Synthesis and characterization of copper(II) Complexes with Salen-Type Bisoxime chelating Ligand

Article abstract of DOI:10.14233/ajchem.2014.15549

Two Cu(II) complexes 1 and 2 have been synthesized by the reaction of copper(II) picrate tetrahydrate and copper(II) perchlorate hexahydrate with a Salen-type bisoxime chelating ligand (H₂L = 6,6'-dimethoxy-2,2'- [ethylenedioxybis(nitrilomethylidyne)]diphenol) and characterized by elemental analyses, IR spectra, UV-visible spectra, TG-DTA analyses and molar conductances. The Salen-type bisoxime is a good tetradentate N₂O ₂-donating ligand and the likely formula of the Cu(II) complexes may be suggested as CuL(HPic)₂ (1) and CuL2H₂O (2).

Full text of DOI:10.14233/ajchem.2014.15549

Asian Journal of Chemistry; Vol. 26, No. 3 (2014), 799-801
http://dx.doi.org/10.14233/ajchem.2014.15549
Synthesis and Characterization of Copper(II) Complexes with
Salen-Type Bisoxime Chelating Ligand
*
YIN-XIA SUN , XIN-RAN LI, RUI-E LU and WEI-SHENG MENG
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P.R. China
*Corresponding author: E-mail: sun_yinxia@163.com
Received: 29 March 2013;
Accepted: 29 May 2013;
Published online: 30 January 2014;
AJC-14640
Two Cu(II) complexes 1 and 2 have been synthesized by the reaction of copper(II) picrate tetrahydrate and copper(II) perchlorate hexahydrate
with a Salen-type bisoxime chelating ligand (H2L = 6,6'-dimethoxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol) and characterized
by elemental analyses, IR spectra, UV-visible spectra, TG-DTA analyses and molar conductances. The Salen-type bisoxime is a good
tetradentate N2O2-donating ligand and the likely formula of the Cu(II) complexes may be suggested as CuL·(HPic)2 (1) and CuL·2H2O
(2).
Keywords: Cu(II) complex, Bisoxime ligand, Synthesis.
a heating rate of 5 °C/min on a ZRY-1P thermoanalyzer. Molar
INTRODUCTION
conductance value measurement was carried out on a model
Oxime-type compounds have long been used as chelating
DDS-11D type conductivity bridge using 1.0 × 10-3 mol dm-3
ligands in the synthesis of transition metal complexes due to
solution in DMF at 25 °C.
their ease of preparation and structural variety. These comp-
Synthesis of ligand (H2L): The ligand H2L was synthe-
ounds can accommodate one, two or more metal centers and
sized with a slightly modified method reported literature4.
form homo- and heteronuclear metal complexes with interes-
Reaction of 1,2-bis(aminooxy)ethane (133.7 mg, 1.45 mmol)
ting properties1-4, such as excellent catalytic activity for epoxi-
with 2 equiv. of 3-methoxy-2-hydroxybenzaldehyde (456 mg,
dation and aziridination5. In addition, they are also used as
3.00 mmol) in ethanol (10 mL) at 55 °C for 6 h.After cooling to
models for reaction centers in metalloenzymes6, non-linear
room temperature, the resulting solid was filtered and washed
optical materials7 and molecular recognition and biological
with ethanol and ethanol/hexane (1:4), respectively. The product
activity8. Herein, a new Salen-type bisoxime chelating ligand
was dried in vacuo and obtained 483.7 mg of colorless micro-
(H2L = 6,6'-dimethoxy-2,2'-[ethylenedioxybis(nitrilomethyli
crystal. m.p. 120-121 °C.
dyne)]diphenol) and its Cu(II) complexes 1 and 2 have been
Synthesis of Cu(II) complex 1: A solution of copper(II)
synthesized and structurally characterized.
picrate tetrahydrate (59.3 mg, 0.10 mmol) in ethanol (3 mL)
EXPERIMENTAL
was added dropwise to a solution of H2L (36.2 mg, 0.10 mmol)
in ethanol (3 mL) at room temperature. A green solution was
obtained and stirred vigorously and refluxed for 3 h. The
resulting solid was filtered off, washed with ethanol/ether (1:4)
and ether, respectively. The product was dried in vacuo and
obtained 47.8 mg of pale-green solid.
3-Methoxy-2-hydroxybenzaldehyde (≥ 98 %) was pur-
chased fromAlfa Aesar and used without further purification.
1,2-Bis(aminooxy)ethane was synthesized according to an
analogous method reported earlier4. The other reagents and
solvents were analytical grade reagents from Tianjin Chemical
Reagent Factory and were used without further purification.
Elemental analysis for Cu was detected by an IRIS ER/S·WP-
1 ICP atomic emission spectrometer. C, H and N analyses were
carried out with a GmbHVariuoELV3.00 automatic elemental
analyzer. FT-IR spectra were recorded on a VERTEX70 FT-IR
spectrophotometer, with samples prepared as KBr (400-4000
cm-1). UV-visible absorption spectra were recorded on a Shimadzu
UV-2550 spectrometer. TG-DTA analyses were carried out at
Synthesis of Cu(II) complex 2: To an ethanol solution
(5 mL) of H2L (35.9 mg, 0.10 mmol) was added an ethanol
solution (5 mL) of copper(II) perchlorate hexahydrate (37.1
mg, 0.10 mmol). After the mixture solution had been stirred
at 55 °C for 4 h, the formed precipitate was separated by filtra-
tion and washed successively with ethanol and ether, respec-
tively. The product was dried under reduced pressure to obtain
25.5 mg of pale-green solid.

800 Sun et al.
Asian J. Chem.
TABLE-1
COLOUR, YIELDS AND ANALYTICAL DATA OF H2LAND ITS COPPER(II) COMPLEXES
Found (calcd.) (%)
Molar conductance
(S cm2 mol-1)
Comp.
H2L
m.f. (m.w.)
Colour
Yield (%)
C
H
N
Cu
–
C18H20N2O6
(360.4)
59.97
(59.99)
40.89
5.87
(5.59)
3.11
7.61
(7.77)
12.58
(12.73)
6.08
Colorless
Pale-green
Pale-green
83.6
54.3
55.7
–
C30H24N8O20Cu
(880.1)
7.15
(7.22)
13.69
1
2
2.78
1.53
(40.94)
47.38
(47.21)
(2.75)
4.66
(4.84)
C18H22N2O8Cu
(457.9)
(6.12)
(13.88)
at 1576, 1545 cm-1 and 1368, 1337 cm-1. This indicates that
some of the nitryl O atoms take part in coordination10. The
broad bands at 3446 cm-1 are ascribed to the vibration of the
water mole-cules in complex 211.
RESULTS AND DISCUSSION
Composition of Cu(II) complexes: The analytical results
of Cu(II) complexes 1 and 2 are given in Table-1. Their compo-
sitions agree with the formula CuL·(HPic)2 for complex 1 and
CuL·2H2O for complex 2. The molar conductance values of
complexes 1 and 2 in 1.0 × 10-3 mol dm-3 DMF solutions are
2.78 and 1.52 S cm2 mol-1 at 21 °C, respectively, indicating
that both are non-electrolytes. This implies that all of the
picrate groups in complex 1 are present in the coordination
sphere maybe through the hydrogen-bonding interactions in
solution or solid state.
UV-visible spectra of H2L and Cu(II) complexes: The
absorption spectra of H2L and its corresponding Cu(II) comp-
lexes 1 and 2 (Table-3), in diluted DMF solution show that the
spectra of complexes 1 and 2, are similar to each other, but are
different from the spectrum of the ligand (H2L). The UV-visible
spectrum of the free ligand H2L exhibits two absorption peaks
at 272 and 318 nm. The former absorption peak at 272 nm can
be assigned to the π-π* transition of the benzene rings and the
latter one at 318 nm can be attributed to the intra-ligand π-π*
transition of the C=N bonds12.
IR spectra of H2L and Cu(II) complexes: The most
important FT-IR spectra data for H2L and its corresponding
Cu(II) complexes are given in Table-2. The characteristic C=N
stretching band of the free ligand H2L appears at 1605 cm-1,
while the C=N bands of Cu(II) complexes 1 and 2 are observed
at 1608 and 1607 cm-1, respectively. TheAr-O stretching bands
occur at 1262 cm-1 for H2L, whereas those at 1256 cm-1 and
1255 cm-1 for complexes 1 and 2, respectively. This shifting
of C=N and Ar-O stretching frequency indicate that the Cu-N
and Cu-O bonds are formed between the Cu(II) ions and the
oxime N atoms and the phenolic oxygen atoms of the ligand
L2- unit4. The O-H stretching band of the free ligand H2L
appears at 3435 cm-1, which disappears in complexes 1 and 2,
indicating the oxygen atoms in the phenolic alcohol groups
have been completely deprotoned and coordinated to Cu(II)
ions. In addition, the OH out-of-plane bending vibration of
the free picric acid at 1150 cm-1 appears in the spectra of com-
plex 1, indicating that the H-atom of the OH group existed in
complex 19. Free picric acid has νas(-NO2) and νs(-NO2) at
1555 and 1342 cm-1, respectively, which split into two bands
Compared with the absorption peak of the ligand, a corres-
ponding absorption peak at 308 and 307 nm is observed in
complexes 1 and 2, respectively, which is hypsochromically
shifted by 10 nm, indicating the coordination of Cu(II) ions
with the ligand. Meanwhile, the absorption band at about 318
nm disappears from the UV-visible spectra of complexes 1 and
2, which indicates that the oxime nitrogen atom is involved in
coordination to the metal atom13,14. In addition, the new bands
observed at 360 and 375 nm for complexes 1 and 2 are assigned
to the n-π* charge transfer transition from the filled pπ orbital
of the bridging phenolic oxygen to the vacant d-orbital of the
Cu(II) ions, which are characteristic of the transition metal
complexes with N2O2 coordination spheres4,15
.
Thermal properties: The thermal decomposition process
of complexes 1 and 2 can be divided into three stages. The
initial weight loss occurs in the range 152-185 °C for complex
1 and 124-150 °C for complex 2, corresponding to an endo-
thermic peak and the TG curve shows that the weight loss
corresponding to this temperature range is 25.9 and 12.1 %
that roughly coincides with the value of 26 and 11.8 %,
respectively, calculated for the loss of two picric acid mole-
cules of complex 1 and two water molecules of complex 2.
On further heating, two exothermic peaks successively at 259
and 329 °C for complex 1 (261 and 341 °C for complex 2) in
the DTA curve and a continued weight loss occurs in the TG
curve. Then, the second strong exothermic peak at 329 °C for
TABLE-2
KEY FT-IR BANDS FOR H2L
AND ITS COPPER(II) COMPLEXES (cm-1)
ν (C=C) benzene
ring skeleton
Comp.
ν(C=N) ν(Ar-O)
ν(O-H)
H2L
1
1605
1608
1607
1262
1256
1255
3435
3452
3446
1594, 1512, 1413
1596, 1413, 1415
1596, 1413, 1416
2
TABLE-3
UV-VISIBLE SPECTRA DATA OF H2L AND ITS COPPER(II) COMPLEXES
First band
Second band
ε2 (×104 L mol-1 cm-1)
Concentration (×10-4 mol L-1)
Comp
λmax1(nm)
ε1 (×104 L mol-1 cm-1)
λmax2(nm)
H2L
1
1.00
1.00
1.00
272
308
307
2.599
32.42
33.12
318
360
375
0.826
25.64
24.65
2

Vol. 26, No. 3 (2014)
Synthesis of Copper(II) Complexes with Salen-Type Bisoxime Chelating Ligand 801
and G.L. Liu, Transition Met. Chem., 32, 702 (2007); (f) W.K. Dong,
complex 1 (at 341 °C for complex 2) accompanied with further
decomposition of the compound and the final solid product is
likely to CuO with a residual value of 10.1 % (theoretical value,
9.0 %) for complex 1 and 18.6 (theoretical value, 17.4 %) for
complex 2 when the temperature is above 800 °C.
J.Y. Shi, J.K. Zhong, Y.Q. Tian and J.G. Duan, Chin. J. Inorg. Chem.,
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ACKNOWLEDGEMENTS
The authors thank theYoung Scholars Science Foundation
of Lanzhou Jiaotong University (2011007) and the Funda-
mental Research Funds (212086) for the Gansu Province
Universities for financial support of this work.
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