gem-Dinitromethyl-Functionalized 5-Amino-1,3,4-oxadiazolate Derivatives: Alternate Route, Characterization, and Property Analysis

Article abstract of DOI:10.1021/acs.orglett.0c01569

A new, safer, and more cost-effective methodology to synthesize salts based on gem-dinitromethyl-functionalized 5-amino-1,3,4-oxadiazolate is given. Cyclization, deprotection, nitration, and neutralization reactions were conducted to obtain products in high yield. All compounds were fully characterized by NMR and IR spectroscopy, elemental analysis, and differential scanning calorimetry. Crystal structure analysis, property tests, and theoretical calculations confirm good detonation performance and high mechanical stabilities of the salts.

Full text of DOI:10.1021/acs.orglett.0c01569

pubs.acs.org/OrgLett
Letter
gem-Dinitromethyl-Functionalized 5‑Amino-1,3,4-oxadiazolate
Derivatives: Alternate Route, Characterization, and Property
Analysis
Jinchao Ma, Jiaheng Zhang,* Gregory H. Imler, Damon A. Parrish, and Jean’ne M. Shreeve*
Cite This: https://dx.doi.org/10.1021/acs.orglett.0c01569
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: A new, safer, and more cost-effective methodology
to synthesize salts based on gem-dinitromethyl-functionalized 5-
amino-1,3,4-oxadiazolate is given. Cyclization, deprotection,
nitration, and neutralization reactions were conducted to obtain
products in high yield. All compounds were fully characterized by
NMR and IR spectroscopy, elemental analysis, and differential
scanning calorimetry. Crystal structure analysis, property tests, and
theoretical calculations confirm good detonation performance and
high mechanical stabilities of the salts.
nergetic materials have been widely used in military and
Ecivilian applications because of their special properties of
releasing a large amount of energy quickly. As a growing
number of scientists join this study, the field of energetic
materials has experienced rapid development in the past few
decades.1−4 Many novel heterocyclic energetic molecules
composed of an energetic framework and some explosive
groups have been reported in recent years, and their energetic
performance has reached a high level.5,6 However, along with
the increasing consideration of safety and the availability of
energetic materials, the research is no longer a simple
successful synthesis and characterization but a move toward
structural design, synthesis and property optimization, and
application development.7−11
Before design of an energetic molecule, the properties of its
composition and effects on the whole must be analyzed.
Oxadiazole, which has played an important role in the
synthesis of high energy density materials,12−15 includes four
isomers, namely, 1,2,5-, 1,2,4-, 1,3,4-, and 1,2,3-oxadiazole
(Figure 1).16−19 Among them, except the unstable 1,2,3-
oxadiazole, the 1,2,5-, 1,2,4-, and 1,3,4-oxadiazoles have been
widely studied as energetic backbones because of their high
nitrogen and oxygen content. Especially for 1,3,4-oxadiazole,
the distribution of heteroatoms is more uniform, and there is
no weak N−O bond (two N−O bonds in 1,2,5-oxadiazole, one
N−O bond in 1,2,4-oxadiazole), which helps to ensure that
this member will show high stability.20,21 The nitro group was
used to improve the density and detonation performance.
However, the incorporation of multiple nitro groups can
significantly reduce the stability of these energetic compounds.
Figure 1. Design selection of energetic molecules.
For example, trinitromethyl-functionalized compounds often
exhibit low thermal and mechanical sensitivities because of the
weak trinitromethyl C−N bond and the large space that the
three nitro groups occupy. One of the best choices to increase
the energy density and enhance stability is the gem-
dinitromethyl group. Unlike the trinitromethyl group, the
gem-dinitromethyl group has a planar structure and a strong
C−N bond, which helps to stabilize energetic com-
pounds.22−24
In this work, gem-dinitromethyl-1,3,4-oxadiazolate deriva-
tives are obtained by using a new, safer, and more cost-effective
Received: May 7, 2020
https://dx.doi.org/10.1021/acs.orglett.0c01569
© XXXX American Chemical Society
Org. Lett. XXXX, XXX, XXX−XXX
A

Organic Letters
pubs.acs.org/OrgLett
Letter
way. All intermediates and energetic products are fully
characterized. Thermal stabilities, impact sensitivities, as well
as calculated detonation performance of AAOD (ammonium
(5-amino-1,3,4-oxadiazol-2-yl)dinitromethanide) and hydrox-
ylammonium salt 8 were determined. The crystal structures of
these compounds were determined. High performance coupled
with low sensitivity suggest that 8 has good potential as an
energy-safe balanced explosive.
materials and removes the necessity to utilize unstable
intermediates. The detailed description of the synthesis process
is given in the experimental section of the Supporting
Information (SI).
Crystals of AAOD (293 K) suitable for single-crystal X-ray
diffraction were obtained by dissolving AAOD in a small
amount of methanol and allowing the solvent to slowly
evaporate. The unit cell of AAOD contains four formula
moieties, with a crystal density of 1.750 g cm−3 at 293 K (SI).
To further examine the structures of 3, 4, and AAOD (173 K)
as well as to evaluate the differences between them, crystal data
of 3, 4, and AAOD (173 K) were studied.25 The structures of
these gem-dinitromethyl-functionalized 5-amino-1,3,4-oxadia-
zoles are a cross-shaped conformation, in which the dihedral
angles between the gem-dinitromethyl group and oxadiazole
are 75.9° (3), 83.9° (4), 78.3° (AAOD (173 K)), and 79.0°
(AAOD (293 K)), respectively. In general, a planar
configuration helps to improve molecular stability;28,29 thus
compound 4 with a high degree of molecular distortion likely
generates hot spots when mechanically stimulated. The free
space per molecule in the unit cells of 3, 4, and AAOD (173
K) is 21, 44, and 50 Å3, respectively. In light of a sensitivity−
free space relationship, the sensitivity value of these
compounds will decrease according to 3 > 4 > AAOD (173
K).30−32
As shown in Scheme 1, in the earlier method, the energetic
AAOD salt was synthesized from a zwitterionic com-
Scheme 1. Synthetic Route to AAOD and 8
From a crystallographic perspective, layer by layer stacking is
beneficial to improve the stability of energetic materials
(Figure 2). However, the premise of layer by layer stacking
pound(5-iminio-4,5-dihydro-1,3,4-oxadiazol-2-yl) dinitro-
methanide (4)which was prepared using a four-step
synthesis route from commercially available ethyl potassium
malonate.25 Among all of the intermediates, the dinitromethyl
potassium salts, specifically potassium (5-amino-1,3,4-oxadia-
zol-2-yl) dinitromethanide (3), have high mechanical
sensitivity. Potassium 2-hydrazinyl-1,1-dinitro-2-oxoethan-1-
ide (2) is unstable and can not be stored for extended
periods. For these reasons, the previous method for the
synthesis of AAOD was limited by utilization of the formation
of unstable intermediates and hidden safety hazards. In this
study, the ammonium salt AAOD and the hydroxylammonium
salt 8 were obtained from 2-(2-methyl-1,3-dioxolan-2-yl)
acetohydrazide (5)26,27 following a three-step route. Initially
5-((2-methyl-1,3-dioxolan-2-yl)methyl)-1,3,4-oxadiazol-2-
amine (6, 88%) resulted from reacting 5 with cyanogen
bromide in a solution of potassium bicarbonate. Compound 6
was deprotected by using a 2 M HCl solution and then treated
with sodium bicarbonate to give 1-(5-amino-1,3,4-oxadiazol-2-
yl)propan-2-one (7, 75%) as a white solid. AAOD and 8 were
obtained after nitrating 7 and subsequently neutralizing it with
the corresponding base. Our process employs inexpensive raw
Figure 2. Planar/cross structures form 2-D and 3-D cube layer by
layer stacking with different arrangements, respectively.
is planar molecular structure. For dinitro-1,3,4-oxadiazole
derivatives, which all possess cross structures, an interesting
3-D cube layer by layer assembly was found.33 gem-
Dinitromethyl-1,3,4-oxadiazolates form a columnar body
through spiral arrangements in a certain direction, and
columnar bodies are arranged to form a 3-D layer. This
interesting arrangement is believed to help the compounds
have optimal balance between stability and performance.
As seen from Figure 3, these materials all exhibit 3-D cube
structures. Moreover, each 3-D cube of these materials consists
of molecules arranged in two distinct ways. For the layered
structure, the interlayer distance is an important parameter that
affects the density and even the performance of the compound.
The average distances between neighboring cubes are 5.0250 Å
(3), 4.1344 Å (4), 4.9541 Å (AAOD (173 K)), and 4.9681 Å
(AAOD (293 K)), respectively. Compound 4 with small
intermolecular spacing is likely to be more dense. In the cubes
of 3 and AAOD, two neighboring molecules generate a large
B
https://dx.doi.org/10.1021/acs.orglett.0c01569
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
the [100] direction, molecules in two different directions in
each quadrilateral channel were stacked in a helical shape, and
the molecular distances in the vertical direction were 9.6783 Å
(3), 13.2779 Å (4), 9.9589 Å (AAOD (173 K)), and 9.9694 Å
(AAOD (293 K)), respectively.
In Table 1, some key physical properties, such as thermal
stability, density, and detonation performance, are given for the
energetic materials. The onset decomposition temperature of
AAOD is 195 °C, which is slightly lower than the literature
value (202 °C).25 The hydroxylammonium salt 8 has a lower
thermal stability than AAOD, decomposing readily at 145 °C;
however, the value was higher than that of the zwitterionic 4
(138 °C). As shown in Figure 4, the sharper peak of 8
Figure 4. DSC curves of compounds AAOD and 8.
compared to that of AAOD implies a more intense exothermic
reaction than that of AAOD. The thermal stability of these
new compounds is less than that of cyclotrimethylene
trinitramine (RDX, 220 °C) and 1,1-diamino-2,2-dinitroethene
(FOX-7, 204 °C).
The densities of AAOD and 8 were determined
experimentally at room temperature using a gas pycnometer.
The density of 8 (1.88 g cm−3) is higher than that of AAOD
(1.75 g cm−3) and comparable to traditional explosives FOX-7
(1.88 g cm−3) and RDX (1.82 g cm−3). The gas-phase heats of
formation were calculated by the Gaussian 03 suite of
programs with isodesmic reactions.36 Based on the exper-
imental densities and the calculated heats of formation,
detonation velocities and detonation pressures were calculated
using EXPLO5 (v6.01).37 Benefiting from the existence of the
oxadiazole backbone, 8 and AAOD have larger ΔfH values
(−0.14 to −0.36 kJ g−1) than FOX-7 (−0.88 kJ g−1) but much
lower than RDX (0.36 kJ g−1). The calculated heat of
formation (−0.36 kJ g−1), detonation velocity (8365 m s−1),
and detonation pressure (29.1 GPa) of AAOD were slightly
lower than those reported in the literature (ΔfH = −0.36 kJ
g−1, D = 8554 m s−1, P = 30.1 GPa) because of the lower
experimental density value used.25 As shown in Figure 5a, the
calculated detonation velocity and pressure of 8 are 8956 m s−1
and 37.1 GPa, respectively, which are slightly higher than those
of FOX-7 (D = 8870 m s−1, P = 34.0 GPa) and RDX (D =
8748 m s−1, P = 34.9 GPa) and comparable to the highly dense
3 (D = 9035 m s−1, P = 33.0 GPa) and zwitterionic 4 (D =
8828 m s−1, P = 34.6 GPa).
Figure 3. (a1)−(d1) Molecular structures of 3, 4, AAOD (173 K),
and AAOD (293 K); (a2)−(d2) three-dimensional packing diagrams
of 3, 4, AAOD (173 K), and AAOD (293 K) along [001]; and (a3)−
(d3) helical structures of 3, 4, AAOD (173 K), and AAOD (293 K)
along [100].
and open quadrilateral channel along the [100] direction. The
distances between the neighboring channels in the same cube
were 7.5626 Å (3), 6.1121 Å (4), 7.8116 Å (AAOD (173 K)),
and 7.8993 Å (AAOD (293 K)), respectively. The length of
the quadrilateral channels varied between 4.3513 and 4.4388
Å. The width of quadrilateral channels ranged between 3.3456
and 3.5042 Å. However, 4 is arranged slightly differently from
3 and AAOD, with the channel being small because the
molecules creating the channel were closely packed. Seen from
The experimental impact and friction sensitivity values were
determined with standard BAM drop hammer and friction
tester techniques.38 AAOD has almost the same friction (160
N) and impact sensitivity values (22 J) as those given in the
C
https://dx.doi.org/10.1021/acs.orglett.0c01569
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Table 1. Physical and Detonation Properties of the Reported Compounds in Comparison with FOX-7 and RDX
a
b
c
d
e
f
g
compd.
Td [°C]
ρ
[g cm−3
]
ΔfH [kJ mol−1/kJ g−1
]
D
[m s−1
]
P [GPa]
IS [J]
FS [N]
AAOD
8
195
145
235
138
202
220
204
1.75
1.88
2.051
1.872
1.776
−73.9/−0.36
−30.3/−0.14
−203.2/−0.89
62.0/0.33
−72.2/−0.35
−130.0/−0.88
80.0/0.36
8365
8956
9035
8828
8554
8870
8748
29.1
37.1
33.0
34.6
30.1
34.0
34.9
22
30
10
25
20
25
7.4
160
240
80
120
160
340
120
h
i
3
4
h
i
h
i
AAOD
j
FOX-7
1.88
1.82
k
RDX
a
b
c
Thermal decomposition temperature (onset) under nitrogen gas (DSC, 5 °C/min). Measured densities at room temperature. Calculated heat of
d
e
f
g
h
i
formation (gas phase). Calculated detonation velocity. Calculated detonation pressure. Impact sensitivity. Friction sensitivity. Ref 25. Crystal
density at 173 K. Ref 34. ref 35.
j
k
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01569.
Synthesis, calculation detail, crystal refinements, NMR
spectra, IR spectra, DSC plots (PDF)
Accession Codes
CCDC 1957886 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Jean’ne M. Shreeve − Department of Chemistry, University of
Idaho, Moscow, Idaho 83844-2343, United States;
orcid.org/0000-0001-8622-4897; Email: jshreeve@
uidaho.edu; Fax: (+1) 208-885-9146
Jiaheng Zhang − Zhuhai Institute of Advanced Technology
Chinese Academy of Sciences, Biomaterials Research Center,
Zhuhai 519003, China; Research Centre of Flexible Printed
Electronic Technology, Harbin Institute of Technology,
Shenzhen 518055, China; orcid.org/0000-0002-2377-
9796; Email: jzhang@uidaho.edu
Figure 5. Detonation performance (a) and sensitivity (b) of the 3, 4,
8, and AAOD in comparison to FOX-7 and RDX.
Authors
Jinchao Ma − Department of Chemistry, University of Idaho,
Moscow, Idaho 83844-2343, United States; Zhuhai Institute of
Advanced Technology Chinese Academy of Sciences,
Biomaterials Research Center, Zhuhai 519003, China
Gregory H. Imler − Naval Research Laboratory, Washington,
D.C. 20375, United States; orcid.org/0000-0002-9686-
9186
literature (IS = 20 J, FS = 160 N).25 For 8, the impact and
friction sensitivity were 30 and 240 J (Figure 5b), respectively,
showing that it is more insensitive than other derivatives and
RDX (IS = 7.4 J, FS = 120 N).
In summary, the gem-dinitromethyl-functionalized 5-amino-
1,3,4-oxadiazolate-based energetic salts AAOD and 8 were
synthesized according to a new route, using less-expensive raw
materials and a safer process. Remarkable 3-D cube layer by
layer stacking and quadrilateral channels as well as helical
structures were observed from crystal structure analyses of 3, 4,
and AAOD. The interesting and structurally compact assembly
imparts these compounds with a good balance between high
energy density and stability. The hydroxylammonium salt 8 has
a high density (1.88 g cm−3) and good detonation properties
(D = 8956 m s−1, P = 37.1 GPa), comparable to those of FOX-
7 (D = 8870 m s−1, P = 34.0 GPa), and low impact sensitivities
(IS = 30 J, FS = 240 N), which indicate its potential as a high-
performance insensitive explosive.
Damon A. Parrish − Naval Research Laboratory, Washington,
D.C. 20375, United States
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01569
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors acknowledge financial support from the Office of
Naval Research (N00014-16-1-2089) and the Defense Threat
Reduction Agency (HDTRA 1-15-1-0028).
D
https://dx.doi.org/10.1021/acs.orglett.0c01569
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J.
J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision
E.01; Gaussian, Inc.: Wallingford, CT, 2003.
REFERENCES
■
(1) Gao, H.; Zhang, Q.; Shreeve, J. M. J. Mater. Chem. A 2020, 8,
4193−4216.
(2) Wang, P.; Xu, Y.; Lin, Q.; Lu, M. Chem. Soc. Rev. 2018, 47,
7522−7538.
(3) Lewczuk, R. Propellants, Explos., Pyrotech. 2018, 43, 436−444.
(4) He, P.; Zhang, J.; Yin, X.; Wu, J.; Wu, L.; Zhou, Z.; Zhang, T.
Chem. - Eur. J. 2016, 22, 7670−85.
(5) Zhang, W.; Zhang, J.; Deng, M.; Qi, X.; Nie, F.; Zhang, Q. Nat.
Commun. 2017, 8, 181.
(6) Hu, L.; Yin, P.; Zhao, G.; He, C.; Imler, G. H.; Parrish, D. A.;
Gao, H.; Shreeve, J. M. J. Am. Chem. Soc. 2018, 140, 15001−15007.
(7) Barton, L. M.; Edwards, J. T.; Johnson, E. C.; Bukowski, E. J.;
Sausa, R. C.; Byrd, E. F. C.; Orlicki, J. A.; Sabatini, J. J.; Baran, P. S. J.
Am. Chem. Soc. 2019, 141, 12531−12535.
(8) Tang, Y.; Huang, W.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M.
J. Am. Chem. Soc. 2020, 142, 7153−7160.
́
(37) Suceska, M. EXPLO5 6.01; Brodarski Institute: Zagreb, Croatia,
2013.
(9) Song, S.; Wang, Y.; Wang, K.; Chen, F.; Zhang, Q. J. Mater.
Chem. A 2020, 8, 5975−5985.
(38) United Nations. Recommendations on the Transport of
Dangerous Goods. Manual of Tests and Criteria, 5th rev. ed.; United
Nations Publication: New York, 2009.
(10) Xu, Y.; Tian, L.; Li, D.; Wang, P.; Lu, M. J. Mater. Chem. A
2019, 7, 12468−12479.
(11) Huang, C.; Yang, Z.; Li, Y.; Zheng, B.; Yan, Q.; Guan, L.; Luo,
G.; Li, S.; Nie, F. Chem. Eng. J. 2020, 383, 383.
̈
(12) Fischer, D.; Klapotke, T. M.; Reymann, M.; Stierstorfer, J.;
̈
Volkl, M. B. R. New J. Chem. 2015, 39, 1619−1627.
(13) Yu, Q.; Yin, P.; Zhang, J.; He, C.; Imler, G. H.; Parrish, D. A.;
Shreeve, J. M. J. Am. Chem. Soc. 2017, 139, 8816−8819.
(14) Fu, Z.; Su, R.; Wang, Y.; Wang, Y. F.; Zeng, W.; Xiao, N.; Wu,
Y.; Zhou, Z.; Chen, J.; Chen, F. X. Chem. - Eur. J. 2012, 18, 1886−9.
(15) Yan, C.; Wang, K.; Liu, T.; Yang, H.; Cheng, G.; Zhang, Q.
Dalton Trans 2017, 46, 14210−14218.
(16) Wei, H.; He, C.; Zhang, J.; Shreeve, J. M. Angew. Chem., Int. Ed.
2015, 54, 9367−9371.
(17) Xiong, H.; Yang, H.; Lei, C.; Yang, P.; Hu, W.; Cheng, G.
Dalton Trans 2019, 48, 14705−14711.
(18) Lu, T.; Wang, C.; Wang, G.; Wang, S.; Song, J.; Yin, H.; Fan,
G.; Chen, F. New J. Chem. 2019, 43, 13330−13333.
(19) Yu, Q.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M. Chem. - Eur.
J. 2017, 23, 17682−17686.
(20) Dacons, J. C.; Sitzmann, M. E. J. J. Heterocycl. Chem. 1977, 14,
1151−1155.
̈
(21) Klapotke, T. M.; Witkowski, T. G. ChemPlusChem 2016, 81,
357−360.
(22) Lei, C.; Yang, H.; Cheng, G. Dalton Trans 2020, 49, 1660−
1667.
(23) Ma, J.; Tang, J.; Yang, H.; Yi, Z.; Wu, G.; Zhu, S.; Zhang, W.;
Li, Y.; Cheng, G. ACS Appl. Mater. Interfaces 2019, 11, 26053−26059.
(24) Zhang, J.; Zhang, J.; Parrish, D. A.; Shreeve, J. M. J. Mater.
Chem. A 2018, 6, 22705−22712.
(25) Liu, T.; Liao, S.; Song, S.; Wang, K.; Jin, Y.; Zhang, Q. Chem.
Commun. 2020, 56, 209−212.
(26) Liu, Z.; Fang, L.; Zhang, H.; Gou, S.; Chen, Li. Bioorg. Med.
Chem. 2017, 25, 2387−2398.
(27) Kubel, B. Monatsh. Chem. 1982, 113, 793−803.
̈
(28) Yin, P.; Zhang, J.; Imler, G. H.; Parrish, D. A.; Shreeve, J. M.
Angew. Chem., Int. Ed. 2017, 56, 8834−8838.
(29) Piercey, D. G.; Chavez, D. E.; Scott, B. L.; Imler, G. H.; Parrish,
D. A. Angew. Chem., Int. Ed. 2016, 55, 15315−15318.
(30) Politzer, P.; Murray, J. S. J. Mol. Model. 2014, 20, 2223.
(31) Politzer, P.; Murray, J. S. J. Mol. Model. 2015, 21, 25.
́
(32) Zeman, S.; Liu, N.; Jungova, M.; Hussein, A. K.; Yan, Q.-L.
Defence Technology 2018, 14, 93−98.
(33) Sun, Q.; Shen, C.; Li, X.; Lin, Q.; Lu, M. Cryst. Growth Des.
2017, 17, 6105−6110.
(34) Bellamy, A. J. Struct. Bonding (Berlin) 2007, 125, 1.
(35) Gao, H.; Shreeve, J. M. Angew. Chem., Int. Ed. 2015, 54, 6335−
6338.
(36) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
E
https://dx.doi.org/10.1021/acs.orglett.0c01569
Org. Lett. XXXX, XXX, XXX−XXX