Synthesis, spectral studies and DFT calculation of copper(II) complexes with mixed ligands

Article abstract of DOI:10.14233/ajchem.2018.21363

The reaction of copper(II) chloride with Schiff bases and alkanolamines in 1:1:1 molar ratio(s) resulted a series of mixed ligand copper(II) complexes of general formula [Cu(sb)(aa)] (1-6), [where sb = Schiff base; salicylidine-1-aminobenzene (sabH) (1,4)

Full text of DOI:10.14233/ajchem.2018.21363

Asian Journal of Chemistry; Vol. 30, No. 7 (2018), 1679-1684
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21363
Synthesis, Spectral Studies and DFT Calculation of Copper(II) Complexes with Mixed Ligands
*
MANOJ KUMAR, AFREEN ANJUM, NITESH JAISWAL and RAJ KUMAR DUBEY
Synthetic Inorganic and Metallo-Organic Research Laboratory, Department of Chemistry, University of Allahabad, Allahabad-211 002, India
*
Corresponding author: E-mail: rajalkoxy@yahoo.com
Received: 2 April 2018; Accepted: 14 May 2018;
Published online: 31 May 2018;
AJC-18954
The reaction of copper(II) chloride with Schiff bases and alkanolamines in 1:1:1 molar ratio(s) resulted a series of mixed ligand copper(II)
complexes of general formula [Cu(sb)(aa)] (1-6), [where sb = Schiff base; salicylidine-1-aminobenzene (sabH) (1,4), salicylidene-4-
chloro-1-aminobenzene (scabH) (2,5), salicylidene-4-methyl-1-aminobenzene (smabH) (3,6) and aa = alkanolamine; ea = ethanolamine
1
-3, pa = propanolamine 4-6]. These complexes were found to be coloured solid and are soluble in DMF and DMSO. All the complexes
were characterized by elemental analysis (C, H, N and Cu), IR, ESI-MS, ESR, PXRD, TG-DTG and SEM-EDAX spectroscopic studies.
In order to provides a theoretical support to experimental observation, energy calculation of synthesized complexes has been done
through the DFT calculations by using Gaussian 09 program with basis set B3LYP. On the basis of these observations distorted square
planar geometry around the copper(II) is tentatively proposed.
Keywords: Copper(II) complex, Schiff base, ESR, DFT, Square planar geometry.
aminobenzene (smabH) and alkanolamine e.g., ethanolamine
ea) or propanolamine (pa) with molecular modeling. In this
INTRODUCTION
(
Mixed ligand metal complexes of Schiff base derived from
present course of investigation, we reported synthesis, spectral,
structural characterization and DFT study of a new mono-
nuclear series of copper(II) complexes having the molecular
formula [Cu(sb)aa] [sb = Schiff base, aa = alkanolamine]. This
study provides insights about the chelation and coordination
mode of two entirely different ligands with copper. A SEM
analysis of the complex was also carried out to see the surface
morphology of these mixed ligand complexes. Powder X-ray
diffraction and quantum chemical calculations are used in order
to confirm the structure of complexes. The spectral study using
FT-IR, ESI-MS and ESR analyses are also investigated in order
to find a correlation between molecular structure and vibra-
tional frequencies of complexes.
salicylaldehyde with aromatic amines have received significant
attention in the recent years [1] because of their interesting
physico-chemical properties [2], varied structural features [3]
and biologically activities [4]. The high affinity for the
chelation of the Schiff bases toward the copper metal ions is
employed in synthesis of their important biologically potent
coordination complexes. Therefore, significant work has been
devoted to the synthesis and characterization of mixed ligand
copper(II) complexes with several Schiff base ligands [5].
Electrochemical studies of some copper (II) complexes show
that the complexes with lower reduction potential are more
biologically active [6]. Copper complexes show significant
antibacterial and antifungal activities [7]. Due to the presence
of nitrogen and oxygen donor sites in the ligands in their back-
bones they form stable and intensely coloured coordination
complexes of copper [8,9]. The occurrence of an amine group
in the alkanolamine offers further possibilities of inter
molecular hydrogen bond [10] formation with Schiff bases,
which may lead to metal complexes with three-dimensional
network structures.
EXPERIMENTAL
The chemicals and solvents of analytical grade were
purchased directly from Sigma-Aldrich and CDH and used
without further purification. Copper was estimated by iodo-
metric titration [11]. The FT-IR spectra were recorded on
-1
spectrometer (4000-450 cm ) in KBr pellets on a Perkin-Elmer
1000 FT-IR spectrophotometer. The elemental analysis was
performed on CHN-932 on Perkin- Elmer 7300 DV elemental
analyzers. Powder X-ray diffraction (PXRD) was recorded on
X’ Pert Pro XRD. HRMS were recorded in ESI mode. X band
Survey of literature reveals that there is no report of synthesis
and structural studies of complexes of copper with mixed ligand
such as salicylidine-1-aminobenzene (sabH), salicylidene-4-
chloro-1-aminobenzene (scabH), salicylidene-4-methyl-1-

1
680 Kumar et al.
Asian J. Chem.
CHO
OH
ESR spectra were done on JES-FA200 Spectrometer. SEM-
EDAX was recorded on JEOL, Japan (JFC 1600, Auto Fine
Coater).
H N
X
2
where,
X = H; 1, 4
The electron density and molecular orbital energy of
ligand and complexes were analyzed by computational method
using density functional theory (DFT). The Gaussian 09 pro-
grams were used for optimization of geometry by employing
a widely used hybrid exchange-correlation functional B3LYP
and LANL2DZ basis set.
Synthesis of Schiff-base ligands: The Schiff bases (sabH,
scabH and smabH) [12,13] were synthesized by refluxing
about 5 h a mixture of an equimolar amount of salicylaldehyde
with corresponding amines (such as aminobenzene, 4-methyl-
MeOH
=
Cl; 2, 5
reflux - 5 h
=
CH3; 3, 6
H
C
N
X
OH
CuCl .2H O Et
N/MeOH
2
2
3
H N
OH
X
H N
OH
2
2
H
C
H
C
N
N
X
1
-aminobenzene and 4-chloro-1-aminobenzene) in methanol
Cu
O
Cu
O
on a water bath. The resulting products were recrystallized by
using methanol. The resulting crystals of Schiff base were filtered
off and washed.
O
O
H N
2
2
H N
1
-3
4-6
Scheme-I: Synthetic route for copper(II) mixed ligand complex 1-6
Synthesis of complexes: An appropriate amount of
CuCl
20 mL), which was further mixed with a boiling methanolic
solution (30 mL) of salicylidene-1-aminobenzene (sabH) (0.578 g,
2
·2H
2
O (0.5 g, 2.93 mmol) is dissolved in hot methanol
are soluble in common organic solvent (chloroform, dichloro-
methane) and also in pyridine, DMSO and THF on slight heating.
Infrared spectra: The characteristic band due to phenolic
(
2.93 mmol) followed by addition of ethanolamine (0.179 g,
2.93 mmol). The mixture was heated on a water bath for about
3 h and filtered. The filtrate was left to stand overnight, yielding
-1
O–H of Schiff bases present in the region 3485-3450 cm were
found to be absent in the copper complexes [12,13]. The
disappearance of this band indicates deprotonation of phenolic
shining dark green crystals of the complex, which were filtered
off. The crystals thus formed were washed with ethanol and
dried in a desiccator over anhydrous silica gel.
All the complexes 1-6 were synthesized through similar
procedure.
-1
O–H and appearance of new band in the region 525-510 cm
indicates coordination of phenolic oxygen to copper. This
coordination mode (Cu-O) was further supported by the lowe-
ring in the frequency of phenolic C-O [14]. The azomethine
band ν(-C=N) of the free Schiff bases appear in the region
[Cu(sab)ea] (1):Yield, 50 %;Anal. calcd. C15
16 2 2
H N O Cu:
-
1
1
1
648-1660 cm shows a lower shift and appear in the region
C, 56.33; H, 5.04; N, 8.76; Cu, 19.87; Found: C, 56.27; H,
–1
644-1606 cm for the metal complexes is indicative of coordi-
-
1
5
1
.00, N, 8.80; Cu, 19.81 %. IR (KBr, νmax, cm ): 3414 (-NH ),
2
nation of the azomethine nitrogen to copper.
644 (-C=N), 689, 613 (Cu-N), 549, 468 (Cu-O).
The alkanolamines shows infrared absorption in the region
[
Cu(scab)ea] (2):Yield, 60 %;Anal. calcd. C15
H
15
N
2
O
2
ClCu:
–
1
3
550-3500 cm due to ν(O-H) and in the region 3460-3448
C, 50.85; H, 4.27; N, 7.91; Cu, 17.94. Found: C, 50.80; H,
–1
cm due to ν(N-H) vibrations [15,16]. The disappearance of
-
1
4
1
.20; N, 7.86; Cu, 17.87 %. IR (KBr, νmax, cm ): 3423 (-NH
2
),
–
1
band in the region 3550-3500 cm and shifting of N-H stret-
ching frequencies in the lower frequency region in complexes
clearly indicates coordination of oxygen and nitrogen atom of
alkanolamines to the copper atom. The above assigned coordi-
nation mode of copper with nitrogen and oxygen of Schiff
base and alkanolamine was further supported by appearance
634 (-C=N), 652, 627, (Cu-N), 512, 465 (Cu-O).
[
Cu(smab)ea] (3): Yield, 50 %;Anal. calcd. C16
18 2 2
H N O Cu:
C, 57.56; H, 5.43; N, 8.39; Cu, 19.03; Found: C, 57.59; H,
-1
5
.40; N, 8.45; Cu 18.94 %. IR (KBr, νmax, cm ): 3437 (-NH
2
),
1
636 (-C=N), 667, 603 (Cu-N), 522, 461 (Cu-O).
[Cu(sab)pa] (4): Yield, 58 %.Anal. calcd. C16
18 2 2
H N O Cu:
-1
of bands in the region 689-590 cm due to Cu-N while in the
C, 57.56; H, 5.43; N, 8.39, Cu, 19.03. Found: C, 56.49; H,
-1
region 459-549 cm due to Cu-O [15]. The IR frequency in
-
1
5
1
.38; N, 8.30; Cu, 18.97 %. IR (KBr, νmax, cm ): 3423 (-NH ),
2
–1
the range 846-806 cm is observed in the Schiff base (scabH)
and in complexes 2 and 4 due to ν(C-Cl) stretching [13,17].
ESI-Mass spectral studies:The mass spectra[18] of comp-
lexes 3 and 5 (Fig. 1) were recorded in positive mode exhibiting
peaks at m/z 319.0287, 333.4534, 333.0149 and 368.9817
606 (-C=N), 689, 617 (Cu-N), 525, 468 (Cu-O).
[
Cu(scab)pa] (5): Yield, 67 %;Anal. calcd. C16
H
17
N
2
O ClCu:
2
C, 52.18; H, 4.65; N, 7.61 Cu, 17.25. Found: C, 52.10; H,
-1
4
6
.58; N, 7.57; Cu, 17.18; IR (cm ): 3423 (-NH
22, 590 (Cu-N), 510, 468 (Cu-O).
2
), 1603 (-C=N),
+
due to complex [Cu(sab)(ea) + H] (cald. m/z 319.8457),
[
Cu(smab)pa] (6): Yield, 61 %.Anal. calcd. C17
H
20
N
2
O Cu:
2
+
+
[
(
Cu(smab)(ea) + H] (calcd m/z 333.8723), [Cu(sab)(pa) + H]
C, 58.69; H, 5.79; N, 8.05; Cu, 18.27. Found: C, 58.60; H, 5.70;
+
calcd. m/z 333.8723) and [Cu(scab)(pa) + H] (calcd. m/z
-1
N, 8.00 %; IR (KBr, νmax, cm ): 3428 (-NH
17, 649 (Cu-N), 519, 459 (Cu-O).
2
), 1623 (-C=N),
3
68.3174), respectively. The result shows there is good 1:1:1
6
binding mode between Schiff base, ethanolamine (1, 3)/propa-
nolamine (4, 5) with copper(II).
RESULTS AND DISCUSSION
ESR spectra: The ESR spectrum of Cu(II) complex (1,
Mixed ligand complexes of Cu(II) are coloured solids,
non-hygroscopic and stable at room temperature have been
synthesized according to Scheme-I. These Cu(II) complexes
2
, 4 and 6) offers information about the geometry and environ-
ment of the ligating sites of the Schiff base and metal ions
19]. The X-band ESR spectrum of Cu(II) complex has been
[

Vol. 30, No. 7 (2018)
Synthesis, Spectral Studies and DFT Calculation of Copper(II) Complexes with Mixed Ligands 1681
5
6
5.0×10
4.5×10
4.0×10
3.5×10
3.0×10
2.5×10
2.0×10
1.5×10
1.0×10
5.0×10
1.6×10
5
5
5
5
5
5
5
5
4
6
1
.4×10
(a)
(b)
6
1
.2×10
6
1.0×10
5
8.0×10
5
6
.0×10
5
4
.0×10
5
2.0×10
0
0
5
0
100 150 200 250 300 350 400 450 500
Counts vs. Mass-to-charge (m/z)
50 100 150 200 250 300 350 400 450 500 550 600
Counts vs. Mass-to-charge (m/z)
Fig. 1. ESI-MS spectra of complex (a) [Cu(smab)ea] (3) and (b) [Cu(scab)pa] (5)
recorded in solid state at room temperature at a frequency of
[22] of complexes 1, 3, 4 and 6 clearly showed crystalline
material. The powder diffraction analysis of metal complexes,
1, 3, 4 and 6 show well defined crystalline peaks (Fig. 3). The
indexing and calculations of unit cell parameters were per-
formed using Powder-X software and scattering angles (2θ)
corresponding to each reflection, inter-planar spacing (d) along
with Miller’s indices and lattice constants were evaluated which
corresponds to cubic crystal system for complexes 1, 3, 4 and
6. For calculation of the crystallite size, we use Debye Scherrer
formula as given bellow,
9
g
1
.1 GHz. The spectrum is shown in Fig. 2. The parameters g||
, gav and G values have been calculated and given in Table-
. The g|| value is an important function for indicating the metal-
,
⊥
ligand bond character, for covalent character g|| < 2.3 and for
ionic character g|| > 2.3 respectively [20]. In these complexes
the g|| value of Cu(II) complex is less than 2.3, indicating an
appreciable covalent character of the metal–ligand bond. The
order of g value is found to be g|| > g
⊥
> g (2.0023) indicating
e
2
the unpaired electron is localized in dx2-y2 orbital with B1g which
is the ground state of Cu(II) square planar complex [21]. In
the present case the observed measurements of Cu(II) complex
D = 0.91 λ/β cos θ
where constant 0.91 is the shape factor, k is the X-ray wave-
is g|| (2.228) > g (2.064) > 2.0023 indicate that the complex is
⊥
length of CuK radiation (1.5406 Å), θ is the Bragg diffraction
α
axially symmetric and copper site has a dx2-y2 ground state.
The geometric parameter (G) is the measure of extent of
exchange interactions and is calculated by using g-tensor
angle and β is the full width at half maximum (FWHM). The
experimental average grain sizes of 1, 3, 4 and 6 complexes
were found to be 16, 32, 24 and 41 nm respectively. Summary
of XRD data and refinement parameters of metal complexes
are given in Table-2. All the peaks were matched with the
JCPDF.
values of the expression G = g|| - 2.0023/g - 2.0023.
⊥
TABLE-1
ESR SPECTRAL DATA FOR COMPLEXES (1, 2, 4 AND 6)
Thermal analysis: The thermal analysis [21,22] of all
complexes (Fig. 4) were performed between 30 to 800 °C in
dynamic nitrogen atmosphere at heating rate 20 °C/min. All
the complexes show two steps of weight loss in the TG curve
accompanied by two endothermic peaks in the DTG curve.
The molecular mass of complex [Cu(sab)ea] (1) is 319.8457
exhibits weight loss between 170 °C and 551 °C constantly due
to loss of 59.68 (18.66 %) which is equal to the approximate
S. No.
Complex
Cu(sab)ea (1)
Cu(scab)ea (2)
Cu(sab)pa (4)
Cu(smab)pa (6)
g||
g⊥
gav
G
1
2
3
4
2.228
2.210
2.190
2.215
2.064
2.050
2.053
2.075
2.916
2.893
2.874
2.906
3.570
4.200
3.580
2.344
Powder XRD analysis: Powder XRD is widely used to
characterize a crystalline solid as it was challenging to isolate
suitable single crystal for X-ray crystallography. XRD spectrum
weight of one coordinated ligands ethanolamine (eaH) [C
2
6
H NO,
2047
2000
(a)
(b)
g = 2.228
|
|
g = 2.190
|
|
0
g⊥ = 2.064
g⊥ = 2.053
-
2000
-
2048
1
01.438
273.546
Magnetic field (mT)
445.654
101.0
273.555
Magnetic field (mT)
445.0
Fig. 2. ESR spectra of (a) [Cu(sab)ea] (1) and (b) [Cu(sab)pa] (4)

1
682 Kumar et al.
Asian J. Chem.
1000
1600
(
a)
(b)
800
600
400
200
0
1400
1
200
000
1
800
600
400
200
0
0
10
20
30
40
50
60
70
0
10
20
30
40
50
60
70
2θ
(°)
2θ (°)
Fig. 3. Powder XRD spectra of complex (a) [Cu(sab)ea] (1) and (b) [Cu(sab)pa] (4)
TABLE-2
REFINEMENT PARAMETERS FOR XRD DATA OF METAL COMPLEXES
Parameter
Complex 1
Complex 3
Complex 4
Complex 5
Formula
F.W.
C H N O Cu
319.8457
298
1.540598
CuKα
Triclinic
C H N O Cu
C H N O Cu
C H N O Cu
15
16
2
2
16 18
2
2
16 18
2
2
17 20
2
2
333.07
298
1.540598
CuKα
333.87
298
1.540598
CuKα
347.08
298
1.540598
CuKα
Temperature (K)
Wavelength
Radiation
Crystal system
Unit cell dimension
a (Å)
Orthorhombic
Triclinic
Triclinic
10.175
12.064
14.483
104.65
90.44
16.491
14.663
16.750
–
10.175
12.064
14.483
104.65
90.44
10.175
12.064
14.483
104.65
90.44
b (Å)
c (Å)
α (°)
β (°)
–
γ (°)
θ (°)
110.85
10-70
–
110.85
10-70
110.85
10-70
2
10-70
1
00
1
100
90
DTG
0
(a)
(b)
DTG
0
9
8
7
6
5
4
3
2
0
0
0
0
0
0
0
0
80
70
60
50
40
30
20
10
-2
-1
-2
-3
-4
-5
-6
-7
-4
-6
-8
-10
TG
TG
-12
5
0 100150200250300350400450500550600650700750800
5
0 100150200250300350400450500550600650700750800
Temperature (°C)
Temperature (°C)
Fig. 4. TG-DTG spectrum of (a) [Cu(sab)ea] (1) and (b) [Cu(sab)pa] (4)
calcd. weight 60.07 (18.78 %)] and 177.00 (55.34 %) which
is corresponds to the weight loss of organic segment of another
ligand sabH [C13H10N, cald. weight 180.22 (56.35 %)]. The
residual weight of 26.00 % (calcd. 24.87 %) corresponds to
copper oxide, CuO, which is stable after 551 °C.
%)]. Thermogram of complex 4 from ambient to 800 °C shows
that total 76.26 % weight loss of the complex. After 590 °C a
stable residue 23.74 % is obtained which is due to CuO (calcd.
weight 23.88 %) is obtained.
SEM and EDX: The SEM images of complex 1, 2 and 4
were recorded [23,24] to study the surface morphology of the
material. SEM image gives information about the surface
morphology of complexes. It was seen from SEM image
(Fig. 5) that the morphology of the all three complexes are
quite similar in appearance with well disseminated stone like
structure. The EDX spectrum of the complexes was recorded
The molecular mass of the complex [Cu(sab)pa] (4) is
3
33.8723 exhibit weight loss of 73.26 (22.00 %), indicating
the loss of one coordinated ligands propanolamine (paH)
NO, calcd. weight 74.10 (22.25 %)] at 225 and at 590 °C
a weight loss of 54.26 % due to organic segment of another
coordinated ligand sabH [C13 10N, calcd. weight 180.22 (54.12
[C
H
3 7
H

Vol. 30, No. 7 (2018)
Synthesis, Spectral Studies and DFT Calculation of Copper(II) Complexes with Mixed Ligands 1683
Fig. 5. SEM image of (a) [Cu(sab)(ea)] (1) and (b) [Cu(sab)(pa)] (4)
in order to get the evidence about the presence of metals. The
EDX spectrum (Fig. 6) of complexes shows that the presence
of copper metal.
donatingability, while LUMO energy characterizes the electron
withdrawing ability of the complex. Energy gap of HOMO and
LUMO shows the molecular chemical stability, which is a critical
parameter in determining molecular electrical transport prop-
erties because it is a measure of electron conductivity. The optim-
ized structure of the complexes suggests slightly distorted square
planar geometry around the metal center and calculated bond
length and bond angles are in accordance with the other reported
square-planner copper(II) complexes of N,O donor ligands
[
26,27].
Conclusion
The present paper includes the synthesis, structural and
spectroscopic studies of six copper(II) mixed ligands comp-
lexes with a bidentate NO donor Schiff base and alkanol-
amines (ethanolamine, 1-3/propanolamine, 4-6). All these
complexes have been synthesized by similar method. The
spectroscopic observation reveals four coordination around
copper. The ESR spectral studies indicate about the square
planar geometry of all complexes. Powder XRD data reveals
that the crystalline nature of complexes. Theoretical calcula-
tions on ligands and their copper(II) complexes suggest a good
agreement between theoretical studies of electronic structure
with the experimental one. SEM analysis shows a stone like
shape of all complexes and EDAX represent a good signature
of copper in all complexes.
Fig. 6. EDX of [Cu(scab)ea] (1)
Computational detail: The most stable, optimized geometry
of ligands and their Cu(II) complexes were calculated by density
functional theory (DFT) using Gaussian 09W Software [25].
The LUMO-HOMO energy gaps were successfully calculated
for ligand, smabH and scabH, and their corresponding comp-
lexes 3 and 5 and its frontier molecular orbital diagram were
shown in Fig. 7. The HOMO energy characterizes the electron
ACKNOWLEDGEMENTS
The authors (M.K.,A.A and N.J.) are grateful to Department
of Chemistry, University ofAllahabad,Allahabad, for providing
the laboratory facilities and U.G.C., New Delhi, India for financial
assistance. The authors also grateful to SAIF, IIT, Mumbai,
for recording ESR spectra, USIC, BBAU Lucknow for providing
SEM-EDX, SAIF Chandigarh, India for PXRD and MNIT Jaipur,
India for mass and IR analysis.
HOMO
HOMO
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