Crystal structures, spectroscopic, electrochemical, and antibacterial properties of a series of new copper(II) Schiff base complexes

Article abstract of DOI:10.1080/00958972.2015.1051476

Two new and two previously reported Schiff base ligands as well as four corresponding new Cu(II) complexes (CuL^1-4) were synthesized and characterized. The Schiff base ligands were synthesized from condensation of 5-bromo-2-hydroxy-3-nitrobenza

Full text of DOI:10.1080/00958972.2015.1051476

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Crystal structures, spectroscopic, electrochemical
and antibacterial properties of a series of new
copper(II) Schiff base complexes
Nasibeh Imania, Mahdi Behzada, Hadi Amiri Rudbarib, Giuseppe Brunoc, Hamideh Samari
Jahromid & Ali Khaleghiane
a Department of Chemistry, Semnan University, Semnan 35351-19111, Iran
b Faculty of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
c Università degli Studi di Messina, dip. Scienze Chimiche. Viale Ferdinando S.
d’Alcontres, 98166 Messina, Italy
d Research Institute of Petroleum Industry (RIPI), Environment and Biotechnology
Division, West Blvd., Azadi Sports Complex, P.O. Box 14665-1998, Tehran, Iran
e Semnan University of Medical Science, Faculty of Medicine, Biochemistry Department,
Semnan, Iran
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Accepted author version posted online: 20 May 2015.
To cite this article: Nasibeh Imani, Mahdi Behzad, Hadi Amiri Rudbari, Giuseppe Bruno, Hamideh Samari Jahromi & Ali
Khaleghian (2015): Crystal structures, spectroscopic, electrochemical and antibacterial properties of a series of new
copper(II) Schiff base complexes, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2015.1051476
To link to this article: http://dx.doi.org/10.1080/00958972.2015.1051476
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Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2015.1051476
Crystal structures, spectroscopic, electrochemical and antibacterial properties
of a series of new copper(II) Schiff base complexes
NASIBEH IMANIa, MAHDI BEHZAD*a, HADI AMIRI RUDBARIb, GIUSEPPE BRUNOc,
HAMIDEH SAMARI JAHROMId and ALI KHALEGHIANe
aDepartment of Chemistry, Semnan University, Semnan 35351-19111, Iran
bFaculty of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
cUniversità degli Studi di Messina, dip. Scienze Chimiche. Viale Ferdinando S. d’Alcontres, 98166 Messina, Italy
dResearch Institute of Petroleum Industry (RIPI), Environment and Biotechnology Division, West Blvd.,
Azadi Sports Complex, P.O. Box 14665-1998, Tehran, Iran
eSemnan University of Medical Science, Faculty of Medicine, Biochemistry Department, Semnan, Iran
Two new and two previously reported Schiff base ligands as well as four corresponding new
Cu(II) complexes (CuL1-4) were synthesized and characterized. The Schiff base ligands were
synthesized from condensation of 5-bromo-2-hydroxy-3-nitrobenzaldehyde with aliphatic
(H2L1-2) or aromatic (H2L3-4) diamines. Crystal structures of CuL2 and CuL3 were determined by
X-ray crystallography. Antibacterial properties of these ligands and complexes were studied
against four human pathogenic bacteria. The complexes showed moderate antibacterial activities,
higher than those of the ligands.
Keywords: Schiff base; Copper(II); Crystal structure; Antibacterial activity
1. Introduction
Transition metal complexes of Schiff base ligands have attracted interest due to their potential
applications in dye and food industries, catalysis and biochemistry [1-10]. This is mainly due to
the fact that such ligands could be easily synthesized and the electronic and/or steric properties
of their complexes could be finely tuned by introducing different substituents on both the
diamine and the aldehyde/ketone moieties. Furthermore, Schiff base ligands usually make stable
complexes with a large number of d- and f-block metal ions, providing the possibility to study
different aspects of such complexes. From the biological standpoint, Schiff base complexes have
*Corresponding author. Emails: mbehzad@semnan.ac.ir; mahdibehzad@yahoo.com
1

been used as models of biological compounds and have been key in the development of
inorganic biochemistry [11]. Having all the above facts in mind, we focused on the synthesis and
study of antibacterial activities of a series of transition metal Schiff base complexes [12-15]. In
our previous studies, we found that the presence of more electronegative substituents on the
salicylaldehyde moieties of the Schiff base ligands increased the antibacterial activity of their
complexes. Therefore, we decided to synthesize new copper(II) complexes of a series of
electronegativity enhanced Schiff base ligands derived from condensation of different aliphatic
and aromatic diamines with 5-bromo-2-hydroxy-3-nitrobenzaldehyde. The antibacterial activities
of the ligands and the corresponding Cu(II) complexes were studied against two Gram-positive
and two Gram-negative human pathogenic bacteria; Escherichia Coli (Gram-negative),
Salmonella typhi (Gram-negative), Staphylococcus aureus (Gram-positive) and Bacillus subtilis
(Gram-positive). Our results showed that these Cu(II) complexes had moderate antibacterial
activities and their activities were higher than those of their corresponding ligands.
2. Experimental
2.1. Materials and methods
All chemicals and solvents were purchased from commercial sources and used as received.
5-Bromo-2-hydroxy-3-nitrobenzaldehyde [16], H2L1 and H2L3 [17, 18] were synthesized as
described elsewhere. Melting points were obtained on a thermoscientific 9100 apparatus.
Elemental analyses were performed on a Perkin-Elmer 2400II CHNS-O analyzer. 1H NMR
spectra were recorded on a 500 MHz Bruker FT-NMR spectrometer using DMSO-d6 as solvent;
chemical shifts (δ) are given in ppm. IR spectra were obtained as KBr plates using a Tensor 27
Bruker FT-IR instrument. UV-Vis spectra were obtained on a Shimadzu UV-1650PC
spectrophotometer. A Metrohm 757 VA computrace instrument was employed to obtain cyclic
voltammograms.
2.2. Synthesis of the Schiff bases
2.2.1. Synthesis of H2L2. Schematic representation of the synthesis procedures is shown in
scheme 1. For this ligand, to a vigorously stirred and boiling solution of 5-bromo-2-hydroxy-3-
nitrobenzaldehyde (0.25 g, 1 mmol) in 15 mL methanol was added a solution of 0.52 g
(0.5 mmol) 2,2-dimethyl-1,3-propanediamine in 15 mL methanol. The reaction mixture was
2

refluxed for 3 h while the progress of the reaction was monitored by TLC. The solid orange
product was collected by filtration, washed with 10 mL of boiling methanol and air dried to yield
0.43 g of the target ligand (78%). M.P. = 216-7 °C. Selected IR (cm-1): 3467, 1647, 1508.
1H NMR (DMSO-d6): 14.82 (2H, br), 8.66 (2H, s), 8.12 (2H, d), 7.82 (2H, d), 3.64 (4H, s), 1.03
(6H, s). UV-Vis. 10-5 M solution in DMF [λmax nm, (ε M-1cm-1)]: 267 (14300), 471 (15500).
Anal. Calcd. for C19H18Br2N4O6: C, 40.88; H, 3.25; N, 10.04. Found: C, 40.79; H, 3.20; N,
10.10.
2.2.2. Synthesis of H2L4. This ligand was prepared similar to H2L2 except 4-methyl-1,2-
phenylenediamine was used instead of 2,2-dimethyl-1,3-propanediamine. Yield was 0.44 g
(67%). Selected IR (cm-1): 3440, 1627, 1500. 1H NMR (DMSO-d6): 8.49 (1H, s), 8.17 (1H, s),
8.02-7.15 (7H, m), 5.46 (3H, s). UV-Vis. 10-4 M solution in DMF [λmax nm, (ε M-1cm-1)]: 264
(16800), 329 (4800), 438 (17000). Anal. Calcd. for C21H14Br2N4O6: C, 43.63; H, 2.44; N, 9.69.
Found: C, 43.58; H, 2.38; N, 9.75.
2.3. Synthesis of the complexes
2.3.1. Synthesis of CuL1. 1 mmol (0.52 g) of H2L1 was dissolved in 10 mL methanol and was
heated to reflux. To this solution was added a methanolic solution of 1 mmol of Cu(OAc)2 (0.2 g
in 10 mL). The reaction mixture was refluxed for 4 h. The brown solid product was collected by
filtration and washed with 15 mL of hot methanol and air dried. Recrystallization from DMSO
yielded 0.51 g (89%) of the target complex in three weeks. Selected IR (cm-1): 1647, 1506.
UV-Vis. 10-5 M solution in DMF [λmax nm, (ε M-1cm-1)]: 265 (17800), 400 (7400), 620 (77).
Anal. Calcd. for C16H10Br2CuN4O6: C, 28.05; H, 1.73; N, 9.70. Found: C, 28.11; H, 1.68; N,
9.75.
2.3.2. Synthesis of CuL2. This complex was prepared following similar procedure as described
for CuL1 except H2L2 was used instead of H2L1. Ether diffusion to an ethanolic solution of the
complex yielded 0.56 g (90%) of the target complex in one week. Selected IR (cm-1): 1633,
1508. UV-Vis. 10-5 M solution in DMF [λmax nm, (ε M-1cm-1)]: 265 (29600), 421 (7100), 614
(175). Anal. Calcd. for C19H16Br2CuN4O6: C, 36.80; H, 2.58; N, 9.04. Found: C, 36.72; H, 2.62;
N, 9.11.
3

2.3.3. Synthesis of CuL3.2DMF. This complex was prepared following similar procedure as
described for CuL1 except H2L3 was used instead of H2L1. Ether diffusion to a DMF solution of
the complex yielded 0.48 g (62%) of the target complex in one week. Selected IR (cm-1): 1616,
1500. UV-Vis. 10-5 M solution in DMF [λmax nm, (ε M-1cm-1)]: 269 (27500), 312 (19900), 435
(18800), 598 (238). Anal. Calcd. for C26H24Br2CuN6O8: C, 40.42; H, 3.11; N, 10.88. Found: C,
40.44; H, 3.17; N, 10.80.
2.3.4. Synthesis of CuL4. This complex was also prepared following similar procedure as
described for CuL1 except H2L4 was used instead of H2L1. Ether diffusion to a DMF solution of
the complex yielded 0.50 g (78%) of the target complex in one week. Selected IR (cm-1): 1618,
1502. UV-Vis. 10-4 M solution in DMF [λmax nm, (ε M-1cm-1)]: 267 (29700) 329 (12800) 432
(18800), 598 (234). Anal. Calcd. for C20H10Br2CuN4O6: C, 38.36; H, 1.60; N, 8.95. Found: C,
38.44; H, 1.67; N, 8.90.
4

NO2
OH
NH2
H2N
Br
OH
O
Y
Br
CH3COOH, HNO3
CH3OH, Reflux
O
H
H
NO2
OH
O2N
NO2
O
O2N
Br
HO
Br
Br
O
Br
Cu(OAc)2.H2O
CH3OH, Reflux
Cu
N
N
N
N
Y
H
H
Y
H
H
Ligand
H2L1
Complex
CuL1
Y
H2L2
CuL2
H2L3
H2L4
CuL3
CuL4
Scheme 1. Syntheses procedures.
2.4. X-ray crystallography
For CuL2, data were collected at room temperature with a Bruker APEX II CCD area-detector
diffractometer using MoKα radiation (λ = 0.71073 Å). Data collection, cell refinement, data
reduction and absorption correction were performed using multiscan methods with Bruker
software [19]. The X-ray diffraction measurement for CuL3 was made on a STOE IPDSII
diffractometer with graphite monochromated MoKα radiation. Data were collected at 293(2) K
in a series of ω scans in 1° oscillations and integrated using the Stoe X-AREA software package
[20]. A numerical absorption correction was applied using PLATON software [21]. The data
were corrected for Lorentz and polarizing effects. Both structures were solved by direct methods
5

using SIR2004 [22]. The non-hydrogen atoms were refined anisotropically by the full matrix
least squares method on F2 using SHELXL [23]. All hydrogens (H) were placed at calculated
positions and constrained to ride on their parent atoms. Details concerning collection and
analysis for both complexes are reported in table 1.
2.5. Electrochemical studies
Electrochemical behavior of the complexes was studied by cyclic voltammetry in the potential
range of 0 to -2.0 volts. DMSO was used as solvent and 0.1 M tetra-n-octylammonium bromide
(TOAB) as supporting electrolyte. The experiments were conducted at room temperature under
N2 using a glassy carbon working electrode, a platinum auxiliary electrode and a Ag/AgCl
reference electrode. The electrochemical data for the complexes are collected in table 3 and are
corrected against Fc+/0.
2.6. Antibacterial studies
2.6.1. Bacterial strains. The metal complexes were tested against Salmonella typhi (ATCC
19430), Escherichia Coli (ATCC 25922), Staphylococcus aureus (ATCC 25923) and Bacillus
subtilis (ATCC 6633).
2.6.2. Determination of minimum inhibitory concentrations (MIC) and minimal
bactericidal concentrations (MBC). Minimum inhibitory concentrations (MICs, μg mL-1) were
determined by the broth micro-dilution method following the procedures recommended by the
National Committee for Clinical Laboratory Standards [24, 25]. MICs were defined as the lowest
concentrations of compounds which inhibit the growth of microorganisms. All tests were
performed in triplicate. Minimal bactericidal concentrations (MBCs) were also measured
following a standard procedure [26]. 100 µL volumes of all clear (no growth) tubes from a
dilution MIC test were spread on separate agar plates and incubated at 37 °C for 24 h. The MBC
(μg mL-1) was defined as the lowest concentration of the complex where no growth occurred.
3. Results and discussion
3.1. Spectroscopic characterization of the ligands and complexes
6

In the 1H NMR of H2L2, the presence of a broad band above 12 ppm was assigned to the
presence of phenolic protons. This signal was not observed for H2L4. This observation has been
previously attributed to the rapid exchange in solution [16, 17]. The signals due to the iminic
protons were observed at 8.66 for symmetric H2L2, and at 8.49 and 8.17 ppm for the
unsymmetric H2L4. Other signals at 7-8.1 ppm were assigned to aromatic protons. The signals
below 6 ppm were also assigned to aliphatic protons with appropriate peak area and were in
agreement with the expected values [16, 17]. NMR spectra of the ligands are provided in
figures S1 and S2. The most characteristic feature in the IR spectra of the Schiff base ligands and
their metal complexes comes from the C=N stretching vibrations. In IR spectra of our ligands,
these stretching vibrations are at 1640 cm-1 confirming the presence of the imine groups. These
signals shifted to lower wavenumbers in the complexes which confirmed the coordination of
Cu(II) to the iminic nitrogens. The presence of broad bands above 3400 cm-1 in IR spectra of the
ligands was attributed to O-H stretching vibrations. These signals were eliminated from IR
spectra of the complexes which confirmed the loss of the phenolic protons and the L2- nature of
the ligands in these complexes. The signals at 1500 cm-1 were also assigned to the NO2
unsymmetrical stretches [27-29]. Electronic spectra of the ligands from the aliphatic amines, i.e.
H2L1 and H2L2, showed two intense bands at 270 and 490 nm, assigned to the π→π* and n→π*
transitions. UV-Vis spectra of H2L3 and H2L4 with aromatic amine moieties showed signals in
similar regions as well as new intense bands at 300 nm. These new bands could be attributed to
π→π* transitions mostly centered on the new aromatic groups. In electronic spectra of CuL
complexes, the above mentioned π→π* signals were present in almost the same area but signals
due to the n→π* transitions disappeared; new signals at 420 20 and 610 20 nm have been
observed. The former intense band could be attributed to the MLCT transitions while the latter
weak bands were due to d-d transitions. These spectroscopic data are in agreement with
previously reported similar complexes [27].
3.2. X-ray crystallography
3.2.1. Description of the crystal structure of CuL2. Dark green crystals were obtained by slow
evaporation of CH3Cl solution of CuL2 after one week. A suitable crystal with dimensions
0.15×0.21×0.30 mm was chosen for X-ray crystallography. Figure 1 shows an ORTEP
representation of CuL2 with atom numbering scheme. A summary of the crystallographic data,
7

and selected bond lengths and angles are collected in tables 1 and 2, respectively. The neutral
species contains one Cu(II) coordinated to a doubly deprotonated ligand (L2)2-. All interatomic
distances can be considered as normal and are in the common range of previously observed
similar complexes [30, 31]. The geometry around the metal center is distorted square planar from
the data collected in table 2. The angle between the planes defined by the two NCCCO chelating
rings which is 30.23° confirms the distortion. No important hydrogen bond or π-π stacking was
observed for CuL2.
3.2.2. Description of the crystal structure of CuL3. Dark green crystals of CuL3 were obtained
by ether diffusion into a DMF solution of the complex in a month. A suitable crystal with
dimensions 0.18×0.25×0.33 was chosen for X-ray crystallography. An ORTEP drawing of this
complex is shown in figure 2. The crystallographic data and selected bond lengths and angles are
collected in tables 1 and 2, respectively. The metal ion is coordinated to (L3)2- similar to CuL2;
however, the angle between the two NCCCO chelating ring systems in this complex is only
5.21° which indicates a very slightly distorted square planar arrangement around the metal
center. The oxygen of one DMF of crystallization is located at 2.711(2) Å to the central metal
ion. This interatomic distance is too long to be considered as a Cu-O bond, but might be
responsible for the more flattened geometry of the Schiff base ligand. The average Cu-O
(1.918 Å) and Cu-N (1.955 Å) bond distances are in the common range of similar complexes
[30, 31].
3.3. Electrochemistry
Table 3 collects the results of the cyclic voltammetry studies and an illustrative example is
shown in figure 3 for CuL2. The complexes showed one quasi-reversible reduction wave at
negative potentials corresponding to CuII/I redox. Comparison of the E0 values showed that the
complexes with aromatic diamines were reduced in more negative values. The data were in the
common range for previously studied similar complexes [30-32].
3.4. Antibacterial studies
The study of the antibacterial properties of Schiff bases and their metal complexes has attracted
interest [33-39]. In our previous studies on the biological activities of the transition metal Schiff
8

base complexes, we found that the presence of more electronegative substituents on the ancillary
ligand increased the antibacterial activity of their corresponding complexes. Similar results have
also been reported by other researchers [33, 34]. Hence, we synthesized a series of Schiff base
ligands with more electronegative substituents. The Schiff base ligands were synthesized from
condensation of 5-bromo-2-hydroxy-3-nitrobenzaldehde with different aliphatic and aromatic
diamines. The MIC and MBC values for the studied complexes against two Gram(+) and two
Gram(-) human pathogenic bacteria are collected in table 4. The ligands did not show significant
antibacterial activity but the complexes were moderately active against both Gram type bacteria.
The increased activity of the complexes compared to the ligands could be explained by
Overtone's concept [40] and Tweedy's theory [41]. The order of the antibacterial activity of the
complexes is CuL2>CuL1>CuL3>CuL4. In this series, complexes with aliphatic amine moieties
were more potent antibacterial agents than the corresponding aromatic analogues. A comparison
with the electrochemical data which is CuL2>CuL1≈CuL3>CuL4 is also interesting. Although it is
too soon to make complete conclusions, this could mean that electronic properties may play key
roles in the designation of such antibacterial agents.
4. Conclusion
A series of Schiff base ligands derived from electronegative salicylaldehyde derivatives were
synthesized. Their corresponding Cu(II) complexes were also synthesized. Crystal structure
analyses showed that the geometry around the metal center was distorted square planar.
Antibacterial studies showed that these complexes had moderate activity against both gram type
bacteria. A correlation with the electrochemical data was also observed.
Appendix A. Supplementary material
CCDC 1005111 and 1048194 contains the supplementary crystallographic data for CuL2 and
CuL3, respectively. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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12

Table 1. Crystallographic data for CuL2 and CuL3.
Crystal data
CuL2
CuL3
Formula
C19H16Br2CuN4O6
619.72
C26H24Br2CuN6O8
771.86
Formula weight
Crystal system
Monoclinic
C2/c
Triclinic
P-1
Space group
T (K)
298(2)
293(2)
λ (Å)
0.71073
0.71073
Unit cell dimensions (Å, °)
a (Å)
7.5373(9)
16.093(2)
17.635(2)
90.00
10.730(2)
11.395(2)
12.547(3)
78.74(3)
85.36(3)
84.66(3)
1494.9(5), 2
1.715
b (Å)
c (Å)
α (°)
β (°)
98.833
90.00
γ (°)
Volume (Å3), Z
Calculated density (Mg m-3)
Absorption coefficient (mm-1)
F(000)
2113.7(5), 4
1.947
4.860
3.461
1220
770
θ range for data collection (°)
Limiting indices
2.79 to 27.00
1.83 to 25.00
-9≤h≤9
-20≤k≤20
-22≤l≤22
-12≤h≤12
-13≤k≤13
-14≤l≤14
Data / restraints / parameters
Total reflections
2313 / 0 / 147
21213
4971 / 0 / 370
9797
Unique reflections (Rint)
2313 [R(int) = 0.0408]
4971[R(int) = 0.0481]
94.2 %
Completeness
99.9 %
Refinement method
Full-matrix least squares
on F2
Full-matrix least squares
on F2
Goodness-of-fit on F2
1.040
1.108
Final R index [I > 2σ(I)]
R1 = 0.035,
R1 = 0.035,
wR2 = 0.0831
wR2 = 0.0831
R index [all data]
R1 = 0.0434,
wR2 = 0.088
R1 = 0.0434,
wR2 = 0.088
Largest diff. peak and hole (e Å-3)
0.518 and -0.638
0.741 and -0.960
13

Table 2. Selected bond lengths and angles around copper for CuL2 and CuL3.
CuL2
CuL3
Bond lengths (Å)
Bond lengths (Å)
Cu(1)-O(1)
Cu(1)-O(1')
Cu(1)-N(1)
Cu(1)-N(1')
1.907(2)
1.907(2)
1.955(3)
1.955(3)
Cu(1)-O(3)
Cu(1)-O(5)
Cu(1)-N(4)
Cu(1)-N(5)
1.912 (4)
1.923 (4)
1.950 (4)
1.959 (4)
Bond angles (°)
O(1)-Cu(1)-O(1')
Bond angles (°)
O(3)-Cu(1)-O(5)
90.80(13)
92.59(10)
160.32(12)
92.59(10)
160.32(12)
90.71(15)
89.27(15)
171.45(17)
93.39(16)
93.53(16)
177.17(16)
83.70(17)
O(1)-Cu(1)-N(1)
O(1)-Cu(1)-N(1')
O(1')-Cu(1)-N(1')
O(1')-Cu(1)-N(1)
N(1)-Cu(1)-N(1')
O(3)-Cu(1)-N(4)
O(3)-Cu(1)-N(5)
O(5)-Cu(1)-N(4)
O(5)-Cu(1)-N(5)
N(4)-Cu(1)-N(5)
14

Table 3. Redox potential data for 10-3 mol L-1 solutions of CuLx
(x = 1-4) complexes in DMSO solutions containing 0.1 mol L-1
TOAB and scan rate 100 mV s-1. Data are in volts.
Complex Epa(1)
Epc(1)
-1.57
-1.20
-1.66
-1.67
ΔE
E0
CuL1
CuL2
CuL3
CuL4
-1.49
-1.09
-1.41
-1.48
0.16
0.11
0.18
0.19
-1.49
-1.15
-1.50
-1.57
15

Table 4. MIC and MBC values (μg mL-1) for the CuL1-4 complexes against the studied bacteria.
CuL1 CuL2 CuL3 CuL4
Kanamycin
MBC MIC MBC MIC MBC MIC MBC MIC MBC MIC
E.coli
625
500
575 575
425 425
425 425
475 575
525 750
375 500
325 750
450 750
625 1250 1000 3.8
4
S.typhi
475 750
750 750
525 3.2
575 3.0
3.3
3.2
4.0
S.aureus 425
B.subtilis 525
675 1125 1125 3.6
16

Figure 1. ORTEP representation of CuL2 with common atom numbering scheme. Displacement
ellipsoids are drawn at the 50% probability level and hydrogens are shown as small spheres of
arbitrary radii.
17

Figure 2. ORTEP representation of CuL3 with common atom numbering scheme. Displacement
ellipsoids are drawn at the 50% probability level and hydrogens are shown as small spheres of
arbitrary radii. Uncoordinated solvents of crystallization (two DMF molecules) are omitted for
clarity.
18

-4.00E-06
-6.00E-06
-8.00E-06
-1.00E-05
-1.20E-05
-1.40E-05
-1.60E-05
-1.80E-05
-2.00E-05
-1.4
-1.3
-1.2
Potential (V)
-1.1
-1
-0.9
Figure 3. Cyclic voltammogram of CuL2.
19

Graphical abstract
20