Benzo[c][1,2,5]selenadiazole organoselenium derivatives: Synthesis, X-ray, DFT, Fukui analysis and electrochemical behavior

Article abstract of DOI:10.1016/j.molstruc.2019.126914

Organo-selenium compounds are of a broad spectrum of potential technical applications. To date, many efforts have been devoted to develop their chemistry. In this context, two benzo[c][1,2,5]selenadiazole compounds have been synthesized and characterized by ¹H NMR, ¹³C NMR, ¹⁹F NMR, MS and UV–Vis spectroscopic techniques. Both structures were confirmed using single-crystal X-ray diffraction analysis. Each compound crystallizes in monoclinic systems, space group P2₁/c forming dimeric units due to the intermolecular Se?N interactions. The dimmers are further linked by weak π···π stacking interactions between 1,2,5-selenadiazole and the six-membered aromatic rings. The electrochemical behavior of the compounds has been investigated by cyclic voltammetry. Additionally, the structural geometrical parameters, vibrational, electronic transition, Fukui analysis and redox properties of the molecules have been rationalized by DFT and TD-DFT methods using B3LYP level of theory in conjunction with 6-311G(d,p) basis set implemented in Gaussian 09 program. As a result, an excellent correlation between the electronic transitions and the electrochemical behavior was found.

Full text of DOI:10.1016/j.molstruc.2019.126914

Journal Pre-proof
Benzo[c][1,2,5]selenadiazole organoselenium derivatives: Synthesis, X-ray, DFT,
Fukui analysis and electrochemical behavior
Halima Ouahine, Ali Hasnaoui, Ismail Hdoufane, Rachid Idouhli, Abdessalam
Abouelfida, Mustapha Ait Ali, Larbi El Firdoussi
PII:
S0022-2860(19)31005-1
DOI:
https://doi.org/10.1016/j.molstruc.2019.126914
MOLSTR 126914
Reference:
To appear in: Journal of Molecular Structure
Received Date: 23 May 2019
Revised Date: 6 August 2019
Accepted Date: 8 August 2019
Please cite this article as: H. Ouahine, A. Hasnaoui, I. Hdoufane, R. Idouhli, A. Abouelfida, M.A. Ali,
L. El Firdoussi, Benzo[c][1,2,5]selenadiazole organoselenium derivatives: Synthesis, X-ray, DFT,
Fukui analysis and electrochemical behavior, Journal of Molecular Structure (2019), doi: https://
doi.org/10.1016/j.molstruc.2019.126914.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.

Benzo[c][1,2,5]selenadiazole organoselenium derivatives:
Synthesis, X-ray, DFT, Fukui analysis and electrochemical
behavior
a
a
b
c
Halima Ouahine , Ali Hasnaoui , Ismail Hdoufane , Rachid Idouhli , Abdessalam
Abouelfida c, Mustapha Ait Ali a and Larbi El Firdoussi a
a
Equipe de Chimie de Coordination et Catalyse, Université Cadi Ayyad, Faculté des Sciences Semlalia, BP 2390,
Marrakech,Morocco.
b Laboratoire de Chimie Moléculaire, Université Cadi Ayyad, Faculté des Sciences Semlalia, BP 2390, Marrakech, Morocco.
c
Physical-Chemistry of Materials and Environment Laboratory, Faculty of Sciences Semlalia, Cadi Ayyad University,
Marrakech, Morocco.
ABSTRACT
Organo-selenium compounds are of a broad spectrum of potential technical applications. To
date, many efforts have been devoted to develop their chemistry. In this context, two
1
benzo[c][1,2,5]selenadiazole compounds have been synthesized and characterized by H
13
19
NMR, C NMR, F NMR, MS and UV-Vis spectroscopic techniques. Both structures were
confirmed using single-crystal X-ray diffraction analysis. Each compound crystallizes in
monoclinic systems, space group P21/c forming dimeric units due to the intermolecular
Se···N interactions. The dimmers are further linked by weak π···π stacking interactions
between 1,2,5-selenadiazole and the six-membered aromatic rings. The electrochemical
behavior of the compounds has been investigated by cyclic voltammetry. Additionally, the
structural geometrical parameters, vibrational, electronic transition, Fukui analysis and redox
properties of the molecules have been rationalized by DFT and TD-DFT methods using
B3LYP level of theory in conjunction with 6-311G(d,p) basis set implemented in Gaussian 09
program. As a result, an excellent correlation between the electronic transitions and the
electrochemical behavior was found.
Keywords
Organo-selenium; X-ray; DFT; Fukui indices; Cyclic voltammetry; Optical properties.
* Corresponding authors:
Prof. Larbi El Firdoussi: (elfirdoussi@uca.ac.ma)

1. Introduction
Over the last few years, there has been an increasing interest in organo-selenium
compounds chemistry [1–4], mainly due to their importance as reagents and intermediates in
organic synthesis and asymmetric transformations, especially as excellent selective reagents
for the allylic oxidation [5,6]. Apart from this, organo-selenium compounds have fascinating
pharmacological activities; they act as antioxidants, antitumor, anti-inflammatory, antifungal,
antibacterial and antiviral agent [6–11]. Furthermore, selenium is a micro nutriment naturally
present in several redox active enzymes including glutathione peroxidase [12]. In addition,
selenium compounds are used in xerography and synthesis of conducting materials and
semiconductors [13,14].
In chemistry, selenium is known to easily take part in redox reactions involving one or
two electron transitions. It should be noticed that organoselenides are considered as toxic and
malodorous compounds [15]. Nevertheless, selenaheterocycles are weakly volatile and their
toxicity is low [16]. Besides, it has been reported that several selenoxides are used as an
effective catalyst for the bromination of organic substrates in presence of sodium bromide and
hydrogen peroxide [17]. Also, organoselenides catalyze the allylic halogenation of alkenes
and α-halogenation of ketones in presence of N-halo-succinimides [18]. Moreover,
electrochemical procedure has been employed as an effective and convenient method because
of its high selectivity in organic chemistry such as the synthesis of α-bromo alkyl aryl ketones
[19]. Recently, we have been performed the cyclic voltammetry to investigate the redox
behavior of a metal complex [20]. Herein, we study the chemistry of organoselenium
compounds as important substructures in a broad range of natural and designed products.
Therefore, in view to prepare organic compounds that could be valuable for the
oxidation of natural molecules, we have used the cyclic voltammetry (CV) [21] as
inexpensive, selective and sensitive electrochemical technique in order to investigate the
redox behavior of these compounds. In the current work, we report the results of our study
dedicated to two organo-selenium derivatives: 5-methyl-benzo[c][1,2,5]selenadiazole (C1)
[22] and 5-fluoro-benzo[c][1,2,5]selenadiazole (C2). The general procedure of the synthetic
path is shown in Scheme 1. Moreover, structural parameters of the titled compounds were
computed by theoretical studies using density functional theory (DFT) and time dependent
density functional theory (TD-DFT) methods. Finally, optical and electrochemical properties

using CV technique of both samples were investigated in order to confirm the chemical
stability as well.
Scheme 1. synthesis of benzo[c][1,2,5]selenadiazole derivatives
2. Experimental
2.1.
Material and methods
4-methyl-o-phenylenediamine (1), 4-fluoro-o-phenylenediamine (2) selenium dioxide
(SeO2) and N,N-dimethylformamide were purchased from sigma Aldrich. Melting point was
measured with Kofler heating bench. NMR spectra was recorded in CDCl3 using a Bruker
Avance 300 MHz spectrometer. Chemical shifts are expressed in ppm relative to external
TMS. GC parameters for capillary columns TG-5MS (30 m x 0.25 mm): injector 230 °C;
detector
200 °C; oven 40 °C for 2 min then 40 °C min-1 until 280 °C for 12 min; column pressure 42.9
kPa. Gas flow 20 mL min-1. For MS detection, the ionization was performed on an ISQ LT
single quadruple mass spectrometer in positive EI modes using a mass scan range of 50 to 400
Da.
2.2.
2.2.1
Synthesis and crystallization
5-methyl--benzo[c][1,2,5]Selenadiazole (C1).
5-methyl-benzo[c][1,2,5]Selenadiazole has been prepared by the condensation of 4-
methyl-o-phenylenediamine and selenium dioxide in N,N-dimethylformamide as described
earlier in our previous work [22].
1
C7H6N2Se colorless. m/z =197.8[M]+ (Fig. S4). Mp=78 °C (from CHCl3). H NMR
(300 MHz, CDCl3, ppm): 2.4 (3H, s), 7.2 (1H, m), 7.5 (1H, m), 7.65 (CH, m). 13C{1H} NMR

(75 MHz, CDCl3, ppm): 25.9 (CH3), 126.3 (CH), 127.6 (CH), 137.7 (CH), 145.1 (Cq), 164.8
(Cq), 166.0 (Cq) (see Fig. S2).
2.2.2
5-fluoro-benzo[c][1,2,5]Selenadiazole (C2).
0.09 g (0.71 mmol) of 4-fluoro-o-phenylenediamine and 0.079 g (0.71 mmol) of SeO2
were dissolved in 5 mL of N,N-dimethylformamide. After stirring for 24 h at room
temperature. The reaction mixture was diluted with 30 mL of water and extracted 3 times with
20 mL of ethyl acetate. The organic phases were dried over MgSO4 and evaporated under
reduced pressure. Pure product was isolated by column chromatography on silica gel using
hexane/ethyl acetate (90/10) as eluent (yield: 84%). Yellowish crystals were obtained by
crystallization from chloroform.
1
C6H3FN2Se color yellowish. m/z = 201.06 [M-F]+ (Fig. S4). H NMR (300 MHz.
CDCl3, ppm) 7.3 (1H, m), 7.4 (1H, Dd, J= 9.3, 2.4 Hz), 7.8 (1H, Dd, J=9.6, 5.7 Hz). 13C{1H}
2
2
NMR (75 MHz, CDCl3, ppm): 105.8 (CH, d, JC-F=22.5 Hz), 122.0 (CH, d, JC-F=30.0 Hz),
124.1 (CH, d, 3JC-F=11 Hz), 158.0 ( Cq, s) , 162.2 (Cq, d, 3JCq-F= 14 Hz), 164.0 (Cq, d, 1JC-F==
254 Hz) . 19F (282 MHz, CDCl3, ppm) : -110.16 ( Td, J= 14.2, 5.5 Hz) (Fig. S3).
2.3.
X-ray crystallography of 5-fluoro-benzo[c][2,1,3]selenadiazole (C2)
A yellowish crystal of (C6H3FN2Se) (Fig. 1) was mounted on a Bruker APEX-II CCD
duo diffractometer using graphite monochromated Mo Kα radiation (λ= 0.71073Å). The
structure was solved by direct method SHELXS-97 and refined by full-matrix least-squares
procedures on F2 [23,24]. XP (Bruker AXS) and Mercury were used for graphical
representations [25].
CCDC 1896845 (C2) contains the supplementary crystallographic data for this paper.
These data are provided free of charge by The Cambridge Crystallographic Data Centre. The
details of refinement parameters are given in Table 1.
Table 1
Crystallographic and structure refinement parameters for [C6H3FN2Se].
Chemical formula
Formula weight
Crystal system
Space group
C6H3FN2Se
201.06
monoclinic
P 21/c

Crystal color
Radiation type
a (Å)
yellowish
Mo Kα
13.2549(6)
3.8667(2)
13.0731(6)
109.309(2)
632.34(5)
4
b (Å)
c (Å)
β
(o)
V (Å3)
Z
T (K)
150 (2)
Rint
0.0241
0.0200, wR2 0.0517
0.0222, wR2 0.0532
Final R indices [I>2σ(I)]*
R indices (all data)
Computer programs: APEX2 (Bruker, 2014), SAINT (Bruker, 2013), SAINT, SHELXS97 (Sheldrick, 2008),
SHELXL2014/7(Sheldrick,2015), Mercury (Macrae et al., 2006), publCIF (Westrip, 2010)
Fig. 1. The molecular structure of C2 with displacement ellipsoids drawn at the 30%
probability level
2.4.
Computational studies
All theoretical calculations presented in this paper were performed using the Gaussian
09 program package [26]. The full geometries of C1 and C2 were optimized employing DFT
method in a vacuum and in 1,4-dioxane as solvent using B3LYP level of theory in
conjunction with 6-311G(d.p) basis set, which was assigned for all atoms [27].
Vibrational frequency calculations were computed in order to ensure that the optimized
geometries are the most stable (only positive values were obtained). Electronic transitions in
the UV absorption spectra based on the optimized geometries were carried out employing
TD-DFT approach [28] in 1,4-dioxane as solvent with the conductor like polarizable
continuum model (C-PCM) [29]. Gaussum program [30] was used to delineate with the rate

contributions of each group to a particular molecular orbital (MO) by means of Natural Bond
Orbital (NBO). Thereafter, the Fukui functions were calculated using NBO analysis [31] at
DFT/B3LYP level in order to understand the transfer of charges or conjugative interactions in
a molecular system.
2.5.
Electrochemical study
The cyclic voltammetry (CV) measurements were performed using a potentiostat PGZ100
with a three-electrode configuration. A platinum wire working electrode, a platinum mesh
auxiliary electrode and Ag/AgCl (Saturated KCl) reference electrode. All references reported
in this manuscript are versus the reference electrode. The CV measurements were achieved in
sodium sulfate solution (Na2SO4 = 1 M) /1,4-dioxane (90/10: v/v) as the supporting
electrolyte (pH=4.53) at 298±1 K with a scanning rate of 50 mV/s. The solutions were
deoxygenated with bubbling nitrogen (N2(g)) at least 10 min during the electrochemical
measurements.
3. Results and discussion
3.1.
Description of the crystal structure of C2
The titled compound was prepared in DMF by reacting 4-Fluoro-o-phenylenediamine
1
with selenium dioxide at room temperature as shown in Scheme 1. The H NMR spectrum
shows only three peacks at 7.3, 7.4 and 7.8 ppm corresponding to the aromatic protons.
Furthermore, the single crystal x-ray diffraction analysis of C2 confirmed the assignments of
the structure from spectroscopic data. The crystal packing of C6H3FN2Se shows that the
molecules are arranged in rods along b axis (Table 2 and Fig. 2).
Table 2
Hydrogen-bond geometry (Å, °) for C2.
D - HꢀꢀꢀA
D - H
0.95
0.95
HꢀꢀꢀA
2.55
2.50
DꢀꢀꢀA
D-HꢀꢀꢀA
169
C(3) -H(3) ꢀꢀꢀN(1)i
C(6) -H(6) ꢀꢀꢀF(1A)ii
3.490(3)
3.446(3)
174
Symmetry codes: (i) x,1/2-y,1/2+z; (ii) x,3/2-y,-1/2+z

Fig. 2. Part of the packing diagram of C2, showing SeꢀꢀꢀN contacts and πꢀꢀꢀπ stacking interactions as
dotted lines. Displacement ellipsoids are drawn at the 30% probability level. For clarity lower
occupancy sites are omitted.
The formation of dimeric units by intermolecular SeꢀꢀꢀN interactions (SeꢀꢀꢀN2 = 2.853(2)
Å) is observed as found for 4,5,6,7-tetramethyl-2,1,3-benzoselenadiazole and their cocrystals
[32]. Additionally, πꢀꢀꢀπ stacking interactions are found between the 1,2,5-selenadiazole and
the six-membered aromatic ring [centroid–centroid distance = 3.596(2) Å and ring slippage =
1 Å].
3.2.
Vibration spectra
The theoretical FT-IR spectra of the titled compounds were calculated at the B3LYP/6-
311G(d,p) level of theory. The scaled vibration modes are obtained at the same level of theory
and scaled with a factor of 0.9619 [33]. It is observed that the stretching vibration modes of
C=N bond for C1 and C2 are respectively located at 1493.07 cm-1 and 1492.77 cm-1 (Fig. S1),
which are closer to their corresponding scaled ones at 1476.36 cm-1 and 1472.45 cm-1. For the
N-Se bond, it is observed that the vibrational frequencies at 745.13 cm-1 and 750.13 cm-1 for
C1 and C2 are in good agreement with the calculated values, whereas the corresponding

scaled ones were found at 720.30 cm-1 and 719.86 cm-1, respectively. The main observed
vibrational modes and their corresponding computed and scaled ones are given in Table 3.
Table 3
Experimental, theoretical and scaled vibrational wavenumbers (cm-1) of the titled
compounds at B3LYP/6-311G(d,p) level and their assignments.
Assignments
Experimental values
Theoretical scaled values
1623.01
1603.78
υ(C=C)
1493.07
1476.36
υ(C=N)
C1
C2
745.13
1621.76
1492.77
720.30
1601.38
1472.45
υ(N-Se)
υ(C=C)
υ(C=N)
750.13
719.86
υ(N-Se)
3.3.
Computational investigations and DFT modeling
DFT modeling is a powerful and a widely used tool for dealing with the stability,
reactivity and selectivity of inorganic and organic molecules. To gain a better understanding
of the electronic structure of the titled compounds, the optimization of C1 and C2 was carried
out in the single ground by DFT method at B3LYP level of theory. The experimental and
computed geometrical parameters of C1 and C2 are listed in Table 4. For both compounds,
all computed bond lengths and bond angles are in good agreement with the experimental
findings.
Table 4
Experimental and theoretical selected geometry parameters (value Å and degree) for C1 and
C2 compounds.
C2
C1
Calculated
Calculated
Gas Solvent
Experimental
Experimental
Gas
Solvent
Bond (Å)
Se-N1
Bond (Å)
Se-N1
1.807
1.808
1.808
1.464
1.506
1.324
1.325
1.792 (17)
1.790 (18)
1.453 (3)
1.505 (3)
1.332 (3)
1.331 (2)
1.795
1.795
1.794
1.453
1.344
1.322
1.330
1.794 (19)
1.795 (18)
1.453 (3)
1.360 (3)
1.330 (3)
1.322 (3)
Se-N2
1.808
1.464
1.507
1.323
1.324
Se-N2
1.794
1.453
1.345
1.322
1.331
C1-C6
C1-C2
C4-C7
C4-F
N1-C1
N1-C1
N2-C6
N2-C2
Angles (°)
N1-Se-N2
Se-N1-C1
Se-N2-C6
Angles (°)
N1-Se-N2
Se-N1-C1
Se-N2-C2
94.242
106.231
106.334
94.086
106.388
106.488
94.54 (8)
106.37 (13)
106.57 (13)
93.968
93.968
93.9 (8)
106.7 (14)
106.8 (14)
106.885 106.885
106.732 106.732

C7-C4-C3
C7-C4-C5
118.449
121.709
118.436
121.733
118.44 (17)
121.81 (18)
F-C4-C5
F-C4-C3
122.557 122.557
116.768 116.768
117.4 (2)
118.4 (2)
Additionally, contour plot for some selected molecular orbitals (MOs) are presented in
Fig. 3. The corresponding energies of these MOs as well as the percent composition of each
element for the titled compounds are summarized in Table 5. The higher energy occupied
molecular orbital (HOMO) to the low-lying virtual orbital (LUMO) band gap energies are
3.99 eV and 4.01 eV for C1 and C2, respectively.
C1
C2
LUMO
LUMO+1
LUMO+2
C1
C2
HOMO-1
HOMO-2
HOMO
Fig. 3 Isodensity surface plots of the frontier molecular orbitals for C1 and C2.

Table 5
Energy and composition of some selected molecular orbitals (MOs) for C1 and C2.
% of composition in C1
% of composition in C2
MOs
Energy (eV)
Se
CH3
L
Energy (eV)
Se
F
L
LUMO+3
LUMO+2
LUMO+1
LUMO
0.12
-0.01
-0.77
-2.58
-6.57
-6.97
-8.08
-8.40
2
2
81
20
3
46
7
18
5
2
0
1
3
2
0
1
93
96
19
79
95
53
93
81
0.09
-0.27
-0.90
-2.80
-6.81
-7.20
-8.33
-8.72
2
2
80
21
5
43
6
19
2
0
0
1
4
1
0
0
96
98
19
78
90
56
94
80
HOMO
HOMO-1
HOMO-2
HOMO-3
3.4.
TD-DFT calculations and electronic spectrum
For both compounds C1 and C2 along with the used reagents 1 and 2, the UV
absorption spectra have been performed using 1,4-dioxane as solvent in the range of 200-900
nm. The experimental spectra for C1 and C2 are shown in Fig. 4 and the corresponding
spectra of 1 and 2 are given in supporting information (Fig. S5). For the compounds 1 and 2,
we observed similar absorption bands at 245 nm and 305 nm with a slight difference in their
intensity. This difference is due to the auxochrome effect caused by the fluorine atom in 2.
Whereas, in the UV region for C1 and C2, all absorption bands are slightly superimposed
until the wavelength 335 nm, where C2 above slightly C1 in terms of absorption band and
wavelength. These results indicate the hyperchromic effect exhibited by the fluorine
auxochrome in C2 which leads to an increase of absorption maxima because of the n-π*
conjugation. Moreover, from 200 nm to 266 nm we have noticed that SeO2, C1 and C2 show
the same band shape. These compounds exhibit the same band at 244 nm and differ in terms
of intensity. While, there is no significant absorption in the visible region (400-800).
Therefore, to study the nature of the excitations in the UV spectra, the absorption bands
of C1 and C2 were carried out by TD-DFT method using 1,4-dioxane as solvent. The
experimental bands with the computed excitation energies, absorption bands, oscillator
strengths and MOs transition configurations are summarized in Table 6. As can be seen from
this table, the electronic transitions shown at 354 nm (f = 0.0458) and 350 nm (f = 0.0577)
correspond to HOMO → LUMO transitions (97% for C1 and 96% for C2), with ligand to
selenium charge transfer character (LSeCT) for C1 and C2, respectively.

Fig. 4. Experimental UV-vis spectrum for SeO2, C1 and C2 in 1,4-dioxane.
Table 6
Experimental and calculated electronic transitions by TDDFT/C-PCM method for C1 and C2 in 1.4-
dioxane.
Ee
(eV)
3.504802
λexp.
(nm)
335
λe
(nm)
354
Osc.
Strength (f)
0.0458
Key transitions
HOMO → LUMO (97%)
H-1 → LUMO (94%)
H–2 → LUMO (99%)
HOMO → L+1 (92%)
H–1 → L+1 (93%)
Character
LSeCT, Pπ (L) → Pπ (Se)
SeLCT, Pπ (Se) → Pπ (L)
LSeCT, Pπ (L) → Pπ (Se)
LSeCT, Pπ (L) → Pπ (Se)
LSeCT, Pπ (L) → Pπ (Se)
LSeCT, Pπ (L) → Pπ (Se)
SeLCT, Pπ (Se) → Pπ (L)
LSeCT, Pπ (L) → Pπ (Se)
LSeCT, Pπ (L) → Pπ (Se)
LSeCT, Pπ (L) → Pπ (Se)
4.041402
4.263602
4.905303
5.069803
3.541302
4.070402
4.234502
4.943403
5.172503
-
307
291
252
244
350
305
293
250
240
0.3364
0.0000
0.0009
0.0002
0.0577
0.3125
0.0000
0.0005
0.0004
-
-
C1
C2
244
332
-
HOMO → LUMO (96%)
H–1 → LUMO (93%)
H–2 → LUMO (99%)
HOMO → L+1 (89%)
H–1 → L+1 (91%)
-
-
243
3.5.
Fukui functions
Fukui function, the most commonly applied local reactivity parameter, is defined as the
derivative of electron density with respect to the charge in the number of electrons density
keeping the positions of the nuclei remaining unaltered [34,35]. Fukui indices give
information about electrophilic/nucleophilic power of such atomic site in a molecular system.

In order to quantify the tendency of each atom in a molecule with a numerical value to
indicate its ability to serve as a reactive site, condensed Fukui functions are investigated. The
condensed Fukui functions on the Kth atom site are represented as:
f +
=
q
k (N+1) -
q
k (N)
(1)
(2)
k
-
f
=
qk (N) -
q
k (N-1)
k
-
ꢀ f(r) = f +
-
f
(3)
k
k
-
Where, f +k for nucleophilic attack and f k for electrophilic attack. In these equations, qk
is the atomic charge at the kth atomic site in the neutral (N), anionic (N+1) or cationic (N-1)
chemical species. In the present study, the values of Fukui function were calculated from
NBO charges. Morrel et al. [36] have proposed a new dual descriptor ꢀ f(r) for the calculation
of nucleophilicity and electrophilicity and is defined as the difference between the
nucleophilic and electrophilic Fukui function. If ꢀ f(r) > 0, the site is prone for nucleophilic
attack, while the site is apt to electrophilic attack when ꢀ f(r) < 0. The condensed Fukui
functions (f +k), (f +k) and dual descriptor ꢀ f(r) are given in Table 7. In the present work, we
found that Se atom in C1 is prone to nucleophilic attack as it has ꢀ f(r) > 0 whereas Se in C2
is prone for electrophilic attack as it has ꢀ f(r) < 0. The such result could be related to the
nature of the substituent.
Table 7
Fukui indices for nucleophilic and electrophilic sites on atoms computed form natural bond
orbital analysis at DFT/6-311G(d.p) in 1,4-dioxane.
C1
C2
-
-
Atom
f +
ꢀf(r)
Atom
f +
ꢀf(r)
f
f
k
k
k
k
C
C
C
H
C
H
C
C
H
N
N
Se
C
H
H
0.0512
0.0235
-0.1945
-0.0269
0.0035
-0.0354
-0.1112
-0.2094
-0.0276
-0.1055
-0.1100
-0.1793
0.0253
-0.0398
-0.0440
-0.0262
-0.0301
-0.0721
-0.0317
-0.0764
-0.0286
-0.0666
-0.0649
-0.0308
-0.1022
-0.1043
-0.3139
0.0119
0.0773
0.0535
-0.1224
0.0048
0.0799
-0.0068
-0.0446
-0.1444
0.0032
-0.0033
-0.0057
0.1346
0.0134
-0.0165
-0.0269
C
C
C
H
C
H
C
C
H
N
N
Se
F
0.0447
0.0116
-0.1737
-0.0280
0.0065
-0.0367
-0.1046
-0.2024
-0.0292
1.6273
-0.0956
-25.5706
23.5509
-0.0172
-0.0329
-0.0768
-0.0324
-0.0931
-0.0289
-0.0474
-0.0725
-0.0315
-0.0988
-0.1039
-0.3217
-0.0428
0.0619
0.0445
-0.0969
0.0044
0.0995
-0.0078
-0.0573
-0.1299
0.0023
1.7261
0.0082
-25.2488
23.5937
-0.0234
-0.0172

H
-0.0199
-0.0238
0.0039
3.6.
Electrochemical studies
Electrochemical analysis focuses in phenomena resulting from combined electrical and
chemical effects. In our study, we used CV as a useful technique to investigate the
electrochemical behavior such as redox process, stability of reaction products, adsorption
processes and the presence of intermediates in redox reactions of considered compounds.
[37]. The influence of different groups (R = CH3, F) on the redox potential was assessed using
CV. Fig. 5 shows the investigation of SeO2, C1 and C2 in Na2SO4 (1M)/1,4-dioxane
electrolyte solution within potential range of -1.0 V to 1.5 V at 50 mV/s scan rate. The
electrochemical parameters are gathered in Table 8.
Fig. 5. Cyclic voltammograms of SeO2, C1 and C2 in Na2SO4/1,4-dioxane (90/10) (v/v).
Table 8
Electrochemical parameters obtained for SeO2, C1 and C2 at 50 mV s-1 scan rate.
Epa (V)
1.012
Epc (V)
0.296
SeO2
C1
0.149
1.012
0.315
1.06
-0.652
-0.161
-0.870
-0.196
-0.863
C2
0.317

The comparison of the electrochemical behavior of both compounds with SeO2 shows
that they exhibit the same anodic behavior (Epa) for the redox potential. Whereas, the cathodic
behavior (Epc) for C1 and C2 shifts to negative values of the potential comparing to the one
associated to SeO2 curve. The peaks at the potential 0.296 V, -0.161 V, -0.196 V and at -0.652
V, -0.870 V, -0.863 V, respectively for SeO2, C1 and C2 are due to the reduction of Se(IV)
[38]. The pH value of the solution was 4.53 and the SeO2 is in the form of selenious acid
-
(HSeO3 ) [39]. As described in the literature, the reaction mechanism that seems be occur was
the reduction of Se(IV) to Se(s) followed by the reduction of Se(s) to H2Se [40–42]:
(4)
(5)
Below -1.0 V, hydrogen evolution begins. The response of the peaks occurring at 0.149,
0.315, 0.317 V and at 1.012, 1.012, 1.06 V respectively for SeO2, C1 and C2 results from the
oxidation of the compounds [41]. Under these observations, it is clear that the electrochemical
oxidation of the compounds (C1 and C2) have become well separated comparing to the peak
of SeO2 (Table 8) [43].
Furthermore, based on cyclic voltammograms curves (Fig. 5), we have noticed that the
intensity in current density of C2 is lower and inhibited than the one of C1. This result could
be explained by the electronic effect of the Fluorine atom in C2. Also, this behavior is
observed from the computed Fukui indices (ꢀ f(r) of 23.59 for F atom) compared to C1 with a
methyl
moiety
(ꢀ f(r) of 0.01 for CH3 group). In addition, for C2, Fluorine atom as the most electronegative
element, its effect on selenium is clearly observed in terms of reactivity. For this reason, this
behavior is shown in the redox process of C2 (see Fig. 5). The obtained cyclic
voltammograms show clearly that both molecules exhibit an irreversible redox process.
3.7.
Optical and electrochemical properties
The UV-visible absorption spectra and CV curve of studied compounds were recorded
in order to study the optical proprieties and molecular orbital energy levels as shown in Fig. 4
and Fig. 5. The maximal absorption wavelength (λmax) and onset wavelength (λ0) values and

oxidation/reduction potentials determined from the onset of the cyclic voltammograms are
reported in Table 9.
Difference of energy levels (Eg) between the LUMO and HOMO were determined using
the onset wavelength [44,45]:
(6)
h is Plank’s constant (h= 6.626 × 10-34 J·s); c is the speed of light (3× 10 8 m/s); and λo is the
onset wavelength (nm).
The LUMO energy level values of the acceptors for SeO2 and the studied compounds
(C1 and C2) relative to ferrocene/ferrocenium (
) as an internal standard, were
estimated using the oxidation potential onset:
(7)
Whereas the values of HOMO energy level were calculated using the following equation:
(8)
Table 9
Optical and electrochemical properties SeO2, C1 and C2.
onset
onset
∆E
Theoretical
--
Eg
Eox
Ered
ELUMO
EHOMO
Compound
λ(abs)max/nm λ0/nm
(eV)
(V)
(V)
(eV)
(eV)
/
(eV)
245
334
272
378
4.57 0.759
3,29 0.796
-0.380
-0.723
-4.470
-4.127
-9.320
-8.977
SeO2
3.99
4.01
C1
C2
332
369
3,37 0.730
-0.767
-4.083
-8.933
Table 9 summarizes the oxidation and the reduction of the onset potentials for the
studied products. It is clear that the onset of oxidation process for the compounds C1 and C2
is almost closer (0.796 V and 0.730 V) to each other. The same observation was observed for

the onset of reduction (-0.723 V and -0.767 V). HOMO energy level of C1 (-8.977 eV) is
slightly lower than the one of C2 (-8.933 eV). Hence, a functional methyl group of the C1
compared to a Fluorine atom of C2 showed exceedingly a reduction of the bandgap values of
3.29 and 3.37 eV, respectively. This observation is confirmed by theoretical finding (∆E
Theoretical). As a result, this reduction is due to the electron-donating of Fluorine atom which
increase the conjugation and delocalization in the compound [46]. These results indicate the
chemical stability of the titled compounds.
4. Conclusion
This research focuses on the synthesis, computational and electrochemical behavior of
two benzo[c][1,2,5]selenadiazole organoselenium derivatives. The structures of the studied
1
13
19
products (C1 and C2) were fully characterized by FT-IR, H NMR, C NMR F NMR UV
visible and Ms-EI. The single crystal analysis shows that each product crystallizes in
monoclinic system with P2/c space group. The optimized geometrical parameters (bond
lengths, bond angles) were theoretically calculated by DFT method and compared with the
experimental values showing a good agreement for both components. The electronic
transitions are also estimated by employing TD-DFT theory and compared with the
experimental UV-Vis spectra. Fukui indices (f+k, f-k) and dual descriptor ꢀ f(r) for Selenium
atom present in both molecules indicated that this atom in C1 is prone to nucleophilic attack,
whereas Se atom in C2 is prone to electrophilic attack. Furthermore, based on CV curves, it
has been shown that both molecules exhibit a good solubility and reactivity with an
irreversible electrochemical behavior. From CV and UV-Vis curves, the acquired
experimental HOMO and LUMO energy level values along with the bandgap energy was
found in good agreement with the theoretical findings which confirm the chemical stability of
the titled compounds. These results are very promising for investigating the semiconducting
properties of the studied products in the photovoltaic devices.
Acknowledgement
The authors are grateful to Ms Anke Spannenberg at the Leibniz-Institut für Katalyse for her
help in obtaining the X-ray analysis.

References
[1] A. Pop, A. Silvestru, Organoselenium compounds with N,C,N pincer groups.
Synthesis,
structure
and
reactivity,
Polyhedron.
(2018).
doi:10.1016/j.poly.2018.12.041.
[2] M. Karthika, L. Senthilkumar, R. Kanakaraju, Hydrogen-bond interactions in hydrated
6-selenoguanine tautomers: a theoretical study, Struct. Chem. 25 (2014) 197–213.
doi:10.1007/s11224-013-0239-8.
[3] S. Panda, A. Panda, S.S. Zade, Organoselenium compounds as fluorescent probes,
Coord. Chem. Rev. 300 (2015) 86–100. doi:10.1016/J.CCR.2015.04.006.
[4] D. Plano, E. Ibáñez, J.A. Palop, C. Sanmartín, Synthesis, characterization, crystal
structure and cytotoxicity of 2,4-bis(selenomethyl)quinazoline, Struct. Chem. 22
(2011) 1233–1240. doi:10.1007/s11224-011-9816-x.
[5] A. Breder, S. Ortgies, Recent developments in sulfur- and selenium-catalyzed oxidative
and isohypsic functionalization reactions of alkenes, Tetrahedron Lett. 56 (2015) 2843–
2852. doi:10.1016/j.tetlet.2015.04.045.
[6] G. Mugesh, H.B. Singh, Synthetic organoselenium compounds as antioxidants:
glutathione peroxidase activity, Chem. Soc. Rev. 29 (2000) 347–357.
doi:10.1039/a908114c.
[7] L. Engman, I. Cotgreave, M. Angulo, C.W. Taylor, G.D. Paine-Murrieta, G. Powis,
Diaryl chalcogenides as selective inhibitors of thioredoxin reductase and potential
antitumor agents., Anticancer Res. 17 (1997) 4599–605.
[8] C.W. Nogueira, E.B. Quinhones, E.A.C. Jung, G. Zeni, J.B.T. Rocha, Anti-
inflammatory and antinociceptive activity of diphenyl diselenide, Inflamm. Res. 52
(2003) 56–63. doi:10.1007/s000110300001.
[9] M. Bień, B. Błaszczyk, K. Kalinowska, J. Młochowski, A.D. Inglot, Antifungal activity
of 2-(4-chlorophenyl)-1,2-benzisoselenazol-3(2H)-one, the analog of Ebselen., Arch.
Immunol. Ther. Exp. (Warsz). 47 (1999) 185–93.
[10] E. V. Ratushnaya, Y.I. Kirova, M.A. Suchkov, B.I. Drevko, V.B. Borodulin, Synthesis
and Antibacterial Activity of Organoselenium Compounds, Pharm. Chem. J. 36 (2002)
652–653. doi:10.1023/A:1023405611793.
[11] H. Wójtowicz, K. Kloc, I. Maliszewska, J. Młochowski, M. Piętka, E. Piasecki,
Azaanalogues of ebselen as antimicrobial and antiviral agents: synthesis and properties,
Farm. 59 (2004) 863–868. doi:10.1016/j.farmac.2004.07.003.
[12] A.S. Hodage, C. Parashiva Prabhu, P.P. Phadnis, A. Wadawale, K.I. Priyadarsini, V.K.
Jain, Synthesis, characterization, structures and GPx mimicking activity of pyridyl and
pyrimidyl based organoselenium compounds, J. Organomet. Chem. 720 (2012) 19–25.
doi:10.1016/j.jorganchem.2012.08.035.

[13] J.M. HARKIN, A. DONG, G. CHESTERS, Elevation of selenium levels in air by
xerography, Nature. 259 (1976) 204–205. doi:10.1038/259204b0.
[14] A. Sahu, L. Qi, M.S. Kang, D. Deng, D.J. Norris, Facile Synthesis of Silver
Chalcogenide (Ag 2 E; E = Se, S, Te) Semiconductor Nanocrystals, J. Am. Chem. Soc.
133 (2011) 6509–6512. doi:10.1021/ja200012e.
[15] C.W. Nogueira, G. Zeni, J.B.T. Rocha, Organoselenium and Organotellurium
Compounds: Toxicology and Pharmacology, Chem. Rev. 104 (2004) 6255–6286.
doi:10.1021/cr0406559.
[16] J. Mochowski, Developments in the chemistry of selenaheterocyclic compounds of
practical importance, Phosphorus, Sulfur Silicon Relat. Elem. 183 (2008) 931–938.
doi:10.1080/10426500801898408.
[17] M.A. Goodman, M.R. Detty, Selenoxides as Catalysts for the Activation of Hydrogen
Peroxide. Bromination of Organic Substrates with Sodium Bromide and Hydrogen
Peroxide, Organometallics. 23 (2004) 3016–3020. doi:10.1021/om049908e.
[18] S.R. Mellegaard-Waetzig, C. Wang, J.A. Tunge, Selenium-catalyzed oxidative
halogenation, Tetrahedron. 62 (2006) 7191–7198. doi:10.1016/j.tet.2005.12.072.
[19] R.S. Kumar, K. Kulangiappar, M.A. Kulandainathan, Convenient Electrochemical
Method for the Synthesis of α-Bromo Alkyl Aryl Ketones, Synth. Commun. 40 (2010)
1736–1742. doi:10.1080/00397910903161710.
[20] A. Hasnaoui, I. Hdoufane, R. Idouhli, B. Therrien, M. Ait Ali, L. El Firdoussi, Crystal
structure of {N-(2-hydroxyethylamino) ethylsalicylaldiminato]-palladium(II) chloride}:
Synthesis, X-ray structure, electrochemistry, DFT and TDDFT studies, J. Mol. Struct.
1176 (2019) 703–710. doi:10.1016/j.molstruc.2018.08.111.
[21] Y. Wang, Y. Bai, M. Liang, W. Zheng, Differential Pulse Voltammetric Determination
of Selenocystine and Selenomethionine Using SAM nanoSe 0 /Vc/SeCys-Film
Modified
Au
Electrode,
Electroanalysis.
21
(2009)
2145–2152.
doi:10.1002/elan.200804649.
[22] H. Ouahine, M. Ait Ali, L. El Firdoussi, A. Spannenberg, 5-Methylbenzo[ d
][2,1,3]selenadiazole, IUCrData. 2 (2017) x170226. doi:10.1107/S2414314617002267.
[23] G.M. Sheldrick, Crystal structure refinement with SHELXL, Acta Crystallogr. Sect. C
Struct. Chem. 71 (2015) 3–8. doi:10.1107/S2053229614024218.
[24] G.M. Sheldrick, A short history of SHELX, Acta Crystallogr. Sect. A Found.
Crystallogr. 64 (2008) 112–122. doi:10.1107/S0108767307043930.
[25] C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M.
Towler, J. Van De Streek, Mercury: Visualization and analysis of crystal structures, J.
Appl. Crystallogr. 39 (2006) 453–457. doi:10.1107/S002188980600731X.
[26] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,

G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
H.P.H. X. Li, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M.
Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J.A.M. Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd,
E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, Normand, J.R. Rendell,
K.A.J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene,
J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.
Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L.
Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg, S.
Dapprich, A.D.D.O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, D.J. Fox,
Gaussian 09, Wallingford CT, (2009). http://gaussian.com/.
[27] A.D. Becke, Density-functional thermochemistry. III. The role of exact exchange, J.
Chem. Phys. 98 (1993) 5648–5652. doi:10.1063/1.464913.
[28] R.E. Stratmann, G.E. Scuseria, M.J. Frisch, An efficient implementation of time-
dependent density-functional theory for the calculation of excitation energies of large
molecules, J. Chem. Phys. 109 (1998) 8218–8224. doi:10.1063/1.477483.
[29] M. Cossi, N. Rega, G. Scalmani, V. Barone, Energies, structures, and electronic
properties of molecules in solution with the C-PCM solvation model, J. Comput.
Chem. 24 (2003) 669–681. doi:10.1002/jcc.10189.
[30] N.M. O’boyle, A.L. Tenderholt, K.M. Langner, cclib: A library for package-
independent computational chemistry algorithms, J. Comput. Chem. 29 (2008) 839–
845. doi:10.1002/jcc.20823.
[31] A.E. Reed, L.A. Curtiss, F. Weinhold, Intermolecular interactions from a natural bond
orbital, donor-acceptor viewpoint, Chem. Rev. 88 (1988) 899–926.
doi:10.1021/cr00088a005.
[32] K. Eichstaedt, A. Wasilewska, B. Wicher, M. Gdaniec, T. Połoński, Supramolecular
Synthesis Based on a Combination of Se⋯N Secondary Bonding Interactions with
Hydrogen and Halogen Bonds, Cryst. Growth Des. 16 (2016) 1282–1293.
doi:10.1021/acs.cgd.5b01356.
[33] M.P. Andersson, P. Uvdal, New Scale Factors for Harmonic Vibrational Frequencies
Using the B3LYP Density Functional Method with the Triple-ζ Basis Set 6-
311+G(d,p), J. Phys. Chem. A. 109 (2005) 2937–2941. doi:10.1021/jp045733a.
[34] W. Yang, W.J. Mortier, The use of global and local molecular parameters for the
analysis of the gas-phase basicity of amines, J. Am. Chem. Soc. 108 (1986) 5708–
5711. doi:10.1021/ja00279a008.
[35] P.W. Ayers, R.G. Parr, Variational Principles for Describing Chemical Reactions: The
Fukui Function and Chemical Hardness Revisited, J. Am. Chem. Soc. 122 (2000)
2010–2018. doi:10.1021/ja9924039.
[36] C. Morell, A. Grand, A. Toro-Labbé, Theoretical support for using the ꢀf(r) descriptor,
Chem. Phys. Lett. 425 (2006) 342–346. doi:10.1016/j.cplett.2006.05.003.

[37] J. David K. Gosser, Cyclic Voltammetry; Simulation and Analysis of Reaction
Mechanisms, 1994. doi:10.1080/00945719408001398.
[38] S. Zein El Abedin, A.Y. Saad, H.K. Farag, N. Borisenko, Q.X. Liu, F. Endres,
Electrodeposition of selenium, indium and copper in an air- and water-stable ionic
liquid at variable temperatures, Electrochim. Acta. 52 (2007) 2746–2754.
doi:10.1016/j.electacta.2006.08.064.
[39] M. Bouroushian, Electrochemistry of the Chalcogens, in: 2010: pp. 57–75.
doi:10.1007/978-3-642-03967-6_2.
[40] M.F. Cabral, V.A. Pedrosa, S.A.S. Machado, Deposition of selenium thin layers on
gold surfaces from sulphuric acid media: Studies using electrochemical quartz crystal
microbalance, cyclic voltammetry and AFM, Electrochim. Acta. 55 (2010) 1184–1192.
doi:10.1016/j.electacta.2009.10.008.
[41] R. Chen, D. Xu, G. Guo, Y. Tang, Electrodeposition of silver selenide thin films from
aqueous solutions, J. Mater. Chem. 12 (2002) 1437–1441. doi:10.1039/b107177g.
[42] M.C. Santos, S.A.S. Machado, Microgravimetric, rotating ring-disc and voltammetric
studies of the underpotential deposition of selenium on polycrystalline platinum
electrodes,
J.
Electroanal.
Chem.
567
(2004)
203–210.
doi:10.1016/j.jelechem.2003.12.026.
[43] G. Jarzabek, Z. Kublik, Determination of traces of selenium(IV) by cathodic stripping
voltammetry at the hanging mercury drop electrode, Anal. Chim. Acta. 143 (1982)
121–130. doi:10.1016/S0003-2670(01)95492-3.
[44] Y.-F. Zhang, C.-Z. Zhang, Experimental and theoretical study on spontaneous
intermolecular charge transfer features and antiaromaticities of unusual bisazo
compounds with antiaromatic cores, J. Mol. Struct. 1189 (2019) 225–232.
doi:10.1016/j.molstruc.2019.04.044.
[45] Y. Zhang, F. Wu, Synthesis of a new W-type of functional polymer for improving
intermolecular charge transfer processes at donor/acceptor interfaces, High Perform.
Polym. 31 (2019) 521–527. doi:10.1177/0954008319827066.
[46] C.-Z. Zhang, D. Shen, Y. Yuan, S.-J. Li, H. Cao, Syntheses and Optoelectronic
Properties of Planar Compounds 3,7-diaryl-1,5,2,4,6,8-dithiotetrazocine, J. Heterocycl.
Chem. 53 (2016) 1813–1819. doi:10.1002/jhet.2491.

Highlight
-Two benzo[1,2,5]selenadiazoles have been synthesized and characterized by different
spectroscopic techniques.
-The structures of both components have been confirmed by single crystal X-ray analysis
-The geometrical parameters, electronic transitions, fukui indices and redox properties the
molecules have been interpreted by DFT and TDDFT calculations.
-Cyclic voltammograms show that the both compounds exhibit an irreversible redox process.