Dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N2O2 Schiff base ligand: Synthesis, crystal structure, characterization, DFT studies, cytotoxicity evaluation, and catalytic activity toward benzyl alcohol oxidation

Article abstract of DOI:10.1002/aoc.5493

Two novel dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N₂O₂ Schiff base ligand (H₂L = N,N′-bis-(4-hydroxysalicylidene)-1,3-diaminopropane) were prepared. The structures of the H₂L ligand,

Full text of DOI:10.1002/aoc.5493

Received: 13 September 2019
DOI: 10.1002/aoc.5493
Revised: 8 December 2019
Accepted: 12 December 2019
F U L L P A P E R
Dinuclear Zn(II) and tetranuclear Co(II) complexes of a
tetradentate N2O2 Schiff base ligand: Synthesis, crystal
structure, characterization, DFT studies, cytotoxicity
evaluation, and catalytic activity toward benzyl alcohol
oxidation
Tahereh Hosseinzadeh Sanatkar1 | Alireza Khorshidi1
| Jan Janczak2
1Department of Chemistry, Faculty of
Two novel dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate
N2O2 Schiff base ligand (H2L = N,N0-bis-(4-hydroxysalicylidene)-1,3-dia-
minopropane) were prepared. The structures of the H2L ligand, [4(Zn2L(μ-
O2CCH3)(O2CCH3)(H2O))]ꢀ4CH3OHꢀ3H2O (complex 1) and [Co4L2(μ-
O2CCH3)2(O2CCH3)2]ꢀ2H2O (complex 2) were unambiguously characterized
by elemental analysis, mass spectrometry, Fourier-transform infrared spectros-
Sciences, University of Guilan, Guilan,
Rasht, 41335-1914, Iran
2Polish Academy of Sciences, Institute of
Low Temperature and Structure Research,
1410, Wrocław, 50-950, Poland
Correspondence
Alireza Khorshidi, Department of
Chemistry, Faculty of Sciences, University
of Guilan, Rasht, Guilan, Iran.
Email: khorshidi@guilan.ac.ir
1
copy (FT-IR), H nuclear magnetic resonance (NMR), and UV–Vis spectros-
copy. Single crystal X-ray diffraction studies revealed that two Zn(II) nuclei of
1 were connected through μ-phenolato and μ-acetato bridges and had distorted
square pyramidal and distorted octahedral coordination geometries. Four
Co(II) nuclei of 2, on the contrary, showed a Co4O4 cubane-like configuration
in which Co(II) cations and O atoms were located at alternating corners of a
distorted cube. Density functional theory studies at the B3LYP/6–31 G(d) level
were carried out to gain an insight into the thermodynamic stability of the
complexes. in vitro cytotoxicity of the ligand and the complexes were evaluated
using the MTT assay against breast cancer MCF7 cells, melanoma cancer A375
cells, and prostate cancer PC3 cells as representative human cancer cell lines.
Complex 1 showed a remarkable activity against A375 and PC3 cancer cell
lines. In addition, 1 and 2 were used as precursors to produce zinc and cobalt
oxide nanoparticles via pyrolysis technique. The resulting ZnO and Co3O4
nanoparticles were characterized using FT-IR spectroscopy, UV–Vis diffuse
reflectance spectroscopy, powder X-ray diffraction, and field emission scanning
electron microscopy. Then, these nanoparticles were used as heterogeneous
catalysts in the oxidation of benzyl alcohol with hydrogen peroxide at room
temperature. Both catalysts showed good recyclability with a negligible
decrease in their efficiency during four catalytic cycles. The results of theoreti-
cal calculations showed that the most stable product was benzaldehyde, which
is in good agreement with the obtained experimental results.
Funding information
Research Council of University of Guilan
Appl Organometal Chem. 2020;e5493.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 19
https://doi.org/10.1002/aoc.5493

2 of 19
SANATKAR ET AL.
K E Y W O R D S
nanoparticles, polynuclear complexes, Schiff base, selective oxidation, tetradentate ligand
1 | INTRODUCTION
these methods have some drawbacks such as long
reaction time and high cost. Therefore, using coordina-
Schiff bases are considered “exclusive ligands” because
they play a key role in the development of coordination
chemistry. Schiff base ligands are prepared easily and can
be readily modified, both electronically and sterically.[1,2]
Schiff base ligands contain multiple potential donor sites,
which allow them to bind metal ions with diverse coordi-
nation geometries such as bidentate and tridentate.[3–6]
Tetradentate Schiff base ligands also provide a suitable
coordination platform for metal ions to provide diverse
metallic complexes.[7–10]
Salpn-type Schiff base ligands are an interesting class
of tetradentate ligands with four donor sites (N2O2).[11]
As shown in Scheme 1, salpn ligand provides an ideal
environment for equatorial coordination to transition
metal ions, leaving two axial sites open for coordination
of extra ligands or substrates to produce metal complexes
of higher coordination number.
tion metal complexes as a precursor can provide a sim-
ple and inexpensive method for the preparation of the
desired metal oxide nanostructures.[36,37] Among metal
oxide nanoparticles, ZnO and Co3O4 have been widely
studied owing to their applications in lithium-ion bat-
teries and supercapacitors,[38–40] sensing materials,[41,42]
solar
cells,[43]
semiconductors,[44]
piezoelectric
devices,[45] UV-shielding materials,[46] photochemical
reactors,[47] gas sensing,[48] biology,[49] agriculture,[50]
and food packaging.[51] Moreover, ZnO and Co3O4
nanoparticles have been used as nontoxic and easy-to-
recycle
catalysts,
for
example,
in
oxidation
reactions.[52–54] Selective oxidation of benzyl alcohols
to the corresponding aldehydes under mild reaction
conditions has always been of interest to researchers,
and the application of metal oxide nanoparticles such
as ZnO and Co3O4 as heterogeneous catalysts is
actively pursued.
Many dinuclear complexes of tetradentate N2O2 Schiff
base ligands with various metal ions have been
In this study, we synthesized a tetradentate N2O2
Schiff base ligand (H2L, Scheme 1) from 2,4-
dihydroxybenzaldehyde and 1,3-diaminopropane. To
investigate the coordination modes of this ligand, two
reported.[12–16]
The
corresponding
dinuclear
Zn(II) complexes have a flexible coordination environ-
ment with a variety of geometries such as tetrahedral,
square planar, trigonal bipyramidal, square pyramidal,
and octahedral.[17–21]
novel
dinuclear
Zn(II)
and
tetranuclear
Co(II) complexes (1 and 2) were synthesized, and the
structures of the ligand and the complexes were
established using elemental analysis, mass spectrometry
(MS), Fourier-transform infrared spectroscopy (FT-IR),
UV–Vis, and 1H nuclear magnetic resonance (NMR)
spectroscopy. Single crystal X-ray crystallography stud-
ies confirmed that H2L acts as a tetradentate ligand.
The results from density functional theory (DFT) cal-
culations (obtained using the B3LYP/6–31 G(d) basis
set) were correlated to those obtained from experimen-
tal studies for complexes 1 and 2. Moreover, antip-
roliferative activity of the ligand and its complexes was
examined against human MCF7 (breast cancer), A375
(melanoma cancer), and PC3 (prostate cancer) cell
lines using MTT assay. In addition, we prepared ZnO
and Co3O4 nanoparticles directly from complexes
1 and 2, respectively. The produced nanoparticles were
characterized using FT-IR, powder X-ray diffraction
(PXRD), and field emission scanning electron micros-
copy (FESEM) imaging. The nanoparticles were used
as heterogeneous catalysts in selective oxidation of
benzyl alcohol in the presence of hydrogen peroxide at
room temperature.
Among polynuclear transition metal complexes, tet-
ranuclear clusters with cubane-like M4O4 core have
been widely studied and have received considerable
attention.[22,23] However, reports on cobalt clusters of
the type Co4O4-containing cubane structure are
scarce.[24,25]
The synthesis and structural studies of polynuclear
metal complexes with Schiff base ligands have increased
in recent years because of their widespread applications
in various fields such as catalysis, biological studies, and
industrial systems.[26–31]
Various methods for the synthesis of metal oxide
nanoparticles are available, which include hydrother-
mal, solvothermal, sol–gel, microwave-assisted tem-
plate-free, and microemulsion methods.[32–35] However,
SCHEME 1 Chemical structure of the ligand H2L

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
3 of 19
2 | EXPERIMENTAL
2.2.2 | Synthesis of complex 1
2.1 | Materials and methods
A methanolic solution of Zn (OAc)2ꢀ2H2O (0.66 g,
3.0 mmol in 10 mL) was added dropwise to a solution of
H2L in the same solvent (0.63 g, 2.0 mmol in 15 mL). The
orange color of the ligand faded gradually with simulta-
neous precipitation of a white microcrystalline com-
pound. The reaction mixture was stirred for 45 min at
room temperature. The crude product was then filtered
off, washed with methanol, and recrystallized from
MeOH/DMF. The solvent was partially evaporated, and
several colorless single crystals suitable for X-ray crystal-
lography were collected after 2 days. Yield: 71% (based on
zinc). Anal. Calc. for C22H24N2O9Zn2ꢀ3/4(H2O)
(MW = 603.4 g mol−1): C, 43.79; H, 5.01; N, 4.64. Fou-
nd: C, 43.55; H, 4.93; N, 4.78%. IR (KBr, cm−1): 3448
(s, νOH), 1609 (s, νC=N), 1552 (m, νasCOO-), 1450 (m,
νsCOO-), 1217 (m, νPhO) 464 (w, νZn–N). UV–Vis: λmax
(nm) (ε, M−1 cm−1) (DMSO): 286 (21300), 348 (16750).
1H NMR (DMSO-d6, 300 MHz, ppm); δ: 9.53 (br, 2H6),
8.10 (s, 2H3), 6.97 (d, 2H4, J = 8.4 Hz), 6.21 (s, 2H7), 6.03
(d, 2H5, J = 8.4 Hz), 3.74 (br, 4H2), 3.39 (s, 3H11), 1.95
(m, 2H1), 1.83 (s, 3H10).
All of the reagents and solvents were of analytical
grade and used without further purification. Elemental
analyses were performed on a Heraeus CHN-O-Rapid
elemental analyzer. Electron impact mass spectroscopy
(EIMS) was performed on an Agilent 6890 Series
(detector: Agilent 5973 Network Mass Selective Detec-
tor, Agilent Technologies; ionization energy: 70 eV).
FT-IR spectra were recorded on a Bruker Alpha spec-
trophotometer using KBr disks over the range of 4000–
400 cm−1. UV–Vis spectra were recorded on a Rayleigh
UV-1800 spectrophotometer. 1H NMR spectra were
recorded in DMSO-d6 using tetramethylsilane as an
internal standard on a Bruker Avance III 300 MHz
spectrometer at 298 K. UV–Vis diffuse reflectance spec-
tra (DRS) were recorded in the wavelength range of
200–800 nm on a Scinco S-4100 spectrophotometer
(Korea). The X-ray powder diffraction (XRD) data were
recorded on a Philips PW1730 (Poland) with Cu Kα
radiation (λ = 1.5406 Å). FESEM images of the syn-
thesized nanoparticles were obtained using a Tescan
Mira III scanning electron microscope (Tescan USA
Inc., PA, USA). HPLC-grade methanol from Kermel
Chemical Reagent Co. (Tianjin, China) was used for
LC–MS analysis.
2.2.3 | Synthesis of complex 2
A methanolic solution of Co (OAc)2ꢀ4H2O (0.25 g,
1.0 mmol in 10 mL) was added dropwise to a suspension
of H2L in dichloromethane (0.31 g, 1.0 mmol in 15 mL).
Color of the mixture immediately changed to dark
brown. The reaction mixture was stirred for about 30 min
at room temperature and then filtered, and the filtrate
was allowed to stand for a few days. The solvent was par-
tially evaporated, and several gray single crystals suitable
for X-ray crystallography were collected after 5 days.
Yield: 78% (based on cobalt). Anal. Calc. for
C42H44N4O16Co4ꢀ2(H2O) (MW = 1132.56 g mol−1): C,
44.54; H, 4.27; N, 4.95. Found: C, 44.67; H, 4.34; N, 5.02%.
IR (KBr pellet, cm−1): 3424 (s, νOH), 1622 (s, νC=N), 1555
(m, νasCOO-), 1450 (m, νsCOO-), 1234 (m, νPhO), 465 (w,
νCo–N). UV–Vis: λmax (nm) (ε, M−1 cm−1) (DMSO):
270 (31250), 368 (6300).
2.2 | Synthesis
2.2.1 | Synthesis of H2L
H2L was synthesized by condensation of 1,3-dia-
minopropane with 2,4-dihydroxybenzaldehyde in metha-
nol. Briefly, 1,3-diaminopropane (0.17 g, 2.00 mmol) was
added
dropwise
to
a
solution
of
2,4-
dihydroxybenzaldehyde (0.55 g, 4.00 mmol) in 25 mL of
methanol at room temperature. The reaction mixture was
then refluxed for 1 h with continuous stirring. After
cooling to room temperature, the orange precipitate was
filtered off and washed with methanol. Yield: 78%. EIMS
(70 eV) m/z: 314.3 [H2L+]. Anal. Calc. for C17H18N2O4
(MW = 314.34 g mol−1): C, 64.96; H, 5.77; N, 8.91. Fou-
nd: C, 64.87; H, 5.82; N, 8.97%. IR (KBr, cm−1): 3447 (s,
νOH), 1641 (s, νC=N), 1236 (m, νPhO). UV–Vis: λmax
(nm) (ε, M−1 cm−1) (DMSO): ~280 (26250), 308 (24650),
410 (1850). 1H NMR (DMSO-d6, 300 MHz, ppm); δ: 12.92
(br, 2H8), 10.79 (br, 2H6), 8.34 (s, 2H3), 7.18 (d, 2H4,
J = 8.40 Hz), 6.30 (dd, 2H5, J = 8.40 and 2.40 Hz), 6.23 (d,
2H7, J = 2.10 Hz), 3.58 (t, 4H2, J = 6.75 Hz), 1.95
(m, 2H1).
2.3 | Crystal structure determination
X-ray intensity data for complexes 1 and 2 were collected
using graphite monochromatic Mo Kα, λ = 0.71073 Å
radiation on a four-circle к geometry KUMA KM-4 dif-
fractometer with a two-dimensional area CCDC detector.
Data collection was made at low temperature (100 (1) K)
using the CrysAlis CCD software.[55] The ω-scan

4 of 19
SANATKAR ET AL.
technique with Δω = 1.0ꢁ for each image was used for
data collection. One image was used as a standard after
every 40 images for monitoring of the crystal stability and
data collection, and no correction on the relative inten-
sity variation was necessary. Integration, scaling of the
reflections, correction for Lorenz and polarization effects,
and absorption corrections were performed using the
CrysAlis Red program.[55] The structures were solved by
direct methods using SHELXT[56] and refined using
SHEXL-2018 program.[57] The data were deposited in
Cambridge Crystallographic Data Center with deposition
number CCDC 1911571 for [4(Zn2L(μ-O2CCH3)
(O2CCH3)(H2O))]ꢀ4CH3OHꢀ3H2O (1) and 1916520 for
[Co4L2(μ-O2CCH3)2(O2CCH3)2]ꢀ2H2O (2). Details of the
crystal parameters, data collection, and refinements for
complexes 1 and 2 are summarized in Table 1.
2.4 | Theoretical calculations
Theoretical studies were performed using density func-
tional theory (DFT) with the hybrid density functional
(B3LYP)/6–31 G(d) basis set. All calculations were done
using the Gaussian 03 program package[58] without speci-
fying any symmetry for the title compounds. No con-
straint was applied in the calculations, and all atoms
were free to optimize.
TABLE 1 Crystal data and structure refinement for complexes 1 and 2
Parameter
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
1
2
4(C21H24N2O9Zn2)ꢀ4(CH4O)ꢀ3(H2O)
2413.60
C42H44N4O16Co4ꢀ2(H2O)
1132.56
100
100
Monoclinic
P21/n
Monoclinic
Cc
16.779 (3)
7.6128 (7)
20.339 (4)
90
11.6158 (3)
19.6198 (3)
20.4742 (5)
90
b (Å)
c (Å)
α (deg)
β (deg )
112.07 (2)
90
93.316 (2)
90
γ (deg )
V (Å3)
2407.6 (7)
1
4658.25 (18)
4
Z
Dx (mg m 3)
1.723
1.615
μ (mm−1
)
2.06
1.48
F (000)
1286
2320
Crystal size (mm)
0.26 × 0.18 × 0.05
2.62–26.00
−20 ≤ h ≤ 20
−9 ≤ k ≤ 9
−25 ≤ l ≤ 25
29301
0.22 × 0.12 × 0.11
2.78–29.41
−15 ≤ h ≤ 16
−27 ≤ k ≤ 26
−28 ≤ l ≤ 27
71869
θ range for data collection (deg)
Index ranges
Reflections collected
Independent reflections (Rint
Reflections with I > 2σ(I)
Data/restraints/parameters
Goodness-of-fit on F2
)
4743 (0.089)
3516
11697 (0.057)
9038
4743/6/350
1.05
11697/2/617
1.06
Final R indexes [I > 2σ(I)]
Final R indexes [all data]
R1 = 0.1110, wR2 = 0.2263
R1 = 0.1498, wR2 = 0.2432
2.315/−0.836
R1 = 0.0653, wR2 = 0.1574
R1 = 0.0917, wR2 = 0.1750
1.70/−0.45
Largest difference in peak/hole
(e Å 3)

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
5 of 19
2.5 | In vitro cytotoxicity
2.7 | Oxidation reaction
The cytotoxic activity of the Schiff base ligand H2L
and its complexes 1 and 2 was evaluated against
MCF7 (breast cancer), A375 (melanoma cancer), and
PC3 (prostate cancer) cell lines using the MTT (3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)
assay kit (Bio-Idea, Houston, TX). Briefly, MCF7, PC3,
and A375 cells were seeded at 7 × 103 cells/well in 96-
well plates. A stock solution of each of the compounds
All of the catalytic benzyl alcohol oxidation reactions
were carried out in a glass reactor at room temperature.
The effect of different reaction parameters such as the
amount of H2O2, reaction time, and amount of catalyst
was studied. The progress of the reaction was monitored
either by TLC (n-hexan/ethyl acetate 4:1) or by GC. To
identify possible reaction intermediates, LC–MS analysis
was used. The mobile phase composition was water:
1, 2, and H2L was provided in DMSO (10 mg mL−1
)
methanol (40:60, v/v), and the flow rate was 1.0 mL min−1
.
and then diluted to different concentrations with cul-
ture medium (12.5, 25, 50, and 100 μg mL−1). A blank
solution containing the same amount of DMSO was
used as a control to monitor the activity of the solvent
in this test. Solutions were added to the wells 24 h
after cell seeding. Doxorubicin hydrochloride (DOX,
20 μg mL−1) was used as a reference drug. After 48 h
of incubation, the medium was replaced with 100 μL
of freshly prepared RPMI medium, and then 10 μL of
the MTT solution (0.5 mg mL−1) was added to each
well. This was incubated for 4 h (5% CO2, 37ꢁC and
95% humidity). The solution was then removed, and
50 μL of dimethylsulfoxide (DMSO, 99.5%) was added
to dissolve the formazan crystals. The plate was incu-
bated for 15 min at room temperature with gentle
shaking. The absorbance was read using an ELISA
plate reader at 490 nm with a reference wavelength of
630 nm. The percentage of cell viability was calculated
using the following equation:
Mass spectra were acquired in the scan range of m/z 50–
400.
2.8 | Computational study of the
oxidation of benzyl alcohol
The optimized structures and energies of the stationary
points were calculated using Gaussian09 program.[59]
Geometry optimization was performed at M062X/6–
311 + g(d,p) level of theory. Single point calculations
were carried out at the CCSD(T)/6–311 + g(d,p)//
M062X/6–311 + g(d,p) level of theory to get more accu-
rate energies along the reaction paths. The potential
energy surface (PES) was obtained at 298.15 K and 1 atm.
A proposed mechanistic pathway for the title reaction is
depicted in Scheme 2. The harmonic vibrational frequen-
cies were calculated at M062X/6–311 + g(d,p) level of
theory to determine the nature of reactants, products,
intermediates, and transition states. All of the species
(except transition states) have real frequencies at M062X/
6–311 + g(d,p) level of theory, whereas transition states
have only one negative eigenvalue of the Hessian matrix,
and therefore one imaginary frequency. The intrinsic
reaction coordinate (IRC)[60] calculations were carried
out to ensure a correct connection between the transition
state and corresponding minima along the reaction paths.
Each IRC terminated upon reaching a minimum using
the default criterion in Gaussian program.
Cell viability ð%Þ = ½ðA490 −A630Þof treated cells=ðA490 −A630Þ of control cellsꢂ × 100:
The cytotoxicity was evaluated based on the percentage
of cell survival in a dose-dependent manner relative to
the negative control and was calculated by a nonlinear
regression using GraphPad Prism software. All tests were
repeated in at least three independent trials.
2.6 | Preparation of nanoparticles
3 | RESULTS AND DISCUSSION
About 0.4 g of each of the complexes 1 and 2 was
introduced into a crucible and heated in an electric
furnace with a heating rate of 10ꢁC min−1 for an
appropriate time (2 h at 650ꢁC for complex 1 and 4 h
at 400ꢁC for complex 2). The obtained nanosized metal
oxides were characterized using FT-IR spectroscopy,
UV–Vis diffuse reflectance spectroscopy (DRS), XRD,
and FESEM.
3.1 | Description of the crystal
structures
The dinuclear Zn(II) complex C21H24N2O9Zn2 crystallizes
as
a
methanol
and
water
solvate,
(4(C21H24N2O9Zn2)ꢀ4(CH3OH)ꢀ3(H2O)) (1), in the mono-
clinic crystal system with a P21/n space group. Methanol
as solvent is ordered, whereas water molecule as solvent
is disordered and occupies equivalent positions in 75%.

6 of 19
SANATKAR ET AL.
SCHEME 2 A proposed mechanistic pathway
for the oxidation reaction of benzyl alcohol by H2O2
based on calculations at the CCSD(T)/6–311 + g(d,
p)//M062X/6–311 + g(d,p) level of theory
The molecular structure of the dinuclear Zn(II) complex
1 together with the coordination polyhedra of the Zn ions
are illustrated in Figure 1. The selected bond lengths and
angles are given in Tables 2 and S1, respectively. Atom
Zn1 is penta-coordinated by N2O2 donors of the L2− unit
(N1, N2, O1, and O4) and one O atom (O6) from the
bridging acetate ion. Atom Zn2 is in a distorted octahe-
dral coordination where the equatorial plane is occupied
by two phenoxo O atoms (O1 and O4) from L2− and two
O atoms (O7 and O8) from the other acetate ligand. The
axial positions are occupied by two O atoms (O5 and
O1W) from bridging acetate ion and H2O, respectively.
The tetranuclear Co(II) complex C42H44N4O16Co4
crystallizes as a dihydrate, C42H44N4O16Co4ꢀ2(H2O) (2),
in a monoclinic crystal system with a Cc space group.
The molecular structure of the tetranuclear
Co(II) complex together with the cubane-type [Co4O4]
core is shown in Figure 2. The asymmetric unit contains
four crystallographically independent Co2+ cations, two
L2− ligands, four acetate ligands, and two water mole-
cules. The core of complex 2 is a cubane-like [Co4O4]
unit, with the Co(II) cations and O atoms from the two
Schiff base ligands located at alternating corners of a dis-
torted cube. Table 3 shows the CoꢀꢀꢀCo and Co–N/O coor-
dination distances. The equatorial plane of Co(1) ion is
occupied by the imine nitrogen atoms (N1 and N2) and
two phenolic oxygen atoms (O1 and O4). The axial posi-
tions are occupied by two O atoms (O41 and O21) from
the bridging acetate and the other L2− ligand, with an
O41–Co1–O21 angle of 162.5 (3). Atom Co2 also adopts a
distorted octahedral geometry, with atoms O1 and O4
(from one L2−) and O51 and O52 from acetate ligand in
the equatorial plane. The axial positions are occupied by
atoms O42 from the bridging acetate and O24 from the
FIGURE 1 (a) View of the molecular
structure of complex 1, showing part of the
atom-numbering scheme. The water and
methanol solvent molecules and all H atoms
have been omitted for clarity. Displacement
ellipsoids are drawn at the 50% probability level.
(b) The coordination polyhedron of Zn(II) in
complex 1

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
7 of 19
TABLE 2 Selected bond lengths (Å) for complex 1
Bond lengths
Zn1–O1
Experimental
2.094 (7)
Theoretical
2.129
Bond lengths
Zn2–O1
Experimental
2.040 (6)
Theoretical
2.143
2.147
2.058
2.122
2.146
2.344
Zn1–O4
2.035 (6)
2.120
Zn2–O4
2.033 (7)
Zn1–O6
2.008 (7)
2.014
Zn2–O5
2.102 (7)
Zn1–N1
2.076 (8)
2.118
Zn2–O7
2.306 (7)
Zn1–N2
2.050 (9)
2.088
Zn2–O8
2.109 (7)
ZnꢀꢀꢀZn
3.0534 (18)
3.165
Zn2–O1W
2.140 (7)
FIGURE 2 (a) View of the molecular
structure of complex 2. The water molecules and
all H atoms have been omitted for clarity.
Displacement ellipsoids are drawn at the 50%
probability level. (b) The cubane-type [Co4O4]
core of complex 2
TABLE 3 Selected bond lengths (Å) for complex 2
Bond lengths
Co1–O1
Experimental
2.089 (7)
2.087 (6)
2.165 (6)
2.102 (6)
2.044 (8)
2.053 (9)
2.058 (6)
2.103 (6)
2.137 (6)
2.019 (7)
2.070 (7)
2.133 (7)
3.002
Theoretical
2.291
2.064
2.083
1.958
2.016
2.074
1.957
2.070
2.121
1.939
2.176
1.992
2.905
3.207
3.126
Bond lengths
Co3–O1
Experimental
2.181 (6)
2.075 (7)
2.038 (6)
2.135 (7)
2.016 (8)
2.051 (8)
2.104 (6)
2.077 (6)
2.070 (6)
2.007 (6)
2.120 (7)
2.085 (7)
3.164
Theoretical
1.990
1.962
1.986
1.982
1.962
2.029
2.087
2.042
1.783
1.926
1.912
1.888
2.982
3.147
2.801
Co1–O4
Co3–O21
Co3–O24
Co3–O61
Co3–N21
Co3–N22
Co4–O4
Co1–O21
Co1–O41
Co1–N1
Co1–N2
Co2–O1
Co2–O4
Co4–O21
Co4–O24
Co4–O62
Co4–O71
Co4–O72
Co2ꢀꢀꢀCo3
Co2ꢀꢀꢀCo4
Co3ꢀꢀꢀCo4
Co2–O24
Co2–O42
Co2–O51
Co2–O52
Co1ꢀꢀꢀCo2
Co1ꢀꢀꢀCo3
Co1ꢀꢀꢀCo4
3.314
3.222
3.186
3.013
other L2− ligand, with an O42–Co2–O24 angle of 169.8
(3)ꢁ. Atoms Co3 and Co4 exhibit similar coordination
environments to Co1 and Co2, respectively. Two acetate
groups connect Co1 and Co2, and Co3 and Co4,
respectively. All of the Co–O–Co and O–Co–O angles
within the cubane core are larger than or smaller than
90ꢁ, indicating that the cubane is slightly distorted.[25]
The Co–O/N–Co and O/N–Co–O/N angles within the

8 of 19
SANATKAR ET AL.
cubane core are listed in Table S2. Although a number of
cubane-type [Co4O4] clusters have been reported thus
far, this study is the first report on a cubane-type complex
bands at 348 and 368 nm arising from n ! π* transitions
of the imine groups and MLCT transitions[64–66] and
intense bands at higher energy (286 and 270 nm for
1 and 2, respectively) associated with the aromatic π ! π*
intraligand charge-transfer transitions were observed.[67]
In the visible region, complex 1 showed no appreciable
absorption bands above 450 nm, indicating the absence
of d–d transitions which is in accordance with the d10
configuration of the Zn(II). Complex 2, however, showed
low-intensity bands in the range of 550–700 nm due to its
expected d–d transitions.
with
the
N,N0-bis-(4-hydroxy-salicylidene)-1,3-dia-
minopropane ligand.
The arrangement of the dinuclear Zn(II) and tetra-
nuclear Co(II) complexes is stabilized by two types of H-
bonds. The crystal structure of 1 is established by O–H…O
and C–H…O intermolecular interactions that form an
extended three-dimensional network (Figure 3a),
whereas for 2 the O–H…O hydrogen bonding interactions
lead to the formation of the two-dimensional layers paral-
lel to the (001) plane (Figure 3b). These layers interact
mainly by the van der Waals forces. The geometry of the
hydrogen bonds is listed in Table 4.
3.4 | 1H NMR spectra
1H NMR spectra of the H2L ligand and its zinc com-
plex were recorded at 298 K in DMSO-d6 (Figures S1
and S2). In the 1H NMR spectrum of the ligand, the
protons’ broad peaks of phenolic OH8 and OH6 moie-
ties were observed at 12.9 and 10.8 ppm, respectively.
The aromatic protons of the ligand resonated in the
range of 6.2–7.2 ppm and unambiguously assigned
according to their coupling constants (see Section 2.2.1).
The expected singlet for the proton of the imine moi-
ety (H3) was observed at 8.3 ppm. Multiplets of the ali-
phatic protons H1 and H2 were also observed at 1.9
and 3.6 ppm with expected multiplicities and coupling
3.2 | FT-IR spectra
In the FT-IR spectrum of the H2L ligand, characteristic
bands of the υ(OH) and υ(C=N)imine were observed at
3447 and 1641 cm−1, respectively. Also, in the FT-IR
spectra of complexes 1 and 2, broad bands of the
υ(OH) moieties were clearly observed at 3448 and
3424 cm−1, respectively. Condensation of the primary
amine group with benzaldehyde was confirmed by the
disappearance of the NH stretching bands in the 3100–
3400 cm−1 region. The ν(C=N) stretching vibrations of
1
constants. In the H NMR spectrum of complex 1, the
complexes 1 and 2 were observed at 1609 and 1622 cm−1
,
broad peak at 9.5 ppm was attributed to remaining
phenolic protons (OH6). The disappearance of the phe-
nolic OH8 proton signal in the spectrum of complex
1 indicates the deprotonation of the ligand and having
taken part in the bond formation to metal through
oxygen. The aromatic and imine protons also appeared
in the anticipated positions. In addition to the afore-
mentioned signals, the spectrum of complex 1 exhibited
five singlets at 1.8, 2.7, 2.9, 3.4, and 8.0 ppm. The sig-
nals at 2.7, 2.9, and 8.0 ppm can be attributed to the
traces of the DMF solvent.[68] Thus, the singlets at 1.8
and 3.4 ppm can be assigned to the methyl groups of
the acetate ligands (H10 and H11, respectively).
respectively. This represents a red shift to lower frequen-
cies by about 20–30 cm−1, which is a direct indication of
the involvement of azomethine nitrogen in coordination.
The νas(C=O) and νs(C=O) vibrations of the acetate
ligands appeared in the 1450–1555 cm−1 region.[61] Also,
ν(PhO) was shifted to lower frequencies in both com-
plexes, which indicates that the M–O bond was formed
between the metal ion and the ligand.[62] In addition, the
spectra of complexes 1 and 2 showed corresponding
ν(Co–N) and ν(Zn–N) vibrations at 464 and 465 cm−1
respectively.
,
3.3 | Electronic absorption spectra
3.5 | Electron impact mass spectroscopy
The electronic absorption spectra of the complexes and
the free ligand were recorded at room temperature
(2 × 10−5 M in DMSO, Figure 4). The Schiff base ligand
H2L showed characteristic absorption bands at 280, 308,
and 410 nm. The highly intense bands at 280 and 308 nm
were assigned to π ! π* and n ! π* transitions of the
H2L, respectively, and the broad band at about 410 nm
was attributed to intraligand charge transfer.[63] On the
contrary, in the electronic spectra of 1 and 2, distinct
In the mass spectrum of the H2L ligand, a molecular ion
peak was observed at m/z 314.3 corresponding to its
molecular weight (Figure S3). The spectrum also
exhibited various fragments of the ligand. The informa-
tion gathered from the EIMS data is in agreement with
the elemental analysis and 1H NMR results.

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
9 of 19
FIGURE 3 Arrangement of (a) 1 and (b) 2 in the unit cell viewed along a-axis. Dashed lines represent the O–HꢀꢀꢀO hydrogen bonds
that stabilized the structural architecture

10 of 19
SANATKAR ET AL.
TABLE 4 Hydrogen bond geometries (Å, deg) in the crystal structures of 1 and 2
D–HꢀꢀꢀA
1
D–H
HꢀꢀꢀA
DꢀꢀꢀA
D–HꢀꢀꢀA
2.370 (15)
Symmetry
O2–H2AꢀꢀꢀO2Wi
C10–H10BꢀꢀꢀO2Wii
C14–H14ꢀꢀꢀO6iii
O3–H3ꢀꢀꢀO2W
C16–H16ꢀꢀꢀO7
C16–H16ꢀꢀꢀO1Wi
C21–H21AꢀꢀꢀO7iv
O1W–H1WAꢀꢀꢀO3i
O1W–H1WBꢀꢀꢀO7i
O9–H9ꢀꢀꢀO1W
2
0.82(1)
0.99
1.83 (14)
2.25
2.370 (18)
3.14 (2)
−x + 1, −y + 1, −z + 1
148
167
−x + 1/2, y − 1/2, −z + 1/2
−x + 1/2, y + 1/2, −z + 1/2
0.95
2.59
3.522 (13)
2.661 (16)
3.176 (12)
3.344 (12)
3.484 (13)
2.808 (10)
2.744 (9)
2.652 (10)
0.82(1)
0.95
1.87 (3)
2.27
162 (8)
158
0.95
2.62
134
−x + 1, −y + 1, −z + 1
−x + 1, −y, −z + 1
0.98
2.62
148
0.82(1)
0.82(1)
0.84
2.10 (5)
2.00 (4)
2.20
145 (8)
151 (8)
114
−x + 1, −y + 1, −z + 1
−x + 1, −y + 1, −z + 1
O2–H2AꢀꢀꢀO2W
O3–H3ꢀꢀꢀO61i
O22–H22AꢀꢀꢀO42ii
O23–H23ꢀꢀꢀO1W
O1W–H1WAꢀꢀꢀO71
0.84
0.84
0.83
0.85
0.89
1.80
1.85
1.97
1.92
1.91
2.621 (15)
2.670 (9)
2.773 (9)
2.76 (2)
164.6
165.5
162.0
166.3
175.5
x + 1/2, y + 1/2, z
x + 1/2, y − 1/2, z
2.796 (15)
aA, acceptor; D, donor.
FIGURE 4 UV–Vis spectra of (A) H2L, (B) complex 1, and (C) complex 2 (CA, B and C = 2 × 10–5 M and Cb = 2 × 10–3 M) in DMSO
at room temperature
3.6 | DFT calculations
HOMO and LUMO is an important parameter for deter-
mining the molecular properties such as stability and
activity.[70] The calculated HOMO and LUMO energies
were found to be −4.88 and −1.48 eV for complex 1 and
−3.81 and −3.22 eV for complex 2. The calculated
HOMO–LUMO energy gaps were found to be 3.40 and
0.59 eV for complexes 1 and 2, respectively (Figure 6).
Soft molecules have a small bandgap, and hard molecules
have a large bandgap.[71] The energy gap of complex
1 may indicate its good stability and low reactivity.[72,73]
On the contrary, the small bandgap of complex 2 indicates
that its electrons are more easily excited from the ground
The optimized structures of complexes 1 and 2, shown in
Figure 5, are in good agreement with the results of sin-
gle-crystal X-ray analysis. Tables 2, 3, S1, and S2 compare
the theoretical bond distances and bond angles of the
optimized structures with those obtained experimentally.
Also, there is a good agreement between the theoretical
and experimental data.
Frontier molecular orbitals, HOMO and LUMO, play
an important role in the study of chemical reactivity and
optical properties.[69] The energy bandgap between

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
11 of 19
FIGURE 5 Optimized molecular structures
of (a) complex 1 and (b) complex 2 in vacuum
using DFT/B3LYP/6–31 G(d) basis set
FIGURE 6 Illustrative presentation of
frontier molecular orbitals of complexes 1 and
2 obtained using B3LYP/6–31 G(d) basis set
state to the excited state. In addition, this gap refers to a
complex with more polarity and conductivity, high chem-
ical and biological activity, and low kinetic stability.[74]
lines were treated with different concentrations (12.5–
100 μg mL−1) of each compound. The antiproliferative
activity results and the observed cytotoxic effects (IC50;
concentration required for 50% cell growth inhibition) of
these compounds are presented in Figure 7 and Table 5.
In the case of H2L, an increase in the concentration
resulted in an increase in the antiproliferative activity on
the MCF7 cells and an adverse effect on A375 cell lines.
Complex 1, however, showed a remarkable activity
against A375 and PC3 cancer cell lines with low IC50
3.7 | In vitro antitumor activity
To evaluate the ability of the H2L ligand and its com-
plexes to inhibit cell proliferation, MCF7 (breast cancer),
A375 (melanoma cancer), and PC3 (prostate cancer) cell

12 of 19
SANATKAR ET AL.
FIGURE 7 Effect of different
concentrations (12.5, 25, 50, and 100 μg mL−1) of
the (a) Schiff base ligand H2L, (b) complex 1,
and (c) complex 2 on the proliferation of MCF7,
A375, and PC3 cells
TABLE 5 Antiproliferative activity (IC50, μM) of the H2L, 1, 2,
and DOX
inhibition on the tested cell lines, which indicates its low
cytotoxic effect. These results emphasize that the cytotox-
icity of dinuclear Zn(II) complex is higher than that of
the tetranuclear Co(II) complex.[75]
Compounds IC50 (μM)
MCF7
(breast
cancer)
137.20
A375
(melanoma
cancer)
441.61
PC3
(prostate
cancer)
495.97
3.8 | Characterization of the
nanoparticles
H2L
1
155.25
190.76
22.70
27.89
172.70
21.03
122.97
175.27
22.96
2
3.8.1 | FT-IR analysis
DOX
The FT-IR spectra of the nanoparticles obtained from
thermal decomposition of complexes 1 and 2 are shown
in Figure 8. Both spectra represent the expected nature of
values in the entire range of concentrations. In compari-
son, complex 2 did not show convincing growth

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
13 of 19
is related to the stretching vibration of Co3+–O2− in octa-
hedral holes.[37]
3.8.2 | XRD analysis and morphology of
the nanoparticles
X-ray diffraction patterns of the synthesized metal oxides
confirmed the formation of ZnO and Co3O4 from com-
plexes 1 and 2. Figure 9e,g shows the XRD patterns for
the obtained ZnO and Co3O4 nanoparticles, respectively.
All of the diffraction peaks correspond to the hexagonal
phase of ZnO (cell constants: a = 3.25, c = 5.21 Å, space
group: P63mc, JCPDS card no. 01–080-0074) and cubic
spinelstructureofCo3O4 (cellconstants:a=b=c=8.085Å,
space group Fd3m, JCPDS card no. 78–1970).[77,78]
The sharp and intense XRD reflections indicate high
crystallinity of the samples. In addition, no reflection
peaks from other phases were observed, which indicates
the high purity of the samples. The average crystallite
size (D) for each sample was calculated using the Debye–
Scherrer equation:
FIGURE 8 FT-IR spectrum of (a) ZnO and (b) Co3O4
nanoparticles
metal oxides. In the FT-IR spectrum shown in Figure 8a,
the broad band at 466 cm−1 is attributable to the Zn–O
stretching vibration mode and confirms the formation of
ZnO nanoparticles. The broad peaks at about 3412 and
1638 cm−1 are assigned to the O–H stretching and bend-
ing modes of the adsorbed water molecules, respec-
tively.[37,76] On the contrary, in the FT-IR spectrum
shown in Figure 8b, two strong bands at 664 and
574 cm−1 are attributable to Co–O stretching modes and
confirm the formation of spinel Co3O4. The peak at
664 cm−1 is attributed to the stretching vibration of
Co2+–O2− in tetrahedral holes and the band at 574 cm−1
D = 0.9λ/βcosθ,
where λ is the wavelength of X-rays (1.5406 Å for Cu
Kα), β is the full width at half maximum (FWHM) of the
diffraction peak, and θ is the Bragg diffraction angle. The
crystallite sizes of ZnO and Co3O4 were estimated to be
34 and 43 nm, respectively (Table 6). Morphology of the
FIGURE 9 FESEM images of (a,b) ZnO and (c,d) Co3O4, XRD patterns of (e,f) ZnO before and after using as catalyst, and (g,h) Co3O4
before and after using as catalyst

14 of 19
SANATKAR ET AL.
TABLE 6 Information obtained from Debye–Scherrer equation
Compound
ZnO
2θ
Θ
cosθ
B1/2 (deg)
0.246
B1/2 (rad)
0.0043
D (nm)
34
36.1333
37.0306
18.0950
18.5153
0.9503
0.9482
Co3O4
0.1968
0.0034
43
obtained nanoparticles was also investigated using the
FESEM technique. The FESEM images of the ZnO and
Co3O4 nanoparticles are shown in Figure 9a–d. ZnO was
obtained as almost uniform spherical nanoparticles, and
Co3O4 was formed as polygonal nanoparticles.[79]
Although both polygonal and spherical morphologies
have been reported for the latter, cubic spinel structure of
Co3O4 has been deduced from XRD data in the
corresponding literature.[37,80–82]
TABLE 7 Effect of the amount of H2O2 on the oxidation of
1.0 mmol of benzyl alcohol in the presence of 1.0 mg of ZnO at
room temperature after 5 h
mmol of
Entry H2O2
Conversion
(%)
Selectivity
(%)
1
2
3
4
5
2
5
60
64
71
82
98
99
99
98
87
63
10
15
30
3.8.3 | DRS analysis
UV–Vis DRS was used to elucidate the absorption behav-
ior of the nanoparticles. Figure S4 shows the UV–Vis
DRS spectra for the obtained ZnO and Co3O4
nanoparticles. As shown in Figure S4a, the ZnO
nanoparticles exhibit an absorption edge at 363 nm,
which may be attributed to the band-to-band transi-
tions.[83,84] On the contrary, Figure S4b shows two
absorption bands in the range of 350–450 and 600–
800 nm for the Co3O4 nanoparticles. The first band can
be attributed to the tetrahedrally coordinated Co2+, and
the second band can be attributed to the octahedrally
coordinated Co3+ [85,86]
TABLE 8 Effect of the amount of H2O2 on the oxidation of
1.0 mmol of benzyl alcohol in the presence of 1.0 mg of Co3O4 at
room temperature after 12 h
mmol of
Entry H2O2
Conversion
(%)
Selectivity
(%)
1
2
3
4
5
2
5
28
39
50
63
75
99
98
98
89
77
10
15
30
To optimize the amount of catalyst and the reaction
3.9 | Catalytic activity studies
time, the oxidation of benzyl alcohol with 10 mmol of
H2O2 was carried out using 1.0, 2.0, 5.0, and 10.0 mg of
each catalyst per millimole of the substrate at different
time periods. As shown in Tables 9 and 10, increasing the
amount of catalyst and time is in favor of conversion of
benzyl alcohol. Amounts higher than 10.0 and 15.0 mg of
To evaluate the catalytic activity of the ZnO and Co3O4
nanoparticles obtained from thermal decomposition of
complexes 1 and 2, the oxidation of benzyl alcohol was
selected as a model reaction, and the effect of various
parameters such as reaction time, temperature, amount
of catalyst and amount of oxidant on the reaction yield,
and selectivity was studied.
The amount of oxidant had a significant effect on the
conversion and selectivity of the oxidation reaction
(Tables 7 and 8). For both catalysts, increasing the
amount of hydrogen peroxide increased the conversion
proportionately. Higher amount of H2O2, however, dras-
tically decreased the selectivity due to the formation of
by-products such as benzoic acid. Therefore, 10 mmol of
H2O2 (30%) was used as the optimum amount of oxidant
for each catalyst (Tables 7 and 8).
TABLE 9 Conversion of 1.0 mmol of benzyl alcohol in the
presence of different amounts of ZnO at different time periods at
room temperature
Conversion (%) after
Amount of catalyst (mg)
1 h
18
29
39
50
2 h
33
38
60
71
3 h
41
48
69
83
4 h
56
69
84
96
5 h
71
77
87
98
1.0
2.0
5.0
10.0

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
15 of 19
TABLE 10 Conversion of 1.0 mmol of benzyl alcohol in the
presence of different amounts of Co3O4 at different time periods at
room temperature
To gain an insight into the stability of the catalysts,
recovery of the ZnO and Co3O4 nanoparticles was evalu-
ated and the results are shown in Figure 10. The catalysts
were reused in successive cycles and showed negligible
decrease in efficiency in terms of conversion after four
runs. Decrease in conversion, however, was more
Conversion (%) after
Amount of catalyst (mg)
1 h
3 h
6 h
9 h
12 h
1.0
4
12
26
37
49
11
21
38
50
58
27
33
43
55
69
38
41
56
64
75
50
59
63
71
88
2.0
5.0
10.0
15.0
ZnO and Co3O4 per millimole of benzyl alcohol, how-
ever, had an adverse effect on the selectivity. Therefore,
the best results were obtained when 1.0 mmol of benzyl
alcohol was transformed selectively to benzaldehyde in
the presence of 10.0 mg of ZnO or 15.0 mg of Co3O4 at
room temperature with 10.0 mmol of hydrogen peroxide
after 5 or 12 h, respectively.
SCHEME 3 A proposed mechanism for the selective
oxidation of benzyl alcohol in the presence of ZnO and Co3O4
nanoparticles
FIGURE 10 Reusability of (up) ZnO and
(bottom) Co3O4 in the oxidation of benzyl
alcohol

16 of 19
SANATKAR ET AL.
FIGURE 11 The PES of the oxidation reaction of benzyl alcohol to benzaldehyde at CCSD(T)/6–311 + g(d,p)//M062X/6–311 + g(d,p)
level of theory
significant for the Co3O4 nanoparticles during four cycles
(up to 9%).
alcohol was separated by H2O2 to form the radical inter-
mediate 1 (IM1), H2O, and OH. The barrier height of
•
At the end of each run, the catalyst was recovered by
centrifugation, washed with water, dried at 100ꢁC for 1 h,
and then reused with fresh starting materials. XRD pat-
terns for the recycled catalysts of the fourth run are com-
pared with those of the fresh catalysts in Figure 9e–h.
The recycled catalysts showed no considerable change in
their crystal structure.
A proposed mechanistic pathway, which is in line
with the reported literature,[87] is outlined in Scheme 3. It
is believed that metal oxide nanoparticles convert 1 mmol
of H2O2 to 2 mmol of hydroxyl radicals.[88] When the
hydrogen of the benzylic carbon is attacked by hydroxyl
radicals, a benzyl radical intermediate as well as a mole-
cule of water is formed. This benzyl radical then com-
bines with the other hydroxyl radical to produce an
intermediate containing two hydroxyl groups. Finally,
dehydration of the latter produces the desired benzalde-
hyde product.
To identify the intermediate of the oxidation reaction
of benzyl alcohol to benzaldehyde, the reaction mixture
was sampled after 1, 3, and 5 h, and was analyzed using
LC–MS. As shown in Figure S5, m/z of the only interme-
diate detected in this reaction was 123.
As shown in PES (Figure 11), the reactants must
undergo a series of continuous reactions to generate the
product. Initially, an H-abstraction reaction occurred,
and the hydrogen atom of the methylene group of benzyl
TS1 was calculated about 14.1 kJ mol−1 at CCSD(T)/6–
311 + g(d,p)//M062X/6–311 + g(d,p) level of theory.
Afterward, the •OH radical was added to IM1 and
resulted in intermediate 2 (IM2) by passing over the TS2
with a 66.1 kJ mol−1 barrier height. Finally, IM2 dissoci-
ated to water and benzaldehyde molecules by passing
over the TS3 with a 73.9 kJ mol−1 barrier height. As
shown in Figure 11, the most stable species in PES is the
benzaldehyde product.
4 | CONCLUSION
A tetradentate N2O2 Schiff base ligand (N,N0-bis-(4-
hydroxy-salicylidene)-1,3-diaminopropane, H2L) was
synthesized
via
condensation
of
2,4-
dihydroxybenzaldehyde and 1,3-diaminopropane and
was utilized in the preparation of two novel dinuclear
Zn(II) and tetranuclear Co(II) complexes. All of the prod-
ucts were unambiguously characterized. Single crystal
diffraction analysis showed that Zn2+ and Co2+ ions, in
the corresponding di- and tetranuclear complexes, were
connected though μ-phenolato and μ-acetato bridges. The
calculated HOMO–LUMO energy gaps were found to be
3.40 and 0.59 eV for Zn(II) and Co(II) complexes, respec-
tively. The in vitro cytotoxicity studies showed that com-
plex 1 had the best antiproliferative activity on A375 and

DINUCLEAR ZN(II) AND TETRANUCLEAR CO(II) COMPLEXES OF A N2O2 LIGAND
17 of 19
[20] H. Sugimoto, A. Ogawa, React. Funct. Polym. 2007, 67, 1277.
[21] H. R. Wen, Y. Wang, J. L. Chen, Y. Z. Tang, J. S. Liao,
C. M. Liu, Inorg. Chem. Commun. 2012, 20, 303.
[22] B. F. Abrahams, T. A. Hudson, R. Robson, Chem. – Eur. J.
2006, 12, 7095.
[23] N. Chopin, G. Chastanet, B. Le Guennic, M. Médebielle,
G. Pilet, Eur. J. Inorg. Chem. 2012, 31, 5058.
PC3 cancer cells. In addition, thermal decomposition of
the synthesized complexes resulted in pure nanostruc-
tured ZnO and Co3O4, which were used as recyclable het-
erogeneous catalysts in selective oxidation of benzyl
alcohol to benzaldehyde. Both catalysts showed excellent
efficiency in terms of conversion and selectivity, along
with acceptable recyclability.
[24] J. Qi, X. S. Zhai, H. L. Zhu, J. L. Lin, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun. 2014, 70, 198.
[25] Y. Wang, Y. Ma, R. Liu, L. Yang, G. Tian, N. Sheng, Z. Sheng,
Anorg. Allg. Chem. 2016, 642, 546.
[26] X. Han, X. Shi, G. Huang, C. Li, S. Mao, K. Shen, H. Wu,
X. Tang, Appl. Organomet. Chem. 2018, 32, 4453.
ACKNOWLEDGEMENTS
We gratefully acknowledge the financial support from
the Research Council of University of Guilan.
_
ꢁ
[27] A. Bi˙li˙ci˙, I. Kaya, F. Dogan, J. Polym. Sci., Part A: Polym.
ORCID
Chem. 2009, 47, 2977.
Alireza Khorshidi https://orcid.org/0000-0002-8990-
8052
[28] P. Seth, L. K. Das, M. G. Drew, A. Ghosh, Eur. J. Inorg. Chem.
2012, 13, 2232.
[29] S. C. Manna, S. Manna, S. Mistri, A. Patra, E. Zangrando,
H. Puschmann, P. A. Goddard, S. Ghannadzadeh, Che-
mistrySelect 2018, 3, 9885.
[30] D. Dey, G. Kaur, A. Ranjani, L. Gayathri, P. Chakraborty,
J. Adhikary, J. Pasan, D. Dhanasekaran, A. R. Choudhury,
M. A. Akbarsha, N. Kole, Eur. J. Inorg. Chem. 2014, 21, 3350.
[31] S. Ghosh, A. Spannenberg, E. Mejía, Helv. Chim. Acta 2017,
100, 1700176.
[32] A. A. AbdelHamid, Y. Yu, J. Yang, J. Y. Ying, Adv. Mater.
2017, 29, 1701427.
[33] H. B. Bohidar, K. Rawat, Design of nanostructures: self-assem-
bly of nanomaterials, John Wiley & Sons, Weinheim 2017.
[34] M. Niederberger, G. Garnweitner, Chem. – Eur. J. 2006, 12,
7282.
[35] Y. Li, K. Keith, N. Chopra, J. Alloys Compd. 2017, 703, 414.
[36] H. M. Aly, M. E. Moustafa, M. Y. Nassar, E. A. Abdelrahman,
J. Mol. Struct. 2015, 1086, 223.
[37] M. Y. Nassar, H. M. Aly, E. A. Abdelrahman, M. E. Moustafa,
J. Mol. Struct. 2017, 1143, 462.
[38] C. Yan, G. Chen, X. Zhou, J. Sun, C. Lv, Adv. Funct. Mater.
2016, 26, 1428.
[39] Q. Liao, N. Li, S. Jin, G. Yang, C. Wang, ACS Nano 2015, 9,
5310.
REFERENCES
[1] A. Gubendran, G. G. V. Kumar, M. P. Kesavan, G. Rajagopal,
P. Athappan, J. Rajesh, Appl. Organomet. Chem. 2018, 32,
4128.
[2] D. Gopalakrishnan, S. Srinath, B. Baskar, N. S. Bhuvanesh,
M. Ganeshpandian, Appl. Organomet. Chem. 2019, 33, 4756.
[3] S. Siangwata, S. Chulu, C. L. Oliver, G. S. Smith, Appl.
Organomet. Chem. 2017, 31, 3593.
[4] Q. Chen, J. Huang, Appl. Organomet. Chem. 2006, 20, 758.
[5] M. N. Uddin, Z. A. Siddique, N. Mase, M. Uzzaman,
W. Shumi, Appl. Organomet. Chem. 2019, 33, 4876.
[6] L. Pogány, J. Moncol, J. Pavlik, M. Mazúr, I. Šalitroš,
ChemPlusChem 2019, 84, 358.
[7] E. Rufino-Felipe, N. Lopez, F. A. Vengoechea-Gómez,
ꢀ
L. G. Guerrero-Ramírez, M. A. Muñoz-Hernández, Appl.
Organomet. Chem. 2018, 32, 4315.
[8] C. Z. Gao, T. S. Wang, Y. Zhang, J. Chen, Y. X. Qian, B. Yang,
Y. J. Zhang, Appl. Organomet. Chem. 2015, 29, 138.
_
[9] B. Dede, I. Özmen, F. Karipcin, M. Cengiz, Appl. Organomet.
Chem. 2009, 23, 512.
[10] S. Biswas, S. Das, J. Acharya, V. Kumar, J. van Leusen,
P. Kögerler, J. M. Herrera, E. Colacio, V. Chandrasekhar,
Chem. – Eur. J. 2017, 23, 5154.
[11] P. Pandey, N. Dwivedi, G. Cosquer, M. Yamashita, S. Sunkari,
ChemistrySelect 2018, 3, 10311.
[12] C. Hopa, I. Cokay, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 2016, 72, 149.
[13] A. Bhattacharyya, S. Roy, J. Chakraborty, S. Chattopadhyay,
Polyhedron 2016, 112, 109.
[14] H. Sun, L. Wu, W. Yuan, J. Zhao, Y. Liu, Inorg. Chem.
Commun. 2016, 70, 164.
[15] M. Sutradhar, L. M. Carrella, E. Rentschler, Polyhedron 2012,
38, 297.
[16] Y. Yahsi, H. Kara, L. Sorace, O. Buyukgungor, Inorg. Chim.
Acta 2011, 366, 191.
[17] D. J. Wilson, C. M. Beavers, A. F. Richards, Eur. J. Inorg.
Chem. 2012, 7, 1130.
[40] D. Ponnamma, J. J. Cabibihan, M. Rajan, S. S. Pethaiah,
K. Deshmukh, J. P. Gogoi, S. K. Pasha, M. B. Ahamed,
J. Krishnegowda, B. N. Chandrashekar, A. R. Polu, Mater. Sci.
Eng. C 2019, 98, 1210.
[41] W. Qiu, H. Tanaka, F. Gao, Q. Wang, M. Huang, Adv. Powder
Technol. 2019, 30, 2083.
[42] X. Dong, Y. Su, T. Lu, L. Zhang, L. Wu, Y. Lv, Sens. Actuators
B 2018, 258, 349.
[43] Z. S. Wang, C. H. Huang, Y. Y. Huang, Y. J. Hou, P. H. Xie,
B. W. Zhang, H. M. Cheng, Chem. Mater. 2001, 13, 678.
[44] H. Parangusan, D. Ponnamma, M. A. A. Al-Maadeed,
A. Marimuthu, Photochem. Photobiol. 2018, 94, 237.
[45] Y. Leprince-Wang, Piezoelectric ZnO nanostructure for energy
harvesting, Vol. 1, John Wiley & Sons, Hoboken, NJ, USA
2015.
[46] H. Rodríguez-Tobías, G. Morales, O. Rodríguez-Fernández,
P. Acuña, J. Appl. Polym. Sci. 2013, 127, 4708.
[47] J. B. Rajesha, A. Ramasami, G. Nagaraju, G. Balakrishna,
Water Environ. Res. 2017, 89, 396.
[18] F. F. Chang, Y. Hu, K. Zhang, H. Q. Chen, W. Huang, Eur.
J. Inorg. Chem. 2017, 3, 540.
[19] Z. L. You, Acta Crystallogr., Sect. C: Cryst. Struct. Commun.
2005, 61, 466.

18 of 19
SANATKAR ET AL.
[48] J. Moon, J. A. Park, S. J. Lee, T. Zyung, ETRI J. 2009, 31, 636.
[49] A. Ayhanci, R. Uyar, E. Aral, S. Kabadere, S. Appak, Biol.
Trace Elem. Res. 2008, 126, 186.
[50] M. Rizwan, S. Ali, B. Ali, M. Adrees, M. Arshad, A. Hussain,
M. Z. ur Rehman, A. A. Waris, Chemosphere 2019, 214, 269.
[51] P. J. P. Espitia, N. D. F. F. Soares, J. S. dos Reis Coimbra, N. J.
de Andrade, R. S. Cruz, E. A. A. Medeiros, Food Bioproc. Tech.
2012, 5, 1447.
[73] A. Arab, M. Habibzadeh, Comput. Theor. Chem. 2015,
1068, 52.
[74] X. H. Li, X. R. Liu, X. Z. Zhang, Spectrochim. Acta A 2011,
78, 528.
[75] E. Ispir, M. Ikiz, A. Inan, A. B. Sünbül, S. E. Tayhan, S. Bilgin,
M. Köse, M. Elmastas¸, J. Mol. Struct. 2019, 1182, 63.
[76] M. Y. Nassar, M. M. Moustafa, M. M. Taha, RSC Adv. 2016, 6,
42180.
[52] Y. Teng, L. X. Song, L. B. Wang, J. Xia, J. Phys. Chem. C 2014,
118, 4767.
[53] J. Zhu, K. Kailasam, A. Fischer, A. Thomas, ACS Catal. 2011,
1, 342.
[54] H. D. Bouras, Z. Isik, E. B. Arikan, N. Bouras, A. Chergui,
H. C. Yatmaz, N. Dizge, Biochem. Eng. J. 2019, 146, 150.
[55] CrysAlis CCD and CrysAlis Red 1.171.38.41, Rigaku Oxford
Diffraction, 2015.
[56] G. M. Sheldrick, Acta Cryst. A 2015, 71, 3.
[57] G. M. Sheldrick, Acta Crystallogr. C 2015, 71, 3.
[58] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, Gaussian 03, Revision D.01,
Gaussian Inc., Wallingford, 2004.
[77] H. Makhlouf, M. Weber, O. Messaoudi, S. Tingry, M. Moret,
O. Briot, R. Chtoutou, M. Bechelany, Appl. Surf. Sci. 2017,
426, 301.
[78] M. Pudukudy, Z. Yaakob, B. Narayanan, A. Gopalakrishnan,
S. M. Tasirin, Superlattices Microstruct. 2013, 64, 15.
[79] L. F. A. Raj, E. Jayalakshmy, Orient. J. Chem. 2015, 31, 51.
[80] E. M. M. M. Ibrahim, L. H. Abdel-Rahman, A. M. Abu-dief,
A. Elshafaie, S. K. Hamdan, A. M. Ahmed, Mater. Res. Bull.
2018, 99, 103.
[81] A. D. Khalaji, R. Rahdari, F. Gharib, J. S. Matalobos, D. Das,
J. Ceram. Process. Res. 2015, 16, 486.
[82] M. Y. Nassar, T. Y. Mohamed, I. S. Ahmed, J. Mol. Struct.
2013, 1050, 81.
[59] M. J. E. A. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. Petersson, H. Nakatsuji, Gaussian 09, Gauss-
ian Inc., Wallingford, CT, 2009.
[60] C. Gonzalez, H. Schlegel, J. Chem. Phys. 1990, 94, 5523.
[61] Z. Li, H. Yan, K. Liu, X. Huang, M. Niu, J. Mol. Struct. 2019,
1195, 470.
[83] R. Bomila, A. Venkatesan, S. Srinivasan, Optik 2018, 158, 565.
[84] K. Qi, X. Xing, A. Zada, M. Li, Q. Wang, S. Y. Liu, H. Lin,
G. Wang, Ceram. Int. 2019, 46, 1494.
[85] J. Yan, M. C. Kung, W. M. Sachtler, H. H. Kung, J. Catal.
1997, 172, 178.
[86] F. E. Trigueiro, C. M. Ferreira, J. C. Volta, W. A. Gonzalez,
P. P. de Oliveria, Catal. Today 2006, 118, 425.
[87] G. Y. Kreitman, J. C. Danilewicz, D. W. Jeffery, R. J. Elias,
J. Agric. Food Chem. 2016, 64, 4105.
[62] H. R. Jia, J. Li, Y. X. Sun, J. Q. Guo, B. Yu, N. Wen, L. Xu,
Crystals 2017, 7, 247.
[63] D. Dey, G. Kaur, M. Patra, A. R. Choudhury, N. Kole,
B. Biswas, Inorg. Chim. Acta 2014, 421, 335.
[88] Q. Yuan, W. Deng, Q. Zhang, Y. Wang, Adv. Synth. Catal.
2007, 349, 1199.
[64] A. Ghaffari, M. Behzad, M. Pooyan, H. A. Rudbari, G. Bruno,
J. Mol. Struct. 2014, 1063, 1.
[65] M. Khorshidifard, H. A. Rudbari, B. Askari, M. Sahihi,
M. R. Farsani, F. Jalilian, G. Bruno, Polyhedron 2015, 95, 1.
[66] A. Golcu, M. Tumer, H. Demirelli, R. A. Wheatley, Inorg.
Chim. Acta 2005, 358, 1785.
[67] A. H. Kianfar, L. Keramat, M. Dostani, M. Shamsipur,
M. Roushani, F. Nikpour, Spectrochim. Acta A 2010, 77, 424.
[68] H. E. Gottlieb, V. Kotlyar, A. Nudelman, J. Org. Chem. 1997,
62, 7512.
[69] A. B. Deilami, M. Salehi, A. Amiri, A. Arab, J. Mol. Struct.
2019, 1181, 190.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
How to cite this article: Sanatkar TH,
Khorshidi A, Janczak J. Dinuclear Zn(II) and
tetranuclear Co(II) complexes of a tetradentate
N2O2 Schiff base ligand: Synthesis, crystal
structure, characterization, DFT studies,
cytotoxicity evaluation, and catalytic activity
toward benzyl alcohol oxidation. Appl
Organometal Chem. 2020;e5493. https://doi.org/10.
1002/aoc.5493
ꢁ
[70] G. Elmacı, H. Duyar, B. Aydıner, I. Yahaya, N. Seferoglu,
ꢁ
E. S¸ahin, S. P. Çelik, L. Açık, Z. Seferoglu, J. Mol. Struct. 2019,
1184, 271.
[71] R. G. Pearson, Proc. Natl. Acad. Sci. 1986, 83, 8440.
[72] A. Arab, F. Gobal, N. Nahali, M. Nahali, J. Cluster Sci. 2013,
24, 273.