Phthalocyanines including 2-mercaptobenzimidazole analogs: Synthesis, spectroscopic characteristics, quantum-chemical studies on the relationship between electronic and antioxidant properties

Article abstract of DOI:10.1016/j.molstruc.2019.127259

In this study, peripherally tetra 2-mercaptobenzimidazole group substituted cobalt and indium phthalocyanine complexes (2 and 3) were prepared from 4-(benzo[d]imidazole-2-ylthio)phthalonitrile (1) for the first time. Antioxidant behaviors and theoretical

Full text of DOI:10.1016/j.molstruc.2019.127259

Journal of Molecular Structure 1202 (2020) 127259
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Phthalocyanines including 2-mercaptobenzimidazole analogs:
Synthesis, spectroscopic characteristics, quantum-chemical studies on
the relationship between electronic and antioxidant properties
,
b,
Hasan Yakan a *, M. Serdar Çavus¸ **, Emre Güzel c, Barıs¸ S. Arslan c, Temelkan Bakır d,
Halit Muglu
d
ꢀ
a Department of Chemistry Education, Ondokuz Mayis University, 55139, Samsun, Turkey
b Department of Biomedical Engineering, Kastamonu University, 37150, Kastamonu, Turkey
c Department of Chemistry, Sakarya University, 54050, Sakarya, Turkey
d Department of Chemistry, Kastamonu University, 37150, Kastamonu, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, peripherally tetra 2-mercaptobenzimidazole group substituted cobalt and indium phtha-
locyanine complexes (2 and 3) were prepared from 4-(benzo[d]imidazole-2-ylthio)phthalonitrile (1) for
the first time. Antioxidant behaviors and theoretical calculations of benzimidazole-substituted metal-
lophthalocyanines are presented. The structures of these compounds were determined by the spectro-
scopic methods (IR, 1H NMR, UVeVis and mass spectroscopies) and elemental analysis. Antioxidant
activities of the compounds (1e3) were measured using 1,1-diphenyl-2-picrylhydrazyl (DPPH) method.
Antioxidant activity was followed by 1 > 3 > 2 > Trolox. In addition, density functional theory (DFT)
calculations were carried out to determine the stable electronic structure, charge density distributions,
FMO energy eigenvalues, and electronegativity of the ligand (1) and complexes (2 and 3). NBO and
QTAIM analysis were performed to investigate the relationship between the electronic properties and
antioxidant activity of the compounds.
Received 4 September 2019
Received in revised form
15 October 2019
Accepted 18 October 2019
Available online 21 October 2019
Keywords:
Phthalocyanine
DFT
QTAIM
Spectroscopic methods
Antioxidant activity
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
effects has been focused on phthalocyanine derivatives as well as
phenolic compounds. Antioxidants show properties such as
Phthalocyanines (Pcs), which are an significant class of macro-
cyclic compounds, have many uses such as enzyme inhibitors [1,2],
gas sensors [3], catalysts [4e6], solar cells [7,8], electrochromic
devices [9,10], liquid crystals [11] and photosensitizers in photo-
singlet-triplet oxygen quencher, a free radical scavenger, and
enzyme inhibitors [26]. Moreover, phthalocyanines have optical
and redox properties as well as antioxidant properties due to high
conjugated hetero atomic p-electronic systems [27].
dynamic
cancer
therapy
(PDT)
[7,12e18].
2-
Recently, substituted phthalocyanines containing heterocyclic
groups have become important for various applications [28]. Also,
to the best of our knowledge, there is no report on the examination
of the antioxidant properties of cobalt and indium phthalocyanine
in the same study. Taking these properties into consideration, in
this study, in order to investigate antioxidant applications,
peripherally tetra benzimidazole-substituted cobalt and indium
phthalocyanine complexes were prepared for the first time. The
compounds were confirmed by using UVevis, IR, 1H NMR spec-
troscopy, mass spectrometry, and elemental analysis techniques.
Furthermore, compatibility of experimental and theoretical spec-
troscopic data of the compounds was analysed and interpreted.
Antioxidant activities of the ligand (1) and metal complexes
(2e3) were measured using the DPPH method. It was
Mercaptobenzimidazole derivatives, which are heterocyclic com-
pounds containing nitrogen and sulfur, exhibit an extensive di-
versity of pharmaceutical and biological activities such as
anticancer [19], antiulcer [20], enzyme inhibition [21], antibacterial
and antimicrobial activities [22,23].
Benzimidazole derivatives had been widely used as an inhibitor
for corrosion [24,25]. The most recent research on the antioxidant
* Corresponding author.
** Corresponding author.
E-mail addresses: hasany@omu.edu.tr (H. Yakan), mserdarcavus@kastamonu.
edu.tr (M.S. Çavus¸ ).
https://doi.org/10.1016/j.molstruc.2019.127259
0022-2860/© 2019 Elsevier B.V. All rights reserved.

2
H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
demonstrated that transition metal complexes exhibit lower anti-
oxidant activities than the corresponding free ligand. Moreover,
QTAIM analysis was used to elucidate the relationship between the
electronic properties of the atoms in the active sides of metal
complexes and antioxidant activity.
to room temperature, the green crude product was cooled,
precipitated by adding diethyl ether or hexane and filtered. Purifi-
cation: After being washed with methanol, purified by column
chromatography on silica gel (THF:Ethanol e 100:1) and finally
dried in vacuo at 100 ꢀC. Solubility: Highly soluble in THF, DMSO,
DMF. Yield: (40%). FT-IR (ATR, ymax/cmꢁ1): 3294 (w, NH), 3052 (m,
Ar. CeH), 1642, 1476, 1448 (m, Ar. eC]N), 1318, 1244, 1162 (m, Ar.
-C-N), 934, 774 (s, -C-S). UVevis lmax (nm) THF: 672, 616, 334. Anal.
Calc. for C60H32CoN16S4: C, 61.90; H, 2.77; Co, 5.06; N, 19.25; S,
11.02%; Found: C, 61.52; H, 2.66; N, 20.82; S, 10.91%. MS (MALDI-
TOF): m/z 1165.25 [MþH]þ.
2. Experimental
2.1. Instruments and chemicals
All starting materials and solvents were purchased from Aldrich,
Acros Organics, and Merck Chemical Company. The homogeneity of
the products was tested in each step by TLC. The solvents were
stored over molecular sieves. Anhydrous potassium carbonate
(K2CO3) was finely ground and dried at 110 ꢀC. Melting points were
recorded with a Stuart SMP 30 electrothermal apparatus, and were
uncorrected. UVeVis studies were performed by a Shimadzu UV
2600 spectrophotometer. UVevis spectra were acquired in a quartz
cuvette on an Agilent Model 8453 diode array spectrophotometer.
Infrared spectra were measured on a PerkinElmer FT-IR spectro-
photometer. A Bruker 300 MHz spectrometer instrument was used
to take 1H NMR and 13C NMR spectra. Mass spectra (MS) were
analysed by MALDI Synapt G2-Si Mass Spectrometry. The elemental
analysis was performed on CHNS-932 (LECO). Absorption mea-
surements for antioxidant activity were determined with Shimadzu
UVM-1240 UVevisible spectrophotometer (Shimadzu Corp., Kyoto,
Japan manufactures).
2.2.3. Synthesis of peripherally substituted chloroindium (III)
phthalocyanine (3)
A mixture of (1) (0.100 g, 2.36 mmol), anhydrous InCl3 (0.024 g,
0.110 mmol) and a catalytic amount of DBU (1,8-diazabicyclo[5.4.0]
undec-7-ene) in quinoline (2 cm3) was refluxed at 160 ꢀC in a sealed
glass tube for 6 h under an argon atmosphere. After cooling to room
temperature, the green crude product was cooled, precipitated by
adding diethyl ether or hexane and filtered. Purification: After being
washed with methanol, purified by column chromatography on
silica gel (THF:Ethanol e 100:1) and finally dried in vacuo at 100 ꢀC.
Solubility: Highly soluble in THF, DMSO, DMF. Yield: 26%. FT-IR (ATR,
ymax/cmꢁ1) 3297 (w, NH), 3048 (m, Ar. CeH), 1646, 1480, 1452 (m,
Ar. eC]N), 1308, 1236, 1160 (m, Ar. -C-N), 928, 762 (s, -C-S). 1H
NMR (300 MHz, CDCl3)
AreH). UVevis lmax (nm) THF: 706, 640, 376. Anal. Calc. for
60H32ClInN16S4: C, 57.40; H, 2.57; Cl, 2.82; In, 9.14; N,17.85; S,10.21
d 12.82 (s, 4H, eNH), 8.96e7.44 (m, 28H,
C
2.2. Synthetic procedures
Found: C, 56.14; H, 2.03; N, 18.44; S, 10.13%. MS (MALDI-TOF): m/z
1221.14[M-Cl þ H]þ.
2.2.1. 4-(benzo[d]imidazole-2-ylthio)phthalonitrile (1)
In
a
100 mL two-necked round bottom flask, 4-
2.3. Antioxidant measurements
nitrophthalonitrile (0.75 g, 5.0 mmol) was dissolved in DMF
(10 mL) at 45 ꢀC, and 2-mercaptobenzimidazole (0.72 g, 4.2 mmol)
was added. After stirring for 30 min, 1.03 g finely ground anhydrous
potassium carbonate (7.5 mmol) was added portion-wise in 3 h
with efficient stirring. The reaction mixture was stirred under ni-
trogen at 50 ꢀC for a further 48 h, color of the reaction was from pale
yellow to brown. TLC was used for reaction monitoring with DCM
and hexane (1:1). The mixture was cooled to room temperature and
then poured into iced water (100 mL). After completion of the
precipitation approximately 30 min, the crude product was filtered,
washed with water, and dried with MgSO4. The crude product was
purified by silica gel column chromatography using hexane/CH2Cl2
(1:1) as the eluent. The yellowish-brown product was soluble in
THF, CHCl3, CH2Cl2, DMF, and DMSO. Yield: 1.00 g (83%). m.p.:
153e155 ꢀC, m.p. 158 ꢀC. FT-IR (ATR, ymax/cmꢁ1): 3289 (w, NH),
3100, 3067 (m, Ar. CeH), 2361 (s, C^N), 1586, 1538 (m, Ar. eC]N),
Antioxidant activities of the phthalonitrile derivative (1) and its
metal complexes were measured using the DPPH method. The test
samples were dissolved in DMSO while the DPPH solution was
prepared in ethanol. For a comparative study, the Trolox solution
was used as an antioxidant standard. All compound solutions were
prepared at 10, 15, 20, 25, 50 and 100 mM concentrations in DMSO.
DPPH solution in ethanol was mixed with different concentrations
of compounds, and the absorbance change at 517 nm was measured
with a spectrophotometer. A control reaction was carried out with
DMSO solution as the blank control. Finally, the mixtures were
shaken vigorously and incubated in an incubator at 25 ꢀC for 60 min
in the dark. Depending on the antioxidant concentration, color
changes were observed in DPPH radical. The percentage inhibition
values were calculated using the following formula [29]:
1270, 1217 (m, -C-N), 819, 750 (s, -C-S). 1H NMR (300 MHz, CDCl3)
d,
% DPPH scavenging activity (% Inhibition) ¼ [(A0 ꢁ A1) /A0] ꢂ 100(1)
ppm 13.2 (s, 1H, eNH), 8.26 (s, 1H, ortho to eS and eCN), 8.08e8.03
(d, 1H, ortho to eS and meta to eCN), 7.81e7.76 (d, 1H, meta to eS
and ortho to CN), 7.58e7.52 (dd, 2H, AreH), 7.23e7.17 (dd, 2H,
Here A0 is the absorbance of the control solution (not added to
the antioxidant), and A1 is the absorption of the compound solution
(when it is antioxidant) [30]. The amount of antioxidant required to
reduce the percentage inhibition by 50% is used to measure anti-
oxidant activity and is called IC50 (mg/mL) [31].
AreH). 13C NMR (75 MHz, CDCl3)
d, ppm 143.1, 142.1, 135.1, 133.7,
133.6, 123.5, 116.4, 116.1, 116.0, 113.2. Anal.Calc. for C15H8N4S: C,
65.20; H, 2.92; N, 20.28; S, 11.60; Found: C, 65.33; H, 2.85; N, 20.18;
S, 11.69. MS (MALDI-TOF): m/z 276.82 [M]þ. 4-(benzo[d]imidazole-
2-ylthio)phthalonitrile was prepared according to the reported
procedure with minor modifications [28].
2.4. Computational studies
All calculations were performed with the Gaussian 09 software
[32] using the Kohn-Sham density functional theory (KS-DFT)
[33,34], with the B3LYP (Becke, three-parameter hybrid functional
combined with LeeeYangeParr correlation functional) and M06
(which is global hybrid meta-GGA) functional. The 6-31G(d,p), cc-
pVDZ and def2-TZVPP basis sets were used for the first and sec-
ond row C, S, N, Cl and H atoms, and the LANL2DZ, def2-SVP and
2.2.2. Synthesis of peripherally substituted cobalt (II)
phthalocyanine (2)
A mixture of (1) (0.100 g, 2.36 mmol), anhydrous CoCl2 (0.030 g,
0.110 mmol) and a catalytic amount of DBU (1,8-diazabicyclo[5.4.0]
undec-7-ene) in n-hexanol (2 cm3) was refluxed at 150 ꢀC in a
sealed glass tube for 6 h under an argon atmosphere. After cooling

H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
3
def2-TZVPP basis set were employed for cobalt and indium metal
atoms, using the genecp approach. The compounds were subjected
to optimization process using B3LYP/6-31G(d,p)–(LANL2DZ), and
QTAIM process with the B3LYP/cc-pVDZ–(LANL2DZ), B3LYP/
LANL2DZ, B3LYP/6-31G(d,p)–(def2-SVP), and M06/def2-TZVPP
methods. The energies of the optimized structures of both ligand
and complexes were the actual energy minimum due to the
absence of imaginary frequencies in the IR calculations.
In the FT-IR calculations, the optimized geometries were per-
formed by using the mixed 6-31G(d,p) with LANL2DZ basis sets
under the B3LYP functional. For NMR calculations, the compounds
were re-optimized in the chloroform phase, and Gauge-
independent atomic orbital (GIAO) method was used for the 1H
and 13C NMR calculations. The CPCM-SCRF (self-consistent reaction
field) procedure was used for modeling the solvent effect. Relative
chemical shift values were calculated by subtracting the TMS
shielding (31.8821 ppm). The frontier molecular orbital (FMO) en-
ergy eigenvalues were used to calculate global chemical reactivity
parameters such as chemical hardness and electronegativity.
Charge distribution on the individual atoms of the compounds
was evaluated using natural bond orbitals (NBOs) population
analysis [35e39]. Moreover, Bader’s quantum theory of atoms in
molecules (QTAIM) [40,41] was also used to analysis the electron
density distributions in the compounds. QTAIM analysis was also
performed to determine the intramolecular interactions and to
determine the ring-critical points (RCPs) of the charge density
distribution and the bond-critical points (BCPs) of the bonding
benzimidazole ring were observed at around 1586-1538 cmꢁ1, -C-N
vibration bands benzimidazole ring was appeared at around 1270-
1217 cmꢁ1, -C-S of benzimidazole and phthalonitrile ring strong
stretching vibrations were observed at 819 and 750 cmꢁ1 respec-
tively. In the FT-IR spectrum of phthalocyanine complexes (2e3),
the sharp peak of the C^N vibration of phthalonitrile compound
(1) at 2234 cmꢁ1 was observed as expected. The characteristic
benzimidazole NeH stretching vibration band of phthalocyanine
the complexes was detected at around 3295 cmꢁ1. Stretching CeS
vibrations of the phenyl ring of phthalocyanine the complexes
were observed at 774 and 762 cmꢁ1, respectively. Stretching CeS
bands of benzimidazole ring of phthalocyanine complexes (2e3)
were observed at 934 and 928 cmꢁ1, respectively. One of the CeN
vibration bands of phthalocyanine complexes (2e3) were
observed at around 1318 and 1308 cmꢁ1, respectively. A very good
agreement was observed between the experimental results and the
theoretical calculations, and the data were given to Table 1.
The calculated harmonic vibrational frequencies were typically
larger than the experimentally observed vibrational frequencies,
besides both experimental and theoretical calculations showed
that vibration frequencies were higher in the complex structures
than those of ligand. Vibration spectra are highly affected by charge
distribution on the molecule so that the shifting of the vibrational
frequencies of the complex compounds to higher regions can be
explained by the charge flow between cyanide group and benz-
imidazole ring, and by the donation of electrons to the empty d-
orbits of metal ions.
atoms. Furthermore, the electron density (
r
) and potential energy
In the 1H NMR spectrum of compound 1, the characteristic NH
peak of the benzimidazole ring appeared at 13.20 ppm. Three ar-
omatic proton signals of the benzene ring including eCN groups
were observed between 7.76 and 8.26 ppm. The aromatic proton
signals (ortho to eS and eCN, 1H) appeared as singlet peak at
8.26 ppm. The aromatic proton signals (ortho to eS and meta to
eCN, 1H) were observed as doublet peaks at 8.08e8.03 ppm. The
aromatic proton signals (meta to eS and ortho to CN, 1H) appeared
as doublet peaks at 7.81e7.76 ppm. The aromatic proton (4H) sig-
nals of benzimidazole ring were observed as multiplied peaks be-
tween 7.58 and 7.17 ppm. The signals observed for aromatic protons
(28H) were observed as multiplets between 8.96 and 7.44 ppm for
complex 3. The 1H NMR peaks of the complex (3) are somewhat
broader than the corresponding peaks of the ligand 1 because of
the presence of four positional isomers which show to tend same
chemical shifts. The other reason for broad signals is that phtha-
locyanines have an equilibrium of aggregation and disaggregation.
1H NMR investigations of phthalocyanine complex (3) provided the
expected chemical shifts for the structure. The characteristic NH
peak of benzimidazole ring of phthalocyanine complex (3) was
appeared at 12.82 ppm. 1H NMR and 13C NMR measurements of the
cobalt phthalocyanine complex (2) were precluded due to its
paramagnetic nature. The experimental and theoretical data are
given in Table 2, based on Fig. 1.
The aromatic carbon of the benzimidazole ring (imidazole CeS-
Ph) appeared at 143.1 ppm. The aromatic carbon of the phthaloni-
trile ring (-S-C-Ph) appeared at 142.1 ppm. The characteristic C^N
peaks of phthalonitrile (1) appeared at 116.0 ppm. The other aro-
matic carbons were also observed at 135.1, 133.7, 133.6, 123.5, 116.4,
116.1,113.2 ppm. The Experimental and theoretical data are given in
Table 3, based on Fig. 2. The theoretical calculations showed that
the chemical shifts of C11 and C13 atoms, which are the closest to
central metal atoms, were more distinct than the other carbon
atoms. The spectroscopic data of the compounds are consistent
with the values of previously reported similar compounds and the
literature [28,42,43].
density (V), and bond path length (BPL) calculations of the NeH
bonds were also determined and associated with the antioxidant
characteristic of the metal complexes.
3. Results and discussion
3.1. Synthesis and characteristics
Scheme 1 shows the synthetic pathway of phthalonitrile de-
rivative (1) and their novel cobalt and indium phthalocyanine
complexes (2 and 3).
Firstly, 1H-benzo[d]imidazole-2-thiol was treated with 4-
nitrophthalonitrile in the presence of anhydrous K2CO3, giving
the corresponding b-substituted phthalonitrile derivative including
benzoimidazole group (1). In contrast to the literature [28], in this
study column chromatography was preferred to purify the phtha-
lonitrile derivative (1) instead of crystallization because of higher
yield. Secondly, targeted peripherally benzoimidazole-substituted
cobalt and indium complexes (2 and 3) were obtained by using
the anhydrous metal salts in appropriate solvents in the presence of
DBU at 150e160 ꢀC, the reaction was stopped when the color of the
reaction mixture turned dark blue-green. Crude products were
washed with methanol several times and purified with column
chromatography on silica gel.
3.2. Spectral properties
In the FT-IR spectrum of compound 1, the asymmetric and
symmetric stretching bands of the nitro group (eNO2) of 4-
nitrophthalonitrile were not observed at 1533-1342 cmꢁ1. The
mercaptan group (SH) signal of the starting material did not appear
near 2600-2550 (weak) cmꢁ1. The results showed that the expected
product was obtained. In the IR spectrum, the characteristic NeH
vibration band of benzimidazole ring was observed 3289 cmꢁ1
the characteristic aromatic CeH vibration band was appeared at
around 3100-3067 cmꢁ1, the sharp peak for the C^N vibration of
the phthalonitrile (1) at 2361 cmꢁ1, eC]N vibration bands of
,
The mass spectra of derivatives, which were obtained by MALDI-
TOF techniques, confirmed the proposed structures. Using the

4
H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
Scheme 1. The synthesis of phthalonitrile derivative (1) and their cobalt and indium complexes (2 and 3) (i) K2CO3, DMSO, 50 ꢀC. (ii) DBU, Hexanol, CoCl2, 150 ꢀC. (iii) DBU,
Quinoline, InCl3, 160 ꢀC.
Table 1
Experimental and calculated FT-IR values of the compounds (cmꢁ1) by B3LYP functional.
Comp.
n
NeH
n
CeH(Ar.)
n
^
C
n -C
]
n
-C-N
n -C-S
N
N
Exp.
1
2
3
1
2
3
3289
3294
3295
3653
3673
3673
3100e3067
3052
3048
3207e3172
3225e3187
3224e3187
2361, 2339
e
1586, 1538
1270, 1217
819, 750
934, 774
928, 762
1095, 982
1071, 980
1067, 980
1642, 1476, 1448
1646, 1480, 1452
1505, 1460
1572, 1517, 1470
1531, 1517, 1469
1318, 1244, 1162
1308, 1236, 1160
1287, 1248
1322, 1303, 1145
1384, 1367, 1304
e
B1
B1eB2
2345, 2340
e
e
B1: 6-31G(d,p), B2: LANL2DZ.
Table 2
Experimental and calculated 1H NMR data by B3LYP functional (
d
, ppm, in chloroform), TMS: 31.8821.
Comp.
H1
H2
H3
H4
H6
H7
H8
H5
Exp.
1
7.58
7.23
7.17
7.52
8.26
8.08e8.03
7.81e7.76
13.2
2
3
precluded due to its paramagnetic nature
aromatic protons (28H) were observed as multiplets between 8.96 and 7.44
12.82
9.39
8.43
9.26
B1
B1eB2
1
2*
3*
8.31
7.95
7.82
7.90
7.58
7.76
7.92
7.47
7.81
7.97
7.42
8.30
7.47
10.46
9.90
7.95
8.81
9.38
8.09
10.20
9.83
*: The chemical shifts of the hydrogens in the identical positions of the four positional isomers were calculated as the same. B1: 6-31G(d,p), B2: LANL2DZ.
instrument’s reflectron mode to compare the theoretical and
experimental monoisotopic m/z values of the metal complexes and
starting materials, the highly resolved signals of each species in the
MALDI-TOF mass spectra were well obtained. After evaluation of
the MALDI-TOF mass spectra, it was found that the desired starting
compounds and complexes were successfully synthesized and
purified using the experimental methods expressed in this study. In
addition, it has been found that the synthesized compounds are
sufficiently stable to detect structures without significant frag-
mentation under the conditions of MALDI-MS. The molecular ion
peaks were observed at m/z: 276.823 [M]þ for 1 (Fig. 3), 1165.255
[MþH]þ for 2, 1256.150 [M]þ for 3.

H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
5
monomers, dimers, and rings into higher-order complexes within
the solvent. For aggregation in phthalocyanines are a number of
parameters such as concentration, the nature of the solvent, sub-
stituents present at the periphery or non-periphery, the metal ion
at the macrocyclic core, and the operation temperature [17,43].
Dilution studies were recorded in THF solvent as to better deter-
mine the solubility and aggregation properties of the complexes. As
an elucidator example, peripherally benzimidazole-substituted
indium complex (3) was studied using concentrations ranging
Fig. 1. The numbering of hydrogens on the compounds.
Table 3
Experimental and calculated13C NMR data by B3LYP functional (
d, ppm, in chloroform), TMS: 182.4656.
Comp.
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
Exp.
B1
B1eB2
1
1
2
3
113
114
95
116
129
109
111
116
127
108
109
113
124
105
106
135
150
129
129
134
139
120
120
143
145
139
132
142
156
124
131
124
133
115
109
116
121
127
124
116
119
139
139
116
115
127
122
116
119
139
140
124
138
110
110
134
132
122
117
97
*: The chemical shifts of the carbons in the identical positions of the four positional isomers were calculated as the same. B1: 6-31G(d,p), B2: LANL2DZ.
Fig. 2. The numbering of carbon atoms of the compounds.
Fig. 4. Absorption spectra of substituted cobalt and indium phthalocyanine complexes
(2 and 3) in THF. Concentration ~1 ꢂ 10ꢁ5 mol/dm3.
Fig. 3. MALDI-TOF mass spectrum of phthalonitrile compound 1.
3.3. Ground state electronic absorption spectra and aggregation
behavior
The electronic absorption spectra of the phthalocyanine com-
plexes 2 and 3 showed typical Soret band between 334 and 376 nm
and strong Q-band in the near-infrared between 672 and 706 nm in
THF (Fig. 4). Red-shifts were detected for studied Pc complexes (2
and 3) following 1H-benzo[d]imidazole-2-thiol substitution
compared to unsubstituted Co (II) and In (III) Pcs. The single (nar-
row) Q bands demonstrated that these complexes were in mono-
meric form in the solvent medium.
Fig. 5. Electronic absorption spectra of
3 in THF at different concentrations: (A)
8 ꢂ 10ꢁ5, (B) 4 ꢂ 10ꢁ5, (C) 2 ꢂ 10ꢁ5, (D) 1 ꢂ 10ꢁ5 mol/dm3. The inset shows the cali-
Aggregation can frequently be explained as the incorporation of
bration plot for Q band maximum.

6
H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
Table 4
from 10 mM to 80 mM (Fig. 5).
The linear regression equations and IC50 values of Trolox and compounds 1e3.
A linear regression analysis was performed between the density
of the Q-band and the concentrations of phthalocyanine complex 3
for indicating compliance with the Lambert-Beer law. At the stud-
ied micromolar concentration, the peripherally substituted cobalt
and indium phthalocyanines were essentially free from aggregation
in THF. The absorption intensity obeys Lambert-Beer’s law, raising
the temperature did not yield new bands on the upper energy side,
which would mean the absence of aggregated species (see the inset
of Fig. 5) [17,44,45].
Concentration Equation (0.1e2.0)x10ꢁ6
M
R2
IC50 (mM)
Trolox
y ¼ 1.57x þ 6.51
y ¼ 2.75x þ 7.07
y ¼ 2.27x þ 7.22
y ¼ 2.65x þ 7.55
0.840
0.985
0.993
0.969
27.70
15.61
18.85
16.02
1
2
3
The average bond lengths of the optimized Co and In complexes
were calculated as 1.93865 and 2.13145 A for Coꢁ(N2, N4, N6, N8)
and Inꢁ(N2, N4, N6, N8), respectively. In the Indium complex, the
bond lengths of the nitrogen atoms and bounded carbon groups
around the central metal were also larger than those of the other
compounds. Besides, the NBO analysis showed that the net atomic
charges on the N(1), N(2), C1, C2, C3 and S atoms of ligand
were ꢁ0.578, ꢁ0.500, ꢁ0.173, 0.216, ꢁ0.197 and 0.340 au, respec-
tively. In the compounds 2 and 3, the charges on these atoms were
calculated as ꢁ0.579, ꢁ0.503, ꢁ0.184, 0.225, ꢁ0.206 and
0.312; ꢁ0.578, ꢁ0.502, ꢁ0.181, 0.223, ꢁ0.204 and 0.317 au,
respectively. While the atomic charge of the triple bound nitrogen
atoms of the ligand was ꢁ0.269 au, it was calculated as ꢁ0.561
and ꢁ0.485 au for the atoms N(2,4,6,8) and N(1,3,5,7) of compound
2, respectively. Similarly, the charge on these atoms for compound
3 was calculated as ꢁ0.722 and ꢁ0.491 au, respectively. These sit-
uations indicated that the net atomic charges on the coordinating
atoms of the ligand were strongly influenced by complexation. This
strong interaction between metal ions and the ligand resulted in
the transfer of charge from phthalonitrile group of ligand to metal.
The calculations revealed that a two-way charge flow occurred:
Phthalonitrile groups form a conjugated structure around the
central metal atoms, and electron delocalization occurs in this re-
gion. The second is that the benzimidazole ring acts as an electron
attractor because of the decrease in the electronegativity of the
Cyanide group which is conjugated around the metal atom,
resulting in an increase in charge density on the benzimidazole
ring. The calculations showed that the charge flow in the complex 3
was greater than that in complex 2. This can be predicted as one of
the reasons why the indium complex exhibits a better antioxidant
property than the cobalt complex. Important electronic properties
of the chemical species can be explained by utilizing the FMOs.
Calculated HOMO-LUMO energies and their corresponding energy
differences are given in Table 6.
3.4. Antioxidant properties
DPPH method is widely used to evaluate the antioxidant activity
of organic and inorganic compounds due to its hydrogen donation
ability [46]. The percent inhibition changes calculated by the DPPH
method for the compounds (1e3) and Trolox at different concen-
trations were given in Fig. 6. It was observed that the compounds
(1e3) showed more percent inhibition at all concentrations against
Trolox as standard antioxidant.
In addition, IC50 values obtained from the linear regression
equation are given in Table 4. Obtained calibration curves were
used to measure the IC50 values of the antioxidants required to
reduce the DPPH radical by 50% for each the phthalocyanine
complexes [47]. When the IC50 values were examined, the antiox-
idant activity as follows: 1 > 3 > 2 > Trolox sequencing. Compound
1 was displayed more effective antioxidant activity than metal
complexes (2,3).
3.5. Theoretical analysis
Geometric and electronic structure calculations of the ligand
and its metal complexes were carried out by the DFT method. The
optimized molecular structures of the compounds with minimum
molecular energy are shown in Fig. 7. Selected bond lengths, bond
angles, and dihedral angles are listed in Table 5.
The calculations showed that the coordination centers were co-
planar with symmetrical bond distances and angles around the
cobalt and indium atoms. Calculations revealed that the bond an-
gles, C1eSeC2 and SeC2eN, were strongly influenced by
complexation.
HOMO and LUMO eigenvalues and energy gap play an important
role in molecule activity. The high chemical reactivity of a molecule
is generally associated with a small FMO energy gap, that is, HOMO-
LUMO energy gap is a measure of kinetic stability of the molecule. A
relatively small HOMO-LUMO energy gap of compounds 2 and 3
(2.19 and 2.08 eV, respectively; Fig. 8) shows that the ones exhibit
low kinetic stability and high chemical reactivity. In this context,
the calculations showed that complex 3 was more reactive than
complex 2, consistent with experimental data, as seen in Table 6.
Furthermore, compounds with higher electronegativity have a
higher tendency to react. The electronegativity of the Indium
complex (4.20 eV) was greater than that of the Cobalt complex
(3.96 eV), and it was also observed that it showed experimentally
better antioxidant properties. All the HOMO, LUMO and electro-
static potential (ESP) maps of the compounds are given in Sup-
plementary A.
Although the effects of intermolecular interactions on molecular
conformation along with external factors such as temperature,
pressure and external variables that affect the system in a reaction
process cannot be directly reflected in the calculation process, the
minimum molecular energy values obtained from the calculations
can be used as a comparison tool. The difference between the
Fig. 6. Variation of percent inhibition calculated by the DPPH method for Trolox, 1, 2
and 3 at different concentrations.

H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
7
Fig. 7. The optimized molecular structures of the ligand (1) and its metal complexes (2, 3).
Table 5
Selected bond lengths (Å), angles and dihedral angles for the investigated ligand and its complexes (B3LYP/6-31G(d,p)-LANL2DZ).
Bond Length (A)
Angles (o)
Dihedral angles
Compound 1
C1eC3
C1eS
1.3982
1.7945
1.7720
1.3792
1.3108
1.00852
C3eC1eS
C1eSeC2
SeC2eN(1)
SeC2eN(2)
C3eC1/C2eN(2)
ꢁ7.891
SeC2
C2eN(1)
C2eN(2)
N(1)-H
Compound 2
C1eC3
C1eS
1.3974
1.8013
1.7722
1.3810
1.3115
1.00838
1.93865
C3eC1eS
C1eSeC2
SeC2eN(1)
SeC2eN(2)
116.502
103.565
119.435
127.357
C3eC1/C2eN(2)
ꢁ17.698
SeC2
C2eN(1)
C2eN(2)
NeH
CoeN(2,4,6,8)
Compound 3
C1eC3
C1eS
SeC2
C2eN(1)
C2eN(2)
NeH
1.3979
1.8003
1.7719
1.3808
1.3116
1.00845
2.13145
C3eC1eS
C1eSeC2
SeC2eN(1)
SeC2eN(2)
116.409
103.584
119.501
127.271
C3eC1/C2eN(2)
ꢁ13.844
IneN(2,4,6,8)
calculated energies of the compounds before and after the reaction
with DPPHꢃ, ie the energy changes, showed an association with
their antioxidant properties. The difference between the molecular
energies of the complex 2 before and after the reaction was
calculated as the highest (1863.13 kJ/mol), indicating that the
tendency to react with DPPHꢃ was lower than the complex 3
(1724.96 kJ/mol).
The QTAIM analysis was also performed to determine the
intramolecular interactions, the ring-critical points (RCPs) of the
charge density distribution and the bond-critical points (BCPs) of

8
H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
Table 6
Calculated electronic parameters of compounds 1e3 by using B3LYP method.
Basis set
Comp.
E (kcal/mol)
E (kcal/mol)
(oxidized)
D
(kJ/mol)
EHOMO (eV)
ELUMO (eV)
D
E
c (eV)
B1
B1eB2
1
2
3
ꢁ748994
ꢁ3087185
ꢁ3286125
ꢁ889741
ꢁ890138
ꢁ748581
ꢁ3086740
ꢁ3285713
1729.15
1863.13
1724.96
ꢁ1662.16
ꢁ6.56
ꢁ5.05
ꢁ5.23
ꢁ5,63
ꢁ6,00
ꢁ2.35
ꢁ2.86
ꢁ3.16
ꢁ2,97
ꢁ3,31
4.21
2.19
2.08
2,66
2,69
4.46
3.96
4.20
4,30
4,65
B1
DPPHꢃ
DPPH(Re)
B1: 6-31G(d,p), B2: lanl2dz, DPPHꢃ: Radical DPPH, DPPH(Re): Reduced DPPH, E: Energy,
D
¼ Eoxidized - E,
D
E¼ ELUMO ꢁ EHOMO
, c :Electronegativity.
Fig. 8. HOMO-LUMO maps of the complexes 2 and 3.
the bonding atoms (Fig. 9; the all QTAIM visualizations of com-
pounds are given Supplementary B). Using the QTAIM analysis, the
relationship between the electronic properties and antioxidant
characteristics of the compounds was demonstrated. The antioxi-
dant characteristic of a compound is based on the concept that a
hydrogen donor is an antioxidant. The antioxidant effect of a
compound is proportional to the oxidation of DPPHꢃ in the test
sample. As a result of the reaction DPPHꢃ þ RH ¼ DPPH þ R, the
higher antioxidant property of a compound requires its active
hydrogen bonds to be weaker, ie, the hydrogen can be easily
removed by DPPHꢃ. The strength of these hydrogen bonds is pro-
was seen that, as the charge density of the NeH bond of the
compound increased, the antioxidant property of the compound
decreased. In this sense, the bond path length (BPL) and bond
length can be used as a measure of the antioxidant activity. As a
result of the calculations using different basis sets and methods, as
given in Table 7, it was observed that the antioxidant properties of
the compounds increased in direct proportion to the BLs and BPLs
of the NeH bonds of the compounds, that is, the compounds with
larger BL and BPL showed higher antioxidant properties. In
contrast, the compounds with lower charge density on the NeH
bond showed higher antioxidant properties. So that, the potential
energy density of the NeH bond can also be used as a method to
portional to the charge density (r) on the active hydrogen bonds. It

H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
9
Fig. 9. QTAIM visualization of compound 2; green points: bond critical points, red points: ring critical points; Dashed lines: interactions of respective atoms.
Table 7
and its peripherally tetrasubstituted metallophthalocyanines (2
and 3) were synthesized for the first time. All the products were
characterized by using different spectroscopic methods UVeVis,
FT-IR, NMR, Mass spectrometry and elemental analyses. Antioxi-
dant activities of the compounds (1e3) were carried out using by
the DPPH method. The experimental and theoretical antioxidant
activity ranking of the compounds was obtained as 1 > 3 >
2 > Trolox. Quantum chemical calculations and QTAIM analysis
revealed the relationship between the antioxidant properties and
electronic data of the synthesized compounds. It was calculated
that the charge density on the bond decreased as the bond lengths
of active hydrogen atoms bound to electronegative atoms
increased, whereby the bond energy was also reduced, so that the
reaction of the compounds with DPPH was easier, which was
associated with an increase in their antioxidant properties.
Furthermore, the potential density of the active hydrogen bond can
also be used to compare the antioxidant properties of the
compounds.
QTAIM data of the NeH bond of the compounds.
Basis set
Comp.
V
N-H (au)
r
NeH (au)
BPLN-H (Å)
BLN-H (Å)
B3LYP/B1eB4
1
2
3
1
2
3
1
2
3
1
2
3
ꢁ0.485222
ꢁ0.485673
ꢁ0.485620
ꢁ0.445110
ꢁ0.445726
ꢁ0.445574
ꢁ0.476597
ꢁ0.477048
ꢁ0.476983
ꢁ0.630472
ꢁ0.631462
ꢁ0.630959
0.331699
0.332086
0.332023
0.314561
0.314892
0.314822
0.330528
0.330892
0.330826
0.351807
0.352345
0.352154
1.828615
1.828270
1.828310
1.866623
1.866253
1.866330
1.830377
1.830087
1.830127
1.854869
1.854213
1.854576
1.01270
1.01241
1.01246
1.01110
1.01086
1.01092
1.01214
1.01188
1.01193
1.00420
1.00385
1.00401
B3LYP/B2
B3LYP/B3eB2
M06/B5
B1: 6-31G(d,p), B2: LANL2DZ, B3: cc-pVDZ, B4: def2-SVP, B5: def2-TZVPP, V: Po-
tential energy density, : Electron density, BPL: Bond path length, BL: Bond length.
r
compare the antioxidant characteristics of the compounds, as seen
in Table 7.
4. Conclusion
Declaration of competing interest
In conclusion, 4-(benzo[d]imidazole-2-ylthio)phthalonitrile (1)
The authors declare that they have no conflict of interest.

10
H. Yakan et al. / Journal of Molecular Structure 1202 (2020) 127259
j.jphotochem.2015.04.003, 54e67.
Appendix A. Supplementary data
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