Nickel(II) Complexes Derived from Bis-Schiff Bases: Synthesis, Crystal Structures, and Antimicrobial Activity

Article abstract of DOI:10.1134/S1070328420020098

Abstract: Nickel(II) complexes derived from the bis-Schiff bases N,N'-bis(5-methylsalicylidene)-1,2-diaminocyclohexane (H₂L^a), N,N'-bis(5-methylsalicylidene)-1,2-diaminoethane (H₂L^b) and N,N’-bis(3,5-difluorosal

Full text of DOI:10.1134/S1070328420020098

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2020, Vol. 46, No. 2, pp. 145–151. © Pleiades Publishing, Ltd., 2020.
Nickel(II) Complexes Derived from Bis-Schiff Bases: Synthesis,
Crystal Structures, and Antimicrobial Activity
L. W. Xuea, b, *, Y. J. Hana, and X. Q. Luoa
aSchool of Chemical and Environmental Engineering, Pingdingshan University, Pingdingshan Henan, 467000 P.R. China
bHenan Key Laboratory of Research for Central Plains Ancient Ceramics, Pingdingshan University,
Pingdingshan Henan, 467000 P.R. China
*e-mail: pdsuchemistry@163.com
Received May 1, 2019; revised June 12, 2019; accepted August 14, 2019
Abstract—Nickel(II) complexes derived from the bis-Schiff bases N,N'-bis(5-methylsalicylidene)-1,2-
diaminocyclohexane (H2La), N,N'-bis(5-methylsalicylidene)-1,2-diaminoethane (H2Lb) and N,N’-bis(3,5-
difluorosalicylidene)-1,2-diaminoethane (H2Lc), respectively, have been prepared and characterized by ele-
mental analyses, IR, UV−Vis and single crystal XRD (CIF files CCDC nos. 1912770 (I), 1912771 (II), and
1912772 (III)). The bis-Schiff base ligands coordinate to the nickel atoms through phenolate O and imine
N atoms. Each metal atom in the complexes is in square planar coordination. The effects of the complexes on
the antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans were studied,
which indicate that the fluoro-substituted groups are essential for the biological process.
Кeуwords: bis-Schiff-bases, crystal structure, antimicrobial activity, intermolecular hydrogen bonds, powder
and single crystal XRD
DOI: 10.1134/S1070328420020098
INTRODUCTION
grade were purchased from Fluka. Other reagents and
solvents were analytical grade and used without fur-
ther purification. Elemental (C, H, and N) analyses
were made on a PerkinElmer Model 240B automatic
analyser. Infrared (IR) spectra were recorded on an
IR-408 Shimadzu 568 spectrophotometer. UV−Vis
spectra were recorded on a Lambdar 35 spectrometer.
X-ray diffraction was carried out on a Bruker SMART
1000 CCD area diffractometer. The powder X-ray dif-
fraction (XRD) spectra were recorded in a 2θ range of
2°–50° using a Bruker D8 Advance detector under
ambient conditions.
Schiff bases are a kind of important ligands in coor-
dination chemistry [1–3]. In recent years, metal com-
plexes of Schiff bases have attracted much attention
due to their versatile biological activity, such as anti-
fungal antibacterial and antitumor [4–6]. It has been
shown that the Schiff base complexes derived from
salicylaldehyde and its derivatives with primary
amines, bearing the N2O, N2S, NO2 or NSO donor
sets have interesting biological activity [7–10]. Recent
research indicates that the halide-substituent groups
in aromatic rings of Schiff bases can severely increase
the antimicrobial activity [11]. In the present paper,
the preparation, characterization and antimicrobial
activity of three nickel(II) complexes, [NiLa] (I),
[NiLb] · CH3OH (II) and [NiLc] (III), with bis-Schiff
bases N,N'-bis(5-methylsalicylidene)-1,2-diaminocy-
clohexane (H2La), N,N'-bis(5-methylsalicylidene)-
Synthesis of I. 5-Methylsalicylaldehyde (0.272 g,
2 mmol) and 1,2-diaminocyclohexane (0.114 g,
1 mmol) were reacted in methanol (30 mL) at ambient
temperature for 1 h. Then, nickel chloride hexahydrate
(0.238 g, 1 mmol) dissolved in methanol (5 mL) were
added dropwise to the solution. The mixture was
stirred for 30 min at ambient temperature. The filtered
solution was allowed to slow evaporate in an uncapped
vial. Several days later, block crystals of complex I
were obtained. The yield was 183 mg (45%).
1,2-diaminoethane (H2Lb) and N,N'-bis(3,5-difluo-
rosalicylidene)-1,2-diaminoethane (H2Lc), respec-
tively, are reported.
EXPERIMENTAL
For C22H24N2O2Ni
Material and methods. 5-Methylsalicylaldehyde,
3,5-difluorosalicylaldehyde, 1,2-diaminocyclohex-
ane, and 1,2-diaminoethane with analytical reagent
Anal. calcd., %: C, 64.90
Found, % C, 64.75
H, 5.94
H, 6.08
N, 6.88
N, 6.77
145

146
XUE et al.
Selected IR data (ν, cm–1): 1626 s, ν(C=N). UV−Vis
data in methanol (λmax, nm (ε, L mol–1 cm–1)): 245
(15320); 256 (14565); 318 (3633); 410 (2720); 578
(550).
Supplementary material has been deposited with
the Cambridge Crystallographic Data Centre (nos.
1912770 (I), 1912771 (II) and 1912772 (III);
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
Synthesis of II. 5-Methylsalicylaldehyde (0.272 g,
2 mmol) and 1,2-diaminoethane (0.060 g, 1 mmol)
were reacted in methanol (30 mL) at ambient tem-
perature for 1 h. Then, nickel chloride hexahydrate
(0.238 g, 1 mmol) dissolved in methanol (5 mL) were
added dropwise to the solution. The mixture was
stirred for 30 min at ambient temperature. The filtered
solution was allowed to slow evaporate in an uncapped
vial. Several days later, block crystals of complex II
were obtained. The yield was 212 mg (55%).
RESULTS AND DISCUSSION
The three Schiff bases were readily prepared by the
condensation of 1 : 2 molar ratio of 1,2-diaminocyclo-
hexane with 5-methylsalicylaldehyde, 1,2-diami-
noethane with 5-methylsalicylaldehyde, and 1,2-
diaminoethane with 3,5-difluorosalicylaldehyde,
respectively, in methanol at ambient temperature. The
Schiff bases were not isolated and used directly to the
synthesis of the complexes with nickel chloride hexa-
hydrate. The complexes are very stable at room tem-
perature in the solid state and soluble in common
organic solvents, such as methanol, ethanol, chloro-
form, and acetonitrile. The results of the elemental
analyses are in accord with the composition suggested
for the complexes.
The molecular structures of the three complexes
are shown in Fig. 1. Selected bond distances and
angles are listed in Table 2. Complex II contains a
mononuclear [NiLb] complex molecule and a metha-
nol molecule of crystallization. Complex III possesses
a crystallographic two-fold rotation axis symmetry.
The nickel complex molecules are similar to each
other with the Ni atoms in square planar geometry.
The Ni atoms in the complexes are coordinated by two
phenolate oxygen atoms and two imino nitrogen
atoms. The Ni–O and Ni–N atoms in the three com-
plexes are similar to each other, and comparable to
those observed in similar nickel(II) complexes with
Schiff bases [16–18].
For C19H22N2O3Ni
Anal. calcd., %
Found, %
C, 59.26
C, 59.41
H, 5.76
H, 5.85
N, 7.27
N, 7.18
Selected IR data (ν, cm–1): 1627 s, ν(C=N). UV−Vis
data in methanol (λmax, nm (ε, L mol–1 cm–1)): 245,
16130; 255, 14723; 330, 3571; 410, 2930; 575, 530.
Synthesis of III. 3,5-Difluorosalicylaldehyde
(0.316 g, 2 mmol) and 1,2-diaminoethane (0.060 g,
1 mmol) were reacted in methanol (30 mL) at ambient
temperature for 1 h. Then, nickel chloride hexahydrate
(0.238 g, 1 mmol) dissolved in methanol (5 mL) were
added dropwise to the solution. The mixture was
stirred for 30 min at ambient temperature. The filtered
solution was allowed to slow evaporate in an uncapped
vial. Several days later, block crystals of complex III
were obtained. The yield was 165 mg (42%).
For C16H10N2O2F4Ni
In the crystal structure of complex I, two molecules
are linked through intermolecular C–H···O hydrogen
bonds (Table 3) to form a dimeric structure (Fig. 2a).
In the crystal structure of complex II, the methanol
molecules are linked to the complex molecules
through O–H···O hydrogen bonds, and the complex
molecules are linked through intermolecular C–H···O
hydrogen bonds (Table 3) to form a dimeric structure
(Fig. 2b). In the crystal structure of complex III, the
complex molecules are linked through intermolecular
C–H···F hydrogen bonds (Table 3) to form a network
(Fig. 2c).
The experimental powder XRD patterns of the bulk
products of complexes I, II and III are in good agree-
ment with the simulated XRD patterns from single
crystal XRD, indicating purity of the bulk samples
(Fig. 3). The simulated patterns of the complexes were
calculated from the single crystal structural data using
the PCW software.
Anal. calcd., %
Found, %
C, 48.41
C, 48.55
H, 2.54
H, 2.43
N, 7.06
N, 7.13
Selected IR data (ν, cm–1): 1627 s, ν(C=N). UV−Vis
data in methanol (λmax, nm (ε, L mol–1 cm–1)): 237,
18320; 250, 16160; 340, 4770; 403, 3835; 580, 610.
X-ray diffraction. Data were collected from selected
crystals mounted on glass fibers. The data for the three
complexes were processed with SAINT [12] and cor-
rected for absorption using SADABS [13]. Multi-scan
absorption corrections were applied with ψ-scans [14].
The structures were solved by direct methods using the
program SHELXS-97 and refined by full-matrix
least-squares techniques on F2 using anisotropic dis-
placement parameters [15]. Hydrogen atoms were
placed at the calculated positions. Idealized H atoms
were refined with isotropic displacement parameters
set to 1.2 (1.5 for methyl and hydroxyl groups) times
the equivalent isotropic U values of the parent carbon
atoms. The crystallographic data for the complexes are
listed Table 1.
The IR spectra of the free Schiff bases contain
strong C–O absorption bands in the region 1240–
1255 cm–1. The bands disappeared on complexation,
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NICKEL(II) COMPLEXES DERIVED FROM BIS-SCHIFF BASES
Table 1. Crystallographic data and experimental details for complexes I–III
147
Value
Parameter
I
II
III
Habit; color
Fw
Block; red
407.1
Block; red
385.10
Block; red
396.97
Temperature, K
Crystal size, mm
Radiation (λ, Å)
Crystal system
Space group
Unit cell dimensions:
a, Å
b, Å
c, Å
α, deg
β, deg
298(2)
298(2)
298(2)
0.15 × 0.15 × 0.13
MoKα (0.71073)
Monoclinic
P21/c
0.23 × 0.22 × 0.20
MoKα (0.71073)
Triclinic
0.20 × 0.15 × 0.15
MoKα (0.71073)
Monoclinic
C2/c
P1
13.4159(15)
13.7566(13)
10.4817(9)
90
102.6130(10)
90
6.7105(11)
10.6650(13)
12.626(2)
87.190(1)
88.876(1)
89.777(1)
902.3(2)
26.0251(18)
8.6780(17)
6.7683(11)
90
100.787(1)
90
γ, deg
V, Å3
1887.8(3)
1501.6(4)
Z
4
2
4
ρ
calcd, g cm–3
1.433
1.417
1.756
F(000)
856
404
800
Absorption coefficient, mm–1
1.047
1.095
1.351
θ Range for data collection,
deg
2.15–25.50
1.62–25.50
1.59–25.49
Reflections collected
Independent reflections (Rint)
10290
3494 (0.1118)
1879
5392
3345
2240
15573
1404 (0.0346)
1097
Reflections with
I > 2σ(I)
Data/parameters
Restraints
3494/246
0
3345/230
0
1404/114
0
Goodness-of-fit on F 2
Final R indices (I > 2σ(I))
R indices (all data)
0.966
1.039
1.065
R1 = 0.0466, wR2 = 0.0845
R1 = 0.1311, wR2 = 0.1113
0.347 and –0.525
R1 = 0.0558, wR2 = 0.1186
R1 = 0.0946, wR2 = 0.1393
0.390 and –0.347
R1 = 0.0257, wR2 = 0.0697
R1 = 0.0361, wR2 = 0.0770
0.200 and –0.185
Largest difference peak and
hole, e Å–3
and new C–O absorption bands appeared in the indicates coordination of the imine nitrogen to the
region 1080–1105 cm–1 in the spectra of the com-
plexes, indicating that the Schiff bases coordinate to
the nickel atoms through deprotonated form. The
infrared spectra of the complexes display intense
absorption bands at 1627 cm–1, which can be assigned
to the C=N stretching frequencies of the Schiff base
ligands, whereas for the free Schiff bases the corre-
sponding absorption bands are observed at higher
wave numbers (1635–1640 cm–1). The shift of these
nickel center [19].
The UV−Vis spectra of the complexes were
recorded in methanol solution. The complexes show
two charge transfer bands at about 255 and 330 nm,
which are attributed to π–π* and n–π* transitions
within the Schiff base ligands. The weak absorption
bands at about 580 nm can be assigned to the d–d
transitions.
Qualitative determination of antimicrobial activity
bands on complexation towards lower wave number was done using the disk diffusion method [20, 21]. The
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148
XUE et al.
(a)
C(10)
C(11)
C(12)
C(9)
C(13)
C(8)
C(14)
C(15)
C(7)
C(6)
N(2)
O(2)
N(1)
C(1)
C(20)
C(19)
Ni(1)
C(16)
C(17)
C(21)
C(18)
C(5)
O(1)
C(2)
C(3)
C(22)
C(4)
(b)
C(9)
C(8)
N(1)
C(10)
N(2)
C(11)
C(12)
C(7)
C(1)
C(16)
C(14)
C(6)
C(5)
C(2)
C(17)
Ni(1)
C(18)
O(1)
C(3)
C(15)
O(2)
C(13)
C(4)
O(3)
C(19)
(c)
C(8)
C(8A)
C(7)
N(1)
C(1)
C(7A)
C(1A)
N(1A)
C(2A)
C(6)
C(6A)
C(5A)
C(5)
C(4)
Ni(1)
O(1)
F(2)
C(2)
F(2A)
O(1A)
C(3A)
C(3)
C(4A)
F(1A)
F(1)
Fig. 1. Molecular structure of complexes I (a), II (b), III (c) with 30% probability thermal ellipsoids.
results are summarized in Table 4. A comparative that the nickel complexes have higher activity than the
study of minimum inhibitory concentration (MIC) free Schiff bases. Generally, this is caused by the
values of the Schiff bases and the complexes indicate greater lipophilic nature of the complexes than the
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NICKEL(II) COMPLEXES DERIVED FROM BIS-SCHIFF BASES
Table 2. Selected bond distances (Å) and angles (deg) for I–III*
149
Bond
d, Å
Bond
d, Å
I
Ni(1)–O(1)
Ni(1)–N(1)
1.842(3)
1.860(3)
Ni(1)–O(2)
Ni(1)–N(2)
1.851(3)
1.835(3)
II
Ni(1)–O(1)
Ni(1)–N(1)
1.849(3)
1.833(4)
Ni(1)–O(2)
Ni(1)–N(2)
1.846(3)
1.847(4)
III
Ni(1)–N(1)
Angle
Ni(1)–O(1)
1.8457(13)
1.8493(17)
Angle
ω, deg
ω, deg
I
N(2)Ni(1)O(1)
O(1)Ni(1)O(2)
O(1)Ni(1)N(1)
177.44(14)
84.46(12)
95.15(15)
N(2)Ni(1)O(2)
N(2)Ni(1)N(1)
O(2)Ni(1)N(1)
94.72(14)
85.86(16)
175.50(14)
II
N(1)Ni(1)O(2)
O(2)Ni(1)N(2)
O(2)Ni(1)O(1)
177.94(15)
94.89(17)
84.21(14)
N(1)Ni(1)N(2)
N(1)Ni(1)O(1)
N(2)Ni(1)O(1)
86.35(18)
94.57(16)
179.02(16)
III
O(1)Ni(1)N(1A)
N(1)Ni(1)N(1A)
O(1)Ni(1)O(1A)
O(1)Ni(1)N(1)
85.47(8)
94.37(7)
177.63(7)
85.89(10)
* Symmetry code for A: –x, 1–y, –z (III).
Table 3. Geometriс parameters of hydrogen воnd for complexes I–III*
Distance, Å
D–H∙∙∙A
Angle D–H∙∙∙A, deg
150(5)
D–H
0.98
H∙∙∙A
D∙∙∙A
I
C(8)–H(8)∙∙∙O(1)#1
2.37(2)
3.259(3)
II
O(3)–H(3A)∙∙∙O(1)
C(9)–H(9A)∙∙∙O(1)#2
0.82
0.97
2.08(3)
2.54(3)
2.890(4)
3.363(4)
169(5)
143(5)
III
C(4)–H(4)∙∙∙F(2)#3
C(8)–H(8B)∙∙∙F(1)#4
0.93
0.97
2.54(2)
3.465(3)
172(4)
163(4)
2.31(2)
3.245(3)
#1
#2
#3
#4
* Symmetry codes: 1 – x, 1 – y, 1 – z (I); –x, 1 – y, 1 – z (II); 1/2 – x, 1/2 + y, 1/2 – z; x, –1 + y, z (III).
ligands. Such increased activity of the metal chelates The same pattern is observed for the free Schiff bases.
H2Lc is more active than the other two. This phenom-
enon obvious indicates that the fluoro-substitute
groups are essential for the biological activity. For
Staphylococcus aureus, the activity of complex III is
less than the control drug Tetracycline. But for Esche-
can be explained on the basis of chelating theory [22].
In general, complexes I and II have similar anti-
bacterial and antifungi activities against Staphylococ-
cus aureus, Escherichia coli, and Candida albicans.
However, complex III has obvious higher activities
against the bacteria and fungi than complexes I and II. richia coli and Candida albicans, the complex has
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150
XUE et al.
(a)
(a)
6000
5000
4000
3000
2000
1000
0
x
z
0
(I)
(I) simulated
10
10
10
20
20
20
30
(b)
40
40
40
50
60
60
60
y
5000
4000
3000
2000
1000
0
(b)
x
(II)
(II) simulated
0
z
30
(c)
50
y
5000
4000
3000
2000
1000
0
(c)
z
y
0
(III)
(III) simulated
30
2θ, deg
50
x
Fig. 3. Experimental and simulated powder XRD patterns
of complexes I (a), II (b), III (c).
Fig. 2. Crystal structure of complexes I (a), II (b), III (c).
Hydrogen bonds are drawn as dashed lines.
In summary, three nickel(II) complexes with bis-
Schiff bases have been prepared and characterized.
The crystal structures of the complexes were con-
firmed by XRD. The nickel atoms in the complexes are
in square planar coordination. The biological test
stronger activities than Tetracycline. Further work
needs to be carried out to investigate the structure−
activity relationship.
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NICKEL(II) COMPLEXES DERIVED FROM BIS-SCHIFF BASES
151
Table 4. MIC values (μg/mL) for the antimicrobial activities of the tested compounds
Compound
Staphylococcus aureus
Escherichia coli
Candida albicans
>1024
H2La
H2Lb
H2Lc
128
128
16
256
256
32
>1024
128
I
II
III
8
8
2
32
32
2
64
64
8
Tetracycline
0.30
2.15
>1024
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base ligand has effective activities against Staphylococ-
cus aureus, Escherichia coli, and Candida albicans.
Fluoro-subsituted groups in the Schiff bases may play
important role in the biological processes.
10. Kaczmarek, M.T., Zabiszak, M., Nowak, M., et al.,
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This research was supported by the Top-class founda-
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2018006 and PXY-PYJJ-2018002).
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