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New Charge-Transfer Complexes of Organochalcogenide Compound
Based on Aryl Acetamide Group with Quinones: Synthesis, Characterization,
Antioxidant, and Computational Study
Attared Fadhel Hassan1, Nahed Hazim Al-Haidery1, Suhad Rajab Kareem1, Sabah Abbas Malik2,
Shaker Abdel Salem Al-Jadaan3, and Nuha Hussain Al-Saadawy4*
1Department of Chemistry, College of Science, University of Basrah, Basrah 61004, Iraq
2Department of Pharmaceutical Chemistry, Branch of Pharmaceutical Chemistry, University of Kufa, Najaf 54001, Iraq
3Department of Pharmaceutical Chemistry, College of Pharmacy, University of Basrah, Basrah 61004, Iraq
4Department of Chemistry, College of Science, University of Thi-Qar, Muthanna 64001, Iraq
* Corresponding author:
email: nuhaalshather@yahoo.com
Received: August 29, 2023
Accepted: October 21, 2023
DOI: 10.22146/ijc.88463
A
bstract: This study aims to prepare charge transfer complexes derived from
organochalcogenide of arylamide derivatives with different quinones. A new charge-
transfer complexes have been developed through a direct reaction between
(PhNHCOCH2)2Se, (o-CH3PhNHCOCH2)2Se, and (PhCH2NHCOCH2)2E, where E = S,
Se, and Te are electron donors and different quinones are electron acceptors. The
quinones used in the reaction were 2,3-dichloro-5,6-dicyanobenzoquinones (DDQ),
7,7’,8,8’-tetracyanoquinodimethane, and tetracyanoethane. The electron donors and
electron acceptor mol were 1:1, and the reaction was conducted in acetonitrile. Infrared,
1H and 13C-NMR spectroscopic data characterized all complexes. The complexes’
antioxidant activity was evaluated through α,α-diphenyl-β-picrylhydrazyl at 10–
0.312 mg/mL. The results showed that all complexes exhibited promising antioxidant
activities. Among them, (PhCH2NHCOCH2)2S·DDQ compound had the least IC50 value
of 6.725 mg/mL, indicating a potent scavenging property compared to other compounds.
The molecular structures of charge-transfer complexes were investigated using hybrid
density functional theory (B3LYP) and basis set 3-21G. We obtained geometrical
structures' highest occupied molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) surfaces and energy gaps through geometric optimization. We also
investigated the molecular shapes and contours of the prepared compounds through
geometrical optimization and compared the HOMO energy of the CT compounds to
investigate donor and acceptor properties.
Keywords: density functional theory; radical scavenging activity; organochalcogenide
compound; quinone charge-transfer complexes; highest occupied molecular orbital
■ INTRODUCTION
Charge-transfer complexes combine an electron
donor with low ionization energy and an electron
acceptor with high electronegativity. Some common
examples of electron-donor compounds include amines,
nitrogen–mixed bases, crown ethers, and
organochalcogenides [1-8]. The spectra of these
complexes are characterized by the appearance of a
charge-transfer absorption band in the visible region
resulting from electron transition between the highest
occupied molecular orbital (HOMO) for a donor with
the lowest unoccupied molecular orbital (LUMO) for
the acceptor. This transition produces the characteristic
intense color for these complexes, which can be used for
quantitative drug estimation [9-10].
Charge-transfer complexes have become a subject
of significant interest because of their unique physical
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and chemical properties and potential application in
various fields. One such area is the use of these complexes
in 3rd generation solar cells, which are organic solar cells
known for their efficient and cost-effective light absorbers
[11-13]. Several physiologically and pharmacologically
active charge-transfer complexes have been developed to
treat various diseases. For example, piperazine and
imidazole derivatives have shown promising anticancer
activity [14-16]. Another exciting discovery involves the
antimicrobial properties of the charge-transfer complexes
formed between 3,5-dinitrosacylic acid and o-
phenylenediamine intact DNA, demonstrating their
antimicrobial activity, potentially valuable for developing
various oncology drugs [17].
In recent decades, growing interest has been shown
in synthesizing an essential class of compounds with
diverse biological properties. The compounds are
quinones that contain selenium or tellurium. The Se or Te
atom is introduced into the quinones as an electrophile,
using a suitable nucleophilic carbon such as a double
bond, arylchalcogenyl halides or dichalcogenides. These
compounds have been found to have a high potential as
bioactive structures. We believe that further research into
these compounds' synthesis and biological evaluation can
lead to new biochemistry tools and new successes in drug
development [18-21]. da Cruz and his co-workers [22]
reported Se-containing quinone based on 1,2,3-triazoles,
evaluating these compounds for antitumor activity in
vitro using several human cancer cell lines. The results
were promising as most compounds showed IC50 below
0.3 μM and were more active than doxorubicin and β-
lapachone, a standard clinical agent for several types of
cancers [21-22].
This study examined the charge-transfer complexes
of organochalcogenide complexes as electron donors with
2,3-dichloro-5,6-dicyanobenzoquinones (DDQ),
tetracyanoethane (TCNE), and 7,7’,8,8’-
tetracyanoquinodimethane (TCNQ) as electron acceptors.
We prepared and characterized these complexes,
evaluating their antioxidant activity experimentally using
α,α-diphenyl-β-picrylhydrazyl (DPPH). To gain a deeper
understanding of these compounds, we also conducted
molecular structure and energy calculations using PM3
and density functional theory (DFT) at the B3LYP/3-
21G level of theory.
■ EXPERIMENTAL SECTION
Materials
All diorganochalogenides were prepared under an
argon atmosphere by the method preparation reported
earlier [23]. Solvents were distilled prior to use and dried
by conventional methods. Ascorbic acid, DPPH, TCNE,
DDQ, and TCNQ with purity of 98% were purchased
from Merck, Sigma-Aldrich.
Instrumentation
The FTIR spectra were measured on FTIR-8400S
SHIMADZU-Japan, 1H (400 MHz) and 13C (100 MHz)
NMR data were run on a Mercury-400 (Bruker
Advance-NEO spectrometer) in DMSO-d6 at ambient
temperature. The UV-vis spectra were recorded on UV-
1650PC: UV-visible spectrophotometer Shimadzu. The
melting point of new charge-transfer complexes was
determined on a Gallenkamp melting point apparatus.
The antioxidant activity for all complexes was measured
on the UV-vis spectrophotometer.
All theoretical calculations were conducted using
computational methods implemented in the
GAUSSIAN09 package [23]. Semi-empirical molecular
orbital theory at the PM3 level was used to optimize the
geometry optimization of the investigated compounds.
The electronic properties of the compounds were
analyzed by applying density functional theory at the
B3LYP/3-21G theoretical level. The hybrid Becke-3-Lee-
Yang-Parr exchange-correlation function (B3LYP) was
used for DFT calculations [24].
Procedure
The following compounds, 2-chloro-N-
phenylacetamide, 2-chloro-N-benzylacetamide, and 2-
chloro-N-(o-tolylacetamide) were prepared according to
the known chemistry literature [25].
Preparation of bis-(N-(o-tolyl)acetamide)selenide
Solution of NaBH4 (0.236 g; 2.90 mmol) in 20 mL
distal water was added to a suspended solution of Se
powder (0.225 g; 6.10 mmol) in 20 mL of distal water
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under an argon atmosphere with gentle heating. A
vigorous reaction occurs with the release of hydrogen
gases. A colorless solution of NaHSe was formed. A
solution of 2-chloro-N-(o-tolylacetamide) (0.53 g;
2.90 mmol) in 30 mL ethanol was added to the above
solution with stirring for 1 h. A violet solution was formed
and filtered. As much as 100 mL of H2O was added to this
solution and extracted the resulting solution with three
portions of chloroform. The solvent was evaporated to a
minimum amount. A violet precipitate was collected,
dried, and recrystallized from ethanol [25]. A violet solid
was obtained (0.41 g) in 79% yield with melting point
(m.p.) of 179 °C. The following compounds, bis(N-
phenylacetamide)selenide (violet) (0.43 g) 82% yield, m.p.
204–205 °C and bis(N-benzylacetamide)selenide (dark
yellow) (0.28 g) 60% yield, m.p.150 °C were also obtained.
Preparation of bis(N-benzylacetamide)sulfide
Solution of Na2S·3H2O (0.325 g; 246 mmol) in
10 mL distal water was added to a solution of 2-chloro-N-
benzylacetamide (0.734 g; 4.92 mmol) in 30 mL of ethanol
with gentle heat and stirring for about 1 h. A pale-yellow
solution was formed, filtered, and added to 100 mL of
distal water and the resulting solution was extracted with
three portions of chloroform. The solvent was evaporated
to a minimum amount. A pale-yellow solid was collected,
dried, and recrystallized from ethanol. A pale-yellow solid
was obtained (0.55 g) in 69% yield, m.p. 138–140 °C.
Preparation of bis(N-benzylacetamide)telluride
A mixture of 0.72 g (5.6 mmol) of Te powder and
0.364 g (5.6 mmol) of KCN in 25 mL of freshly distilled
DMSO was stirred for 1 h at 100 °C under an Argon
atmosphere. A pale-yellow solution of KTeCN formed,
after cooling the mixture to laboratory temperature,
solution of 1.68 g (11.2 mmol) of 2-chloro-N-
benzylacetamide in 25 mL DMSO was added to it
dropwise for 15 min and then stirred for 3 h at 100 °C
[25]. The solution is filtered while it is hot, and then it is
cooled and poured into 300 mL of cold distal water. A
pale-yellow crystal was formed, filtered, washed several
times with ethanol, and dried. A pale-yellow solid
obtained in 70% yield, m.p. 105 °C [26].
Preparation of bis(N-benzylacetamide)chalcogenide.
DDQ charge-transfer complex; E = S, Se, and Te
Solution of DDQ (0.227 g; 1 mmol) in 25 mL dry
acetonitrile was added to the solution of bis(N-
benzylacetamide)chalcogenide (0.222 g, 1 mmol) in
25 mL dry acetonitrile. The mixture was stirred with
gentle heat for 2 h. A reddish solution was obtained
directly, filtered, and evaporated to a minimum amount.
Dark red crystals were collected, dried, and
recrystallized from ethanol with 70–75% yield.
Bis(N-benzylacetamide)sulfide. DDQ CT complex (I):
dark red color, 0.314 g (70%) yield, m.p. 120–123 °C.
(N-benzylacetamide)selenide. DDQ CT complex (II):
dark red color, 0.43 g (75%) yield, m.p.105–107 °C.
Bis(N-benzylacetamide)telluride. DDQ CT complex
(III): red color, 0.44 g (70%) yield, m.p. 167–170 °C.
The following compounds were prepared by the
same procedure described [19].
Bis(N-(o-tolyl)acetamide)selenide. DDQ CT complex
(IV); dark red solid, 0.439 g (73%) yield, m.p. 155–
157°C.
Bis(N-phenylacetamide)selenide. DDQ CT complex
(V); dark red solid, 0.39 g (68%) yield, m.p. 89–91 °C.
Preparation of bis(N-benzylacetamide) E. TCNE CT
complex, where E = S (VI), Se (VII)
A mixture of 1 mmol tetracyanoethane in 25 mL
dry acetonitrile and 1 mmol of (PhCH2NHCOCH2)2E in
25 mL dry acetonitrile was heated quietly with stirring
for 2 h. The olive-green solution was obtained, filtered,
and evaporated to a minimum amount. An olive green
solid was collected, dried, and then recrystallized from
ethanol. Olive-green solid was obtained in 75–80% yield.
Preparation of bis(N-benzylacetamide)selenide.
TCNQ CT complex (VIII)
A mixture of 7,7’8,8’-tetracyanoquinodimethane
(0.204 g; 1 mmol) in 25 mL dry acetonitrile and
(PhCH2NHCOCH2)2S (0.328 g; 1 mmol) in 25 mL dry
acetonitrile was heated gently with stirring for 2 h. A
green solution was obtained, filtered and evaporated to
a minimum amount. A dark green precipitate was
collected, dried, and recrystallized from ethanol. A bright
green solid was obtained 0.425 g (80%) yield, m.p. 96–
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98 °C. The preparation of charge-transfer complexes has
been carried out following reaction (Scheme 1).
Studying capacities for antioxidants
These complexes' antioxidant activity was evaluated
experimentally using DPPH assay. The assay is a reliable
analytical method for measuring various antioxidants’
free radical scavenging capacities. The radical in the
DPPH has a strong absorption maximum at 517 nm
purple color. When this radical reacts with the
antioxidant, the absorbance of DPPH decreases [27-28].
An aliquot of the test sample (1 mL) was added to 3 mL of
0.2 mM solution of DPPH prepared in methanol. Then,
the reaction mixture was vortexed for 2 min and kept at
room temperature for 30 min in the dark. The decreased
absorbance was measured at 517 nm. The radical-
scavenging activity was obtained using the Eq. (1);
Ct
C
AA
Scavenging activity (%)= 100
A
(1)
where AC = Absorbance of blank, At = Absorbance of the
sample. The required concentration mg/mL for
inhibiting 50% of DPPH (IC50) values was determined by
linear regression (Table 1).
Scheme 1. Preparation of new charge-transfer complexes (I-VIII)
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Table 1. Physical properties and UV-vis data for CT complexes
Comp. Chemical structure m.p. (°C) Color Yield (%) λmax (UV-vis, nm)
I (PhCH2NHCOCH2)2S·DDQ 120–122 Dark-red 70 217, 251, 354
II (PhCH2NHCOCH2)2Se·DDQ 105–107 Red 75 221, 233, 351, 391, 655
III (PhCH2NHCOCH2)2Te·DDQ 167–170 Red 70 215, 250, 351, 590
IV (PhNHCOCH2)2Se·DDQ 155–157 Red 73 222, 256, 350, 474
V (o-CH3PHNHCOCH2)2Se·DDQ 89–91 Dark-red 68 214, 249, 364, 393
VI (PhCH2NHCOCH2)2S·TCNE 115–117 Green 75 214, 296, 396, 473, 647, 742
VII (PhCH2NHCOCH2)2Se·TCNE 192–195 Brown 80 215, 211, 276, 393
VIII (PhCH2NHCOCH2)2S·TCNQ 96–98 Bright-green 80 263, 311, 399, 474, 610, 735
■ RESULTS AND DISCUSSION
The reaction of (PhNHCOCH2)2Se, (o-
CH3PhNHCOCH2)2Se, and (PhCH2NHCOCH2)2E, where
(E = S, Se, and Te) as electron donors and quinones such
as DDQ, TCNQ, and TCNE as electron acceptors in
acetonitrile solution yield solid complexes 1:1
stoichiometry. Table 1 shows the structure and physical
properties of new complexes. We focused on identifying
functional groups in the quinones, specifically the C=O
The and C≡N groups, by studying FTIR spectra of charge-
transfer complexes. Additionally, we identified essential
bands in organic chalcogenide such as N–H, C=O, C=C,
C–E (E = S, Se, Te), C–H aliphatic, and C–H aromatic.
The FTIR spectra study of DDQ complexes I-V
revealed some interesting findings. A slight shift was
observed in the stretching vibration of the C≡N group,
about ± 20 cm−1. There was also a shift in the stretching
vibration of the C=O group toward a large wavenumber
with a change in the shape and some alteration in the
intensity, indicating an interplay between the
components of these complexes.
The TCNE charge-transfer complex VI exhibited a
strong absorption band at 2,214 cm−1, returning to the
stretching vibration of the C≡N group. On the other hand,
complex VII showed two bands at 2,210 and 2,075 cm−1,
returning to the stretching vibration of the C≡N group.
Notably, the frequency of the C≡N group in free TCNE
is 2,222 cm−1. The TCNQ CT complex VIII exhibited a
strong absorption band at 2,187 cm−1 due to the stretching
vibration of the C≡N group in the TCNQ− ion radical.
This mechanism indicates that the charge transfer from
donor to acceptor is complete, and the TCNQ reduction
to TCNQ− is complete [27-28]. Other unsymmetrical
vibrations for C–H aromatic, C–H aliphatic, C=O and
N–H for amide group, and C–E (E = S, Se and Te), were
found at the expected region [24,29-30] as shown in
Table 2 and Fig. S1-S8.
The study conducted in ethanol solvent at 200–
800 nm examined the UV-vis spectra of charge-transfer
complexes and their component. The results were
included in Table 1 and Fig. S9. Organic molecules such
as quinones have electron systems and possess strong
absorption bands that appear in the UV region of the
Table 2. FTIR spectra data of prepared CT complexes
Comp. N–H C=O amide C≡N C–Halip. C–Har. C=O DDQ E–C
E= S, Se or Te C–Cl
I 3294 1647 2249 2924 3051 1801 698 748
II 3271 1643 2249 2924, 2866 3036 1740 613 775
III 3275 1643 2245 2854 3078 1710 498 732
IV 3255 1654 2222 2812 3070 1790 597 756
V 3240 1658 2245 2858 3032 1739 613 752
VI 3298 1647 2214 2924 3043 - 698 -
VII 3452 1647 2210, 2079 - 609 -
VIII 3298 1647 2187 2920 3039 - 698 -
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spectrum due to the permitted transitions of type π-π* and
n-π*. When these compounds bind with
organochalcogenide compounds, a slight change occurs
in the spectra of the new compounds. Additionally, new
absorption bands emerge in the visible region, which can
be attributed to charge transfer bands. DDQ charge-
transfer complexes I-V show multi charged transfer bands
at 350–364 nm, and new bands at 587, 474, and 393 nm,
for CT complexes III, IV, and V, respectively. These bands
are attributed to the electron transition from HOMO for
the donor to LUMO for the acceptor [7,29-30]. Moreover,
TCNE charge-transfer complex VI exhibited new bands
at 396, 473, 647, and 742 nm, while CT VII showed a new
band at 393 nm. TCNQ CT complex VIII exhibited new
bands at 399, 474, 610, and 744 nm due to electron
transfer from HOMO for the donor to LUMO for the
acceptor [7,29-30].
1H-NMR spectra of all new CT charge-transfer
complexes in DMSO-d6, and the results are tabulated in
Table 3, Fig. S10-S16 and Scheme 2. The 1H-NMR spectra
displayed signals showing all the expected peaks. CT
complexes I-VIII exhibited signals at 8.5–10.17 ppm that
belonged to NH-amid proton [22,26,28]. The aromatic
proton gives multiple signals in the range 6.69–
7.59 ppm, while the aliphatic protons of CH2E where (E
= S, Se, and Te) displayed signals in the range 3.36–
3.76 ppm [22,26,28]. However, we found that all
complexes except IV and V exhibited signals in the range
4.27–4.49 ppm attributed to the proton of CH2N
[22,28,30].
13C-NMR spectra of CT complexes were recorded
in DMSO-d6, and their data were summarized in Table 3
and Fig. S17-S22. Scheme 3 represents the numbering of
carbon atoms of CT complexes. The 13C-NMR spectra
for new complexes agreed with their structures, further
validating the characterization of these complexes. All
CT complexes exhibit a low field signal in the range of
168.77–171.05 ppm attributed to the carbon of C=O
(amide) group, they also exhibit low field signals of
aromatic carbon atoms in the 119.55–139.73 ppm range.
The DDQ CT complexes I-V displayed signals at 151,
114, and 102 ppm attributed to the carbon of C=O, C≡N,
and C–CN, respectively [29,31-32]. Complexes I, VI,
and VIII exhibited signals at 35.46–35.48 ppm belonging
Table 3. 1H- and 13C-NMR spectral data of selected CT complexes
Comp. 1H-NMR (ppm), DMSO-d6 13C-NMR (ppm), DMSO-d6
I 8.75(s)NH; 7.22–7.33(m)Ar–H;
4.33–4.37(s)H8,H9; 2.54(s)H6,H7
169.18 (C7); 114.18 (C≡N); 102.13 (C9); 151.29 (C10, C13); 139.67 (C11, C12);
42.78, 43.05 (C6); 35.48 (C8); 135.06, 129.96, 129.63, 128.77, 127.91, 127.68,
127.29 (Ar C)
II 8.56(s)NH; 7.22–7.45(m)Ar–H;
4.29(s)H8,H9; 3.39–3.38(s)H6,H7
170.32 (C7); 114.19 (C≡N); 102.14 (C9); 151.31 (C10, C13); 139.73 (C11, C12);
42.77 (C6), 26.07 (C8); 129.66, 128.77, 127.77, 127.66, 127.28 (Ar C)
III 8.56(s)NH; 7.22–7.46(m)Ar–H;
4.26–4.31(s)H8,H9; 3.52(s)H6,H7
166.57, 164.84 (C7); 112.57 (C≡N); 100.50 (C9); 149.69 (C10, C13); 137.87,
137.68 (C11, C12), 41.50, 41.33 (C6); 37.95, 37.74 (C8); 128.04, 127.17, 127.03,
126.35, 126.15, 126.05, 125.78, 125.75 (Ar C)
IV 10.17(s)NH; 7.26–7.32(m); 7.03–7.06
Ar–H; 3.52(s)H6,H7
169.15 (C7); 114.23 (C≡N); 102.10 (C9; C14); 151.31, 145.11 (C10, C13); 139.51
(C11, C12); 34.86 (C6); 27.40, 27.08 (C8); 136.74, 129.65, 129.23, 123.82, 119.55,
118.55 (Ar C)
V 9.68(s)NH; 7.01–7.32(m)Ar–H;
3.40(s)H6,H7; 2.16(S)H(CH3)
169.29, 168.77 (C7); 114.19 (C≡N); 102.13 (C9, C14) 102.13; 151.31 (C10, C13);
136.59 (C11, C12); 26.73 (C8); 18.35 (CH3); 131.82, 130.79, 129.64, 126.43,
126.19, 125.62, 125.03 (Ar C)
VI 8.58(s)NH; 7.21–7.34(M)Ar–H;
4.33(s)H8,H9; 3.32(s)H6,H7
169.17 (C7); 42.77 (C6); 35.47 (C8); 139.68 (C9, C10); 58.26, 128.78,
128.54,127.69, 127.30 (Ar C)
VII 8.46(s)NH; 6.79–6.9(m)Ar–H;
4.43(s)H8,H9; 3.83(s)H6,H7
171.05 (C7); 45.39 (C6); 23.17 (C8); 132.12, 127.21, 119.22 (Ar C); 104.9 (C≡N);
96.22 (C9, C10)
VIII 8.6(s)NH; 6.9–7.43(m)Ar–H;
4.31(s)H8,H9; 3.21(s)H6,H7
169.33 (C7); 42.76 (C6); 35.46 (C8); 128.83, 127.72, 127.33 (Ar C); 112.58 (C≡N);
139.73 (C11, C14); 96.55 (C10, C15); 120.93 (C10-13)
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Scheme 2. Expected structure for new CT complexes
Scheme 3. The numbering of carbon atoms of CT complexes
to a carbon of CH2–S, while complexes II, IV, V, and VI
gave a signal in the range of 23.17–27.40 ppm, with the
carbon of CH2–Te exhibited at 37.95 ppm [7,30,33].
Antioxidant Study
Antioxidants are essential molecules capable of
preventing or slowing down the oxidation of free radicals
through various mechanisms. One method to measure
the antioxidant potential of compounds or specific
extracts is through the DPPH free radical scavenging
methods. This method reduces the odd electron on the N
atom in the stable free radical DPPH by receiving a H
atom from the antioxidant to the corresponding
hydrazine, as shown in Scheme 4.
DPPH free radical was used at a concentration of
10–0.312 mg/mL to investigate the antioxidant activity
of new complexes. All CT complexes showed
encouraging antioxidant activities. The compounds'
effectiveness can be arranged as follows:
I > IV > VIII > III > VI > II > V
(PhCH2NHCOCH2)2Se·DDQ compound (I) has
the lowest IC50 value of 6.72 mg/mL compared to other
CT complexes, as shown in Table 4. The lower the IC50
value, the greater the oxidant potency in a compound.
Scheme 4. Free radical (DPPH) and its reduction by an antioxidant A–H compound
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Table 4. The IC50 for new CT complexes
Compound IC50 (mg/mL)
I 6.72
II 36.87
III 10.67
IV 8.35
V 42.7
VI 21.8
VIII 10.4
Computational Study
We used the computational methods in the
GAUSSIAN09 package to perform all theoretical
calculations in this work [22]. The theoretical planes
B3LYP/3-21G* and B3LYP/6-31G* were used to obtain
the optimized geometries of the compounds. However,
we only used the B3LYP/3-21G* method for frequencies
and could not perform B3LYP/3-21G* frequencies due to
computational constraints [22-23]. Our study found that
the DFT-B3LYP method accurately predicted the
experimental parameters [34]. In recent years, DFT-based
theoretical approaches have emerged as a viable
alternative to traditional ab initio methods for
investigating the structure and reactivity of chemical
systems. Therefore, we used this method to optimize the
geometry of stationary points using the Berny analytical
gradient optimization method.
HOMO and LUMO energies are electronic states that
denote a specific location where electrons with quantized
energy and molecular orbitals are linearly coupled to
atomic orbitals. The difference between the HOMOs gives
the energy band gap (Eg) as a crucial property in solids
because it can predict whether it is a conductor, insulator,
or semiconductor. The energy band represents the energy
difference between lower virtual and higher full energy
levels [35]. Table 5 displays the comparison of HOMO
and LUMO energies. All the prepared compounds’ E
gap
configurations indicated that the Egap was highest in the
VII compound and lowest in the VI compound [7,28-29]
as shown in Table 5 and Fig. S23-S30.
VII > III > VIII > II > I > V> IV > VI
Electronegativity (χ) is a captivating concept, measuring
an atom’s tendency to attract a pair of shared electrons to
itself. On the other hand, relative rate constants measure
the electrophilicity of different electrophilic reagents as
they react with a common substrate (usually involving
an attack on a carbon atom). In Table 6, the
electronegativity of VII is greater than that of the rest
compounds, as shown as follows:
VII > VIII > VI > III > I > II > IV > V
Compound VII has the highest electrophilicity (ω),
while compound VI has the least ω. As this arrangement:
VI > IV > V > VIII > VII >I > II > III
Ionization potential (I) explains this trend, which
measures the bonding force between electrons and atoms.
Ionization potential indicates the energy required to
remove one electron from a neutral atom in a gaseous
state. On the other hand, electron affinity is the energy
released when an atom gains an electron. It corresponds
to the energy required to remove one electron from a
negative ion. According to Koopman's theorem, the
ionization potential and electron affinity depend on the
energies of the valence and conduction bands [23], Table
6 shows the values of ionization potential and electron
affinity for compounds I-VIII, according to Koopman's
Table 5. Showing the electronic structure of a prepared
compound
Comp. HOMO LUMO EGap
I −4.46516 −3.7305 0.7347
II −4.5223 −3.6706 0.8517
III −4.60937 −3.6244 0.985
IV −4.26653 −3.891 0.3755
V −4.32367 −3.8284 0.4952
VI −4.33183 −4.0298 0.302
VII −5.83655 −4.6828 1.1537
VIII −5.70594 −4.7835 0.9224
Table 6. Conformational parameters (eV) of all
optimized structures
Comp. (I) (A) (χ) (η) (σ) (ω)
I 4.4652 3.7305 4.098 0.367 2.722 22.86
II 4.5223 3.6706 4.096 0.426 2.348 19.70
III 4.6094 3.6244 4.117 0.493 2.03 17.21
IV 4.2665 3.891 4.079 0.188 5.326 44.30
V 4.3237 3.8284 4.076 0.248 4.039 33.55
VI 4.3318 4.0298 4.181 0.151 6.622 57.87
VII 5.8365 4.6828 5.26 0.577 1.734 23.98
VIII 5.7059 4.7835 5.245 0.461 2.168 29.82
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theorem. From the table, we can see the arrangement of
the prepared compounds according to the decrease in
ionization potential [35-36]:
VII > VIII > III > II > I > VI > V > IV
It is beneficial that less energy is required for electrons to
escape from the surface [34-35]. The electron affinity (A)
decreased as follows:
VIII > VII > VI > IV > V > I > II > III
This principle describes the behavior of molecules or
atoms compared to the acids and bases in chemistry.
Notably, bases represent donors but acids stand for
acceptors [34,36-38]. When comparing compounds I–
VIII, the hardness (η) of VII is greater than that of the rest
of the prepared compounds, and thus VII behaves as a
hard base. In contrast, VI is a soft base, as its softness is
greater than VII’s [7,35,37-39].
VII > III > VIII > II > I > V > IV > VI
According to Table 6, the behavior of the prepared
compounds can be classified as donor or acceptor
[7,35,37-39].
VI > IV > V > I > II > VIII > III > VII
■ CONCLUSION
This study prepared a new series of CT complexes
based on the reaction of organochalcogenides as electron
donors with DDQ, TCNE, and TCNQ as electron
acceptors in acetonitrile. Various spectroscopic
techniques characterize all prepared complexes, and all
complexes showed promising antioxidant activity using
DPPH free radicals at different concentrations. Complex
I exhibited the most potent scavenging property
compared to other compounds compared to other
charge-transfer compounds with the least IC50 value of
6.725 mg/mL. Our theoretical studies found that the DFT
is a powerful method, and the B3LYP functional is an
efficient function suitable for studying the electronic
properties of these structures. We used DFT to analyze the
prepared compounds' geometrical optimization and
electronic properties using the B3LYP functional. The
geometry and donor-acceptor system for all energies
indicates that this structure is more stable. We found that
the donor-acceptor system is more reactive than the
donor-acceptor system, with a larger average polarization
ratio. These results help select the type of bridge that
interacts with the donor and acceptor and calculate the
physical properties of the donor-bridge-acceptor
system.
■ ACKNOWLEDGMENTS
The authors express their gratitude to I.A. Al-
Timimi (Department of Chemistry, University of Basrah)
for her assistance in performing the UV-vis analysis.
■ CONFLICT OF INTEREST
The authors declare no conflict of interest.
■ AUTHOR CONTRIBUTIONS
Conceptualization and experimental design:
Attared Fadhel Hassan, Nahed Hazim Al-Haidery and
Shaker Abdel Salem Al-Jadaan; antioxidant study: Sabah
Abbas Malik; computational study: Nuha Hussain Al-
Saadawy; experimental work: Attared Fadhel Hassan,
Nahed Hazim Al-Haidery and Suhad Rajab Kareem;
data analysis, writing-original draft preparation: Attared
Fadhel Hassan and Nuha Hussain Al-Saadawy. All
authors have read and agreed to a published version of
the manuscript.
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