Synthesis, spectral characterization, crystal structure determination and antimicrobial activity of Ni(II), Cu(II) and Zn(II) complexes with the Schiff base ligand derived from 3,5-dibromosalicylaldehyde

Article abstract of DOI:10.1016/j.molstruc.2020.129842

Three new mononuclear metal complexes of the type ML, (M = Ni, Cu and Zn), with salen type tetradentate (ONNO) Schiff base, N,N′-bis(3,5-dibromosalicylidene)-1,3-diaminopropane (H₂L), have been prepared and characterized using FT-IR, ¹H NMR and elemental (CHN) analyses. In addition, the crystal structures of all complexes were analyzed by single crystal X-ray diffraction (SC-XRD) technique. The SC-XRD data explored that in the nickel and copper complexes a monoclinic crystal system was present and the coordination sphere around the metal centers consists of two oxygen atoms and two nitrogen atoms from chelating ligands to give a square planar geometry, while the zinc complex has orthorhombic crystal system and in addition to the atoms from chelating ligand, two O-atoms from the water molecules also coordinate to Zn atom to give distorted octahedral geometry. The in vitro antibacterial activities of the ligand and complexes were elaborated by screening them against Gram (+ve) (Staphylococcus aureus and Bacillus cereus) Gram (-ve) (Escherichia coli and Pseudomonas aeruginosa). All the synthesized compounds showed significant activity against the tested bacterial strains.

Full text of DOI:10.1016/j.molstruc.2020.129842

Journal of Molecular Structure 1229 (2021) 129842
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Synthesis, spectral characterization, crystal structure determination
and antimicrobial activity of Ni(II), Cu(II) and Zn(II) complexes with
the Schiff base ligand derived from 3,5-dibromosalicylaldehyde
Hadi Kargara,∗, Amir Adabi Ardakanib, Muhammad Nawaz Tahirc, Muhammad Ashfaqc,
Khurram Shahzad Munaward,e
a Department of Chemical Engineering, Faculty of Engineering, Ardakan University, P.O. Box 184, Ardakan, Iran
b Department of Chemistry, Ardakan Branch, Islamic Azad University, Ardakan, Iran
c Department of Physics, University of Sargodha, Punjab, Pakistan
d Department of Chemistry, University of Sargodha, Punjab, Pakistan
e Department of Chemistry, University of Mianwali, Mianwali, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new mononuclear metal complexes of the type ML, (M = Ni, Cu and Zn), with salen type tetraden-
ꢀ
Received 7 November 2020
Revised 15 December 2020
Accepted 22 December 2020
Available online 29 December 2020
tate (ONNO) Schiff base, N,N -bis(3,5-dibromosalicylidene)-1,3-diaminopropane (H2L), have been prepared
and characterized using FT-IR, 1H NMR and elemental (CHN) analyses. In addition, the crystal structures
of all complexes were analyzed by single crystal X-ray diffraction (SC-XRD) technique. The SC-XRD data
explored that in the nickel and copper complexes a monoclinic crystal system was present and the co-
ordination sphere around the metal centers consists of two oxygen atoms and two nitrogen atoms from
chelating ligands to give a square planar geometry, while the zinc complex has orthorhombic crystal sys-
tem and in addition to the atoms from chelating ligand, two O-atoms from the water molecules also
coordinate to Zn atom to give distorted octahedral geometry. The in vitro antibacterial activities of the
ligand and complexes were elaborated by screening them against Gram (+ve) (Staphylococcus aureus and
Bacillus cereus) Gram (-ve) (Escherichia coli and Pseudomonas aeruginosa). All the synthesized compounds
showed significant activity against the tested bacterial strains.
Keywords:
Schiff base complexes
Spectral characterization
X-Ray structure
Antibacterial activity
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
donor sites derived from halogenated salicylaldehyde were widely
investigated due to their potential antitumor, antifungal and an-
The species having azomethine group make an excellent class of
ligands which are matchless in their versatility, resemblance with
natural biological molecules and have relevancy with metabolic
processes taking place in biological systems [1]. The synthe-
sis, spectral characterization and structure activity relationship of
Schiff bases were studied in depth by numerous investigators pre-
viously [2–4]. The development of coordination chemistry by pro-
viding lone pairs from electron rich nitrogen and/or oxygen atoms
to transition metals made them more interesting due to their
physico-chemical, catalytic, photochromic, biological and therapeu-
tic activities [5–10].
tibacterial activities [14–18].
Schiff bases complexes of Ni(II), Cu(II) and Zn(II) have dis-
tinctive properties and novel reactivity which serves as a base
for the evolution of complex compounds for potential applica-
tion in various fields [19,20]. These new and unusual properties
open a new horizon to study their medical, analytical and biolog-
ical prospects [21]. It is well known that several Schiff base com-
plexes of Ni(II), Cu(II) and Zn(II) are used as anti-inflammatory, an-
tipyretic, chemosensor, anti-diabetic, anti-bacterial, anti-cancer and
anti-HIV (human immunodeficiency virus) [22–24].
In the present study tetravalent Schiff base ligand is selected on
the basis of many reasons: a) single step preparation by the con-
densation of diamines with dibromo substituted salicylaldehydes;
b) form effortlessly isolate able stable complexes with variety of
metals; c) metal complexes display easily available axial Lewis acid
sites for further coordination with either solvents of crystallization
or with co ligands [25].
It was reported that salen type Schiff bases containing one or
two halo-atoms in the aromatic rings have a broad range of ap-
plications [11–13]. The chelated Schiff bases containing N and O
∗
Corresponding author.
E-mail addresses: h.kargar@ardakan.ac.ir, hadi_kargar@yahoo.com (H. Kargar).
https://doi.org/10.1016/j.molstruc.2020.129842
0022-2860/© 2020 Elsevier B.V. All rights reserved.

H. Kargar, A.A. Ardakani, M.N. Tahir et al.
Journal of Molecular Structure 1229 (2021) 129842
˚
In the current research we have focused our endeavor to the
synthesis, structural elucidation and antimicrobial properties of
bromo substituted salen type Schiff base and its complexes with
Ni(II), Cu(II) and Zn(II).
(λ = 0.71073 A). The brown, dark red and yellow single crys-
tals of Ni(L), Cu(L) and Zn(L) suitable for X-ray analysis were
obtained from methanol solution and mounted on a glass fiber
for data collection on Bruker Apex-II software [27]. The struc-
tures were solved by direct methods and subsequent difference
Fourier maps on SHELXS97 [28] and then refined on F2 by a
full-matrix least-squares procedure using anisotropic displacement
parameters. Atomic factors are from the international tables for
X-ray Crystallography [29]. All non-hydrogen atoms were refined
with anisotropic displacement parameters. Hydrogen atoms were
placed in ideal positions and refined as riding atoms with rela-
tive isotropic displacement parameters. All refinements were per-
formed using the SHELXL-2018/3 and WinGX-2014.1 programs
[30,31]. The method to collect data was ω-scans and integrated
using Bruker SAINT [32] software package. The crystallographic il-
lustrations for complexes were prepared using ORTEP-3 [33] and
platon [34]. Experimental parameters pertaining to single-crystal
X-ray analysis of complexes are given in Table 1.
2. Experimental
2.1. Physical measurements
Microanalysis of the complexes were done using a Heraeus
CHN-O-FLASH EA 1112 elemental analyzer. FT-IR spectra were
recorded on a FT-IR Prestige 21 spectrophotometer from 400-
4000 cm−1 using KBr pellets. 1H NMR spectroscopy in DMSO-
d6 (400 MHz, Bruker) was carried out by using tetramethylsilane
(TMS) as internal standard. Chemical shifts for proton resonances
are reported in ppm (δ) relative to tetramethylsilane and DMSO-
d6.
2.2. Synthesis of the Schiff base (H2L)
2.5. Antimicrobial activity
All the chemicals and solvents used for the syntheses were of
commercially available reagent grade and were used without fur-
ther purification. Schiff base ligand was prepared following the
literature procedure [26]. To a stirred ethanolic (25 mL) solution
of 3,5-dibromosalicylaldehyde (2 mmol) was added an ethanolic
(25 mL) solution of the 1,3-propanediamine (1 mmol). The reac-
tion mixture was refluxed for 1-3 h in a water bath. The resulting
solution was cooled to room temperature and the precipitates ob-
tained were collected by suction filtration and washed with cold
ethanol (3 × 10 mL) to afford the desired Schiff base.
The Schiff base ligand and its metal(II) complexes were stud-
ied to assess their potentials as antibacterial agents. The tested
microorganisms were the standard strains of two Gram-positive
(Staphylococcus aureus PTCC1431, Bacillus cereus PTCC1015), and
two Gram-negative (Escherichia coli PTCC1394, Pseudomonas aerug-
inosa PTCC1074) bacteria. In order to compare the results, ery-
thromycin (15 mg/disk) was used as an antibiotic reference drug.
The compounds were dissolved in DMSO at 50 μg/mL concentra-
tion. Determination of the antibacterial activity was carried out by
spot-on the lawn method. Antibacterial activity of ligand and its
corresponding complexes were tested by spotting the solution of
20 μL of ligand and its complexes onto the soft agar lawn, seeded
with 107 cells/ml of standard strains. Each solution of ligand and
its complexes were placed on the surface-inoculated TSA agars and
incubated at 37°C for 24 h. Inhibition zone around the specimens
was used to indicate antibacterial activity of each compound. Each
test was performed in triplicate.
2.3. General procedure for the synthesis of the complexes
In order to synthesize the nickel(II) complexes [Ni(L)], the
metal precursor Ni(OAc)2.4H2O (0.248 g, 1 mmol), for copper(II)
complexes [Cu(L)], the metal precursor Cu(OAc)2.H2O (0.200 g,
1
mmol), for zinc(II) complexes [Zn(L)], the metal precursor
Zn(OAc)2.2H2O (0.220 g, 1 mmol) was added to a hot methano-
lic solution (30 mL) of the corresponding ligand H2L (1.0 mmol).
The resultant mixture was refluxed for 3 h and then it was filtered,
washed thoroughly with methanol and dried.
3. Results and discussion
[Ni(L)], Yield: 81 %. Calculated for C17 H12Br4N2NiO2: C 31.19,
H 1.85, N 4.28 %. Analysis found: C 31.31, H 1.92, N 4.17. FT-IR
3.1. Syntheses
(KBr, cm−1): υ C H(aromatic): 3063, υ C H(aliphatic): 2941, 2878,
–
–
The Schiff base ligand H2L was prepared by the reac-
tion of 1,3-diaminopropane with the corresponding 3,5-
dibromosalicylaldehyde in nearly 78 % yield in ethanol. Treatment
of the Schiff base ligands H2L with the respective Ni(OAc)2.4H2O,
=
=
–
–
υ HC N: 1618, υ C C and C N: 1578, 1508, 1442, 1375, υ C O:
1319, υ Ni-N: 534, υ Ni O: 415. 1H NMR [d6-DMSO, δ (ppm)]: 8.58
–
– =
(s, 2 H, H C N), 7.58 (d, 2 H, J = 2.4 Hz, H arom.), 7.41 (d, 2 H,
J = 2.4 Hz, H arom.), 3.73 (t, 4 H, CH2-N), 2.08 (br, 2 H, CH2-C).
[Cu(L)], Yield: 85 %. Calculated for C17 H12Br4CuN2O2: C 30.96,
H 1.83, N 4.25 %. Analysis found: C 31.11, H 1.89, N 4.12. FT-IR
(KBr, cm−1): υ C-H(aromatic): 3064, υ C-H(aliphatic): 2941, 2868,
Cu(OAc)2.H2O and Zn(OAc)2.2H2O in
a 1:1 ratio under reflux
condition led to the nickel(II), copper(II) and zinc(II) complexes,
respectively. The spectroscopic data is in good agreement with
the chemical formula proposed for Schiff base complexes. The
synthetic procedure of Schiff base ligand and their complexes is
presented in Scheme 1.
=
=
–
υ HC N: 1622, υ C C and C N: 1577, 1508, 1440, 1382, υ C-O:
1309, υ Cu N: 545, υ Cu O: 425.
–
–
[Zn(L)], Yield: 68 %. Calculated for C17 H12Br4N2O2Zn: C 30.88,
H 1.83, N 4.24 %. Analysis found: C 30.97, H 1.92, N 4.02. FT-IR
(KBr, cm−1): υ C-H(aromatic): 3062, υ C-H(aliphatic): 2924, 2854,
3.2. Crystal structures of complexes
=
=
–
–
υ HC N: 1620, υ C C and C N: 1575, 1508, 1440, 1384, υ C O:
In NiL (Fig. 1, Table 1), the asymmetric unit consists of half
of the molecule with nickel atom at the special position i.e. on
two fold axis and the other half of the molecule is symmetri-
cally generated with symmetry code (–x, -y,1/2-z). The coordina-
tion sphere around the Ni-atom consists of two oxygen atoms
and two nitrogen atoms from chelating ligands. In the coordina-
1298, υ Ni N: 542, υ Ni O: 410. 1H NMR [d6-DMSO, δ (ppm)]:
–
–
– =
8.27 (s, 2 H, H C N), 7.63 (d, 2 H, J = 2.6 Hz, H arom.), 7.38 (d, 2
H, J = 2.6 Hz, H arom.), 3.77 (t, 4 H, CH2-N), 1.97 (br, 2 H, CH2-C).
2.4. Crystallographic methods
–
–
tion sphere, the bond lengths Ni O and Ni N are 1.863 (2) and
˚
The X-ray diffraction measurement of Ni(L), Cu(L) and Zn(L)
complexes were carried out on Bruker Kappa APEXII CCD X-
ray diffractometer with graphite monochromated Mo-Kα radiation
1.879 (3) A, respectively whereas the bond angles range from 84.69
(1)° to 92.00 (2)°, thus slightly distorted square planar geome-
try is formed. The 3-iminopropan-1-ol group A (C1/C6/C7/N1/O1)
2

H. Kargar, A.A. Ardakani, M.N. Tahir et al.
Journal of Molecular Structure 1229 (2021) 129842
Table 1
Crystal data and structure refinement parameters for complexes.
Identification code
NiL
CuL
ZnL
Chemical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
17H12Br4N2NiO2
C17H12Br4CuN2O2
659.47
C17H16Br4N2O4Zn
654.60
296
697.33
296
296
Monoclinic
C2/c
Monoclinic
P21/n
Orthorhombic
Pnma
˚
a (A)
25.632(4)
10.2255(14)
6.9951(8)
90
13.975(2)
7.011(1)
19.961(3)
90
7.9472(3)
24.5752(12)
10.4656(4)
90
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
96.188(4)
90
109.459(4)
90
90
90
3
˚
Volume (A )
1822.7(4)
4
1844.0(5)
4
2043.97(15)
4
Z
Calculated Density (Mg/m3)
Absorption coefficient (mm−1
F(000)
2.386
2.375
2.266
)
9.848
9.867
9.048
1248
1252
1336
Crystal Shape
Needle
Brown
0.35 × 0.14 × 0.12
Rod
Block
Crystal color
Dark red
0.46 × 0.26 × 0.24
Yellow
0.36 × 0.22 × 0.18
Crystal size (mm)
Data Collection
Absorption correction
multi-scan (SADABS; Bruker, 2005)
7369, 1981, 1422
multi-scan (SADABS; Bruker, 2005)
3637, 3637, 1731
multi-scan (SADABS; Bruker, 2005)
9459, 2476, 1908
No. of measured, independent and
observed [I> 2s(I)] reflections
Rint
0.032
0.049
0.028
Theta range for data collection
Index ranges
1.598° to 27.000°
1.564° to 26.000°
2.115° to 27.923°
-32≤ h ≤32, -12≤ k ≤13, -8≤ l ≤5
0.639
-17≤ h ≤16, -8≤ k ≤8, -24≤ l ≤24
0.617
-10≤ h ≤10, -22≤ k ≤32, -13≤ l ≤9
0.659
−1
˚
(sin θ/λ)max (A
)
Refinement
R[F2> 2σ(F2)], wR(F2), S
0.032, 0.054, 1.01
0.049, 0.126, 0.99
0.0289, 0.055, 1.01
No. of reflections
1981
3637
2476
No. of parameters
H-atom treatment
119
236
139
H-atom parameters constrained
H-atom parameters constrained
H-atoms treated by a mixture of
independent and constrained
refinement
−3
˚
ꢀρmax, ꢀρmin (e A
)
0.43, −0.48
1.35, −1.35
0.42, −0.54
Fig. 1. ORTEP diagram of NiL drawn at the probability level of 50%. H-atoms are shown by small circles of arbitrary radii.
˚
and 3,5-dibromobenzene group B (C1-C6/Br1/Br2) are planar with
amplitude Q = 0.741(4) A, θ = 90.0(2)° and ϕ = 270.0(2)°. The
˚
ꢀ
r.m.s deviation of 0.0425 and 0.0454 A, respectively. The C-atoms
–
molecules are connected with each other through C H O bonding
˚
(C8/C9) are deviated by 0.4317 (5) and -0.6895 (6) A above and
to form zigzag chains that run along the c crystallographic axis as
shown in Figure S1 and given in Table 2. In addition to H-bonding,
a weak interaction of type π-π stacking is found which helps in
further stabilization of crystal packing. Benzene ring (C1-C6) lo-
cated at the asymmetric position is involved in offset π-π stacking
interaction with benzene ring located at (x,-y,-1/2+z) with inter-
below the plane of group A, respectively. The dihedral angle be-
tween A/B is 9.04 (6)°. Ring Puckering investigation shows that
the chelating ring (C1/C6/C7/N1/O1/Ni1) has puckering amplitude
˚
Q = 0.388(2) A, θ = 69.5(4)° and ϕ = 3.3 (5)°. It is also inferred
that the ring (C8/C8i/C9/N1/N1i/Ni1) adopts T-form with puckering
3

H. Kargar, A.A. Ardakani, M.N. Tahir et al.
Journal of Molecular Structure 1229 (2021) 129842
Scheme 1. The synthesis pathways of the ligand and its complexes.
Table 2
˚
Hydrogen-bond geometry (A, °) for complexes.
•••
•••
•••
•••
D—H A
NiL
D—H
A
D—H
H
A
A
D
A
i
••
C8—H8B O1
0.97
2.65
2.59
3.315 (4)
126
ii
•••
C8—H8B
O1
0.97
3.482 (4)
153
•••
•••
•••
•••
D—H
140
ZnL
D—H
A
D—H
0.97
H
D
A
A
A
ii
•••
C8—H8A
Br1
2.99
3.781 (2)
iii
•••
O2—H2
O2—H2
O3—H3A
O3—H3A
Br1
0.73 (2)
0.73 (2)
0.72 (3)
0.72 (3)
D—H
0.93
2.93 (3)
2.18 (2)
3.08 (3)
2.4312 (16)
2.862 (3)
128 (3)
155 (3)
132 (3)
148 (3)
iii
•••
O1
iv
iv
•••
•••
Br1
O1
3.5990 (17)
2.17 (3)
2.804 (3)
•••
•••
•••
•••
•••
•••
CuL
D—H
A
H
A
D
A
D—H
155
136
155
131
129
141
135
155
152
v
C3—H3
Br3
3.09
3.11
2.55
3.04
3.03
2.86
3.07
2.56
3.09
3.955 (4)
vi
C8—H8A
C8—H8B
C9—H9A
C9—H9A
C9—H9B
Br1
0.97
3.867 (12)
3.459 (15)
3.750 (17)
3.711 (15)
3.670 (17)
3.823 (13)
3.459 (15)
3.935 (15)
vii
•••
•••
O1
0.97
vii
vi
Br1
0.97
•••
•••
Br4
0.97
viii
Br4
0.97
vi
•••
•••
C10—H10A
Br4
0.97
viii
C10—H10B
O2
0.97
ix
•••
C15—H15
Br2
0.93
Symmetry codes: (i) x, −y, z+1/2; (ii) −x, −y, −z+1; (ii) x, y, z−1; (iii) x+1/2, −y+1/2,
−z+3/2; (iv) x−1/2, y, −z+3/2; (v) x−1/2, −y+1/2, z+1/2; (vi) x−1/2, −y+1/2, z−1/2;
(vii) −x+1/2, y−1/2, −z+1/2; (viii) −x+1/2, y+1/2, −z+1/2; (ix) x+1, y, z.
4

H. Kargar, A.A. Ardakani, M.N. Tahir et al.
Journal of Molecular Structure 1229 (2021) 129842
˚
Fig. 2. Graphical representation of π-π stacking interaction for NiL. Distance shown are measured in A. H-atoms are not shown for clarity.
Fig. 3. ORTEP diagram of CuL drawn at the probability level of 50%. H-atoms are shown by small circles of arbitrary radii.
˚
˚
˚
centroid separation of 4.128 A having ring-off of 2.648 A. Similarly,
benzene rings related by symmetry code (x,-y,1/2+z) are involved
in off-set π-π stacking interaction with inter-centroid separation
with r.m.s deviation of 0.0177 and 0.0143 A, respectively. The C-
˚
atom (C10) is deviated by 0.2135 (2) A above the plane of group
C, respectively. The dihedral angle between C/D is 4.1 (2)° in-
dicating that group C and D are also almost parallel to each
other. Ring Puckering investigation shows that the chelating ring
˚
˚
of 4.128 A having ring-off of 1.998 A as shown in Fig. 2.
In CuL (Fig. 3, Table 1), the coordination sphere around the Cu-
atom consists of two oxygen atoms and two nitrogen atoms from
the chelating ligands. In coordination sphere, the bond lengths
˚
(C8/C10/N1/N2/Cu1) has puckering amplitude Q = 0.761(12) A,
θ = 90.3(9)° and ϕ = 273.9(9)°. The molecules are connected with
…
each other through C H O and C H…Br bonding to form zigzag
chains that run along b crystallographic axis as shown in Figure S2
and given in Table 2. In addition to H-bonding, a weak interaction
of type π-π stacking is found which helps in further stabilization
of crystal packing. π-π stacking interaction is found between dif-
–
–
–
–
–
–
Cu O1, Cu O2, Cu N1 and Cu N2 are 1.891 (1), 1.908 (1), 1.949 (2)
˚
and 1.9732 (2) A, respectively, whereas the bond angles range from
88.2 (4)° to 94.2 (5)°, thus slightly distorted square planar geome-
try is formed. In the first chelating ligand, the 3-iminopropan-1-ol
group A (C1/C6/C7/N1/O1) and 3,5-dibromobenzene group B (C1-
˚
˚
C6/Br1/Br2) are planar with r.m.s deviation of 0.0083 and 0.0119 A,
ferent rings with inter-centroid distance ranges from 3.434 A to
˚
˚
˚
respectively. The C-atoms (C8/C9) are deviated by -0.2287 (2) and
4.421 A with slippage ranges from 0.540 A to 2.987 A as shown in
Fig. 4.
˚
0.9465 (2) A below and above the plane of group A, respectively.
The dihedral angle between A/B is 4.7 (3)° indicating that group
A and B are almost parallel to each other. In the second chelat-
ing ligand, the 3-iminopropan-1-ol group C (C11/C12/C17/N2/O2)
and 3,5-dibromobenzene group D (C12-C17/Br3/Br4) are planar
In ZnL (Fig. 5, Table 1), the asymmetric unit consists of half of
the molecule with zinc atom at the special position i.e. on two
fold axis and the other half of the molecule is symmetrically gen-
erated with symmetry code (x,1/2-y,z). The coordination sphere
5

H. Kargar, A.A. Ardakani, M.N. Tahir et al.
Journal of Molecular Structure 1229 (2021) 129842
˚
Fig. 4. Graphical representation of π-π stacking interaction for CuL. Distance shown are measured in A. H-atoms are not shown for clarity, where Cg(1), Cg(2), Cg(3), Cg(4)
are the centroid of ring (C1/C6/C7N1/O1/Cu1), (C11/C12/C17/N2/O2/Cu1), (C1-C6), (C12-C17), respectively.
Fig. 5. ORTEP diagram of ZnL drawn at the probability level of 50%. H-atoms are shown by small circles of arbitrary radii.
around the Zn-atom consists of two oxygen atoms and two nitro-
gen atoms from chelating ligands and two O-atoms from the water
molecules. In the coordination sphere, the bond lengths of Zn-O
direction, where OH is from water and acceptor O-atom is from
3-iminopropan-1-ol group as shown in Figure S3 and given in
Table 2. In addition to H-bonding, a weak interaction of type π-
π stacking is found which helps in further stabilization of crystal
packing. Benzene ring (C1-C6) located at the asymmetric position
is involved in offset π-π stacking interaction with benzene ring lo-
cated at (1/2+x,y,3/2-z) and (-1/2+x,y,3/2-z) interaction with inter-
˚
and Zn-N ranges from 2.0794 (2) to 2.1791 (3) A and 2.1157 (2) to
˚
2.1158 (2) A, respectively. The bond angles range from 87.00 (7)° to
95.86 (8)°, bond lengths and bond angles are such that a slightly
distorted octahedral geometry is formed. The 3-iminopropan-1-ol
group A (C1/C6/C7/N1/O1) and 3,5-dibromobenzene group B (C1-
˚
˚
˚
centroid separation of 3.963 A having ring-off of 1.419 A to 1.471 A
as shown in Fig. 6.
˚
C6/Br1/Br2) are planar with r.m.s deviation of 0.0238 and 0.0264 A,
respectively. The C-atoms (C8/C9) are deviated by 0.1903 (4) and -
˚
3.3. lH NMR spectra
0.8298 (5) A above and below the plane of group A, respectively.
The dihedral angle between A/B is 4.7 (5)°. Ring Puckering inves-
1H NMR spectra of the ligand was recorded in deuterated chlo-
roform (CDCl3), while the spectra of the complexes were recorded
in DMSO-d6. The 1H NMR data of the metal complexes are given
in the experimental section. In the 1H NMR spectra of the H2L sig-
nal at δ = 14.52 ppm, which corresponds to the phenolic OH res-
onance is disappeared in the spectra of the nickel and zinc com-
tigation shows that the chelating ring (C1/C6/C7/N1/O1/Zn1) has
˚
puckering amplitude Q = 0.3022(2) A, θ = 64.6(4)° and ϕ = 4.6
(5)° whereas the ring (C8/C8i/C9/N1/N1i/Zn1) has puckering am-
˚
plitude Q = 0.535(3) A, θ = 138.7(2)° and ϕ = 360.0(4)°. The
molecules are connected with each other through O H…O bond-
–
ing to form one dimensional chain along [100] crystallographic
6

H. Kargar, A.A. Ardakani, M.N. Tahir et al.
Journal of Molecular Structure 1229 (2021) 129842
˚
Fig. 6. Graphical representations of π-π stacking interaction for ZnL. Distances shown are measured in A. H-atoms are omitted for clarity.
plexes (Figure S4). This clearly indicates that the Schiff base ligand
is coordinated as an anionic ligand to the Ni(II) and Zn(II) ions.
In the 1H NMR spectra of the complexes, the signals at δ = 8.58,
– =
8.27 ppm are attributed to the H C N- proton of imine, for nickel
and zinc complex, respectively. There is a slight shift of the imine
proton to down field in the obtained 1H NMR spectra of the nickel
and zinc complexes compared to the ligand one. This shift con-
firms the coordination of the phenolic oxygen and imine nitrogen
to metal ions. The aromatic protons of the Ni(II) and Zn(II) com-
plexes appear in the range of δ = 7.41–7.58 ppm and δ = 7.37–
7.63 ppm, respectively. The –CH2–N protons of the NiL and ZnL
complexes appear as a triplet at δ = 3.73 and 3.77 ppm, re-
spectively. The broad signals at δ = 2.08 and 2.03 ppm are at-
tributed to the –CH2–C protons of the NiL and ZnL complexes,
respectively.
Fig. 7. A histogram shows the antibacterial evaluation of the investigated H2L Schiff
base ligand and its corresponding complexes.
3.4. FT-IR spectra
3.5. Antibacterial activities
The comparison between the selected bands in the FT-IR spec-
To contribute in the field of bioinorganic chemistry, all the com-
tra of Schiff base ligand and its metal complexes are presented in
pounds were screened for their antibacterial activity. Results have
Table 3 and Figure S5. In the FT-IR spectra of complexes, the ν
been recorded in the form of inhibition zones and activities are
=
–
(HC N) and ν (C O) bands shifted to lower and higher wavenum-
bers, respectively, in comparison with their corresponding free
ligand thereby indicating a coordinative interaction between the
iminic nitrogen and phenolic oxygen atoms with central metals.
The iminic nitrogen and phenolic oxygen coordination could also
be confirmed by the appearance of weak bands located at the low
illustrated in Fig. 7. It has to be mentioned that DMSO did not ex-
hibit any noticeable antibacterial activity, thus the solvent did not
influence the biological activity of the studied compounds. On the
basis of results, it is worth noting that: a) H2L ligand showed the
same antibacterial activity comparable to that of the standard. Fur-
ther, the antibacterial activity of complexes may be significantly
more to that of standards; b) The inhibition zones of the Schiff
base ligand and corresponding complexes showed that the all com-
pounds were more toxic towards gram positive strains. The reason
is the difference in the structure of the cell walls. The cell mem-
brane of the bacteria consists of peptidoglycan which is thicker in
the gram positive bacteria [35]; c) On the basis of Overtone’s con-
cept [36] and tweedy’s theory [37], metal ions play a significant
role in enhancing the antibacterial activity on chelation [38]. How-
ever, in the present study the complexes are slightly more active
than the free Schiff base ligand due the cell permeability. Another
reason may be because of the lower lipophilicity the penetration
of the complexes through the lipid membrane was decreased and,
hence, they could neither block nor inhibit the growth of the mi-
croorganisms [39].
–
–
wavenumbers which are assigned to (M N) and (M O) at 530-
545 cm−1 and 410-425 cm−1 respectively.
Table 3
FT-IR spectral data of ligand and its corresponding com-
plexes (cm−1
)
H2L
NiL
CuL
ZnL
υ(=CH)(aromatic)
υ(-CH)(aliphatic)
υ(HC=N)
3064
2943
1631
1166
-
3062
2941
1618
1319
534
3064
2941
1622
1309
545
3062
2924
1620
1298
542
υ(C–O)
υ(M–N)
υ(M–O)
-
415
425
410
7

H. Kargar, A.A. Ardakani, M.N. Tahir et al.
Journal of Molecular Structure 1229 (2021) 129842
4. Conclusion
[4] A. Rauf, A. Shah, K.S. Munawar, S. Ali, M.N. Tahir, M. Javed, A.M. Khan, Syn-
thesis, physicochemical elucidation, biological screening and molecular dock-
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(2020) 1130–1141.
In summary, we have prepared a series of three novel met-
als complexes, NiL, CuL and ZnL, with a salen-type Schiff base
derived by the condensation of 3,5-dibromosalicylidene and 1,3-
diaminopropane by using alcohol as solvent. The synthesized com-
plexes were characterized using various physico and spectrochem-
ical techniques. Furthermore, the molecular structures of all com-
plexes have been confirmed by single crystal X-ray diffraction. The
results showed that the stoichiometry in complexes is 1:1 (lig-
and:metal). The coordination sites are azomethine nitrogens and
phenolic oxygens as evident from 1H-NMR and FT-IR. Only in the
zinc complex the apical sites were involved in coordination with
water molecules to increase the coordination number from four to
six to make distorted octahedral geometry instead of square planar
around the metal atom as confirmed by SC-XRD. The antibacterial
screening tests disclosed that the number of live bacterial strains
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Schiff base ligand alone. The antibacterial data revealed that the
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We would like to make a statement about the main contribu-
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characterized them by different techniques; AAA was responsible
for biological data acquisition and analysis; MNT, MA and KSM
collected the single-crystal X-ray diffraction data and determined
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Appendix A. Supplementary data
CCDC No. 2042418 (for NiL), CCDC No. 2042419 (for ZnL) and
CCDC No. 2042420 (for CuL) contain the supplementary crystal-
lographic data for this contribution. Copies of the data may be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EB, UK (Fax: +44-1223-336-033; E-mail: de-
posit@ccdc.cam.ac.uk or http://www. ccdc.cam.ac.uk).
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Declaration of Competing Interest
The authors declare that they have no conflict of interest.
Acknowledgement
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The support of this work by Ardakan University is gratefully ac-
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Supplementary materials
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Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2020.129842.
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9