An asymmetric salen-type bisoxime ligand and its supramolecular copper(II) complex: Synthesis, crystal structure and spectral properties

Article abstract of DOI:10.1515/znb-2012-0303

A supramolecular Cu(II) complex [CuL(H₂O)] with an asymmetric salen-type bisoxime ligand (H₂L = 4-nitro-6'-methoxy-2,2'- [ethylenediyldioxybis(nitrilomethylidyne)]diphenol) has been synthesized and characterized by elemental analysis, IR and UV/Vis spectroscopy, TG-DTA analysis, and molar conductance measurements. The crystal structure of the Cu(II) complex has been determined by single-crystal X-ray diffraction. The Cu(II) atom is penta-coodinated by N₂O₂ donor atoms from the asymmetic salen-type bisoxime L^2- unit and one oxygen atom from the coordinated water molecule, resulting in an almost regular square-pyramidal geometry. With the help of intermolecular O-H· · · O, C-H···O hydrogen bonding and π ··· π stacking interactions, a self-assembled 3D supramolecular structure is formed.

Full text of DOI:10.1515/znb-2012-0303

An Asymmetric Salen-type Bisoxime Ligand and Its Supramolecular
Copper(II) Complex: Synthesis, Crystal Structure and Spectral Properties
a
a
a
a
b
Wen-Kui Dong , Yin-Xia Sun , Si-Jia Xing , Yuan Wang , and Xiong-Hou Gao
a
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070,
P. R. China
Lanzhou Petrochemical Research Center, PetroChina, Lanzhou 730060, P. R. China
b
Reprint requests to Prof. Wen-Kui Dong. E-mail: dongwk@126.com
Z. Naturforsch. 2012, 67b, 197 – 203; received February 17, 2012
A supramolecular Cu(II) complex [CuL(H O)] with an asymmetric salen-type bisoxime ligand
2
ꢀ ꢀ
H L = 4-nitro-6 -methoxy-2,2 -[ethylenediyldioxybis(nitrilomethylidyne)]diphenol) has been syn-
2
(
thesized and characterized by elemental analysis, IR and UV/Vis spectroscopy, TG-DTA analysis,
and molar conductance measurements. The crystal structure of the Cu(II) complex has been deter-
mined by single-crystal X-ray diffraction. The Cu(II) atom is penta-coodinated by N O donor atoms
2
2
from the asymmetic salen-type bisoxime L2 unit and one oxygen atom from the coordinated water
molecule, resulting in an almost regular square-pyramidal geometry. With the help of intermolec-
ular O–H···O, C–H···O hydrogen bonding and π ···π stacking interactions, a self-assembled 3D
supramolecular structure is formed.
−
Key words: Asymmetric Salen-type Bisoxime Ligand, Cu(II) Complex, Synthesis, Crystal Structure
Introduction
izaton in the context of the infinite coordination poly-
mer structures (different functionality allows to use
different metals in the polymerization process) [12].
It has been reported that metal complexes derived
from asymmetric salen ligands sometimes exhibit bet-
ter enantioselectivities when compared with their sym-
metric counterparts [13]. In order to study the struc-
tural features and spectral characteristics of transition
metal complexes with asymmetric salen-type bisoxime
ligands, we herein report a supramolecular complex
ꢀ
Transition metal complexes with the N,N -bis-
salicylaldehydo)ethylenediamine (salen) ligand or its
(
analogs have been synthesized and characterized abun-
dantly in the last few decades [1 – 3]; they played im-
portant roles in the development of catalysis, medical
imaging, optical materials [4, 5] and others. Symmetric
salen-type bisoxime ligands and their complexes have
also attracted much attention for their novel structures
and spectral characteristics [6, 7], especially for their
excellent photoluminescence [8] and interesting mag-
netic [9] properties. Furthermore, salen-type Cu(II)
complexes with symmetric bisoxime ligands have been
studied for their fluorescence properties [10].
[
CuL(H O)] with an asymmetric salen-type bisoxime
2
ligand.
Expermental Section
Compared with symmetric salen-type bisoxime lig- Materials and physical measurements
1
ands, the composition (R -CH=NO(CH )nON=CH-
2
2-Hydroxy-5-nitrobenzaldehyde and 2-hydroxy-3-meth-
2
R ) is rather unusual. A selective synthesis of asym-
oxybenzaldehyde were purchased from Aldrich and used
without further purification. The other reagents and solvents
were of analytical grade from Tianjin Chemical Reagent
Factory.
Elemental analysis for Cu was carried out by an IRIS
ER/S·WP-1 ICP atomic emission spectrometer, C, H and N
analyses with a VarioEL V3.00 automatic elemental an-
alyzer. IR spectra were recorded on a Vertex70 FT-IR
metrical salen-type bisoxime ligands is important be-
cause the electronic and steric effects of the ligands
on salen-metal-assisted catalysis may be controlled by
introduction of different substituents into the two ben-
zene rings [11]. The asymmetric configuration would
offer opportunities for a greater structural variation and
infinite coordination polymers, which would be ex-
pected to lead to novel characteristics. Further, this spectrophotometer, with samples prepared as KBr (500 –
−1
−1
change could create better ways to control polymer- 4000 cm ) and CsI (100 – 500 cm ) pellets. UV/Vis ab-
ꢀ
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198
W.-K. Dong et al. · An Asymmetric Salen-type Bisoxime Ligand and Its Copper(II) Complex
Scheme 1. The synthetic route
to the asymmetric salen-type
bisoxime ligand.
sorption spectra were recorded on a Shimadzu UV-2550 (0.334 g, 2 mmol) in ethanol (20 mL), and the mixture was
◦
spectrometer. TG-DTA analyses were carried out at a heating heated at 50 – 55 C for 6 h. After cooling to r. t., a col-
◦
−1
1
rate of 5 C min on a ZRY-1P thermoanalyzer. H NMR orless precipitate was collected on a suction filter to give
spectra were recorded on a Mercury-400B spectrometer. The a colorless powder unlike the yellowish H salen analogs.
crystal structure was determined on a Rigaku Saturn CCD Yield 80 %. M. p. 129.5 – 130.5 C. – H NMR (400 MHz,
2
◦
1
area detector. Melting points were measured by the use of CDCl ): δ (ppm) = 3.92 (s, 3H), 4.30 (t, J = 4.4 Hz, 2H),
3
a ×10 microscopic melting point apparatus made by Bei- 4.37 (t, J = 4.4 Hz, 2H), 6.80 (dd, J = 7.7, 1.6 Hz, 1H),
jing Taike Instrument Limited Company, and are uncor- 6.85 (t, J = 7.6 Hz, 1H), 6.92 (dd, J = 7.6, 1.6 Hz, 1H), 6.99
rected.
(d, J = 7.6 Hz, 1H), 7.17 (dd, J = 7.6, 1.6 Hz, 1H), 7.29
t, J = 7.6 Hz, 1H), 8.24 (s, 2H), 9.88 (s, 2H). – Analysis
(
Preparation of [H L]
for C17H17N3O7 (375.33): calcd. C 54.40, H 4.57, N 11.20;
found C 54.26, H 4.66, N 11.10.
2
The synthetic route to the ligand is shown in Scheme 1.
1
,2-Bis(phthalimidooxy)ethane was prepared by an anal-
ogous method reported earlier [10].
,2-Bis(aminooxy)ethane was prepared by a similar
method [14]. Yield: 77 %. Analysis for C H N O : calcd.
Preparation of [CuL(H O)]
2
1
A solution of Cu(II) acetate hydrate (0.0199 g, 0.1 mmol)
in ethanol (10 mL) was added dropwise to a solution of H L
2
8
2
2
2
C 26.08, H 8.76, N 30.42; found C 25.98, H 8.90, N 30.37.
(
0.0375 mg, 0.1 mol) in methanol-MeCN (1 : 2) (15 mL) at
r. t. The color of the solution turned to brown immediately.
The mixture was filtered, and the filtrate was allowed to stand
at r. t. for about three weeks. The solvent was partially evap-
orated, and several pale-brown needle-shaped single crystals
suitable for X-ray crystallographic analysis were obtained.
Yield 24 %. Analysis for C H CuN O (454.88): calcd.
3
-Methoxysalicylaldehyde O-(1-ethyloxyamide)oxime
A solution of 1,2-bis(aminooxy)ethane (0.98 g, 10.6
mmol) in ethanol (10 mL) was added to a solution of 2-hydr-
oxy-3-methoxybenzaldehyde (0.806 g, 5.3 mmol) in ethanol
◦
17 17
3
8
(20 mL), and the mixture was heated at 50 – 55 C for 5 h.
C 44.89, H 3.77, N 9.24, Cu 13.97; found C 44.62, H 3.86,
N 9.08, Cu 13.95.
The solution was concentrated in vacuo, and the residue
was purified by column chromatography (SiO , chloroform-
2
ethyl acetate 50 : 3) to afford crystals of the monooxime com-
pound. Yield 72 %. M. p. 96 – 97 C. – H NMR (400 MHz,
◦
1
X-Ray crystallography of [CuL(H O)]
2
CDCl ): δ (ppm) = 3.91 (s, 3H), 3.97 (t, J = 4.4 Hz, 2H), 4.37
3
The crystal data and parameters pertinent to data collec-
(
t, J = 4.4 Hz, 2H), 5.52 (brs, 2H), 6.81 (dd, J = 7.7, 1.6 Hz,
tion and structure refinement for [CuL(H O)] are given in
2
1
1
H), 6.86 (t, J = 7.7 Hz, 1H), 6.91 (dd, J = 7.7, 1.6 Hz,
H), 8.23 (s, 1H), 9.87 (s, 1H). – Analysis for C10H N O
Table 1. The single crystal of [CuL(H O)] was placed on a
2
14
2
4
Rigaku Saturn CCD area detector diffractometer. The reflec-
(
226.23): calcd. C 53.09, H 6.24, N 12.38; found C 52.90,
tions were collected using graphite-monochromatized MoKα
H 6.39, N 12.21.
˚
radition (λ = 0.71073 A) at 143(2) K. The structure was
solved using the program SHELXS and difference Fourier
techniques, and refined by full-matrix least-squares methods
on F using SHELXL. All hydrogen atoms were added in cal-
ꢀ
ꢀ
4
-Nitro-6 -methoxy-2,2 -[ethylenediyldioxybis(nitrilo-
methylidyne)]diphenol (H L)
2
2
culated positions.
A solution of 3-methoxysalicylaldehyde O-(1-ethyloxy-
amide)oxime (0.452 g, 2 mmol) in ethanol (20 mL)
CCDC 832647 contains the supplementary crystallo-
was added to a solution of 2-hydroxy-5-nitrobenzaldehyde graphic data for this paper. These data can be obtained free
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W.-K. Dong et al. · An Asymmetric Salen-type Bisoxime Ligand and Its Copper(II) Complex
199
Table 1. Crystal data and structure refinement
for [CuL(H O)].
2
Molecular formula
Molecular weight, g mol
Color, habit
C17H17CuN3O8
454.88
pale-brown, needle-like
0.32×0.08×0.06
monoclinic
P21/c
13.094(3)
7.5888(15)
18.410(4)
−
1
3
Crystal size, mm
Crystal system
Space group
˚
a, A
˚
b, A
˚
c, A
β, deg
99.82(3)
1802.4(6)
˚
3
V, A
Z
T, K
Dcalcd, g cm
µ(MoKα ), mm
F(000), e
4
143(2)
1.68
1.3
932
−
3
Fig. 1 (color online). ORTEP drawing of the Cu(II) complex
with the atom numbering. Displacement ellipsoids for non-H
atoms are drawn at the 30 % probability level.
−
1
hkl range
± 17, ± 9, ± 24
2.52 – 27.89
21053 / 4283 / 0.0524
4283 / 2 / 272
0.0574 / 0.1424
0.0659 / 0.1482
1.096
θ range for data collection, deg
Reflections collected / unique / Rint
Data / restraints / parameters
The crystal structure of [CuL(H2O)]
The crystal structure and atom numbering of the
a,b
Final R1 / wR2 indices [I ≥ 2σ(I)]
Cu(II) complex [CuL(H O)] is shown in Fig. 1. Se-
2
a,b
R1 / wR2 indices (all data)
lected bond lengths and bond angles are listed in Ta-
ble 2. The Cu(II) complex crystallizes in the mono-
2
c
Goodness-of-fit (F )
Largest diff. peak / hole, e A
˚
−3
0.96 / −1.09
clinic space group P2 /c with Z = 4. The molecu-
a
b
2
2
2
2
2 1/2
1
R1 = ΣꢁFo|−|Fcꢁ/Σ|Fo|; wR2 = [Σw(Fo −Fc ) /Σw(Fo ) ]
,
2
2
2
−1
2
2
lar structure of the Cu(II) complex consists of one
w = [σ (F ) + (AP) + BP] , where P = (Max(Fo ,0) + 2F )/3;
o
c
c
2
2
2
1/2
2−
GoF = [Σw(Fo −Fc ) /(nobs −nparam)]
.
Cu(II) atom, one L unit, and one coordinated wa-
ter molecule. The value of τ = 0.015 [16] clearly in-
˚
Table 2. Selected bond lengths (A) and bond angles (deg) dicates that the environment of the Cu(II) atom could
for [CuL(H O)] with estimated standard deviations in paren-
2
be best described as a square-pyramidal topology with
the metal atom being penta-coordinated. The two phe-
nolic oxygen atoms (O2 and O5) and the two oxime
nitrogen atoms (N1 and N2) of the L unit constitute
the basal plane (Cu1–O2, 1.926(2); Cu1–O5, 1.961(2);
theses.
Cu1–O2
Cu1–N2
Cu1–O8
1.926(2)
1.990(3)
2.260(2)
Cu1–O5
Cu1–N1
1.961(2)
2.006(3)
2
−
O5–Cu1–N1
O5–Cu1–N2
O2–Cu1–O5
O2–Cu1–O8
N2–Cu1–O8
168.40(10)
87.65(10)
83.35(9)
93.92(9)
92.83(10)
O2–Cu1–N2
O2–Cu1–N1
N2–Cu1–N1
O5–Cu1–O8
N1–Cu1–O8
169.30(9)
89.52(10) Cu1–N1, 2.006(3) and Cu1–N2, 1.990(3) A˚ ), and one
98.40(11)
96.48(9)
93.11(10)
O atom (O8) of the coordinated water molecule is oc-
cupying the axial position (Cu1–O8, 2.260(4) A). It is
˚
obvious that the axial bond length Cu1–O8 is longer
than all of the others which form the basal plane. The
bond lengths of Cu–N and Cu–O are similar as those
of analogous Cu(II) complexes with symmetric salen-
type bisoxime ligands [6, 17].
of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data request/cif.
Results and Discussion
The four coordinated atoms in the basal plane de-
The ligand H L is remarkably soluble in polar apro- viate slightly from the mean plane, with O2 and N2
2
˚
tic solvents such as DMF, DMSO and MeCN, and above on average by 0.029(2) and 0.025(2) A, and O5
also soluble in ethanol, methanol, THF, CH Cl and and N1 below on average by 0.029(2) and 0.025(2) A,
˚
2
2
CHCl , but insoluble in Et O, n-hexane, water, and respectively. These deviations indicate a very minor
3
2
petroleum ether. The Cu(II) complex is only soluble in distortion of the basal plane toward a tetrahedron.
˚
DMF and DMSO, but insoluble in the other sovents The Cu(II) atom is displaced by 0.138(3) A from the
mentioned above. The molar conductivities in DMF mean plane. The dihedral angle between the planes
◦
solution indicate that H L and the Cu(II) complex are O2–Cu1–N1 and O5–Cu1–N2 is 11.38 . Although the
2
non-electrolytes [15].
molecule of the ligand H L contains two different
2
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W.-K. Dong et al. · An Asymmetric Salen-type Bisoxime Ligand and Its Copper(II) Complex
D–H···A
D–H
0.81
0.81
0.81
0.95
0.95
0.98
0.99
0.99
0.99
0.95
0.99
0.99
0.98
H···A
2.00
2.09
2.54
2.36
2.47
2.68
2.51
2.71
2.70
2.36
2.71
2.60
2.60
D···A
D–H···A
165
158
119
154
150
169
158
133
141
150
140
156
Symmetry code
Table 3. Hydrogen bonding dis-
˚
O8.-H8A···O5
O8.-H8B···O1
O8.-H8B···O2
C10–H10···O6
C12–H12···O6
C17–H17C··· O7
C8–H8D···O2
C8–H8D···O5
C9–H9A···O1
C5–H5···O7
2.784(3)
2.853(3)
3.016(3)
3.238(3)
3.326(3)
3.644(3)
3.518(3)
3.460(3)
3.525(3)
3.216(3)
3.528(3)
3.523(3)
3.509(3)
−x+2, −y+2, −z
−x+2, −y+2, −z
−x+2, −y+2, −z
−x+1, −y+1, −z
−x+1, −y+1, −z
x, −y+3/2, z−1/2
−x+2, −y+1, −z
−x+2, −y+1, −z
−x+2, y+−1/2, −z+1/2
x+1, −y+3/2, z+1/2
−x+2, −y+1, −z
−x+2, y+−1/2, −z+1/2
x, −y+3/2, z−1/2
tances (A) and angles (deg).
C8–H8C···O4
C9–H9B···O8
C17–H17B··· O3
155
units of salicylaldehyde [sal(1) and sal(2)], they have the Cu(II) complex molecules to form a dimer with the
˚
a similar degree of distortion. The mean plane (N O ) nearest Cu···Cu distance of 4.948(4) A [18].
2
2
and sal(1) (N1–C7–C6–C1–O2) have a dihedral angle
Moreover, every dimer is further interlinked
of 15.48 , and the dihedral angle of sal(2) (N2–C10– with four other adjacent dimers into an infinite
C11–C16–O5) and the mean plane is 16.56 . In addi- 2D supramolecular structure in the crystallographic
◦
◦
tion, the ethylenedioxime carbon atoms (C8 and C9) in ab plane by intermolecular C10–H10···O6, C12–
the Cu(II) complex are buckled asymmetrically from H12···O6 and C17–H17C···O7 hydrogen bonds be-
the Cu1–N1–N2 plane.
tween the -C10H10 units of the oxime groups, the –
C12H12 units of the benzene rings and the –C17H17C
units of the methoxy groups and the nitro oxygen
Supermolecular structure of [CuL(H2O)]
2
−
unit, respectively
atoms (O6 and O7) of the L
Fig. 3) [19, 20].
As shown in Fig. 4, the dimers are interlinked
The introduction of a coordinated water molecule
in the Cu(II) complex leads to the assembly of the
(
[
CuL(H O)] units by intermolecular hydrogen bonds.
2
by C8–H8D···O2, C8–H8D···O5 and C9–H9A···O1
hydrogen bonding interactions into a 1D structure
along the b axis. This linkage is further stabilized by
the π ···π stacking interactions of the two benzene
rings (C1–C6 and C11–C16) of neighboring dimers
As illustrated in Fig. 2, three pairs of intermolec-
ular hydrogen bonds, O8-H8A···O5 O8-H8B···O1
and O8-H8B···O2 are formed. One of the pro-
tons (-O8H8A) of the coordinated water molecule is
hydrogen-bonded to one of the µ-phenoxo oxygen
˚
with a centroid-centroid distance of 3.989(4) A. In
2
−
atoms (O5) of the L unit. The other one (-O8H8B) is
addition, the adjacent chains along the b axis are
held together to form an infinite 2D supramolecular
structure by C5–H5···O7 hydrogen bonding interac-
tions (Fig. 5). The dimers are further interlinked by
six pairs of C8–H8C···O4, C9–H9B···O8 and C17–
H17B···O3 hydrogen bonding interactions to form an-
other 2D structure (Fig. 6) [21].
hydrogen-bondedto the other µ-phenoxo oxygen atom
2
−
(
O2) and the methoxy oxygen atom (O1) of the L
unit, respectively (Table 3). Consequently, these hy-
drogen bonding interactions have stabilized a pair of
To sum up, with the help of intermolecular O–H···O
and weak C–H···O hydrogen-bonding and π ···π
stacking interactions, the crystal structure shows a self-
assembled 3D supramolecular aggregate.
IR spectra of [H2L] and [CuL(H2O)]
The IR spectra of the free ligand H L and its cor-
2
responding Cu(II) complex exhibit various vibration
−
1
Fig. 2 (color online). A dimeric unit of the Cu(II) complex bands in the 100– 4000 cm region (Table 4). The
formed by intermolecular hydrogen bonds.
free ligand H L shows a broad characteristic band of
2
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W.-K. Dong et al. · An Asymmetric Salen-type Bisoxime Ligand and Its Copper(II) Complex
201
Fig. 3 (color online). Pro-
jection of the infinite 2D
supramolecular network
of the Cu(II) complexes
onto the ab plane (hydro-
gen atoms, except those
forming hydrogen bonds,
are omitted for clarity).
Fig. 4 (color online). View of the infi-
nite chain motif of the Cu(II) complexes
along the b axis (hydrogen atoms, except
those forming hydrogen bonds, are omit-
ted for clarity).
Fig. 5 (color online). View of the infi-
nite 2D supramolecular network of the
Cu(II) complexes on the bc plane (hydro-
gen atoms, except those forming hydro-
gen bonds, are omitted for clarity).
the OH group at 3466 cm−1. The disappearance of this 1263 – 1213 cm range as reported for similar salen-
−1
−
1
band in the FT-IR spectrum of the Cu(II) complex is type ligands [22– 24]. This band occurs at 1269 cm
indicative of the fact that the phenolic OH group of the for H L, and at 1231 cm for the Cu(II) complex. The
−
1
2
tetradentate ligand H L has been deprotonized and co- Ar–O stretching band is shifted to lower frequency,
2
ordinated to the Cu(II) atoms [17]. The Ar–O stretch- indicating that Cu–O bonds are formed between the
ing frequency appears as a strong band within the Cu(II) atom and the oxygen atoms of the phenolic
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W.-K. Dong et al. · An Asymmetric Salen-type Bisoxime Ligand and Its Copper(II) Complex
Fig. 6 (color online). Projection of the in-
finite 2D supramolecular network of the
Cu(II) complexes onto the bc plane (hydro-
gen atoms, except those forming hydrogen
bonds, are omitted for clarity).
Table 4. Selected FT-IR bands for the ligand and its Cu(II)
−
1
complex (cm ).
Compound ν(PhO–H) ν(C=N) ν(Ar–O) ν(Cu–N) ν(Cu–O)
H2L
Complex
3466
–
1612
1608
1269
1231
–
467
–
412
groups. The free ligand H L exhibits a characteristic
2
−
1
C=N stretching band at 1608 cm , which is shifted
in the Cu(II) complex to 1612 cm indicating a weak
−
1
π-acceptor ability of the deprotonated ligand [25].
The infrared spectrum of the Cu(II) complex shows
the expected absorption bands at ca. 3422, 1630 and
Fig. 7. UV/Vis absorption spectra of H L and the Cu(II)
2
−
1
5
37 cm , assigned to the effect of the coordinated
water molecule, as is substantiated by the crystal
structure [17].
complex in dilute DMF solution at room temperature (c =
−5
−1
5
×10 mol L ).
about 316 nm disappears, which indicates that the
oxime nitrogen atom is involved in coordination to the
Cu(II) atom [28]. The intraligand π-π transition of the
The far-infrared spectrum of the Cu(II) complex
−
1
was obtained in the region 500– 100 cm in order
to identify frequencies due to the Cu–O and Cu–N
bonds. The spectrum shows ν(Cu–N) and ν(Cu–O)
∗
benzene ring of salicylaldehyde is slightly shifted in
the Cu(II) complex and appears at 280 nm. The new
band observed at 372 nm for the Cu(II) complex is as-
signed to an L→M charge-transfer transition which is
characteristic of a transition metal complex with N O
−
1
vibration frequencies at 467 and 412 cm [25]. As
pointed out by Percy and Thornton [26], the metal-
oxygen and metal-nitrogen frequency assignments are
at times very difficult.
2
2
coordination sphere [29].
UV/Vis spectra of H2L and [CuL(H2O)]
Thermal properties
The UV/Vis absorption spectra of H L and its
2
Cu(II) complex [CuL(H O)] were determined in 5.0×
The thermal decomposition of the Cu(II) complex
2
−
5
−1
1
0
mol L DMF solution (Fig. 7). The spectrum can mainly be divided into two stages. First, the initial
◦
of the salen-type bisoxime ligand H L consists of two weight loss occurs in the range of 128.0 to 145.4 C,
2
relatively intense bands centered at 273 and 316 nm, corresponding to an endothermic peak, and the TG
∗
assigned to the π-π transitions of the benzene ring curve shows that the weight loss corresponding to this
of the salicylaldehyde and oxime groups [27]. Upon temperature range is 4.3 % that roughly coincides with
coordination of the ligand, the absorption band at the value of 4.0 %, calculated for the loss of one co-
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W.-K. Dong et al. · An Asymmetric Salen-type Bisoxime Ligand and Its Copper(II) Complex
203
ordinated water molecule; The Cu(II) complex has no Cu(II) atom in the complex is penta-coordinated by
2
−
melting point. The Cu(II) complex is thermally more one bisoxime L unit and one water molecule. The
stable than its ligand H L. Its second weight loss starts new complex contains two different salicylaldehyde
2
◦
at around 278.2 C. Subsequently, continuous mass molecules which could be helpful for the development
◦
loss was observed up to 650 C. At this temperature, of new metal-organic complexes and be worth to study
CuO is formed. The total mass loss found (80.6%) was their potential value of applications.
approximately consistent with that calculated (82.5 %).
Acknowledgement
Conclusion
This work was supported by the Foundation of the Edu-
We have reported the synthesis and structural char- cation Department of Gansu Province (no. 0904-11) and the
acterization of a supramolecular Cu(II) complex with ‘Jing Lan’ Talent Engineering Funds of Lanzhou Jiaotong
University, which is gratefully acknowledged.
an asymmetric salen-type bisoxime ligand H L. The
2
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[
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