Cu(II) coordination architectures with two positionally isomeric triazole-bipyridine ligands

Article abstract of DOI:10.3184/174751912X13419420224362

The Cu(II) coordination polymer, {[Cu(p-bdc)(4,4′-bpt)]}_n shows a 2D layer structure bridged by a p-bdc anion and the polymer {[Cu(H ₂btc)(3,3′-bpt)₂(H₂O)₂]. 2H₂O}_n, whose thermal stability has been briefly investigated, shows a 1D chain structure bridged by an H₂btc anion. [p-H₂bdc = 1,4-benzenedicarboxylate acid, H₄btc = 1,2,4,5-benzenetetracarboxylic acid, 4,4′-bpt = 1H-3,5-bis(4-pyridyl)-1,2, 4-triazole, 3,3′-bpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole] Both complexes have been prepared by the reaction of the relevant carboxylate acid and positional isomeric triazole-bipyridine ligand with Cu(II) salts under hydrothermal conditions. Both structures are further extended through intermolecular interaction to form 3D supramolecular frameworks.

Full text of DOI:10.3184/174751912X13419420224362

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 545
SEPTEMBER, 545–548
Cu(II) coordination architectures with two positionally isomeric
triazole–bipyridine ligands
Wei Luo, Haiye Li, Fuping Huang, Qing Yu and Hedong Bian*
Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources (Ministry of Education of China), Department of
Chemistry and Chemical Engineering of Guangxi Normal University, Guilin 541004, P. R. China
The Cu(II) coordination polymer, {[Cu(p-bdc)(4,4’-bpt)]}n shows a 2D layer structure bridged by a p-bdc anion and the
polymer {[Cu(H2btc)(3,3’-bpt)2(H2O)2]·2H2O}n, whose thermal stability has been briefly investigated, shows a 1D chain
structure bridged by an H2btc anion. [p-H2bdc = 1,4-benzenedicarboxylate acid, H4btc = 1,2,4,5-benzenetetracarbox-
ylic acid, 4,4′-bpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole, 3,3′-bpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole] Both complexes
have been prepared by the reaction of the relevant carboxylate acid and positional isomeric triazole–bipyridine
ligand with Cu(II) salts under hydrothermal conditions. Both structures are further extended through intermolecular
interaction to form 3D supramolecular frameworks.
Keywords: Cu(II) coordination polymers, crystal structure, positional isomer, triazole–bipyridine ligands
The design and construction of coordination polymers has
given rise to many architectures and topologies of potential
applications in luminescence, catalysis, nonlinear optics, gas
adsorption, magnetism, medicine and crystal engineering.1–6
Since several factors influence the structures of the final
products, for example solvent systems, temperature, ligand
structure and pH value, it is a challenge to predict and prepare
their exact structures.7–13 A helpful tool in the design of
such structures and controllable synthesis of the molecular
architecture, is the use of well-designed organic ligands that
can bridge or act as terminal groups to metal ions, and many
have been developed.14–17 Such organic ligands can affect the
final structural topologies of coordination solids.18–21
We have designed and synthesised two positionally isomeric
N,N′-donor ligands, 1H-3,5-bis(4-pyridyl)-1,2,4-triazole (4,4′-bpt)
and 1H-3,5-bis(3-pyridyl)- 1,2,4-triazole (3,3′-bpt) (Fig. 1),
via introducing the 1H-1,2,4-triazole moiety between two
4-pyridyl or 3-pyridyl groups. These ligands give interesting
coordination polymers.22 In addition, the different positions of
the pyridyl-N atoms in the positionally isomeric ligands may
allow the formation of different topological structures, which
may be useful in crystal engineering and supramolecular
chemistry.23 With this in mind, we have selected two carbox-
ylic acid and positionally isomeric N,N′-donor ligands and
obtained two Cu(II) complexes: {[Cu(p-bdc)(4,4′-bpt)]}n (1),
and {[Cu(H2btc)(3,3′-bpt)2(H2O)2]·2H2O}n (2). [p-H2bdc =
1,4-benzenedicarboxylate acid, H4btc = 1,2,4,5-benzenetetra-
carboxylic acid, 4,4′-bpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole,
3,3′-bpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole]. Structural
analysis reveals that 1 is bridged by p-bdc anions giving a 2-D
layer, and 2 is bridged by H2btc anions giving a 1-D chain,
respectively. The structures of both complexes are further
extended through intermolecular interaction to form 3-D
supramolecular frameworks. In addition, the thermal stability
of 2 has been briefly investigated.
Experimental
The ligands 4,4′-bpt and 3,3′-bpt were prepared according to the
literature,24 other reagents and solvents for synthesis and analysis
were commercially available and used as received. IR spectra were
taken on a Perkin-Elmer Spectrum One FT-IR spectrometer in the
4000–400 cm−1 region as KBr pellets. Elemental analyses for C, H
and N were carried out on a Model 2400 II, Perkin-Elmer elemental
analyser. TG-DTA tests were performed on a Perkin-Elmer thermal
analyser from room temperature to 1000 °C under an N2 atmosphere
at a heating rate of 5 °C min−1.
{[Cu(p-bdc)(4,4′-bpt)]}n (1): A mixture containing Cu(NO3)2·3H2O
(120 mg, 0.5 mmol), 4,4′-bpt (112 mg, 0.5 mmol), p-H2BDC (83 mg,
0.5 mmol), NaOH (40 mg, 1 mmol), water (12 mL) and ethanol
(3 mL) was sealed in a Teflon-lined stainless steel vessel (23 mL),
heated at 140 °C for 72 h then slowly cooled to room temperature
at 5 °C h−1. Blue crystals of 1 were obtained, washed with distilled
water then dried in air. Yield: 48% [based on Cu(II)]. Anal. Calcd for
C20H13CuN5O4: C, 53.22; H, 2.88; N, 15.52. Found: C, 53.34; H, 2.96;
N, 15.36%. IR (KBr, cm−1): 3611m, 3407w, 3199w, 1717m, 1613m,
1580s, 1500 m, 1410s, 1283m, 1011w, 930s, 831m, 735s, 563m,
469w.
{[Cu(H2btc)(3,3′-bpt)2(H2O)2]·2H2O}n (2): A mixture containing
Cu(NO3)2·3H2O (120 mg, 0.5 mmol), 3,3′-bpt (112 mg, 0.5 mmol),
H4btc (127 mg, 0.5 mmol), NaOH (40 mg, 1 mmol) and water (10 mL)
was sealed in a Teflon-lined stainless steel vessel (23 mL), heated at
110 °C for 72 h then slowly cooled to room temperature at 5 °C h−1.
Green crystals of 2 were obtained, washed with distilled water
then dried in air. Yield: 46% (based on Cu(II)). Anal. Calcd for
C34H30CuN10O12: C, 48.91; H, 3.60; N, 16.78. Found: C, 48.86; H,
3.52; N, 16.87%. IR (KBr, cm−1): 3533s, 3412s, 3120w, 3055m,
1698m, 1579s, 1405 m, 1333w, 1053w, 988w, 790w, 749w, 700w,
656w.
X-ray crystallography
X-ray single-crystal diffraction data for 1 and 2 were recorded at
room temperature on a Bruker Smart CCD apparatus using graphite-
monochromated MoKα radiation (λ = 0.71073 Å). Absorption effects
were corrected by semi-empirical methods. The structure was solved
by direct methods, successive Fourier difference synthesis and refined
by the full matrix least squares based on F2.25 The non-hydrogen atoms
were refined anisotropically. The H atoms of the water molecules
were located in a difference Fourier map. The C-bound H atoms were
positioned geometrically with C–H = 0.93 Å. Crystal data and details
of the structure are summarised in Table 1. Selected bond lengths and
angles are listed in Table 2.
Results and discussion
Crystal structure of 1: Complex 1 has a 2D polymeric coordi-
nation layer structure. The Cu1(II) atom is coordinated by four
carboxylic O atoms from four p-bdc ions [O1, O3A, O2B, and
O4, Cu1–O = 1.958(4)–1.9887(4) Å] and one N atom from
one 4,4′-bpt ligand [Cu1–N1 = 2.188 (4) Å] [Fig. 2(a)].
The geometry around the metal centre is a slightly distorted
Fig. 1 The positional isomeric triazole–bipyridine ligands.
* Correspondent. E-mail: gxnuchem312@yahoo.com.cn

546 JOURNAL OF CHEMICAL RESEARCH 2012
Table 1 Crystal data and structure refinement for 1 and 2
p-bdc spacers to generate a 2D layer structure. From a topo-
logical perspective, the [Cu2(CO2)4]n unit connecting four
ligands acts as the four-connected node and the p-bdc ligand
can be viewed as the linker. In this way, this framework can
be simplified to be a four-connected 2D (4,4)-sql layer
architecture [Fig. 2(b)]. The intermolecular packing is further
controlled by hydrogen bonds (N3—H3A···N5 #1, symmetry
code: #1 x, −y−1, z−3/2, Table 3) between the triazole N
atoms and pyridine N atoms to generate a 3D supramolecular
architecture [Fig. 2(c)].
Complex
1
2
Empirical formula
Formula weight (M)
C20H13CuN5O4
450.9
C34H30CuN10O12
834.23
Crystal system
Space group
a (Å)
Monoclinic
C2/c
22.454 (4)
10.911 (2)
18.135 (4)
90.00
117.25 (3)
90.00
3949.9 (17)
8
1.516
Triclinic
P-1
8.2740 (17)
9.875 (2
11.255 (2)
69.93 (3)
89.37 (3)
83.59 (3)
858.0 (3)
1
b (Å)
c (Å)
α (°)
β (°)
Crystal structure of 2: Complex 2 has a 1D polymeric
coordination layer structure. The Cu(II) atoms lie on inversion
centres and are coordinated by four O atoms from two H2btc
ions [O1 and O1A, Cu1–O1 = 1.955(4) Å], two water mole-
cules [O5 and O5A, Cu1–O5 = 2.436(6) Å] and two N atoms
from two 3,3′-bpt ligands [N1 and N1A, Cu1–N1 = 2.009(5)
Å), Fig. 3(a)]. The geometry around the metal centre is a
slightly distorted octahedron. The H2btc spacers bridge adja-
cent Cu(II) atoms with the Cu···Cu separation of 11.255(2) Å,
leading to a 1-D chain along the crystallographic c axis
[Fig. 3(b)]. Both the carboxylic groups in the H2btc ligand in 2
adopt monodentate modes to connect with two Cu atoms,
and the 3,3′-bpt ligands are in the monodentate coordination
fashion. Furthermore, the complex is assembled in a 3-D
supramolecular framework via intermolecular hydrogen
bonding (N3—H3···O2#1, O5—H5A···N4#2, O5—H5B···O6,
N5—H5C···O4#3, O6—H6A···O3#4 and O6—H6B···N2;
symmetry codes: #1 −x+1, −y+1, −z+1; #2 x, y+1, z; #3 x−1,
y−1, z; #4 x−1, y, z, Table 3) among the uncoordinated triazole
N atoms, uncoordinated pyridine N atoms, uncoordinated
carboxyl O atoms and coordinated water molecules [Fig. 3(c)].
Both the 4,4′-bpt and 3,3′-bpt ligands coordinated to the
metal atoms in 1 and 2 are monodentate, but the 4,4′-bpt and
3,3′-bpt ligands have the ability to adopt versatile coordination
modes to arrange the metal ions in a variety of structures.26–32
In addition, the complexes can further extend to 3-D supramo-
lecular frameworks via intermolecular hydrogen bonding of
4,4′-bpt and 3,3′-bpt ligands.33–35
γ (°)
V/(Å3)
Z
Dc (g m−3)
1.615
25.25
4987/3063
θ range for data collection (°) 25.00
Reflections collected / unique 15316/3474
[R(int) = 0.100] [R(int) = 0.078]
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
1.006
1.002
R1 = 0.0782
ωR2 = 0.2236
R1 = 0.1095
ωR2 = 0.2022
R1 = 0.0956
ωR2 = 0.2217
R1 = 0.1248
ωR2 = 0.2494
R indices (all data)
Table 2 Selected atomic distances (Å) and bond angles (deg)
for complex 1–2
1
Atomic distances/Å
Cu1—O1
1.958 (4)
1.980 (4)
1.987 (4)
Cu1—O4
Cu1—N1
1.988 (4)
2.188 (4)
Cu1—O3A
Cu1—O2B
Bond Angles [°]
O1—Cu1—O3A
O1—Cu1—O2B
91.02 (17)
O2B—Cu1—O4
O1—Cu1—N1
O3A—Cu1—N1
O2B—Cu1—N1
O4—Cu1—N1
87.87 (17)
98.76 (17)
94.21 (17)
93.95 (17)
98.01 (16)
167.29 (15)
O3A—Cu1—O2B 88.12 (17)
O1—Cu1—O4
O3A—Cu1—O4
Symmetry codes: A −x, y, −z+1/2; B −x, y+1, −z+1/2
90.27 (17)
167.37 (15)
2
Atomic distances/Å
Cu1—O1
Cu1—N1
Thermal stability of complex 2: In order to estimate the ther-
mal stability of complex 2, its thermal behaviour was studied
by thermogravimetric analyses (TGA) (see Fig. 4). There are
several mass loss steps, although without a clear plateau. The
first observed weight loss of 9.1% in the region of 29–202 °C
(peak at 161 °C) corresponds to the dehydration process (cal-
culated 8.63%). The residual framework starts to decompose
owing to the expulsion of the lattice water and the coordinated
water molecules beyond 202 °C with a series of complicated
weight losses (peaks at 280 and 391 °C) and does not stop until
heating ends at 971 °C.
1.995 (4)
2.009 (5)
Cu1—O5
2.436 (6)
Bond angles/°
O1A—Cu1—N1
O1—Cu1—N1
87.8 (2)
92.2 (2)
N1—Cu1—O5
88.2 (2)
91.8 (2)
N1A—Cu1—O5
O1A—Cu1—N1A 92.2 (2)
O1A—Cu1—O5A 82.6 (2)
O1—Cu1—N1A
O1A—Cu1—O5
O1—Cu1—O5
87.8 (2)
97.4 (2)
82.6 (2)
O1—Cu1—O5A
N1—Cu1—O5A
97.4 (2)
91.8 (2)
N1A—Cu1—O5A 88.2 (2)
Symmetry codes: –x,–y+2, –z+1
Table 3 Selected hydrogen-bond geometry/Å for 1 and 2
Conclusions
D—H···A
D—H
H···A
D···A
D—H···A
In this study, we have synthesised and characterised two new
Cu(II) coordination polymers based on two isomeric ligands
4,4′-bpt and 3,3′-bpt in combination with two carboxylic acids.
The 4,4′-bpt and 3,3′-bpt are not bridging ligands, but the work
shows that the isomers of bpt and carboxylic acid ligands
have versatile coordination modes to form diverse network
structures.27,35 We will further study the effect of mixed bpt iso-
mers and carboxylic acid as bridging ligands on the molecular
architecture of coordination structures.
1
N3—H3A···N5 #1
0.87
2.08
2.943 (10)
172
Symmetry code: #1 x, −y−1, z−3/2
2
N3—H3···O2#1
O5—H5A···N4#2
O5—H5B···O6
N5—H5C···O4#3
O6—H6A···O3#4
O6—H6B···N2
0.87
0.86
0.84
0.87
0.86
0.85
1.87
2.36
2.04
1.73
2.05
2.50
2.742 (7)
3.116 (9)
2.856 (9)
2.598 (8)
2.845 (9)
3.021 (9)
180
147
163
179
154
120
Symmetry codes: #1 −x+1, −y+1, −z+1; #2 x, y+1, z; #3 x−1,
y−1, z; #4 x−1, y, z.
We gratefully acknowledge the National Nature Science
Foundation of China (Nos. 21061002, 21101035), Guangxi
Natural Science Foundation of China (2010GXNSFF013001,
2012GXNSFBA053017, 2012GXNSFAA053035), the Foun-
dation of Key Laboratory for Chemistry and Molecular
Engineering of Medicinal Resources (CMEMR2011-20)
and the Nature Science Foundation of Guangxi Normal
University.
tetragonal-pyramid. The carboxylic groups of the p-bdc ligands
adopt syn-syn modes to connect with four Cu(II) atoms. Based
on these connection modes, two Cu(II) ions are coordinated by
four carboxylic groups of p-bdc ligands to give a [Cu2(CO2)4]n
unit. These [Cu2(CO2)4]n units are further interlinked through

JOURNAL OF CHEMICAL RESEARCH 2012 547
Fig. 2 (a) structure of 1 showing the local coordination environments of the Cu(II) atom; (b) the 2D layer of 1; (c) the 3D-dimensional
packing drawing of 1.
Fig. 3 (a) structure of 2 showing the local coordination environments of the Cu(II) atoms; (b) the 1-D chain of 2; (c) 3D-dimensional
packing drawing of 2.

548 JOURNAL OF CHEMICAL RESEARCH 2012
9
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Received 23 May 2012; accepted 9 July 2012
Paper 1201331 doi: 10.3184/174751912X13419420224362
Published online: 28 August 2012
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