Delicate modulated assembly of a new kind of trinuclear copper(II) motif governed by N-containing agents

Article abstract of DOI:10.1039/c4ce00898g

A new kind of trinuclear copper(ii) motif [Cu₃L] was prepared in situ by adopting a multidentate ligand, N′²,N′^2′-bis(2-hydroxybenzoyl)biphenyl-2,2′-dicarbohydrazide (H₆L), in the presence of a series N-containing agents. Featuring five different assembly styles, [Cu₃L(DMF)_2.5(hmta)]·3H₂O (1), [Cu₃L(DMA)(H₂O)(Hmor)] (2), [Cu₃L(py)₂]·DMF (3), [Cu₃L(DMF)(H₂O)]·2DMF (4), and [Cu₃L(DMA)(H₂O)]·0.5DMA (5) (hmta = hexamethylenetetramine, Hmor = morphiline, py = pyridine) were obtained. In these assemblies, the [Cu₃L] units are connected with each other into one-dimensional chains via bridging of N-containing agents or via sharing an oxygen atom of L^6- to fuse together. Furthermore, the connecting styles are found to be governed by the character of the N-containing agents used, which is discussed in detail. Thermal gravimetric analysis and magnetic measurement of some complexes were performed.

Full text of DOI:10.1039/c4ce00898g

Volume 16 Number 42 14 November 2014 Pages 9755–9948
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PAPER
Shu-Ting Wu et al.
Delicate modulated assembly of a new kind of trinuclear copper(II) motif
governed by N-containing agents

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PAPER
Delicate modulated assembly of a new kind
of trinuclear copper(II) motif governed by
Cite this: CrystEngComm, 2014, 16,
N-containing agents†
ab
9792
Hong-Liang Tang,a Shu-Mei Lu,a Qiao-Yan Ye,a Xi-He Huang,ab
*
Shu-Ting Wu,
Chang-Cang Huang,a Xiao-Lin Hua and Shou-Tian Zhenga
A new kind of trinuclear copper(II) motif [Cu3L] was prepared in situ by adopting a multidentate
ligand, N′2,N′2′-bis(2-hydroxybenzoyl)biphenyl-2,2′-dicarbohydrazide (H6L), in the presence of a series
N-containing agents. Featuring five different assembly styles, [Cu3L(DMF)2.5(hmta)]·3H2O (1),
[Cu3L(DMA)(H2O)(Hmor)] (2), [Cu3L(py)2]·DMF (3), [Cu3L(DMF)(H2O)]·2DMF (4), and [Cu3L(DMA)(H2O)]·0.5DMA
(5) (hmta = hexamethylenetetramine, Hmor = morphiline, py = pyridine) were obtained. In these assemblies,
the [Cu3L] units are connected with each other into one-dimensional chains via bridging of N-containing
agents or via sharing an oxygen atom of L6− to fuse together. Furthermore, the connecting styles are found
to be governed by the character of the N-containing agents used, which is discussed in detail. Thermal
gravimetric analysis and magnetic measurement of some complexes were performed.
Received 28th April 2014,
Accepted 5th June 2014
DOI: 10.1039/c4ce00898g
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Hydrazide-based coordination compounds have shown fasci-
nating properties in magnetism,12 molecular recognition,13
Introduction
In the last two decades, coordination supramolecular chemis-
try has seen great development because of the potential appli-
cations in catalysis,1 small molecule capture or separation,2
photoluminescence3 and imaging,4 biology,5 electronics6 etc.
In the exploration of novel materials with demanded function,
the self-assembly process of supramolecular coordination com-
plexes becomes crucial.7 The concept of molecular building
blocks (MBBs) made the complicated self-assembly process
become a two-step arrangement.8 The first step is to build up
MBBs with covalent bonds or strong coordination bonds,9 and
the second step is to assemble MBBs via weak coordination
bonds and molecular interactions, such as hydrogen bonds,
π⋯π stacking, hydrophobic or hydrophilic, and van der Waals
interactions.10 Consequently, the design and construction of
MBBs is the foundation of supramolecular architecture.
biological sensing,14 etc. As we mentioned above, H6L, which
is armed with a pair of hydrazides that are spaced by a biphe-
nyl group (Scheme 1), might be a good candidate to build up
stable coordination motifs, and further assemble into supra-
molecular networks. Five copper(II) coordination polymers that
were constructed from L6− were yielded by employing different
N-containing agents. Based on the analysis and discussion of
the syntheses and structural features, the modulation of
N-containing agents on the assembly process was presented
and discussed.
Experiment section
Reagents and instruments
Materials used for synthesis were of reagent grade and used
In this paper, we designed a flexible multidentate ligand
H6L that was embedded with a pair of hydrazides with ten
potential coordination atoms. It is well-known that the coor-
dination of hydrazide ligands and metal ions always leads to
chelated coordination rings, which are stable in solution.11
1
without further purification. H NMR (DMSO-d6) was carried
out on a BRUKER AVANCE III 400 nuclear magnetic reso-
nance spectrometer. IR spectra were recorded in the range of
4000–400 cm−1 on a Perkin-Elmer FT-IR spectrum 2000 spec-
trometer using the KBr pellet technique. X-ray powder
a College of Chemistry, Fuzhou University, Fuzhou, 350116, PR China.
E-mail: shutingwu@fzu.edu.cn
b State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the
Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China
† Electronic supplementary information (ESI) available: Characterization of H6L,
XRPD patterns and bond length lists of complexes 1–5. CCDC 983128, 983130,
and 1005328–1005330. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4ce00898g
Scheme 1 The structure of H6L.
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diffraction (XRPD) measurements were performed on a
Rigaku D/max-3c with Cu Kα radiation (λ = 1.5406 Å) in the
angular range of 2θ = 5–50° at 293 K. Elemental analyses were
performed using a Vario MICRO, CHNOS Elemental Analyzer.
The instrument for thermal gravimetric measurements was a
Netzsch STA 449C Jupiter. Magnetic susceptibility data were
collected over the temperature range of 2–300 K in a mag-
netic field of 1000 Oe on a MPMS (SQUID)-XL magnetometer.
The fluorescence spectrum for H6L was recorded on an Edin-
burgh Instrument FL/FS-920 fluorescent spectrometer.
dissolved in a mixed solvent of DMF (3 mL) and acetonitrile
(3 mL). Blue columnar crystals were obtained in two weeks,
in 37.03% yield (on the basis of Cu). Anal. calcd. (found) for
C
37H39Cu3N7O10 (%): C, 47.28 (47.62); H, 4.45 (4.10); N, 8.12;
(10.51). IR (KBr, cm−1): 3400w, 3060w, 2928w, 1647s, 1600s,
1564m, 1500s, 1476m, 1406s, 1385s, 1322w, 1230m, 1156m,
1103m, 1048w, 905m, 847m, 756m, 699m, 581w, 545w, 453w.
[Cu3L(DMA)(H2O)]·0.5DMA (5). The preparation of 5 was
similar to that of 4, but 5 mL DMA that was dissolved with
piperazine hexahydrate (0.025 mmol, 4.9 mg) was used as the
solvent instead of the mixed solvent. Blue square plate-like
crystals were obtained in two weeks, in 55.74% yield (on the
basis of Cu). Anal. calcd. (found) for C68H59Cu6N11O17 (%): C,
48.30 (48.47); H, 4.10 (3.73); N, 9.56; (9.15). IR (KBr, cm−1):
3369w, 3069w, 1603s, 1511s, 1480s, 1397s, 1379s, 1303m,
1227s, 1157m, 1103m, 1046m, 906s, 847s, 750s, 695m, 670m,
595m, 464m, 443m.
Synthesis of the ligand and title complexes
2,2′-Biphenyldicarbonyl
chloride.
A
mixture
of
2,2-biphenyldicarboxylic acid (1.452 g, 6.0 mmol) and thionyl
chloride (10 mL) was refluxed for 9 h, with one drop of DMF
(N,N-dimethylformamide). After reaction, solvent and excess
thionyl chloride were removed by rotary evaporation, leaving a
colorless solid of 2,2-biphenyldicarbonyl chloride. Yield: 88.37%.
N′2,N′2′-Bis(2-hydroxybenzoyl)biphenyl-2,2′-dicarbohydrazide
(H6L). A 10 mL DMF solution of 2,2-biphenyldicarbonyl chlo-
ride (5.0 mmol) and 10 mL DMF solution of triethylamine
(1.4 mL) and salicylhydrazide (13.7 mmol) were mixed within
an ice-bath. The mixture was warmed to room temperature
and refluxed for 9 h. The solvent was removed with reduced
pressure distillation to obtain the crude product as a reddish
brown solid. After washing with ethanol for several times, a
white product was obtained with 78.54% yield. The product
was characterized by 1H NMR (DMSO-d6), IR spectroscopy
and fluorescence spectroscopy, the data for which are listed
in the ESI,† Fig. S1–S3.
X-ray crystallography. Diffraction data for complex 1 were
collected on an Agilent technologies SuperNova Micro Focus
diffractometer. Diffraction data for complexes 2 and 3 were
collected on a RIGAKU/SATURN 724 CCD diffractometer. Data
for complexes 4 and 5 were collected on a Rigaku R-AXIS
RAPID diffractometer. All diffractometers were operated using
graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å) in
the ω scan mode. Absorption coefficients were applied using
a multi-scan technique. All the structures were solved by the
direct method of SHELXS-97 and refined by full-matrix least-
squares techniques using the SHELX-97 program.15 Non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
of organic molecules were generated geometrically and
refined by a riding mode. The SQUEEZE subroutine of the
PLATON software suite16 was applied for the data of com-
plexes 2 and 5 to avoid diffraction interference. The resulting
new HKL files were used for further refinement. A summary
of crystallographic data and structure determination for 1–5
is provided in Table 1.
[Cu3L(DMF)2.5(hmta)]·3H2O (1). H6L (0.0125 mmol, 6.4 mg),
Cu(Ac)2·H2O (0.0375 mmol, 7.5 mg) and hmta (hexamethylene-
tetramine, 0.0375 mmol, 5.3 mg) were mixed and dissolved in
5 mL DMF. Blue rhombic plate-like crystals were obtained in
five days, in 13.54% yield (on the basis of Cu).
[Cu3L(DMA)(H2O)(Hmor)] (2). H6L (0.0125 mmol, 6.4 mg)
and Cu(Ac)2·H2O (0.0375 mmol, 7.5 mg) were mixed and
dissolved in 5 mL DMA (N,N-dimethylacetamide) with one
drop of Hmor (morphiline, ca. 0.58 mmol). Dark blue block-
shaped crystals were obtained in two months, in 18.31% yield
(on the basis of Cu). IR (KBr, cm−1): 3245w, 3055w, 2973w,
2932w, 2844w, 1600s, 1562m, 1500s, 1464m, 1400s, 1321m,
1250s, 1186m, 1155m, 1109m, 1092m, 1019m, 873m, 852m,
750s, 700m, 637m, 543w, 462m, 433m.
Results and discussion
Crystal structures and discussion
[Cu3L(DMF)2.5(hmta)]·3H2O (1). Complex 1 crystallizes in
the monoclinic system, space group C2/c, featuring a 1D
infinite structure which forms a 2D supramolecular bilayer
structure by hydrogen bonding. The asymmetric unit for 1
contains three crystallographically unique CuII ions, one L6−
,
[Cu3L(py)2]·DMF (3). H6L (0.05 mmol, 25.5 mg) and
Cu(Ac)2·H2O (0.15 mmol, 30.4 mg) were mixed and dissolved
in 5 mL DMF with one drop of pyridine. Dark blue column-like
crystals were obtained in two weeks, in 56.01% yield (on the
basis of Cu). Anal. calcd. (found) for C41H33Cu3N7O7 (%): C,
52.85 (53.14); H, 3.51 (3.51); N, 10.35; (10.58). IR (KBr, cm−1):
3689w, 3060w, 3005w, 2925w, 2107w, 1675s, 1600s, 1500s,
1450m, 1400s, 1324m, 1253m, 1217m, 1153w, 1091w, 1063m,
901m, 848m, 780m, 754s, 641m, 572w, 437w.
one hmta, two and a half DMF molecules, and three lattice
water molecules. Three kinds of distinct coordination
geometries around CuII are observed (Fig. 1a). Cu1 adopts a
distorted octahedral geometry. The equatorial plane is
completed by three atoms from L6− (O1, N1, O3) and one
N atom from hmta. Axial positions of the octahedron are
occupied by two O atoms from DMF molecules, adopting
elongated bond lengths (2.6367(83) and 2.5011(57) Å), which
could be attributed to the Jahn–Teller effect. Cu2 displays a
compressed tetrahedral geometry, with two pairs of N and
O atoms from L6− (O2, O5, N2, O3). The geometry around
[Cu3L(DMF)(H2O)]·2DMF (4). H6L (0.025 mmol, 12.8 mg)
and Cu(Ac)2·H2O (0.075 mmol, 15.0 mg) were mixed and
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Table 1 Crystal data and structure refinement parameters for complexes 1–5
Complex
1
2a
3
4
5a
Formula
Mr
Crystal system
a/Å
b/Å
c/Å
α/°
C41.5H51.5Cu3N10.5O11.5
1072.05
Monoclinic
41.720(3)
8.6534(5)
28.881(2)
90
C36H36Cu3N6O9
887.33
Monoclinic
25.985(5)
13.713(3)
24.798(5)
90
C41H33Cu3N7O7
926.36
Monoclinic
14.760(3)
14.694(3)
18.395(4)
90
C37H39Cu3N7O10
932.37
C68H63Cu6N11O17
1683.50
Orthorhombic
22.533(4)
23.066(5)
14.201(3)
90
Monoclinic
9.6951(19)
21.832(4)
19.246(4)
90
β/°
120.329(5)
90
8999.6(10)
113(2)
112.39(3)
90
8170(3)
113(2)
98.88(3)
90
3941.7(14)
293(2)
97.76(3)
90
4036.4(14)
293(2)
90
90
7381(3)
293(2)
γ/°
V/Å3
T/K
Space group
Z
C2/c
8
C2/c
8
P21/c
4
P21/c
4
Pba2
4
Rint
0.0602
28 465
1.050
0.0634
0.0808
27 620
1.136
0.0746
0.1692
0.0499
36 450
0.922
0.0421
0.1233
0.1194
37 325
0.959
0.0720
0.0801
68 086
0.850
0.0535
0.1312
0.374(14)
Reflections collected
GOF on F2
R1[I > 2σ(I)]b
wR2 (all data)c
Flack parameter
0.1486
0.1626
a
The formula and Mr of 2 and 5 in the table are results of excluding the disordered solvent that was removed by the SQUEEZE process.
The overall formula for 2 should be C36H42Cu3N6O12, with Mr 941.33, F(000) 3868. The overall formula for 5 should be C68H64Cu6N11O17.5, with
P
P
P
P
b
2
Mr 1692.50, F(000) 3452. R1 = ‖Fo| − |Fc‖/ |Fo|. c wR2 = [ w(Fo − Fc2)2/ w(Fo2)]1/2
.
Fig. 1 (a) Ellipsoid representation of the coordination environment for CuII ions in complex 1 (ellipsoid probability 50%). Hydrogen atoms and
lattice solvent molecules are omitted for clarity. Symmetry code: A = x, 2 − y, 0.5 + z. (b) Side view of the hydrogen bonding bilayer structure for 1
(hydrogen bonds show as blue dashed lines). The green and pink chains represent separate one-dimensional structures. The biphenol groups of
L6− fill the void space of the bilayers, which is shown in space filling mode in only one channel for clarity. (c) Representation of the 1D chain in 1.
Hydrogen atoms and solvent molecules (coordinated and lattice) are omitted for clarity.
Cu3 is an axially elongated square-pyramid, with three atoms
from L6− (O4, N4 and O6) one N atom from hmta, and one
O atom from DMF.
The as-synthesized ligand is completely deprotonated,
behaving as an organic host that embeds three CuII ions, in
situ generating a [Cu3L] motif. As shown in Fig. 1c, the [Cu3L]
motifs are linked by hmta into an infinite one-dimensional
structure, which means the [Cu3L] motifs could serve as
MBBs for further assembly if the linker hmta is substitutable.
There are multiple hydrogen bonds between lattice water
molecules and hmta, DMF, and deprotonated hydroxyl
groups of L6−, which direct the supramolecular bilayer struc-
ture in the (011) plane. As shown in Fig. 1b, the void space in
the bilayer structure is filled by the biphenyl group of L6−.
[Cu3L(DMA)(H2O)(Hmor)] (2). By substituting hmta with
Hmor, crystals of 2 were obtained, featuring a distinct one-
dimensional structure. The asymmetric unit contains three
crystallographically unique CuII ions, one L6−, one Hmor, one
DMA molecule, and one lattice water molecule. A similar
[Cu3L] motif exists in the structure. Major differences are the
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coordination geometries around Cu1 and Cu3. Both Cu1 and
Cu3 adopt similar distorted square-pyramid geometries. As
shown in Fig. 2a, the equatorial plane of Cu1 is completed by
three atoms from L6− (O1, N1 and O2) and one N atom from
Hmor. The axial position is occupied by an O atom from a
DMA molecule. Differently, symmetrically related Hmor coor-
dinates to Cu3 at the axial site. The equatorial plane of Cu3
is completed by one water molecule and three atoms from
L6− (O5, N4 and O6). The resulting one-dimensional structure
shows a waved chain along the c axis (Fig. 2c). Coordinated
water molecules (O1W) serve as hydrogen bonding donors,
affording hydrogen bonds with oxygen atoms (O1S) of DMA
style as AxAx. The 1D chains pack with each other with
embedded lattice DMF molecules occupying the void space.
[Cu3L(DMF)(H2O)]·2DMF (4). The crystal structure for 4
also features one-dimensional structures constructed from the
[Cu3L] motif, however, with a different assembly style. The
asymmetric unit includes one [Cu3L] motif, three DMF mole-
cules and one water molecule. As shown in Fig. 3c, both Cu1
and Cu3 display distorted square-pyramidal geometries. The
axial position of Cu1 is occupied by a water molecule, leaving
an equatorial position for an O1A atom from a symmetrically
related L6−. On the other hand, one DMF molecule coordinates
to Cu3 equatorially (O1S), leaving the axial position for O6B
from another symmetrically related L6−. Consequently, adjacent
[Cu3L] motifs connect with each other via sharing a pair of
μ2-O atoms into a one-dimensional structure (Fig. 3d). Due to
the different coordination environments around Cu1 and Cu3,
the assembly style present in 4 could be labelled as EqAx.
[Cu3L(DMA)(H2O)]·0.5DMA (5). X-ray single crystal diffraction
analysis reveals that 5 crystallizes in non-centrosymmetric space
group Pba2. The asymmetric unit includes two [Cu3L] motifs,
three DMA molecules and two water molecules. The two [Cu3L]
motifs feature similar structures and assembly styles, so only
one of them will be described herein. As shown in Fig. 3e, both
Cu1 and Cu3 display distorted square-pyramidal geometries,
with one water molecule and one DMA molecule coordinated
to Cu1 and Cu3 respectively at the axial position. There are
μ2-O atoms (O6A and O1B) that coordinate to Cu1 and Cu3 in
the equatorial plane, leading [Cu3L] motifs to fuse with each
other (Fig. 3f). The assembly style found in complex 5 can be
labelled as EqEq.
molecules and deprotonated hydroxyl groups (O6) of L6−
,
which leads to a 2D supramolecular layer structure (Fig. 2b).
Compared to the crystal structure of 1, in which linker
hmta connects [Cu3L] motifs by a pair of equatorial coordina-
tion bonds, the linker Hmor in 2 displays another kind of
connecting style by one equatorial bond and one axial bond.
To distinguish both assembly styles, we opt to label the assem-
bly style in 1 as Eq-hmta-Eq and that in 2 as Eq-Hmor-Ax.
[Cu3L(py)2]·DMF (3). Complex
monoclinic system, space group P21/c. The asymmetric unit
contains three crystallographically unique CuII ions, one L6−
3 crystallizes in the
,
two pyridine molecules and one lattice DMF molecule. A
similar [Cu3L] motif is also observed. In the [Cu3L] motif,
both Cu1 and Cu3 display distorted square-pyramidal geome-
tries, with two pyridine molecules coordinated to Cu1 and
Cu3 in the equatorial plane (Fig. 3a). The axial positions of
the geometries around Cu1 and Cu3 are occupied by O atoms
from symmetrically related L6−. In this way, the [Cu3L] motifs
are self-assembled in a stepwise fashion into one-dimensional
structure (Fig. 3b). Because the axial coordination bonds play
a key role in the assembly, we denote this kind of assembly
Synthesis and structural discussion. The bihydrazide ligand
H6L is a multidentate compound which offers up to ten available
coordination atoms. Structural analysis of complexes 1–5
Fig. 2 (a) Ellipsoid representation of the coordination environment for CuII ions in complex 2 (ellipsoid probability 50%). Hydrogen atoms and
lattice solvent molecules are omitted for clarity. Symmetry code: B = x, 2 − y, −0.5 + z. (b) Top view of the 2D hydrogen bonding structure for 2.
The green and pink waved chains represent separate one-dimensional structures. (c) Representation of the 1D chain in 2. Hydrogen atoms and sol-
vent molecules (coordinated and lattice) are omitted for clarity. The colour scheme is the same as Fig. 1.
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Fig. 3 Ellipsoid representations of the coordination environment for CuII ions (a, c, e) and 1D structures (b, d, f) observed in complex 3–5
respectively (ellipsoid probability 50%). Hydrogen atoms and lattice solvent molecules are omitted for clarity. The colour scheme is the same as Fig. 1.
Symmetry code: (a) A = 1 − x, 1 − y, −z, B = 2 − x, 1 − y, 1 − z; (c) A = 1 − x, 1 − y, 1 − z, B = −x, 1 − y, 1 − z; (e) A = 0.5 − x, −0.5 + y, z, B = 0.5 − x, 0.5 + y, z.
revealed that deprotonated L6− could form ten coordination
bonds with three CuII ions, leading to a [Cu3L] motif. As shown
in Fig. 4, the [Cu3L] motif in 1–5 shows four active
coordination sites for further assembly. Considering the typical
elongated Jahn–Teller effect of CuII coordination geometry, the
equatorial coordination bond length of CuII would be shorter
than the axial one (tables of bond lengths for 1–5 are listed in
the ESI†), the strength of equatorial bond must be stronger
than the axial bond. Consequently, the involved N-containing
agent, which is available for coordination, is able to play a key
role in the assembly of the [Cu3L] motif. In our study, hmta,
Hmor, pyridine, acetonitrile, and piperazine, with diverse coor-
dination abilities and structural features were introduced,
directing five kinds of assembly styles. It should be mentioned
that although DMF and DMA are also N-containing agents, this
paper won't discuss their influence, because their properties
are similar, and they are the major solvents in the synthesis of
each complex.
First, the N-containing agents act as linkers in the assem-
bly of [Cu3L] motifs, exhibiting Eq-hmta-Eq (complex 1) and
Eq-Hmor-Ax (complex 2) styles. Hmta features an adamantine-
like structure, offering four identical tertiary amines for coordina-
tion. Those tertiary amines compete to coordinate with CuII ions
at equatorial sites. However, it is difficult for hmta to act as a
three-connected or four-connected linker because of the steric
effect of the [Cu3L] motif. In practice, two tertiary amines are
observed to coordinate with the [Cu3L] motif equatorially,
resulting in Eq-hmta-Eq style for 1. Whereas Hmor features a
chair-shaped conformation, offering a secondary amine and an
ether group, which is a less competitive ligand. Perhaps because
the Hmor was added greatly in excess, both amine and ether
groups of Hmor coordinate with CuII. The ether group, which
has lower reaction activity, coordinates with CuII on the axial site,
while the secondary amine coordinates equatorially. As a result,
the assembly style for the [Cu3L] motif in 2 is Eq-Hmor-Ax.
Second, the N-containing agents act as structure-directing
agents, leading to the self-assembly of [Cu3L] motifs. The
[Cu3L] motifs were self-assembled through a pair of μ2-O
bridges, showing AxAx, EqAx, and EqEq styles in the struc-
tures of 3–5, respectively. The choice of these styles is also
related to the coordination ability of the N-containing agents.
In the structure of complex 3, pyridine, which is a good can-
didate to coordinate with CuII, occupies both equatorial
active sites of the [Cu3L] motif. As a result, the assembly of
[Cu3L] motifs in 3 is AxAx style. When the N-containing agent
is acetonitrile or piperazine, complex 4 or 5 is obtained
respectively, although their crystal structures do not contain
these agents. Further experiments showed that if acetonitrile
or piperazine are omitted from the reaction, complex 4 or 5
would not be obtained, which indicates both agents might be
structure-directing agents. The coordination abilities of aceto-
nitrile and piperazine are weaker than pyridine. However, the
large amount of acetonitrile may provide a good chance for
acetonitrile to coordinate with CuII randomly, which gives
rise to the EqAx assembly style for 4. It is worth mentioning
that crystals of complex 4 were not easy to reproduce, which
might indicate that the EqAx style is an “unstable state” in
the assembly process. The EqEq assembly style exists in 5,
which might be attributed to the weak coordination ability
and small amount of addition of piperazine.
As shown in Fig. 4, the diverse assembly styles of [Cu3L]
motifs give rise to various Cu⋯Cu distances between two
adjacent [Cu3L] motifs. It is obvious that self-assembly of
[Cu3L] motifs reduces the Cu⋯Cu distance. The minimum
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Fig. 4 The assembly of the [Cu3L] motif modulated by N-containing agents. On the left, the diagram represents a typical structure of the [Cu3L]
motif with orange arrows indicating the active coordination sites. “Eq site” means potential equatorial assembly style, while “Ax site” means poten-
tial axial assembly style. On the right, the differences among complexes 1–5 are highlighted with orange coloured areas which represent linkers
(complexes 1 and 2) or joints (complexes 3–5). Green dashed lines and numbers in green represent the Cu⋯Cu distances. The colour scheme for
atoms is the same as Fig. 1.
value of the Cu⋯Cu distance is 2.996 Å with the EqEq assem-
bly style for complex 5.
sharp decline when the temperature becomes higher, which
means that the decomposition temperature for 3 is about
380 °C. A similar thermal stability study was also undertaken
for complex 5. Upon heating from room temperature, the
sample of complex 5 loses weight gradually, with 17.6% mass
loss before 280 °C (Fig. 5a), corresponding to the contained
solvent molecules (theoretical value 17.7%). In the range of
280 °C to 400 °C, there is a plateau. When the temperature is
higher than 400 °C, significant weight loss occurs, indicating
that complex 5 might decompose at 400 °C. Comparing the
two thermal gravimetric curves, 5 shows better thermal stabil-
ity than 3, which indicates that the EqEq assembly style for 5
benefits the thermal stability.
Thermal stabilities and magnetism study
Owing to the low yield of complexes 1 and 2, only complexes
3–5 were studied by X-ray powder diffraction (XRPD) to con-
firm the phase purity (Fig. S4–S6 in ESI†). Further investiga-
tion on thermal stabilities and magnetism were carried out
for complexes 3 and 5; the two complexes with distinct
assembly styles (AxAx for 3, EqEq for 5).
Upon heating from room temperature, complex 3 remains
stable up to 120 °C. When the temperature goes higher, an
obvious weight loss (19.7%) occurs in the range of 120 °C to
310 °C, which is lower than the theoretical value (25.0%) for
the sum of DMF (7.9%) and pyridine molecules (17.1%). This
might be attributed to the stable coordination bonds of CuII
and nitrogen atoms from pyridine (bond distances 2.014(3)
and 2.006(3) Å in Table S7†). There is a slight weight loss in
the range of 310 °C (80.3%) to 380 °C (79.1%), followed by a
Magnetic behaviors of complexes 3 and 5 are depicted in
−1
Fig. 5 in the form of χmT vs. T and χm vs. T. For complex 3,
the room temperature value for χmT is 1.29 cm3 mol−1 K,
which is slightly higher than that of three non-interacting
CuII with S = 1/2 (1.125 cm3 mol−1 K). Upon cooling, the value
of χmT decreases gradually. When the temperature is lower
than 100 K, the χmT value decreases significantly, reaching a
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−1
Fig. 5 (a) The thermal gravimetric curves for complex 3 (red line) and 5 (black line). (b, c) Temperature dependence curves of χmT (■) and χm ( )
for complex 3 (b) and 5 (c).
minimum value of 0.48 cm3 mol−1 K at 10 K. There is an
increase from 10 K to 2 K, with χmT value changing from 0.48
to 0.54 cm3 mol−1 K. The curve of χm−1 vs. T for complex 3 fol-
lows the Curie–Weiss law above 46 K, with Curie constant
C = 1.40 cm3 mol−1 K and Weiss constant θ = −20.5 K, which
indicates the antiferromagnetic property of complex 3.
of Research on the Structure of Matter, Chinese Academy of
Sciences (20110006 and 20140010) and the Startup Fund
(022220) of Fuzhou University. We thank Prof. Long's lab in
Xiamen University for technical support.
Notes and references
The magnetic behavior upon cooling for complex 5 is sig-
nificantly different from complex 3. The value of χmT at 300 K
is 1.12 cm3 mol−1 K, which is close to the theoretical value of
three non-interacting CuII ions with S = 1/2 (1.125 cm3 mol−1 K).
The decline slope for the χmT ~ T curve of complex 5 in the
range of 300 K to 100 K is larger than that for complex 3.
A minimum χmT value (0.38 cm3 mol−1 K) exists at 2 K. The
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Five coordination polymers based on
a multidentate
bihydrazide ligand H6L and CuII were synthesized and charac-
terized, which revealed the assembly of a new kind of [Cu3L]
motif. The [Cu3L] motif shows four active coordination sites,
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Acknowledgements
We thank the financial support from the National Natural
Science Foundation of China (21001026 and 61008040), the
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