Synthesis, Antioxidant, and Antibacterial Studies of Zn(II), Cd(II), and Hg(II) Complexes with 3-Formylpyridinethiosemicar bazone and Its N 4-Methyl Analogue

Article abstract of DOI:10.1134/S1070363219050232

Evaluation of stability constants of the complexes formed in solution by the biologically important ligands and metal ions can aid in understanding the application of metal complexes in chelation therapy. Hence, complexation equilibrium studies of the ligands (L), 3-formylpyridinethiosemicarbazone (H3FPT) and 3-formylpyridine-N⁴-methylthiosemicarbazone (H3FP4MT) with Zn(II) and Cd(II) metal ions (M) are carried out in 70% v/v DMF-water medium at 0.1M KNO₃ ionic strength and the stability constants are determined pH-metrically at 303 K. The binary complexes are formed in 1: 1 (M: L) ratio and are fairly stable. The binary complexes of H3FPT and H3FP4MT (L) with Zn(II), Cd(II) and Hg(II) ions are synthesized and characterized by various analytical and spectral techniques including elemental analysis, molar conductance, LC-MS, TGA, IR and ¹H NMR spectroscopy. According to the accumulated information, the complexes are polymeric (ML)n with n > 2, except that of Hg(II)-H3FP4MT, which is ML₂. The antioxidant activity of the ligands and their Zn(II) and Hg(II) complexes demonstrate higher activity than their corresponding ligands Cd(II) complexes. Antibacterial activity of the ligands and the complexes is tested against gram positive: Staphylococcus aureus, Bacillus subtilis and gram negative: Escherichia coli and Klebsiella pneumonia bacterial strains. Activity of complexes is determined to be higher than that of the corresponding free ligands.

Full text of DOI:10.1134/S1070363219050232

ISSN 1070-3632, Russian Journal of General Chemistry, 2019, Vol. 89, No. 5, pp. 1015–1022. © Pleiades Publishing, Ltd., 2019.
Synthesis, Antioxidant, and Antibacterial Studies of Zn(II), Cd(II),
and Hg(II) Complexes with 3-Formylpyridinethiosemicarbazone
and Its N4-Methyl Analogue
S. P. Mydhilia, B. Sireeshab, and Ch. Venkata Ramana Reddyc*
a Department of Chemistry, Loyola Academy Degree and PG college, Secunderabad, India
b Department of Chemistry, Nizam College, Osmania University, Hyderabad, India
c Department of Chemistry, Jawaharlal Nehru Technological University Hyderabad, Hyderabad, India
*e-mail: vrr9@jntuh.ac.in; vrr9@yahooo.com
Received February 6, 2019; revised April 7, 2019; accepted April 18, 2019
Abstract—Evaluation of stability constants of the complexes formed in solution by the biologically important
ligands and metal ions can aid in understanding the application of metal complexes in chelation therapy.
Hence, complexation equilibrium studies of the ligands (L), 3-formylpyridinethiosemicarbazone (H3FPT) and
3-formylpyridine-N4-methylthiosemicarbazone (H3FP4MT) with Zn(II) and Cd(II) metal ions (M) are carried
out in 70% v/v DMF–water medium at 0.1M KNO3 ionic strength and the stability constants are determined
pH-metrically at 303 K. The binary complexes are formed in 1 : 1 (M : L) ratio and are fairly stable. The binary
complexes of H3FPT and H3FP4MT (L) with Zn(II), Cd(II) and Hg(II) ions are synthesized and characterized
by various analytical and spectral techniques including elemental analysis, molar conductance, LC-MS, TGA,
IR and 1H NMR spectroscopy. According to the accumulated information, the complexes are polymeric (ML)n
with n > 2, except that of Hg(II)–H3FP4MT, which is ML2. The antioxidant activity of the ligands and their
Zn(II) and Hg(II) complexes demonstrate higher activity than their corresponding ligands Cd(II) complexes.
Antibacterial activity of the ligands and the complexes is tested against gram positive: Staphylococcus aureus,
Bacillus subtilis and gram negative: Escherichia coli and Klebsiella pneumonia bacterial strains. Activity of
complexes is determined to be higher than that of the corresponding free ligands.
Keywords: metal complexes, pH-metry, stability constant, characterization, antioxidant, antibacterial
DOI: 10.1134/S1070363219050232
INTRODUCTION
pyridine-N4-methylthiosemicarbazone (H3FP4MT) (L)
with Zn(II) and Cd(II) ions (M) in 70% v/v DMF-
water medium at 303K and 0.1M KNO3 ionic strength.
Herein the synthesis, characterization, antioxidant and
antibacterial activities of Zn(II), Cd(II) and Hg(II)
complexes are also presented.
2-Formylpyridinethiosemicarbazone demonstrates
anticancer activity, while 3-aminopyridine-2-carboxal-
dehydethiosemicarbazone (Triapine) and 2-acet-
aminobenzaldehydethiosemicarbazone (thiacetazone)
are known for their antitubercular activity [1,2].
Complexation of these organic compounds with metal
ions may increase their activity and/or decrease their
side effects [3]. 3-Formylpyridine thiosemicarbazone
with isoniazid is used as antitubercular drug and its
activity is influenced by the nature of the substituent
on thiosemicarbazone moiety. Presence of an
additional potential binding site along with bulky
groups at the N4 position of the thiosemicarbazone
moiety can significantly enhance its biological activity
[4, 5]. The present study is devoted to the formation
and stability of binary complexes of 3-formyl-
pyridinethiosemicarbazone (H3FPT) and 3-formyl-
RESULTS AND DISCUSSION
pH-Metric equilibrium studies. Determination of
proton dissociation constants (pKa) of the ligands. The
pH-metric titration curves are presented in Fig. 1.
From the acid vs base and the acid+ligand vs base
titration curves, the proton dissociation constant (pKa)
was determined [6-8]. On the basis of the linear plots
of log [(1 –n¯A)/n¯A] vs pH, the proton-ligand
dissociation constants (pKa) were found to be 12.70 for
H3FPT and 12.91 for H3FP4MT. The higher value of
pKa for H3FP4MT could be due to presence of the
1015

1016
MYDHILI et al.
(a)
(b)
2.3
2.5
2.7
2.3
2.5
2.7
Fig. 1. pH-Metric titration curves of (a) H3FPT and (b) H3FP4MT (inset: expanded curves between pH 12.0 and 13.2): (1, 5) free
acid, (2) H3FPT, (3) Zn(II)-H3FPT, (4) Cd(II)-H3FPT, (6) H3FP4MT, (7) Zn-H3FP4MT, and (8) Cd-H3FP4MT.
methyl group on thioamide nitrogen which made the
ligand more basic [9]. The pKa value makes it evident
that both ligands possess only one dissociable proton
each via their thiol-1 form (Schemes 1and 2).
than H3FPT complexes, due to the greater basicity of
the former one.
Characterization of the metal complexes. The
solid complexes obtained were coloured, micro-
crystalline, stable in the air and moisture, soluble in
DMSO and DMF. Elemental analysis and mass spectra
indicated that Cd(II)-H3FPT, Hg(II)-H3FPT, Zn(II)-
H3FP4MT, and Cd(II)-H3FP4MT complexes were
polymeric, (ML)n, where n > 2, and composition of
Hg(II)-H3FP4MT was ML2. Molar conductivity of
10–3 M solutions of the complexes in DMSO at room
temperature ranged between 0–8 Ω–1 cm2 mol–1, and
indicated the non-electrolytic nature of Cd(II)-H3FPT,
Hg(II)-H3FPT and Cd(II)-H3FP4MT complexes, while
the values of 98 and 220 Ω–1 cm2 mol–1 for Zn(II)-
Determination of stability constants of metal
complexes. According to the titration curves (Fig. 1),
the metal-ligand curves run below the free acid and
ligand curves indicating formation of the metal
complexes in solutions. The values of n¯ varied
between 0.10 to 0.97, suggesting formation of 1 : 1
(M : L) complexes [10, 11]. The stability constants
(log K) of the complexes derived from linear plots of
log [(1 – n¯)/ n¯] vs pL (Table 1) indicated that the Zn(II)
complexes were more stable than Cd(II) complexes
[12]. The complexes of H3FP4MT were more stable
Scheme 1. Thiol-thione tautomeric forms of the ligands H3FPT and H3FP4MT.
H
H
N
R
N
H
R
N
H
H
N
R
N
N
N
N
H
N
H
N
N
SH
SH
N
S
Thiol-1
Thiol-2
Thione
R = H, CH3.
Scheme 2. Dissociation of the ligands.
H
R
H
H
N
R
N
H
H
R
N
N
N
N
+ H+
N
H
N
H
N
H
S−
N
N
SH
R = H, CH3.
N
S
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 5 2019

SYNTHESIS, ANTIOXIDANT, AND ANTIBACTERIAL STUDIES OF Zn(II), Cd(II), AND Hg(II)
1017
Table 1. Stability constants (log K) of the complexes
H3FP4MT and Hg(II)-H3FP4MT complexes respec-
tively indicated their electrolytic nature.
Complex (ML)
Zn(II)-H3FPT
log K
9.166
7.625
9.777
8.642
LC-MS. All the complexes demonstrated single
peak with retention time in the range of 0.539 to 0.622
min indicating their purity.
Cd(II)-H3FPT
Zn(II)-H3FP4MT
Cd(II)-H3FP4MT
MS. Cd(II)-H3FPT. In the mass spectrum the peak
at m/z 361 indicated monomeric unit [ML·Cl·2H2O] of
the complex. Peaks at m/z 327 and 291 were due to
loss of two coordinated water molecules and chloride
ion, respectively. Peak at m/z 726 represented the
polymeric nature of the complex, (ML)n with n > 2.
new C=N band at 1606–1602 cm–1 due to thione-thiol
tautomerization in the ligand. The bands ν(C=N) and ν
(C=S) shifted to lower frequencies in the spectra of
complexes due to coordination of azomethine nitrogen
and thiolate sulphur to metal ions. The spectra of
complexes showed increase in pyridine ring deforma-
tion frequencies, indicating the coordination of
pyridine nitrogen with the metal ions. Thus, the ligand
was tridentate with its azomethine nitrogen, ring
nitrogen and sulphur coordinated to metal ions forming
five membered chelates [13–15].
Hg(II)-H3FPT. [ML·Cl·2H2O]. MS: m/z: 450. The
peaks at 415 and 379 were due to the loss of two
coordinated water molecules and coordinated chloride
ion, respectively.
Cd(II)-H3FP4MT. [ML·Cl·2H2O]. MS: m/z: 377.
Peaks at 341 and 306 indicated loss of two coordinated
water molecules and one coordinated chloride ion,
respectively. The peak at m/z 754 indicated polymeric
nature of the complex, (ML)n with n > 2.
In the spectrum of Hg(II)-H3FP4MT shift of the
band attributed to ν(C=N) to lower frequency and
ν(C=S) to higher frequency was due to coordination of
azomethine nitrogen and sulphur atom to the metal
ions [15]. Thus H3FP4MT acted as a bidentate ligand
forming five membered chelate.
Hg(II)-H3FP4MT. MS: m/z: 696. Loss of two
water molecules and two lattice chloride ions was
confirmed by the peaks at m/z 625 and 589, respec-
tively. A peak at m/z 388 indicated presence of two
ligand moieties in the complex, ML2.
Thermogravimetric analysis of the complexes
demonstrated their decomposition in the range of 180–
300°C due to loss of coordinated water molecules,
followed by multistep decomposition of the complexes.
In far IR region of the spectra of the complexes, the
bands attributed to ν(M–N) (480–459 cm–1), ν(M–S)
(381–372 cm–1), ν(M–Cl) (330–320 cm–1), and ν(M–
OH2) (406–404 cm–1) were observed.
1H NMR spectra. Absence of signals corresponding
to hydrazine proton in the spectra of Cd(II)-H3FPT, Zn
(II)-H3FP4MT and Cd(II)-H3FP4MT and one of the
thioamide protons in the spectrum Hg(II)-H3FPT
along with thiol signal at 4.0 ppm [3] indicated the
IR spectra. In the spectrum of Cd(II)-H3FPT
complex ν(N–H) band of the hydrazine group and in
Hg(II)-H3FPT complex ν(N–H) band of the thioamide
group were replaced by new C=N stretching vibration
bands due to thione-thiol tautomerism in the ligand.
Shift of ν(C=N) band to lower frequency in Cd(II)-
H3FPT and to higher frequency in Hg(II)-H3FPT
indicated coordination of azomethine nitrogen with the
metal ions. In both complexes the band of ν(C=S) was
shifted to lower frequency, indicating sulphur atom as
potential donor site [13]. A shift in ring deformation
bands to higher frequency supported binding of
pyridine nitrogen atom with the metal ions [14, 15].
Thus, H3FPT acted as a tridentate ligand with pyridine
ring nitrogen, azomethine nitrogen and sulphur atom as
coordination sites.
Table 2. Antioxidant activity of the ligands and their complexes
Ligand/Complex
H3FPT
IC50, µM
7.82
Cd(II)-H3FPT
Hg(II)-H3FPT
H3FP4MT
8.59
5.33
21.87
12.13
23.93
17.50
Zn(II)-H3FP4MT
Cd(II)-H3FP4MT
Hg(II)-H3FP4MT
In IR spectra of Zn(II)-H3FP4MT and Cd(II)-
H3FP4MT, hydrazine ν(N–H) band was replaced by a
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 5 2019

1018
MYDHILI et al.
(a)
N
(b)
NH
NH2
S
S
Hg
Cd
NH
N
N
H2O
Cd
H2O
Hg
N
N
NH
NH2
S
S
Cl
NH
N
Cl
N
N
H2O
H2O
N
N
Cd
Hg
n
n
Fig. 2. Proposed structures of (a) Cd(II) and (b) Hg(II) complexes with H3FPT (n > 2).
ligands binding to metal ions in their thiolate form, and
in Hg(II)-H3FP4MT thione sulphur binding with metal
ions took place.
nature of a compound. The DPPH (1,1-diphenyl-2-
picrylhydrazyl) free radical is very stable and is
characterized by λmax 517 nm. The purple DPPH
turned yellow when it was reduced by the test
compounds to DPPH-H. Depending upon the change
in colour and decrease in absorbance of DPPH, the
scavenging potential of the compounds could be
estimated.
13C NMR spectra. Complexation through pyridine
nitrogen in Cd(II)-H3FPT and Hg(II)-H3FPT
complexes was evidenced from downfield shifts of C2
13
and C6 carbons in the corresponding C NMR spectra
of the ligands in the complexes.
The IC50 values obtained from the plots of con-
centration of the sample vs SCV, % (Fig. 4), gave the
concentration of the sample that led to its 50%
reduction of the free radical [16] (Table 2). The
accumulated data indicated that Zn(II) and Hg(II)
On the basis of the above data the structures of the
complexes were assumed as presented in Figs. 2 and 3.
Antioxidant activity. The DPPH scavenging assay
is one of the methods used to monitor antioxidant
Table 3. Antibacterial activity of the ligands and their complexes
Zone of inhibition, mm
gram positive
S. aureus B. subtilis
gram negative
K. pneumoniae
Ligand/Complex
E.coli
–
H3FPT
–
–
–
Cd(II)-H3FPT
Hg(II)-H3FPT
H3FP4MT
15
16
–
16
25
–
15
16
06
–
10
18
–
Zn(II)-H3FP4MT
Cd(II)-H3FP4MT
Hg(II)-H3FP4MT
06
–
12
20
30
–
16
20
12
18
25
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 5 2019

SYNTHESIS, ANTIOXIDANT, AND ANTIBACTERIAL STUDIES OF Zn(II), Cd(II), AND Hg(II)
1019
(a)
H
(b)
H
N
CH3
CH3
N
N
S
S
Zn
Cd
N
N
N
H
H
H2O
H2O
CH3
CH3
N
N
N
N
S
S
(OAc)n
Zn
Cd
H2O
N
N
Cl
N
N
H2O
H2O
N
N
Zn
Cd
n
n
(c)
N
H
H2O
Hg
H3C N
S
N
NH
Cl2
HN
N
CH3
S
N
H2O
H
N
Fig. 3. Proposed structures of (a) Zn(II), (b) Cd(II), and (c) Hg(II) complexes with H3FP4MT.
complexes performed as better antioxidants than the
corresponding ligands, while Cd(II) complexes were
less active than the corresponding ligands.
complexes of H3FP4MT were determined to be more
active than H3FPT complexes, which could be
assigned to more basic nature of H3FP4MT, which, in
turn, increased lipophilicity of its complexes [3].
Antibacterial activity. The ligands and complexes
were tested for their bacterial growth inhibitory
activity [3] against gram positive: Staphylococcus
aureus, Bacillus subtilis and gram negative:
Escherichia coli and Klebsiella pneumonia bacterial
strains by the disc diffusion method using DMSO as a
control and gentamicin as a standard (Table 3). The
EXPERIMENTAL
All chemicals used were of reagent grade, obtained
from Sigma-Aldrich. A digital Elico (L1-120) pH
meter equipped with glass and calomel electrodes was
used for equilibrium studies. LC-MS spectra were
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 5 2019

1020
MYDHILI et al.
(a)
(b)
Fig. 4. Plots of concentration vs scavenging activity for (a) H3FPT [(1) H3FPT, y = 5.7021x + 5.4255; (2) Cd-H3FPT, y = 2.7463x +
27.016; (3) Hg-H3FPT, y = 1.7708x + 40.553] and (b) H3FP4MT [(1) H3FP4MT, y = 2.087x + 4.3478; (2) Zn-H3FP4MT, y =
3.6886x + 4.6108; (3) Cd-H3FP4MT, y = 2.0769x + 0.2885, (4) Hg-H3FP4MT, y = 2.4615x + 6.92131] , and their complexes.
measured on a Shimadzu LCMS 2010A spectrometer.
Elemental analysis was carried out on a Thermo
Finnigan 1112 elemental analyzer. Molar conductivity
of the complexes was measured using a Digisun 909
digital conductivity meter. Thermo gravimetric
analysis was carried out on a TG balance TA (Q/50) in
the temperature range of 0 to 1000°C with a ramp of
20°C per min. IR spectra were recorded on a
s (1H, Ar-H), 11.59 s (1H, N–N–H). 13C NMR
spectrum, δ, ppm: 124.2, 130.6, 134.3, 139.8, 149.2,
150.4, 178.6. Found, %: С 46.58; Н 4.36; N 31.26.
C7H8N4S. Calculated, %: С 46.66; Н 4.44; N 31.11.
(2E)-N-Methyl-2-(pyridin-3-ylmethylidene)hyd-
razinecarbothioamide (H3FP4MT). Yield 84%, mp
190–192°C. IR spectrum, ν, cm–1: 410, 630, (δAr ring),
804 (C=S), 1265 (N–CS–N), 1612 (C=N), 3143 (N–H
hydrazine), 3358 (N–H thioamide). 1H NMR spectrum,
δ, ppm: 3.02 s (3H, N–CH3), 7.41–7.45 d.d (1H, Ar-H,
J = 7.48, 4.77 Hz), 8.06 s (1H, H–C=N), 8.23–8.25 d
(1H, Ar-H, J = 7.78 Hz), 8.55–8.56 d (1H, Ar-H, J =
4.77 Hz), 8.64–8.65 d (1H, N–CS–NH, J = 4.52 Hz),
8.96 s (1H, Ar-H), 11.67 s (1H, N–N–H). 13С NMR
spectrum, δ, ppm: 31.3, 123.8, 130.1, 133.8, 138.9,
148.4, 150.0, 177.5. Found, %: С 49.5; Н 5.21; N
28.72. C8H10N4S. Calculated, %: С 49.48; Н 5.15; N
28.86.
1
Schimadzu (Prestige-21) FTIR spectrophotometer. H
and 13C NMR spectra were measured on a Varian
400MHz NMR spectrometer. UV-Vis spectra in
DMSO were recorded on a Schimadzu UV 2450
spectrophotometer. Antibacterial activity was studied
following the disc diffusion method in sterile nutrient
agar medium [3].
Synthesis of 3-formylpyridinethiosemicarbazone
(H3FPT) and 3-formylpyridine N4-methylthio-
semicarbazone (H3FP4MT). Equimolar (2.5 mmol)
solutions of thiosemicarbazide/N4-methylthiosemi-
carbazide and 3-formyl pyridine were stirred for 2 h at
room temperature. Solid precipitate formed was
filtered off, washed with water and dried. The
corresponding product was recrystallized from 1 : 1
ethanol – water mixture [8, 9].
Synthesis of metal complexes. To hot methanolic
solution of the corresponding ligand (2.6 mmol),
aqueous solution of zinc(II) acetate/cadmium(II) chloride/
mercury(II) chloride (1.3 mmol) was added and
refluxed for 12–18 h. pH of the solution was adjusted
with methanolic ammonium hydroxide solution. The
resultant solid complexes were filtered off, washed
with hot methanol, water, petroleum ether, and dried in
vacuum [8, 9].
(2E)-2-(Pyridin-3-ylmethylidene)hydrazinecarbo-
thioamide (H3FPT). Yield 80%, mp 224–228°C. IR
spectrum, ν, cm–1: 416, 624 (δAr ring), 827 (C=S), 987
(N–N), 1278 (N–CS–N), 1591 (C=N), 3130 (N–H
hydrazine), 3340, 3263 (N–H thioamide). 1H NMR
spectrum, δ, ppm: 7.39–7.43 d.d (1H, Ar-H, J = 7.46,
4.4 Hz), 8.05 s (1H, H–C=N), 8.15 s (1H, N–CS–NH),
8.24–8.27 d.t (1H, Ar-H, J = 8.0, 2.0 Hz), 8.30 s (1H,
N–CS–NH), 8.53–8.55 d (1H, Ar-H, J = 6.8 Hz), 8.91
Cd(II)-H3FPT. Pale yellow solid, yield 80%, mp
>300°C. IR spectrum, ν, cm–1: 428, 645 (δAr ring), 813
(C=S), 1585, 1610 (C=N), 3442, 3315 (N–H thioamide).
1Н NMR spectrum, δ, ppm: 7.35–7.38 d.d (1H, Ar-H,
J = 8.0, 5.2 Hz), 7.46 s (1H, N–CS–NH), 7.59 s (1H,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 5 2019

SYNTHESIS, ANTIOXIDANT, AND ANTIBACTERIAL STUDIES OF Zn(II), Cd(II), AND Hg(II)
1021
N–CS–NH), 8.12 s (1H, H–C=N), 8.13–8.15 d (1H,
Ar-H, J = 8.0 Hz), 8.47–8.48 d (1H, Ar-H, J = 4.4 Hz),
8.77 s (1H, Ar-H). Found, %: С 24.46; Н 3.31; N
15.51. С7Н11ClCdN4O2S. Calculated, %: С 23.15; Н
3.30; N 15.43
double distilled water using the corresponding metal
nitrates. pH-Metric titrations were carried out in 70%
v/v DMF–water medium at 303 K and 0.1 M KNO3
ionic strength. Titration of 50 mL of the following sets
of solutions against 0.1 M NaOH solution was carried
out: (1) HNO3 (4.0×10–3 M), (2) HNO3 (4.0×10–3 M) +
Ligand (1.0×10–3 M), (3) HNO3 (4.0×10–3 M) + Ligand
(1.0×10–3 M) + Metal ion (2.0×10–4 M).
Hg(II)-H3FPT. White solid, yield 70%, mp >300°C.
IR spectrum, ν, cm–1: 426, 632 (δPy ring), 821 (C=S),
1594, 1605, (C=N), 3163 (N–H hydrazine), 3284 (N–
1
H thioamide). Н NMR spectrum, δ, ppm: 7.44–7.47
The titration curves, VNaOH vs pH (Fig. 1), linear
plots of log [(1 – n¯A)/ n¯A] vs pH and log [(1 – n¯)/ n¯] vs
pL, ligand dissociation constant (pKa), and stability
constant of the complexes (log K) were obtained
accordingly [6, 8, 9].
d.d (1H, Ar-H, J = 7.6, 4.4 Hz), 8.18 s (1H,
H–C=N), 8.30–8.32 d (1H, Ar-H, J = 9.2 Hz), 8.59–
8.60 d (1H, Ar-H), 8.97 s (1H, Ar-H), 9.01 s (1H, N–
CS–NH,), 12.35 s (1H, N–N–H). Found, %: С 18.15;
Н 2.46; N 12.85. С7Н11ClHgN4O2S. Calculated, %: С
18.57; Н 2.43; N 12.38
Antioxidant activity. Antioxidant nature of the
ligands and the complexes was determined according
to 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay [16,
17]. 50µM Sample solutions were prepared from their
stock solutions. The test compounds of various
concentrations (1.25, 2.5, 3.75, 5.0, 6.25 µM) were
added to1.0 mL of 0.1 mM methanolic solution of
DPPH and stirred vigorously. The antioxidant activity
was measured as the decrease in absorbance of DPPH
at 517 nm by UV-Vis spectrophotometer after 30 min
of incubation at room temperature in darkness.
Solution of DPPH was used as a control. Ascorbic acid
was used as a reference [16, 17].
Zn(II)-H3FP4MT. Pale yellow solid, yield 40%,
mp >300°C. IR spectrum, ν, cm–1: 443, 638 (δPy ring),
798 (C=S), 1588, 1602, (C=N), 3215 (N–H thio-
1
amide). Н NMR spectrum, δ, ppm: 2.94 br.s (3H,
N–CH3), 7.43 s (1H, H–C=N), 7.52 br (1H, Ar-H),
7.77 br (1H, N–CS–NH), 8.56–8.60 m (1H, Ar-H),
8.86–8.87 d (1H, Ar-H, J = 7.53 Hz), 9.42 s (1H, Ar-H).
Found, %: С 31.95; Н 4.83; N 24.51. С12Н18ZnN4O5S.
Calculated, %: С 32.43; Н 4.86; N 25.94
Cd(II)-H3FP4MT. Pale yellow solid, yield 80%,
mp >300°C. IR spectrum, ν, cm–1: 433, 644 (δAr ring),
792 (C=S), 1593, 1606 (C=N), 3348 (N–H thioamide).
1Н NMR spectrum, δ, ppm: 3.02 s (3H, N-CH3), 7.37–
7.40 d.d (1H, Ar-H, J = 7.91, 4.89 Hz), 7.88 br (1H,
N–CS–NH), 8.08 s (1H, H–C=N), 8.13–8.14 d (1H,
Ar-H, J = 7.78 Hz), 8.47–8.49 d (1H, Ar-H, J =
4.77 Hz), 8.81 s (1H, Ar-H). Found, %: С 24.51; Н
3.49; N 14.59. С8Н13ClCdN4O2S. Calculated, %: С
24.57; Н 3.44; N 14.85
Antibacterial studies. Antibacterial activity of the
ligands and complexes was tested by the disc diffusion
method [3] against gram positive: Staphylococcus
aureus, Bacillus subtilis and gram negative:
Escherichia coli, and Klebsiella pneumonia bacterial
strains. Bacterial inoculum (0.10 mL) was spread on
sterile nutrient agar medium by spread plate technique.
Sterile discs of 5 mm diameter (5 μL capacity) dipped
in solution of test samples in DMSO were placed at
equal distance to each other. Disc dipped in DMSO
was used as a control. Gentamicin was used as a
standard. Antibacterial activity was evaluated as zone
of inhibition in mm after incubation for 24 h at 37°C.
Hg(II)-H3FP4MT. White solid, yield 70%, mp
>300°C. IR spectrum, ν, cm–1: 819 (C=S), 1589
(C=N), 3118 (N–H hydrazine), 3203 (N–H thioamide).
1Н NMR spectrum, δ, ppm: 3.14 s (3H, N–CH3), 7.55–
7.58 d.d (1H, Ar-H, J = 7.91, 4.89 Hz), 8.20 s (1H,
H–C=N), 8.38–8.40 d (1H, Ar-H, J = 7.78 Hz), 8.66–
8.67 d (1H, Ar-H, J = 3.51 Hz), 9.06 s (1H, Ar-H),
9.41 s (1H, N–CS–NH), 12.34 s (1H, N–N–H). Found,
%: С 28.08; Н 3.48; N 16.15. С16Н24Cl2HgN8O2S2.
Calculated, %: С 27.60; Н 3.45; N 16.10
CONCLUSIONS
The pH-metric equilibrium studies indicate the
formation of 1 : 1 (M : L) binary complexes in
solutions and their relative stability. Except Hg(II)-
H3FP4MT, all other synthesized solid complexes are
polymeric, (ML)n. All the ligands and complexes
demonstrate antioxidant activity and inhibit bacterial
growth. The complexes of H3FP4MT exhibit higher
activity than complexes of H3FPT.
pH-Metric equilibrium studies. The Irving-
Rossotti titration technique [6,8] was employed for the
complexation equilibrium studies. Standard solutions
of Zn(II) and Cd(II) metal ions were prepared in
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 5 2019

1022
MYDHILI et al.
and Lobana, T.S., J. Coord. Chem., 2010, vol. 63,
FUNDING
p. 1220. doi 10.1080/00958971003735457
The authors are thankful to Jawaharlal Nehru
Technological University Hyderabad, Hyderabad,
India for providing research facilities.
8. Mydhili, S.P., Sireesha, B., Reddy, Ch.V.R., and
Nagarjuna, P.A., Der Pharma Chemica, 2016, vol. 8,
p. 138.
9. Reddy, G.S., Sireesha, B., Saraladevi, Ch., Mohiuddin, R.,
Gyanakumari, C., and Ramreddy, M.G., J. Indian.
Chem. Soc., 1998, vol. 75, p. 290.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
10. Vijayarohini, P., Kavitha, G., and Alwar, S.B.S., Der
Pharma Chemica, 2017, vol. 9, p. 25.
11. Bhargavi, G., Sireesha, B., and Saraladevi, Ch., J. Indian.
Chem. Soc., 2002, vol. 79, p. 826.
1. Elsayed, S.A., El-Hendawy, A.M., Mostafa, S.I., and
Butler, I.S., Inorg. Chim. Acta., 2010, vol. 363, p. 2526.
doi /10.1016/j.ica.2010.04.018
12. Gemechu, Z.B., Kebede, T., Demissie, E.G., Woyes-
sa, G.W., and Kassa, S.B., Afr. J. Pure Appl. Chem.,
2015, vol. 9, p. 175. doi 10.5897/AJPAC2015.0636
13. Lima, R.L. de., Carneiro, T.M.G., and Beraldo, H.,
J. Braz. Chem. Soc., 1999, vol. 10, p. 184. doi 10.1590/
S0103-50531999000300005
14. Mendes, I.C., Teixeira, L.R., Lima, R., Carneiro, T.G.,
and Beraldo, H., Transition. Met. Chem., 1999, vol. 24,
p. 655. doi 10.1023/A:1006918604467
15. Bermejo, E., Castineiras, A., Garcia, I., and West, D.X.,
Polyhedron., 2003, vol. 22, p. 1147. doi 10.1016/S0277-
5387(03)00100-1
2. Pelosi, G., The Open Crystallograph. J., 2010, vol. 3,
p. 16. doi 10.2174/1874846501003010016
3. Chandra, S., Parmar, S., and Kumar, Y., Bioinorg.
Chem. Appl., 2009, Article ID 851316. doi
10.1155/2009/851316
4. Jain, S.K., Garg, B.S., and Bhoon, Y.K., Spectrochim.
Acta. A., 1986, vol. 42, p. 959. doi 10.1016/0584-8539
(86)80003-4
5. Bermejo, E., Castineiras, A., Garcia, I., and West, D.X.,
Polyhedron., 2003, vol. 22, p. 1147. doi 10.1016/S0277-
5387(03)00100-1
16. Ashok, D., Madhuri, E.V.L., Sarasija, M., Sreekanth, S.,
and Vijjulatha, M., RSC Adv., 2017, vol. 7, p. 25710.
doi 10.1039/C7RA01550J
6. Irving, H.M. and Rossotti, H.S., J. Chem. Soc., 1954,
p. 2904. doi 10.1039/JR9540002904
17. Ikechukwu, P.E. and Peter, A.A., Molecules, 2015,
vol. 20, p. 9788. doi 10.3390/molecules20069788
7. Rakesh, K.M., Kulwinder, K.V., Poonam, A., Rekha, S.,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 5 2019