Synthesis, structural, spectroscopic, and thermal studies of some transition-metal complexes of a ligand containing the amino mercapto triazole moiety

Article abstract of DOI:10.1002/aoc.5591

A new series of transition-metal complexes of Schiff base ligand containing the amino mercapto triazole moiety (HL) was prepared. The Schiff base and its metal complexes were elucidated by different spectroscopic techniques (infrared [IR], ¹H nuclear magnetic resonance, UV–Visible, mass, and electron spin resonance [ESR]), and magnetic moment and thermal studies. Quantum chemical calculations have been carried out to study the structure of the ligand and some of its complexes. The IR spectra showed that the ligand is chelated with the metal ion in a neutral, tridentate, and bidentate manner using NOS and NO donors in complexes 1–6, 10–12, and 7 and 8, respectively, whereas it behaves in a monobasic tridentate fashion using NOS donor sites in copper(II) nitrate complex (9). The magnetic moment and electronic spectra data revealed octahedral and square pyramidal geometries for complexes 2, 11, 12, and 5–8 and 10, respectively. However, the other complexes were found to have tetrahedral (4), trigonal bipyramidal (1 and 3), and square planar (9) structures. Thermal studies revealed that the chelates with different crystallized solvents undergo different types of interactions and the decomposition pathway ended with the formation of metal oxygen (MO) and metal sulfur (MS) as final products. The ESR spectrum of copper(II) complex 10 is axial in nature with hyperfine splitting with ²B_1g as a ground state. By contrast, complexes 7 and 8 undergo distortion around the Cu(II) center, affording rhombic ESR spectra. The HL ligand and some of its complexes were screened against two bacterial species. Data showed that complex 12 demonstrated a better antibacterial activity than HL ligand and other chelates.

Full text of DOI:10.1002/aoc.5591

Received: 8 November 2019
DOI: 10.1002/aoc.5591
Revised: 25 January 2020
Accepted: 27 January 2020
F U L L P A P E R
Synthesis, structural, spectroscopic, and thermal studies of
some transition-metal complexes of a ligand containing the
amino mercapto triazole moiety
1
1,2
1
Sanaa M. Emam | Dina A. Tolan
| Ahmed M. El-Nahas
1
Chemistry Department, Faculty of
A new series of transition-metal complexes of Schiff base ligand containing the
amino mercapto triazole moiety (HL) was prepared. The Schiff base and its
metal complexes were elucidated by different spectroscopic techniques (infra-
Science, Menoufia University, Shebin el
Kom, 32512, Egypt
2
Department of Chemistry, College of
Science and Humanities in Al-Kharj,
Prince Sattam bin Abdulaziz University,
Al-Kharj, 11942, Saudi Arabia
1
red [IR], H nuclear magnetic resonance, UV–Visible, mass, and electron spin
resonance [ESR]), and magnetic moment and thermal studies. Quantum
chemical calculations have been carried out to study the structure of the ligand
and some of its complexes. The IR spectra showed that the ligand is chelated
with the metal ion in a neutral, tridentate, and bidentate manner using NOS
and NO donors in complexes 1–6, 10–12, and 7 and 8, respectively, whereas it
behaves in a monobasic tridentate fashion using NOS donor sites in copper(II)
nitrate complex (9). The magnetic moment and electronic spectra data rev-
ealed octahedral and square pyramidal geometries for complexes 2, 11, 12, and
Correspondence
Dina A. Tolan, Department of Chemistry,
College of Science and Humanities in Al-
Kharj, Prince Sattam bin Abdulaziz
University, Al-Kharj 11942, Saudi Arabia.
Email: d_tolan2005@yahoo.com
5–8 and 10, respectively. However, the other complexes were found to have tet-
rahedral (4), trigonal bipyramidal (1 and 3), and square planar (9) structures.
Thermal studies revealed that the chelates with different crystallized solvents
undergo different types of interactions and the decomposition pathway ended
with the formation of metal oxygen (MO) and metal sulfur (MS) as final prod-
ucts. The ESR spectrum of copper(II) complex 10 is axial in nature with hyper-
2
fine splitting with B1g as a ground state. By contrast, complexes 7 and
8
undergo distortion around the Cu(II) center, affording rhombic ESR spectra.
The HL ligand and some of its complexes were screened against two bacterial
species. Data showed that complex 12 demonstrated a better antibacterial
activity than HL ligand and other chelates.
K E Y W O R D S
1
,2,4-triazole, antimicrobial, DFT calculations, metal complexes, Schiff base
1
| INTRODUCTION
demand to overcome this problem. The chemistry of
,2,4-triazoles and their derivatives have received consid-
1
The microbial resistance of antibiotics is considered one
of the challenges in medicinal chemistry. Designing new
antimicrobial agents with different chemical characteris-
tics from those of existing ones is considered a critical
erable attention owing to their effective pharmacological
activities including antimicrobial, analgesic, antineoplas-
tic, anti-inflammatory, local anesthetic, antineoplastic,
anticonvulsant, antineoplastic, antimalarial, antiviral,
Appl Organometal Chem. 2020;e5591.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 26
https://doi.org/10.1002/aoc.5591

2
of 26
EMAM ET AL.
antiproliferative, and anticancer properties. 1–3] Further,
[
determined by gravimetric analyses.
[29]
In addition, the
1
,2,4-triazoles and their derivatives play an important
chloride and bromide ions were evaluated by
[4]]
[29]
role in agricultural and industrial applications. Among
them, Schiff bases involving the 1,2,4-triazole moiety
have attracted wide attention due to their extended bio-
logical activities, chemical, physical, and photochromic
argentometry.
Molar conductivity estimations were
−
3
made in dimethylformamide (DMF) solution (10 M)
using a Tacussel conductometer type CD6N. The
1
H
nuclear magnetic resonance (NMR) spectra were
[
5,6]
properties as well as their analytical applications.
obtained in dimethyl sulfoxide (DMSO)-d on a Varian
6
Schiff base metal complexes containing the triazole moi-
ety have been studied because of their use as drugs and
their various industrial and biological applications.
XL Gemini 300 spectrophotometer at 300 MHz at room
temperature. The infrared spectra were recorded as KBr
plates on a Nicolet FT-IR spectrophotometer within the
range 4000–400 cm . The electronic spectra were
obtained as Nujol mulls on a Perkin-Elmer Lambda 4B
spectrophotometer. Magnetic susceptibilities were mea-
sured at room temperature by the Gouy method using
the Johnson Matthey magnetic susceptibility balance.
[
7–11]
−
1
On the other side, ligands containing pyrazoles have
been important compounds because of their surprising
structural features, coordination chemistry, momentous
physical and chemical properties as well as their pharma-
[12–15]]
cological applications.
One of the most important
derivatives of antipyrine is 4-aminoantipyrine which
shows great applications in medicinal chemistry.
Diamagnetic corrections were determined using Pascal's
[
16–18]
[30]
constants.
The effective magnetic moments were
corrt
1/2
Schiff bases containing 4-aminoantipyrine and their
metal complexes have different biological applications
that include antifungal, antibacterial, analgesic, antipy-
ascertained from the relation μ = 2.84(XM
where XM
T)
,
eff
corrt
is the molar magnetic susceptibility
corrected for diamagnetism of all atoms in the com-
pounds. The thermal analyses (thermogravimetric
[TG] and differential thermal analysis [DTA]) were car-
ried out using a Shimadzu DAT/TG-50 thermal analyzer
[16–19]
retic, and anti-inflammatory.
Chelation of organic
compounds with metal causes important change in the
biological properties of both the metal and the ligand
moiety. It has been reported that biological activities of
most Schiff bases improved upon coordination with dif-
ferent transition elements, with chelation reported to
ꢀ
with a heating rate of 10 C/min under a nitrogen envi-
ronment with a streaming rate of 20 mL/min from room
ꢀ
temperature to 1000 C utilizing platinum crucibles. The
[20–28]
cure many diseases including cancer.
In this work,
electron
spin
resonance
(ESR)
spectra
for
a new Schiff base ligand was prepared by condensation of
Cu(II) complexes were obtained using a Varian E-109C
model spectrometer outfitted with a field modulation
unit at frequency 100 kHz. measurements were affected
in the X-band with a microcrystalline powder at room
temperature . Melting points were measured using the
Stuart melting point apparatus. The antimicrobial activity
of HL ligand and some of its complexes was estimated
against positive bacteria (Streptococcus pyogenes) and
negative bacteria (Escherichia coli).
0
4
-formyl antipyrine with 3-(3 -pyridyl)-4-amino-5-mer-
capto-1,2,4-triazole, which was further reacted with
Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) metal ions to
form the corresponding metal complexes. The Schiff base
ligand and its metal complexes were characterized by dif-
ferent analytical and spectroscopic methods. In addition,
the antimicrobial activities of some selected compounds
were investigated against different types of bacteria.
Quantum chemical calculations also have been per-
formed to support and interpret experimental findings.
2.2 | Synthesis of the ligand HL
2
2
| EXPERIMENTAL
The HL ligand was prepared by a two-step process. The
first one involves synthesis of 3-(3 -pyridyl)-4-amino-
0
.1 | Analytical and physical
5-mercapto-1,2,4-triazole and 4-formylantipyrine as
[
31,32]
measurements
reported previously
(Scheme 1), while the second
step is concerned with the preparation of a Schiff base
ligand – (E)-1,5-dimethyl-2-phenyl-4-({(3-[pyridin-3-yl]-
5-thioxo-1,5-dihydro-4H-1,2,4-triazol-4-yl)imino}methyl)-
1,2-dihydro-3H-pyrazol-3-one.
All chemicals were of analytical grade (BDH or Sigma
Aldrich) including all metal salts and were used as
obtained without further purification. Elemental analyses
(
C, H, and N) were performed at the Microanalytical
The ligand was synthesized by addition of an
ethanolic solution (20 mL) containing 4-formylantipyrine
(0.40 mmol, 2.16 g) to a hot ethanolic solution (30 mL)
containing an equimolar concentration of 3-(3 -pyridyl)-
4-amino-5-mercapto-1,2,4-triazole. Then, the reaction
Unit, Cairo University, Egypt. Cobalt(II), nickel(II), and
copper(II) ions of metal complexes were estimated by
complexometric titration using ethylenediaminetetra-
acetic acid, whereas cadmium(II) and zinc(II) ions were
0

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
3 of 26
standard antibacterial agent and DMSO was employed as
the negative control for these bacteria. Bacterial cells
were swabbed in 50 mL nutrient broth in a 250-mL flask
ꢀ
with vigorous shaking and incubated at 37 C for 16 h. A
sterile glass spreader was used to spread bacterial cul-
tures (100 μL) on nutrient agar plates and cells incubated
ꢀ
[34,35]
at 37 C for 24 h
The tested compounds were dis-
solved in DMSO to obtain stock solutions. The required
concentrations (100, 200, and 500 mg/mL) were prepared
by appropriate dilutions using the stock solutions. The
sterile petri dishes containing agar medium were seeded
3
with 0.5 mL of each of the tested bacteria (6 × 10 CFU).
After solidification, sterilized filter papers were saturated
with 0.1 mL of the tested compounds. Then, the plates
ꢀ
were incubated at 37 C for 24 h, on which clear or inhi-
bition zones were measured (in millimeter). DMSO
(
0.1 mL) was used as the control for each organism to
detect the resulting diameter of inhibition zone.
0
SCHEME 1 Synthesis of 3-(3 -pyridyl)-4-amino-5-mercapto-
1
,2,4-triazole and 4-formylantipyrine (HL)
2
.5 | Theoretical methods
mixture was refluxed on a water bath for 6 h in the pres-
ence of few drops of glacial acetic acid. After that, the
reaction mixture was left overnight at room temperature.
The resulting off-white solid was filtered off, washed sev-
eral times with cold ethanol, crystallized from absolute
ethanol, and dried under vacuum.
The quantum mechanical study using the density func-
tional theory (DFT)
Gaussian 98W
were carried out at the B3LYP functional
[
36,37]
was carried out using the
package. Geometrical optimizations
[
38]
[
39–41]
level
with the 3-21G(d) basis set. All the calculations
were performed in the gas phase. Frequency calculations
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. The absence of negative eigenvalues in the
force constant matrices indicates that all of the
obtained stationary points are minimal. The distribution
of the highest occupied and lowest unoccupied
frontier molecular orbitals (FMOs; i.e. highest occupied
molecular orbital [HOMO] and lowest unoccupied
molecular orbital [LUMO], respectively) and the molecu-
lar electrostatic potential (MEP) of the ligand and
2.3 | Synthesis of HL ligand metal
complexes
Ethanolic solution (20 mL) of appropriate metal salt
(
(
0.50 mmol) was added dropwise to ethanolic solution
30 mL) containing an equimolar concentration of Schiff
base and stirred with gentle warming. The reaction mix-
ꢀ
ture was magnetically stirred under reflux at 60 C for
6
h and then allowed to cool down at room temperature.
Then, the excess of solvent was evaporated under
reduced pressure, affording the solid product that was
washed with a small volume of ethanol several times and
dried over P O in vacuum.
[42]
complexes were analyzed. The Chemcraft program
was used for displaying the computational results and
plotting FMOs.
2
5
2
.4 | Antimicrobial activity
3 | RESULTS AND DISCUSSION
3.1 | Chemistry
The synthesized ligand (HL) and some of its metal com-
plexes (1, 2, 4, 5, 11, and 12) were tested to develop new
antimicrobial agents and evaluate their growth inhibitory
activity against two reference strains of microscopic
organisms (E. coli as Gram-negative bacteria and
S. pyogenes as Gram-positive bacteria) by the disk diffu-
0
The preparation of 3-(3 -pyridyl)-4-amino-5-mercapto-1,-
2,4-triazole involved four steps as illustrated in Scheme 1.
Initially, nicotinic acid (a) was esterified using ethyl alco-
hol to obtain 3-ethyl nicotinate (b) which is converted to
3-nicotinic acid hydrazide (c) using hydrazine hydrate.
[33]
sion method.
Amoxicillin was used as the positive

4
of 26
EMAM ET AL.
1
The formed hydrazide was then reacted with carbon
disulfide in the presence of alcoholic KOH to form
potassium-3-dithiocarbazate salt (d), followed by the
827 cm− attributable to thioamide I {δ (NH) + ν(C=N)},
thioamide II {ν(C=N) + ν (C=S)}, thioamide III{ν(C–N)-
as
+ ν (C=S)}, and thioamide IV that is mainly from
s
0
[52,53]
addition of hydrazine hydrate and HCl to obtain 3-(3 -
δ(C=S).
Moreover, the ligand spectrum displays a
−
1
pyridyl)-4-amino-5-mercapto-1,2,4-triazole. The novel
Schiff base was prepared by refluxing an ethanolic solu-
high-intensity band at 1585 cm
stretching frequency of the azomethine group ν(C=N).
Therefore, the ligand contains NCSH and NHCS groups
with the expectation of delocalized thioamide vibrations.
In addition, the appearance of weak bands characteristic
of NH, SH, and C=S groups suggested that Schiff base
exhibits thiol–thione tautomerism.
assignable to the
[54]
0
tion containing an equimolar concentration of 3-(3 -pyr-
idyl)-4-amino-5-mercapto-1,2,4-triazole and 4-formyl
antipyrine. The structure of the ligand was elucidated
using elemental analyses and spectral methods. More-
over, the ligand was utilized for chelation with various
metal(II) salts having different geometrical structures. All
the solid metal chelates were steady at room temperature;
nonhygroscopic; partially soluble in most organic sol-
vents, such as chloroform, methanol, ethanol, and aceto-
nitrile; and completely soluble in DMSO and DMF. The
molar conductance value of the metal complexes in DMF
solution (10− M), except that of complexes 2, 4, and 7–9
The spectra of all metal complexes except complex (9)
revealed the absence of ν(S–H) (2566 cm ) and the exis-
−
1
−
1
tence of ν(N–H) bands in the region 3110–3292 cm ,
indicating their existence in the thione form (Figures S2–
S12). The disappearance of ν(S–H) and ν(N–H) bands in
complex 9 (Table 2) confirms the loss of a proton by
thioenolization of the SH group. This is further con-
firmed by the existence of new bands at 747 and
3
1
2
−1
(
Table 1), of 12–42 Ω− cm mol revealed that all com-
1
[27,55]
plexes are nonelectrolytes, and their ions are directly
1513 cm− due to ν(C–S) and ν(C=N), respectively.
[
43,44]
coordinated to metal ions,
5
whereas the value of
For all complexes except 7 and 8, the thioamide bands I,
II, and III show change in their intensity and position
compared with those of the ligand, whereas the thio-
amide IV band, which mainly arises from δ(C=S),
undergoes downshift by 4–18 cm− in all complexes
except 7 and 8 (Table 2), suggesting the coordination of
the metal ion with the sulfur atom of the C=S group. The
δ(C=S) band does not have a change in its shape and
position upon chelation in complexes 7 and 8. Further,
the ν(C=S) stretching frequency of the ligand
(1291 cm ) undergoes upshift at 5–29 cm in all com-
plexes except 7–9, supporting its participation in complex
formation. For complex 9, the spectrum does not show
any characteristic bands for the thioamide group (I, II,
III, and IV), indicating that the HL ligand coordinates
with the Cu(II) ion with the deprotonated SH group. The
antipyrine carbonyl vibrations (ν and δ) are shifted to
9–83.8 Ω− cm mol for complexes 2, 4, and 7–9 typi-
fied the 1:1 electrolyte composition.
1
2
−1
[43]
1
3.2 | Infrared studies
The IR spectral results of HL ligand, its metal complexes,
and their assignments are summarized in Table 2. An
investigation of the HL ligand spectrum (Figure S1) rev-
ealed several fundamental weak-broad bands at 3434,
−1
−1
3
120 and 3229, 3018 and 3061, 2917 and 2820, and 2760
−1
and 2566 cm , which are assigned to stretching vibra-
tions of the adsorbed water molecule, υ(N–H), aromatic
and aliphatic C–H, and stretching vibration of the SH
[45–47]
group,
respectively. Furthermore, the spectrum
−
1
shows a band at 1291 cm assignable to ν (C=S). The
as
−
1
additional bands located at 1433 and 1390, 1025 and
lower and higher frequencies at 20–28 and 8–25 cm ,
respectively, implying that the metal binds with the oxy-
gen atom of the carbonyl group. The bands due to νas and
−
1
1
073, and 698 and 757 cm are restricted to bending
deformation of CH groups, (C–H) in-plane deformation,
3
and out-of-plane (C–H) bending for the aromatic benzene
ν of the acetate group are displayed within the ranges
1590–1598 and 1404–1420 cm , respectively, in com-
s
[48,49]
−1
skeleton, respectively.
Moreover, the HL spectrum
displays strong and medium bands at 1602, 961, 627 and
plexes 3, 6, and 10. The difference between the two bands
−
1
−1
4
26, and 1542 and 1498 cm assignable to aromatic
(173–186 cm ) can be taken as an evidence for the
[
56–59]
ν(C=C), pyridine ring breathing, C–H in-plane and out-
of-plane pyridine ring bending along with triazole ring
stretching, and NH in-plane deformation vibration,
monodentate character.
In complexes 2, 5, 9, and
−
12, the ν (NO ) was observed at 1447, 1448, 1450, and
1444 cm , whereas the ν (NO ) appeared at 1266,
1273, 1270, and 1260 cm , respectively; their separation
as
1
3
−
−
s
3
[50,51]
−1
respectively.
In addition, the IR spectrum of HL
ligand illustrates strong and medium bands at 1661 and
1
is small in accordance with the monodentate character of
125, 583 cm− attributed to the C=O stretching and in-
1
the nitrate group.
plexes 2 and 9 exhibited bands at 1380 cm , which can
be attributed to the ionic nitrate.
[54]
By contrast, the spectra of com-
−
1
plane, out-of-plane bending vibrations (υ and δ, γ) of the
[20]
[60]
antipyrine carbonyl group, respectively.
For the free
The nonligand bands
occurring in the 561–606 and 446–525 cm− ranges have
1
ligand, four bands appeared at 1542, 1333, 1073, and

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
5 of 26

6
of 26
EMAM ET AL.

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
7 of 26

8
of 26
EMAM ET AL.
been assigned to ν(M–O) and ν(M–N), respec-
with Cd(II) ion. In addition, the aromatic proton signals
are found at δ = 7.38–8.88 ppm, showing slight shift
upon chelation.
[46,48,61]
tively.
The existence of coordination and/or lattice
water molecules in the chelates is indicated by a broad
−
1
band within the range 3351–3530 cm , which can be
[44]
attributed to ν(OH) of the water molecules
and con-
firmed using thermal analyses.
3.4 | Mass spectra of complexes
These arguments show that the ligand exhibits
thione–thiol tautomerism as given in Figure 1. The exis-
tence of thioamide bands in the IR spectra of the free
ligand and its complexes except 9 indicates that they exist
as thione tautomer in the solid state, which is in agree-
Fast atom bombardment (FAB) mass spectroscopy analy-
sis of complexes CoCl , Co(NO ) , and Ni(OAc)
2
2
3 2
(Figures S13–S15) were performed. The molecular ion
peaks observed for these complexes were found to be at
m/e = 565.89, 596.90, and 590.30, respectively, indicating
that they have a monomeric nature. The spectrum of the
cobalt(II) chloride complex (Scheme 2) displayed species
at m/e = 564, 560, 485.1, 392.1, 214.2, and 179.2 amu,
[
52,53,55]
ment with previous studies on the triazole family.
The IR data established that the ligand reacts with the
metal ions in a neutral tridentate manner through NOS
sites in all complexes except 7–9. By contrast, the ligand
binds with Cu(II) ion in a neutral bidentate manner via
NO donors and behaves as monobasic tridentate via NOS
in complexes 7–9, respectively.
+
pointing to [C H N O SCoCl] , [C H N O
19
25
7
5.5
19 24.5
7
5.25
+
+
+
SCoCl] ,
[C H N O SCo] ,
[C H N OS] ,
19 17 7
1
9
20
7
3
+
+
[C H N S] , and [C H N S] , respectively. The spectrum
9
7
5
7
6 4
of cobalt(II) nitrate complex showed fragments at
m/e = 563, 512, 466.2, 392.1, 266.2, 214.2, and 179.2 amu,
1
+
+
3
.3 | H NMR spectra of HL ligand and
referring to [C H N O SCo] , [C H N O SCo] ,
19 22 8 7 19 21 7 4.5
+
+
+
its cadmium complex
[C H N O SCo] , [C H N OS] , [C H N OS] ,
19 18 7 2 19 17 7 17 6 5
[
+
9 6 5 7 6 4
+
C H N S] , and [C H N S] , respectively. Furthermore,
1
The H NMR spectral data of HL ligand reveals two sin-
glet signals in the range of δ 2.49–2.56 and 3.31–3.37 ppm
assigned to three protons of C–CH and N–CH , respec-
The NH and the azomethine proton signals
were observed at δ 9.33 and 9.17 ppm in the spectrum of
the FAB spectrum of nickel(II) acetate chelate denotes
different fragmentations (Scheme 3) at m/e = 590.3,
562.0, 488.8, 451.0, 392.1, 308.8, 214.2, and 179.2 amu,
3
3
[20]
+
tively.
corresponding
to
[C H N O SNi] ,
21
28 7 7.5
+
+
[C H N O SNi] , [C H N O SNi] , [C H N
19 17 7
21
25
+
7
6
19 20.5
+
7
3.25
[31,62]]
+
+
the ligand.
Besides, two doublets and one
OSNi] , [C H N OS] , [C H N OS] , [C H N S] ,
19 17 7 13 7 7 8 5 6
+
singlet along with multiplet signals appeared in the range
and [C H N S] , respectively. Inside the spectra of all
7 6 4
of δ = 8.70–8.72, 7.58–7.60, and 8.28–8.31 ppm, and these
complexes, the fundamental peak, which has the higher
intensity and appears at 392.1 amu, represents the more
steady, charged fragment ion in Schiff base (HL).
[63]
are attributed to four pyridine protons.
By contrast,
the signals corresponding to the five aromatic protons are
[64]
observed within range δ = 7.38–7.54 ppm.
trum of Cd(II) complex, the peak corresponding to –SH
11.12 ppm) is not observed, but another signal appeared
In the spec-
(
3.5 | Electronic absorption spectra
at δ 9.98 ppm, which was assignable to the NH group.
This clearly indicates the thione form for the ligand dur-
ing complex formation, confirming the participation of
sulfur atom of the C=S group in chelation. The signal
due to the azomethine proton undergoes upfield shift,
pointing to the coordination of the azomethine nitrogen
The ultraviolet and visible spectral data in Nujol mull
and magnetic moments of metal complexes are collected
and presented in Table 3. The ultraviolet spectra of all
complexes usually show two absorption maxima at
239–255 nm and 287–326 and 345–432 nm. The absorp-
tion at 287–326 nm is due to the presence of the chromo-
phore group (C=S).
3.5.1 | Cobalt complexes
Cobalt(II) complexes 1, 3, and 2 showed magnetic
moment values 4.82, 4.9, and 5.1 BM at room tempera-
ture, suggesting high-spin trigonal bipyramidal (TBP)
[
64]
and octahedral structures.
The electronic spectra of
0
FIGURE 1 Structure of ligand (HL) and its thiol form (HL )
complexes
1
and 3, [Co(HL)Cl(OH)]ꢁ3.5H O, and
2

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
9 of 26
SCHEME 2 Proposed mass fragmentation of complex 1
[
Co(HL)(OAc)(OH)]ꢁ4.25H Oꢁ0.25EtOH depict bands at
transitions, respectively. This indicated an SP structure
2
[
64]
6
95–751, 542–632, and 498–502 nm assignable to
around the nickel(II) ion.
Meanwhile, the spectrum of
4
0
0
4
0
4
0
4
00
A (F)
!
E
(F),
A (F)
!
E (P), and
complex 4 revealed three electronic absorption peaks at
2
2
4
4
0
3
3
A (F) ! A (P) transitions, respectively. These transi-
857, 795, and 658 nm attributable to T (F) ! T (F),
2
2
1
2
3 3 3 3
tions are indicative of high-spin TBP geometry around
the cobalt(II) ion.
T (F) ! T (P), and T (F) ! A (F) nm transitions,
1
1
1
2
[64]
By contrast, the electronic spectrum
respectively. This is consistent with the tetrahedral geom-
[
48,66]
of complex 2 [Co(HL)(OH)(H O) ]NO ꢁ1.75H O displays
etry around the nickel(II) ion.
2
2
3
2
absorption bands at 801, 524, and 502 nm assignable to
4
4
4
4
T (F) ! T (F) (υ ), T (F) ! A (F) (υ ), and
1
g
2g
1
1g
2g
2
4
4
T (F) ! T (P) (υ ) transitions, indicating to high-spin
3.5.3 | Copper complexes
1g
1g
3
[65]
octahedral geometry around the cobalt(II) ion.
Complexes 7, 8, and 10 depict three absorption bands at
8
00–811, 690–769, and 440–550 nm, which were attrib-
2
2
2
2
2
2
3.5.2 | Nickel complexes
uted to B1g ! A , B ! B , and B ! E transi-
1g
1g
2g
1g
g
tions, respectively, affording distorted SP geometry
[
67]
The room temperature magnetic moment values of
nickel(II) complexes 4, 5, and 6 were estimated at 3.23,
around the Cu(II) ion.
However, complex 9 displays
2
2
two bands at 665 and 502 nm assignable to B ! B
1g
2g
2
2
3
.36, and 3.52 BM, respectively. These values were within
and B1g ! E transitions, respectively, pointing to the
g
the range except for tetrahedral and square pyramidal
distorted square planar structure around the copper(II)
[
64]
[46,67,68]
(SP) geometries for mononuclear Ni(II) complexes.
ion.
The magnetic moment values for copper(II)
The electronic spectra of isostructural nickel(II) com-
plexes 5 and 6 displayed three broad peaks that appeared
within ranges 789–805, 622–664, and 432–435 nm assign-
complexes 7–10 fall in the range 1.75–2.1 BM.
Based on elemental analyses and spectral methods,
the suggested chemical structures for the synthesized
metal complexes are represented in Figure 2.
2
2
2
2
2
2
able to B1g
!
A , B1g
1g
!
B2g, and B1g
!
Eg

10 of 26
EMAM ET AL.
SCHEME 3 Proposed mass fragmentation of complex 6
−
1
−1
3.5.4 | Ligand field parameters
contrast, the 10D (8600 cm ), LFSE (191 cm ), ν /
q
3
ν (1.595), and ν /ν (1.043) values are in agreement with
1
3
2
The ligand field parameters for high-spin octahedral
cobalt(II) complex 2, including ligand field splitting
those reported for high-spin octahedral cobalt(II)
complex.
[
65]
energy (10D ), Racah interelectronic repulsion (B),
q
nephelauxetic ratio [β = B/B , where B for free
º
º
−
1
Co(II) ion is 971 cm ], and ligand field stabilization
3.6 | Thermal studies
energy (LFSE), were calculated using ν /ν and ν /ν2
3
1
3
[66]
ratios.
The results demonstrated that the inter-
The TG and DTA temperature ranges, the decomposition
stages as well as the weight loss percentage of complexes
are listed in Table 4. The TG data were recorded using
−1
electronic repulsion factor of complex 2 is 688 cm ,
which is smaller than that of the free ion, indicating a
considerable orbital overlap and delocalization of elec-
trons in d-orbitals. In addition, the nephelauxetic ratio
ꢀ
2–5 mg of samples at a constant heating rate of 10 C/min
under a nitrogen atmosphere using a thermal analyzer.
The thermal behavior of chloride complexes 1, 4, and
11 was investigated by TG analysis, with results pres-
ented in Scheme 4. The thermal degradation occurs in
(
β) was found to be less than one (0.71), denoting a par-
tial covalent character for the σ bond created between
[65,66]
the Co(II) ion and the chelating ligand.
The covalent
ꢀ
property of this bond led to a decrease of the positive
charge on the Co(II) ion due to the inductive effect of the
ligand, which led to an increase in radial extension of d-
orbitals and a decrease in electron–electron repulsion. By
three major stages within temperature ranges 25–263 C,
ꢀ
ꢀ
211–451 C, and 343–772 C. The first one refers to the
desolvation stage, which does not point, in general, to a
single event but rather to two overlapping events. The

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
11 of 26
TABLE 3 Electronic spectral data and magnetic moments of the HL ligand and its metal complexes
No.
Compound
LꢁH
Spectral bands (nm)
Assignment
μ
eff. (BM) per metal ion
H
2
2
O
256, 301
π–π*
–
3
4
74
56
n–π*
1
[Co(HL)Cl(OH)]ꢁ3.5H
2
O
246, 287
Intraligand transitions
4.82
3
4
4
6
6
11, 432
70
LMCT
4
4
4
0
4
0
2
(P)
98
A
2
A
2
A
2
(F) ! A
0
4
00
32
´ (F) ! E (P)
4
0
0
95
´ (F) ! E (F)
2
3
4
[Co(HL)(OH)(H
2
O)
2
]NO
3
ꢁ1.75H
2
O
242,382
Intraligand transitions
5.10
4.90
3.23
426
502
524
801
LMCT
4
4
4
4
T
T
T
1g(F) ! T1g(P) (υ
3
)
4
1g(F) ! A2g(F) (υ
2
)
4
1g(F) ! T2g(F) (υ
1
)
[Co(HL)(OAc)(OH)]ꢁ4.25H
2
Oꢁ0.25EtOH
239, 333
Intraligand transitions
350
502
542
751
4
4
4
0
4
0
2
(P)
A
2
A
2
A
2
(F) ! A
0
4
00
´ (F) ! E (P)
0
4
0
´ (F) ! E (F)
[Ni(HL)Cl]Clꢁ4.5H
2
O
252, 351
Intraligand transitions
386
405
658
795
857
LMCT
3
3
3
3
T
T
T
1
1
1
(F) ! A
(F) ! T
(F) ! T
2
(F)
3
2
(P)
(F)
3
2
5
6
7
8
[Ni(HL)(NO
3
)
2
]ꢁ4.5H
2
O
247, 332
Intraligand transitions
3.36
3.52
2.10
1.75
363
435
664
789
2
2
LMCT + B1g ! E
B
g
2
2
1g ! B2g
1g ! A1g
2
2
B
[Ni(HL)(OAc)(OH)]ꢁ4H
2
Oꢁ0.25EtOH
249, 337
Intraligand transitions
352
432
622
805
2
2
LMCT + B1g ! E
B
g
2
2
1g ! B2g
1g ! A1g
2
2
B
[Cu(HL)(OH)(H
[Cu(HL)(OH)(H
2
O)
2
]Clꢁ4H
2
O
248, 350
Intraligand transitions
384
395
550
769
LMCT
2
2
2
B
1g ! E
g
2
B
1g ! B2g
2
O)
2
]Brꢁ3.5H
2
Oꢁ0.25EtOH
250, 345
59
Intraligand transitions
3
(
Continues)

12 of 26
EMAM ET AL.
TABLE 3 (Continued)
No. Compound
Spectral bands (nm)
Assignment
μ
eff. (BM) per metal ion
2
2
540
B
1g ! E
g
2
2
2
7
8
60
11
B
1g ! B2g
2
B
1g ! A
g
9
[Cu(L)(H
2
O)]NO
3
ꢁ4.25H
2
O
246, 326
Intraligand transitions
1.81
1.85
393
438
502
665
LMCT
2
2
2
B
1g ! E
g
2
B
1g ! B2g
1
0
[Cu(HL)(OAc)(OH)]ꢁ2.25H
2
O
254, 327
Intraligand transitions
345
440
690
800
2
2
LMCT + B1g ! E
B
g
2
2
1g ! B2g
1g ! A1g
2
2
B
1
1
2
[Zn(HL)Cl(OH)(H
2
O)]ꢁ6.5H
2
O
255
Intraligand transitions
Diamagnetic
Diamagnetic
3
4
40
50
LMCT
1
[Cd(HL)(NO
3
)
2
(H
2
O)]ꢁ2.25H
2
Oꢁ0.25EtOH
250
Intraligand transitions
3
4
45
60
LMCT
ꢀ
desolvation stage takes place within ranges 25–211 C,
crystallized water and complete desolvation with weight
ꢀ
ꢀ
3
3
3–264 C, and 31–233 C attributable to removal of
losses of 8.71% and 11.27% for complexes 7 and 8, respec-
tively. The complexes lose their water below 200 C due
ꢀ
, 4.25, and 3.25 mol of water molecules of crystallization
with weight losses of 9.96%, 12.64%, and 9.19% for com-
plexes 1, 4, and 11, respectively. This degradation step is
to hydration, showing that water/solvent molecules in
[
69]
the complexes are absorbed.
Afterward, the coordi-
confirmed by weak DTA peaks observed at T
= 42
nated water, anion, and the ligand partially decomposed
max
ꢀ
and 149; 73, 131, 190; and 50, 130, and 157 C, respec-
tively. Then, the desolvation stage is followed by the sec-
in the second stage, corresponding to weak–strong endo-
ꢀ
thermic DTA peaks at Tmax = 212, 298, and 327 C,
ꢀ
ond one in the 211–451 C range corresponding to the
which point to the removal of coordinated H O, lattice
2
loss of chloride ion and along with the elimination of the
remaining lattice water and two terminal methyl groups
in the antipyrine moiety. This step is associated with
H O, and ionized halogen, respectively, along with par-
2
tial ligand pyrolysis (3-pyridyl-1,2.4-triazole, C H N ;
7
5 4
Table 4). Finally, complete ligand pyrolysis occurs in
association with the removal of remaining lattice and
coordinated water molecules together with the removal
of coordinated OH, with weight losses of 32.98% and
41.03% for complexes 7 and 8, respectively. This step
endothermic peaks located at 347, 320, 297, 351, and
ꢀ
4
3
38 C. Finally, the third decomposition stage between
ꢀ
43 and 772 C refers to a single process which points to
removal of the remaining lattice and coordinated water
molecules as well as the elimination of the coordinated
anions and the substituted 1,2,4-triazole ring. The resid-
ual part of the thermal decomposition is consistent with
[
70,71]
ended with the formation of CuO (Table 4).
By con-
trast, the CuBr complex showed a higher thermal stabil-
2
ity than the CuCl2 complex. This behavior can be
interpreted based on nucleophilic power of the halide ion
(electron-donor constants: Cl = 1.24 and Br = 1.51),
[26]
metal sulfide mixed with carbon.
The SP Cu(II) complexes 7 and 8 are isothermal and
isostructural. The thermal behavior of these complexes
occurs in three decompositions stages within temperature
[
72]
which stabilizes the activated intermediate.
The acetate complexes 3 and 6 thermally decompose
in three degradation steps within temperature ranges
ꢀ
ranges 23–259, 205–359, and 357–800 C (Scheme 5). The
ꢀ
ꢀ
ꢀ
first one is the desolvation step which is associated with
25–230 C, 227–414 C, and 397–850 C. The first one
corresponds to weight losses of 14.70% and 13.44% attrib-
uted to complete desolvation, which takes place in more
weak-medium endothermic DTA peaks at T
= 52,
max
ꢀ
1
65, and 59 and 164 C attributed to loss of 3 mol of

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
13 of 26
ꢀ
occurs between 26 and 238 C, the thermogram depicts
a weight loss of 6.92%, which can be attributed to loss
of 2.25 mol of crystallized water molecules. This event
is associated with two weak endothermic peaks at
ꢀ
Tmax = 47 and 196 C. Then, the anhydrous complex
decomposes in two separate steps: the first one occurs
ꢀ
between 238 and 349 C with a weight loss of 33.77%,
which can be attributed to loss of 1 mol of coordinated
acetate ion, 1 mol of coordinated OH ion, and partial
ligand degradation (C H N ). This step is clarified by a
6
4 3
ꢀ
weak exothermic DTA peak at Tmax = 314 C. Finally,
ꢀ
the last step occurring between 349 and 600
C
denotes complete pyrolytic decomposition of the com-
pound that produces a mixture of CuO and carbon as
[
49,67,70]
a final residue.
The thermal decomposition can
be explained as follows :
The TG curves of nitrato complexes 2, 5, and 12 reveal
four decomposition steps within temperature ranges
ꢀ
ꢀ
ꢀ
ꢀ
2
3–234 C, 195–320 C, 300–566 C, and 450–908
C
(
Table 4). The first step is accompanied by estimated
mass losses of 14%, 12.71%, and 7.35% attributable to par-
tial desolvation together with removal of ionic nitrate for
complex 2 and complete desolvation for complexes 5 and
1
2, respectively. This step is associated with weak endo-
ꢀ
thermic peaks appearing at 137 and 217 C, 40 and
1
FIGURE 2 Structure of complexes 1–12
ꢀ ꢀ
34 C, and 100 C for complexes 2, 5, and 12, respec-
tively. The DTA curves confirm that the surface water
ꢀ
than one event for complex 3. This is confirmed by
molecules adsorbed are lost up to 100 C in these com-
weak/medium endothermic DTA peaks at T
= 70 and
plexes, with endothermic peaks characterized for com-
max
ꢀ
1
92, and 74 C for complexes 3 and 6, respectively. After-
plexes 5 and 12. Beyond this temperature, the complexes
ꢀ
ward, the coordinated acetate ion and the ligand are par-
tially decomposed (C H ) in the second stage within
experience decomposition at 234, 216, 195 C (Table 4),
respectively. This represents the second step associated
with mass loses of 15.08%, 18.38%, and 20.20% assignable
to removal of coordinated water, hydroxyl, and coordi-
nated nitrate ions, respectively, as well as partial ligand
pyrolysis (C H ) and elimination of remaining lattice
6
5
ꢀ
temperature ranges 230–414 and 227–397 C, which are
associated with estimated weight losses of 22.07% and
2
3.14% for complexes 3 and 6, respectively. This step is
clarified by weak endothermic DTA peaks at T
= 374
max
2
4
ꢀ
and 318 C. Finally, complete decomposition of the com-
pound with the elimination of the coordinated OH ion
occurs in association with weight losses of 45.74% and
water (complex 2). This step is clarified by a medium exo-
ꢀ
thermic DTA peak at 265 and 252 C corresponding to
removal of coordinated nitrate in complexes 5 and 12,
[
73,74]
4
6.0% for complexes 3 and 6, respectively. This step
respectively.
The second step is followed by the sub-
ended with the formation of metal oxide contaminated
sequent elimination of the ligand in the third and fourth
decomposition steps to obtain stable metal oxide at high
temperatures contaminated with traces of carbon as
[20,49,70]
with carbon residues
Table 4.
as observed in Scheme 6 and
[
48,70,74]
The TG curve of complex Cu(HL)(OAc)
the final product.
This is supported by
(
OH)]ꢁ2.25H O (10) shows three thermal decomposition
endothermic and exothermic peaks through all decompo-
sition stages.
2
ꢀ
stages between 26 and 600 C. In the first stage, which

14 of 26
EMAM ET AL.

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
15 of 26

16 of 26
EMAM ET AL.

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
17 of 26
SCHEME 4 Thermal decomposition mechanism of complexes 1, 4, and 11
SCHEME 5 Thermal decomposition mechanism of
complexes 7 and 8
3
.7 | ESR studies
Table 5. This spectral strategy gives information about
the binding mode around the copper(II) ion. In the solid
state, the ESR spectra of copper(II) complexes 7, 8, and
10 at room temperature display distinctive types of sym-
metrical species. The ESR spectra of copper(II) complexes
7, 8, and 10 are shown in Figures S16–S18.
The ESR spectra of complexes 7, 8, and 10 confirmed
their electronic spectra which are consistent with dis-
torted SP geometries. The polycrystalline ESR spectral
parameters of copper(II) chelates are summarized in

18 of 26
EMAM ET AL.
SCHEME 6 Thermal decomposition mechanism of
complexes 3 and 6
TABLE 5 Electron spin resonance bonding and reduction parameters for Cu(II) complexes
Complex
7
8
10
g
g
g
g
g
g
g
3
2.230
2.150
–
2
2.090
2.045
–
1
2.026
2.008
–
a
av
||
2.115
2.068
–
–
–
2.18
2.03
2.08
6.56
–
⊥
–
–
b
iso
–
–
c
G
4.28
6.13
d
R
A
A
0.457
0.352
c
||
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
178.08
23.69
12,500
15,385
0.72
0.58
0.50
0.53
0.46
0.35
c
⊥
f
Δ
1
f
Δ
2
2
α
K
K
K
||
⊥
d
2
β
1
2
γ
1
h
f
–
–
122.41
2
2
2
Ground state
B
1g
B
1g
B
1g
a
c
g
av = g
1
+ g
2
+ g
3
d
/3, G = g|| − 2.0023/g
⊥
– 2.0023.
b
g
iso = 2g
⊥
−4
+ g||/3, R = (g
2
– g
1
)/(g
3
– g
2
).
c
A in 10 cm , Δ in cm−1.
−1 f
d
h
⊥
K = 2K + K||/3, f = g||/A|| in centimeter.

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
19 of 26
The X-band ESR spectra of complexes 7 and 8 give
the d–d electronic transitions (Δ , Δ ). The orbital reduc-
1
2
2
2
three g values, g = 2.026 and 2.008, g = 2.090 and 2.045,
tion factors (K and K ) can be calculated using the fol-
1
2
||
⊥
and g = 2.23 and 2.15, with g value of 2.115 and 2.068
lowing relations:
3
av
(
Table 5), respectively, affording rhombic distortion in
ꢀ
ꢁ
[64,75]
Àα2β2Á = K2
À
Á
2 2
the coordination sphere.
The spectra with three
=
g – 2:0023 Δ1=8λ
ꢀ
and α γ = K2⊥ = ðg⊥ – 2:0023ÞΔ2=2λ½46,76ꢂ
k
k
g values are clearly indicative of a penta-coordinated
Cu(II) complex with a geometrical TBP or the SP struc-
ture. The geometric parameter (R) has been calculated
using this ratio R = (g – g )/(g – g ) to set up the ground
where K , K , λ , Δ , and Δ are parallel and perpendicu-
1 2
ꢀ
|
|
⊥
lar orbital reduction factors; the spin-orbit coupling con-
2
1
3
2
[64,75]
2 1
−1
2
2
state.
If R > 1, (d ) represents the ground state in
stant, which is −828 cm for the Cu(II) ion; B ! B ;
z
1g
2g
2
2
the TBP geometrical structure, whereas if R < 1, the gro-
und term has a (d
For the Cu(II) complexes 7 and 8 R values are 0.457 and
and B1g ! E , respectively. The nature of metal–ligand
g
2
x –y
2 1
) configuration in the SP structure.
bonding can be elucidated and clarified using these fac-
[
76]
tors. According to Hathaway and Billing,
K K and
|| ⊥z
0
.352, suggesting the existence of the unpaired electron
K < 1 imply the presence of out-of-plane π-bonding and
2
2
2
2
2
in (d
), giving ( B ) as the ground state with configu-
covalent nature of M–L bonds. Moreover, the α , β , and
x –y
1g
2
4
2
1
2
ration (e ) (b ) (a ) (b ) , which is characterized as SP
γ values are less than unit, which is attributed to signifi-
g
2g
1g
1g
Cu(II) complexes.
cant in-plane σ-bonding and in-plane π-bonding.
By contrast, the spectrum of complex 10 displays
broad signal with two g values and an axial-type ESR sig-
nal with g = 2.03 and g = 2.18 (g value is 2.08). This
3.8 | DFT studies
⊥
||
iso
[
46,49,64]
change in the gav value suggests axial symmetry.
In addition, the observed g is less than 2.3, pointing to
Because of our unsuccessful trials to obtain crystalline
samples for X-ray crystallography, DFT calculations were
performed to better understand the structures of the
ligand and complexes 1, 4, 7, 8, and 9. The optimized
structures of HL ligand and its complexes are presented
in Figure 3. No imaginary frequencies were recorded,
which indicates that the investigated systems represent
minima on their potential energy surface.
||
the covalent nature of the copper-ligand bond. According
[76]
to Hathaway and Billing,
the parameter G = (g −2)/
|
|
(
g⊥–2) is used to measure the exchange interaction
between copper centers in polycrystalline solids. In com-
plexes 7, 8, and 10, the G parameter is equal to 4.28–6.56,
indicating the absence of exchange interaction between
copper centers. The ESR spectra of Cu(OAc) complex 10
2
presented a well-defined hyperfine structure at the lower
field than that observed within the high field region
−
4
−1
(
A = 178.08 and A = 23.69 × 10 cm ). This is due to
3.8.1 | Structure of the ligand
|
|
⊥
weak interaction between electron spin and nuclear spin
of the Cu(II) ion (I = 3/2). The empirical factor (f = g /
The calculations in the gas phase for the ligand indicated
|
|
A ) can be used for diagnosing the stereochemistry of
that the thione form (HL) is more stable than the thiol
form (HL ) by 27 kcal/mol. Selected geometrical parame-
|
|
[44,46]
0
copper(II) complexes.
For the investigated complex,
the f value was 122 cm, indicating tetragonal distorted
ters for the ligand HL are shown in Tables 6 and 7. To
shed light into the electronic structures of the ligand and
its complexes, the natural bond orbital analysis was car-
ried out. Charges from natural population analysis over
some atoms in the ligand and its complexes are listed in
Table 8. The negative charge on the oxygen atom O1
(−0.531) is larger than that for the nitrogen atoms N2
and N5 (−0.254 and −0.253, respectively), whereas both
oxygen and nitrogen atoms are more negative than the
sulfur atom (−0.220). Therefore, it is expected that the
metal ion will preferably bind with the oxygen atom than
with the nitrogen and sulfur atoms.
[76]
copper(II) complex.
electron residues in the (3d
The interaction of the unpaired
2
2 1
) orbital (antibonding
x –y
orbital) of the Cu(II) ion with the σ orbitals of the ligand
is considered in the following equation:
ꢀ
ꢁ
2
α = A=0:036 + g – g + 3ðg – g Þ=7 + 0:04
k
e
⊥
e
2
where the α value measures the covalent nature of M–L
bonding (i.e. the in-plane σ-bonding). The calculated in-
2
plane σ-covalence parameter (α ) value of 0.72 for com-
plex 10 clarifies that this complex has more covalent
To further understand the interaction between the
ligand and the metal ion, the FMOs are calculated as
depicted in Figure 4. HOMO is the highest energy orbital
containing electrons and is closely related to reactivity
toward electrophilic attack, whereas LUMO is the lowest
2
character for σ-bonding. The bonding parameters (β )
2
and (γ ), which measure the covalence of in-plane and
out-of-plane (π) bonding, respectively, can be calculated
using ESR parameters g , A , g , A and the energies of
||
||
⊥
⊥,

20 of 26
EMAM ET AL.
0
FIGURE 3 Optimized structures of the complexes, the ligand (HL), and its tautomer (HL )
energy orbital that can accept electrons and correlates
well with reactivity toward nucleophilic attack. The
HOMO of the ligand HL is mainly located on oxygen,
nitrogen, and sulfur atoms, implying that these are the
centers ready for electron donation to electron-deficient
metal ions. Moreover, the HOMO–LUMO energy gap
reflects the chemical activity of the molecule and serves
as a simple measure of its kinetic stability. The HOMO–
LUMO gap represents the chemical hardness of the mole-
[
77]
cule as reported by Pearson.
The chemical hardness is
defined as the resistance toward deformation or polariza-
[
78]
tion of the electron cloud of the molecules
which
implies an increase in the molecular stability with hard-
ness. From the data of the HOMO and LUMO energies,
the
parameters
that
indicate
the
stability/reactivity/sensitivity such as energy gap, ΔE;

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
21 of 26
TABLE 6 Selected bond lengths (B, ) for the studied complexes
M–O1
M–N5
M–S1
M–O(H
2
O)
M–Cl
M–O (OH)
3
M–O (NO )
1
4
7
2.03
1.92
2.69
1.78
2.29
1.92
1.97
1.91
1.91
2.40
2.13
1.94
1.917
1.92
9
1.868
1.863
2.21
1.88
ꢀ
TABLE 7 Selected bond angles ( ) for the studied complexes
O1–M–Cl
O1–M–N5
88.60
N5–M–S1
79.84
86.81
–
S1–M–Cl
86.28
O1–M–O2
S1–M–O1
S1–M–O2
S1–M–O2
123.30
–
1
4
7
9
85.16
103.74
–
106.81
121.51
99.53
112.98
93.66
114.41
–
–
–
92.80
123.05
94.61
97.40
93.12
–
145.51
98.13
TABLE 8 NBA charges of the ligand and the studied complexes at B3LYP/3-21G(d)
Atom/compound
HL
1
4
7 and 8
9
O1
N5
S1
M
−0.531
−0.253
−0.220
−0.561
−0.411
−0.078
0.817
−0.597
−0.363
−0.054
0.892
−0.569
−0.384
−0.201
0.933
−0.597
−0.363
−0.181
0.893
FIGURE 4 Density functional theory-computed highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital
LUMO) diagrams of the ligand (HL)
(
absolute electronegativity, χ; chemical potentials, Pi;
absolute hardness, η; absolute softness, σ; global electro-
philicity, ω; global softness, S; and additional electronic
charge, ΔNmax have been calculated and presented in
Table 9.
LUMO energy gap (3.85 eV) and it has high biological
activity due to the high ω value.
3.8.2 | Structure of the complexes
From the theoretical calculations, it was concluded
that the free ligand is soft and reactive toward forming
complexes with metal ions due to the small HOMO–
Complex 1 presents a TBP structure with the Co(II) ion
coordinated to one azomethine nitrogen atom (N5),

22 of 26
EMAM ET AL.
TABLE 9 Various quantum chemical parameters of free ligand (HL) and its complexes
E (a.u.)
HL
8.75
1
4
7 and 8
11.50
−8.27
−5.20
3.07
9
Dipole moment (D)
11.16
13.09
19.80
−8.26
−5.53
2.73
E
E
HOMO (eV)
LUMO (eV)
−5.65
−1.79
3.85
−4.17
−2.30
1.86
−8.66
−5.68
2.98
ΔE (eV)
χ (eV)
3.72
3.23
7.17
6.73
6.89
η (eV)
σ (eV−
1.925
0.519
−3.72
0.259
3.594
−1.932
0.935
1.069
−3.235
0.534
5.596
3.459
1.490
0.671
−7.17
0.335
17.25
4.812
1.535
0.651
−6.73
0.325
14.75
4.384
1.38
1
)
)
0.724
−6.89
0.362
17.20
4.99
Pi (eV)
S (eV−
ω (eV)
ΔNmax
1
Abbreviations: HOMO, highest occupied molecular orbital; LUMO, lowest unoccupied molecular orbital.
−
oxygen atom of the OH group, and chloride ion. These
three atoms form a distorted plane with the carbonyl oxy-
gen atom (O1) and the thione sulfur atom coordinated to
the Co(II) ion in the z axis, forming a TBP structure.
Complexes 7 and 8 adopt an SP structure with the
Cu(II) ion coordinated to one azomethine nitrogen atom,
geometry for the copper(II) ion. Moreover, the sum of the
ꢀ
ꢀ
bond angles around Co(II) and Cu(II) is 340 and 339 ,
ꢀ
ꢀ
which implies a pyramidization degree of 20 and 21 for
complexes 1 and 7 and 8, respectively.
Complexes 4 and 9 have a tetrahedral structure and a
square planar geometry, respectively, where the ligand
coordinated in a tridentate mode with the metal center
through azomethine nitrogen, oxygen, and sulfur atoms
(one each). The calculated binding energies of the com-
plexes in the gas phase are given in Table 10. The nega-
tive sign of the binding energies indicates that the
investigated complexation reactions are thermodynami-
cally favored. Although the oxygen atom O1 carries the
highest negative charge in the ligand than the nitrogen
and sulfur atoms, the calculations showed that the M–N5
bond length is the shortest compared with M–O1 and M–
S1 bond distances. The smaller M–N bond length may be
attributed to back donation between metal center and
ligand nitrogen atom (N5), which leads to the significant
increase in the negative charge of N5 in the complexes
than in the ligand as shown in Table 7. It is known that
the bond length between the metal atom and the ligand
−
one oxygen of the OH group, and two oxygen atoms of
two water molecules. These four atoms form a distorted
plane with the carbonyl oxygen atom of the ligand
(
O1) coordinated to the Cu(II) ion in the z axis. Starting
the optimization process with a regular octahedral struc-
ture for complexes 7 and 8, where the ligand coordinated
to the Cu(II) ion in the tridentate mode through the car-
bonyl oxygen atom, nitrogen and sulfur lead gradually to
the distorted SP structure, where the sulfur atom leaves
the coordination sphere. All these observations support
the experimental results of the distorted SP structure for
complexes 7 and 8. There are two common structures for
a five-coordinated Cu(II) center, SP or TBP geometry,
which can be evaluated by the angular structural parame-
ter (τ). τ is defined as [(θ – Φ)/60], where θ and Φ are the
two largest coordination angles. It was reported that
[79]
τ = 0 for a perfect SP and τ = 1 for ideal TBP.
culated τ values of complexes 1 and 7 and 8 are 0.520
and 0.451 , respectively, which confirmed the distorted
TBP geometry for the cobalt(II) ion and distorted SP
The cal-
is shortened considerably due to the multiple-bond char-
ꢀ
[80]
acter produced by back donation.
By contrast, the neg-
ꢀ
ative charge on S decreases largely in complexes 1, 4, and
9 relative to the free ligand with the M–S bond lengths
TABLE 10 Calculated binding energies (kcal/mol) for the studied complexes in the gas phase
Compound
ΔE
0
ΔE298
ΔH298
ΔG298
1
4
7
9
−1549.26
−995.214
−1098.97
−253.663
−1549.03
−994.778
−1100.37
−254.037
−1550.81
−995.963
−1102.74
−255.222
−1523.92
−979.865
−1062.05
−235.444

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
23 of 26
FIGURE 5 Molecular electrostatic potential (MEP) mapped on the electron density surface calculated by the DFT/B3LYP method for
the ligand and its studied complexes. DFT, density functional theory
being the longest compared with the M–N and M–O
bonds, which highlights their weaker nature. In addition,
the ligand binds with the Cu(II) ion in complexes 7 and
Debye (Table 8), implying that all the complexes are
highly polar compounds.
Regarding HOMO and LUMO energies in the free
ligand and complexes, it is evident that the HOMO level
in complexes 4, 7, and 9 is stabilized by about 2.74 eV rel-
ative to ligand, whereas the LUMO is stabilized by about
3.74 eV compared with the ligand, which causes a
decrease in energy gap in these complexes. In complex 1,
the HOMO is destabilized by 1.48 eV, whereas the LUMO
is stabilized by 0.61 eV, which leads to a significant
8
as a bidentate ligand coordinated through N5 and O1,
whereas the sulfur did not participate in coordination,
which may be attributed to the weakness of the M–S
bond. Besides, the charge on the metal ion in the com-
plexes is less than +1 e, which indicates charge transfer
from the ligands to the central metal ion. The dipole
moments (D) for the complexes range from 11.16 to 19.8

24 of 26
EMAM ET AL.
TABLE 11 Antimicrobial activity of the HL ligand and its metal complexes
Streptococcus pyogenes
Escherichia coli
Compound
100 ppm
30.0
200 ppm
60.0
500 ppm
100.0
160.0
140.0
150.0
120.0
230.0
250.0
100 ppm
20.0
200 ppm
50.0
500 ppm
100.0
160.0
100.0
220.0
120.0
240.0
250.0
HL
1
40.0
75.0
50.0
90.0
2
40.0
90.0
30.0
70.0
4
50.0
80.0
60.0
100.0
70.0
5
40.0
70.0
31.0
1
1
1
2
60.0
120.0
120.0
60.0
110.0
150.0
70.0
80.0
reduction in the energy gap to 1.86 eV. The low energy
gap (ΔE = ELUMO – EHOMO) of the complexes than that of
the ligand suggests a strong activity of the former
Moreover, the metal complexes have activity against
E. coli (Gram negative) with inhibitory zone range of
5.0–25.0 mm. The order of biological activity is as follows:
(12) (11) (4) (1) (5) (2). The variation in the activity of
different complexes against investigated organisms
depends on the impermeability of microbial cells. The
better activity of metal complexes can be demonstrated
on the basis of Overtone's concept and Tweedy's chela-
(Table 9). The HOMO and LUMO diagrams of the com-
plexes are shown in Figure S19.
MEP is suitable for predicting the reactive sites
toward electrophilic and nucleophilic attack. The MEP of
the ligand (HL) and the complexes is shown in Figure 5.
The red and yellow regions (negative sites) of the MEP
are related to electrophilic reactivity and the blue regions
[
82]
tion theory.
Upon complexation, the polarity of the
central metal atom is reduced, due to the partial sharing
of its positive charge with the donor sites within the com-
plex. This process causes an increase in the lipophilic
nature of the metal, favoring its permeation through lipid
(positive sites) are related to nucleophilic reactivity. It
can be seen from Figure 5 that the negative MEP regions
of the ligand are concentrated on the carbonyl oxygen
atom, azomethine nitrogen atom, and sulfur atom in
addition to the pyridine nitrogen atom. Coordination of
the ligand to the metal ion shifts the electrostatic poten-
tial to more positive values, which matches the higher
global electrophilicity (ω) of the complexes compared
with the ligand. The electrophilicity represents a suitable
descriptor of the biological activity as there is a linear cor-
relation between the electrophilicity and the biological
[
83]
layers of the microorganism to be destroyed.
4 | CONCLUSIONS
In this paper, Co(II), Ni(II), Cu(II), Zn(II), and
0
Cd(II) complexes with Schiff base ligand bearing 3-(3 -
pyridyl)-4-amino-5-mercapto-1,2,4-triazole were synthe-
sized. The investigated compounds were fully character-
ized using spectral methods and thermal and magnetic
studies. Based on spectral results, octahedral geometries
were suggested for complexes 2, 11, and 12, and SP
geometries for 5–8 and 10. By contrast, complexes 1 and
3, 4, and 9 adopt a TBP, tetrahedral, and square planar
geometrical structure, respectively. The ligand acts as a
neutral and monobasic tridentate moiety, and coordi-
nates to the metal ion through NOS donors in com-
plexes 1–6, 10–12, and (9), respectively. By contrast, in
complexes 7 and 8 the ligand behaves as a neutral bid-
entate, chelating to the Cu(II) ion though NO donors.
The ESR spectrum of copper(II) complex 10 is axial in
[81]
activity of molecules,
which indicates a higher biologi-
cal activity of the studied complexes compared with the
ligand.
3.9 | Antibacterial studies
The bactericidal activities of Schiff base (HL) and its
metal complexes 1, 2, 4, 5, 11, and 12 were investigated
using the agar plate technique on pathogenic bacteria
and the data are listed in Table 11. The listed results
show that the HL ligand has moderate sensitivity toward
S. pyogenes than E. coli. Besides, metal complexes are
observed to inhibit the investigated bacteria at different
rates. These results revealed that the metal complexes
have good inhibitory zones ranging from 7.0 to 25.0 mm
for S. pyogenes (Gram positive). The biological activity
has the following order: (12) (11) (1) (4) (2) (5).
2
nature with hyperfine splitting with B1g as a ground state.
Complexes 7 and 8 undergo distortion around the
Cu(II) center affording rhombic ESR spectra. The thermal
studies revealed different types of crystallized solvents
attached to the chelates. DFT calculations support the

TRANSITION METAL COMPLEXES OF NEW SCHIFF BASE LIGAND
25 of 26
experimental characterization of the ligand structure and
its complexes. The antimicrobial screening assay of the
compounds revealed higher activity of the metal com-
plexes than the ligand (HL) toward S. pyogenes and E. coli.
[24] R. Zhang, Q. Wang, Q. Li, C. Maa, Inorg. Chim. Acta 2009,
3
62, 2762.
25] A. K. Singh, O. P. Pandey, S. K. Sengupta, Spectrochim. Acta A
012, 85, 1.
26] K. Singh, M. S. Barwa, P. Tyagi, Eur. J. Med. Chem. 2006,
1, 147.
27] G. B. Bagihalli, P. G. Avaji, S. A. Patil, P. S. Badami, Eur.
J. Med. Chem. 2008, 43, 2639.
28] K. Singh, Y. Kumar, P. Puri, M. Kumar, C. Sharma, Eur.
J. Med. Chem. 2012, 52, 313.
[
[
[
[
2
4
ORCID
Dina A. Tolan https://orcid.org/0000-0003-3917-2822
Ahmed M. El-Nahas https://orcid.org/0000-0002-8547-
7
574
[29] 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
REFERENCES
1978.
[
[
[
[
[
[
[
[
[
1] S. Banerjee, S. Ganguly, K. K. Sen, J. Adv. Pharm. Edu. Res.
[
[
30] J. Lewis, R. G. Wilkins, Modern Coordination Chemistry, Inter-
science, New York 1960 403.
31] P. Tgagi, S. Chandra, B. S. Saraswat, D. Yadav, Spectrochim.
Acta A 2015, 145, 155.
2
013, 3, 102.
2] S. U. Cicekli, T. Onkol, S. Ozgen, M. F. Sahin, Rev. Roum.
Chim. 2012, 57, 187.
3] A. M. Hammam, M. A. EL-Gahami, Z. A. Khafagi, M. S. AL-
Sadimi, S. A. Ibrahim, J. Mater. Environ. Sci. 2015, 6, 1596.
4] H. Khanmohammadi, M. H. Abnosib, A. Hosseinzadeh,
M. Erfantalab, Spectrochim. Acta A 2008, 71, 1474.
[
[
32] Y. Zasshi, J. Pharm. Soc. Japan 1956, 76, 167.
33] S. O. Oyedemi, A. J. Afolayan, Asian Pac. J. Trop. Med. 2011,
4
, 952.
[
[
[
34] A. A. Abdulkarem, J. Biophys. Chem. 2017, 8, 13.
5] V. Reddy, N. Patil, T. Reddy, S. D. Angadi, Oriental J. Chem.
35] I. P. Ejidike, P. A. Ajibade, Bioinorg. Chem. Appl. 2015, 2015, 1.
36] R. G. Parr, W. Yang, Density-Functional Theory of Atoms
and Molecules, Oxford University Press, New York, Oxford
2
008, 24, 201.
6] H. Khanmohammadi, M. Erfantalab, G. Azimi, Spectrochim.
Acta A 2013, 105, 338.
1989.
7] S. A. Patil, M. Manjunatha, A. D. Kulkarni, P. S. Badami,
Complex Metals 2014, 1, 128.
[37] T. Ziegler, Chem. Rev. 1991, 91, 651.
[
38] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski,
J. A. Montgomery Jr., R. E. Stratmann, J. C. Burant,
S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin,
M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi,
R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford,
J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui,
K. Morokuma, P. Salvador, J. J. Dannenberg, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski,
J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox,
T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon,
E. S. Replogle, J. A. Pople, Gaussian 98, Gaussian, Inc, Pitts-
burgh, PA 1998.
8] P. G. Avajiy, S. A. Patil, P. S. Badami, J. Coord. Chem. 2008, 61,
1
884.
9] V. Reddy, N. Patil, T. Reddy, S. D. Angadi, E J. Chem. 2006,
, 529.
5
[
[
[
10] K. Singh, Y. Kumar, P. Puri, C. Sharma, K. R. Aneja, Phospho-
rus, Sulfur Silicon Relat. Elem. 2012, 187, 1498.
11] B. Namratha, L. Santosh, Gaonkar, Int. J. Pharm. Pharm. Sci.
2
014, 6, 73.
12] I. M. El-Deen, A. F. Shoair, M. A. El-Bindary, J. Mol. Liq. 2018,
49, 533.
2
[
13] S. El-Metwally, A. K. Khalil, Acta Chim. Slov. 2010, 57, 941.
14] A. M. Farghaly, A. A. Hozzaa, M. S. Abouzeit-Har,
F. M. Sharabi, Pharmazie 1980, 35, 596.
[
[
15] S. Manfredini, C. B. Vicentini, M. Manfrini, N. Bianchi,
C. Rutigliano, C. Mischiati, R. Gambari, Bioorg. Med. Chem.
2
000, 8, 2343.
16] Y. Li, Y. Liu, H. Wang, X. Xiong, P. Wei, F. Li, Molecules 2013,
8, 877.
[39] A. D. Becke, J. Chem. Phys. 1993, 98, 5648.
[40] C. Lee, W. Yang, R. G. Parr, Phys. Rev. 1988, 37, 785.
[41] P. J. Stephens, F. J. Devlin, C. Chabalowski, M. J. Frisch,
J. Phys. Chem. 1994, 98, 11623.
[42] G. A. Zhurko, D. A. Zhurko, ChemCraft version 1.7 (build
132), http://www.chemcraftprog.com.
[43] S. Saikat, N. S. Kumar, C. A. Prasun, D. Kamalendu, Ind.
J. Sci. 2015, 12, 17.
[44] S. A. AbouEl-Enein, S. M. Emam, M. W. Polis, E. M. Emara,
J. Mol. Struct. 2015, 1099, 567.
[
[
[
[
[
1
17] T. Rosu, S. Pasculescu, V. Lazar, C. Chifiriuc, R. Cernat, Mole-
cules 2006, 11, 904.
18] G. Turhan-Zitouni, M. Sivaci, F. S. Kilic, K. Erol, Eur. J. Med.
Chem. 2001, 36, 685.
19] M. Manjunath, A. D. Kulkarni, G. B. Bagihalli, S. Malladi,
S. A. Patil, J. Mol. Struct. 2017, 1127, 314.
20] S. M. Emam, S. A. Abouel-Enein, F. I. Abouzayed, Appl.
Organomet. Chem. 2017, 4073, 1.
[45] I. Ledeti, A. Alexa, V. Bercean, G. Vlase, T. Vlase, L.-M. Suta,
A. Fulias, Int. J. Mol. Sci. 2015, 16, 1711.
[46] S. M. Emam, I. E.-T. El Sayed, M. I. Ayad, H. M. R. Hathout,
J. Mol. Struct. 2017, 1146, 600.
[
[
21] S. Chandra, L. K. Gupta, Spectrochim. Acta A 2005, 61, 269.
22] R. J. R. Sorenson (Ed), Biology of Copper Complexes, Human
Press, Clifton, NJ 1987.
[
23] J. Joseph, K. Nagashri, G. A. B. Rani, J. Saudi, Chem. Soc.
[47] N. Upmanyu, J. K. Gupta, K. Shah, P. Mishra, J. Pharm. Bio-
allied Sci. 2011, 3, 259.
2
013, 17, 285.

26 of 26
EMAM ET AL.
[
[
[
[
48] S. M. Emam, S. A. AbouEl-Enein, E. M. Emara, J. Therm.
Anal. Calorim. 2017, 127, 1611.
49] S. M. Emam, S. A. AbouEl-Enein, E. M. Abdel-Satar, Appl.
Organomet. Chem. 2019, 33, 1.
[68] A. F. Shoair, A. A. El-Bindary, N. A. El-Ghamaz, G. N. Rezk,
J. Mol. Liq. 2018, 269, 619.
[69] H. A. El-Boraey, J. Therm. Anal. Calorim. 2005, 81, 339.
[70] S. M. Emam, J. Mol. Struct. 2017, 1134, 444.
[71] E.-S. A. El-Samanody, S. A. AbouEl-Enein, E. M. Emara, Appl.
Organomet. Chem. 2018, 33, 1.
[72] A. M. Donia, Thermochim. Acta 1998, 320, 187.
[73] H. A. El-Boraey, F. A. El-Saied, S. A. Aly, J. Therm. Anal.
Calorim. 2009, 96, 599.
[74] F. A. El-Saied, S. A. AbouEl-Enein, S. M. Emam, H. A. El-
Shater, Polish J. Chem. 2009, 83, 1871.
50] A. Jha, Y. Murty, G. Durga, Res. J. Pharm. Bio. Chem. Sci.
2
015, 6, 1306.
51] R. D. Hunashal, P. M. Ronad, V. S. Maddi, D. Satyanarayana,
M. A. Kamadod, Arabian J. Chem. 2014, 7, 1070.
[
[
52] R. V. Gadag, M. R. Gajendragad, Talanta 1978, 25, 418.
53] C. N. R. Rao, R. Venkataraghavan, T. R. Kasturi, Can. J. Chem.
1
964, 42, 36.
54] X.-X. Ye, Z.-F. Chen, A.-J. Zhang, L.-X. Zhang, Molecules 2007,
2, 1202.
[
[
[
[75] T. Rosu, M. Negoiu, S. Pasculescu, E. Pahontu, D. Poirier,
A. Gulea, Eur. J. Med. Chem. 2010, 45, 774.
1
55] K. Singh, P. Puri, Y. Kumar, C. Sharma, K. R. Aneja, Bioinorg.
Chem. Appl. 2011, 2011, 1.
56] A. Szorcsik, L. Nagy, J. Sletten, G. Szalontai, E. Kamu,
T. Fiore, L. Pellerito, E. Kalman, J. Organomet. Chem. 2004,
[76] B. J. Hathaway, D. E. Billing, Coord. Chem. Rev. 1970, 6, 143.
[77] R. G. Pearson, J. Chem. Sci. 2005, 117, 369.
[78] S. Kaya, C. Kaya, Mol. Phys. 2015, 113, 1311.
[79] B. J. Hathaway, G. Wilkinson, R. Gillard, J. McCleverty, Com-
prehensive Coordination Chemistry, Vol. 5, Pergamon, Oxford
1987.
6
89, 1145.
57] V. C. Wei, L. Y. Tuan, L. D. Zheng, Chin. J. Chem. 2000,
8, 351.
58] B. S. Grag, D. N. Kumar, M. Sarbhai, Spectrochim. Acta A
005, 61, 141.
[
[
1
[80] C. K. Kim, K. A. Lee, C. K. Kim, B.-S. Lee, H. W. Lee, Chem.
Phys. Lett. 2004, 391, 321.
2
[81] R. Parthasarathi, V. Subramanian, D. R. Royb,
P. K. Chattarajb, Bioorg. Med. Chem. 2004, 12, 5533.
[82] B. G. Tweedy, Phytopathology 1964, 55, 910.
[83] S. I. Al-Resayes, M. Shakir, N. Shahid, M. Azam, A. U. Khan,
Arab. J. Chem. 2016, 9, 335.
[
[
[
59] M. S. Nair, R. S. Joseyphus, Spectrochim. Acta A 2008, 70, 749.
60] V. P. Singh, Spectrochim. Acta A 2008, 71, 17.
61] H. A. Sahyon, A. A. El-Bindary, A. F. Shoair, A. A. Abdellatif,
J. Mol. Liq. 2018, 255, 122.
[
62] R. K. Dani, M. K. Bharty, S. Paswan, S. Singh, N. K. Singh,
Inorg. Chim. Acta 2014, 421, 519.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
[
63] R. K. Mali, R. R. Somani, M. P. Toraskar, K. K. Mali,
P. P. Naik, P. Y. Shirodkar, Inter. J. Chem. Tech Res. 2009,
1, 168.
[
[
64] S. M. Emam, S. A. AbouEl-Enein, S. M. El-Seady, J. Chin.
Chem. Soc. 2017, 64, 261.
65] a) N. Kavitha, P. V. A. Lakshmi, J. Saudi Chem. Soc. 2017, 21,
S457; b) A. P. Mishra, R. K. Jain, J. Saudi Chem. Soc. 2014,
How to cite this article: Emam SM, Tolan DA,
El-Nahas AM. Synthesis, structural, spectroscopic,
and thermal studies of some transition-metal
complexes of a ligand containing the amino
mercapto triazole moiety. Appl Organometal Chem.
1
8, 814.
[
[
66] A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier,
Amsterdam 1968.
67] S. M. Emam, T. El Sayed, N. Nassar, Spectrochim. Acta A 2015,
1
38, 942.
2020;e5591. https://doi.org/10.1002/aoc.5591