Single crystal X-ray of 1-[(1,2,4-triazole-4-yl)imino]diacetyl monoxime (L) as a novel triazole and the characterization and biological studies of its chelates of Co2+, Pd2+, and Fe3+

Article abstract of DOI:10.1002/aoc.5734

A novel and efficient synthesis of 1-[(1,2,4-triazole-4-yl)imino]diacetyl monoxime (L) is described. The advantages of this method are that it is inexpensive, the starting reactants are readily available, and it has good yield and short reaction times. The hull of the product was suggested by elemental analyses, spectral and single crystal X-ray. Novel Co²⁺, Pd²⁺, and Fe³⁺ chelates derived from L were characterized by Fourier transform infrared spectroscopy, suggesting that L acts as bidentate via the two azomethine groups. Tetrahedral geometry for Fe³⁺ and Co²⁺ and square-planar geometry around the Pd²⁺ chelate were suggested depending on the spectral and magnetic data. The results of density functional theory were applied to illustrate the geometry of L towards the metal ions. Coats–Redfern and Horowitz–Metzger methods were applied to investigate the kinetic and thermodynamic parameters of the chelates. Cyclic voltammetry was carried out to study the stability of the Co²⁺ and Fe³⁺ chelates. L and its complexes were tested against three types of cancer cells, antibacterial and antifungal.

Full text of DOI:10.1002/aoc.5734

Received: 31 January 2020
DOI: 10.1002/aoc.5734
Revised: 27 February 2020
Accepted: 23 March 2020
F U L L P A P E R
Single crystal X-ray of 1-[(1,2,4-triazole-4-yl)imino]diacetyl
monoxime (L) as a novel triazole and the characterization
and biological studies of its chelates of Co2+, Pd2+, and Fe3+
Mohsen M. Mostafa
| Abdelmonem H. Elaskalany | Doaa E. El-Kkholy
Chemistry Department, Faculty of
Science, Mansoura University, Egypt
A novel and efficient synthesis of 1-[(1,2,4-triazole-4-yl)imino]diacetyl mono-
xime (L) is described. The advantages of this method are that it is inexpensive,
the starting reactants are readily available, and it has good yield and short
reaction times. The hull of the product was suggested by elemental analyses,
spectral and single crystal X-ray. Novel Co2+, Pd2+, and Fe3+ chelates derived
from L were characterized by Fourier transform infrared spectroscopy,
suggesting that L acts as bidentate via the two azomethine groups. Tetrahedral
geometry for Fe3+ and Co2+ and square-planar geometry around the Pd2+ che-
late were suggested depending on the spectral and magnetic data. The results
of density functional theory were applied to illustrate the geometry of
L towards the metal ions. Coats–Redfern and Horowitz–Metzger methods
were applied to investigate the kinetic and thermodynamic parameters of the
chelates. Cyclic voltammetry was carried out to study the stability of the Co2+
and Fe3+ chelates. L and its complexes were tested against three types of
cancer cells, antibacterial and antifungal.
Correspondence
Mohsen M. Mostafa, Chemistry
Department, Faculty of Science,
Mansoura University, Egypt.
Email: mmostafa84@hotmail.com
K E Y W O R D S
1-[(1,2,4-triazole-4-yl)imino]diacetyl monoxime (L), biological studies, single crystal X-ray,
spectral studies
1 | INTRODUCTION
interest as ligands to transition metal ions since the coor-
dination geometry of both pyrazoles and imidazoles act-
Derivatives of triazoles are applied as organic heterocyclic
compounds that used as ligands containg several donor
sites. 1,2,4-Triazole is a cyclic hydrazone that is synthe-
sized with hydrogen atoms (or substitution) on either the
hydrazide N atom or an amide N atom. In recent years
1,2,4-triazoles have gained significant attention as ligand
systems due to the additional N-donor atoms that create
mono-, bi-, or tridentate binding sites which improve the
stability of complexes due to the chelation effect.
Noncovalent interactions, such as dipole–dipole, hydro-
gen bonding lone pair (N)–π and π-stacking, can engage a
large variety of 1,2,4-triazoles with biological targets.[1,2]
The 1,2,4-triazole system and its derivatives have gained
ing as bridging ligands between two metal centers.[3]
Various biological activities, such as antiasthamatic,[4,5]
antiviral,[6] antifungal,[7] antimicrobial,[8] sandman,[9]
pesticide,[10] mastectomy cancer preventive,[11,12] anti-
convulsant, anticancer, anti-inflammatory,[13–22] Central
nervous system depression,[23] antitumor,[24] and antihy-
pertensive activities,[25,26] have been reported. 1,2,4-
Triazoles have plant growth regulating and anticogulant
properties.[27] Three metal chelates with the general for-
mulae [CoLCl2(EtOH) (H2O) ], [Fe2LCl3(EtOH) ]3Cl,
½
½
½
and [Pd2LCl4(H2O)3] were synthesized and characterized
by chemical, spectral (Fourier transform infrared [FT-IR],
1
UV–visible [UV-Vis], H NMR, 13C NMR, Electron spin
Appl Organomet Chem. 2020;e5734.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5734

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MOSTAFA ET AL.
resonance [EPR]), Thermal gravimetric analysis (TGA),
and magnetic measurements. L and its chelates were
tested against biological activity.
glacial acetic acid. The reaction mixture was refluxed for
12 hr with gentle heating and continuous stirring, then
the solution was evaporated to its half volume. Finally,
the solution was left to cool at ambient temperature until
the ligand precipitated out. Recrystallization was carried
out several times by dissolving in the product in EtOH
and filtering it over charcoal. The powdered product
(m.p. 206–210ꢀC) was dried in a vacuum desiccator over
P4O10. White crystals with cubic shapes of the ligand
were formed on leaving the filtrate for 2 weeks at room
temperature (25ꢀC). The product was colorless. Yield
70%, m.p. 208–210ꢀC; νmax (KBr): 3125 (s), 2980 (m), 2784
(w), 1678 (m), 1579 (m), 1509 (s), 1373 (s), 1210 (m), 1183
(m), 1129 (m), 1068 (s), 1027 (s), 983 (s), 860 (s), 776 (s),
677 (m), 647 (m), 621 (m), 497 (w),422 (w); δH (500 MHz,
DMSO-d6): 2.057 (3 H; s, CH3, C=N–), 2.165 (3 H; s, CH3,
C=N–OH), 8.735 (H; s, CH), 12.418 (H; s, OH); δC 9.407
(CCH3): 14.281 (CCH3), 140.139 (CH=N), 153.95 (C=N–
N), 171.196 (C=NOH). Anal. calcd for C6H9N5O 167.178
(%): C 43.11, H 5.43, N 41.90; found (%): C 43.52, H 5.85,
N 41.91. The experimental value of the mass spectrum of
L equals 168, which agrees with the molecular weight of
the ligand (167.172).
2 | EXPERIMENTAL
2.1 | Material and methods
All the compounds used in this investigation were of
Analytical reagent (AR) quality and used as support. 2,3-
Butanedione monoxime (BDH), hydrazine hydrate (Fisher
Scientific), ethyl formate (Merck), anhydrous FeCl3,
CoCl2.6H2O, PdCl2, DMSO, ether (BDH or Merck), etha-
nol (Fisher), HNO3 (Aldrich), ethylenediaminetatraacetic
acid disodium salt (EDTA), Eriochrome black T, and
AgNO3 were of AR quality and used as provided.
Elemental analyses were determined in the Microanalyti-
cal Unit, Cairo University, Egypt. The percentages of iron,
palladium, and chloride were determined using gravimet-
ric methods while the cobalt content was determined by
the volumetric method.[28] Spectral (IR, 1H NMR, 13C
NMR, UV–Vis, EPR), magnetic, thermal, conductance,
cyclic voltammetry, and single crystal measurements were
carried out as reported earlier in our previous work.[29,30]
2.2 | Preparation of solid chelates
2.2.1 | Preparation of Fe3+ chelate
1-[(1,2,4-triazole-4yl)imino]diacetyl
monoxime(L)
(Figure 1) was prepared in two steps. First, 30 ml of
hydrazine hydrate was added dropwise with shaking to
30 ml of ethyl formate in the presence of 30 ml of EtOH.
The reaction mixture was refluxed with gentle heating
and stirring for 8 hr. This solution was evaporated to one-
third of its volume, then left to cool in an ice bath until
the product formed. The resulting compound was crystal-
lized several times using EtOH in the presence of char-
coal. Finally, the solution was dried in a desiccator over
CaCl2. The melting point of this product was 65–68ꢀC. In
the second step 1.2 g of the first product was dissolved in
15 mLof EtOH and added to 2.02 g of 2,3-butanedione
monoxime dissolved in 20 ml of EtOH in a few drops of
The ligand (1 mmol) was dissolved in10 ml of CH3CN
and 5 ml of EtOH and then added to a solution of FeCl3
(1 mmol) dissolved in 10 ml of EtOH. The pH of the
solution was 4 and it was refluxed with stirring on a hot
plate for 12 hr. The mixture was evaporated on a water
path almost to dryness until a brownish precipitate was
obtained. The product was filtered off, washed several
times with diethyl ether, and dried in a desiccator over
P4O10. The general formula of the isolated Fe(III) chelate
is [Fe2LCl6(H2O) (EtOH) ]Cl3. Yield 50%, m.p. 220ꢀC;
½
½
brown powder,. Elemental analyses: anal. found for
C7H13Cl6Fe2N5O2 (%): C 16.9, H 2.9, Cl 40.2, Fe 20.31;
calcd (%): C 16.1, H 2.5, Fe 21.3, Cl 40.6. Λm (DMSO):
114 Ω−1 cm2 mol−1 and μeff: 4.45 BM.
2.2.2 | Preparation of Co2+ chelate
[CoLCl2(H2O) (EtOH) ] was synthesized by mixing the
½
½
ligand (0.167 g, 1 mmol) dissolved in a mixture of 10 ml
of CH3CN and 2 ml of EtOH to CoCl2.6H2O (0.237 g,
1 mmol) de-iced in 10 ml of CH3CN at pH 5–6). The reac-
tants were kept under reflux with stirring on a hot plate
for 5 hr and the color of the product changed from blue
to bluish green. Finally, the resulting precipitate was fil-
tered, washed with absolute EtOH followed by ether then
FIGURE 1 Structure of L

MOSTAFA ET AL.
3 of 15
the product was kept in a vacuum desiccator over anhy-
drous P4O10. Yield 60%, m.p. 240ꢀC. Elemental analyses:
anal. found for C7H13Cl2Co N5O2 (%): C 25.4, H 4.01, Co
18.8, Cl 21.9; calcd (%): C 25.6, H 4.0, Co 17.9, Cl 21.5.
Ʌm: 30 ohm−1 cm2 mol−1 and μeff: 4.3 BM.
2.6.2 | Ant-hemolytic assay
The erythrocyte hemolysis procedure was applied as
reported earlier.[34]
2.2.3 | Synthesis of Pd2+ chelate
2.6.3 | Cytotoxic activity
[Pd2LCl4(H2O)3] was formed by mixing PdCl2 (0.355 g,
2 mmol) dissolved in 25 ml of 3 moles of HCl. The reac-
tants were refluxed for 5 min then the ligand (0.334 g,
2 mmol) dissolved in 10 ml of EtOH was added. The reac-
tion mixture was acidic with pH 1. A deep yellow precipi-
tate was formed at once then the reactant was refluxed
with stirring on a hot plate for 5 hr. The resulting solid
chelate was filtered off, washed with absolute EtOH and
diethyl ether, and kept in a vacuum desiccator over anhy-
drous P4O10. Yield 60%, m.p. 240ꢀC. Elemental analyses:
anal. found for C6H15Cl4Pd2N5O5 (%): C 12.2, H 1.9, Pd
35.6, Cl 25.3; calcd (%): C 12.5, H 2.6, Pd 36.2, Cl 24.6.
Ʌm: 12 ohm−1 cm2 mol−1 and μeff: diamagnetic.
The in vitro cytotoxicity of the ligand and some of its
chelates was examined using 3-(4,5-dimethylthiazol-
2-yl)-2,5-diphenyl tetrazolium bromide (MTT)-based
assays. The colorimetric technique was used to
determine cytotoxicity and to measure cell growth, as
reported earlier.[29]
2.6.4 | Colorimetric assay for compounds
that bind DNA
DNA methyl green (20 mg) was suspended in 100 ml of
0.05 M tris-HCl buffer (pH 7.5) containing 7.5 mM
MgSO4, then the mixture was stirred at 37ꢀC for 24 hr.
Test samples (10, 100, and 1000 mg) were dissolved in
EtOH after that the solvent was separated under vacuum,
and to each tube was added 200 μl of DNA/methyl green
solution. Samples were incubated in the dark at ambient
temperature. After 24 hr, the final absorbance of the sam-
ples was determined at 642.5–645 nm. The results were
corrected for premier absorbance and normalized as the
percentage of the untreated standard.
2.3 | Single-crystal X-ray crystallography
The crystallographic analysis of L was carried out using
the same procedure as reported earlier.[29]
2.4 | Molecular modeling
3 | RESULTS AND DISCUSSION
3.1 | IR spectra
2.5 | Computational details (molecular
modeling)
The structures were performed by cluster calculations
using the DMOL3 program without any symmetry restric-
tion in the Materials Studio Package, which is designed
for the realization of large-scale density functional theory
(DFT) calculations.[30,31]
The FT-IR spectrum of L in KBr (Supporting Information
Figure S1) shows absorption bands at 3216(sh), 3125(s),
2980(m) and 2784(m) cm−1 which were attributed to OH,
NH, CH, and CH3, respectively. Three bands attributed to
the azomethin groups (C=N) at 1678 cm−1 (C=NOH),
1658 cm−1 (C=N-N), and 1597 cm−1 (azomethin) triazole
were relocated to lower wavelengths in the metal chelates,
indicating the involvement of these groups in bonding.
Two bands at 3216 and 3125 cm−1 were assigned to OH
(free) and OH (hydrogen bonded). In the case of 2:1
(metal:ligand) chelates, the second metal ion (Pd2+ and
Fe3+) was coordinated via the triazole nitrogen (N–
CH=N) as shown in Supporting Information Figures S2
and S3. The ligand coo167rdinates to the Co2+ ion
through the two azomethin groups only (Supporting
Information Figure S4). The appearance of broad weak
bands in the 2000–2400 and 2500–2800 cm−1 regions
2.6 | Biological activity
2.6.1 | Antibacterial and antifungal
activity
The ligand and its compounds were tested against two
antibacterials (Gram-positive, Staphylococcus aurous;
Gram-negative, Escherichia coli) and two antifungals
(Candida albicans and Aspergillum flavus) using the disc
diffusion method.[32,33]

4 of 15
MOSTAFA ET AL.
suggests the presence of interhydrogen bonding, as shown
in Figure 2. The new band in the 437–459 cm−1 region
was assigned to ν (M–N) vibration.[35] Peaks for the (M–
O) bond in the Pd2+ and Fe3+ chelates were observed at
1 mole of 2,3-butanedione monoxime and two drops of
glacial acetic acid to produce [(3-(3H-1,2,4-triazole-
4-(5H)-ylimino)butane-2-one-oxime (L) is proposed.
1
508 and 505 cm−1, respectively. The H NMR spectrum
(Supporting Information Figure S5) exhibited two sharp
singlet signals at 12.42 and 8.74 ppm due to the hydroxyl
and CH groups, respectively, along with two singlet sig-
nals at 2.17 and 2.06 ppm indicating the presence of two
CH3 groups. The OH signal disappeared on adding D2O,
as shown in Supporting Information Figure S6. The 13C
NMR spectrum (Supporting Information Figure S7)
shows five distinct singlet signals at 171.19, 153.95,
140.14, 14.28, and 9.41 ppm attributed to C=N-N,
C=NOH, CH, H3C–C=NOH, and H3C–C=N–N, respec-
tively. These results are in good agreement with the
expected structure and the existence of hydrogen bonding
(Figure 2). A possible reaction mechanism (Scheme 1)
involving the formation of formic acid hydrazide by the
reaction of ethyl formate with N2H4 in the presence of
3.2 | X-ray structural analysis
Crystals elicited for single-crystalX-ray analysis were
grown by slow evaporation of the reaction of ethyl
formate and hydrazine hydrate in the presence of
1 mole of 2,3-butanedione monoxime and two drops of
glacial acetic acid to produce 1-[(1,2,4-triazole-4-yl)
imino]diacetyl monoxime (L). A view of the asymmetric
crystal structure of the new ligand form is illustrated in
Figure 3. The compound crystallizes in the ortho-
rhombic space group Pbca with Z = 8 in the unit cell.
The unit cell parameters of the title molecule have the
following values: a = 6.9624 (4) Å, b = 12.1261 (8) Å,
c = 19.279 (2) Å, and α = γ = β = 90 (4), as shown in
Table 1. The bond distances and angles are listed in
Supporting Information Table S1. The crystal of the
new ligand appeared in reptile form, the head consists
of a triazole ring with two methyl groups as arms and
an OH group as the tail; zigzag aliphatic chain with
trans-methyl groups are perpendicular on flatten
triazole ring which links to the chain through a central
nitrogen atom. The molecules in the unit cell are inter-
linked through hydrogen bonds O–H … N and C–H …
O is depicted in Figure 4 and the types of hydrogen
bonding are shown in Table 2. The π … π stacking
between triazole rings by Cg1(N4-C7-N8-N3-C9) … Cg2
(N8-N3-C9-N4-C7) with centroid–centroid distance
3.7 Å is recorded in Figure 5. The packing diagrams of
the crystal along the a, b, and c planes are shown in
Figure 6 having a chain structure.
FIGURE 2 Hydrogen bonding in L
SCHEME 1 Reaction mechanism of 3-(3H-1,2,4-triazole-
4-(5H)-ylimino)butan-2-one-oxime (L)
FIGURE 3 Perspective view of L

MOSTAFA ET AL.
5 of 15
TABLE 1 Crystal data and structure refinement parameters of
3-(3H-1,2,4-triazole-4-(5H)-ylimino)butan-2-one oxime
Compound
L
Empirical formula
Formula weight
Temperature
C6H9N5O
167.178
298 K
Wavelength
0.71073 Å
Orthorhombic
Pbca
Crystal system
Space group
Unit cell dimensions
a = 6.9624 (4) Å
b = 12.1261 (8) Å
c = 19.279 (2)Å
1627.7 (2)Å3
8
α = 90ꢀ
β = 90ꢀ
γ = 90ꢀ
Volume
FIGURE 4 Hydrogen bond
Z
Density (calculated)
1.460 Mg/m3
Theta range for data collection 30.17ꢀ
of Ueff for the Co2+ chelate is 4.3 BM agrees with the
suggested geometry for the Co(II) ion.[38,39] The visible
spectrum of the Pd2+ complex (Supporting Information
Limiting indices
h = 0 ! 9, k = 0 ! 16,
l = 0 ! 27
0.161
R (int)
Figure S10) shows only one band at 26178 cm−1, which
1
can be attributed to the A1g
!
1B1g transition in a
Absorption correction
Multi-scanTmin = 0.876,
Tmax = 1.12
square-planar geometry around the metal ion.[40] The
diamagnetic nature of the Pd2+ chelate is taken as strong
evidence of d8 square-planar geometry. Finally, the elec-
tronic spectrum of the Fe3+ chelate in Nujol and DMSO
(Supporting Information Figure S11a,b) shows two bands
at 17605 and 18726 cm−1 (DMSO) and 24690 and
26109 cm−1 (Nujol). The first two bands are assigned to
Refinement method
Full-matrixleast-squares on
F2
Data/restraints/parameters
339/0/133
Final R indices [I > 3sigma(I)]
R (all) = 0.290, wR
(ref) = 0.064
R indices (all data)
R (gt) = 0.029, wR
(all) = 0.130, wR
(gt) = 0.064 S (ref) = 1.031,
S (all) = 0.752, S
(gt) = 1.031
6A1 ! T1 and A1 ! T2(G) transitions while the latter
4
6
4
two bands are attributed to 6A1
!
4E, 4A1 and
4
6A1 ! T2(D) transitions in a tetrahedral geometry. The
value of the magnetic moment of the Fe(III) chelate
(4.45 BM) suggests a tetrahedral geometry around the Fe3
+ion.[38,39]
Calculated weights sigma
Δ/σmax = 0.048,
Δ/ρmax = 0.96e A3,
Δ/ρmin = −1.00e A3
3.3 | Spectral and magnetic
3.4 | Thermal analysis
measurements
TGA plays important role in discussing the characteris-
tics of the metal chelates. The curves are accomplished
to make sure the suggested formulae and the
structures of the complexes under investigation. TGA
was performed from 20 to 1000ꢀC and the results were
used to evaluate and compute mass loss in addition to
the results of the microanalyses. The decomposition
steps for [Pd2LCl4(H2O)3] are shown in Supporting
Information Figure S12. The first step from 28 to
378ꢀC occurs with the loss of three molecules of H2O
and three Cl ions (found 28.2%, calcd 27.9%). The
second and third steps show losses in the region from
378 to 800ꢀC corresponding to the fragments
The spectra of L and its Co2+, Pd2+, and Fe3+ chelates
are depicted in Supporting Information Figures S8–S11.
The electronic spectrum of the free ligand (Supporting
Information Figure S8) shows bands at 45871, 41666, and
38759 cm−1. The first two bands are attributed to π ! π*
transitions while the last band refers to an n ! π* transi-
tion.[36] The Co2+ chelate (Supporting Information
Figure S9) elucidates four bands, suggesting a tetrahedral
structure around the Co2+ ion. The first band at
36496 cm−1 is due to an n ! π* transition, while the
other three bands at 23041, 16233, and 14836 cm−1 are
4
4
attributed to the A2g ! T1g(p) transitions.[37] The value

6 of 15
MOSTAFA ET AL.
TABLE 2 The unit cell inter-linked together through hydrogen bonds
D–H … …A
Symmetry
x-1/2,y,1/2-z
x-1/2,y,1/2-z
x-1/2,y,1/2-z
1/2 + x,y,1/2-z
x-1/2,y,1/2-z
x,1/2-y,z-1/2
x-1/2,y,1/2-z
1-x,-y,-z
D–H (Å)
0.920
0.942
1.091
0.948
0.941
0.960
1.011
1.091
1.091
0.960
0.960
H … …A (Å)
2.95 (4)
D … …A (Å)
3.557
D–H …. A (ꢀ)
108.95
66.85
C12–H12Cii … …O1
C9–H9ii … ….O1
C7– H7ii … O1
2.67 (3)
3.657
2.93 (3)
3.252
81.78
C10–H10Aiii … …N2
C10–H10Cii … …N2
O1– H1iv … …N3
C12–H12Cii … …N5
C7–H7v … …C7
C7–H7v … …N8
O1–H1iv … …N8
O1–H1iv … …C9
2.303 (4)
2.93 (4)
2.746
107.85
140.03
173.66
131.95
116.35
145.23
144.50
159.28
2.746
1.781 (3)
2.95 (3)
2.737
3.709
2.71 (3)
3.337
1-x,-y,-z
2.36 (4)
3.310
x,1/2-y,z-1/2
x, ½-y, z-½
2.627 (4)
2.743 (4)
3.454
3.552
3.4.1 | TGA degradation steps and kinetic
data for the Fe3+ and Pd2+ chelates
The kinetic data for the Fe3+ and Pd2+ chelates were esti-
mated by Horowitz–Metzger[41] and Coats–Redfern[42]
methods (Figures 7–9). Erying's equation[43] was used to
calculate the thermodynamic parameters of activation
and the results are recorded in Table 4 showing the fol-
lowing points:
i. The stages of decomposition illustrate the best fit for
n = 1. Other values of n do not lead to best
correlation.
ii. The free energy of the final residue is higher than
that of the initial compound, illustrating from the
positive value of ΔG*, and the decomposition steps
are nonspontaneous. The value of TΔS* exceeds than
the value of ΔH* since the ΔG* values increase.[44,45]
FIGURE 5 π–π stacking
iii. The affirmatory values of ΔH* indicate that the
behavior of all decomposition stages is endothermic.
iv. The ΔS* values indicate that the decomposition steps
are disordered structure for the energize fragments
than of the undecomposed chelate and illustrating
the slowness of the decomposition reaction.[43]
FIGURE 6 (a) Backing along the a axis, (b) backing along the
b axis, and (c) backing along the c axis
3.5 | Cyclic voltammetry
H9N5Cl + 3C (found 26.66%, calcd 26.19%). The resi-
due in the range 800–1000ꢀC corresponds to 2PdC3O,
in which the calculated loss of 45.9% matches the
found loss of 45.2%. The chelates shown in Supporting
Information Figures S13 and S14 show the TGA results
of the other chelates and the thermal decomposition
steps are tabulated in Table 3.
The redox properties of the Fe3+ and Co2+ chelates
were investigated by cyclic voltammetry as shown in
Figures 10 and 11, respectively. The measurements for
the Fe3+ and Co2+ chelates (10−3 M) were officiated in
nonaqueous DMF solution containing the supporting
electrolyte 0.1 M of [(n-Bu)4N]PF6 within the potential
range 1.6 to −0.2 V at scan rate 100 mV/s. The Fe3+

MOSTAFA ET AL.
7 of 15
TABLE 3 TGA decompositions steps for the metal chelates
Weight loss (%)
Compound
Decomposition steps
First
Temperature range (ꢀC)
28–378
Removed species
3H2O + 3Cl
9H + Cl + 5 N
3C
Found
28.2
Calcd
[Pd2LCl4(H2O)3]
27.9
Second
Third
378–448
19.96
6.7
19.89
6.3
448–800
Residue
First
800–1000
30–121
2Pd + 3C + O
½H2O + 4Cl
2Cl + 3 N
45.2
45.9
[Fe2LCl6(H2O) (EtOH) ]
28.79
21.99
22.9
28.8
½
½
Second
Third
121–466
21.57
23.71
25.92
12. 9
45.89
18.56
22.78
466–800
5C + 2 N + 12H + 1½O
2Fe+2C
Residue
First
800–1000
13–187
26.29
12.59
46.14
17.81
23.46
[CoLCl2(H2O) (EtOH) ]
2C + 4H + N
2Cl + 8H + 4 N + O
5C+ H
½
½
Second
Third
187–460
460–636
Residue
636–1000
Co + O
FIGURE 7 Coats–Redfern of (a), (a−) and
Horowitz–Metzger of (b), (b−) first step of Pd2+
and Fe3+ chelates
FIGURE 8 Coats–Redfern of (a), (b) and
Horowitz–Metzger of (c), (d) second and third
steps of Pd2+ chelate
chelate exhibited a quasi-reversible oxidation wave
at positive potentials for one-electron transfer and
E1/2 = 0.125 V and ΔE = 171 mV, where Epc = +0.039 V
and Epa = +0.21 V (Fe3+/Fe2+). The Co2+ chelate
shows one irreversible oxidation peak of high oxidation
current at Epa = +1.38 V, which was assigned to the
oxidation of Co2+ to higher oxidation states, for exam-
3.6 | Mass spectra
The experimental value of the mass spectrum of
L (Figure 12) equals 168 which agrees with the molecu-
lar weight of the ligand (167.172). The peaks at m/z
68.16 and 14.23 with 100% and 14.43% abundance
(calcd 68.06 and 41.03) correspond to the [C2H2N3]
and [CHN2] fragments, respectively, and the dissociation
ple Co4+or Co5+
.

8 of 15
MOSTAFA ET AL.
FIGURE 9 Coats–Redfern of
(a), (b) and Horowitz–Metzger of
(c), (d) second and third steps
of Fe3+ chelate
TABLE 4 Kinetic parameters of Fe and Pd chelates evaluated by the Horowitz–Metzger(HM) and Coats-Redfern(CR) equations
Step
Mid temperature (K)
Method
Ea (kJ/mol)
A(S−1
)
ΔH* (kJ/mol)
ΔS* (kJ/mol)
ΔG* (kJ/mol)
Pd complex
First
203
413
624
CR
101.40
64.7
1.02 × 1010
2.01 × 106
1.66 × 1013
1.13 × 1011
2.3 × 1024
3.8 × 107
98.53
61.04
−0.054
−0.146
0.003
117.38
126.27
193.59
195.5
HM
CR
Second
Third
199.89
173.4
195.26
167.65
369.23
272.37
HM
CR
−0.04
0.214
374.76
278.59
226.2
HM
0.083
229.6
Fe complex
First
76
294
633
CR
34.41
40.29
35.92
46.39
134.57
147.8
7.4 × 103
6.1 × 103
35.01
6.07 × 102
2.3 × 106
1.8 × 107
31.54
37.34
31.29
42.47
129.03
141.1
−0.191
0.173
97.63
99.06
154.02
154
HM
CR
Second
Third
0.220
HM
CR
−0.195
−0.129
−0.114
215.23
213.23
HM
Arrhenius pre-exponential factor s−1
.
is shown in Scheme 2. The mass spectrum of [CoL-
The mass spectrum of [Fe2LCl3(H2O) (EtOH) ]3Cl
½ ½
Cl2(H2O) (EtOH) ] (Supporting Information Figure S12)
(Supporting Information Figure S16) shows a molecular
ion peak at m/z 525.9, which agrees with the theoretical
value (523.6). This shows that the suggested formula of
this compound is agreed with the experimental data.
Supporting Information Scheme S2 shows the fragments
of the Fe3+chelate (1:1). The data from the elemental and
thermal analyses also are taken as evidence for that
assumption. The mass spectrum indicates the
dissociation of Fe chelate.
½
½
shows a peak at m/z 330.6, which agrees with the
estimated value (329.06), suggesting that the formula of
the compound is emend. The fragmentation of the Co2+
chelate (1:1) is depicted in Supporting Information
Scheme S1. The results of the elemental and thermal ana-
lyses were used to confirm the proposed formula.
The spectrum shows the dissociation of Co(II) chelate
(Figure S12).

MOSTAFA ET AL.
9 of 15
FIGURE 10 Cyclic
voltammogram of Fe3+ chelate
FIGURE 11 Cyclic
voltammogram of Co2+ chelate
The mass spectrum of [Pd2LCl4(H2O)3] has molecu-
lar ion peaks which is in agreement with its formula.
The mass spectrum of [Pd2C6H9N5OCl4(H2O)3] shows
fragmentation corresponding to the consecutive degrada-
tion of the complex. The first peak at m/z 576.62 with
13.69% abundance (Supporting Information Figure S17)
represents the molecular ion peak (calcd 575.87).
The peaks at m/z 450.0, 216.81, 69.05, and 55.11
with 10.8%, 19.49%, 30.66%, and 100% abundance
(calcd 450.92, 215.52, 68.05, and 56.04) correspond to
the [Pd2C6H9N5OCl2], [PdC4H5N4]+, [C2H2N3]+, and
[CH2N3] fragments, respectively. The successive degrada-
tion of the Pd2+ complex is shown in Supporting Infor-
mation Scheme S3.

10 of 15
MOSTAFA ET AL.
FIGURE 12 Mass spectrum of the
free ligand
iii. The Co2+ and Fe3+ chelates have bond angles that
support a tetrahedral geometry, while the Pd2+ che-
late shows a square-planar geometry, where the bond
lengths and bond angles of L are similar to these
found from the X-ray diffraction analysis.
iv. The results in Table 5 indicate that the increase in
molecular weight is followed by a decrease in energy
in the gas phase.
SCHEME 2 Fragmentation pattern of the ligand
v. The energies of the HOMO and LUMO are the essen-
tial parameters in quantum studies, in which the
HOMO orbital acts as an electron donor and the
LUMO orbital is an electron acceptor. These
molecular orbitals are known as frontier molecular
orbitals (FMOs) (Supporting Information Figures S18
and S21).
3.7 | DFT calculation of molecular
computation
The structures of L and its metal chelates showing the
atom numbering are depicted in Supporting Information
Figures S18–S21. The following statements can be made
from examination of the bond angles and lengths:
The results of the DFT explain the chemical reac-
tivity and selectivity of the molecular systems. Both
the energies of the FMOs (EHOMO + ELUMO) and the
energy band gap (EHOMO – ELUMO) illustrate the end
charge-transfer interaction within the molecule, electro-
negativity (χ), chemical potential (μ), global hardness
(η), global softness (S), and global electrophilicity index
(ω),[36,46,47] are listed in Table 5. The kinetic stability
and chemical reactivity of the ligand and chelates
depend on the energy difference (EHOMO – ELUMO),
which is the former stability index that assists for the
description. Soft compounds are those with small gap
i. The slightly longer bond distances of N(11)–C(30), N
(12)–C(18), N(22)–C(24), and N(27)–C(29) in the che-
lates than in L is suggested from the formation of M–
O and M–N bonds.
ii. Modification of the bond angles in L are decreased or
increased on chelation to some extent upon coordina-
tion such as N(11)–N(34)–C(29), N(11)–N(34)–C(24),
C(18)–C(30)–N(11), N(34)–C(29)–N(27), N(22)–N
(27)–C(29), C(24)–N(22)–N(27), C(30)–C(18)–N(12),
and C(1)–C(18)–N(12).

MOSTAFA ET AL.
11 of 15
TABLE 5 Calculated EHOMO, ELUMO, energy band gap (EH-EL), chemical potential (μ), electronegativity(X), global hardness (χ), global
softness(S), and global electrophilicity index (ω) for L and its chelates
Compound
EH (eV)
−5.845
−5.272
−5.860
−7.961
EL (eV)
−2.500
−3.922
−4.021
−7.581
(EH-EL) (eV)
−3.345
X (eV)
4.17
μ (eV)
−4.17
−4.59
−4.94
−7.77
χ (eV)
1.67
S (eV−1
0.84
)
ω (eV)
5.21
σ (eV)
0.6
Lignad, C6H9N5O
Co2+ chelate
Pd2+ chelate
Fe3+ chelate
−1.35
4.597
4.94
0.68
0.34
15.49
13.26
158.88
1.47
1.09
5.26
−1.839
0.92
0.46
−0.38
7.771
0.19
0.09
that which is more reactive and more polarized than
the hard compound due to its ease in donating elec-
tron to an acceptor.
insoluble, becomes soluble on addition of a suitable
solvent to form the colored solution. Consequently, the
absorbance at a specific wavelength of the colored
solution was determined. In comparing the manipu-
lated cells with the chelates and that obtained by
unreacted control cells of the amount of purple
formazan formed, as so we get the efficacy of the che-
lates in triggering death of cells concluded by the for-
mation of a potion response curve. The data obtained
show that the estimating of L has availed chemother-
apy since it exhibits very strong activity towards mam-
mary gland breast (MCF-7) and Epitheliod carcinoma
cervix (Hela) with IC50 values of 7.91 and 6.83 μg/ml,
respectively. The ligand also has strong activity against
the prostate cell line PC-3 with an IC50 value of
12.13 μg/ml. On the other hand, the Pd2+ and Co2+
chelates have moderate IC50 values in PC-3 and MCF-
7. The Fe3+ chelate has a weak IC50 value in the PC-3
and MCF-7 cell lines. In the Hela cell line Fe3+and
Co2+ chelates exhibit a moderate cytotoxicity effect,
while the Pd2+chelate has a weak IC50 value in the
same cancer cell line. The extent of the activities of
ligand and its chelates lies between very strong and
moderate to weak, as shown in Figure 13.
3.8 | EPR studies
The powder EPR spectrum of the Fe3+ compound at
ambient temperature (25ꢀC) shows a spectrum suggesting
that the Fe3+ ion has a tetrahedral structure. The breadth
of the single line (H = 394 G) with g value 2.0032 sup-
ports a tetrahedral geometry in which the Fe3+ ion exists
in a weakly tetrahedral structure.[48,49] The absence of
the fine structure of Fe3+ (s = 5/2) is accepted with the
tetrahedral structure.
3.9 | Biological studies
3.9.1 | Cytotoxic activity
The in vitro cytotoxicity of the ligand and some of its
chelates was examined by MTT-based assays and the
results are shown in Table 6.[38,50] Through col-
orimetric technique, MTT assay is considered a good
method to determine cytotoxicity and measure cell
growth. [MTT; 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl
tetrazolium bromide] is yellow and on reduction
changes to purple formazan via mitochondrial dehy-
drogenases of the cells. The purple formazan, which is
TABLE 6 Cytotoxic activity of the ligand and metal chelates
against human tumor cells
Compound
DOX•
PC-3
8.87
MCF-7
4.17
Hela
5.57
Ligand
12.13
48.09
59.54
45.80
7.91
6.83
Pd(II) complex
Fe(III) complex
Co(II) complex
42.75
73.13
31.26
51.02
38.91
29.28
FIGURE 13 The scavenging capacities (IC50) of the ligand
and its metal chelates toward prostate cancer (PC-3), epithelioid
carcinoma cervix cancer (Hela), and mammary gland breast cancer
(MCF-7). Doxorubicin standard antitumor
Note. IC50 (μg/ml): 1–10, very strong; 11–20, strong; 21–50, moder-
ate; 51–100, weak; above 100, noncytotoxic. DOX, doxorubicin.

12 of 15
MOSTAFA ET AL.
TABLE 8 Antioxidant assay for the new compounds
Erythrocyte hemolysis A/B × 100
3.9.2 | DNA/methyl green colorimetric
assay of the DNA-binding compounds
Absorbance of samples
No. Compound (A)
%
Green methyl dye reacts with DNA to give a dyed
DNA/methyl green compound in which the product of an
addition reaction reversibly. This color does not change at
neutral pH, whereas free methyl green obscured at this pH
value. DNA-binding active compounds dislodge DNA
from the methyl green complex. On alteration of DNA
from methyl green by DNA inter-collators, so adding of
water to the dye was allowed, that leading to development
of the pale carbinol, then the absorbance declines colori-
metric. The displacement was determined by a spectro-
photometric assay as a decrease in the absorbance at
630 nm. The results were announced as inhibition concen-
tration 50% value (IC50) calculated by linear regression of
data plotted on a semi-log scale and are shown in Table 7.
In this assay doxorubicin was used as a control. The ligand
displayed very strong inhibitory activity and powerfully
intercalated DNA at a decreased IC50 value ranging from
29.18 1.6 μM. The Co2+, Fe3+, and Pd2+ chelates have
Hemolysis
Absorbance of H2O 0.875
(B)
–
Vitamin C
0.030
0.056
0.134
3.4%
6.4%
1
2
Ligand
Pd(II)
chelate
Fe(III)
chelate
Co(II)
chelate
15.3%
3
4
0.227
0.071
25.9%
8.1%
3.9.4 | Antibacterial and antifungal
activity
Ampicillin, an antibacterial agent and broad-field antibi-
otic, acted as a positive control for the antibacterial test,
while DMSO was utilized as the negative control and sol-
vent. The diameter of the inhibition zone of ampicillin
towards E. coli is 25 mm and towards S. aurous is 21 mm.
Table 9 shows the results of the antibacterial tests on
the chelates towards Gram-negativeE. coli and Gram-
positiveS. aurous. The Co(II) chelate has maximum
antibacterial activity towards E. coli with an 18 mm
inhibition zone diameter. The Pd(II) and Fe(III) chelates
weak IC50 values of 56.94
2.3, 61.40
2.5, and
67.23 2.4 μM, respectively.
3.9.3 | Antioxidant activities
The ligand (L) and its metal chelates were examined for
their antioxidant activity by erythrocyte hemolysis. The
screened antioxidant activity compared with vitamin C is
depicted in Table 8 and Figure 14. The ligand exhibited
high antioxidant activity. With respect to erythrocyte
hemolysis, the activity of the tested chelates has the order
Co(II) > Pd(II) > Fe(III) compared to vitamin C with
respect to erythrocyte hemolysis.
showed
a
sensible antibacterial activity towards
E. coli with 12 and 11 mm inhibition zone diameters,
respectively. The Co(II) chelate showed the strongest
antibacterial activity of all the tested chelates towards
S. aurous with a 19 mm inhibition zone diameter. The
antibacterial effectiveness of the Pd(II) and Fe(III)
TABLE 7 DNA binding activity of the ligand and its metal
chelates
DNA active compound
DNA/methyl green (IC50, μM)
31.27 1.8
DOX
Ligand
Co(II)
Fe(III)
Pd(II)
29.18 1.6
56.94 2.3
61.40 2.5
67.23 2.4
Note. Values represent the concentration (mean SD, n = 3–5 sep-
arate determinations) required for a 50% decrease in the initial
absorbance of the DNA/methyl green solution. DOX, doxorubicin.
FIGURE 14 Antioxidant activities through
erythrocyte hemolysis

MOSTAFA ET AL.
13 of 15
TABLE 9 Antibacterial and antifungal inhibition zone diameter (mm/mg) of the ligand and its metal chelates
Inhibition zone diameter (mm/mg sample)
Bacteria
Fungi
E. coli
(G−)
%
AI
S. aureus
(G+)
%
AI
A. flavus
(fungus)
%
AI
C. albicans
(fungus)
%
AI
Sample
Standard Ampicillin:
25
100
21
100
–
–
–
–
antibacterial agent
Amphotericin B: antifungal
agent
–
–
–
–
17
100
21
100
Control: DMSO
0.0
0.0
18
11
12
0.0
0.0
72
44
48
0.0
0.0
19
14
13
0.0
0.0
90
66
61
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
13
0.0
0.0
62
Ligand
Co(II) chelate
Fe(III) chelate
Pd(II) chelate
0.0
10
0.0
47
Note. % AI, % activity index; G–, Gram-negative; G+, Gram-positive.
chelates against S. aurous was 13 and 14 mm, respec-
tively. Amphotericin B (an antifungal agent) recorded
antifungal activities towards the fungal strains A. flavus
and C. albicans of 17 and 21 mm, respectively. The
Co(II) and Pd(II) compounds showed moderate antifun-
gal effectiveness towards C. albicans with 13 and 10 mm
inhibition zone diameters, respectively. The Fe(III) che-
late did not display any antifungal reactivity towards
C. albicans. The Co(II), Fe(III), and Pd(II) compounds
did not show any antifungal activity against A. flavus. It
was perceived that the ligand has no effect against bacte-
ria or fungi, as shown in Table 9. The antimicrobial activ-
ities of L and its chelates are shown in Figure 15. The
efficiency and effectiveness propagation of compounds
via cell membrane or interaction with microorganism cell
wall give rise to a high antibacterial activity, which is
known as lipophilic characteristics, that is, penetrating
the lipid cell wall linked to the polarity of central metal
ion and raised with formation of chelation ring which
sharing the positive charge on metal ion with the N-
donor atom of L1 causing π-electrondelocalization on the
chelation ring also corroborate this (Figures 16–18).[51–53]
FIGURE 16 The scavenging capacities (IC50) of the ligand
and its metal chelates toward prostate cancer (PC-3), epithelioid
carcinoma cervix cancer (Hela), and mammary gland breast cancer
(MCF-7). Doxorubicin standard antitumor
FIGURE 15 Antibacterial activity through
FIGURE 17 Antioxidant activities through
erythrocyte hemolysis
erythrocyte hemolysis

14 of 15
MOSTAFA ET AL.
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