Synthesis, spectroscopic characterization, DFT and antibacterial studies of newly synthesized cobalt(II, III), nickel(II) and copper(II) complexes with salicylaldehyde N(4)-antipyrinylthiosemicarbazone

Article abstract of DOI:10.1016/j.ica.2018.08.013

Salicylaldehyde N(4)-antipyrinylthiosemicarbazone (H₂L) and its complexes of Co(III, II), Ni(II) and Cu(II) have been prepared and characterized. Elemental analyses, molar conductivities, magnetic measurements, spectral (IR, UV–vis, ¹H and ¹³C NMR and ESR) and thermogravimetric studies have been used to characterize the complexes. The infrared spectra show that the thiosemicarbazone ligand behaves as tridentate ligand (ONS), either in the thione or thiolato form. Stereochemistries are proposed for the complexes on the basis of both spectral and magnetic properties. Along with the experimental spectral data of the starting ligand, its corresponding predicted ones were obtained using the state of art density functional theory (DFT) in gas and solvent phases. The obtained results showed a relatively good correlation between the calculated and experimental spectral data. Some of the complexes showed antibacterial activity against Staphylococcus aureus and Escherichia coli representing Gram-positive and Gram-negative bacteria respectively when compared with Enrofloxacin as a standard antibiotic.

Full text of DOI:10.1016/j.ica.2018.08.013

Accepted Manuscript
Research paper
Synthesis, spectroscopic characterization, DFT and antibacterial studies of new-
ly synthesized cobalt(II, III), nickel(II) and copper(II) complexes with Salicy-
laldehyde N(4)-antipyrinylthiosemicarbazone
Ayman K. El-Sawaf, Maged A. Azzam, Amr M. Abdou, El Hassane Anouar
PII:
S0020-1693(18)30824-7
https://doi.org/10.1016/j.ica.2018.08.013
ICA 18413
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
28 May 2018
11 August 2018
12 August 2018
Please cite this article as: A.K. El-Sawaf, M.A. Azzam, A.M. Abdou, E.H. Anouar, Synthesis, spectroscopic
characterization, DFT and antibacterial studies of newly synthesized cobalt(II, III), nickel(II) and copper(II)
complexes with Salicylaldehyde N(4)-antipyrinylthiosemicarbazone, Inorganica Chimica Acta (2018), doi: https://
doi.org/10.1016/j.ica.2018.08.013
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis, spectroscopic characterization, DFT and antibacterial studies of newly
synthesized cobalt(II, III), nickel(II) and copper(II) complexes with Salicylaldehyde N(4)-
antipyrinylthiosemicarbazone
Ayman K. El-Sawaf,a,b,* Maged A. Azzam, a,b Amr M. Abdou, El Hassane Anouar
c
b,*
a
Department of Chemistry, Faculty of Science, Menoufia university, Shebin El-Kom, Egypt.
Department of Chemistry, College of Science and Humanities, Prince Sattam Bin Abdulaziz
b
university, BP 830, Al Kharj, Saudi Arabia.
c
Department of Microbiology and Immunology, National Research Centre 12622 Dokki, Giza,
Egypt.
Corresponding author
Dr. Ayman K. El-Sawaf
E-mail: elsawaf2008@yahoo.com
Dr. El Hassane Anouar
E-mail: anouarelhassane@yahoo.fr
1

Abstract
Salicylaldehyde N(4)-antipyrinylthiosemicarbazone (H
2
L) and its complexes of Co(III, II),
Ni(II) and Cu(II) have been prepared and characterized. Elemental analyses, molar conductivities,
1
13
magnetic measurements, spectral (IR, UV-vis, H and C NMR and ESR) and thermogravimetric
studies have been used to characterize the complexes. The infrared spectra show that the
thiosemicarbazone ligand behaves as tridentate ligand (ONS), either in the thione or thiolato form.
Stereochemistries are proposed for the complexes on the basis of both spectral and magnetic
properties. Along with the experimental spectral data of the starting ligand, its corresponding
predicted ones were obtained using the state of art density functional theory (DFT) in gas and
solvent phases. The obtained results showed a relatively good correlation between the calculated
and experimental spectral data. Some of the complexes showed antibacterial activity against
Staphylococcus aureus and Escherichia coli representing Gram-positive and Gram-negative
bacteria respectively when compared with Enrofloxacin as a standard antibiotic.
Keywords: Salicylaldehyde N(4)-antipyrinylthiosemicarbazone; complexes; spectral methods;
thermal studies; DFT; antibacterial activity.
2

1
. Introduction
The chemistry of thiosemicarbazones has conventional extensive attention because of their
variable bonding manners, structural variety, ion-sensing capability [1, 2]. They are also known by
their various biological implications such as antibacterial, antimalarial, antiviral and antitumor
activities [3-5]. Thiosemicarbazones generally act as chelating agents with transition and non-
transition metal ions tie through sulfur and nitrogen atoms, although in rare cases they behave as
unidentate ligand with sulfur as the binding atom [6]. It was established that the dibasic tridentate
thiosemicarbazones with ONS donor atoms are of enormous importance as they have a extensive
variety of medicinal properties and can also offer dimetallic or polymeric species with uncommon
structural and magnetic properties [7]. Great work is done on the biological activities of metal
complexes of thiosemicarbazones [8-10]. The biological action of thiosemicarbazones is related to
its chelating capability with metal ions, connecting through nitrogen, nitrogen and sulfur or
oxygen, nitrogen and sulfur [11-13]. Previously, we have reported on the iron(III), cobalt(II, III),
nickel(II), copper(II) and zinc(II) complexes of N(4)-antipyrinylthiosemicarbazone of 4-
formylantipyrine and 2-formylpyridine [14, 15]. Recently, we have synthesized, characterized and
investigated in vitro antibacterial activities of some Schiff base metal complexes[16]. Many metal
complexes have potent antimicrobial activities and are already in common day-to-day use in
medical field [17].
In the present paper, we report the synthesis, characterization and investigation of
antibacterial activity of cobalt(II,III), nickel(II) and copper(II) complexes with salicylaldehyde
N(4)-antipyrinylthiosemicarbazone (H L). Furthermore, DFT and TD-DFT calculations have been
2
carried out in gas and polarizable continuum model phases at the B3LYP/LANL2DZ level of
theory to predict the electronic and optical properties of the starting material salicylaldehyde N(4)-
antipyrinylthiosemicarbazone.
3

2
. Materials and methods
2
.1. Reagents and instruments
All reagents and solvents were used as obtained from the suppliers or recrystallized as
necessary. Infrared spectra were recorded on a Nicolet FT-IR spectrophotometer in the range
-1
1
13
6
4
000-400 cm . The H and C NMR spectra were recorded in DMSO-d by using
tetramethylsilane (TMS) as the internal solvent on a Bruker-400 MHz instrument. The electron
paramagnetic resonance (EPR) spectra were recorded on a Varian E-109c spectrometer equipped
with a field modulation unit at 100 kHz. Measurements were effected in the X-band on a
microcrystalline powder at room temperature; the microwave power was around 10 mW. A Varian
Cary 5000 spectrophotometer was used to perform the absorption electronic spectra as
polycrystalline solid samples. Nujol mull electronic spectra were recorded on Whatman No.1 filter
paper and referenced against another filter paper saturated in mineral oil. The electronic spectra of
dimethylsulfoxide solutions of both the thiosemicarbazone ligand and its metal complexes were
recorded in 1 cm quartz cells and molar absorptivities were calculated using Beer's law. Molar
-3
conductivity measurements were made in DMF solution 10 M using a type CD6N Tacussel
conductimeter. The thermal analysis (TG) was carried out by using a Shimadzu DAT/TG-50
ο
thermal analyzer with a heating rate of 10 C/min under N
2
atmosphere from the room temperature
ο
up to 1000 C using platinum crucibles. Magnetic susceptibilities were measured at room
temperature by a modified Gouy method by using a Johnson Matthey magnetic susceptibility
balance. Diamagnetic corrections were calculated using Pascal’s constants. The effective magnetic
moments were calculated from the equation µeff =2.84(X corrt
T) . Melting points were measured
1/2
M
by using Stuart melting point apparatus. Biochemical measurements were carried out at The
Department of Parasitology and Animal Diseases, National Research Center, Dokki, Egypt.
4

2
.2. Synthesis of salicylaldehyde N(4)-antipyrinylthiosemicarbazone (H L)
2
The synthesis of N(4)-antipyrinylthiosemicarbazide was carried out in three steps (Scheme
), as previously reported [14].
1
Scheme 1. Synthesis steps of salicylaldehyde N(4)-antipyrinylthiosemicarbazone ligand (H L).
2
The new Schiff base salicylaldehyde N(4)-antipyrinylthiosemicarbazone (H
IV) by condensing N(4)-antipyrinylthiosemicarbazide with salicylaldehyde in the presence of few
drops of H SO to form a yellow product (Yield= 85% and m.p. 152 °C).
2
L) was prepared (step
2
4
2
.3. Synthesis of the metal complexes with H L
2
The metal complexes were prepared as follows: a solution of appropriate metal salt (3.15
3
mmol) in EtOH (30 cm ) was mixed with a solution of the organic ligand (1.2g, 3.15 mmol) in
3
EtOH (50 cm ) and the mixture was stirred under reflux for 2 hours. The resulting solids were
5

o
filtered, washed with anhydrous diethyl ether and placed on a warm plate (35 C) until required for
characterization.
2
.4. Theoretical calculations
Geometry optimization and frequency calculations of the stable conformers of
salicylaldehyde N(4)-antipyrinylthiosemicarbazone (H L) have been performed using DFT
2
method at the B3LYP/LanL2DZ level of theory[18]. The calculated vibrational modes were scaled
by a factor of 0.9679 [19]. The maximum electronic absorption bands, vertical electronic
excitations and oscillator strengths (f>0 for allowed transition) of the ligand salicylaldehyde N(4)-
antipyrinylthiosemicarbazone was calculated using TD-DFT method at the same level of theory
[
(
20, 21]. NMR magnetic isotropic shielding tensors () were predicted using the GIAO approach
Gauge-Independent Atomic Orbital) [22], using the above mentioned hybrid functionals. The
isotropic shielding values were used to calculate the isotropic chemical shifts  with respect to
tetramethylsilane (Si(CH ). iso(X) = TMS(X) – iso(X), where iso is isotropic chemical shift and
iso isotropic shielding constant. The predicted chemical shifts were obtained using the equation
exp=acal+b, where cal=iso. The theoretical calculation in solvent were obtained using polarisable
continuum model (PCM), in which the solute is embedded into a cavity surrounded by a dielectric
continuum solvent described by its dielectric constant (e.g., εCDCl = 4.7113) [23]. The PCM has
)
3 4


3
been reported to correctly model major solvent effects such as electrostatic effects of the medium
providing no specific solute-solvent interactions such as hydrogen bond interactions, dipole-dipole
interactions, or induced dipole-dipole interactions are considered [24]. Theoretical calculations
were performed using Gaussian09 package [25].
6

2
.5. Screening for the antibacterial activity
The bacterial cultures used in this study were Staphylococcus aureus as representative for
Gram-positive bacteria and Escherichia coli as representative for Gram-negative bacteria. The test
organisms were kindly provided by The Department of Parasitology and Animal Diseases,
National Research Center, Dokki, Egypt. The test organisms were maintained on agar slant at 4 °C
and subcultured on a fresh agar plates. For disc diffusion assay, bacterial liquid cultures were
initiated by placing a loop of bacteria from the slant into 10 ml of lysogeny broth (LB) media.
Agar diffusion test was conducted to detect the bacterial susceptibility to the prepared compounds
[
26]. A volume of 100 μL of cell culture suspension matching with 0.5 Mc-Farland of each test
organism were spread onto the surface of solid agar medium (Muller Hinton agar). The prepared
compounds were adjusted to a concentration of 50 mg/mL using DMSO as solvent. Filter paper
discs with a diameter of 7 mm each were impregnated with 15 μL of each of the different
compounds. Then the agar plates containing microorganisms, soaked with paper discs (5 μg) were
incubated at 37 ± 0.1 °C for 24 h. The inhibition of bacterial growth was evaluated by measuring
the diameter (cm) of the clear zone around each disc. Enrofloxacin antibiotic discs were used as
positive control. Filter paper discs impregnated with 15 μL of DMSO were also used as control for
the solvent.
3
. Results and discussion
3
.1. Elementary analyses
The stoichiometries of the salicylaldehyde N(4)-antipyrinylthiosemicarbazone (H
2
L) and
its complexes are shown Table 1. Complexes of the monobasic ligand (i.e., loss of OH proton) are
formed with the chlorides of cobalt(II) and nickel(II), cobalt(II) nitrate, Cu(II) acetate and Cu(II)
perchlorate. Complexes of the dibasic ligand (i.e., loss of OH and N(2)H protons) are formed on
complexation with cobalt(II) acetate. In addition [Co(HL)(L)] was isolated with a combination of
mono and dibasic ligands. All complexes obtained are stable to air and moisture and are
7

appreciably soluble in DMF and DMSO. The colors, partial elemental analysis, molar
conductivities and magnetic susceptibilities of the metal complexes are shown in Table 1. The
green, brown, red and blue colors are common to complexes involving thiosmeicarbazone
coordination owing to the sulfur to metal charge transfer bands, which dictate their visible spectra
[
27]. The values of 
m
showed in Table 1, indicated that all the metal complexes have
conductivity values lie in the range characteristics for the non-electrolytic performance of these
complexes due to lack of counter ions in the suggested structures of these complexes [28]. The
fairly higher values detected for the chloro complexes may due to partial decomposition of these
complexes in solution with the DMF solvent molecules relocating the halo ligands [15].
8

Table 1
Colors, partial elemental analyses, molar conductivities and magnetic susceptibilities of the metal complexes of salicylaldehyde N(4)-
antipyrinylthiosemicarbazone.
Found (Calcd. %)
F.W.
Color
M. p.
(ᵒC)
a
μ(B.M.)
No
Chemical formula
Λ
M
C
H
N
M
Cl
3
81.461
60.21
4.97
18.18
-
-
-
-
-
-
-
-
-
-
H
2
L C19
H
19
N
5
O
2
S
152
198
142
170
210
175
240
205
-
-
-
Pale yellow
818.828
Dark brown
546.501
Brown
932.95
Brown red
531.15
Yellow
519.207
Buff
547.012
Dark brown
543.581
Dark brown
575.495
Green
(59.82) (5.02) (18.36)
55.23 4.62 17.62
(55.74) (4.31) (17.11)
41.88 4.73 12.38
(41.76) (5.35) (12.82)
50.96 4.78 15.63
(50.21) (5.29) (15.01)
44.87 5.01 13.31
(44.09) (4.65) (13.19)
43.46 4.88 13.67
(43.95) (5.05) (13.49)
42.24 3.72 12.87
(41.72) (4.66) (12.80)
46.27 4.89 13.79
(46.40) (4.73) (12.88)
42.08 4.11 11.89
(41.74) (3.85) (12.17)
[
C
[
C
[
C
[
C
Co(HL)(L)]
SCo
O)].5H
SCo
].5H O.0.5EtOH
Co
Ni(HL)Cl].2.5H O. 0.25 EtOH
7.32
1
2
3
4
5
6
7
8
9.3
0.0
19
H
29
N
5
O
8
(7.20)
10.07
(10.78)
6.53
(6.32)
10.85
Co(L)(H
19
2
2
O
10.4
8.7
1.97
4.82
2.21
0.0
H
29
N
5
O
8
Co(HL)
39
2
2
H
49
N
10
O
9.5
S
2
2
6.85
11.7
10.9
14.3
12.7
12.4
19.5
H
24.5
N
5
O
4.75SNiCl
(11.05) (6.67)
[
Ni(L)H
2
O].3.5H
5
2
O
11.21
(11.30)
11.83
-
-
C
19
H
26
N O6.5SNi
[
C
[
C
Cu(HL)Cl].3.75H
19
2
O
6.34
1.78
1.70
1.73
H
25.5
N
5
O
5.75SCuCl
3
(11.17) (6.48)
Cu(HL)(CH
21
COO)].2.25H
2
O
11.35
(11.69)
11.67
-
-
-
-
H
25.5
N O6.25SCu
5
[
Cu(HL)(ClO
SCuCl
a10 M in DMF and expressed as Ω cm mol
4
)].0.5H
2
O. 0. 5 EtOH
C
20
H
22
N
5
O
7
(11.04)
-3
-1
2
-1
9

1
13
3
.2. H and C NMR spectra
To get an insight into the demonstrated ligand structure (H L, Fig. 1), its calculated and
2
1
13
6
experimental H and C NMR chemical shifts in DMSO-d have been carried out and approves its
preparation (Table 2). The absence of a signal from thiol –SH (Fig. 2) which would be expected
around 4 ppm,[29] strongly confirms the presence of the ligand thione form. The spectrum shows
the phenolic OH proton at δ (p.p.m.) = 11.83 (s, 1H, O-H), suggesting intramolecular hydrogen
bonding to N(1)[30] the N(2)H at δ (p.p.m.) = 9.95 (s, 1H, N(2)H), the N(4)H at δ (p.p.m.) = 9.32
(
s, 1H, N(4)H). The spectrum also shows the formyl proton, CH=N at δ (p.p.m.) = 8.48 (s, 1H, C-
H). The other resonances in the spectrum of the ligand are at δ (p.p.m.) = 7.34-7.23 (m, 5H)
corresponding to the phenyl protons, δ (p.p.m.) = 3.40 (s, 3H, N-CH ) and δ (p.p.m.) = 2.51 (s,
H, C-CH ) corresponding to N-CH and C-CH of the antipyrinyl moiety, respectively. Signals
3
3
3
3
3
for aromatic protons are found as multiplets in the 8.08-6.83 ppm range[31]. Somehow, the
1
experimental H NMR chemical shifts are well produced, mainly those bonded to carbon atom.
For instance, the experimental and calculated chemical shifts of H8 are 8.47 and 8.48 ppm,
respectively. The 13C NMR spectrum exposed the presence of anticipated number of signals
related to different types of carbon atoms present in the compounds (Table 1 and Fig. 3). The
signals observed at 178.55 and 162.85 ppm ppm are due to C=S and C=O of the pyrazolone ring,
respectively. The spectrum of the ligand shows a strong signal at δ 157.03 ppm due to C=N group.
1
3
Similarly, the calculated C chemical shift are relatively in agreement with the observed ones. For
instance, a variation of about 0.51 ppm is obtained between the experimental and calculated
chemical shifts of C8 (Table 2).
1
0

Fig. 1. The optimized structures of the stable conformers of ligand (H L) obtained at the
2
B3LYP/LANL2DZ level of theory.
1
1

Table 2
Calculated and experimental H and C NMR chemical shifts (ppm) of salicylaldehyde N(4)-
antipyrinylthiosemicarbazone (H
L) in DMSO-d6.
1
13
2
Calculated
Experimental
1H-NMR
H1
7.79
8.07
7.68
7.88
7.88
8.47
8.19
5.94
2.23
7.61
8.21
8.16
8.19
8.09
3.46
H2
H3
H4
7
.34-7.23
H7 (OH)
H8
H10 (NH)
H13 (NH)
H19
11.83
8.48
9.95
9.32
2.51
H22
H23
H24
H25
8.08-6.83
3.4
H26
H27
C-NMR
C1
1
3
122.48
137.02
124.78
137.83
120.74
165.76
157.54
199.22
109.80
169.20
159.23
15.54
139.22
129.19
134.12
132.20
133.88
132.50
41.01
116.55
110.28
116.55
120.78
140.33
129.56
157.03
178.55
154.94
162.85
162.85
140.33
11.68
135.79
-
129.56
127.32
126.57
123.83
C2
C3
C4
C5
C6
C8
C11
C14
C15
C18
C19
C21
C22
C23
C24
C25
C26
C27
1
2

1
Fig. 2 H NMR spectrum of the ligand H L
2
1
3
Fig. 3 C NMR spectrum of the ligand H L
2
1
3

Consistent with its loss on complexation, the signals due to phenolic OH and N(2)H protons are
1
absent in the H NMR spectra of the Co(III), complex (1), and square planar Ni(II), complex (5),
(Figs. S1 and S2). The spectra of these complexes features the N(4)H peak shifted slightly
downfield compared to the free ligand because of coordination of the thiol sulfur resulting in
reduced electron density at N(4) position [32] (δ = 9.32 to 9.56 and 9.59 for complexes 1 and 5
respectively). Also, the formyl proton, CH=N, shfits downfield from δ = 8.48 to 8.78 and 8.62 for
complexes 1 and 5 respectively due to coordination of the azomethine nitrogen and indicating that
the metal centers has drawn considerable electron density from the azomethine group as has been
noticed previously [33].
3
.3. Infrared spectra
The main experimental infrared spectral data of the free thiosemicarbazone ligand (H
2
L)
and its metal complexes with cobalt(II, III), nickel(II) and copper(II) are presented in Table 3 and
-1
shown in Fig. S3. The absence of any band in 2500-2000 cm region which is due to ν(S-H) in the
spectra of the complexes indicates that the ligand exists mainly in the thione form[34]. It has been
recognized that the salicylaldehyde thiosemicarbazone of complexes 2, 4, 6, 7 and 8 act as
monodeprotonated tridentate ligand and are coordinated to the central ions via deprotonated
phenolic oxygen, azomethinic nitrogen and sulfur atom creating five and six membered
-1
metalocycles [12, 35]. The spectrum of the free ligand shows a broad band at 3430 cm related to
phenolic group ν(OH). This band disappeared from the IR spectra of all complexes. Additionally,
this is confirmed by the shift of ν(C-O) stretching vibration bands observed in the range of 1210-
-1
1
150 cm in the spectra of the complexes. This is further confirmed by the presence of the band
-1
looking in the region 490-450 cm assigned to the ν(M-O) frequency [36]. The medium intensity
-1
band at 1610 cm in the spectrum of the free ligand has been assigned to ν[(C(7)=N(1)]. Its
-1
corresponding scaled value obtained at B3LYP level of theory is appeared at 1589 cm with a
-1
-
variation of 21 cm to the experimental value. This band shifts to lower wavenumbers by 5-15 cm
1
in the spectra of the complexes, indicating bonding to the azomethine nitrogen in coordination
[
37]. In addition, the ν(C=N) mode may be joined with ν(C=S) to give the intense band detected at
1
4

-1
1
360 cm [38], and the lower frequency shift of this band in the spectra of the complexes supports
-1
coordination of the azomethine nitrogen. The band at 950 cm in the spectrum of H L attributed to
2
ν(N-N) endures a positive shift in all complexes which is owing to the increase in double bond
character off-setting the loss of electron density through donation to the metal ion. This confirms
the coordination of the azomethine nitrogen to the metal ions [39]. The appearance of a ν(M-N)
-1
-1
band at 530-485 cm provides further support for the nitrogen donor [40]. The band at 1360 cm
in the H L spectrum, which has ν(C=S) character, disappears in the spectrum of complex 5,
Ni(L)H O], due to the alteration in the nature of NH-C(=S)-N to N=C(-S)-N on
2
[
2
-1
complexation[41]. The high intensity band at 860 cm in the spectrum of the thiosemicarbazone
ligand, due to the thioamide IV band, which has a substantial contribution from ν(CS), shifts to ca.
-1
-1
8
00 cm for complexes with the monobasic ligand and at 755 cm for the dibasic ligand,
representing coordination of the thione/thiolato sulfur atom [42]. As is expected, larger decreases
in the thioamide IV band occur for dibasic form of the ligand due to C-S formally becoming a
-1
single bond[43]. In addition, a band at ca. 420 cm is due to ν(MS), which approves coordination
of the thione/thiolato sulfur [44]. The presence of the water molecule in the coordination sphere of
complexes 2 and 5 is reinforced by the occurrence of bands at ca. 3600, ca. 1580, 980 and ca. 630
-1
cm owing to ν(OH), (H
2
O), rock(H
2
O) and wagg(H O), respectively [45]. The last two modes
2
are absent from the spectra of the rest of the isolated complexes with water molecules,
representing hydrate rather than coordinated water [46]. The acetato group in complex (7) acts as a
-1
unidentate ligand based on the appearance of two new bands at 1610 and 1330 cm , which are
assignable to ν (CO ) and ν (CO ), respectively [47]. Further, the complex exhibits (COO) at 760
cm , which is considered indicative for unidentate acetate ligands[48]. The spectrum of the
perchlorate complex, [Cu(HL)(ClO )], (Fig. 4) shows bands at 1107 (ν ), 910 (ν ), 630 (ν ) and
) cm , suggesting the monodentate coordination of perchlorate ion to copper ion[49].
a
2
s
2
-1
4
3
1
4
-1
4
90 (ν
2
1
5

Table 3
Selected IR band assignments of the ligand (H L) and its metal complexes.
2

(C-O)
No.
Ligand/complex
[N(2)H] (C=N)
1610(m)
(N-N)
(C-S)
(M-N)
(M-O)
(M-S)
phenolic
H
2
L
1250(s)
950(m)
860(m)
--
--
--
3
190(br)
[Co(HL)(L)]
[Co(L)(H O)].0.5 H
[Co(HL) ].5H O.0.5EtOH
[Ni(HL)Cl].2H
[Ni(L)H O].3.5H
[Cu(HL)Cl].3.75H
[Cu(HL)(CH COO)].2.25H2
Cu(HL)(ClO )].0.5H O. 0. 5
EtOH
3110(s)
3135(s)
3130(m)
1
1
600(m) 1170(m)
602(m) 1175(w)
980(s)
1000(s)
959(m)
950(s)
995(s)
760(m)
745(s)
810(w)
825(w)
755(s)
500(m)
485(m
515(m
495(w)
520(m)
530(m)
490(w)
485(sh)
470(w)
490(sh)
460(w)
465(s)
435(w)
420(s)
1
2
3
4
5
6
7
2
2
O
1
595(w) 1180(w)
600(m) 1210(w)
135(m) 1600(w) 1180(m)
445(s)
2
2
1
435(w)
415(sh)
405(w)
420(w)
2
O. 0.25 EtOH 3050(w)
2
2
O
3
3
110(w)
1604(s)
1599(s)
1150(w) 1035(w) 835(w)
200(m) 1090(w) 850(w)
1105(s) 820(w)
490(s)
2
O
1
450(w)
3
3233(w)
[
4
2
8
3220(w) 1605(w) 1205(m)
490(s)
460(w)
435(w)
1
6

3
.4. Magnetic susceptibilities and Electronic spectra
The electronic absorption spectra are frequently very helpful in the estimation of results provided
by other methods of structural analysis. The tentative assignments of the major electronic spectral
bands of ligand and its metal ion complexes in solid state are shown in Table 4. Omitted from
-1
Table 4 are the higher energy π→π* transitions at ca. 37000 cm (270 nm), of the free ligand H L,
2
which are slightly shifted upon the complexation of free ligand with the tilted metals. The shift of
the π→π* bands to lower energy in complexes is the result of the C=S bond being faded and the
conjugation system enhanced on complexation[50]. The n→π* transition associated with the
-1
phenol function at 31710 cm (315 nm) in the ligand spectrum generally shifts to higher energy by
-1
ca. 800 cm (324 nm) in the spectra of the complexes [51]. The second n→π* band, which
-1
appears at 29670 cm (337 nm) in the uncomplexed thiosemicarbazone spectrum, merges with the
first n→π* band in the spectra of some of complexes (Fig. 4). The corresponding calculated λmax
(
nm) of the second n→π* (HOMO-1 → LUMO) band for both stable conformers of the ligand
L in gas and solvent phases at the B3LYP/LANL2DZ level of theory are presented in Table 5.
The results clearly show the strong effect of the solvent, which induces an hypsochromic shift of
max. This shift is mainly due to the solute-solvent interaction, which stabilizes the HOMO-1 and
H
2
λ
LUMO orbitals by 0.72 and 0.28 eV, respectively. The experimental λmax is well produce with the
chose methodology, with a variation less the 2 nm compared to the experimental value. The choice
of methodology is in good settlement with our previous studies [52, 53]. The conformation has no
strong effect of λmax shift, which is less than 2 nm for the current conformers. This results is in
accordance with our previous studies [54].
1
7

Fig. 4 Solid state Nujol mull electronic absorption spectra of 1, 5, 7 and 8 complexes.
1
8

-1
Table 4 Solid state electronic spectra (cm ) of the ligand and its metal complexes
No. Compound Intraligand and charge transfer bands
d-d bands
3
1710, 29670
2680, 28010, 24200, 20450
2570, 28490, 25770
H L
2
3
16830, 13470, 10990
18050, 10710
1
2
3
4
5
6
7
8
[Co(HL)(L)]
[Co(L)(H O)].5H
[Co(HL) ].5H O.0.5EtOH
[Ni(HL)Cl].2.5H O. 0.25 EtOH
[Ni(L)H O].3.5H
[Cu(HL)Cl].3.75H
[Cu(HL)(CH COO)].2.25H
[Cu(HL)(ClO )].0.5H O. 0. 5 EtOH
3
2
2
O
3
3
3
3
3
3
2790, 28740, 26110, 23530
2840, 28250, 25840, 23470
2410, 28330, 26420, 22350
2410, 28410, 25670, 24300
3330, 28330, 25740, 23280
2950, 28330, 25710, 24450
18920, 14710, 11420
14490, 12000, 11420, 11010
16720, 16200
2
2
2
2
2
O
14340, 11010
2
O
11060
3
2
O
16960, 11050
4
2
Table 5 Calculated λmax (nm) of the stable conformers of the ligand H
2
L in gas and solvent phases at the B3LYP/LANL2DZ level of theory.
Calculated
Experimental
-1
max (cm-1)
λ
max (cm )
λmax (nm)
f
λ
λmax (nm)
Gas
Conf. 1
Conf. 1
657474
28458
353
351
0.36
0.35
2
9670
337
IEF-PCM
Conf. 1
Conf. 1
29435
29586
340
338
0.41
0.39
1
9

This band, which includes transitions inside the thiosemicarbazone moiety [mainly, C=N
and C=S groups], is of reduced intensity and shifts to higher energy on complexation. Two ligand-
-1
-1
to-metal charge transfer bands are found at 24000-27000 cm and 21000-25000 cm in the spectra
of the metal complexes (Fig. 4). In agreement with studies of previous thiosemicarbazone
complexes [55] , the higher energy band is assigned to S() → M(II, III) transitions [56]. The band
-1
in the 21000-25000 cm range is related to phenoxy O → M(II,III) transitions [57].
Co(HL)(L)] is diamagnetic, µeff = 0, confirming its oxidation to cobalt(III) during
[
preparation, which commonly occurs with heterocyclic thiosemicarbazones [14]. Assuming O
h
symmetry the assignments for the d → d bands are as follows: A1ɡ→1T1ɡ (υ
1
) 20450 cm , A1ɡ
-1 1
→
1
1T2ɡ (υ
) 24200 cm , A1ɡ → 3T1ɡ (υ
the ligand field parameters give D
nephelauxetic parameter, , indicates the significant covalent character for the metal-ligand -
bonds[55]. The brown [Co(L)(H O)].0.5H O complex shows a magnetic moment of 1.97 B.M.
suggesting a square planar cobalt(II) species with spin-orbit coupling [56]. The electronic
-1
1
) 6850 cm and A1ɡ → 3T2ɡ (υ
-1
1
) 16830 cm . Calculations of
-1
2
3
4
-
1
-1
q
= 2016 cm , B = 741 cm and  = 0.67 [51]. The value of the
2
2
-1
spectrum of this complex exhibits three bands at 9100, 9800 and 15820 cm . The first and third
bands may be assigned to A1ɡ→2E
2
and A1ɡ→ É2 transitions, respectively, assuming square
2
4
g
g
-1
planar geometry around Co(II). The band at 9800 cm is considered as characteristic band for
Co(II) in a square planar environment [51]. This band may be taken as equal to 15 B from which B
-1
is calculated as 653.3 cm . The calculated magnetic susceptibility for [Co(HL)
.82 B.M., which indicating a spin quartet cobalt(II) ground state and is in the range generally
accepted for octahedral structures [57]. The electronic absorption spectrum of this complex
2
].5H O.0.5EtOH is
2
4
-1
exhibits three bands at 15620, 18470 and 20950 cm . These bands are related to the transitions
4T1ɡ(F) → 4T2ɡ(F)( υ
); 4T1ɡ(F) → A2ɡ(F)( υ
4
) and 4T1ɡ(F) → 4T2ɡ(P)( υ
) respectively suggesting
1
2
3
an octahedral geometry [58].
2
0

The magnetic moment observed for the [Ni(HL)Cl].2H
2
O. 0.25 EtOH complex is 3.58 B.M
which is consistent with the tetrahedral stereochemistry of the complex [59] and the electronic
-1
-1
spectrum of the complex shows two bands at 9740 cm and 14490 cm which may be assigned to
3T
(F)→ A
3
(υ
2
) and 3T
(F)→3T
(F)→3T
(P) (υ
) transitions, respectively, for the tetrahedral
1
2
1
2
3
nickel(II)[55]. The transition 3T
(υ
) is expected to be in the range of 3000-5000 cm and
-1
1
2
1
-1
the theoretical calculation of this band is 4460 cm . The assigned energies were used to calculate
the following spectral parameters for [Ni(HL)Cl].2H O. 0.25 EtOH: Dq = 520, B = 717 and  =
.69. These values agree well with those reported for tetrahedral nickel(II) complexes [56].
At room temperature the, [Ni(L)H O].3.5H O, complex shows a diamagnetic performance which
shows the square planar situation around Ni(II) ion [60, 61]. The spectrum of this diamagnetic
2
0
2
2
-1
1
1
complex shows a band at 22350 cm due to a combination of A1ɡ→ B1g and S →Ni(II)
transitions and bands at 18850 and 16570 cm attributable to the 1A1ɡ→ A2g and A1ɡ→1E
-
1
1
1
g
transitions, consistent with square-planar geometry around the nickel(II) ion [48, 62]. The room
temperature magnetic moment of the solid copper (II) complexes 6,7 and 8 was found in the range
1
.70–1.78 BM, revealing one unpaired electron per Cu(II) [63] and the two low intensity bands for
-1
-1
copper(II) complexes are in the ranges 18600-17540 cm and 16240-14280 cm are consistent
with d → d transitions of square planar copper(II) complexes [17].
The solution electronic (DMSO) maxima of H
2
L and its metal complexes are presented in
Table S1. The Schiff base ligand and its metal complexes exhibit three absorption peaks at lower
-1
-1
energy region (˂ 40000 cm ). The stronger and higher energy peak (Fig. S4) at 38000 cm was
attributed to the π→π* transitions of the azomethine chromophore and the phenyl ring and is
nearly unshifted in the spectra of all complexes, while the weaker and less energetic peak at 29670
-1
cm is owing to the n→π* transition associated with the thione portion of the thiosemicarbazone
-1
moiety. The band at 32750 cm (log  = 4.21) in the spectrum of the organic ligand, H
2
L, is
assigned to the n→π* transition of the azomethine portion.
-1
The solution spectra of the complexes exhibit an intense transition in the range 33760-3462 cm (
log  = 4.36-4.61) owing to a n→π* transition of the azomethine portion of the thiosemicarbazone.
2
1

Also, the band associated with the n→π* transition of the thione portion of the thiosemicarbazone
moiety is shifted to higher energy in the spectra of all complexes and sometimes merges with the
n→π* transition of the azomethine portion of the thiosemicarbazone. Bands in the 23240-25530
-1
cm range are due to S →metal(II,III) and other ligand to metal charge transfer bands [63]. The
d→d spectra of the metal complexes show different energies in solution compared to the solid
state indicating significant interactions with the DMSO solvent.
3
.5. Thermal studies
The thermogravimetric data of the ligand and some of its metal complexes are given in
Table 6 and represented in Fig. 5. The thermogram of the ligand reveals that no detectable weight
ᵒ
ᵒ
loss within 25-155 C range indicating that the ligand exhibits thermal stability up to 155 C, which
is compatible with its measured melting point (Table 6). Also, the absence of any residual solvent
in the tested sample. After that the ligand starts its thermal decomposition through one well-
ᵒ
defined step at temperature range 155-420 C with weight loss 80.86% equivalent to removal of
ᵒ
C
13
H
19
N
5
O
2
S. This stage is associated with a sharp DTG peak at Tmax.=255 C. Indicating that the
ligand pyrolysis proceed fast in progressive nature [16]. The last stage involves a weight loss of
ᵒ
1
1.34% corresponding to complete ligand pyrolysis at temperature range 420-1000 C. The
complexes [Co(L)H
2
O].5H
2
O (2) and [Ni(L)H
2
O].3.5H O (5) are isostructural and the TG data
2
(Table 6) show similar thermal degradation patterns (isothermal behavior). The thermal behavior
for complex (2) will be presented as a model example (Scheme 2). The TG curve displayed weight
ᵒ
losses at temperature range 25-140 C corresponding to removal of five molecules of water. The
dehydration processes is followed by thermal decomposition stage associated with 40.02% TG
ᵒ
weight loss at 140-350 C range. This weight loss compatible with removal of C11
H
12
N
3
O fragment
ᵒ
and coordinated water molecule and characterized by DTG peaks at Tmax.=168 and 248 C
ᵒ
respectively. The final pyrolysis step demonstrated by a broad DTG peak at 770 C and by TG
ᵒ
weight loss of 28.42% up to 1000 C due to removal of C7.75
H
5
2
N S and leaving 14.20% of
CoO+0.25C as final residue. The proposed thermal degradation mechanism is shown in scheme 2.
The TG curve of the octahedral [Co(HL)
2
].5H O.0.5EtOH complex (3), showed weight losses at
2
ᵒ
ᵒ
temperature ranges 25-135 C and 137-175 C due to removal of 0.5 ethanol molecule and five
ᵒ
water molecules, respectively. The thermal decomposition begins at 175 C via a progressive stage
ᵒ
associated by 55.97% weight loss. This step is characterized by a sharp DTG peak at Tmax.=236 C
and corresponding to ligand pyrolysis (2C12
H
13
N
4
OS). The decomposition is continued within the
O. The
ᵒ
temperature range 390-1000 C with weight loss equivalent to removal of C13
H
10
N
2
2
2

thermogram
Cu(HL)(CH
of
[Ni(HL)Cl].2.5H
2
O.0.25EtOH
(4),
[Cu(HL)Cl].3.75H
2
O
(6)
and
[
3
COO)].2.25H
2
O (7) complexes establish that they are isothermal for all the three
ᵒ
complexes. The dehydration and/desolvation processes occur within range 25-250 C. The thermal
decomposition stage associated with 41.63, 41.32 and 44.92% TG weight losses at (210-450),
ᵒ
(
250-400) and (200-410 C) regions for (4), (6) and (7) respectively. The TG weight losses are
compatible with removal of (C11
H
11
N
2
O) fragment along with elimination of anions. Also, the
ᵒ
weight loss is continued in the range 450-1000 C leaving metal oxide and variable amount of
organic residue.
2
3

120
0
.46 mg
100
80
60
40
20
Ligand
0
0
200
400
600
800
1000
o
Temperature ( C)
1
20
120
100
80
0
.4 mg
0
.60 mg
100
8
0
60
60
40
40
20
20
2
3
0
0
0
0
200
400
600
800
1000
200
400
600
800
1000
o
o
Temperature ( C)
Temperature ( C)
1
20
00
120
1
.91mg
0
.89 mg
100
1
80
8
0
0
0
0
6
0
40
6
4
2
20
0
5
4
0
200
400
600
800
1000
0
200
400
600
800
1000
o
o
Temperature ( C)
Temperature ( C)
110
120
3
.12 mg
3
.3 mg
100
100
90
80
80
70
60
60
40
50
7
40
20
6
0
200
400
600
800
1000
30
o
0
200
400
600
800
1000
Temperature ( C)
o
Temperature ( C)
Fig. 5 Thermograms of ligand and its metal complexes (1-6)
2
4

Table 6 Thermal decomposition of the ligand and its metal complexes
Mass Loss %
ο
ο
No.
Compound
TG range ( C)
DTG peak ( C)
Assignments*
Found
Calcud.
2
5-155
-
-
-
-
1
4
55-420
20-1000
At 1000
5-140
40-350
255
80.86
11.34
7.69
16.15
41.79
81.10
11.81
7.08
16.48
41.13
19 5 2
Loss of C13H N O S
2
H L
Loss of 3.75 C
r
2.25 C
2
1
118
168
249
770
Loss of 5 H
O molecules a
2 12 3
Loss of (H O+C11H N O)
2
2
3
4
[Co(L)H
[Co(HL)
2
2
2
O].5H O
3
50-1000
At 1000
5-135
35-175
175-390
28.42
14.20
29.13
14.26
Loss of (C7.75
CoO+0.25C
H
5
N
2
S)
r
2
-
2.56
10.01
55.79
23.01
9.26
2.47
9.66
56.02
22.53
9.32
Loss of 0.5 EtOH molecule b
a
1
154
236
740
Loss of 5 H
Loss of 2(C12
2
O molecules
OS)
].5H
2
O.0.5EtOH
H
13
N
4
3
90-1000
Loss of (C13
CoO+C
Loss of (0.25 EtOH + 0.5 H
H
10
N
2
O)
r
At 1000
b
Oa)
)
2
5-100
00-210
210-500
-
4.42
7.33
3.86
6.78
2
a
1
200
260
680
Loss of 2 H
Loss of (C11H N
Loss of (C0.75
NiO+7.25C
2
O molecules
O + 0.5Cl
S)
[Ni(HL)Cl].2.5H
2
O.0.25EtOH
41.63
16.32
30.28
1.39
10.91
43.05
28.99
14.54
12.33
41.32
9.3
37.62
7.78
63.34
44.92
13.85
28.74
41.92
16.78
30.46
1.83
10.41
42.42
28.73
14.33
12.35
40.71
8.61
38.15
7.47
63.72
45.31
14.19
28.63
11 2
2
5
00-1000
H
6
N
3
r
At 1000
2
1
a
5-100
00-180
70
150
253
Loss of 0.5 H
Loss of 3 H O molecules
2 17 5 2
Loss of (H O+C19H N O S)
2
O molecule
a
2
5
6
7
[Ni(L)H
2
O].3.5H
2
O
180-1000
7
23
Loss of (C
NiO
7
H
5
N
2
S)
O molecules a
2
r
At 1000
2
5-250
50-400
00-1000
At 1000
5-200
00-400
220
317
437
Loss of 3.75 H
Loss of (C11
Loss of (HNS)
CuO+ organic residue
Loss of 2.25 H
Loss of acetate ion
Loss of C11
2
4
H
11
N
2 2
O + 0.5Cl )
2
[Cu(HL)Cl].3.75H O
r
2
49
311
429
O molecule a
2
2
[Cu(HL)(CH
3
COO)].2.25H
2
O
11 2
H N O
4
00-1000
At 1000
CuO+ organic residue r
* a dehydration, desolvation and final residue.
b
r
2
5

Scheme 2. The proposed mechanism for thermal degradation of the complex [Co(L)(H
2
O)].5H O
2
2
6

3
.6. Electronic spin resonance (ESR) spectral studies
The ESR spectra of the solid copper(II) complexes (6-8) were recorded at room
temperature on the X-band at frequency 9.71 GHz and the g factors were quoted relative to the
standard marker DPPH (g = 2.0037). The ESR parameters for the polycrystalline state at 298 K are
given in Table 7.
Table 7
ESR spectral parameters of the copper(II) complexes of salicylaldehyde N(4)-antipyrinylthio-
semicarbazone.
Parameter
Complex (6)
Complex (7)
Complex (8)
g
‖
2.103
2.030
2.054
3.635
2.151
2.064
2.093
2.410
2.197
2.078
2.118
2.572
164.3
48.7
g
┴
a
g
av
G
-4
A̸ ̸ x 10 (cm-1)
-4
Ax 10 (cm-1)
Δ
Δ
2
14680
18260
14280
17540
0.68
16240
18600
0.43
3
0
.60
0
.59
0.65
0.66
0.49
K
0.59
0.47
0.59
0.41
0.74
129
2
α
β
2
γ2
F
The spectra of the complexes 6 - 8 display absorption typical for Cu(II) chelates and showed
typical axial type symmetry (Fig. 7), with well-defined g׀׀ and g values [60]. In all copper(II)
(2.0023), indicating the unpaired electron lies predominantly in dx2-y2
┴
complexes, g׀׀ > g
┴
> g
e
2
orbital, giving B1g as the ground state [62]. In addition, exchange coupling interaction between
two Cu(II) ions is explained by Hathaway expression G = (g׀׀ - 2.0023)/( g
value G < 4.0, a considerable exchange coupling is present in solid complexes (G= 2.410 – 3.635)
64]. Kivelson and Neiman showed that for an ionic environment g׀׀ is normally 2.3 or larger, but
┴
- 2.0023). When the
[
for covalent environment g׀׀ are less than 2.3 [65]. Since the g values for the complexes (Table 7)
are less than 2.3, this indicates significant covalent character in the metal–ligand bonding. The
2
7

spectrum of complex 8 (Fig. S5), display a hyperfine spectral lines at the lower field where the
2
2
2
values of the g
̸
̸

̸
̸

, A and A have been predicated (Table 7). The bonding factors α , β and γ
which can be used as a measure of the covalence of the in- plane σ bonds, in-plane and out-of-
2
plane π- bonds respectively, have been calculated. α was calculated by the following equation
2
2
[
60] α = A
̸
̸
/0.036 + (g
̸
̸
- 2.0023) + 3/7(g

- 2.0023) + 0.04. If the value of α = 0.5, this means a
2
complete covalent character, while a value of α = 1 proposes complete ionic bonding. The
2
calculated value of α for [Cu(HL)(ClO
4
)]complex is 0.59 indicating portion of unpaired electron
and K which may be used to
density sited on the Cu(II) ion. The orbital reduction factors K
̸
̸

measure the degree of covalency of the in-plane π–bonding and out-of plane π–bonding,
respectively can be calculated using the following expressions [67].
2
K
̸
̸
= (g
= (g
where λ is the spin-orbit coupling of the free copper(II) ion (λ
̸
̸
- 2.0023)Δ
2
/8λ
0
K2
-2.0023)Δ
/2λ


3
0
–
1
o
0
= – 828 cm )
Hathaway [68] refers that, for pure sigma bonding, K
; while for out-of-plane π–bonding, K  K . For [Cu(HL)Cl] and [Cu(HL)(CH
complexes, it is observed that K  K which shows the occurrence of significant out-of-plane π–
bonding while, for [Cu(HL)(ClO )] complex K
̸
̸
 K

 0.77 and for in-plane π–bonding, K
̸
̸

K

̸
̸

3
COO)]
̸
̸

4
̸
̸
< K

indicating considerable in-palne π-bonding
[
69]. Moreover, the lower values of K than unity (0.47- 0.66) are revealing of their covalent
2
2
environment [70]. In addition, the values of β and γ (0.41 and 0.74) for this complex indicating
the presence of in-plane and out-of-plane π-bonding character for the Cu–ligand bond [71].
2
8

Fig. 6 ESR spectra of the solid copper(II) complexes
3
.8. Biological activity
The in vitro antibacterial activity of the prepared ligand and its metal complexes were
evaluated against the human pathogenic bacteria, Gram positive Staphylococcus aureus and Gram
negative Escherichia coli using disc diffusion method. The radial growth of the colony was
recorded on completion of the incubation, and the mean diameter for each compound at a
concentration of 5 mg/mL was recorded. DMSO was used as a solvent and the mean inhibition
zone were measured and compared with standard antibiotic, Enrofloxacin (5 mg/mL). The results
are described in Table 8.
Table 8
In vitro antibacterial activity by a gar diffusion method of tested compounds
Compds.
Microorganism inhibition zone diameter (mm)
Gram +ve bacteria
Gram -ve bacteria
Staphylococcus aureus
Escherichia coli
HL
1
2
3
4
5
6
7
8
7.4
7.6
7.4
7.9
7.9
7.5
17.8
17.6
8.0
-
6.2
7.2
7.8
7.6
8.4
8.1
15.9
10.8
9.5
-
DMSO
Enrofloxacin
26.3
-
2
9