Synthesis, spectral characterization, density functional theory studies, and biological screening of some transition metal complexes of a novel hydrazide–hydrazone ligand of isonicotinic acid

Article abstract of DOI:10.1002/aoc.6205

Novel Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) complexes (1–7) of hydrazide–hydrazone ligand (H₂L) derived from the condensation of isonicotinic acid hydrazide with (Z)-N′-(2-nitrobenzylidene)-3-oxobutanehydrazide have been prepared. The ligand and its chelates were characterized based on elemental analysis, spectral, thermal analysis, molar conductance, and magnetic moment measurements. Besides, density functional theory (DFT) computations have been conducted to study structures and energetics of the ligand and its complexes. The IR spectra showed that the ligand was chelated with the metal ion in a monobasic tridentate manner using ONO donors in all complexes except Zn(II) complex (5) where the ligand binds with Zn(II) ion as a dibasic tridentate utilizing ONO donors. The magnetic moment and electronic spectral data revealed octahedral and square pyramidal geometries for complexes (1, 7) and (2, 4, 5), respectively, whereas a square planar geometry was suggested for 3. DFT studies show that the Cd(II) center reveals interesting structural deviations from regular octahedral geometry in the resulting hexa-coordinated complex [Cd(H₂L)₂].2H₂O (6) assumes a trigonal prismatic (TP) structure for this complex. The antibacterial and antifungal activities of the ligand and its complexes have been investigated with different bacterial and fungal strains. The data revealed that Hg(II) complex (7) demonstrated a very good antibacterial and antifungal activity than others. Highlights: A new hydrazide–hydrazone ligand of isonicotinic acid was synthesized. Seven mononuclear Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) complexes of the new ligand were prepared and characterized by different tools. DFT studies have been carried out to study the structure of the ligand and its complexes. Antimicrobial activities of the ligand and its complexes were studied against a variety of bacterial and fungal strains by using disk diffusion method and results were compared with standard drugs.

Full text of DOI:10.1002/aoc.6205

Received: 20 September 2020
DOI: 10.1002/aoc.6205
Revised: 26 December 2020
Accepted: 3 February 2021
F U L L P A P E R
Synthesis, spectral characterization, density functional
theory studies, and biological screening of some transition
metal complexes of a novel hydrazide–hydrazone ligand of
isonicotinic acid
1
,2
2
3
Dina A. Tolan
| Tahani I. Kashar
2
| Kazunari Yoshizawa
|
Ahmed M. El-Nahas
1
Department of Chemistry, College of Science and Humanities, Prince Sattam bin Abdulaziz University, Al-Kharj, 11942, Saudi Arabia
Chemistry Department, Faculty of Science, Menoufia University, Shebin El-Kom, 13829, Egypt
2
3
Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, 819-0395, Japan
Correspondence
Novel Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) complexes
Tahani I. Kashar, Chemistry Department,
Faculty of Science, Menoufia University,
Shebin El-Kom 13829, Egypt.
Email: tahanikashar@science.menofia.
edu.eg
(
1–7) of hydrazide–hydrazone ligand (H L) derived from the condensa-
2
0
tion of isonicotinic acid hydrazide with (Z)-N -(2-nitrobenzylidene)-
3-oxobutanehydrazide have been prepared. The ligand and its chelates were
characterized based on elemental analysis, spectral, thermal analysis, molar
conductance, and magnetic moment measurements. Besides, density func-
tional theory (DFT) computations have been conducted to study structures and
energetics of the ligand and its complexes. The IR spectra showed that the
ligand was chelated with the metal ion in a monobasic tridentate manner using
ONO donors in all complexes except Zn(II) complex (5) where the ligand binds
with Zn(II) ion as a dibasic tridentate utilizing ONO donors. The magnetic
moment and electronic spectral data revealed octahedral and square pyramidal
geometries for complexes (1, 7) and (2, 4, 5), respectively, whereas a square pla-
nar geometry was suggested for 3. DFT studies show that the Cd(II) center
reveals interesting structural deviations from regular octahedral geometry in
the resulting hexa-coordinated complex [Cd(H L) ].2H O (6) assumes a trigo-
2
2
2
nal prismatic (TP) structure for this complex. The antibacterial and antifungal
activities of the ligand and its complexes have been investigated with different
bacterial and fungal strains. The data revealed that Hg(II) complex (7) demon-
strated a very good antibacterial and antifungal activity than others.
Highlights
•
•
A new hydrazide–hydrazone ligand of isonicotinic acid was synthesized.
Seven mononuclear Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and
Hg(II) complexes of the new ligand were prepared and characterized by
different tools.
Appl Organomet Chem. 2021;35:e6205.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
1 of 24
https://doi.org/10.1002/aoc.6205

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TOLAN ET AL.
•
•
DFT studies have been carried out to study the structure of the ligand and
its complexes.
Antimicrobial activities of the ligand and its complexes were studied against
a variety of bacterial and fungal strains by using disk diffusion method and
results were compared with standard drugs.
K E Y W O R D S
DFT calculations, hydrazide, metal complexes, Schiff base, spectral studies
1
| INTRODUCTION
changes in the biological properties of both metal and the
ligand moiety.
[
35–39]
Designing new antimicrobial agents with different chem-
ical characteristics from currently used antibiotics and
chemotherapeutic agents is considered as a critical
demand to overcome the rising rates of antibacterial
In the present work, a new hydrazide–hydrazone
ligand (H L) was prepared from condensation of
2
0
isonicotinic
acid
hydrazide
with
(Z)-N -(2-
nitrobenzylidene)-3-oxobutanehydrazide, which was
further reacted with Mn(II), Co(II), Ni(II), Cu(II), Zn(II),
Cd(II), and Hg(II) chlorides to form the corresponding
metal complexes. The structures of the targeted ligand
and its complexes were characterized by different analyti-
cal and spectroscopic tools. The antimicrobial and anti-
fungal activities of these compounds were measured
against different bacterial and fungi strains. Quantum
chemical calculations also have been carried out to sup-
port and interpret experimental findings. In this project,
density functional theory (DFT) calculations have been
performed aiming to determine the stability of the com-
plexes formed, binding energies, ligand and complexes
geometries in addition to various quantum chemical
[1]
resistance. Consequently, there is a need to search for
novel compounds with significant antibacterial and anti-
[2,3]
fungal activity.
Hydrazine, hydrazone, and their ana-
logs are potential group of compounds that have
[
4–10]
significant biological and pharmacological activities.
The most important activity reported for hydrazine and
[
4–7]
its derivatives is the free radicals scavenging effect.
Also, the antibacterial and antifungal potentials of such
nitrogenous compounds against different types of bacte-
[
8,10,11]
ria were studied by various researchers.
zine derivatives play also vital role as
chemotherapeutic agent for the management of
The hydra-
a
a
[12–14]
tuberculosis.
Further, the hydrazide–hydrazones
with ( CO NH N CH ) moiety have gained an
important place in medicinal chemistry as antibacterial,
antifungal, antitumor, anticonvulsant, anti-inflamma-
parameters of the free ligand (H L) and its complexes.
2
[
15–30]
tory, antimalaria,l and antituberculosis agents.
2 | EXPERIMENTAL
Moreover, isonicotinic acid and its derivatives showed
important properties like antibacterial, antioxidant, and
2.1 | Analytical and physical
measurements
[
14,31–33]
anticancer agents.
isoniazid; INH) is widely applied as a first line drug for
the treatment of tuberculosis and still the most effective
Isonicotinic acid hydrazide
(
All chemicals and solvents were pure chemicals from
BDH or Aldrich and used as received. Melting points
were determined using Fisher–Johns melting point appa-
ratus. The infrared spectra were recorded using Mattson–
5000 Fourier transform infrared (FTIR) spectrometer
with KBr disk method at the Faculty of Science, Cairo
[
14,31–33]
antituberculosis drug, recommended by WHO.
Designing derivatives from this molecule has been a chal-
[31–33]
lenge taken up by several research groups
as the
pharmacokinetic properties and cellular permeability of
the drug can be enhanced by derivatization to
[34]
1
13
bioreversible forms of this drug as hydrazones.
On the
University. The H NMR and C NMR spectra were
other hand, organic antibiotics generally have a single
obtained in DMSO-d on a Varian XL Gemini 300 spectro-
6
[35]
molecular target.
One of the approaches to overcome
photometer at 300 MHz at room temperature. MS were
run on a GCMS-Q1000-EX Shimadzu and GCMS 5988-A
HP spectrometer at 70 eV. Elemental analyses (C, H, and
N) were carried out at the Microanalytical Unit of the
University of Cairo. Metal ions were determined using
atomic absorption with a Perkin Elmer (model 2380)
this problem is the use of metal ions and metal com-
[
35–38]
pounds as alternatives for traditional antibiotics.
These metal-containing compounds possess various
mechanisms of action as antimicrobial agents. Chelation
of organic compounds with metal causes important

TOLAN ET AL.
3 of 24
spectrophotometer. Additionally, the chloride ions were
[
40]
evaluated by argentometry.
Molar conductivity was
−
3
made in DMF solution (10 M) utilizing a type CD6N
Tacussel conductmeter. Electronic absorption spectra in
the 200- to 1000-nm region were recorded on a Perkin–
Elmer 550 spectrophotometer in DMF solution. The
thermal analyses (thermogravimetry analysis [TGA]\
differential thermogravimetry [DTG]) were carried out
on a Shimadzu TG-50 thermal analyzer from room tem-
ꢀ
ꢀ
−1
perature to 1000 C range at a heating rate of 10 C min .
Powder X-ray diffraction (XRD) patterns collected by
2
SCHEME 1 Synthesis of ligand (H L)
1
8-kW diffractometer (Bruker; model D8Advance) with
monochromated Cu-Ka radiation (1.54178 Å). Magnetic
susceptibilities were measured at room temperature by
Gouy method employing Johnson Matthey Magnetic Sus-
ceptibility Balance. Diamagnetic corrections were deter-
The reaction mixture was magnetically stirred and
refluxed for about 3–5 h. The refluxed solution was
cooled overnight and filtered. The solid product formed
was washed several times with ethanol then dried under
vacuum.
[41]
mined using Pascal's constants.
The effective magnetic
moments were ascertained from the relation μ = 2.84
eff
corrt
1/2
corrt
(
XM
T) where, XM
is the molar magnetic suscep-
tibility corrected for diamagnetism of all atoms in the
compounds. The antimicrobial screening of H L ligand
2.4 | Antimicrobial activity
2
and its complexes was carried out against gram-positive
bacteria (Staphylococcus aureua) and gram-negative bac-
teria (Escherichia coli), while the antifungal activity was
measured against Aspergillusflavus and Candida albicans.
Antimicrobial activity of the ligand and its metal com-
plexes were determined using a modified Kirby–Bauer
[
43]
disk diffusion method.
Briefly, 100 μl of the bacterial/
fungi under investigation were grown in 10 ml of fresh
8
media until they reached a count of approximately 10
5
2
.2 | Synthesis of the ligand
cells/ml for bacteria or 10 cells/ml for fungi. One hundred
microliters of microbial suspension was spread onto agar
plates. The tested compounds were dissolved in DMSO
giving stock solutions. Blank paper disks (Schleicher &
Schuell, Spain) with a diameter of 8.0 mm were impreg-
nated with 10 μl of the required concentration of the tested
Synthesis of the ligand occurred via four steps. The first
and second steps involve the preparation of
3
-ketobutanehydrazide (a) and isonicotinic acid hydra-
[42]
zide (isoniazid, d) as reported previously.
mixture of 3-ketobutanehydrazide (0.01 mol) and 2-nitro
benzaldehyde (b) (0.01 mol) was added in ethanol
After that, a
−
1
compounds (100 mg ml ). After that, the filter paper disk,
impregnated with the tested compounds, was placed on
the agar. The compounds were diffused from the disk into
the agar. Standard disks of ampicillin (antibacterial agent)
and amphotericin B (antifungal agent) served as positive
controls for antimicrobial activity but filter disks impreg-
nated with 10 μl of solvent dimethylsulfoxide (DMSO)
were used as a negative control. Plates inoculated with fila-
(20 ml). The mixture was refluxed for 8 h, concentrated,
0
and cooled. The precipitate which formed (Z)-N -(2-
nitrobenzylidene)-3-oxobutanehydrazide (c) was filtered
off, washed several times with cold ethanol, and dried
under vacuum. The last step involves the addition of the
resulting Schiff base (c) (0.01 mol) and isonicotinic acid
hydrazide (d) (0.01 mol) in ethanol (30 ml), and then the
mixture was refluxed for 4 h; the yellow precipitate
formed was filtered off, recrystallized from dilute ethanol.
and dried under vacuum (Scheme 1).
ꢀ
mentous fungi as Aspergillusflavus at 25 C for 48 h; Gram
(+) bacteria and Gram (−) bacteria as Staphylococcus
ꢀ
aureua was incubated at 35–37 C for 24–48 h, and yeast as
ꢀ
Candida albicans was incubated at 30 C for 24–48 h, and
then the diameters of the inhibition zones were measured
in millimeters.
2.3 | Synthesis of metal complexes
An ethanolic solution (20 ml) of the metal chlorides salt
of Cu(II), Co(II), Ni(II), Mn(II), Zn(II), Cd(II), and
Hg(II) were added to an ethanolic solution (20 ml) con-
2.5 | Computational methods
[
44,45]
The quantum mechanical study using DFT
ried out using the Gaussian 09 package.
was car-
[
46]
taining an equimolar concentration of the ligand (H L).
Geometry
2

4
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TOLAN ET AL.
optimizations were carried out utilizing B3LYP func-
[47,48]
[49]
tional
with LANL2DZ
basis set for metals and
6
-311G(d) basis set for other atoms. Frequency calcula-
tions were performed for all optimized geometries at the
same level of theory to verify their nature as minima or
transition states on the potential energy surface of these
systems. In our systems, absence of negative eigenvalues
in the force constant matrices indicates that all of the
obtained stationary points are minima. The vibrational
modes were examined by using the ChemCraft pro-
[50]
gram.
The calculated vibrational frequencies were
scaled by 0.9682 to account for the anharmonicity of the
experimental frequencies. Thermodynamic parameters
such as the energy (E), enthalpy (H = E + PV), entropy
(S), and Gibbs energy (G = H − TS for T = 298.15 K)
were calculated using the same level of theory. The distri-
bution of the highest occupied and lowest unoccupied
frontier molecular orbitals (HOMO, LUMO, and FMO) as
well as the molecular electrostatic potential (MEP) of the
ligand and its complexes has been analyzed. The
ChemCraft program was used for displaying the compu-
tational results and plotting FMOs.
FIGURE 1 Amido–imido tautomers of the hydrazide—
hydrazone ligand
3
3
| RESULTS AND DISCUSSION
.1 | Chemistry
in 10− M DMF solution at room temperature of
3
0–31 Ω cm− mol reveal that all complexes are non-
2
−1
1
[36,51]
The preparation of the hydrazide–hydrazone ligand
occurred via four steps as shown in Scheme 1. Initially,
electrolyte.
The analytical and physical data are
compatible with the suggested structures.
3
-ketobutanehydrazide and isonicotinic acid hydrazide
[42]
(isoniazid) were prepared as reported previously.
After
that, the 3-ketobutanehydrazide was reacted with 2-nitro
benzaldehyde in equimolar ratio in EtOH followed by the
elimination of one water molecule results in the forma-
tion of the Schiff base (c). Finally, The formed Schiff
base (c) was reacted with isonicotinic acid hydrazide in
3.2 | Infrared studies
The IR spectrum of the free ligand (H L) is compared
with IR spectra of its metal complexes, to investigate the
mode of bonding of the hydrazine-hydrazone ligand to
2
0
equimolar ratio in EtOH affording N -((E)-4-(2-((Z)-2-
the metal ions. The IR spectral results of H L ligand, its
2
nitrobenzylidene)hydrazineyl)-4-oxobutan-2-ylidene) iso-
metal complexes and their assignments are collected in
nicotinohydrazide ligand H L (Figure 1). The structure
Table 2. An inspection of H L ligand spectrum (Supple-
2
2
of the ligand was elucidated using elemental analyses
and spectral methods.
mentary Information) reveals several fundamental weak-
broad bands at 3435, 3295 and 3191, and 3107–2855 cm
−
1
An ethanolic solution of H L reacts with an EtOH
assigned to stretching vibrations of adsorbed water mole-
cule, two amide υ(N H), and aromatic and aliphatic
(C H), respectively. The additional bands located at
1413, 1040 and 1065, and 689 and 744 cm− correspond
2
solution of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II),
and Hg(II) chlorides and forms the corresponding coordi-
nation compounds, 1–7 (Figure 2). Complexes (5–7) have
yellowish white and white colors, whereas complexes
1
to bending deformation of (CH ) group, (C H) in-plane
3
(
2–4) are colored complexes (Table 1). All the complexes
deformation, and out-of-plane (C H) bending for the
[
35,51,52]
are stable towards air and insoluble in most common
organic solvents but soluble in DMF and/or DMSO. The
elemental analysis shows 1 L:1 M except complexes
aromatic benzene skeleton.
Furthermore, the H2L
IR spectrum illustrates strong and medium bands at 1516
and 1354, 930, and 1439 cm− assignable to stretching
1
(
1 and 6) are 2 L:1 M stoichiometry (Table 1). The mea-
vibrations of (NO ), pyridine ring breathing, and
2
sured values of the molar conductance of the complexes
(NH) in-plane deformation vibration, respectively.

TOLAN ET AL.
5 of 24
with the ligand. Moreover, a new band appeared in the
−
1
range (1214–1223 cm ) could be assigned to ν(C O) of
the coordinated carbonyl group after enolization with
complexation to the metal ion. Furthermore, in complex
(5), the intense peaks due to ν(N H) and ν(C O)
appeared for the ligand, disappeared upon complexation
with Zn(II) ion, whereas new bands appeared at 1264
and 1298 cm− attributed to ν(C O) of the two carbonyl
groups after enolization. The intensity and position of
the amide bands (I, II, III, and IV) change relative to the
ligand, the amide I, which is mainly arising from
1
−1
ν(C O) undergoes downshift by (5–30 cm ) in all com-
plexes confirming the coordination through the carbonyl
group O2 (suggested by DFT studies). For complex (5),
the spectrum does not show any characteristic bands for
the amide group (I, II, III, IV) indicating that H L ligand
2
coordinates with Zn(II) ion through deprotonated car-
bonyl groups (O1 and O2). Thus, H L behaves as a
2
monobasic tridentate ONO donor ligand in all com-
plexes except 5 in which the ligand coordinates through
its azomethine N, enolic O1 atom, and carbonyl O2
atom. On the other hand, the ligand binds with
Zn(II) ion in complex 5 as a dibasic tridentate ONO
donor ligand through azomethine N and both enolic O1
and O2 atoms. The coordination of carbonyl O and
azomethine N atoms is further supported by the appear-
ance of new nonligand bands between 470–500 and
11–419 cm− due to the υ(M O) and υ(M N) vibra-
1
FIGURE 2 Structure of complexes (1–7)
4
[
35,36]
tions in all complexes.
These bands are in the
expected order as υ(M N) occurs at lower energy than
υ(M O) as expected due to greater electronegativity of
the O atom than N atom, the greater dipole moment of
M O bond, and shorter M O bond length than the
Moreover, the IR spectrum of H L ligand displays strong
2
−
1
and medium bands at 1678 and 1146 and 578 cm attrib-
uted to the C O stretching and in-plane, out-of-plane
bending vibrations (υ and δ, γ) of the amide carbonyl
groups. For the free ligand, four bands appeared at 1678,
[
55,56]
M N bond length,
which confirmed later with
DFT studies. The absorptions due to the presence of
water molecules in all complexes are evidenced by the
−
1
1
440, 1272, and 853 cm attributable to amide I {C O
−
1
stretching
bending
+
+
C N stretching}, amide II {N H
C N stretching}, amide III {N H
broad absorptions around 3400 cm .
deformation + C N stretching}, and amide IV band that
[36,53,54]
1
13
mainly results from δ(C O).
Besides, the ligand
3.3 | H and C NMR of the ligand
spectrum displays a medium intensity band at 1608 cm−
assignable to stretching frequency of azomethine group
ν(C N). In general, the spectrum of the ligand shows the
appearance of characteristic bands of ν(N H) and
ν(C O), these observations suggest that the hydrazide–
hydrazone ligand exists in the amido form (Figure 1).
The IR spectra of all metal complexes show a shift in
ν(C N) (azomethine) stretching to a lower value by
1
1
The H NMR (DMSO-d ; , ppm) spectral data of H L
ligand illustrate two singlet peaks at
2.44 ppm for the three protons of CH and the two
protons of ( CH2 ), respectively
signals that appeared in the range of δ 7.50–8.86 ppm
are attributed to four aromatic protons (Supplementary
Information). In addition to two doublets at δ 8.08 and
8.12 ppm corresponding to pyridine protons and three
singlets at 8.80, 8.89, and 12.39 ppm attributed to the
three protons of CH N, NHCO (adjacent to aliphatic
moiety), and NHCO (adjacent to aromatic moiety),
6
2
2.26 and
3
[
36,42]
Also, multiplet
−
1
7
–11 cm , indicating coordination through the
azomethine N atom. In addition, the spectra of all metal
complexes except complex (5) revealed the presence of
−
1
only one υ(N H) band in the range (3180–3214 cm )
with disappearance of the other υ(N H) band compared
[
36,56]
respectively.

6
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TOLAN ET AL.

TOLAN ET AL.
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8
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TOLAN ET AL.
2
TABLE 3 Electronic spectral data and magnetic moments of H L ligand and its metal complexes
No.
Compound
L. H
Spectral bands (nm)
220,314
90,460
212,310
96
220,312
Assignment
μeff. (B.M.) per metal ion
H
2
2
O
π–π*
—
3
n–π*
1
2
[Mn (HL)
2
].H
2
O
Intraligand transitions
6.02
5.06
3
[Co (HL)Cl(H
2
O)].2H
2
O
Intraligand transitions
LMCT
395
418
524
600
680
4
4
4
0
4
0
2
(P)
A
A
A
2
(F) ! A
2́
0
4
00
(F) ! E (P)
2́
0
4
0
(F) ! E (F)
3
4
[Ni (HL)Cl].2H
2
O
210,310
Intraligand transitions
Diamagnatic
1.82
3
4
94
30
1
1
LMCT + A2g ! A1g
[Cu (HL)Cl (H
2
O)].H
2
O
216,314
Intraligand transitions
3
4
6
7
46,390
30
2
2
LMCT + B1g ! E
B
g
2
2
80
1g ! B2g
1g ! A1g
2
2
76
B
5
[Zn (L)(H
2
O)
2
].H
2
O
212,314
Intraligand transitions
Diamagnetic
3
4
96
18
LMCT
6
7
[Cd (HL)
2
].2H
2
O
212,312
94
210,310
74
Intraligand transitions
Diamagnetic
Diamagnetic
3
[Hg (HL)Cl (H
2
O)
2
]
Intraligand transitions
3
1
The C NMR (DMSO-d ; , ppm) spectral data of H L
6
2
ligand ((DMSO-d ; , ppm) exhibit peaks at 14 and
6
1
7 ppm for CH and CH2 , respectively. Also, the sig-
3
nals corresponding to the aromatic and pyridine carbon
atoms are observed at δ 112, 121, 124, 128, 130, 133,
1
40, and 144 ppm. On the other hand, the peaks at
1
48, 149, 150, and 161 are attributed to carbon atoms of
CH N, C N, C O (adjacent to aliphatic moiety), and
[56]
C O (adjacent to aromatic moiety), respectively.
3.4 | Mass spectra
The mass spectra of the ligand and complexes 2 and
(Supplementary Information) have been performed.
4
The molecular ion peaks observed for these compounds
are found to be at m/z = 386.47, 497.86 and 502.66 amu,
respectively, in complete agreement with results of ele-
mental analysis and indicating that the complexes have
monomeric nature.
FIGURE 3 UV–Vis absorption spectra of ligand H L and its
transition metal complexes (1–7) in DMF
2

TOLAN ET AL.
9 of 24
TABLE 4 Thermal analyses (TG/DTG) data for hydrazide-hydrazone (H
2
L) metal complexes
Mass loss (%)
TG temp
ꢀ
ꢀ
No. Compound
L. H
range ( C) DTG ( C)
Found Calcd
Assignment
T
s
a
H
2
2
O
20–180
171
277
4.17
89.73
6.10
2
4.07 Loss of 1 mol of crystallized H O
b
1
81–1000
At 1000
20–100
89.72 Complete ligand pyrolysis
c
6.21 2C
a
1
2
3
[Mn (HL)
2
]. H
2
O
50
2.20
2.22 Loss of one mol of crystallized H
stable zone
2
O
260
220
195
1
2
00–260
60–301
294
53.01
5 4
52.80 Partial ligand pyrolysis, −(2 mol of C H N and
b
2
7 5 2
mol of C H NO )
b
3
01–600
313, 531
38.91
5.86
38.16 Complete ligand pyrolysis (C10
H
12
N
8
O
4
)
c
At 600
6.80 (Mn)
a
[Co (HL)Cl
2
HO)].2H O
20–220
65, 120
254
7.11
6.97 Loss of 2 mol of crystallized (H
25.30 loss of coordinated H O, 0.5 Cl
2
O)
(
2
20–290
24.94
2
b
2
and partial ligand
5 3
pyrolysis ( C H N)
b
2
5
90–500
317,400
725
23.51
32.46
11.98
7.30
23.46 Partial ligand pyrolysis ( C
6
H
3
NO
2
)
b
00–1,000
32.84 Complete ligand pyrolysis
c
At 1000
11.43 (Co)
a
[Ni (HL)Cl].2H
2
O
20–195
72, 167
267
7.23 Loss of 2 mol crystallized H
2
O
1
95–304
22.69
22.61 loss of 0.5 Cl
2
and partial ligand pyrolysis
b
(
5 3
C H N)
b
3
3
04–395
385
24.19
24.32 Partial ligand pyrolysis (C
6
H
3
NO
2
)
b
95–1000
620, 750, 950 33.64
12.18
33.98 Complete ligand pyrolysis
c
At 1000
11.80 (Ni)
a
4
6
7
[Cu (HL)Cl
O)] H
20–200
40, 130
224
3.68
7.19
3.58 Loss of 1 mol crystallized H
2
O
200
260
150
(H
2
2
O
b
200–256
7.06 Loss of 0.5 Cl
2
b
256–1,000
264, 802
63.61
63.97 Loss of 1 mol of coordinated (H
2
O) and complete
b
ligand pyrolysis
c
At 1000
25.52
4.25
25.09 (CuO + 4C)
a
[Cd (HL)
2
]. 2H
2
O
20–200
77, 175
308
2
4.06 Loss of 2 mol of crystallized H O
200–440
49.95
5 4
49.23 Partial ligand pyrolysis; −(2 mol of C H N and
b
2
7 5 2
mol of C H NO )
b
440–950
590
34.54
11.25
—
12 8 4
34.90 Complete ligand pyrolysis (C10H N O )
c
At 950
12.71 (Cd)
[Hg (HL)Cl
O)
20–150
—
Stable zone
Complete ligand pyrolysis and sublimation of Hg.
(H
2
2
]
b
150–350
187, 226, 302 98.5
100
Abbreviations: DTG, differential thermogravimetry; T
S
: thermal stability.
a
Dehydration.
b
Decomposition.
c
Final residue.
3
.4.1 | UV–Vis absorption and magnetic
metal complexes were collected in Table 3 and depicted
in Figure 3. The electronic spectra of the Schiff base
ligand consisted of relatively intense bands in the region
of 220 and 314 nm assigned to π–π* transitions and bands
at 400 and 460 nm due to n–π* transitions of the C N
measurements
The ultraviolet and visible (UV–Vis) spectra of all com-
plexes were recorded at room temperature in high-
performance liquid chromatography (HPLC) grade DMF
solvent. The UV–Vis data and magnetic moments of
II
II
II
II
II
II
and C O moieties. Mn , Co , Ni , Cu , Zn , Cd , and
II
Hg chelates show three bands at 208–220, 308–314, and

10 of 24
TOLAN ET AL.
SCHEME 2 Thermal decomposition mechanism of
complexes (1) and (6)
3
90–396 nm, which are attributed to the π–π* and n–π*
in the normal range observed for octaherdal Mn(II)
[
66,67]
transitions, respectively, within the H L ligand. The shift
complexes.
This indicates that Mn(II) complex is
2
to a lower wavelength of n–π* bands in the complexes
were attributed to the coordination of M(II) ion with the
imine nitrogen and carbonyl oxygen atoms. In the elec-
tronic spectra of some complexes, there is a band around
probably octahedral. On the other hand, the μeff value
(5.06 and 1.82 BM) for Co(II) and Cu(II) complexes,
respectively, falls within the range normally observed for
[
35,36]
five coordinate Co(II) and Cu(II) complexes.
Mag-
4
18–430 nm. This band is assigned as a LMCT
netic susceptibility measurements reveal that Ni(II)
complex are diamagnetic which is quite obvious for
[57–59]
transition.
The electronic spectrum of complex 2 [Co
[
62–64]
(
5
H L)Cl(H O)]H O shows d–d bands at 680, 600, and
square planar nickel(II) complexes.
The zinc, cad-
2
2
2
00 nm, which were consistent with five-coordinate cobalt
mium, and mercury complexes are diamagnetic, the ele-
[59–61]
complexes.
The electronic spectra of 3 [Ni(H L)
mental analysis shows that Zn(II) complex (5) has five-
2
[
68,69]
Cl].2H O shows one d–d transition band of lower intensity
at 430 nm. A lack of any electronic transition at longer
coordinate structure,
whereas Cd(II) and Hg(II)
2
[
70–72]
complexes have hexa-coordinate structures.
wavelength, due to forbidden d–d transition, compatible
Based on elemental analyses and spectral methods,
the suggested chemical structures for the synthesized
metal complexes are displayed in Figure 3.
[
62]
with the square planar geometry of Ni(II) complexes. In
1
1
general, three bands corresponding to A2g
!
A ,
1g
1
1
1
1
B1g ! A and E ! A transitions are expected for
1g
g
1g
[63,64]
square planar diamagnetic nickel(II) complex.
But
the long tail of strong interligand and charge transfer tran-
3.4.2 | Thermal studies
[
65]
sitions hide some or all of these bands in many cases.
Complex (4) [Cu(H L)Cl(H O)]H O reveals three absorp-
Thermal studies were undertaken in order to study the
thermal stability for the complexes and as supportive data
for the proposed molecular formulae. The results of such
analysis have been summarized in Table 4. The thermal
behavior of the ligand and its complexes was character-
ized on the basis of TGA∕ DTG method (Supplementary
Information).
2
2
2
tion bands at 776, 680, and 430 nm attributed to
2
2
2
2
2
2
B1g ! A , B ! B , and B ! E transitions
1g
1g
2g
1g
g
affording distorted square pyramidal geometry around
Cu(II) ion.
in d system are spin forbidden and hence, in complex 1,
[
35,36]
It is well known that the d–d transitions
5
one low intensity broad band can be observed in the range
6
00–700 nm which may be attributed to octahedral
The TG curve of the free ligand (H L) shows two
2
[66,67]
Mn(II) d–d transition.
decomposition steps. The first stage includes the thermal
ꢀ
Magnetic measurements were recorded at room tem-
dehydration of the ligand, which starts between 25 C and
ꢀ
perature. The effective magnetic moment (μ ) values of
180 C with a mass loss (found: 4.15; calc.4.07:%) due to
eff
the complexes are given in Table 3. The μeff value at room
temperature of the Mn (II) complex is 6.03 BM, which is
the loss of lattice water molecule with DTG peak at
171 C, whereas the second step starts between 181 C and
ꢀ
ꢀ

TOLAN ET AL.
11 of 24
SCHEME 3 Thermal decomposition mechanism of
complexes (2) and (3)
ꢀ
ꢀ
ꢀ ꢀ
started at 220 C and 195 C, respectively, in the second
1
000 C with DTG peak at 277 C due to complete decom-
ꢀ
ꢀ
position of the ligand.
The TG curves of complexes (1) and (6) reveal three
decomposition steps within temperature ranges
0–200 C, 200–440 C, and 310–950 C (Table 4)
Scheme 2). The first step shows mass losses of 2.20%
step with DTG peaks at 400 C and 385 C associated with
mass loses of 24.94% and 22.69%, respectively, assignable
to the removal of coordinated chloride ion as well as par-
tial ligand pyrolysis ( C H N) in addition to the loss of
ꢀ
ꢀ
ꢀ
2
(
5
3
coordinated water complex 2 (Table 4). The next step is
and 4.25%, respectively, is assigned to the liberation of
lattice water and complete desolvation within the tem-
followed by complete pyrolysis of ligand leaving free
metallic residue at high temperatures.
The thermal behavior of the square pyramidal
Cu(II) complex (4) occurs in three decomposition stages
[
73–77]
ꢀ
perature range 20–200 C. The second step of decomposi-
ꢀ
tion within temperature range 200–440 C with DTG
ꢀ
ꢀ
ꢀ
ꢀ
peaks at 294 C and 308 C corresponding to the loss of
within temperature ranges 20–200 C, 200–256 C, and
ꢀ
2
mol of C H N (pyridine moiety) and 2 mol of
256–1000 C. The first one is the desolvation step which
is associated with weak DTG peaks at 40, 130 C attrib-
5
4
ꢀ
C H NO from the two ligand molecules with weight
7
5
2
loss of 53.01% and 49.95%, respectively. The final step
involves complete ligand pyrolysis leaving free metallic
residue.
uted to a loss of 1 mol of crystallized water and com-
plete desolvation with weight losses (found: 3.68; calc.
3.58%). Afterward, the coordinated chloride ion is lost in
[73–77]
ꢀ
The TG curves of complexes (2) and (3) show four
the second stage corresponding to DTG peak at 224 C.
decomposition steps within temperature ranges
Finally, complete ligand pyrolysis takes place associated
with the removal of the rest coordinated water molecule
with weight loss 63.61%. This step is ended with the for-
mation of CuO contaminated with carbon residue
(Table 4). The thermal decomposition is observed as
follows:
ꢀ
ꢀ
ꢀ
ꢀ
2
0–220 C, 195–304 C, 290–500 C, and 395–1,000 C
(Scheme 3). The first step is accompanied with estimated
[35,74]
mass losses of 7.11% and 7.30%, respectively, attributable
ꢀ
to complete desolvation with DTG peaks at 120 C and
ꢀ
1
67 C. After that, the decomposition of the complexes

12 of 24
TOLAN ET AL.
The mercury complex (7) was found to be an anhy-
drous one by elemental analysis and was confirmed by
ꢀ
the thermogravimetric studies. It is stable up to 150 C
and decomposes in a single step, which is represented by
ꢀ
the DTG peaks at 188, 226, 280, 302 C (Table 4). As
expected, for mercury complexes, sublimation of Hg and
only traces of carbon residue was left on heating up to
ꢀ
[78]
8
00 C.
3.4.3 | XRD of the copper oxide
Copper oxide (CuO) obtained from the thermal decom-
position of copper(II) complex (4) was confirmed by the
characteristic peaks observed in the XRD pattern, as
shown in Figure 4. XRD analysis showed intense peaks
FIGURE 4 X-ray diffraction (XRD) pattern of copper oxide
obtained from the thermal decomposition of complex 4
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
at 36.5 , 42.0 , 44.59 , 58.9 , and 64.9 , consistent with
2
FIGURE 5 Optimized structures of the ligand (H L) tautomers

TOLAN ET AL.
13 of 24
the standard values of JCPDS file no. 00-003-0897. The
observed diffraction reflections were comparable with
studied hydrazide-hydrazone molecule can exist in dif-
ferent tautomeric forms. Hydrazide–hydrazone ligand
[79,80]
other literature data.
In addition, XRD is a conve-
(H L) can exist either in the amido (keto) or in imido
2
nient method for determining the mean size of nano
crystallites. The average crystalline size (D) of the nano
CuO particles was calculated by Scherer's equation
affording diameter of 19 nm. CuO NPs is broadly used
in number of fields such as catalysis, sensing materials,
ceramics, thermoelectric materials, glass, supercon-
(enol) form as illustrated in Figure 1. The
optimized structures of the investigated tautomers are
shown in Figure 5. The B tautomer involves proton
transfer from N2 to O1, whereas in the C and
D tautomers, the proton transfers from N5 to O2 and
from C17 to O2, respectively. Proton transfer between
N2 and O1 and between N5 and O2 takes place in the
di-enol tautomer E, whereas the di-enol tautomer
F involves transfer of protons from N2 to O1 and from
C17 to O2. Among all forms, the di keto tautomer
A is the most stable structure in the gas phase as
presented in Table 5. However, the enol tautomer
B is more stable than other enol tautomers, whereas
the enol form D is less stable than tautomer C by
15.51 kcal mol . From theoretical point of view,
the studied ligand exists in the diketo form A,
which agrees with the experimental finding. Natural
bond orbital (NBO) analysis was carried out to shed
light on the electronic structures of the ligand and
its complexes. The atomic natural charges for the opti-
mized geometries over some atoms in the ligand
forms and its complexes are listed in Table 6. The
negative charge on the oxygen atoms O1 and O2
(−0.590, −0.580 e) is larger than that on the nitrogen
atoms N2, N3, N4, and N5 as given in Table 6.
Therefore, it is expected that the metal ion will bind
preferably with the oxygen atoms than with nitrogen
atoms.
[81]
ducting materials, and antimicrobial activity.
The
XRD spectrum also shows diffraction peaks characteris-
tic for cuprous oxide that consistent with the JCPDS file
no 00-003-0892.
3.5 | DFT studies
−
1
In order to provide a more comprehensive analysis of the
metal ligand bonding in some selected complexes, a DFT
computational study was carried out on the ligand and
complexes (2, 4, 5–7).
3.5.1 | Structure of the ligand
Due to the presence of labile hydrogens, double
bond, and protonable heteroatoms in the ligand, the
TABLE 5 The relative energies (kcal/mol) calculated for
different tautomers of the ligand (H L) at B3LYP∕ 6-311G(d,p)
2
Tautomer
ΔE
ΔE
0
ΔE298
0
ΔH298
0
ΔG298
0
In order to further understand the interaction
between the ligand and metal ions, the frontier molec-
ular orbitals (FMO) are calculated as depicted in
Figure 6. HOMO, the highest energy orbital
containing electrons, represents the ability to donate
electrons where LUMO is the lowest energy orbital
that can accept electrons. HOMO spreads over
benzene ring, N4, N5, and O2, whereas there is no
A
B
C
D
E
F
0
0
6.67
6.52
7.77
6.43
7.76
23.18
8.16
16.09
6.43
7.17
23.18
8.16
16.09
6.78
6.71
21.90
60.53
16.02
7.94
23.45
8.27
22.97
8.28
16.18
16.27
TABLE 6 NBA charges of the ligand and the studied complexes
Compound
O1
O2
N2
N3
N4
N5
M
—
—
Cl
A
B
2
−0.590
−0.697
−0.758
−0.545
−0.601
−0.554
−0.541
−0.580
−0.575
−0.622
−0.352
−0.616
−0.407
−0.374
−0.437
−0.349
−0.441
−0.313
−0.309
−0.344
−0.329
−0.319
−0.347
−0.344
−0.349
−0.439
−0.399
−0.333
−0.447
−0.443
−0.428
−0.316
−0.317
−0.315
−0.312
−0.230
−0.217
−0.229
0.110
—
—
0.958
−0.604
−0.557
—
4
0.576
1.069
1.028
0.829
5
−0.235
−0.108
−0.110
6
—
7
−0.582

14 of 24
TOLAN ET AL.
spatial HOMO distribution on O1, N2, and N3 in
the diketo tautomer A. After enolization of O1 in
the most stable enol form B, the HOMO was
located on N3 and N2 in addition to the benzene ring,
N4, N5, and O2 as shown in Figure 6. These results
confirm that the metal ion will prefer binding with O2
in its keto form while the deprotonation after
enolization is essential for coordination of metal ion
FIGURE 6 Density functional theory (DFT) computed highest occupied molecular (HOMO) and lowest unoccupied molecular orbital
LUMO) diagrams of ligand (H L) tautomers (A and B) and its complexes 4 and 6
(
2

TOLAN ET AL.
15 of 24
with O1, which supports our experimental finding
that the chelation with metal ions takes place through
the enol form of the ligand. The DFT studies
predicted that the enol tautomer B is the most stable
enol form.
five-coordinate geometries. The two common geome-
tries for five-coordinate species are trigonal bipyrami-
dal (tbp) and square-based pyramidal (sp) metal
environments. Complexes 2, 4, and 5 are not homo-
leptic compounds, so they are expected to undergo
deviations from the ideal geometries. It is possible to
assign approximate tbp or sp metal coordination geome-
try using a simple quantitative measure derived from a
simple calculation of the angular structural parameter
(τ). τ defined as τ = [(θ − )/60], where θ and are the
two largest coordination angles and τ = 0 for perfect sp
and one for ideal tbp. The deviations from ideal geome-
tries can happen when the metal center is displaced out
of the ligand plane or due to ligand bite angle restric-
tions. For complexes 2, 4, and 5, the τ parameters are
0.15, 0.45, and 0.31 respectively, indicating that these
complexes adopted coordination geometries that can best
be described as distorted square-based pyramidal (sp).
Moreover, the sum of the bond angles around Co(II),
Also, the energy gap between HOMO and LUMO
characterizes the chemical stability, reactivity and
[35,82]
hardness of the molecule.
Hardness is one of the
highly useful concepts for understanding the
behavior and reactivities of chemical systems. It is
coupled with the softness, electronic chemical poten-
[
83,84]
tial, or absolute electronegativity in this respect.
Hardness is a direct measure of the stability of mole-
cules, whereas softness is a direct measure of reactivity
of molecules. From the data of HOMO and LUMO
energies, the energy gap, ΔE, absolute electronegativ-
ity, χ, chemical potentials, Pi, absolute hardness, η,
absolute softness, σ, global electrophilicity, ω, global
softness, S, and additional electronic charge, ΔNmax
,
ꢀ ꢀ ꢀ
have been calculated and presented in Table 7 to
give indications about the stability and reactivity of
the ligand and its complexes. The calculations
demonstrated that the free ligand has a small HOMO-
LUMO energy gap (3.85 eV) which increases its soft-
ness and reactivity toward the reaction with the metal
ions and it has high biological activity due to high ω
value.
Cu(II), and Zn(II) are 340 , 360 , and 343 , which
ꢀ
ꢀ
ꢀ
implies a pyramidization degree of 42 , 0 , and 17 for
complexes 2, 4, and 5, respectively. In Complex 2, the
basal plane was defined by one imine nitrogen donor
(N3), carbonyl oxygen donor (O2), enolic oxygen donor
(O1) of the H L ligand, and oxygen donor (O5) of water
2
molecule. The pseudo-apical position is occupied by
chloride ion. In case of complex 4, the basal plane is
occupied by one imine nitrogen donor (N3), enolic oxy-
gen donor (O1) of the H L ligand, oxygen donor (O5) of
2
3
.5.2 | Structure of the complexes
water molecule, and chloride ion, whereas the carbonyl
oxygen donor (O2) stays in the pseudo-apical position.
On the other hand, in complex 5, the Zn ion coordinated
to imine nitrogen donor (N3), two enolic oxygen atoms
The geometries of the optimized structures of the
studied complexes (2, 4–7) are depicted in Figure 7.
Complexes 2, 4, and 5 adopted mononuclear, distorted
of the H L ligand (O1 and O2), and oxygen donor
2
TABLE 7 Various quantum
E (a.u)
H
2
L(A)
2
4
5
6
7
chemical parameters of free ligand
Dipole moment (D)
3.55
−6.38
−2.59
3.79
15.02
9.92
9.00
3.851
12.22
2
(H L) and its complexes
E
E
HOMO (eV)
LUMO (eV)
−6.21
−3.52
2.69
−6.44
−3.77
2.67
−5.93
−2.80
3.13
−5.80
−3.30
2.50
−6.17
−3.40
2.77
ΔE (eV)
χ (eV)
4.485
1.895
0.527
−4.485
0.527
5.300
2.366
4.865
1.345
0.743
−4.865
0.743
8.798
3.617
5.105
1.335
0.749
−5.105
0.748
9.76
4.365
1.565
0.638
−4.365
0.638
6.087
2.789
4.550
1.250
0.800
−4.550
0.800
8.281
3.640
4.785
1.385
0.722
−4.785
0.722
8.265
3.454
η (eV)
σ (eV−
1
)
)
Pi (eV)
S (eV−
ω (eV)
ΔNmax
1
3.823

16 of 24
TOLAN ET AL.
FIGURE 7 Optimized structures of the complexes
(O6) of the water molecule in the basal plane. These
of the H O ligand (O5) coordinated to Zn(II) ion in
2
four atoms form a distorted plane with the oxygen atom
Z axis. Starting the optimization process with a regular

TOLAN ET AL.
17 of 24
octahedral structure for complex (5) where there are two
water molecules coordinated to Zn(II) ion in the z axis
leads gradually to the distorted square pyramidal struc-
ture where one water molecule leaves the coordination
sphere.
(O5, O2, N3 and O1, O6, N6) with an average side
(s) of 3.791 Å. Triangles are slightly tilted with a dihe-
dral angle of 9.4 and an intertriangular separation
ꢀ
between the centroids (distance between O2 and 06) of
3.204 Å (h). The torsion angles N3 O2 O6 O1 and
ꢀ
ꢀ
The DFT studies show that the Cd(II) complex has tri-
gonal prismatic geometry. Although octahedral coordina-
tion geometries are the most common fundamental
geometries of transition metal hexa-coordinated com-
plexes, the trigonal prismatic geometry for a metal ion
N9 O6 O2 O5 are 9.9 and 14.9 are close to that of
a regular trigonal prismatic geometry ( = 0). The s/h
ratio in complex 6 is 1.18, revealing an elongation rela-
tive to an ideal trigonal prism with square faces
[
82]
(s = h, s/h = 1.00).
On the other side, in complex
10
with a d electronic configuration is not rare because
7, Hg(II) ion coordinated to O1, O2, and N3 from the
[
85,86]
there is no crystal field stabilization energy (CFSE).
tridentate ligand (H L) and chloride ion in the equato-
2
The majority of metal complexes without CFSE were
predicted to have structures with twist angles <5 ,
rial plane while coordinated with two water molecule
ꢀ
in the z axis forming octahedral structure. The angles
ꢀ
suggesting that experimentally they will have trigonal
O5 Hg O6, N3 Hg Cl, and O2 Hg O1 are 167 ,
[87]
ꢀ
ꢀ
prismatic structures.
Perfectly prismatic structure of
155 , and 135 , which are deviated from the ideal octa-
ꢀ
Cd(II) was observed in the potassium salt of the tris
hedral structure (180 ). Moreover, the torsion angles
[87]
ꢀ
ꢀ
(
acetylacetonato) complex , and distorted trigonal
O2 O6 Cl O5 and N3 O1 O5 Cl are 42 and 79 ,
predicting distortion than regular octaheral geometry
( = 60), while the s/h ratio in complex 7 is 1.3
matching with octahedral structures shown in the
prisms were found with other ligands such as nitrates,
carboxylates, triamines, oxalato, and a derivative of
[88–90]
triazacyclonon.
Another examples of trigonal pris-
[
85]
matic complexes containing saturated amine ligands such
as [Cd((Me) tricosane))] (PF ) and [Hg((Me) tricosane))]
literature.
The calculated binding energies of the complexes
in the gas phase are collected in Table S1. The
negative sign of the binding energies indicates that the
investigated complexation reactions are thermodynami-
cally favored. The binding energy is more negative for
copper complex (4) which implies that it is formed
more spontaneously than the other complexes. The
order of thermodynamic stability of the investigated
complexes is Cu(II) > Co(II) > Hg(II) > Cd(II) > Zn
(II). Selected bond lengths and bond angles for the
complexes are listed in Table 8. The calculations
indicated that the bond length between the metal
ion and enolic oxygen (M O1) is the shortest
compared with M N3 and M O3 bond distances. The
negative charges on O1 and O2 increased in complexes
5
6 2
5
(
PF6)2 ((Me) tricosane
=
1,5,9,13,20-pentamethyl-
5
3
,7,11,15,18,22-hexaazabicyclo[7.7.7] tricosane) were
[89]
studied previously.
Janiak and coworkers showed
that the Cd(II) complex with tetradentate pyridyl di-
Schiff-base ligands, N,N0-bis-(1-pyridin-2-yl-ethylidene)-
propane-1,3-diamine has trigonal prismatic geome-
[85]
try.
The ideal octahedron consists of two exactly
parallel, staggered equilateral triangles of side (s) with
an intertriangular distance (h) (Figure 8). The trigonal
distortion for the hexa-coordinated complexes can be
measured by evaluating the s/h ratio and twist angle
[85,89]
() value.
In complex 6, Cd(II) ion coordinated to
two tridentate ligand (H L), the coordination sphere
2
can be described as being constituted of two triangles
FIGURE 8 Octahedron and
trigonal prism with enhanced
triangular faces and relevant
parameters for the assessment of
their relationship and distortion.
is the twist angle between the
enhanced triangles around the
[85]
C3 axis

18 of 24
TOLAN ET AL.
2
and
4
relative to their values in the free
ligand. Besides, the negative charge on N3 increased in
all complexes that revealed the back donation
between metal center and ligand nitrogen atom
(
N3) in addition to O1 and O2 (in complexes 2 and 4),
which leads to a significant increase in its negative
charge. Moreover, the charges on the metal ions in the
complexes are equal or less than +1 e; this indicates
charge transfer from the ligands to the central metal
ion. The dipole moments (D) for the complexes except
complex 6 range from 9.0–15.02 Debye (Table 7),
implying that these complexes are highly polar
compounds.
Wiberg bond order for each of the five different
metal–ligand interactions, M O1, M O2, M N3,
M Cl, and M O(H O), is presented in Table 9. The
2
total bond order is further resolved into contributions
from the d-orbital occupancy for the α- and β-electrons
to the overall bond order for Co(II) and
Cu(II) complexes. A low degree of covalency for M O
and M N bonds, which is less than 0.45, was observed
in all complexes. The Co(II) and Cu(II) complexes
1
0
show higher M O and M N bond order than d
metal complexes which is consistent with the values of
bond lengths as the Cu O1 and Cu N3 are the
shortest compared with the other complexes. In con-
trast, the bond orders for M Cl interaction is larger
than M O and M N bond orders which can be
attributed to the fact that the chloride ligand displays
both σ and π donation to the metal centers. When
this feature is considered, the overall bond order is
also rather low with average total values of only 0.66
for Co(II) and Cu(II) complexes while 0.43 for
Hg(II) complex. In general, the wiberg bond orders
obtained for the M O1, M O2, and M N3
moieties correlate with our calculated bond length
variations.
Regarding HOMO and LUMO energies in the free
ligand and complexes, the HOMO level in all complexes
is destabilized by 0.21–0.81 eV, whereas LUMO is stabi-
lized by 0.17–0.58 eV relative to the ligand which cau-
ses a decrease in energy gap in these complexes.
Besides, the electron cloud of the HOMO in complexes
2
and 4 is spread over the metal and its coordination
sphere, whereas in complexes 5–7, HOMO is localized
on the coordination sphere surrounded the metal only
and there is no HOMO observed on the metal
(
Figures 6 and S7). This observation arises from the
strong interaction between the metal and the ligand in
complexes 2 and 4 than other complexes, which eluci-
dated before by the higher M-N and M-O bond order in
10
complexes 2 and 4 than the studied d metal com-
plexes (5–7).

TOLAN ET AL.
19 of 24
TABLE 9 computed wiberg bond
order for metal–nitrogen, metal–oxygen
and metal chloro bonds from the
optimized structures of the studied
metal complexes
Compound/bond
2
M O1
M O2
M N3
M Cl
2
M O(H O)
a
a
a
a
a
0.298
0.190
0.260
0.574
0.124
0.698
0.474
0.158
0.632
0.209
b
b
b
b
c
a
b
c
b
0.059
0.039
0.052
0.044
c
c
c
c
0.358
0.229
0.312
0.253
a
b
c
a
a
a
4
5
0.311
0.159
0.297
0.227
b
b
b
0
0
.120
.431
0.042
0.130
0.081
c
c
c
0.201
0.427
0.308
0.255
0.188
0.224
—
0.185
0.198
6
7
0.170
0.177
0.119
0,119
0.158
0.204
—
—
0.431
0.1149
.0025
0
a
Contributions from the α-electron orbital occupancy.
Contributions from the β-electron orbital occupancy.
b
c
Total contributions.
−
1
MEP provides the key to predict the reactive sites
towards electrophilic and nucleophilic attack and in
studies of biological recognition and hydrogen bonding
and 1608 cm , respectively. In the complexes, C O
group of ligand actively participates in chelation, and it
shows
a
change in frequency to lower value,
[91]
interactions.
complexes are shown in Figure 9. The negative sites
red) of the MEP are related to electrophilic reactivity
The MEP of the ligand (H L) and the
corresponding to the partial loss of double bond charac-
ter, whereas C N is shifted to higher or lower values
in the complexes compared to ligand. Theoretically, the
stretching of coordinated C O and C N bonds is
shifted toward lower frequencies compared with the
uncoordinated ones on the other side of the ligand.
Besides, the stretching vibrations of M O and M N
occurred at 411–510 cm− in the FTIR spectrum match
well with the calculated vibrational frequencies. The
good agreement between the calculated values of the
vibrational spectra with the experimentally observed
data shows that the method used in this study is well
adapted to predict the FTIR spectrum of the ligand and
its complexes.
2
(
while the positive sites (blue) are related to nucleo-
philic reactivity. It can be seen from Figure 9 that the
negative MEP regions of the ligand are concentrated
on the carbonyl oxygen atom, azomethine nitrogen
atom in addition to the pyridine nitrogen atom. The
electrostatic potential was shifted to more positive
values with the coordination of the ligand to the metal
ion, which is consistent with the higher global electro-
philicity (ω) of the complexes in comparison with the
ligand. The usefulness of electrophilicity index in
unraveling the toxicity of many compounds has been
analyzed as there is a linear correlation between the
electrophilicity and the biological activity of mole-
1
[92]
cules.
The higher values of the electrophilicity of
3.6 | Biological studies
the complexes relative to the ligand give a sign for the
higher biological activity of the studied complexes
compared with the ligand.
The IR frequencies of the ligand and its complexes
were obtained theoretically by DFT using the hybrid
B3LYP functional. The calculated values of the vibra-
tional spectra were compared with the corresponding
experimentally measured values in the gas phase
The antibacterial and antifungal activities of the
hydrazide–hydrazone ligand and its metal complexes
were measured as the diameter of the inhibition
zone, and the data were listed in Table 11 and
represented graphically in Figure 10. The H L ligand
2
was found to have moderate activity against
Staphylococcus aureus (G + ve) bacteria but less than
the standard antibiotics, whereas low activity against
Esherichia coli (G -ve) bacteria. The complexes were
found to have remarkable antimicrobial activity
compared with that of the free ligand. It was noticed
(Table 10). The computed N H, C O, and C N
stretching vibrational modes of the ligand of
−
1
3
260,1711–1737 and 1602–1668 cm match well with
the corresponding experimental values at 3295, 1680,

20 of 24
TOLAN ET AL.
FIGURE 9 Electrostatic potentials
mapped on the electron density surface
calculated by DFT/B3LYP method for
the ligand and its complexes
[
36,93]
that Hg(II) complex (7) showed higher antibacterial
activity against both gram +ve and gram –ve bacteria
followed by the Cu(II) complex, whereas Mn(II) (1)
and Zn(II) (5) complexes show the lowest antibacterial
activity compared with the other complexes. The
the chelation theory.
This suggested that chelation
could increase the lipophilic nature of the metal and
promote the ability of such complexes to pass through
the cell membrane of the microorganism to be des-
troyed. On the other hand, Hg(II) complex was found
also to possess higher antifungal activity against Asper-
gillus flavus and Candida albicans comparing with all
the studied compounds and the standard.
antibacterial
7) > (4) > (2) > (3) > (6) > (5) > (1). The better
activity of metal complexes can be explained based on
activity
has
the
order:
(

TOLAN ET AL.
21 of 24
TABLE 10 Selected vibrational modes and IR of the ligand and its complexes
ν(N H)
ν(C O)
ν(C N)
ν(M O) and ν(M N)
a
a
a
a
Compd
Calcd.
Exp.
Calcd.
Exp.
Calcd.
Exp.
Calcd.
Exp.
b
b
b
b
H
2
L
3260
3295(br)
3191(br)
3188(br)
3214(br)
—
1711, 1737
1680
1602–1668
1608
—
—
3
118
2
4
5
6
3309
3306
—
1669
1672
1664
—
1602–1628
1622–1627
1597–1627
1601–1627
1616
1615
1617
1601
474–590
415–548
455–614
450–526
433–510
411–481
413–500
419–497
1693
—
b
b
3309
3183(br)
1630, 1692
1674
3
308
7
3308
3187(br)
1677
1675
1607–1629
1602
467–594
415–500
a
Calculated at the B3LYP/LANL2DZ for metal ions and 6-311G(d,p) for other atoms (scale factor 0.9682).
b
Broad band centered at this position.
2
TABLE 11 Antimicrobial and antifungal activities of H L ligand and its metal complexes
Inhibition zone diameter (mm)
Fungi
G(+ve)
G(−ve)
Compound
Aspergillus flavus
Candida albicans
Staphylococcus aureus
Escherichia coli
H
1
2
3
4
5
6
7
2
L
0
0
0
0
14
11
20
21
25
12
17
30
18
—
0
9
13
20
12
0
0
20
18
24
11
16
28
22
—
0
12
0
20
34
—
17
16
23
—
18
Ampicillin
Amphotericin B
FIGURE 10 Antimicrobial and
antifungal activity of the ligand (H
and its complexes (1–7)
2
L)

22 of 24
TOLAN ET AL.
4
| CONCLUSIONS
[2] A. R. M. Coates, G. Halls, Y. Hu, Br. J. Pharmacol. 2011,
163, 184.
[
3] Ł. Popiołek, A. Biernasiuk, A. Berecka, A. Gumieniczek, A.
Malm, M. Wujec, Chem. Biol. Drug Des. 2018, 91, 915.
4] N. Belkheiri, B. Bouguerne, F. Bedos-Belval, H. Duran, C.
Bernis, A. Nègre-Salvayre, M. Baltas, Eur. J. Med. Chem. 2010,
A new hydrazide–hydrazone ligand (H L) was success-
2
fully prepared from condensation of isonicotinic acid
[
0
hydrazide
with
(Z)-N -(2-nitrobenzylidene)-
3
-oxobutanehydrazide. The investigated ligand was used
45, 3,019.
to synthesize a new series of Mn(II), Co(II), Ni(II),
Cu(II), Zn(II), Cd(II), and Hg(II) transition metal com-
plexes that were fully characterized by thermal and ele-
mental analyses, FTIR, mass and electronic spectra. FTIR
spectra indicated that the ligand acts as a tridentate and
coordinated to the metal ion through ONO donors in all
complexes with 1 L:1 M stoichiometry except complexes
[5] G. Gürkök, T. Coban, S. Suzen, J. Enzyme, Inhib. Med. Chem.
2009, 24, 506.
[6] E. A. Musad, R. Mohamed, B. A. Saeed, B. S. Vishwanath,
K. M. L. Rai, Bioorg. Med. Chem. Lett. 2011, 21, 3536.
[7] A. D. Yilmaz, T. Coban, S. Suzen, Med. Chem. 2012, 27, 428.
[8] E. Akbas, I. Berber, Eur. J. Med. Chem. 2005, 40, 401.
[9] T. I. Kashar, K. M. Emran, Int. J. Eng. Manag. Res. 2016,
3, 156.
(
1) and (6) where the ligand binds to Mn(II) and
[10] M. Sönmez, I. Berber, E. Akba, Eur. J. Med. Chem. 2005,
Cd(II) ions in 2 L:1 M stoichiometry. Spectral characteri-
zation of the novel complexes suggested octahedral
geometry for complexes (1, 7) and square pyramidal
geometry for complexes (2, 4, 5). However, complexes (3)
and (6) adopt square planar and trigonal prismatic geo-
metrical structure, respectively. DFT calculations have
been carried out to study the structure of the ligand tau-
tomers and metal complexes of the most stable form. The
antimicrobial screening assay revealed that the metal
chelates show greater inhibitory effects than the parent
hydrazide–hydrazone ligand towards the studied bacte-
rial and fungal organisms.
41, 101.
[11] I. J. Selikoff, E. H. Robitzek, G. G. Ornstein, Q. Bull. Sea View
Hosp. 1952, 13,17.
12] E. H. Robitzek, I. J. Selikoff, G. G. Ornstein, Q. Bull. Sea View
Hosp. 1952, 13, 27.
13] V. Judge, B. Narasimhan, M. Ahuja, D. Sriram, P. Yogeeswari,
E. D. Clercq, C. Pannecouque, J. Balzarini. Med. Chem. Res.
[
[
2012, 21, 1,451.
[
14] P. Vicini, M. Incerti, I. A. Doytchinova, P. La Colla, B.
Busonera, R. Loddo, Eur. J. Med. Chem. 2006, 41, 624.
[15] N. Terzioglu, A. Gürsoy, Eur. J. Med. Chem. 2003, 38, 781.
[
[
[
16] A. H. Abadi, A. A. H. Eissa, G. S. Hassan, Chem. Pharm. Bull.
003, 51, 838.
2
17] D. Kumar, N. M. Kumar, S. Ghosh, K. Shah, Bioorg. Med.
Chem. Lett. 2012, 22, 212.
18] V. M. Rahman, S. Mukhtar, W. H. Ansari, G. Lemiere, Eur.
J. Med. Chem. 2005, 40, 173.
[19] J. R. Dimmock, S. C. Vashishtha, J. P. Stables, Eur. J. Med.
Chem. 2000, 35, 241.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able in the supplementary material of this article.
[
[
[
[
20] R. Yapia, M. P. La Mara, G. H. Massieu, Biochem. Pharmacol.
AUTHOR CONTRIBUTIONS
1967, 16, 1211.
Dina Tolan: Formal analysis; methodology; resources;
software; validation. Tahani Kashar: Formal analysis;
methodology; resources; software; validation. Kazunari
Yoshizawa: Formal analysis; methodology; resources;
software; validation. Ahmed El-Nahas: Conceptualiza-
tion; formal analysis; methodology; project administra-
tion; resources; software; validation; visualization
21] G. Sava, L. Perissin, L. Lassiani, G. Zabucchi, Chem.-Biol.
Interact. 1985, 53, 37.
22] Y. L. Xia, F. Chuan-Dong, B. X. Zhao, J. Zhao, D. S. Shin, J. Y.
Miaom, Eur. J. Med. Chem. 2008, 43, 2,347.
23] P. Melnyk, V. Leroux, C. Serghergert, P. Grellier, Bioorg. Med.
Chem. Lett. 2006, 16, 31.
[24] O. O. Ajani, C. A. Obafemi, O. C. Nwinyi, D. A. Akinpelu, Bio-
org. Med. Chem. 2010, 18, 214.
[25] L. W. Zheng, L. L. Wu, B. X. Zhao, W. L. Dong, Y. J. Miao, Bio-
org. Med. Chem. 2009, 17, 1957.
ORCID
Dina A. Tolan https://orcid.org/0000-0003-3917-2822
Tahani I. Kashar https://orcid.org/0000-0002-4492-
[
26] M. G. Saulnier, U. Velaprthi, K. Zimmermann, in Progress in
Heterocyclic Synthesis, (Eds: G. Gribble, J. A. Joule) Vol. 16,
Elsevier Science, Amsterdam, The Netherlands 2005 228.
27] E. I. Short, Tubercle 1962, 43, 33.
0
779
Kazunari Yoshizawa https://orcid.org/0000-0002-6279-
722
Ahmed M. El-Nahas https://orcid.org/0000-0002-8547-
574
[
[
[
28] A. Faroumadi, Z. Kiano, F. Soltani, Farmaco 2003, 58, 1,073.
29] V. T. Angelova, V. Valcheva, N. G. Vassilev, R. Buyukliev, G.
Momekov, I. Dimitrov, L. Saso, M. Djukic, B. Shivachev, Med.
Chem. Lett. 2017, 27, 223.
9
7
[
[
30] T. Scior, S. J. Garcés-Eisele, Curr. Med. Chem. 2006, 13, 2,205.
31] A. Imramovsky, S. Polanc, J. Vinsova, M. Kocevar, J.
Jampilek, Z. Reckova, J. Kaustova, Bioorg. Med. Chem. 2007,
15, 2,511.
REFERENCES
[
1] J. H. Rex, H. F. Lynch, I. G. Cohen, J. J. Darrow, K. Outterson,
Nat. Commun. 2019, 10, 1.

TOLAN ET AL.
23 of 24
[
[
32] K. Manna, Y. K. Agrawal, Eur. J. Med. Chem. 2010, 45, 3,831.
33] D. Sriram, P. Yogeeswari, K. Madhu, Bioorg. Med. Chem. Lett.
[55] D. Kumar, A. Syamal, A. Gupta, M. Rani, P. K. Gupta, J.
Indian, Chem. Soc. 2010, 87, 1185.
2
006, 16, 876.
34] S. M. Soliman, S. E. Elsilk, J. Photochem. Photobiol. B, Biol.
018, 187, 48.
[56] R. M. Mohareb, D. H. Fleita, O. K. Sakka, Molecules 2011,
[
[
[
[
[
[
[
16, 16.
2
[57] S. Naskar, S. Biswas, D. Mishra, B. Adhikary, L. R. Falvello, T.
35] S. M. Emam, D. A. Tolan, A. M. El-Nahas, Appl. Organomet.
Chem. 2020, 34, 5,591.
36] H. A. El-Boraey, S. M. Emam, D. A. Tolan, A. M. El-Nahas,
Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2011, 78, 360.
37] J. Joseph, K. Nagashri, G. A. B. Rani, J. Saudi, Chem. Soc.
Soler, C. H. Schwalbe, S. K. Chattopadhyay, Inorg. Chim. Acta
2004, 357, 4257.
[
[
58] R. Gup, B. Kırkan, Spectrochim. Acta Part a 2005, 62, 1188.
59] K. Fujisawa, T. Kakizaki, Y. Miyashita, K. Okamoto,
Inorganica Chim. Acta 2008, 361, 1134.
2
013, 17, 285.
38] R. Zhang, Q. Wang, Q. Li, C. Ma, Inorganica Chim. Acta 2009,
62, 2,762.
[
[
[
[
[
[
[
[
[
60] J. S. Thompson, T. Sorrell, T. J. Marks, J. A. Ibers, J. Am.
Chem. Soc. 1979, 101, 4193.
61] F. E. Jacobsen, R. M. Breece, W. K. Myers, D. L. Tierney, S. M.
Cohen, Inorg. Chem. 2006, 45, 7306.
3
39] A. K. Singh, O. P. Pandey, S. K. Sengupta, Spectrochim. Acta
Part A Mol. Biomol. Spectrosc. 2012, 85, 1.
40] J. Bassett, R. C. Denney, G. H. Jeffery, J. Mendham, Vogel's
Textbook of Quantitative Inorganic Analysis Including Elemen-
tary Instrumental Analysis, 4th ed., Longman Group, London
62] S. Saha, S. Jana, S. Gupta, A. Ghosh, H. P. Nayek, Polyhedron
2016, 107, 183.
63] R. Takjoo, R. Centore, L. Rhyman, P. Ramasami, J. Coord.
Chem. 2012, 65, 1569.
64] Y.-P. Tian, C.-Y. Duan, Z.-L. Lu, X.-Z. You, H.-K. Fun, S.
Kandasamy, Polyhedron 1996, 2263.
65] A. Bhattacharyya, A. Bauzá, A. Frontera, S. Chattopadhyay,
Polyhedron 2016, 119, 451.
66] A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd ed. Vol.
1
978.
[
[
[
[
41] J. Lewis, R. G. Wilkins, Modern Coordination Chemistry, Inter-
science, New York 1960 403.
42] D. Kumar, S. Chadda, J. Sharma, P. Surain, Bioinorg. Chem.
Appl. 2013, 2013, 1.
43] S. O. Oyedemi, A. J. Afolayan, Asian Pac. J. Trop. Med. 2011,
33, Elsevier Science, Amsterdam, The Netherlands 1984.
4, 52.
67] S. Shit, J. Chakraborty, B. Samanta, A. M. Z. Slawin, V.
Gramlich, S. Mitra, Struct. Chem. 2009, 20, 633.
68] E. Almaraz, W. S. Foley, J. A. Denny, J. H. Reibenspies,
M. L. Golden, M. Y. Darensbourg, Inorg. Chem. 2009, 48,
44] R. G. Parr, W. Yang, Density-Functional Theory of Atoms and
Molecules, Oxford University Press, New York, Oxford 1989.
45] T. Ziegler, Chem. Rev. 1991, 91, 651.
[
[
46] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li,
H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L.
Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H.
Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F.
Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N.
Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, R. L. Martin, K. Morokuma, V. G.
Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S.
Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz,
J. Cioslowski, D. J. Fox, Gaussian 09, revision A.02, Gaussian,
Inc., Wallingford CT, 2009.
5288.
[
69] M. Franks, A. Gadzhieva, L. Ghandhi, D. Murrell, A. J. Blake,
E. S. Davies, W. Lewis, F. Moro, J. McMaster, M. Schrӧder,
Inorg. Chem. 2013, 52, 660.
70] F. Karipcin, E. Kabalcilar, Acta Chim. Slov. 2007, 54, 242.
71] M. M. Omar, G. G. Mohamed, Spectrochim. Acta Part a 2005,
[
[
6
1, 929.
72] G. Pandey, K. K. Narang, Synth. React. Inorg. Met. Chem. 2004,
4, 291.
[
[
[
[
[
[
[
[
[
[
3
73] G. Marino, G. O. Chierice, C. D. Pinheiro, A. G. Souza,
Thermochim. Acta 1999, 328, 209.
74] L. V. Ababei, A. Kriza, A. Musuc, C. Andronescu, E. Rogozea,
J. Therm. Anal. Calorim. 2010, 101, 987.
75] E. R. Souaya, E. H. Ismail, A. A. Mohamed, N. E. Milad,
J. Therm. Anal. Calorim. 2009, 95, 253.
76] C. K. Modi, M. N. Patel, J. Therm. Anal. Calorim. 2008,
94, 247.
77] N. M. El-Metwally, I. M. Gabr, A. M. Shallaby, A. A. El-Asmy,
J. Coord. Chem. 2005, 1145.
78] K. K. Aravindakshan, K. Muraleedharan, J. Therm. Anal.
Calorim. 1991, 37, 803.
79] T. Yi, C. Guo, S. Zhao, K. Zhan, W. Gao, L. Yang, G. Du, Eur.
J. Wood Wood Prod. 2020, 78, 471.
80] M. Nasrollahzadeh, S. M. Sajadi, A. Rostami-Vartooni, S. M.
Hussin, J. Colloid Interface Sci. 2016, 466, 113.
81] V. Bhuvaneshwari, D. Vaidehi, S. Logpriya, Microbiol Curr
Res. 2018, 2, 9.
[
[
47] A. D. Becke, J. Chem. Phys 1993, 98, 5,648.
48] P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch,
J. Phys. Chem. 1994, 98, 11,623.
[
[
49] P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 270.
50] G. A. Zhurko, D. A. Zhurko, ChemCraft version 1.7 (build
1
32), http://www.chemcraftprog.com
[
51] S. M. Emam, S. A. AbouEl-Enein, E. M. Abdel-Satar, Appl.
Organomet. Chem. 2019, 33, 1.
[
52] S. Saikat, N. S. Kumar, C. A. Prasun, D. Kamalendu, Ind.
J. Sci. 2015, 12, 17.
[82] R. Darugar, M. Vakili, A. R. Nekoei, S. F. Tayyari, R. Afzali, J.
Mol, Struct 2017, 427, 1150.
[83] R. G. Pearson, J. Chem. Sci. 2005, 117, 369.
[84] S. Kaya, C. Kaya, Mol. Phys. 2015, 113, 1311.
[
[
53] M. C. Chang, J. Tanaka, Biomaterials 2002, 23, 4811.
54] J. R. Ferraro, Low Frequency Vibrations of Inorganic and Coor-
dination Compounds, PlenumPress, NewYork, NY, USA 1971.

24 of 24
TOLAN ET AL.
[
[
[
[
[
[
[
[
[
85] S. Banerjee, A. Ghosh, B. Wu, P.-G. Lassahn, C. Janiak,
SUPPORTING INFORMATION
Polyhedron 2005, 24, 593.
86] L. J. Alcock, G. Cavigliasso, A. C. Willis, R. Stranger, S. F.
Ralph, Dalton Trans. 2016, 45, 9036.
87] T. M. Greaney, C. L. Raston, A. H. White, E. N. Maslen,
Dalton Trans. 1975, 10, 876.
88] S.-L. Li, T. C. W. Mak, J. Chem. Soc. Dalton Trans. 1995, 9,
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
How to cite this article: Tolan DA, Kashar TI,
Yoshizawa K, El-Nahas AM. Synthesis, spectral
characterization, density functional theory studies,
and biological screening of some transition metal
complexes of a novel hydrazide–hydrazone ligand
of isonicotinic acid. Appl Organomet Chem. 2021;
35:e6205. https://doi.org/10.1002/aoc.6205
1
519.
89] A. M. T. Bygott, R. J. Geue, S. F. Ralph, A. M. Sargeson, A. C.
Willis, Dalton Trans. 2007, 42, 4,778.
90] R. K. Sharma, G. Kedarnath, A. Wadawale, V. K. Jain, B.
Vishwanadh, Inorganica Chim. Acta 2011, 365, 333.
91] J. S. Murray, K. Sen, Molecular Electrostatic Potentials, Con-
cepts and Applications, Elsevier, Amsterdam 1996.
92] R. Parthasarathi, V. Subramanian, D. R. Roy, P. K. Chattaraj,
Bioorg. Med. Chem. 2004, 12, 5533.
93] W. H. Mahmoud, G. G. Mohamed, M. M. I. El-Dessouky,
Spectrochim. Acta 2014, 122, 598.