Synthesis and structure characterization of copper(II) complexes with 5,5'-dihydroxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol

Article abstract of DOI:10.14233/ajchem.2013.15626

A new tetradentate bis-oxime chelating ligand, 5,5'-dihydroxy-2,2'- [ethylenedioxybis(nitrilomethylidyne)]diphenol (H₄L) and its two Cu(II) complexes 1 and 2 have been synthesized by the reaction of H₄L with copper(II) acetate monohydrate and copper(II) picrate tetrahydrate, respectively. The complexes have been characterized by elemental analyses, IR spectra, UV-visible spectra, TG-DTA and molar conductances. The salen-type bisoxime chelating ligand is a good tetradentate N₂O ₂-donating ligand and the likely formulae of the Cu(II) complexes may be suggested as [Cu(H₂L)]CH₃CH₂OH ₂H₂O (1) and [Cu₂ (H₂L)(picrate) ₂]H₂O (2).

Full text of DOI:10.14233/ajchem.2013.15626

Asian Journal of Chemistry; Vol. 25, No. 16 (2013), 9359-9361
http://dx.doi.org/10.14233/ajchem.2013.15626
Synthesis and Structure Characterization of Copper(II) Complexes with
5,5'-Dihydroxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol
*
YU-HUA YANG, LI-SHA ZHANG, GANG LI , MENG-MENG ZHAO, ZHENG-KUN WANG, XIN-YING ZHANG and JIAO-LONG MENG
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P.R. China
*Corresponding author: E-mail: li_gang78@126.com
(Received: 12 April 2013;
Accepted: 25 September 2013)
AJC-14178
A new tetradentate bis-oxime chelating ligand, 5,5'-dihydroxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol (H4L) and its two
Cu(II) complexes 1 and 2 have been synthesized by the reaction of H4L with copper(II) acetate monohydrate and copper(II) picrate
tetrahydrate, respectively. The complexes have been characterized by elemental analyses, IR spectra, UV-visible spectra, TG-DTA and
molar conductances. The salen-type bisoxime chelating ligand is a good tetradentate N2O2-donating ligand and the likely formulae of the
Cu(II) complexes may be suggested as [Cu(H2L)]·CH3CH2OH·2H2O (1) and [Cu2(H2L)(picrate)2]·H2O (2).
Key Words: Cu(II) complex, Salen-type bisoxime compound, Synthesis, Characterization.
spectrometer. C, H and N analyses were carried out with a
GmbH VariuoEL V3.00 automatic elemental analyzer. FT-IR
spectra were recorded on a VERTEX70 FT-IR spectropho-
tometer, with samples prepared as KBr (4000-400 cm-1). UV-
VIS absorption spectra were recorded on a Shimadzu UV-2550
spectrometer. TG-DTA analyses were carried out at a heating
rate of 5 ºC/min on a ZRY-1P thermoanalyzer. Melting points
were obtained by use of an X4 microscopic melting point
apparatus made in Beijing Taike Instrument Limited Company
and were uncorrected. Molar conductance value measurements
were carried out on a model DDS-11D type conductivity bridge
using 1.0 × 10-3 mol dm-3 solution in DMF at 25 °C.
INTRODUCTION
In recent years, transition metal complexes bearing an
N,N-disalicylideneethylenediamine (Salen) ligand or its
analogues are extensively studied because these complexes
are used as catalysts in various organic reactions1, non-linear
optical materials2 and exhibit interesting magnetic properties3.
The oxime-type ligands should be stable enough to resist the
metathesis of the C=N bonds4. Linear derivatives bearing two
salicylaldoxime moieties at both ends have been reported. In
this paper, a new Salen-type chelating ligand based on
O-alkyloxime instead of the imine moiety, 5,5'-dihydroxy-2,2'-
[ethylenedioxybis(nitrilomethylidyne)]diphenol (H4L) (Fig. 1)
and the corresponding copper(II) complexes were synthesized
and characterized.
Synthesis of ligand H4L: A solution of 1,2-bis(amino-
oxy)ethane (92.5 mg, 1.00 mmol) in ethanol (8 mL) was added
to a solution of 2,4-dihydroxybenzaldehyde (290.1 mg, 2.10
mmol) in ethanol (8 mL) and the mixture solution was heated
to 55 ºC under stirring for 6 h. After cooling to room tempera-
ture, the precipitate was filtered and washed successively with
ethanol and ethanol/n-hexane (1:4), respectively. The product
was dried under reduced pressure and purified with recrystalli-
zation from ethanol to yield 277.6 mg of pale-pink crystalline
O
N
O
N
CHO
OH
EtOH
+
H2NO ONH2
OH HO
55 °C, Stirring
OH
HO
OH
H4L
1
Fig. 1. Synthetic route to salen-type bisoxime compound
solid. Yield 83.6 %. m.p. 219-220 ºC. H NMR (400 MHz,
CDCl3) δ: 4.28 (s, 4H), 6.29 (d, J = 7.6, 1.4 Hz, 4H), 7.30 (d,
J = 8.0 Hz, 2H), 8.27(s, 2H), 9.80 (s, 2H), 9.94 (s, 2H).
Synthesis of Cu(II) complex 1: A solution of copper(II)
acetate monohydrate (20.1 mg, 0.10 mmol) in ethanol (3 mL)
was added dropwise to a solution of H4L (33.2 mg, 0.10 mmol)
in ethanol (3 mL) at room temperature. The colour of the
mixing solution turned to black and then continuing stirring
EXPERIMENTAL
2,4-Dihydroxybenzaldehyde (≥ 99.0 %) was purchased
from Alfa Aesar and was used without further purification.
1,2-Bis(aminooxy)ethane was synthesized according to an
analogous method reported earlier5-9. Elemental analysis for
Cu was detected by an IRIS ER/S·WP-1 ICP atomic emission

9360 Yang et al.
Asian J. Chem.
for 10 h at room temperature. the resulting solid was filtered
off, washed with ethanol/ether (1:4) and ether, respectively.
The product was dried in vacuo and obtained 33.5 mg of black
solid. Yield 70.6 %.
solvents such as DMF and DMSO, but insoluble in weakly
polar and non-polar organic solvent; the complex 2 have a
good solubility, not only soluble in strongly polar solvents
such as DMF and DMSO but also soluble in methanol, ethanol,
etc. weakly polar solvents, but insoluble in n-hexane, benzene
and acetonitrile.
Synthesis of Cu(II) complex 2: To an ethanol solution
(5 mL) of H4L (33.2 mg, 0.10 mmol) was added an ethanol
solution (5 mL) of copper(II) picrate tetrahydrate (59.5 mg,
0.10 mmol). After the mixture solution had been stirred at
room temperature for 10 h, the formed precipitate was sepa-
rated by filtration and washed successively with ethanol/ether
(1:4) and ether, respectively. The product was dried under
reduced pressure to obtain 71.2 mg of yellow solid.Yield 76.6 %.
The most important FT-IR spectral data for H4L and its
corresponding Cu(II) complexes are given in Table-2. The
characteristic C=N stretching band of the free ligand H4L
appears at 1608 cm-1, while the C=N bands of Cu(II) comp-
lexes 1 and 2 are observed at 1617 and 1610 cm-1, blue shift of
2-9 cm-1, respectively. TheAr-O stretching band occurs at 1246
cm-1 for H4L, whereas those at 1215 and 1217 cm-1 for comp-
lexes 1 and 2, red shift of 29-31 cm-1, respectively. These shifts
of C=N and Ar-O stretching frequencies indicate that the
Cu-N and Cu-O bonds are formed between the Cu(II) ions
and the oxime N and the phenolic O atoms of deprotonated
(L)2- unit8. Meanwhile, the OH out-of-plane bending vibration
of the free HPic at 1148 cm-1 appears in the spectrum of
complex 2, indicating that the H-atom of the OH group existed
in complex 211. The free HPic has νas(-NO2) and νs(-NO2) at
1555 and 1342 cm-1, respectively, which split into two bands
at 1577, 1543, 1372 and 1332 cm-1. This indicates that some
of the nitryl O atoms take part in coordination12,13. In addition,
the infrared spectra of the complexes 1 and 2 show the ex-
pected absorptions due to the stretching and bending modes
of water at 3226 and 1630 cm-1, respectively, indicating the
presence of a water molecule8f.
RESULTS AND DISCUSSION
5,5'-Dihydroxy-2,2'-[ethylenedioxybis(nitrilomethyli-
dyne)]diphenol (H4L) and its two Cu(II) complexes 1 and 2
have been synthesized and the composition are confirmed
by elemental analyses, IR, UV-visible spectra and TG-DTA
analyses.
The colour, yields, melting points and elemental analy-
tical, molar conductance results of the synthesized salamo-
type bisoxime compounds H4L and its two Cu(II) complexes
1 and 2 are presented in Table-1.
The elemental analysis data of H4L and its two Cu(II)
complexes 1 and 2 are very close to the theoretical values, to
prove the accuracy of analytical results. Copper(II) acetate
monohydrate forms a 1:1 type (M:L) complex with the ligand
H4L which contains one ethanol and two water molecules in
the complex 1 molecule, whereas the copper(II) picrate
tetrahydrate forms a 2:1 type (M:L) complex in the complex 2
molecule which contains two picrate and one water molecules.
The molar conductance values of complexes 1 and 2 in 1.0 ×
10-3 mol dm-3 DMF solutions are 7.81 and 8.87 S cm2 mol-1 at
21 ºC, respectively, indicating that both are non-electrolytes10.
Both Cu(II) complexes aren’t easy to absorb moisture and have
a fairly good stability in air. The ligand H4L can be dissolved
in most solvents. The complex 1 is soluble in strongly polar
The absorption spectra data of H4L and its corresponding
Cu(II) complexes 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 H4L.
The UV-visible spectrum of the free ligand H4L exhibits two
absorption peaks at 276 and 311 nm. The former absorption
peak at 276 nm can be assigned to the π-π* transition of the
benzene rings and the latter one at 311 nm can be attributed to
the intra-ligand π-π* transition of the C=N bonds14.
TABLE-1
COLOUR, YIELDS AND ANALYTICAL DATA OF H4L AND ITS COPPER(II) COMPLEXES
Found (calcd.) (%)
Yield
(%)
Molar conductance
(S cm2 mol-1)
Compound
m.f. (m.w.)
Colour
C
H
N
Cu
H4L
1
C10H10N2O6 (332.1)
C18H24CuN2O9 (475.1)
C28H20Cu2N8O21 (929.9)
Pale-pink
Black
83.6
70.6
76.6
58.03 (57.83) 5.08 (4.85)
45.24 (45.42) 4.89 (5.08)
7.96 (8.43)
6.02 (5.89)
–
–
13.56 (13.35)
7.81
8.87
Yellow
36.25 (36.10) 2.11 (2.16) 11.88 (12.02) 13.42 13.64)
2
TABLE-2
MOST IMPORTANT FT-IR BANDS FOR H4LAND ITS COPPER(II) COMPLEXES (cm-1)
Compound
ν(C=N)
1631
ν(Ar-O)
1209
ν(O-H)
3356
δ(H2O)
1627
ν(C=C) benzene ring skeleton
1517, 1467, 1430
H4L
1
1617
1215
3226
1630
1543, 1443, 1341
1610
1270
3371
1632
1610, 1437, 1340
2
TABLE-3
UV-VIS SPECTRAL DATA OF H4LAND ITS COPPER(II) COMPLEXES
First band
Second band
C (× 10-4 mol L-1)
Compound
λmax1 (nm)
276
ε1 (× 104 L mol-1 cm-1)
λmax2 (nm)
311
ε2 (× 104 L mol-1 cm-1)
H4L
1
1.00
1.00
1.00
2.54
3.72
2.78
2.09
2.03
4.71
296
356
299
372
2

Vol. 25, No. 16 (2013)
Synthesis and Structure Characterization of Copper(II) Complexes 9361
TABLE-4
THERMAL ANALYSIS DATA OF H4L AND ITS COPPER(II) COMPLEXES
Weight loss rate (%)
Residual weight rate (%)
Endothermic
peak temp. (ºC)
Exothermic
peak temp. (ºC)
Final
product
Compound
Found
Calcd.
24.8
Found
–
Calcd.
–
H4L
1
220
25.1
241
–
85, 154
128, 206
9.4, 7.7
2.1, 49.1
9.7, 7.6
1.9, 49.3
284, 336
278, 342
16.5
16.9
16.7
17.1
CuO
CuO
2
Compared with the absorption peak of the free ligand, a
corresponding absorption peak at 296 and 299 nm is observed
in complexes 1 and 2, respectively, which is hypsochromically
shifted by 12-15 nm, indicating the coordination of Cu(II) ions
with deprotonated (H2L)2- unit8. In addition, the new bands
observed at 356 and 372 nm for complexes 1 and 2 are assigned
to the n-π* charge transfer transition from the filled p-π 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 spheres15.
accompanied with further decomposition of the complex and
the final solid product is likely to CuO with a residual value of
16.5 % (theoretical value, 16.7 %) for complex 1 and 16.9 %
(theoretical value, 17.1 %) for complex 2 when the temperature
is above 800 ºC.
REFERENCES
1. T. Katsuki, Coord. Chem. Rev., 140, 189 (2009).
2. P.G. Lacroix, Eur. J. Inorg. Chem., 14, 339 (2001).
3. J.-P. Costes, F. Dahan and A. Dupuis, Inorg. Chem., 39, 165 (2000).
4. K. Koehler, W. Sandstrom and E.H. Cordes, J. Am. Chem. Soc., 86, 2413
(1964).
Thermal properties: The experimental results show that
the thermal behaviour of the free ligand H4L is significantly
different from the Cu(II) complexes. The free ligand H4Lhas
a small sharp endothermic peak at 220 ºC in DTA curve, with
no weight loss in the TG curve, which is its melting point. On
further heating, the free ligand H4L has a exothermic peak at
241 ºC, with a weight loss in the TG curve and the ligand
decompose completely by one step. Thermal analysis data of
H4L and its copper complexes are given in Table-4.
5. M. Maneiro, M.R. Bermejo, M. Fondo, A.M. González, J. Sanmartin,
J.C. Garcia-Monteagudo, R.G. Pritchard andA.M. Tyryshkin, Polyhedron,
20, 711 (2001).
6. H.-B. Zhu, Z.-Y. Dai, W. Huang, K. Cui, Sh.-H. Gou and Ch.-J. Zhu,
Polyhedron, 23, 1131 (2004).
7. S. Akine, T. Matsumoto, S. Sairenjia and T. Nabeshima, Supramol.
Chem., 23, 106 (2011).
8. (a) W.K. Dong, X.N. He, H.B. Yan, Z.W. Lv, X. Chen, C.Y. Zhao and
X.L. Tang, Polyhedron, 28, 1419 (2009); (b) W.K. Dong, Y.X. Sun,
G.H. Liu, L. Li, X.Y. Dong and X.H. Gao, Z. Anorg. Allg. Chem., 638,
1370 (2012); (c) W.K. Dong, S.J. Xing, Y.X. Sun, L. Zhao, L.Q. Chai
and X.H. Gao, J. Coord. Chem., 65, 1212 (2012); (d) W.K. Dong, Y.X.
Sun, S.J. Xing,Y. Wang and X.H. Gao, Z. Naturforsch., 67b, 197 (2012);
(e) W.K. Dong, Y.X. Sun, Y.P. Zhang, L. Li, X.N. He and X.L. Tang,
Inorg. Chim. Acta, 362, 117 (2009); (f) W.K. Dong and J.G. Duan, J.
Coord. Chem., 61, 781 (2008).
Compared to the free ligand H4L, the endothermic peaks
of complex 1 appear at 85 and 154 ºC in DTA curve and the
TG curve shows that the weight loss corresponding to this
temperature range is 9.4 and 7.7 % that roughly coincides with
the values of 9.7 and 7.6 %, respectively, calculated for the
loss of one coordinated ethanol and two coordinated water
molecules of complex 1, which is consistent with the results
of infrared spectroscopy. The DTA curve of complex 2 shows
two endothermic peaks at 128 and 206 ºC with the weight
losses of 2.1 and 49.1 %, respectively, which are agreement
with the losses of one water (1.93 %) and two picric acid
(49.3 %) molecules. On further heating, two exothermic peaks
successively at 284 and 336 ºC for complex 1 (278 and 342 ºC
for complex 2) in the DTA curve and a continued weight loss
occurs in the TG curve. Then, the second strong exothermic
peak at 336 ºC for complex 1 (at 342 ºC for complex 2)
9. D.K. Aliakbar, A. Mehdi and T. Smail. Inorg. Chim. Acta, 362, 587
(2009).
10. W.J. Geary, Coord. Chem. Rev., 7, 81 (1971).
11. X.Q. Song, J.R. Zheng, W.S. Liu and Z.H. Ju, Spectrochim. Acta A, 69,
49 (2008).
12. S.X. Liu, W.S. Liu, M.Y. Tan and K.B. Yu, J. Coord. Chem., 10, 391
(1996).
13. X.Q. Song, W.S. Liu, W. Dou, Y.W. Wang, J.R. Zheng and Z.P. Zang,
Eur. J. Inorg. Chem., 1901 (2008).
14. T. Ghosh, B. Mondal, T. Ghosh, M. Sutradhar, G. Mukherjee and
M.G.B. Drew, Inorg. Chim. Acta, 360, 1753 (2007).
15. L. Gomes, E. Pereira and B. Castro, J. Chem. Soc. Dalton Trans., 1373
(2000).