A new double layered 2-D copper(II) coordination polymer based on a semi-rigid ligand

Article abstract of DOI:10.1080/00958972.2016.1190450

A new 2-D Cu(II) coordination polymer, [Cu₂(L)(H₂O)₃]·4.5H₂O (1) [H₄L?=?5,5′-(pyrazine-2,3-diylbis(azanediyl))diisophthalic acid], has been synthesized from the reaction of Cu(NO₃)₂

Full text of DOI:10.1080/00958972.2016.1190450

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
A new double layered 2-D copper(II) coordination
polymer based on a semi-rigid ligand
Shichen Yan, Zhanfeng Ju & Daqiang Yuan
To cite this article: Shichen Yan, Zhanfeng Ju & Daqiang Yuan (2016): A new double layered
2-D copper(II) coordination polymer based on a semi-rigid ligand, Journal of Coordination
Chemistry, DOI: 10.1080/00958972.2016.1190450
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1190450
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Date: 16 June 2016, At: 18:25

Journal of Coordination Chemistry, 2016
http://dx.doi.org/10.1080/00958972.2016.1190450
A new double layered 2-D copper(II) coordination polymer based
on a semi-rigid ligand
Shichen Yana, Zhanfeng Jub and Daqiang Yuanb
aCollege of Chemistry, fuzhou university, fuzhou, Pr China; bfujian institute of research on the structure of matter,
Chinese academy of sciences, fuzhou, Pr China
ABSTRACT
ARTICLE HISTORY
received 19 January 2016
accepted 8 march 2016
A
new 2-D Cu(II) coordination polymer, [Cu2(L)(H2O)3]·4.5H2O (1)
[H4L = 5,5′-(pyrazine-2,3-diylbis(azanediyl))diisophthalic acid], has been
synthesized from the reaction of Cu(NO3)2·3H2O with H4L under solvothermal
conditions. H4L was prepared and characterized by 1H NMR, 13C NMR,
elemental analysis (EA), and infrared spectroscopy (IR). X-ray single-crystal
diffraction analysis reveals that 1 crystallized in the hexagonal space group
P6522 with a = 16.318(1), b = 16.318(1), c = 35.632(6) Å, V = 8217.0(8) Å3, Z = 12
and afforded 2-D grid-like double layers with a [3,5] topology network. The
staggered arrangement of the 2-D layers afforded a dense structure through
H-bonds. Further characterizations for 1 were performed by powder X-ray
diffraction, thermogravimetric analysis, EA, IR, etc. Magnetic measurements
revealed antiferromagnetic interactions between the adjacent Cu(II) centers
within 1.
KEYWORDS
Coordination polymer;
solvothermal; topology
network; 2-d layers;
antiferromagnetic
1. Introduction
Design and synthesis of coordination polymers (CPs) have attracted considerable attention in coordi-
nation chemistry owing to their diverse structures and potential applications in magnetism [1], lumi-
nescence [2], gas separation and storage [3–8], sensors [9], and catalysis [10–12]. During construction of
CPs, metal ions or clusters are nodes while ligands serve as linkers; these two main building blocks are
combined through coordination bonds, which affect the properties of CPs. Multidentate carboxylates
CONTACT Zhanfeng Ju
juzf@firsm.ac.cn; daqiang yuan
ydq@firsm.ac.cn
© 2016 informa uK limited, trading as taylor & francis Group

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S. YAN ET AL.
that have various coordination modes and geometries induce formation of diverse CPs. N-donor lig-
ands are often used as a second ligand. The basic N-donor ligands may have strong affinity with carbon
dioxide, thus metal–organic frameworks (MOFs), one type of CPs, may have high capacity for storage
and separation of carbon dioxide at room temperature. Amine functionalized MOFs have been reported
for CO2 separation [13–17]. Additionally, amine groups can act as active sites for catalysis in MOFs. For
example, amine-functionalized MOFs can be employed as heterogeneous catalysts for Knoevenagel
condensation reactions [18–20] and Friedel–Crafts reactions [21–24]. Furthermore, N-donor ligands
offer coordination modes differing from carboxylates. N-donor ligands with strong coordination affinity
can satisfy and even mediate the geometric requirement of metal centers [25–31].
Furthermore, semi-rigid multi-carboxylate ligands have a nonmetallic atom (C, O, S, or N atoms)
connecting rigid benzene-polycarboxylic moieties, which adds flexibility into the ligand [32–40]. Based
on these semi-rigid ligands, some CPs with interesting structures can be obtained.
Among various potential applications of CPs, magnetism has attracted interest to contribute to
understanding fundamental magnetic phenomena and to develop new magnetic materials in applica-
tion of information storage. Paramagnetic metals influence the magnetic behavior, and suitable ligands
also play key roles for the exchange of magnetism [41].
Our strategy is to design and synthesize semi-rigid ligands which contain both multi-carboxylate and
amine-functionalized parts. In principle, based on such ligands, structures and the expected functions
may be realized during construction of CPs. Paramagnetic transition metal ions present various coor-
dination modes, which may be related to the pathways of magnetic exchange [41–43]. Understanding
fundamental magnetic phenomena is crucial for designing new magnetic materials. Thus, assembly of
semi-rigid V-shaped ligands containing both multi-carboxylate and amine with paramagnetic transition
metals is fundamental to functional CPs’preparation.
Herein, we report the design and synthesis of 5,5′-(pyrazine-2,3diylbis(azanediyl))diisophthalic
acid (H4L); reaction of H4L with Cu(NO3)2·3H2O under solvothermal conditions gives a 2-D double lay-
er-shaped CP. The structure and magnetic properties are investigated.
2. Experimental
2.1. Materials and general methods
Reagents and solvents were commercially available and used without purification. NMR spectra were
measured on a Bruker Avance III 400 M NMR spectrometer. Infrared spectra were recorded as KBr pel-
lets on a Bruker VERTEX70 spectrometer from 4000–400 cm−1. Elemental analyses (C, H, O, and N) were
performed on a Elementar Vario El-Cube analyzer. Thermogravimetric analysis (TGA) of the complex was
recorded on a NETZSCH STA 449F3 thermal analyzer under N2. The operational range of the instrument
was from ambient temperature to 880 °C. Powder X-ray diffraction (PXRD) data were collected on a
Rigaku MiniFlex600 diffractometer with Cu Kα radiation from 2θ of 5–50° at room temperature. Magnetic
data were recorded on polycrystalline samples with Quantum Design MPMS-XL systems.
2.2. Preparation of the ligand and the CP
2.2.1. Synthesis of 5,5′-(pyrazine-2,3-diylbis(azanediyl))diisophthalic acid (H4L)
(5,5′-(Pyrazine-2,3-diylbis(azanediyl))diisophthalic acid) (H4L) was synthesized using a modified
literature method [44] (scheme 1). 5-Aminoisophthalic acid (0.91 g, 5.03 mmol) and anhydrous eth-
anol (20 mL) were added to a 50 mL two-necked flask, the mixture was stirred and thionyl chloride
(1.5 mL) was added dropwise under an ice bath, and then heated to 80 °C for 5 h. After cooling to room
temperature, the resultant mixture was concentrated under reduced pressure and extracted with
methylene dichloride (10 mL). The organic phase was washed with saturated aqueous NaHCO3 and
dried with magnesium sulfate. After filtration, the solvent was removed under reduced pressure and

JOURNAL OF COORDINATION CHEMISTRY
3
Scheme 1. synthesis road of the ligand.
diethyl 5-aminoisophthalate was obtained. Subsequently, a mixture of 2,3-dichloropyrazine (0.34 g,
2.28 mmol) and diethyl 5-aminoisophthalate (1.08 g, 4.56 mmol) was added into a 50 mL round bot-
tom flask and heated to 140 °C under N2 for 8 h. The resultant yellow solid was extracted with dichlo-
romethane (10 mL) and washed with saturated aqueous NaHCO3 and saturated brine, respectively.
The combined organic phase was dried with anhydrous MgSO4 and evaporated under vacuum. The
residue was then purified by silica gel column chromatography to give the ethyl ester of H4L (light
orange solid) in 50% yield.
Finally, the ethyl ester of H4L (0.63 g) was added to a mixture of methanol (10 mL), tetrahydrofuran
(10 mL), and potassium hydroxide in H2O (10 mL); the reaction mixture was refluxed overnight. After
cooling to room temperature, methanol and tetrahydrofuran were removed under reduced pressure.
1 M HCl was added into the resultant solution until the pH was 5. The precipitate was filtered off and
washed with water (3 × 5 mL). The resultant solid was dried at 70 °C and brown powder of H4L (0.45 g,
45%) was obtained. Anal. Calcd for H4L·6H2O, C20H14O8N4 (%): C, 43.96; H, 4.76; N, 10.26. Found: C, 44.29;
H, 4.08; N, 9.84. 1H NMR (400 MHz, DMSO-d6 δ, ppm): 9.43 (s, 2H), 8.56 (s, 4H), 8.12 (s, 2H), 7.70 (s, 2H). 13
C
NMR (400 MHz, DMSO-d6 δ, ppm): 168.02, 141.52, 141.16, 133.67, 131.27, 123.68. IR (KBr pellet, ν cm−1):
3390, 1708, 1602, 1537, 1426, 1292, 1146, 762, 685.
2.2.2. Synthesis of [Cu2(L)(H2O)3]·4.5H2O (1)
In a 10 mL vial, Cu(NO3)2·3H2O (0.015 g, 0.06 mmol) and H4L (0.005 g, 0.01 mmol) were dissolved in
a mixture of DMF (1 mL) and H2O (0.5 mL). Subsequently, five drops of HBF4 was added. After the
solution was heated at 65 °C for 12 h, green spindle crystals of 1 were obtained. Anal. Calcd for [Cu2(L)
(H2O)3]·7H2O (%): C, 32.39; H, 4.05; N, 7.56. Found: C, 32.69; H, 3.90; N, 7.89. IR (KBr pellet, ν cm−1): 3485,
3215, 1641, 1572, 1402, 1354, 1130, 991, 771, 731. (Note: there are seven water molecules in the formula
from elemental analysis, which may be due to moisture adsorption of the test sample.)
2.3. X-ray structure determination
The data of 1 were collected on an Agilent Super Nova CCD diffractometer equipped with a multi-
layer mirror Cu-Kα radiation (λ = 1.5418 Å) using a ω scan mode at 100 K. This structure was resolved
by the direct method and refined by full-matrix least-squares fitting on F2 by SHELX-2014 software
package [45]. All non-hydrogen atoms were refined with anisotropic thermal parameters. All hydro-
gens except those on water were located at geometrically calculated positions and refined by riding.
More details on the crystallographic studies as well as atomic displacement parameters are given in
Supporting Information as the CIF file. Crystallographic data for the structure reported in this article
have been deposited in the Cambridge Crystallographic Data Center with CCDC reference number
1444964 for 1. The crystallographic data as well as selected bond lengths and angles of 1 are listed
in tables 1 and 2.

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S. YAN ET AL.
Table 1. Crystal data and structure refinements for 1.
Formula
C40H46N8Cu4O31
formula weight
temperature (K)
Wavelength (Å)
Crystal system
space group
a (Å)
1389.01
100.0(2)
1.54184
hexagonal
P6522
16.3181(3)
16.3181(3)
35.633(2)
120
b (Å)
c (Å)
γ (°)
Volume (Å3)
Z
8217.1(6)
6
1.684
Dc (mg m−3)
μ (mm−1)
2.652
f(0 0 0)
4236
5473 [Rint = 0.0531]
373
1.074
0.0858
unique data
Parameters
Goodness-of-fit on F2
R1a [I > 2σ(I)]
b
wR2
0.2325
aR1 = ∑||Fo| − |Fc||/∑|Fo|.
2
2
bwR2 ={∑[w(Fo2 - Fc )2]/∑[w(Fo )2]}1/2.
Table 2. selected bond lengths (Å) and angles (°) for 1.
Bond lengths (Å)
Cu1–n3
Cu1–o7B
Cu2–o1
Cu2–o9
Cu2–o11
1.978(10)
1.941(8)
1.947(8)
1.916(14)
2.319(14)
Cu1–n4
1.993(9)
1.926(8)
1.908(7)
1.905(12)
Cu1–o3C
Cu2–o6a
Cu2–o10
Bond angles (°)
n3–Cu1–n4
81.1(4)
91.9(3)
170.7(4)
88.7(6)
92.3(4)
88.0(4)
87.4(4)
175.3(4)
o7B–Cu1–o3C
n4–Cu1–o3C
n4–Cu1–o7B
o1–Cu2–o9
o10–Cu2–o11
o9–Cu2–o11
o6a–Cu2–o11
o1–Cu2–o6a
94.6(3)
94.0(4)
164.9(4)
92.2(4)
89.8(7)
91.3(7)
95.6(6)
175.7(4)
n3–Cu1–o7B
n3–Cu1–o3C
o1–Cu2–o11
o1–Cu2–o10
o10–Cu2–o6a
o9–Cu2–o6a
o9–Cu2–o10
symmetry codes: a, −1 + x, y, z; B, x, x − y, 0.83333 − z; C, x, 1 + x − y, 0.83333 - z.
Figure 1. Coordination environment of Cu(ii) (30% thermal ellipsoid). symmetry codes: a, −1 + x, y, z; B, x, x − y, 0.83333 − z; C, x,
1 + x − y, 0.83333 – z. note: hydrogens and free water molecules are omitted for clarity.

JOURNAL OF COORDINATION CHEMISTRY
5
Figure 2. the 2-d double layered net, (a) along the a axes; (b) along the c axes, and (c) along the b axes. note: hydrogens and free
water molecules are omitted for clarity.
Figure 3. (a) 2-d double layered net simplified as a [3,5] topology network; (b) the staggered net and dense-packed structure figure.
3. Results and discussion
3.1. Crystal structure description
Compound 1 crystallizes in the hexagonal P6522 space group. The asymmetric unit consists of one L4−
,
two Cu(II) ions, three coordinating waters, and four and a half free waters, as shown in figure 1. There
are two kinds of crystallographically independent Cu(II) centers (Cu1 and Cu2) existing in different
coordination environments. Cu1, which lies on a crystallographic inversion center, has four-coordinate
distorted quadrilateral N2O2 environment. The coordination sphere of Cu1 is completed by two nitro-
gens from L4− and two oxygens from two different L4− ligands. Cu2 has distorted square-pyramidal
coordination geometry (figure 1). The axial site is occupied by O11 from water. The equatorial posi-
tions are occupied by O1 and O6 atoms from two L4− linkers and O9 and O10 of waters. The Cu–N/O

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S. YAN ET AL.
bond lengths are 1.905(12)–2.319(14) Å, and the trans and cis angles around Cu are 81.4–94.9° and
164.9–175.8° (table 2), respectively. All the Cu–O and Cu–N bond distances are comparable to values
in the literature [42, 46]. Through these coordination bonds, as shown in figure 2, a double-layered
coordination net is formed. This 2-D double layered net can be simplified as a (3,5)-connected topology
with the point symbol of {42.67.8}{42.6}, shown in figure 3(a). H-bonds also exist in the structure. The
adjacent coordination spheres show O–H···O interactions between carboxylate O and coordinated
water H (figure 4), which exist in both the inner double layered net (figure 4(a)) and adjacent nets. The
adjacent nets are connected by O–H···O hydrogen bonds (figure 4(b)) between coordinated water O9
and uncoordinated carboxylate O, by which a 3-D supramolecular structure is formed. Consequently,
the staggered layers afford a dense-packed structure, as shown in figure 3(b). Xie et al. have reported
a flexible carboxylate ligand based on quinoxaline (H2DDQ = N,N′-dibenzoic acid-2,3-diaminoquinox-
aline), which also contain both carboxylate and N functional units. The distinct difference between
Figure 4. (a) h-bonds between Cu2 and Cu2C coordination spheres in one layer; (b) h-bonds in a double layered net and between
the nets. symmetry codes: a, −1 + x, y, z; C, x, 1 + x - y, 0.83333 − z, d, −1 + x, x − y, 0.83333 - z.
Figure 5. the experimental and simulated XrPd diagrams of 1.

JOURNAL OF COORDINATION CHEMISTRY
7
H2DDQ and H4L are in the carboxylate unit, which makes the Cu complex based on H2DDQ significantly
different from 1. In the reported structure, five-coordinate Cu ions connect the 1D chains into 2-D layers
to afford a 2-D undulating network with a 4-connected (44·62) kgm net topology. Adjacent 2-D layers
are further interconnected by π···π stacking interactions between the quinoxaline rings to form the
3-D open framework [47]. Comparing with the reported Cu complex, 1 adopts different coordination
and a diverse topological net. Although channels are not found in the dense-packed structure of 1, the
double-layered 2-D coordination net gives ring structure along the b direction (figure 2(b)). This would
be helpful to further construct 2-D porous materials.
3.2. Powder X-ray diffraction pattern and thermogravimetric analysis
The phase purity of 1 was confirmed by X-ray powder diffraction analysis (PXRD, figure 5). The PXRD
patterns match well with those simulated from single-crystal X-ray data, indicating that pure phases
were obtained. The different intensities between the simulated and experimental patterns may be
caused by the preferred orientation of the powder samples. The thermal stability was examined by
TGA from 25 to 880 °C at a heating rate of 10 °C min−1 under nitrogen. TGA of 1 exhibits a weight loss
of 22.26% from room temperature to 183 °C, corresponding to loss of independent and coordinated
water molecules. The polymer is stable to 251 °C and then starts to decompose after that temperature.
The weight of the final residue (29.28%) could be assumed to mixture of Cu and C) (figure 6).
Figure 6. the tGa diagram of 1.
Figure 7. temperature dependence of χm and χmt for 1 under 1 koe between 2 and 300 K.

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S. YAN ET AL.
3.3. Magnetic property
The magnetic properties of 1 were measured from 2 to 300 K under 1000 Oe. The χM and χMT versus T
plots of 1 are shown in figure 7. The χMT for 1 at 300 K is 0.79 cm−3 K mol−1, which is close to the expected
spin-only value (0.75 cm3 K mol−1 with S = 1/2 and g = 2) of two magnetically isolated Cu(II) ions [41].
Upon cooling, the χMT value decreases gradually between 300 and 25 K and then descends deeply to
the minimum value of 0.28 cm3·K·mol−1 at 2 K, indicating a weak antiferromagnetic interaction between
adjacent Cu(II) ions within 1 [48]. By structure analysis, although strong magnetic exchange pathway is
missing, H-bonds between coordinated water and uncoordinated carboxylate O exist and the experi-
mental weak antiferromagnetic interaction should be due to the effects of H-bonds (figure 4(b)).
4. Conclusion
A new 2-D double layered CP has been constructed by a semi-rigid ligand and Cu(II) ions. Hydrogen
bonds exist in both inner double layers and the adjacent nets, forming a 3-D supramolecular structure.
Magnetic study shows weak antiferromagnetic interaction between the adjacent Cu(II) ions within the
polymer. In this CP, the secondary amines are coordinated by Cu(II) and the dense structure limits more
function of the CP. Despite that, other interesting CPs constructed by this ligand with metal ions may
be prepared and some fascinating functions such as catalysis could be found.
Supplementary material
CCDC-1444964 contains the supplementary crystallographic data for this article. These data can be obtained free of charge
at http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from Cambridge Crystallographic Data Center, 12 Union Road,
Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-033; or E-mail: deposit@ccdc.cam.ac.uk.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
We gratefully thank the financial support of the National Natural Science Foundation of China [grant number 21271172],
[grant number 21390392], the “One Hundred Talent Project”from Chinese Academy of Sciences.
ORCID
Daqiang Yuan
http://orcid.org/0000-0003-4627-072X
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