2-Chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benzamide and its Co(II), Ni(II) and Cu(II) metal complexes: Synthesis, characterization, thermal decomposition, electrochemical behavior and antioxidant activity

Article abstract of DOI:10.1007/s10973-015-5221-9

A novel thiourea derivative 2-chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benzamide ligand (HL) and its transition metal complexes (ML₂; M: Co²⁺, Ni²⁺ and Cu²⁺) were synthesized and characterized by elemental analysis, FTIR and ¹H-NMR techniques. The HL was also characterized by single-crystal X-ray diffraction method. It crystallizes in the monoclinic space group P 1 2₁/c 1, with Z?=?4, and unit-cell parameters, a?=?6.7140(15)??, b?=?13.667(3)??, c?=?15.524(4)??. Thermal decomposition of the complexes has been studied by TG/TDA combined system. Cyclic voltammetry technique was utilized to understand the electrochemical behavior of the complexes. Furthermore, the complexes were screened for their antioxidant activities which were measured by using the DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) assays.

Full text of DOI:10.1007/s10973-015-5221-9

J Therm Anal Calorim (2016) 124:1029–1037
DOI 10.1007/s10973-015-5221-9
2-Chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benzamide
and its Co(II), Ni(II) and Cu(II) metal complexes
Synthesis, characterization, thermal decomposition, electrochemical behavior and
antioxidant activity
Tuncay Yes¸ilkaynak1
Received: 17 September 2015 / Accepted: 16 December 2015 / Published online: 18 January 2016
´
´
Ó Akademiai Kiado, Budapest, Hungary 2016
Abstract A novel thiourea derivative 2-chloro-N-((5-
chloropyridine-2-yl)carbamothioyl)benzamide ligand (HL)
and its transition metal complexes (ML2; M: Co2?, Ni2?
and Cu2?) were synthesized and characterized by ele-
Introduction
Thiourea derivatives have been found to be useful ligands
for the potential determination of traces of the transition
metals [1]. Thiourea derivatives can form chelates with
monodentate or bidentate depending on the protonation
states as neutral ligands or mono-/di-anions. Some thiourea
monoanion complexes of transition metals and their com-
plexation capacity have been reported in the literature
[1–8]. Furthermore, the potential application of thiourea
derivatives for the liquid–liquid extraction and separation
of some transition metals such as Cu, Au, Pd and Pt have
been investigated [9–12]. Metal complexes of thiourea
derivatives, commonly called semi-organics, include the
advantages of both organic and inorganic part of the
complex. In addition, thiourea derivatives have been
studied as antitubercular, antibacterial, antifungal, anti-
thyroidal and insecticidal properties [13–16].
1
mental analysis, FTIR and H-NMR techniques. The HL
was also characterized by single-crystal X-ray diffraction
method. It crystallizes in the monoclinic space group P 1
21/c 1, with Z = 4, and unit-cell parameters, a =
˚
˚
˚
6.7140(15) A, b = 13.667(3) A, c = 15.524(4) A. Ther-
mal decomposition of the complexes has been studied by
TG/TDA combined system. Cyclic voltammetry technique
was utilized to understand the electrochemical behavior of
the complexes. Furthermore, the complexes were screened
for their antioxidant activities which were measured by
using the DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS
(2,20-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) assays.
Keywords Synthesis Á Thiourea Á Chlorobenzamide Á
Complex Á Single-crystal structure
In present paper, we report the preparation and charac-
terization of 2-chloro-N-((5-chloropyridin-2-yl)carbamoth-
ioyl) benzamide ligand (HL) (Fig. 1) and its transition
metal complexes, (ML2; M: Co2?, Ni2? and Cu2?). Fur-
thermore, electrochemical and thermal behavior and
antioxidant activities of the metal complexes (ML2; M:
Co2?, Ni2? and Cu2?) were investigated.
Experimental
Electronic supplementary material The online version of this
article (doi:10.1007/s10973-015-5221-9) contains supplementary
material, which is available to authorized users.
Synthesis of the HL
& Tuncay Yes¸ilkaynak
tyesilkaynak@ksu.edu.tr
All chemicals used for the synthesis of the HL were of
reagent-grade quality. A solution of 2-chlorobenzoyl
chloride (0.01 mol) in acetone (50 cm3) was added drop-
wise to a suspension of KSCN (0.01 mol) in acetone
1
˙
Afsin Vocational School, Su¨tcu¨ Imam University,
46500 Kahramanmaras, Turkey
123

1030
T. Yes¸ilkaynak
Bis(2-chloro-N-((5-chloropyridin-2-yl)carbamothioyl)ben-
zamide) copper(II), CuL2: Brown. Yield: 82 %, Anal.
found: C, 42.8; H, 2.3; N, 12.1; S, 8.7; C26H16Cl4N6O2-
S2Cu, calc.: C, 43.7; H, 2.3; N, 11.8; S, 9.0 %.), IR (ATR,
cm-1): t(C=N) 1524 (s). 1H-NMR (CDCl3): 8.09–7.50 (m,
14H, Ar–H), 3.74 (m, 1H, N–H) ppm.
Cl
S
C
O
N
N
H
N
H
Instrumentals
FTIR spectra were obtained using ATR component
(4000–30 cm-1) on a PerkinElmer LX-125000B FTIR
1
spectrophotometer. H-NMR spectra were recorded on a
Cl
Fig. 1 Molecular structure of the HL
Bruker Avance III 400-MHz NMR spectrometer, using
1
CDCl3 as solvent and TMS as internal standard. H-NMR
(30 cm3). The reaction mixture was heated under reflux for
30 min and then cooled to room temperature. A solution of
2-amino-5-chloropyridine (0.01 mol) in acetone (10 cm3)
was added, and the resulting mixture was stirred for 2 h.
HCl (0.1 N, 300 cm3) was added and the solution was
filtered. The solid product was washed with H2O and
purified by recrystallization from EtOH/CH2Cl2 [17].
signals were recorded with the aid of 2D COSY spectra
where necessary. Elemental analyses were carried out on a
Costech ECS 4010 instrument. Melting point of HL was
determined on a digital melting point instrument (Stuart
model SMT30). TG/DTA studies were carried out on a
SEIKO-II instrument. The thermal analysis system was
used over the temperature range 25–1000 °C. The samples
were placed in Pt crucibles, and a-Al2O3 was used as
reference material. Measurement was performed by using a
dynamic nitrogen furnace atmosphere at a flow rate of
2-chloro-N-((5-chloropyridin-2-yl)carbamothioyl)benza-
°
mide, HL: Light yellow. Yield: 89 %, m.p. 147–149 C.
(Anal. found: C, 48.1; H, 2.7; N, 13.0; S, 9.8; C13H9Cl2-
N3OS calc.: C, 47.9; H, 2.8; N, 12.9; S, 9.8 %.) FTIR
(ATR, cm-1): t(N–H) 3165, t(C–H aro.)3022, t(C=O)
50 mL min-1. The heating rate was set to 10 °C min-1
.
Crystallographic data of the HL were recorded on a Bruker
D8 Venture single-crystal X-ray diffractometer equipped
with PHOTON 100 CMOS detector and KryoFlex II low-
temperature device operating at 100 K, using graphite-
1
1678 (s), t(C=S) 1385, t(C–Cl) 764. H-NMR (CDCl3):
8.88 (s, 1H, N–H), 7.82–7.28 (m, 7H, Ar–H), 4.10 (s, 1H,
N–H) ppm.
˚
monochromatized MoKa radiation (k = 0.71073 A). All of
the data were corrected for absorption effects using the
multi-scan technique. The structure was solved by direct
methods and refined on F2 by full-matrix least-squares
using SHELXL 2013 [19]. All non-hydrogen atoms were
refined with anisotropic displacement parameters. The
molecular structure plots were prepared using Mercury
CSD 2.4 [20]. The crystal and instrumental parameters
used in the unit-cell determination and data collection are
summarized in the supporting information. The crystallo-
graphic data of the HL are given as CCDC 1055242
(supplementary file) for this paper. Voltammetry mea-
surements with glassy carbon electrode were performed
using a BAS 100-W (Bioanalytical System, USA) elec-
trochemical analyzer. A glassy carbon working electrode
(BAS; U: 3 mm diameter), an Ag/AgCl reference electrode
(BAS; 3 M KCl), platinum wire counter electrode and a
standard one-compartment three electrode cell of 10-mL
capacity were used in all experiments. The glassy carbon
electrode was polished manually with aqueous slurry of
alumina powder (U: 0.01 cm) on a damp smooth polishing
cloth (BAS velvet polishing pad) prior to each measure-
ment. The measurements were performed at room tem-
perature. Mettler Toledo MP 220 pH meters were used for
Synthesis of the complexes (ML2)
The complexes were prepared using the following general
procedure. MCl2ÁxH2O (M: Co2?, Ni2? and Cu2?
)
(0.001 mol) in ethanol (10 cm3) was added dropwise to
ligand (0.002 mol) dissolved in ethanol (40 cm3) in the
presence of a few drops of Et3N with a constant stirring for
30 min. The precipitate formed was filtered, washed with a
small amount cold ethanol and dried in desiccator [18].
Bis(2-chloro-N-((5-chloropyridin-2-yl)carbamothioyl)ben-
zamide) cobalt(II), CoL2: Dark green. Yield: 80 %, Anal.
found: C, 43.0; H, 2.4; N, 11.9; S, 9.0; C26H16Cl4N6O2-
S2Co, calc.: C, 43.8; H, 2.3; N, 11.9; S, 9.0 %.), FTIR
(ATR, cm-1): t(C=N) 1551 (s). 1H-NMR (CDCl3):
8.05–7.16 (m, 14H, Ar–H), 4.12 (m, 1H, N–H) ppm.
Bis(2-chloro-N-((5-chloropyridin-2-yl)carbamothioyl)ben-
zamide) nickel(II), NiL2: Green. Yield: 85 %, Anal.
found: C, 43.8; H, 2.4; N, 11.8; S, 8.7; C26H16Cl4N6O2-
S2Ni, calc.: C, 44.0; H, 2.3; N, 11.9; S, 9.0 %.), FTIR
(ATR, cm-1): t(C=N) 1549 (s). 1H-NMR (CDCl3):
8.02–7.36 (m, 14H, Ar–H), 4.09 (m, 1H, N–H) ppm.
123

2-Chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benzamide and its Co(II), Ni(II) and Cu(II)…
1031
1H-NMR studies of the compounds
pH measurements via a combined electrode (glass elec-
trode reference electrode) with an accuracy of 0.05 pH.
1
The H-NMR spectra of the all compounds are consistent
1
with the structural results. The H-NMR spectrum of the
Results and discussion
HL shows a single peak at 8.88 ppm corresponds to the N–
H group. Another N–H peak is also observed at 4.10 ppm.
The aromatic C–H bonds are shown as multiplet peaks at
7.82–7.28 ppm. The N–H peak which is observed at
8.88 ppm does not appear in the metal complexes. These
data agree with the complexation reaction and structure of
the complexes. The aromatic C–H protons are shown at
8.05–7.16 ppm for CoL2, 8.02–7.36 ppm for NiL2 and
8.09–7.50 ppm for CuL2.
FTIR studies of the compounds
The FTIR spectra of all compounds were recorded in the
region 400–4000 cm-1. The selected vibration bands are
given in Table 1. The FTIR spectrum of the HL shows a
broad vibration band at 3165 cm-1 corresponds to the N–
H group. The most intensity band is observed at
1678 cm-1 ascribed to the stretching vibration of the
carbonyl group. After the complexation reaction, the
vibration band of the carbonyl group shifted to lower
wavenumber (*135 cm-1). The stretching vibration band
of the C=S group in the ligand has been observed at
1385 cm-1. The shifted vibration band of the C=S group
in the complexes cannot be observed because of over-
lapping with the other bands in that region. The stretching
vibration band of the N–H group (3165 cm-1) cannot be
observed in the FTIR spectra of the metal complexes due
to deprotonation of the HL when it is bonded to the metal
atom (Table 1).
Crystal structure analysis of the HL
Molecular structure of the HL with the atom numbering
scheme is given in Fig. 2. Crystal data and structure
refinement parameters are given in Table 2. Some experi-
mental geometric parameters are given in the supporting
information. The sample which has 0.100 mm 9 0.300 mm 9
1.000 mm approximately dimensions was used for the X-ray
crystallographic analysis. The X-ray intensities were measured
on a Bruker D8 VENTURE system equipped with a multilayer
˚
monochromator and a MoKa sealed tube (k = 0.71073 A). A
Complexation reaction is confirmed by the disappear-
ance of the N–H band and shifting of the C=O and C=S
bands. These results are in good agreement with our pre-
vious results [21].
total of 1557 frames were collected. The total exposure time was
10.81 h. The frames were integrated with the Bruker SAINT
software package using a wide-frame algorithm. The integration
of the data using a monoclinic unit cell yielded a total of 26,603
Table 1 Selected vibration bands of HL and their complexes
t(N–H)/cm-1
t(C–H) (aro.)/cm-1
t(C=O)/cm-1
t(C=N)/cm-1
t(C=S)/cm-1
t(C–Cl)/cm-1
HL
3165
3022
3016
2993
3003
1678
–
1385
764
745
746
752
CoL2
NiL2
CuL2
–
–
–
–
–
–
1551
1549
1524
–
–
–
Fig. 2 ORTEP view of the HL,
thermal ellipsoids are shown at
the 50 % probability level
O1
C11
C9
C1
N1
C7
C8
C13
C2
C5
N2
C12
N3
C10
C3
C4
C6
Cl2
S1
123

1032
T. Yes¸ilkaynak
Table 2 Crystal data and structure refinement details for HL
Empirical formula
Formula weight/g mol)
T/K
C13H9Cl2N3OS
326.19
298
˚
k/A
0.71073
Monoclinic
P 1 21/c 1
Crystal system
Space group
˚
Unit-cell dimensions: (A, °)
a
b
c
6.7140(15)
13.667(3)
15.524(4)
90
a
b
c
92.871(7)
90
3
˚
V/A
1422.7(6)
4
Z
l/mm-1
0.600
q/g cm-3
1.523
F(000)
664
Crystal size/mm
h range for data collection/°
Index ranges
0.1 9 0.3 9 1.0
2.63 to 25.40
-8 B h B 7
-16 B k B 16
-18 B l B 18
26,603
Fig. 3 Crystal packing of the HL in P 1 21/c 1
Reflections collected
Independent reflections
Coverage of independent ref.
Data/parameters
2598
21/c 1, with Z = 4 for the formula unit, C13H9Cl2N3OS.
The final anisotropic full-matrix least-squares refinement
on F2 with 181 variables converged at R1 = 5.70 %, for
the observed data and wR2 = 15.39 % for all data. The
goodness of fit was 1.047. The largest peak in the final
99.3 %
2598/181
1/0.795
Maximum and minimum transmission
R1, wR2 [I C 2r(I)]
0.0570
0.1379
-
3
˚
difference electron density synthesis was 0.542 e /A ,
R1, wR2 (all data)
GOF on F2
0.0881
-
and the largest hole was -0.282 e /A with an RMS
3
˚
0.1539
-
3
˚
deviation of 0.090 e /A . On the basis of the final model,
the calculated density was 1.523 g cm-3 and F(000),
664 e-.
1.047
-3
˚
Dqmax, Dqmin /e A
0.542/-0.282
The molecular structure and packing diagram are
depicted in Figs. 2 and 3, respectively. The bond lengths
and angles (Table 3) in the HL are typical for thiourea
derivatives; C6-S1 and C7-O1 bonds show a typical dou-
˚
reflections to a maximum h angle of 25.40° (0.83 A res-
olution), of which 2598 were independent (average
redundancy 10.240, completeness = 99.3 %, Rint
=
˚
ble-bond character with 1653(4) and 1216(4) A, respec-
8.22 %, Rsig = 4.42 %) and 1846 (71.05 %) were greater
2
˚
tively. The bond lengths of the N2–C6, N3–C6, N2–C5 and
than 2r(F ). The final cell constants of a = 6.7140(15) A,
˚
˚
N3–C7 were determined as 1341(4), 1.399(4), 1.417(4) and
˚
1367(5) A, respectively. These results indicate the bonds
b = 13.667(3) A, c = 15.524(4) A, b = 92.871(7)°, vol-
3
ume = 1422.7(6) A are based upon the refinement of the
˚
have partial double-bond character.
XYZ-centroids of 8681 reflections above 20 r(I) with
5.255° \ 2h \ 50.11°. Data were corrected for absorption
effects using the multi-scan method (SADABS). The ratio
of minimum to maximum apparent transmission was
0.795.
The carbonyl and thiocarbonyl part bound angles
(Table 4) are N2–C6–S1, 128.0(3); N3–C6–S1, 119.0(3);
N3–C7–O1, 123.5(3) and O1–C7–C8, 121.1(3)°. The crystal
packing is shown in Fig. 4. There is one intermolecular, N–
HÁÁÁO hydrogen bonds which the bond length is HÁÁÁO,
The structure was solved and refined using the Bruker
SHELXTL software package, using the space group P 1
˚
1902 A [22].
123

2-Chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benzamide and its Co(II), Ni(II) and Cu(II)…
1033
10 °C min-1 heating rate under N2 atmosphere by DTA/
TG. The DTA/TG curves of the CoL2 are given in Fig. 4,
and thermo-analytical results are presented in Table 5.
The TG curve shows that the decomposition process of
the CoL2 takes place in three stages. The decomposition
ranges determined by TG and DTG signals. The first
decomposition stage occurs in temperature range of
122–381 °C. In this step, the elimination of 1 mol ligand
left an experimental mass loss of 44.30 % (calc.
*45.7 %). At the end of this stage, the intermediate
product formed as given CoL formula. The second
decomposition is observed in temperature range of
381–633 °C with mass loss of 14.10 % (calc.: *15 %).
At this stage, 1/3 mol ligand was broken up and turned
into the gas products and formed intermediate product
with CoL2/3 formula. The last decomposition is observed
in temperature range of 633–935 °C. The residual product
of the decomposition is estimated as Co2S3 corresponds to
an experimental mass of 30.90 %, which is equal to the
expected theoretical mass (calc. *30.0 %) [23–30].
Thermal decomposition mechanism of the CoL2 is rec-
ommended as follows Eq. (1) (based on the TG data);
˚
Table 3 Bond lengths (A) for the HL
S1–C6
1.653(4)
Cl1–C2
1.735(3)
Cl2–C10
N3–C7
1.741(4)
1.367(5)
0.86
O1–C7
N3–C6
N2–C6
N2–H2
N1–C1
C5–C4
C8–C9
C2–C3
C3–C4
C4–H4
C9–C11
C12–C13
C13–C11
C11–H11
1.216(4)
1.399(4)
1.341(4)
0.86
N3–H3
N2–C5
1.417(4)
1.328(5)
1.493(5)
1.382(5)
1.384(5)
1.363(6)
0.93
N1–C5
1.338(5)
1.369(5)
1.386(5)
1.368(5)
1.385(5)
0.93
C7–C8
C8–C10
C10–C12
C2–C1
C3–H3A
C1–H1
0.93
1.375(6)
1.375(6)
1.370(7)
0.93
C9–H9
0.93
C12–H12
C13–H13
0.93
0.93
Table 4 Bond angles (°) for the HL
C7–N3–C6
C6–N3–H3
C6–N2–H2
C5–N1–C1
O1–C7–C8
N1–C5–C4
C4–C5–N2
C10–C8–C7
N2–C6–N3
N3–C6–S1
129.5(3)
115.2
C7–N3–H3
C6–N2–C5
C5–N2–H2
O1–C7–N3
N3–C7–C8
N1–C5–N2
C10–C8–C9
C9–C8–C7
115.2
132.3(3)
113.9
122À381 ꢀ
C
381À633 ꢀ
C
633À935 ꢀ
III
C
CoL2 ÀÀÀÀÀÀ! CoL ÀÀÀÀÀÀ! CoL2=3 ÀÀÀÀÀÀ! Co2S3 ð1Þ
113.9
I
II
117.7(3)
121.1(3)
123.6(3)
126.2(3)
122.2(3)
113.0(3)
119.0(3)
119.8(3)
119.7(3)
119.4(3)
120.7
123.5(3)
115.3(3)
110.2(3)
118.3(3)
119.4(3)
128.0(3)
121.5(4)
118.6(3)
120.9(3)
118.6(4)
120.7
Thermal analysis of the NiL2
The thermal decomposition reactions of the NiL2 that used
7.80 mg sample mass were investigated 10 °C min-1
heating rate under N2 atmosphere by DTA/TG. The
decomposition ranges determined by DTA and DTG sig-
nals. The DTA/TG curves of the NiL2 are given in Fig. 5,
and thermo-analytical results are tabulated in Table 6. The
TG curve shows that the decomposition process of the NiL2
takes place in three stages. The first decomposition stage
occurs in the range of 183–372 C. In this step, the elimi-
nation of 1 mol ligand carried out in an experimental mass
loss of 45.80 % (calc. *45 %) and the intermediate pro-
duct formed as given NiL formula. The second decompo-
sition is observed between 372 and 468 °C with mass loss
of 15.30 % (calc.: *15 %). In this stage, 1/3 mol ligand
was broken up and formed intermediate product with NiL2/3
formula. The third decomposition is observed between 468
and 835 °C. The residual product of the decomposition is
estimated as NiS corresponds to an experimental mass of
11.80 %, which is equal to the expected theoretical mass
(calc. *12.76 %) [23–28].
N2–C6–S1
C8–C10–C12
C12–C10–Cl2
C3–C2–Cl1
C2–C3–C4
C8–C10–Cl2
C3–C2–C1
C1–C2–Cl1
C2–C3–H3A
C5–C4–C3
C3–C4–H4
N1–C1–H1
C11–C9–C8
C8–C9–H9
C13–C12–H12
C11–C13–C12
C12–C13–H13
C13–C11–H11
C4–C3–H3A
C5–C4–H4
N1–C1–C2
C2–C1–H1
C11–C9–H9
C13–C12–C10
C10–C12–H12
C11–C13–H13
C13–C11–C9
C9–C11–H11
118.1(4)
121.0
121.0
122.3(4)
118.8
118.8
120.7(4)
119.6
119.6
118.5(4)
120.7
120.7
121.1(4)
119.5
119.5
119.8(4)
120.1
120.1
Thermal behavior of the complexes
Thermal analysis of the CoL2
Thermal decomposition reactions of the NiL2 are
recommended as follows Eq. (2) (based on the TG
data);
183À372 ꢀ
C
372À468 ꢀ
C
468À835 ꢀ
III
C
The thermal decomposition reactions of the CoL2 that
used 8.05 mg sample mass were investigated
NiL2 ÀÀÀÀÀÀ! NiL ÀÀÀÀÀÀ! NiL2=3 ÀÀÀÀÀÀ! NiS
ð2Þ
I
II
123

1034
T. Yes¸ilkaynak
Fig. 4 DTA/TG curves of the
CoL2 (10 °C min-1 heating
rate, N2 atmosphere, 8.05 mg
sample mass)
20.00
15.00
10.00
5.00
100.0
80.0
60.0
40.0
20.0
150.00
100.00
50.00
TG
I
Mass loss –43.30 %
DTG
DTA
0.00
II
Exo
0.00
Mass loss –14.12 %
–50.00
–100.00
III
Mass loss –10.71 %
Endo
–5.00
Vh= 10 °C min–1
200.0
–10.00
–200.00
400.0
600.0
800.0
Temperature/°C
Table 5 Thermo-analytical results of the decomposition reactions of the CoL2
Complex
Stage
DTA peak/
°C
TG temp. range/°C
Mass loss/%
Exper.
Intermediate
(or residue)
Theor.
CoL2
I
233
512
773
122–381
381–633
633–935
44.3
14.1
10.7
45
15
10
CoL
II
III
CoL2/3
Co2S3
Fig. 5 DTA/TG curves of the
NiL2 (10 °C min-1 heating rate,
N2 atmosphere, 7.80 mg sample
mass)
100.0
500.00
400.00
300.00
100.00
0.00
TG
20.00
10.00
0.00
I
80.0
60.0
40.0
20.0
0.0
Mass loss –45.79 %
II
DTG
DTA
–15.31 %
Mass loss
–100.00
–200.00
–300.00
–400.00
Exo
III
Mass loss –27.13 %
Endo
–10.00
V
h
= 10 °C min–1
200.0
800.0
400.0
600.0
Temperature/°C
Thermal analysis of the CuL2
heating rate under N2 atmosphere by DTA/TG. The
decomposition ranges determined by TG and DTG signals.
The DTA-TG curves of the CuL2 are given in Fig. 6, and
determined results are tabulated in Table 7.
The thermal decomposition reactions of the CuL2 that used
7.95 mg sample mass were investigated 10 °C min-1
123

2-Chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benzamide and its Co(II), Ni(II) and Cu(II)…
Table 6 Thermo-analytical results of the decomposition reactions of the NiL2
1035
Complex
Stage
DTA
peak/
°C
TG
temperature
range/°C
Mass loss/%
Exper.
Intermediate
(or residue)
Theor.
NiL2
I
248
415
542
183–372
372–468
468–835
45.8
15.3
27.1
45
15
27
NiL
II
III
NiL2/3
NiS
Fig. 6 DTA/TG curves of the
CuL2 (10 °C min-1 heating
rate, N2 atmosphere, 7.95 mg
sample mass)
20.00
15.00
10.00
5.00
I
100.0
80.0
60.0
40.0
20.0
Mass loss
–15.30 %
100.00
50.00
TG
II
Mass loss
–29.38 %
0.00
DTG
DTA
0.00
Exo
III
–50.00
–100.00
Mass loss –30.29 %
–5.00
–10.00
Endo
Vh
= 10 °C min–1
IV
Mass loss –2.8 %
200.0
400.0
600.0
800.0
Temperature/°C
Table 7 Thermo-analytical results of the decomposition reactions of the CuL2
Complex
Stage
DTA
peak/°C
TG temp.
range/°C
Mass loss/%
Intermediate
(or residue)
Exper.
Theor.
CuL2
I
134
284
578
675
115–214
214–378
378–665
665–897
15.3
29.4
30.2
2.8
15
30
30
3
CuL5/3
CuL
II
III
IV
CuL1/3
Cu1.96
S
The TG curve shows that the decomposition process
of the CuL2 occurs in four stages. The first decomposi-
tion stage where the elimination of 1/3 mol ligand occurs
with experimental mass loss of 15.30 % (calc. *15 %)
takes place in temperature range of 115–214 °C. At the
end of this stage, the intermediate product formed as
given CuL5/3 formula. The second decomposition is
observed between 214 and 378 °C with mass loss of
29.40 % (calc.: *30 %). In this stage, 2/3 mol ligand
was decomposed and turned into the gas products and
formed intermediate product with CuL formula. The
third decomposition stage occurs in temperature range of
378–665 °C with mass loss of 30.30 % (calc.: *30 %)
according to 2/3 mol ligand and formed intermediate
product with CuL1/3 formula. The last decomposition is
also observed in temperature of [665 °C. The residual
product of the decomposition is estimated as Cu1.96S
corresponds to an experimental mass of 22.30 %, which
is equal to the expected theoretical mass (calc.
*21.9 %) [23–28, 31].
Thermal decomposition reactions of the CuL2 are given
as follows Eq. (3) (based on the TG data);
115À214 ꢀ
C
214À378 ꢀ
C
378À665 ꢀ
III
C
CuL2 ÀÀÀÀÀÀ! CuL5=3 ÀÀÀÀÀÀ! CuL ÀÀÀÀÀÀ!
I
II
665À897 ꢀ
IV
C
CuL1=3 ÀÀÀÀÀÀ! Cu1:96
S
123

1036
T. Yes¸ilkaynak
Antioxidant activity of complexes
typical scan rate curves of the CuL2 are given in Fig. 7.
Scan rate studies were investigated between the
25–750 mV s-1 and at 1 9 10-5 M concentration. The
linear dependence of peak current Ip (l) upon the square
root of the scan rate v1/2 (mV s-1) was found by GCE,
demonstrating diffusional behavior. The equations about
scan rate studies are depicted below (4);
The antioxidant properties of the synthesized metal com-
plexes were studied in cell culture systems. The antioxidant
activities of the complexes were measured by using the
DPPH and ABTS assays. The antioxidant activities are
given in Table 8.
À
Á
p
The antioxidant activity is proportional to DPPH, ABTS
and reduction power values. Considering the values in the
table, the CoL2 complex shows better antioxidant proper-
ties than others.
Log Ip ðlAÞ ¼ 0:0532 v mV sÀ1
À
Á
À 0:4642 r2 ¼ 0:8491
ð4Þ
The linear relationship between Log Ip and Log v were
also investigated, and the equations about these relation-
ships are given below (5);
The electrochemical behavior of the complexes
À
Á
Log IpðlAÞ ¼ 0:9652 Log v mV sÀ1
À
Á
À 0:9098 r2 ¼ 0:9286
ð5Þ
Cyclic voltammetric technique was utilized to understand
the electrochemical behavior of the CuL2. CV studies of
the CuL2 were run at glassy carbon electrode (GCE) in a
cathodic direction. pH effect on the CuL2 was also inves-
tigated in Britton–Robinson buffer (BRB) solution with pH
range of 2–12. There are not any peaks in an acidic med-
ium (pH 2–7), but there is a reduction peak at about
-0.6 V. Current of this peak increases by increasing the
basicity of the medium. Sharpest and the biggest peak
current were determined at pH 11 in Britton–Robinson
buffer solution. To investigate whether the process at GCE
was under the diffusion- or absorption-controlled scan rate,
studies were carried out. Scan rate studies were investi-
gated in pH 11, Britton–Robinson buffer solution. The
The slope of the relationship is fit to the theoretically
expected value for an ideal reaction under diffusion con-
trolled [32].
Conclusions
2-Chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benza-
mide ligand (HL) and its cobalt (II), nickel (II) and copper
(II) complexes were synthesized and characterized by
elemental analysis, FTIR and 1H-NMR techniques. The HL
was characterized by single-crystal X-ray diffraction
method. It crystallizes in the monoclinic space group P 1
21/c 1, with Z = 4, and unit-cell parameters, a =
Table 8 Antioxidant activities of the metal complexes
˚
˚
˚
6.7140(15) A, b = 13.667(3) A, c = 15.524(4) A. Ther-
mal behaviors of the complexes were investigated by TG/
TDA combined system according to TG curves, the CoL2,
NiL2, CuL2 complexes are thermally stable up to 122, 183
and 115 °C, respectively. The melting point of metal
complexes could not be observed due to decomposition.
The CoL2 and NiL2 complexes were decomposed in three
stages, while the CuL2 complex was degraded in four steps.
The antioxidant activities of the complexes were also
investigated. Antioxidant activities of the complexes were
measured by using the DPPH and ABTS assays. The
comparison of other complexes, the CoL2, shows better
antioxidant properties. Cyclic voltammograms of the CuL2
shows a reduction peak at about -0.6 V in an acidic
medium (pH 2–7).
Complex
DPPH
ABTS
Red. P.
CoL2
NiL2
CuL2
38.974 0.349
14.458 0.225
8.648 0.153
134.484 0.354
77.331 0.433
11.936 0.118
51.862 0.435
3.030 0.311
1.209 0.146
DPPH, ABTS and reduction power; mg trolax eq./100 mg sample
+100
500 mV/s
250 mV/s
100 mV/s
50 mV/s
25 mV/s
+60
+20
–20
–60
Supplementary material
–100
+2.0
+1.5
+1.0
+0.5
0
–0.5
–1.0
–1.5
–2.0
Crystallographic data for the structure reported in this
paper have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC), CCDC 1055242 for the HL.
Potential/V
Fig. 7 Cyclic voltammograms of the CuL2 with different scan rates
123

2-Chloro-N-((5-chloropyridine-2-yl)carbamothioyl)benzamide and its Co(II), Ni(II) and Cu(II)…
1037
15. Blanz EJ, Frech FA. The carcinostatic activity of 5-hydroxy-2-
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heteroaromatic compounds III. Primary correlation. J Med Chem.
1966;9:585–9.
These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif. [Fax: int code ?44(1223)
336-033; e-mail: deposit@ccdc.cam.ac.uk].
¨
¨ ¨
17. Arslan H, Florke U, Kulcu N. Synthesis, characterization and
crystal structure of 1-(4-chloro-benzoyl)-3-naphthalen-1-yl-
thiourea. J Chem Crystallogr. 2003;33:919–24.
Acknowledgements This work was supported by Kahramanmaras¸
˙
Su¨tc¸u¨ Imam University Research Fund (BAP-Project No. 2013/4-28M).
18. Gunasekaran N, Jerome P, Ng SW, Tiekink ERT, Karvembu R.
Tris-chelate complexes of cobalt (III) with N-[di (alkyl/aryl)
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123