Ligand-dependent assembly of dinuclear, linear tetranuclear and one-dimensional Zn(ii) complexes with an aroylhydrazone Schiff base

Article abstract of DOI:10.1039/C6CE02292H

Three complexes, [Zn(H₂L¹)(CH₃COO)]₂·CH₃OH (1), [Zn₄(H₂L²)₂(CH₃COO)₄]·4DMF (2) and {[Zn₄(L³)₂(CH

Full text of DOI:10.1039/C6CE02292H

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Ligand-dependent assembly of dinuclear, linear tetranuclear and
one-dimensional Zn(II) complexes with aroylhydrazone Schiff base
Received 00th January 20xx,
Accepted 00th January 20xx
†
Guohong Xu,a Bei-bei Tang,a Liang Hao,a Gui-lei Liu*b and Hui Li*a
DOI: 10.1039/x0xx00000x
Three complexes [Zn(H2L1)(CH3COO)]2·CH3OH (1), [Zn4(H2L2)2(CH3COO)4]·4DMF (2) and {[Zn4(L3)2(CH3COO)4]·DMSO}n (3)
(H3L1 = 4-hydroxy-benzoic acid (2-hydroxy-5-nitro-benzylidene)-hydrazide, H4L2 = 4-hydroxy-3-methoxy-benzoic acid (2,3-
dihydroxy-benzylidene)-hydrazide, H2L3 = (4-nitro-phenoxy)-acetic acid (2-hydroxy-3-methoxy-benzylidene)-hydrazide))
have been synthesized and studied, in which three kinds of ligands have been designed by introducing diversified bridging-
functional groups. The X-ray single-crystal diffraction analysis showed that the 1, 2 and 3 are dinuclear, linear tetranuclear
and 1D chain coorddination complexes, respectively, which achieved the controlled synthesis of multinuclear complexes
through ligand design. The luminescent properties of these crystalized complexes have been investigated both in solution
and solid state.
www.rsc.org/
literature reports10 have indicated that aroylhydrazone ligands
have the potential to construct multinuclear complexes. As an
extension of our research, three novel aroylhydrazone ligands
(H3L1 = 4-hydroxy-benzoic acid (2-hydroxy-5-nitro-benzylidene)
-hydrazide, H4L2 = 4-hydroxy-3-methoxy-benzoic acid (2,3-
dihydroxy-benzylidene)-hydrazide, H2L3 = (4-nitro-phenoxy)-
acetic acid (2-hydroxy-3-methoxy-benzylidene)-hydrazide)
have been successfully designed and synthesized, which
possess different substituent groups and chelating/bridging
mode (Scheme 1,2).
Introduction
Multinuclear metal complexes have received enormous
attentions for decades, not only for their structural diversity,1
but also for their fascinating potential application in various
fields such as water splitting, fluorescent recognition, biological
activity, single-molecule magnets, gas absorption, and
catalysis.2-4 In this regard, multidentate Schiff base ligands can
serve as excellent candidates to construct the above
mentioned complexes. Very recently, by using the chelating
Schiff base ligands, a wide variety of resultant structural motifs
have been obtained, such as cage,5 cubane,6 linear,7 helicates8
and so on. Although the earlier predesign and assembly of
novel crystalline material by structure directing factors, such as
central metal ions, metal-ligand ratio, solvents, temperature,
pH value, and templates, have been validated and summarized,
the most effective way to realize the structural diversity of
Schiff base complexes is the design of novel chelating ligands,
which might provide further insights in designing new
crystalline materials.
Herein, we choose the combination of aroylhydrazone
ligand and zinc acetate as a precursory binary system, and
focus on the effect of different substituent groups of ligands
on mediating the conditions of crystallization under room
temperature synthesis conditions. And three new coordination
complexes [Zn(H2L1)(CH3COO)]2·CH3OH
(
1
), [Zn4(H2L2)2-
(CH3COO)4]·4DMF
were obtained.
(
2)
and {[Zn4(L3)2(CH3COO)4]·DMSO}n
(3)
Complex
complex
1
display a binuclear structure, by comparison,
2
presented a discrete linear tetranuclear cluster
when additional hydroxyl group was introduced at the 3-
position of the benzylidene part, which provided suitable,
disposable bridging groups to control the stereochemistry of
the metallic centers as well as the number of metal ions within
the cluster motifs.6a What’s more, the introduction of the
potential coordination atom (phenoxy O atom) in major
skeleton of the ligand is beneficial to the construction of one-
In our previous work, by using aroylhydrazone Schiff base
ligands, we have successfully obtained linear tetranuclear Zn(
Ⅱ) complex and “less common” cubane Zn4O4 clusters, and
the novel luminescent properties of these complexes have
been studied in detail.6a,9 Our preliminary study and related
dimensional (1D) coordination polymer
3. Particularly worth
mentioning that, the amido (–NH–) group of the ligand in
3
was induced to coordinate with metal ion by the phenoxy O
atom of major skeleton, which is still comparatively rare in
previous reports.11 Furthermore, the luminescent properties of
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filtration, washed with ethanol and diethyl ether, and dried in
air (Scheme S1). Yield: (69%). Selected IR (KBr pellet, cm-1):
ν(O–H) 3202; ν(C
＝O) 1656 ; ν(C＝
N) 1603(s). 1H NMR (400
MHz, DMSO-d6) δ (ppm) 12.45 (s, 1H), 12.11 (s, 1H), 10.22 (s,
1H), 8.71 (s, 1H), 8.58 (s, 1H), 8.17 (d, J = 7.4, 1H), 7.85 (s, 2H),
7.12 (d, J = 6.7, 1H), 6.89 (s, 2H). 13C NMR (175 MHz, DMSO-d6)
δ (ppm) 163.16, 163.08, 161.52, 144.27, 140.32, 130.32,
126.74, 124.51, 123.47, 120.35, 117.54, 115.59.
Synthesis of the ligands H4L2 and H2L3. The procedure for
synthesis of the ligands H4L2 and H2L3 are similar to that of H3L1
except for the replacement of 5-Nitrosalicylaldehyde and 4-
Hydroxybenzhydrazide with 2, 3-dihydroxybenzaldehyde and
vanillic acid hydrazide in H4L2 and 2-hydroxy-3-
methoxybenzaldehyde and (4-Nitro-phenoxy)-acetic acid
hydrazide in H2L3, respectively. For H4L2: Yield: (76%). Selected
Scheme 1 Representation of the effect of substituent of ligand on the structure
of complexes 1-3. The turquoise, red, blue and grey balls represent the zinc,
oxygen, nitrogen and carbon, respectively.
three complexes in the solid state and MeOH solution have
been investigated in detail.
IR (KBr pellet,cm-1): ν(O–H) 3490, 3272; ν(C
＝O) 1636 ; ν(C＝N)
1598. 1H NMR (400 MHz, DMSO-d6) δ (ppm) 11.90 (s, 1H),
11.31 (s, 1H), 9.80 (s, 1H), 9.20 (s, 1H), 8.57 (s, 1H), 7.49 (m,
2H), 6.95 – 6.75 (m, 4H), 3.86 (s, 3H). 13C NMR (175 MHz,
DMSO-d6) δ (ppm) 162.90, 150.87, 148.76, 147.86, 146.50,
146.05, 123.92, 121.90, 120.58, 119.60, 119.27, 117.74, 115.54,
112.08, 56.20. For H2L3: Yield: (65%). Selected IR (KBr
Experimental
Materials and measurements
All starting materials and solvents used in this work were of
analytical grade and used as purchased from Alfa Aesar
Chemical Company without further purification. Organic
solvents with analytical purity were supplied by commercial
sources and used as received. Elemental analyses (C, H, N)
were performed on a Flash EA1112 microanalyzer at the
Beijing Institute of Technology. FT-IR spectrum is recorded in
the Nicolet-360 FT-IR spectrometer as KBr pellets in the 4000–
400 cm-1 region. The UV-vis absorption spectra were examined
on a JASCO UV-1901 spectrophotometer in the wavelength
range of 200−800 nm. The photoluminescent (PL) spectra were
pellet,cm-1): ν(O–H) 3090; ν(C
＝O) 1674 ; ν(C＝
N) 1612. 1H
NMR (400 MHz, DMSO-d6): δ (ppm) 11.85 (s, 1H), 11.66 (s, 1H),
10.60 (s, 1H), 9.37 (s, 1H), 8.56 (s, 1H), 8.36 (s, 1H), 8.25 – 8.20
(m, 2H), 7.42 – 7.09 (m, 3H), 7.09 – 6.94 (m, 1H), 6.87 – 6.82
(m, 1H), 5.33 (s, 1H), 4.89 (s, 1H), 3.83 (s, 3H). 13C NMR (175
MHz, DMSO-d6) δ (ppm) 168.32, 164.11, 163.74, 163.41,
148.50, 148.43, 148.40, 147.50, 146.45, 141.91, 141.82, 141.40,
126.29, 126.16, 120.87, 120.84, 119.59, 119.55, 119.38, 118.21,
115.81, 115.65, 114.29, 113.42, 67.05, 65.91, 56.30, 56.26.
Synthesis of [Zn(H2L1)(CH3COO)]2·CH3OH (1). The solution of
Zn(CH3COO)2·2H2O (44 mg, 0.2 mmol) in 2 mL acetonitrile was
added to methanol solution (14mL) of H3L1 (15mg, 0.05 mmol)
with continuous stirring ca. 30 min. The result solution was
then filtered and left at room temperature to give a yellow
solution. Yellow single crystal suitable for X-ray analysis was
produced by slow evaporation of the mother liquor for two
days. Yield: 68%. Anal. Calc. for C33H30N6O15Zn2: C, 44.93; H,
3.40; N, 9.53. Found: C, 44.85; H, 3.43; N, 9.48. Selected IR (KBr
recorded by using
a
Hitachi F-7000 luminescence
spectrophotometer equipped with a 450 W xenon lamp as the
excitation source, and the measurements were performed at
room temperature. The photomultiplier tube voltage was 700
V, the scan speed was 1200 nm·min–1, and the slit width was
2.5 nm (5.0 nm). Thermo-gravimetric analyses (TGA) were
carried out on a SEIKO TG/DTA 6200 thermal analyzer from
room temperature to 800 °C at a ramp rate of 10 °C/min in a
flowing 50 mL/min nitrogen atmosphere. X-ray powder
diffraction (XPRD) of samples were measured using a Japan
pellet, cm-1): ν(O–H) 3434, 3178; ν(C
νasym (COO-) 1612; νsym (COO-) 1362.
＝O) 1598 ; ν(C＝N) 1533;
Synthesis of [Zn4(H2L2)2(CH3COO)4]·4(DMF) (2). The solution
Rigaku D/Max
γ A X-ray diffractometer equipped with
graphite-monochromatized Mo-Kα radiation (λ = 0.71073 Å).
1H NMR and 13C NMR spectra were recorded on Bruker Avance
of Zn(CH3COO)2·2H2O (44 mg, 0.2 mmol) in 6 mL methanol was
added to DMF solution (4mL) of H4L2 (15mg, 0.05 mmol) with
continuous stirring ca. 30 min. The result solution was then
filtered and left at room temperature to give a yellow solution.
Yellow single crystal suitable for X-ray analysis was produced
by slow evaporation of the mother liquor for one day. Yield:
60%. Anal. Calc. for C50H64N8O22Zn4: C, 43.21; H, 4.47; N, 8.07.
Found: C, 43.25; H, 4.46; N, 8.03.Selected IR (KBr pellet, cm-1):
Ⅲ HD (400 and 175 MHz, respectively) spectrometers in
DMSO-d6 with Me4Si as the internal standard.
Synthetic procedures
Synthesis of the ligand H3L1. The ethanol (20mL) solution of
5-Nitrosalicylaldehyde (1.671g, 0.01mol) was added dropwise
to the ethanol (20mL) solution of 4-Hydroxybenzhydrazide
(1.522g, 0.01mmol) with stirring. The addition of 1 drop of
concentrated hydrochloric acid induced a colour change along
with immediate precipitation. Then, the mixture was refluxed
for 8 hours with vigorous stirring and subsequently cooled to
room temperature. The yellow solid was collected by vacuum
ν(O–H) 3225; ν(C
sym (COO-) 1391.
Synthesis of {[Zn4(L3)2(CH3COO)4]·DMSO}n (3). The solution
＝O) 1609 ; ν(C＝
N) 1556; νasym (COO-) 1653;
ν
of Zn(CH3COO)2·2H2O (88 mg, 0.4 mmol) in 9 mL isopropanol
was added to DMSO solution (1.6mL) of H2L3 (34mg, 0.1 mmol)
with continuous stirring ca. 1 hour. The result solution was
2 | J. Name., 2012, 00, 1-3
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then filtered and left at room temperature to give a yellow
solution. Yellow single crystal suitable for X-ray analysis was
produced by slow evaporation of the mother liquor for five
days. Yield: 76%. Anal. Calc. for C42H44N6O21SZn4: C, 39.92; H,
3.49; N, 6.65. Found: 39.88; H, 3.44; N, 6.68. Selected IR (KBr
pellet, cm-1): ν(O–H) 3411; ν(C
(COO-) 1627; νsym (COO-) 1341.
＝O) 1595 ; ν(C＝N) 1553; νasym
X-ray crystallography
Suitable single crystals with dimensions of 0.44 × 0.17 × 0.09
mm, 0.41 × 0.17 × 0.05 mm and 0.17 × 0.11 × 0.06 mm for
Scheme 2 (a) The η2:η1: η1:μ2 chelating/bridging mode of ligand in
η1: η1:μ3 chelating/bridging mode of ligand in . (c) The η1: η2:η1: η1: η1: η1:μ3
chelating/bridging mode of ligand in
1
. (b) the η2: η2:
2
complexes 1, 2 and 3 were selected for single-crystal X-ray
3.
diffraction analysis, respectively. Diffraction intensities for the
three complexes were collected on a Rigaku RAXIS-RAPID CCD
diffractometer equipped with a graphite-monochromatic Mo-
Kα radiation (λ =0.71073Å) using a ω scan mode for complexes
were located from the different Fourier map and refined
isotropically. Crystallographic data are given in Table 1.
Selected bond distances and angles are given in Table S1, ESI.†
CCDC 941209 (1), CCDC 938714 (2) and CCDC 938713 (3)
contain the supplementary crystallographic data for this paper.
1
at 296(2) K and
were collected in the
26.00° for and 1.92
2,
3
at 153(2) K. Diffraction intensity data
range of 1.71 25.01° for , 2.44
29.19° for . The collected data were
θ
～
～
1
～
2
3
reduced using the SAINT program, and empirical absorption
corrections were performed using the SADABS program.12
Three structures were solved by direct methods13 and refined
using full-matrix least square techniques on F2 (ref. 14) with
the program SHELXL-97.12 All non-hydrogen atomic positions
were located in difference Fourier maps and refined
anisotropically. Some of hydrogen atoms were placed in their
geometrically generated positions and other hydrogen atoms
Results and Discussion
Crystal structure of [Zn(H2L1)(CH3COO)]2·CH3OH (1)
X-ray crystallographic analysis revealed that
1 is a binuclear
molecule and crystallizes in the triclinic space group of P-1, and
its asymmetric unit contains one Zn(II) ion, one partially
Table 1 Crystal data and structure refinement of complexes 1, 2 and 3
Complexes
1
2
3
Formula
M/mol-1
C33H30N6O15Zn2
881.41
C50H64N8O22Zn4
1390.56
Triclinic
P-1
C42H44N6O21SZn4
1262.37
Monoclinic
C2/c
Crystal system
Space group
Triclinic
P-1
a
/Å
8.8740(18)
9.5171(18)
11.986(2)
84.921(3)
85.114(4)
74.714(4)
970.6(3)
1
8.4550(17)
13.485(3)
14.017(3)
115.54(3)
95.02(3)
94.99(3)
1422.6(5)
1
38.142(8)
11.411(2)
29.647(6)
90
b/Å
c
/Å
/°
/°
/°
α
β
129.94(3)
90
γ
V/Å3
9893(3)
8
Z
T(K)
296(2)
153(2)
153(2)
ρ
/g·cm-3
μ/mm-1
1.508
1.621
1.695
1.311
1.752
2.044
F(000)
450
714
5136
θmin
S
,
θ
max/°
1.71, 25.01
1.171
2.44 , 26.00
1.023
1.92, 29.19
1.061
Rint
0.0347
0.0336
0.0514
0.0730
R1 [I>2σ(I)]
0.0845
0.0332
wR2 [I>2σ(I)]
max,min(e Å-3)
0.2257
0.0797
0.2008
ꢀ
ρ
1.137, -1.135
0.568 , -0.432
1.514, -1.798
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Fig. 2 (a) ORTEP picture showing the coordination environment of the Zn(Ⅱ) ion and
ligand in complex 2 (50% probability ellipsoids, hydrogen atoms are omitted for clarity).
(b) The polyhedral representations of the 1D chain structure in 2 by H-bonding (O8–
H8B···O11: 1.901, 2.635, 148.5, C24–H24F···O5: 2.586, 3.451, 150, dashed line).
Fig. 1 (a) ORTEP picture showing the coordination environment of the Zn(Ⅱ) ion and
ligand in complex 1 (50% probability ellipsoids, hydrogen atoms are omitted for clarity).
(b) The polyhedral representations of the 1D chain structure in 1 by H-bonding (O3–
H3···O4: 1.871, 2.662, 161.73, dashed line). (c) The 2D layer structure of 1 by H-
bonding (N1–H1···O5: 1.961, 2.741, 150.17, pink dashed line). (d) Packing diagram of 1
showing non-conventional H-bonding between different 2D layers (C2–H2B···O6: 2.473,
3.274, 151.3; C12–H12B···O7: 2.477, 3.338, 154.1, blue dashed line).
Different to the complex
[Zn2(H2L2)(CH3COO)2] in
1
,
the two asymmetrical units
2
are bridged through the 3-position
deprotonated hydroxyl group oxygen atom (O1) in the ligand
to form linear Zn4 cluster, and each [H2L2]2- ligand coordinates
to three Zn(II) ions with the imine–N, carbonyl–O and the two
bridging phenoxo–O atoms combining with two bridging
acetate ligands (syn-syn mode). The distance of Zn1–Zn2 in the
asymmetrical unit is 3.2973Å and that of Zn2–Zn2# between
the two asymmetrical units is 3.2280 Å. The coordination
deprotonated [H2L1]- ligand and one acetate. As shown in Fig.
1a, Each Zn(II) center is in a NO4 distorted square pyramidal
coordination geometry with one oxygen atom (O4) from
acetate in axis positions with Zn–O4 of 2.003(7) Å and three
mode of [H2L2]2- ligand in
2
displays η2: η2: η1: η1:μ3
oxygen atoms (O1, O2, O2#1; #1: -x+1,-y+1,-z+2) and one
nitrogen atom (N2) from two equivalent [H2L1]- ligands in the
equatorial positions, which is reflected by the τ value (0.317)
defined by Addison et al. (τ= 0 for an ideal square pyramid, and
1 for an ideal trigonalbipyramid).15 The basal plane of the
square pyramid is defined by O1, O2, N2 and O2#1 atoms, with
the bond distances ranging from 2.015(6) to 2.095(7) Å and
bond angles ranging from 77.0 to 155.1°. The Zn(II) ion lies
approximately in the equatorial position with a deviation
(0.2084 Å) from the basal plane. The coordination mode of the
chelating/bridging mode (Scheme 2b). The Zn(II) centers are
also five coordinated with slightly different coordination
environments of Zn1–NO4 and Zn2–O5, respectively.
Alternatively, the coordination geometry of Zn(II) in
2 can be
regarded as intermediate between a squared-based pyramid
and a trigonal bipyramid (Zn(1): τ= 0.54; Zn(2): τ= 0.43). The
coordination mode of acetate in
2 is different from that in 1,
which plays the role of bridge ligand in the
[Zn2(H2L2)(CH3COO)2] fragment. The linear Zn4(H2L2)2 fragment
[H2L1]- ligand in
1
displays η2:η1:η1:μ2 chelating/bridging mode
is almost coplanar (Fig. S10, ESI†). The coordinated acetate
ligands are located up and down the plane, which is similar to
tetranuclear Zn(II) complex in our previous report.6a
(Scheme 2a). The Zn(1)–Zn(1)#1 distance is 3.146 Å, implying
the existence of d10–d10 weak interactions.16 The benzene rings
of one ligand are non-coplanar and the dihedral angle is 13.1°.
The linear Zn4 clusters are linked by H-bonding between
solvent DMF molecules and neighboring [Zn2(H2L2)(CH3COO)2]2
fragments to 1D chains (Fig. 2b), which are extended to a 2D
layer by non-conventional H-bonding between acetates and
terminal –OCH3 groups of neighbouring fragments (Fig. S11a,
As expected, each molecule of
1 interacts with two
neighbours to form 1D chains by H-bonding between
uncoordinated hydroxyl and acetate (O3–H3···O4: 1.871, 2.662,
161.73, Fig. 1b). In addition, the adjacent 1D chains were
further assembled by N1–H1···O5 between acetate group and
amido to form 2D layer structure (Fig. 1c). Further, the 2D
layers aggregate together through non-conventional H-
bonding between aromatic rings (C-H) and terminal nitro
groups (Fig. 1d).
ESI
terminal –OCH3 group in the ligand (H4L2) influence the
supramolecular structure of which is different from
tetranuclear Zn(II) complex reported in literature.6a
Complex is different from , which indicated that the
†). It is worth mentioning that the solvent molecule and
2,
2
1
additional hydroxyl group at the 3-position of salicylaldehyde
ring can play a bridging role to control the stereochemistry of
metallic centers as well as the number of metal ions within the
cluster motifs. On the other hand, the methoxy group at
hydrazide ring can only be involved in H-bonding to
contributing the supramolecular structure.
Crystal structure of [Zn4(H2L2)2(CH3COO)4]·4(DMF) (2)
To investigate the influence of substituent (-OH) at the 3-
position of salicylaldehyde ring on the structure of resulting
complex, reaction of the ligand H4L2 and Zn(CH3COO)2
·2H2O
was carried out and complex
2 was isolated. Complex 2 is a
linear tetranuclear cluster crystallizes in triclinic space group P-
1, and its asymmetric unit contains two Zn(II) ions (Zn1, Zn2),
one partially deprotonated [H2L2]2- ligand and two acetates.
Crystal structure of {[Zn4(L3)2(CH3COO)4]·DMSO}n (3)
In complexes 1 and 2, the amido (–NH–) group of ligand
does not coordinate with metal ion as in previous reports,10
and has no contribution to the expansion of the coordination
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Metal-organic complexes have been reported to have
abilities that affect the emission wavelength and intensity of
the organic material through metal coordination.17 Therefore,
it is important to investigate the luminescent properties of
metal-organic complexes in view of potential applications.
Therefore, the photoluminescent properties of complexes 1-3
as well as the relative ligands were investigated at room
temperature in the solid state (Fig. 4). It is shown that complex
1
has a broad emission with maximum at 498 and 524 nm,
accompanied by a shoulder peak at 400nm (λex = 293 nm),
while the H3L1 ligand displays a broad emission at 494 and 542
nm (λex = 293 nm). Apparently, the emission at 498 and 524
nm of complex
1
is similar to that of the ligand H3L1, indicating
is L-based emission, and the
Fig. 3 (a) ORTEP picture showing the coordination environment of the Zn(Ⅱ) ion and
ligand in complex 3 (50% probability ellipsoids, hydrogen atoms are omitted for clarity).
(b) The polyhedral representations of the 1D chain structure in 3.
that the dinuclear complex
1
relatively lower peak at 400 nm can be attributed to ligand-to-
metal charge transfer (LMCT) transition. Meanwhile, under λex
= 316 nm excitation, the emission for molecular cluster
2 is at
polymer. Complex
3 with 1D chain structure was successfully
548 nm, accompanied by a lower peak at 388 nm, compared to
the emission of the ligand H4L2 (λem = 436, 470 and 552 nm, λex
= 316 nm), the peaks at 388 and 548 nm can be attributed to
ligand-to-metal charge transfer (LMCT) and π-π* intraligand (IL)
transitions, respectively. In the same way, when λex = 312 nm,
obtained by the self-assembly of ligand H2L3 and
Zn(CH3COO)2·2H2O. The phenoxy group at the major skeleton
and the methoxy group at the 3-positon of salicylaldehyde ring
have significant effects on the coordination geometry of Zn(II)
ions and the coordination mode of the ligand, which leads to
the complex
3 exhibits green luminescence with the peak at
different connections of Zn(II) ions relative to the complexes
and
1
533 nm, accompanied by a shoulder peak at 379 nm,
compared to the emission of the ligand H2L3 (λem = 413, 468
2
.
X-ray crystallographic analysis revealed that
3
crystallizes in
and 521 nm, λex = 312 nm). In a word, complexes 1–3 display
the monoclinic space group of C2/c. The asymmetric unit of
3
ligand-based fluorescence emissions mainly and accompanied
by a ligand-to-metal charge transfer (LMCT) transition in the
solid state.
contains four Zn(II) ions, two completely deprotonated [L3]2-
ligand, four acetate groups (syn-syn mode) and one DMSO
molecule. The amido (–NH–) group of H2L3 is also
deprotonated and coordinate with Zn(II) ion. The Zn1 and Zn4
ions are all five coordinated with coordination environments of
Zn–NO4 (imine–N, carboxide–O, phenolic–O and acetate–O).
The coordination geometry of Zn1 can be regarded as
distorted square pyramidal geometry (Zn1: τ= 0.231), where
the oxygen atom of acetate group (O2) occupies the apical
position. The Zn1 ion is placed at 0.4122 Å from the basal
plane. The coordination geometry of Zn4 can be regarded as
intermediate between a squared-based pyramid and a trigonal
bipyramid (Zn4: τ= 0.566). The Zn2 and Zn3 ions are all six
coordinated with coordination environments of Zn–NO5
(amido–N, methoxy–O, phenoxy–O, phenolic–O and acetate–O)
and can be regarded as a distorted octahedral geometries. The
distance of Zn1–Zn2, Zn2–Zn4 and Zn1–Zn3 in asymmetrical
unit is 4.8134Å, 3.2084 Å and 3.1463 Å, respectively. The
The UV-vis spectra and photoluminescent properties of
ligands H3L1
,
H4L2
,
H2L3 and complexes
1
-
3
in the MeOH
solution were also studied to further understand their solution
fluorescent behaviour (section 6, ESI ). It is shown that
complexes have a broad emission with maxima at 443, 498
and 458 nm respectively, while the ligands H3L1 H4L2 and H2L3
have a broad emission at 488, 431 and 415 nm respectively.
Compared with the ligands, a blue-shift (45 nm) for and red-
shift (67 nm and 43 nm) for and emissions are observed.
†
1-3
,
1
2
3
coordination mode of [L3]2- ligand in
3
displays
η1:η2:η1:η1:η1:η1:μ3 chelating/bridging mode (Scheme 2c). Each
[L3]2- ligand acts as a double-chelating and bridging ligand
linking Zn(II) ions to form 1D chains, which is very unusual
coordination mode for aroylhydrazone ligands. Again, these 1D
chains are assembled through non-conventional H-bonding
between aromatic rings (C-H) with terminal nitro groups and
methylene groups (C-H) with acetates to 2D layer structure (Fig. S12,
ESI†).
Fig. 4 Normalized emission spectra of the H3L1, H4L2, H2L3, 1, 2 and 3 in the solid state at
Luminescent Properties
room temperature (λex = 293 nm for H3L1 and 1, λex = 316 nm for H4L2 and 2 and λex
312 nm for H2L3 and 3).
=
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ARTICLE
Journal Name
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Y. Wu, L. Zhao, C. He and C. Y. Duan, Chem. Eur. J., 2014, 20
Combining previous studies, these red-shifts and blue-shift may be
caused by a ligand-to-metal charge-transfer (LMCT) transition.
Complexes 1-3 display ligands-based fluorescence emissions in
MeOH solution.
,
2224–2231. (e) S. R. Hermida, A. B. Lago, R. Carballo, O.
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Conclusions
In summary, three aroylhydrazone ligands and their Zn(II)
coordination complexes have been synthesized in this work.
The complex
1
displayed a binuclear Zn(II) structure,
2
3
presented a discrete linear tetranuclear Zn(II) structure and
is 1D coordination polymer. It is a successful story to control
the nuclear number and molecular structures of multi-nuclear
coordination complex based on rational ligand design.
Importantly, it is the first time to realize the amido (–NH–)
group of aroylhydrazone ligand can coordinate to metal ion
and exhibits a double-chelating and bridging coordination
mode. So, the substituent at the 3-position of salicylaldehyde
ring can provide potential coordination donors (phenoxy O
atom) will be beneficial to the construction of coordination
polymers. The ligand-based fluorescence emissions of
Mukhopadhyay and S. K. Bhutia, Dalton Trans., 2014, 43
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6
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complexes 1–3 in the solid state and MeOH solution have been
studied according to their crystal strcutures. We believe that
the three complexes presented here can provide us an
opportunity to further design and construct coordination
polymers with specific structures and photoluminescent
properties, which are now underway.
7
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This work was financially supported by the National Natural
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6 | J. Name., 2012, 00, 1-3
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Table of Contents
The controlling of multinuclear Zn(II) coordination complexes from dinuclear, linearly tetranuclear to extending 1D structures has been
achieved based on ligand design.
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