Synthesis, crystal structures, and antimicrobial activities of copper(II) complexes with bis-Schiff bases

Article abstract of DOI:10.1080/24701556.2020.1813175

Three newly synthesized copper(II) complexes with the general formula [CuL], where L is the dianionic form of N,N′-bis(3,5-difluorosalicylidene)ethane-1,2-diamine (H₂L¹) for 1, N,N′-bis(3,5-difluorosalicylidene)propane-1,3-diamine (H

Full text of DOI:10.1080/24701556.2020.1813175

Inorganic and Nano-Metal Chemistry
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Synthesis, crystal structures, and antimicrobial
activities of copper(II) complexes with bis-Schiff
bases
Hai-Yun Zhu
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INORGANIC AND NANO-METAL CHEMISTRY
https://doi.org/10.1080/24701556.2020.1813175
Synthesis, crystal structures, and antimicrobial activities of copper(II) complexes
with bis-Schiff bases
Hai-Yun Zhu
College of Energy and Chemical Engineering, Ningxia Vocational Technical College of Industry and Commerce, Yinchuan, P.R. China
ABSTRACT
ARTICLE HISTORY
Received 13 June 2020
Accepted 26 July 2020
Three newly synthesized copper(II) complexes with the general formula [CuL], where L is the
dianionic form of N,N -bis(3,5-difluorosalicylidene)ethane-1,2-diamine (H
difluorosalicylidene)propane-1,3-diamine (H
hydroxy-1,3-propanediamine (H L ) for 3, have been obtained and structurally characterized by
spectroscopic method and single-crystal X-ray determination. The Cu atoms in the complexes are
in square planar coordination, with the two imino N and two phenolate O atoms of the Schiff
base ligands. The in vitro antimicrobial activities of the compounds indicate that they are interest-
ing antibacterial agents.
0
1
0
2
L ) for 1, N,N -bis(3,5-
2
0
2
L ) for 2, and N,N -bis(3,5-difluorosalicylidene)-2-
3
KEYWORDS
2
Schiff base; copper
complex; synthesis; X-ray
crystal structure;
antimicrobial activity
Introduction
from Bide Chemical Reagent Co. Ltd. The other chemicals
with AR grade were obtained commercially and used as
received. CHN elemental analyses were performed on a
PerkinElmer 240C elemental analyzer. IR spectra were meas-
ured with a FT-IR 170-SX (Nicolet) spectrophotometer. UV-
Schiff bases with the central group –CH ¼ N– are of particu-
lar interest in biological fields. These compounds have been
reported to show interesting biological activities like anti-
microbial, antifungal, anticonvulsant, analgesic, antiplatelet,
antitubercular, anti-inflammatory, as well as antitumor.
The transition metal complexes with Schiff bases have been
widely studied for their facile synthesis, versatile structures,
Vis spectra were measured with
spectrophotometer.
a
Lambda 35
[
1–4]
[
5–8]
1
and excellent biological properties.
In recent years, a Synthesis of [CuL ] (1)
number of Schiff base complexes are reported to show
[
9–13]
3,5-Difluorosalicylaldehyde (0.32 g, 2.0 mmol) and 1,2-etha-
nediamine (0.060 g, 1.0 mmol) were mixed and stirred in
methanol (50 mL) for 30 h at ambient temperature. Then,
copper acetate monohydrate (0.20 g, 1.0 mmol) was added
and stirred for a further 30 min. The solution was left to
slow evaporation of the methanol for five days, yielding blue
block-shaped single crystals. The crystals were filtered out
and washed with methanol. Yield: 0.23 g (50%). Analysis
Calcd. (%) for C H CuF N O : C, 47.83; H, 2.51; N, 6.97.
Found (%): C, 47.67; H, 2.62; N, 7.12. IR (KBr; ꢀmax, cm ):
1623, 1558, 1465, 1355, 1327, 1261, 1122, 1050, 987, 853,
826, 577, 533, 510. UV-Vis data (methanol; kmax, nm): 220,
270, 370, 562.
effective antimicrobial activities.
However, the Schiff
bases derived from fluoro-substituted salicylaldehyde are
relatively rare. Moreover, the compounds bearing halide
substituents such as F, Cl, and Br usually possess effective
[
14, 15]
antimicrobial activities.
zone compounds with antimicrobial activities.
suit of new antimicrobial agents, in this article, three
We have reported some hydra-
[
16–18]
In pur-
1
2
3
copper(II) complexes, [CuL ] (1), [CuL ] (2), and [CuL ]
16
10
4 2 2
(
3), derived from the fluoro-substituted bis-Schiff
ꢀ
1
0
bases
(
N,N -bis(3,5-difluorosalicylidene)ethane-1,2-diamine
1
0
H L ),
N,N -bis(3,5-difluorosalicylidene)propane-1,3-
2
2
0
diamine (H L ), and N,N -bis(3,5-difluorosalicylidene)-2-
hydroxy-1,3-propanediamine (H L ), respectively, are
2
3
2
presented in Scheme 1.
2
Synthesis of [CuL ] (2)
Experimental
3,5-Difluorosalicylaldehyde (0.32 g, 2.0 mmol) and 1,3-pro-
panediamine (0.072 g, 1.0 mmol) were mixed and stirred in
methanol (50 mL) for 30 h at ambient temperature. Then,
Materials and methods
3
,5-Difluorosalicylaldehyde, 1,2-ethanediamine, 1,3-propane- copper acetate monohydrate (0.20 g, 1.0 mmol) was added
diamine, and 2-hydroxy-1,3-propanediamine were purchased and stirred for a further 30 min. The solution was left to
CONTACT Hai-Yun Zhu
zhuhaiyun76@126.com
College of Energy and Chemical Engineering, Ningxia Vocational Technical College of Industry and
Commerce, Yinchuan 750021, P.R. China.
Supplemental data for this article can be accessed at the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
H.-Y. ZHU
Scheme 1. The bis-Schiff bases.
slow evaporation of the methanol for seven days, yielding peptone water from 24-h cultures of microorganisms were
blue block-shaped single crystals. The crystals were filtered adjusted to 0.5 McFarland. Muller–Hinton Petri dishes of
out and washed with methanol. Yield: 0.18 g (43%). Analysis 90 mm were inoculated using these suspensions. Paper disks
Calcd. (%) for C H CuF N O : C, 49.10; H, 2.91; N, 6.74. (6 mm in diameter) containing 10 mL of the substance to be
1
7
12
4 2 2
ꢀ
1
Found (%): C, 48.92; H, 3.01; N, 6.67. IR (KBr; ꢀmax, cm ): tested (at a concentration of 2048 mg/mL in DMSO) were
1
8
3
621, 1558, 1467, 1354, 1323, 1263, 1122, 1053, 990, 853, placed in a circular pattern in each inoculated plate.
28, 577, 525. UV-Vis data (methanol; kmax, nm): 220, 270, Incubation of the plates was done at 37 C for 18–24 h.
ꢁ
70, 567.
DMSO impregnated disks were used as negative controls.
Toxicity tests of the solvent, DMSO, showed that the con-
centrations used in antimicrobial activity assays did not
interfere with the growth of the microorganisms. Reading of
the results was done by measuring the diameters of the
inhibition zones generated by the test substance. Penicillin
was used as a reference.
3
Synthesis of [CuL ] (3)
3
,5-Difluorosalicylaldehyde (0.32 g, 2.0 mmol) and 2-
hydroxy-1,3-propanediamine (0.090 g, 1.0 mmol) were mixed
and stirred in methanol (50 mL) for 30 h at ambient tem-
perature. Then, copper acetate monohydrate (0.20 g,
Determination of MIC (minimum inhibitory concentra-
tion) was done using the serial dilutions in liquid broth
method. The materials used were 96-well plates, suspensions
of microorganism, Muller–Hinton broth, and stock solutions
of each substance to be tested (2048 mg/mL in DMSO). The
following concentrations of the substances to be tested were
obtained in the 96-well plates: 1024, 512, 256, 128, 64, 32,
1
.0 mmol) was added and stirred for a further 30 min. The
solution was left to slow evaporation of the methanol for
three days, yielding blue block-shaped single crystals. The
crystals were filtered out and washed with methanol. Yield:
0
4
.26 g (46%). Analysis Calcd. (%) for C H CuF N O : C,
17 12 4 2 3
7.28; H, 2.80; N, 6.49. Found (%):C, 47.40; H, 2.89; N, 6.61.
ꢁ
ꢀ
1
16, 8, 4, 2, and 1 mg/mL. After incubation at 37 C for
IR (KBr; ꢀmax, cm ): 3445, 1634, 1558, 1461, 1390, 1351,
260, 1123, 1048, 985, 852, 822, 577, 555, 527. UV-Vis data
methanol; kmax, nm): 220, 270, 370, 555.
1
8–24 h, the MIC for each tested substance was determined
1
by microscopic observation of microbial growth. It corre-
sponds to the well with the lowest concentration of the
(
tested
substance
where
microbial
growth
was
X-ray structure analysis
clearly inhibited.
X-ray diffraction intensities were collected using a Bruker
SMART 1000 CCD area detector equipped with graphite- Results and discussion
ꢀ
monochromated Mo-Ka radiation (k ¼ 0.71073 Å) at 298(2)
[
19]
Chemistry
K. Absorption corrections were applied by SADABS.
The
structures of the complexes were solved by direct methods The complexes were facile prepared by the reaction of 1:1
2
and refined on F by full-matrix least-squares methods with molar ratio of the Schiff bases with copper acetate in metha-
[
20]
SHELXTL.
All non-hydrogen atoms were refined aniso- nol. The anions of the copper salts, like nitrate, chloride,
tropically. The hydrogen atoms in the complexes were located perchlorate, have no influence on the structures of the cop-
in difference Fourier maps and refined isotropically. The C8- per complexes. The element analyses are in good agreement
C9-C10-O3 group of complex 3 is disordered over two sites, with the formulae proposed for the complexes determined
with occupancies of 0.65(2) and 0.35(2). The details of the by single-crystal X-ray diffraction. The crystals of the com-
crystallographic data are summarized in Table 1.
pounds are stable in air at room temperature, and easily to
Supplementary material for structure I and II has been be solved in methanol, ethanol, chloroform, dichlorome-
deposited with the Cambridge Crystallographic Data Centre thane, and acetonitrile.
(CCDC nos. 2006254 (1), 2006255 (2), 2006256 (3); depos-
it@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Crystal structure description of the complexes
The molecular structures of complexes 1, 2, and 3 are
shown in Figures 1–3, respectively. The structures of the
Antimicrobial test
Qualitative determination of antimicrobial activity was done three complexes are similar. The molecules of complexes 1
using the disk diffusion method. Suspensions in sterile and 2 possess crystallographic two-fold rotation axis

INORGANIC AND NANO-METAL CHEMISTRY
3
Table 1. Crystallographic data and structure refinement for the complexes.
1
2
3
Molecular formula
Molecular weight
Crystal system
Space group
C
16
H
10CuF
4
N
2
O
2
C
17
H
12CuF
4
N
2
O
2
C
17
H
12CuF
4 2 3
N O
401.8
Monoclinic
C2/c
25.9831(9)
8.6085(13)
6.8409(10)
103.125(1)
1490.2(30
4
415.8
Orthorhombic
Pccn
25.5649(11)
6.9249(7)
18.0883(12)
431.8
Monoclinic
C2/c
ꢀ
a (Å)
8.3140(10)
ꢀ
b (Å)
26.7317(11)
14.5706(10)
99.481(1)
3194.0(5)
8
ꢀ
c (Å)
ꢁ
b ( )
ꢀ
3
V (Å )
3202.3(40
8
1.725
Z
D
ꢀ
3
calc (g cm
)
1.791
1.525
1.796
1.434
ꢀ1
Absorption coefficient (mm
)
1.422
T
min/Tmax
0.6836/0.7206
4320
1.61–25.49
0.7544/0.7838
17783
1.59–25.50
0.7527/0.8136
9328
1.52–25.50
Reflections measured
h limit ( )
ꢁ
Total no. of unique data
No. of observed data, I > 2r(I)
No. of variables
1400 [Rint ¼ 0.0404]
2989 [Rint ¼ 0.0666]
2964 [Rint ¼ 0.0503]
1139
1659
2059
114
237
263
No. of restraints
Goodness of fit on F
0
0
1
2
1.049
0.0385, 0.0713
1.027
0.0462, 0.1095
0.0961, 0.1404
1.013
0.0471, 0.0888
0.0824, 0.1002
a
R
R
a
1
, wR
, wR
2
[I ꢃ 2r(I)]
a
1
2
(all data)
0.0532, 0.0763
P
P
P
P
2
2 2
2 2 1/2
R
1
¼
jjFoj – jFcjj/ jFoj, wR
2
¼ [ w(Fo – Fc ) / w(Fo ) ]
.
while those in complexes 2 and 3 are in tetragonal distorted
geometry. This can be evidenced by the average deviation
(0 Å for 1, 0.354–0.417 Å for 2, and 0.410–0.416 Å for 3) of
the constituent atoms from the corresponding least-squares
N O plane. All the related bond lengths and angles (Table
2
2
2
) in the complexes are similar, and within the ranges of the
bond values observed in reported copper complexes with
[
21–23]
Schiff base ligands.
The hydrogen bonds are listed in Table 3, and the short
p-electron ring–p-electron ring interactions with Cg–Cg dis-
[
24]
tances < 5.0 Å that are specified in Table 4.
The self-
assembly in complex 1 is two-dimensional, generated by
two C–HꢂꢂꢂF hydrogen bonds. The two-dimensional sheets
are stacked along the c-axis by pꢂꢂꢂp stacking interactions
Figure 1. Molecular structure of 1 at 30% probability displacement.
(
Figure 4). The self-assembly in complex 2 is two-dimen-
sional, generated by two C–HꢂꢂꢂF and two C–HꢂꢂꢂO hydro-
gen bonds. The C–HꢂꢂꢂF hydrogen bonds link the
molecules along the z-axis to form one-dimensional chains,
which are further linked through C–HꢂꢂꢂO hydrogen bonds
and pꢂꢂꢂp stacking interactions along the b-axis (Figure 5).
The self-assembly in complex 3 is also two-dimensional,
generated by C–HꢂꢂꢂF, C–HꢂꢂꢂO, O–HꢂꢂꢂF, and O–HꢂꢂꢂO
hydrogen bonds. The C–HꢂꢂꢂF hydrogen bonds link the
molecules along the c-axis to form one-dimensional chains,
which are further linked through the remaining hydrogen
bonds and pꢂꢂꢂp stacking interactions along the b-axis
(Figure 6).
Figure 2. Molecular structure of 2 at 30% probability displacement.
Antimicrobial activities of the compounds
The antimicrobial activities of the compounds against the
symmetry. There are two independent molecules in complex organisms Streptococcus pyogenes (S. pyogenes), Streptococcus
. The Cu atoms occupy the N O compartment by forming agalactiae (S. agalactiae), Staphylococcus aureus (S. aureus),
2
2
2
four bonds with the phenolate oxygen and imino nitrogen Bacillus anthracis (B. anthracis), Klebsiella pneumonia (K.
atoms, generating square planar geometry. Due to the differ- pneumonia), and Pseudomonas aeruginosa (P. aeruginosa)
ent coordination environments of the two N atoms, the Cu are summarized in Table 5. The results show that the com-
atom in complex 1 is in perfect square planar geometry, plexes have broad antimicrobial activities against all the

4
H.-Y. ZHU
Table 4. p–p stacking interactions.
Cg Distance between ring centroids (Å)
ꢁ
Dihedral angle ( )
1
#
#
#
#
#
9
Cg(1)ꢂꢂꢂCg(1)
Cg(1)ꢂꢂꢂCg(1)
Cg(1)ꢂꢂꢂCg(2)
Cg(1)ꢂꢂꢂCg(2)
Cg(2)ꢂꢂꢂCg(2)
2
4.0893(6)
3.4587(5)
3.6475
4.5365
3.8279
0
3
10
10
11
10
5.336
5.336
2
Cg(1)ꢂꢂꢂCg(2)
Cg(1)ꢂꢂꢂCg(2)
Cg(1)ꢂꢂꢂCg(3)
Cg(1)ꢂꢂꢂCg(3)
Cg(4)ꢂꢂꢂCg(2)
Cg(4)ꢂꢂꢂCg(2)
Cg(4)ꢂꢂꢂCg(3)
Cg(4)ꢂꢂꢂCg(3)
3
3.4220(3)
3.5132(4)
4.4593
3.9367
4.3265
4.0755
4.5889
3.7321
2.090
2.090
3.076
3.076
3.965
3.965
3.371
3.371
#
#
#
#
2
2
2
2
Figure 3. Molecular structure of 3 at 30% probability displacement. Only the
major component of the disordered group C8-C9-C10-O3 is shown.
#13
#14
Cg(1)ꢂꢂꢂCg(1)
Cg(1)ꢂꢂꢂCg(1)
Cg(1)ꢂꢂꢂCg(3)
Cg(1)ꢂꢂꢂCg(3)
Cg(2)ꢂꢂꢂCg(2)
Cg(2)ꢂꢂꢂCg(3)
Cg(2)ꢂꢂꢂCg(4)
Cg(3)ꢂꢂꢂCg(3)
Cg(4)ꢂꢂꢂCg(4)
4.0149
3.7299
4.2215
3.7787
3.4429
4.9541
4.1852
3.5195
3.9071
10
0
#
#
13
14
8.886
5.803
2
40.798
3.940
4
ꢁ
#13
Table 2. Selected bond lengths (Å) and bond angles ( ) for the complexes.
#
#
#
#
14
13
13
13
1
Cu(1)–O(1)
1.897(2)
91.18(11)
90.85(12)
92.25(9)
Cu(1)–N(1)
1.936(2)
O(1)–Cu(1)–O(2)
O(1)–Cu(1)–O(1A)
O(1)–Cu(1)–N(1)
2
O(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(1A)
N(1)–Cu(1)–N(1A)
155.00(12)
176.72(10)
84.66(15)
2
For complex 1, Cg1 and Cg2 are the centroids of the Cu1-O1-C2-C1-C7-N1 and
C1-C2-C3-C4-C5-C6 rings, respectively. For complex 2, Cg1, Cg2, Cg3, and
Cg4 are the centroids of the Cu1-O1-C2-C1-C7-N1, Cu2-O2-C11-C10-C16-N2,
C10-C11-C12-C13-C14-C15, and C1-C2-C3-C4-C5-C6, respectively. For complex
3, Cg1, Cg2, Cg3, and Cg4 are the centroids of the Cu1-O1-C2-C1-C7-N1,
Cu1-O2-C13-C12-C11-N2, C1-C2-C3-C4-C5-C6, and C12-C13-C14-C15-C16-C17,
respectively. Symmetry codes: #9: – x, – y, 2 – z; #10: x, – y, –1/2 þ z; #11:
x, – y, 1/2 þ z; #12: 2 – x, y, 3/2 – z; #13: 2 – x, – y, 1 – z.
Cu(1)–O(1)
Cu(2)–O(2)
1.894(3)
1.902(3)
87.09(17)
93.96(14)
87.16(17)
93.61(14)
Cu(1)–N(1)
Cu(2)–N(2)
O(1)–Cu(1)–N(1A)
N(1)–Cu(1)–N(1A)
O(2)–Cu(2)–N(2A)
N(2)–Cu(2)–N(2A)
1.946(3)
1.942(3)
155.85(14)
94.8(2)
157.32(14)
94.3(2)
O(1)–Cu(1)–O(1A)
O(1)–Cu(1)–N(1)
O(2)–Cu(2)–O(2A)
O(2)–Cu(2)–N(2)
3
Cu(1)–O(1)
Cu(1)–N(1)
O(2)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
1.887(2)
1.946(3)
94.45(12)
155.26(12)
Cu(1)–O(2)
Cu(1)–N(2)
O(1)–Cu(1)–N(1)
N(2)–Cu(1)–N(1)
1.910(2)
1.932(3)
94.89(12)
90.10(13)
ꢁ
Table 3. Distances (Å) and angles ( ) involving hydrogen bonding of
the complexes.
D–HꢂꢂꢂA
d(D–H) (Å) d(HꢂꢂꢂA) (Å) d(DꢂꢂꢂA) (Å) Angle(D–HꢂꢂꢂA) (ꢁ)
1
#
1
C(4)–H(4)ꢂꢂꢂF(2)
0.93
0.97
2.50
2.38
3.410(3)
3.324(3)
168(4)
164(4)
#
2
C(8)–H(8A)ꢂꢂꢂF(1)
2
#3
C(8)–H(8A)ꢂꢂꢂO(2)
0.97
0.97
0.97
0.97
2.60
2.49
2.56
2.52
3.451(3)
3.333(3)
3.431(3)
3.363(3)
147(3)
146(3)
150(3)
145(3)
#
4
C(8)–H(8B)ꢂꢂꢂF(1)
#
5
C(17)–H(17A)ꢂꢂꢂO(1)
#6
C(17)–H(17B)ꢂꢂꢂF(3)
3
#
7
O(3)–H(3A)ꢂꢂꢂF(3)
0.82
0.82
0.93
0.97
2.53
2.20
2.46
2.46
2.918(4)
2.989(4)
3.360(4)
3.293(4)
110(5)
161(5)
162(5)
144(5)
#7
O(3)–H(3A)ꢂꢂꢂO(2)
#
8
C(6)–H(6)ꢂꢂꢂO(3)
#7
C(10)–H(10A)ꢂꢂꢂF(3)
Symmetry codes: #1: 1/2 – x, –1/2 þ y, 5/2 – z; #2: x, 1 þ y, z; #3: 1/2 – x, 1/2
y, z; #4: x, 3/2 – y, 1/2 þ z; #5: 1/2 – x, 3/2 – y, z; #6: x, 1/2 – y, –1/2 þ z;
7: –1 þ x, y, z; #8: 1 – x, – y, 1 – z.
–
#
tested organisms. The complexes have higher activities
against S. pyogenes, S. agalactiae, and S. aureus when com-
pared to the Penicillin. In general, complex 3 has better
activities than the other two. Complex 3 has the most active
against S. agalactiae with the MIC value of 8 mg/mL, which
Figure 4. Molecular packing of 1, viewed along the c-axis. Hydrogen bonds are
deserves further investigation for the development of new drawn as dashed lines.
antimicrobial drugs.

INORGANIC AND NANO-METAL CHEMISTRY
5
Figure 5. Molecular packing of 2, viewed along the b-axis. Hydrogen bonds are drawn as dashed lines.
Table 5. Antimicrobial activities of the compounds as MIC values (mg/mL).
1
2
3
Penicillin
S. pyogenes
S. agalactiae
S. aureus
B. anthracis
K. pneumonia
P. aeruginosa
64
32
32
64
128
256
64
16
16
64
64
256
16
8
16
16
64
128
230
65
250
12
5
>1024
Conclusion
In summary, three mononuclear copper(II) complexes with
bis-Schiff base ligands were prepared and structurally char-
acterized. The donor atoms of the square planar coordin-
ation comprise two imino nitrogen and two phenolate
oxygen of the Schiff base ligands. The complexes have effect-
ive activities against various organisms, which deserve fur-
ther study.
Disclosure statement
No potential conflict of interest was reported by the author.
Funding
This work was supported by the Natural Science Foundation of
Ningxia Province (2018AAC03198) and the Science Research
Foundation of Ningxia Colleges and Universities (NGY2018209).
Figure 6. Molecular packing of 3, viewed along the b-axis. Hydrogen bonds are
drawn as dashed lines.

6
H.-Y. ZHU
Theoretical and Antimicrobial Studies of Schiff Base Ligand and
Its Co(II) and Cu(II) Complexes. J. Serb. Chem. Soc. 2020, 85,
215–225. DOI: 10.2298/JSC181128049V.
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