Pyrido[1',2':1,5]pyrazolo[4,3-b]quinolines as New Fluorescent Heterocyclic Systems for Dye-Sensitized Solar Cells

Article abstract of DOI:10.1134/S1070363220070233

Abstract: New fluorescent heterocyclic compounds pyrido[1',2':1,5]pyrazolo[4,3-b]quinolines have been synthesized by the reaction of 3-nitropyrazolo[1,5-a]pyridine with different arylacetonitriles in high yield. Structural assignments of the new compounds

Full text of DOI:10.1134/S1070363220070233

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 7, pp. 1345–1350. © Pleiades Publishing, Ltd., 2020.
Pyrido[1',2':1,5]pyrazolo[4,3-b]quinolines as New Fluorescent
Heterocyclic Systems for Dye-Sensitized Solar Cells
Z. Aghelia, M. Pordela,*, A. Davoodniaa, and S. A. Beyramabadia
a Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, 9187147578 Iran
*e-mail: mehdipordel58@mshdiau.ac.ir
Received May 8, 2020; revised June 17, 2020; accepted July 2, 2020
Abstract—New fluorescent heterocyclic compounds pyrido[1',2':1,5]pyrazolo[4,3-b]quinolines have been syn-
thesized by the reaction of 3-nitropyrazolo[1,5-a]pyridine with different arylacetonitriles in high yield. Structural
assignments of the new compounds are based on their spectral data. The study of optical properties of the com-
pounds has revealed their high fluorescence quantum yields. Electrochemical properties of the compounds have
been studied by cyclic voltammetry. The IPCE spectra and the I–V curves of the florescence compounds have been
obtained, and their photovoltaic performance of 5.12–6.59 % has been achieved.
Keywords: pyrido[1',2':1,5]pyrazolo[4,3-b]quinolones, fluorescent heterocyclic system, dye-sensitized solar cells,
cyclic voltammetry; density functional theory
DOI: 10.1134/S1070363220070233
INTRODUCTION
RESULTS AND DISCUSSION
Synthesis and structures of the new compounds
5a–5c. Pyrazolo[1,5-a]pyridine (1) was synthesized
according to the developed earlier method [16]
(Scheme 1). Its following nitration by HNO3–H2SO4 led
to 3-nitropyrazolo[1,5-a]pyridine (2) in high yield [17].
Reaction of the intermediate 2 with aryl acetonitriles
3a–3c gave the corresponding oximes 4a–4c in excellent
yields [18]. Finally, acylation of compounds 4a–4c with
acetyl chloride in pyridine afforded the corresponding
pyrido[1',2':1,5]pyrazolo[4,3-b]quinolone derivatives
5a–5c via the intramolecular electrophilic aromatic
substitution (Scheme 1) [19].
Quinoline and its fused heterocyclic derivatives
have been traced in various natural products [1], and
are used in the synthesis of bioactive compounds [2]
and pharmaceuticals [3]. Some quinolone derivatives
demonstrated interesting optical properties in dyes and
fluorescent compounds [4–7]. Their optical and electronic
properties can be used in solar cells [8–11]. The sensitized
dyes are among the most important components of
dye-sensitized solar cells (DSSCs). Based on the above
and in continuation of our research in the synthesis of
new fluorescent heterocyclic systems [12–15], we have
synthesized three new pyrido[1',2':1,5]pyrazolo[4,3-b]-
quinolone derivatives for dye-sensitized solar cells.
Structures of the synthesized compounds were supported
by spectral data. The density functional theory (DFT) at
the level of B3LYP/6-311+G(d,p) was used to obtain the
frontier orbitals of the new components. Electrostatic
potential maps and electron density maps of the dyes were
determined by atoms in molecules (AIM) analysis. For
evaluating electrochemical properties of the dyes, cyclic
voltammetry was employed and a reversible oxidation
wave was observed for the new components. IPCE
spectra and the I–V curves elucidated the photovoltaic
performance parameters of the fluorescent heterocyclic
compounds.
Structures of the products 5a–5c were elucidated from
1H and 13C NMR, and FT-IR spectra.
Computational characterizations and QTAIM
analysis. According to optimized geometries the
species 5a–5c predictably have the planar structure. The
calculated bond lengths and angles are in the expected
range, and confirm suitability of the optimized geometries.
1H NMR spectra of the 5a–5c compounds deduced
by DFT calculations were in good agreement with the
corresponding experimental data.
Comparison of the experimental and DFT-calculated
vibrational frequencies showed good correlation between
those.
1345

1346
AGHELI et al.
Scheme 1. Synthesis of the new compounds 5a–5c.
Predictably, both HOMO and LUMO orbitals were
donating –OCH3 group increased ρ(r) of the benzene
ring in the dye 5c.
mainly localized on the whole of the molecules indicating
HOMO-LUMO electron transitions to be of π→π nature.
The Cl and OCH3 substituents contributed only in the
HOMO orbitals of the compounds 5b and 5c, respectively.
The calculated energy gaps for compounds 5a–5c were
3.02, 2.95, and 2.91 eV, respectively, demonstrating
stability of the compounds [20–22].
Photophysical properties of compounds 5a–5c.
The bands in absorption spectra of dyes 5a–5c (Fig. 1)
were recorded in the ranges of 365–370 and 450–455 nm
(in chloroform), and the intramolecular charge transfer
(ICT) states [23] from the donor site (endocyclic N) to
the acceptor moiety (CN group) were recorded in the
visible area of the spectra. The fluorescence quantum
yield (ΦF) of compounds 5a–5c was determined via
the comparison method, using fluoresce of the standard
sample in 0.1 M NaOH and MeOH solutions [24]. The
emission quantum yields of the compounds 5a–5c were
0.81–0.89, which was higher than the quantum yield of
Based on the AIM analysis and electronic density
[ρ(r)] of the aromatic rings, the pyrazole ring was
characterized by the highest electron density in the
structures of compounds 5a–5c. Accordingly, the
electron-withdrawing Cl substituent decreased ρ(r) of the
benzene ring in the dye 5b, on the contrary, the electron
Fig. 1. Visible absorption (10–5 mol/L) of dyes (1) 5a, (2) 5b,
and (3) 5c in chloroform solution.
Fig. 2. Emission spectra (5×10–7 mol/L) of dyes (1) 5a, (2)
5b, and (3) 5c in chloroform solution.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 7 2020

PYRIDO[1',2':1,5]PYRAZOLO[4,3-b]QUINOLINES
1347
Table 1. Photophysical data for absorption and fluorescence
of compounds 5a–5c in chloroform at 298 K
Table 2. Electrochemical properties of the compounds 5a–5c
in scan rates 100 mV/s
Dye
5a
5b
5c
Compound
Ferrocene
Epa, mV
Epc, mV
∆EP, mV
λabs, nm
370, 455 365, 450 365, 450
556
469
87
ε×10–3, (mol/L)–1 cm–1
37
62
81
5a
5b
5c
–110
–198
–89
–188
–270
–149
78
72
60
λex, nm
λflu, nm
ΦF
365
500
0.81
365
480
0.85
365
490
0.89
the well-known fluorescent dye, fluorescein (0.79). The
fluorescence intensity and emission quantum yield in
compound 5c containing the methoxy group were the
highest (Fig. 2, Table 1), which correlated well with DFT
and AIM analysis.
Visible spectrophotometer and Varian Cary Eclipse
spectrofluorophotometer. FT-IR (KBr discs) spectra were
recorded on a Tensor 27 spectrophotometer. 1H (300 MHz)
and 13C (75 MHz) NMR spectra were measured on a
Bruker Avance DRX-300 spectrometer using DMSO-d6
as a solvent and TMS as an internal standard. Mass spectra
were measured on a Varian Mat, CH-7 at 70 eV. Elemental
analysis was performed on a Thermo Finnigan Flash EA
microanalyzer. Cyclic voltammograms were recorded on
a 797 VA Computrace Metrohm. Tetrabutylammonium
perchlorate (TBAP) was used as the supporting
electrolyte, platinum wire served as a counter electrode,
andAg/AgCl (3M KCl) was used as a reference electrode.
The concentrations used to obtain each voltammogram are
given in the corresponding figure caption. Voltage-current
analysis was carried out on a Potentiostat-Galvanostat
model EIS-26H at ±5V.
Electrochemicalpropertiesofthecompounds5a–5c.
Redox properties of compounds 5a–5c were approached
by cyclic voltammetry. Ferrocene/ferrocenium (Fc/Fc+)
was used as the internal reference.
Cyclic voltammogram of the dye 5b (–1 to +1 V )
(Fig. 3) demonstrated an oxidation wave with an anodic
peak potential of –0.198 V and a cathodic peak potential
of –0.270 V versus SCE (ipa/ipc ≈ 1). The quasi-reversible
behavior of the redox couple was found by the observed
peak separation for the reversible waves which was higher
than the value of 59/n mV expected for a reversible system
[25] (Table 2).
Photovoltaic properties. For evaluating the properties
of the solar cells based on compounds 5a–5c, TiO2
nanoparticles in rutile phase standard electrolyte, acetic
acid, ethanol, and FTO glasses were used. IPCE spectra
and the I–V curves of dyes 5a–5c are presented in
Fig. 4. The photovoltaic performance parameters of dyes
5a–5c are listed in Table 3. The high electron-injection
efficiency was due to the high LUMO level, and the faster
charge recombination was due to the BODIPYcore in the
compounds 5a–5c. The above could be the main reasons
for high photovoltaic performances of DSSCs based on
these dyes.
EXPERIMENTAL
The reagents were purchased from Merck and Sigma–
Aldrich.All solvents were dried according to the standard
procedures.
Melting points were determined on an Electrothermal
type-9100 melting-point apparatus. UV-Vis and fluore-
scence spectra were recorded on a Varian 50-bio UV-
Fig. 3. Cyclic voltammogram of compound 5b in DMF
(2×10–4 M) at scan rate 100 mV/s.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 7 2020

1348
AGHELI et al.
Fig. 4. (a) I–V curves and (b) IPCE spectra of (1) 5a, (2) 5b, and (3) 5c compounds.
10-Chloropyrido[1',2':1,5]pyrazolo[4,3-b]-
Compounds 1, 2 and 4a–4c were synthesized
quinoline-7-carbonitrile (5b). Yield 85%, mp 309–
according to the procedures reported in literature [16–18].
1
311°C. IR spectrum, ν, cm–1: 2203 (CN). Н NMR
Synthesis of compounds 5a–5c. To a solution of
KOH (40 g, 714 mmol) in MeOH (70 mL), compound 2
(3.26 g, 20 mmol) and an appropriate arylacetonitrile
3a–3c (24 mmol) were added. The mixture was refluxed
upon stirring for 3 h, and then poured into water. The
precipitate was collected by filtration and then neutralized
with dilute HCl solution. The crude products 4a–4c were
washed with water, dried in the air and crystallized from
acetone. Then, acetyl chloride (1.65 g, 21 mmol) was
added upon stirring to a solution of a compound 4a–4c
(15 mmol) in dry pyridine (100 mL), and the mixture
was refluxed for 4 h. The solvent was evaporated, and
the crude product was purified by crystallization from
ethanol to give shiny yellow needles of the corresponding
compounds 5a–5c.
spectrum, δ, ppm: 8.04–8.09 m (3H, HAr), 8.54 d (1H,
J = 7.5 Hz, HAr), 8.66 d (1H, J = 2.1 Hz, HAr), 8.89 d (1H,
J = 8.2 Hz, HAr), 9.19 d (1H, J = 6.9 Hz, HAr). 13С NMR
spectrum, δС, ppm: 103.4, 109.8, 111.4, 119.2, 120.1,
122.1, 131.3, 135.1, 134.8, 137.5, 138.2, 144.8, 147.1,
148.3, 149.0. MS: m/z: 278 [M]+. Found, %: C 64.79; H
2.57; N 20.49. Calculated, %: C 64.64; H 2.53; N 20.10.
10-Methoxypyrido[1',2':1,5]pyrazolo[4,3-b]quino-
line-7-carbonitrile (5c). Yield 79%, mp 299–301°C.
IR spectrum, ν, cm–1: 2210 (CN). 1Н NMR spectrum, δ,
ppm: 4.12 s (3H, OMe), 7.68 d (1H, J = 2.4 Hz, HAr),
7.77 d. d (1H, J = 9.2 Hz, J' = 2.4 Hz, HAr), 7.98–8.01 m
(2H, HAr), 8.43 d (1H, J = 7.5 Hz, HAr), 8.75 d (1H,
J = 9.2 Hz, HAr), 9.12 d (1H, J = 6.9 Hz, HAr). 13С NMR
spectrum, δС, ppm: 55.6, 102.5, 111.3, 111.9, 113.5, 118.6,
123.2, 135.8, 136.4, 137.5, 139.2, 144.4, 146.2, 147.9,
149.1, 157.2. MS: m/z: 274 [M]+. Found, %: C 70.34; H
3.70; N 20.77. Calculated, %: C 70.07; H 3.67; N 20.43.
Pyrido[1',2':1,5]pyrazolo[4,3-b]quinoline-7-carbo-
nitrile (5a). Yield 82%, mp 264–266°C. IR spectrum, ν,
cm–1: 2205 (CN). 1Н NMR spectrum, δ, ppm: 7.87 t (1H,
J = 7.5 Hz, HAr), 7.91 t (1H, J = 7.1 Hz, HAr), 8.11–8.13 m
(2H, HAr), 8.55–8.57 m (2H, HAr), 8.93 d (1H, J = 8.1 Hz,
HAr), 9.17 d (1H, J = 7.1 Hz, HAr). 13С NMR spectrum,
δС, ppm: 103.2, 105.2, 111.7, 118.3, 120.8, 123.5, 128.4,
133.7, 134.8, 138.3, 144.2, 147.6, 148.1, 149.0, 150.3.
MS: m/z: 244 [M+]. Found, %: C 73.99; H 3.35; N 23.11.
Calculated, %: C 73.76; H 3.30; N 22.94.
Computational details. All DFT method calculations
have been performed by using the B3LYPfunctional [26]
and 6-311+G(d,p) basis sets. The Gaussian 03 program
[27] was used. Geometry of the compounds was fully
optimized and used for the complementary calculations.
The optimized geometries did not show any imaginary
frequencies. The calculated vibrational frequencies were
improved by applying the scale factor of 0.9614 [28].
The gauge-including atomic orbital (GIAO) method
Table 3. Photovoltaic parameters of the compounds 5a–5c
JSC, mA/cm2
12.81
VOC, V
0.53
0.55
FF, %
59
64
η, %
5.12
5.89
6.59
1
Dye
5a
5b
[29] was used to predict H NMR chemical shifts of
the investigated compounds with respect to TMS. The
NBO analysis was performed to identify HOMO and
LUMO frontier orbitals. Chemcraft 1.7 program was
13.75
16.65
5c
0.65
70
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 7 2020

PYRIDO[1',2':1,5]PYRAZOLO[4,3-b]QUINOLINES
1349
employed for visualization of structures [30]. QTAIM
calculations were performed using theAIMALLpackage
[31]. QTAIM calculations were based on the topological
analysis of the electron density, ρ(r) [32]. The kinetic
energy density (Gb), potential energy density (Vb), total
energy density (Hb), electron density (ρ), and its Laplacian
fluorescein.According toAIM analysis the pyrazole rings
carry the highest electron density in molecular structures
of the compounds. Cyclic voltammogram of the dyes
exhibit an oxidation wave with an anodic peak potential
of –0.89 – –0.198 V and a cathodic peak potential of
–0.149 to –0.270 V versus SCE.
Δ
( ρ) at a bond critical point (BCP) were related to the
electron density.
ACKNOWLEDGMENTS
We would like to express our sincere gratitude to Research
Office, Mashhad Branch, Islamic Azad University, Mashhad-
Iran, for financial support of this work.
Photoelectrochemical measurements. Titanium
dioxide (TiO2) nanoparticles in rutile phase (p-25),
(I–/I3–) standard electrolyte, acetic acid (99% sigma
Aldrich), ethanol (99% Merck), and FTO glasses were
used to study the properties of the solar cells made by
the synthesized dyes (DSSCs). FTO glasses were cleaned
3 times with deionized water, acetone and ethanol
in ultrasonic bath for DSSCs fabrication, and their
conductivity was determined by an Ohm meter. Then
TiO2 paste was deposited on one of those by the Doctor
Blade’s method [33]. TiO2 paste was prepared using TiO2
nano powder (2 g) grinded in mortar with three drops of
acetic acid making colloidal paste with fluid of uniform
consistency. In the next step, 0.2 g polyethylene glycol
(2000) and deionized water were mixed with the paste
thoroughly for making it sticky. Then the paste was dried
to some extent, and the slides were heated in an oven at
450°C for 30 min. The dried slides were placed in dyes
for 20 h.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
1. Cseke, L.J., Kirakosyan, A., Kaufman, P.B., Warber, S.,
Duke, J.A., and Brielmann, H.L., Natural Products from
Plants, Boca Raton: CRC Press, 2016.
2. Afzal, O., Kumar, S., Haider, M.R., Ali, M.R., Kumar, R.,
Jaggi, M., and Bawa, S., Eur. J. Med. Chem., 2015,
vol. 97, p. 871.
https://doi.org/10.1002/chin.201532305
3. Bando, M., US Patent 13923858, 2013.
4. Shinotsuka, R., Oba, T., Mitome, T., Masuya, T., Ito, S.,
Murakami, Y., Kagenishi, T., Kodama, Y., Matsu-
da, M., Yoshida, T., and Wakamori, M., J. Photoch.
Photobio. A, 2019, vol. 382, p. 111900.
Counter electrodes were fabricated depositing Pt paste
on FTO. The deposited FTO were connected to those with
TiO2 paste and sealed completely. Then an electrolyte
was injected into the empty space between two electrodes
(effective surface 0.25 cm2).
https://doi.org/10.1016/j.jphotochem.2019.111900
5. Park, S., Kwon, D.I., Lee, J., and Kim, I., ACS Comb.
Sci., 2015, vol. 17, no. 8, p. 459.
https://doi.org/10.1021/acscombsci.5b00031
6. Karimi, R., Yousefi, F., Ghaedi, M., and Rezaee, Z.,
Polyhedron, 2019, vol. 170, p. 60.
A solar simulator system under 1.5 AM and intensity
of 100 mW/cm2 (SIM 1000, Sharif solar) was applied for
determining photovoltaic characteristics including short
circuit current, open circuit voltage, fill factor, and cells
efficiency.
https://doi.org/10.1016/j.poly.2019.05.038
7. Czaplinska, B., Spaczynska, E., and Musiol, R., Med.
Chem., 2018, vol. 14, no. 1, p. 19.
https://doi.org/10.2174/1573406413666171002121817
CONCLUSIONS
8. Mao, M., Zhang, X., Zhu, B., Wang, J., Wu, G., Yin, Y.,
and Song, Q., Dyes Pigm., 2016, vol. 124, p. 72.
https://doi.org/10.1016/j.dyepig.2015.09.002
Pyrido[1',2':1,5]pyrazolo[4,3-b]quinolone derivatives
have been synthesized by the reaction of 3- nitropyra-
zolo[1,5-a]pyridine with different arylacetonitriles
in high yield. The structural assignments of the new
compounds are based on the analytical and spectral
data, and are in good agreement with the experimental
and DFT-computed chemical shifts and IR vibrational
frequencies. The compounds are characterized by
higher fluorescence quantum yield in comparison with
9. dos Santos, G.C., Oliveira, E.F., Lavarda, F.C.,
and da Silva-Filho, L.C., J. Mol. Model., 2019, vol. 25,
no. 3, p. 75.
https://doi.org/10.1007/s00894-019-3958-y
10. Katsumata, K., Matsui, H., Yamaguchi, T., and Tanabe, N.,
Inorg. Chim. Acta, 2017, vol. 463, p. 118.
https://doi.org/10.1016/j.ica.2017.04.030
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 7 2020

1350
AGHELI et al.
11. Mao, M., Wang, J.B., Liu, X.L., Wu, G.H., Fang, X.Q., and
Song, Q.H., Spectrochim Acta A., 2018, vol. 190, p. 23.
https://doi.org/10.1016/j.saa.2017.09.002
12. Pordel, M., Beyramabadi, S.A., and Mohammadinejad, A.,
Dyes Pigm., 2014, vol. 102, p. 46.
https://doi.org/10.1016/j.dyepig.2013.10.021
13. Ramezani, S., Pordel, M., and Davoodnia, A., Appl. Or-
ganomet. Chem., 2017, vol. 32, p. e4178.
https://doi.org/10.1002/aoc.4178
14. Baf, M.M., Pordel, M., and Daghigh, L.R., Tetrahedron Lett.,
2014, vol. 55, p. 6925.
https://doi.org/10.1016/j.tetlet.2014.10.118
15. Ramezani, S., Pordel, M., and Beyramabadi, S., J. Fluoresc.,
2016, vol. 26, p. 513.
https://doi.org/10.1007/s10895-015-1736-5
16. Boekelheide, V., and Fedoruk, N.A., J. Org. Chem.,
1968, vol. 33, no. 5, p. 2062.
22. Tezer, N., and Karakus, N., J. Mol. Model., 2009,
vol. 15, p. 223.
https://doi.org/10.1007/s00894-008-0397-6
23. Moon, C.K., Suzuki, K., Shizu, K., Adachi, C., Kaji, H.,
and Kim, J., J. Adv. Mater., 2017, vol. 29, no. 17,
p. 1606448.
24. Umberger, J.Q., and La Mer, V. K., J. Am. Chem. Soc.,
1945, vol. 67, p. 1099-1109.
https://doi.org/10.1002/adma.201606448
25. Chowdhury, N.R., and Kant, R., Electrochim. Acta, 2018,
vol. 281, p. 445.
https://doi.org/10.1016/j.electacta.2018.05.140
26. Lammers, E., Nusstein, J., Reader, A., Drum, M., Beck,
M., and Fowler, S., J. Endod., 2014, vol. 40(9), p. 1287.
https://doi.org/10.1016/j.joen.2014.04.015
27. Peralta, J.E., Scuseria, G.E., and Frisch, M.J., Phys. Rev.
B., 2007, vol. 75(12), p. 125119.
https://doi.org/10.1021/jo01269a075
17. Tanji, K.I., Sasahara, T., Suzuki, J., and Higashino, T.,
Heterocycles, 1993, vol. 35, no. 2, p. 915.
28. Young, D.C., Computational Drug Design: A Guide for
Computational and Medicinal Chemists, John Wiley and
Sons, 2009.
https://doi.org/10.3987/com-92-s(t)85
18. Agheli, Z., Pordel, M., and Beyramabadi, S.A., J. Mol.
Struct., 2020, vol. 1202, p. 127228.
29. Ditchfield, R., Mol. Phys., 1974, vol. 27, no. 4, p. 789.
https://doi.org/10.1080/00268977400100711
30. Zhurko, and G., Zhurko, D., Chemcraft, Version
1.7 (build 365) (accessed March 27, 2016).
http://www.chemcraftprog.com.
https://doi.org/10.1016/j.molstruc.2019.127228
19. Zonozi, F., Beyramabadi, S.A., Pordel, M., and Morsali, A.,
Res. Chem. Intermed., 2017, vol. 43, no. 3, p. 1829.
https://doi.org/10.1007/s11164-016-2733-2
20. Snehalatha, M., Ravikumar, C., Joe, I.H., Sekar, N.,
and Jayakumar, V., Spectrochim. Acta. Part A, 2009,
vol. 72, p. 654.
31. Keith, T.A., AIMAll (Version 13.11. 04)., TK Gristmill
Software, Overland Park KS, USA, 2013.
32. Bader, R.F., Chem. Rev., 1991, vol. 91, no. 5, p. 893.
https://doi.org/10.1021/cr00005a013
https://doi.org/10.1016/j.saa.2008.11.017
33. Dinh, N.N., Quyen, N.M, Ha Chi, L., Thuy, T.T.,
and Trung, T.Q., InAIP Conference Proceedings,
2009, vol. 1169, no. 1, p. 25.
21. Habibi, M., Beyramabadi, S.A., Allameh, S., Khashi, M.,
Morsali, A., Pordel, M., and Khorsandi-Chenarboo, M.,
J. Mol. Struct., 2017, vol. 1143, p. 424.
https://doi.org/10.1016/j.molstruc.2017.04.114
https://doi.org/10.1063/1.3243261
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 7 2020