmer 240C analyzer. Ther-
mogravimetric analysis (TGA) was performed on a Perkin-
◦
Elmer TG-7 analyzer in the range from 40 to 800 C un-
The preparation of 2 was similar to that of 1 ex-
der nitrogen gas. The UV/Vis absorption spectrum of 2 was cept that 1,4-H2bdc and Cu(NO3)2 · 2.5H2O were used in-
collected on a finely ground sample with a Cary 500 spec- stead of 1,4-H2bdc and Pb(NO3)2, respectively. Yield: 31 %
trophotometer equipped with a 110 mm diameter integrating based on Cu(II). – Anal. for C27H15CuFN4O4 (541.97):
sphere. Temperature-dependent magnetic susceptibility data calcd.
C 59.83, H 2.79, N 10.34; found C 59.41,
for polycrystalline compound 2 was obtained on a Quantum H 2.50, N 10.71. – IR (KBr, cm−1): ν = 2160m, 1658s,
Design MPMSXL SQUID magnetometer under an applied 1612w, 1450m, 1409w, 1221w, 1201w, 1168m, 847w,
field of 1000 Oe over the temperature range of 2 – 300 K.
784w.
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Z.-L. Xu et al. · Pb(II) and Cu(II) Coordination Polymers
X-Ray structure determination
of rigid groups. The H atoms of the water molecules in 1
were located from a difference Fourier map.
Single-crystal X-ray diffraction data for complex 1 (Ta-
ble 2) were recorded at a temperature of 293(2) K on a Bruker
Apex CCD diffractometer, using the omega scan technique
CCDC 821322 (1) and 782105 (2) contain the supple-
mentary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data request/
cif.
˚
with MoKα radiation (lambda = 0.71073 A). Single-crystal
X-ray diffraction data for 2 (Table 2) were collected on a
Rigaku RAXIS-RAPID diffractometer using ω scans with
MoKα radiation. The structures were solved by Direct Meth-
ods with SHELXS-97 [17] and refined by full-matrix least-
squares techniques using SHELXL-97 [18]. Non-hydrogen
Acknowledgement
This work was supported by the Key Project of the Chi-
atoms were refined with anisotropic displacement parame- nese Ministry of Education (No. 210053) and the Technology
ters, and hydrogen atoms of the ligands were refined as part Development Program of Jilin Province (No. 20100549).
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