Design, synthesis and investigations of a series of energetic salts through the variation of amines and concentration of picrate anions

Article abstract of DOI:10.1039/d0ce00772b

Eight new energetic salts combining N-bases (amines) with picrate ions were synthesized in high yields and characterized by NMR (1H and 13C), IR spectroscopy, elemental analysis, and differential thermal analysis. Single-crystal structural studies were pe

Full text of DOI:10.1039/d0ce00772b

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Design, synthesis and investigations of a series of energetic salts through the
variation of amines and concentration of picrate-anion
Ramling S. Mathpatia, Srinivas Dharavathb, Nikhil Kumara, Vikas D. Ghule a*, Avijit Kumar Paula* and Ram Kumar
Tittala
aDepartment of Chemistry, National Institute of Technology Kurukshetra, Kurukshetra-136119, Haryana, India.
bDepartment of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, Uttar Pradesh, India.
ABSTRACT
Eight new energetic salts combining N-bases (amines) with picrate ion were synthesized in high yields and
characterized by NMR (1H and 13C), IR spectroscopy, elemental, and differential thermal analysis. Single-crystal
structural studies were performed to confirm the structures, packing, and various interactions in the salts. Interestingly,
salts 1 and 7 exist in different polymorphic forms and the effect of solvent on polymorphism was examined (i.e.
solvatomorphism). Thermal stabilities, impact, and friction sensitivities were also determined to understand the
relationship between structures and properties. Salt 3 with hydrazinium cation showed higher performance (d = 1.82
g/cm3; Td = 255.2 ˚C; D = 7.95 km/s; P = 28.2 GPa; IS = >30 J; FS = > 350 N) towards energetic applications.
However, salts 4, 7, and 8 also exhibit good performance parameters, which are marginally better as compared to that
of TNT. The tuning of the physiochemical properties and performances was carried out with the modification of the
cationic-amine molecules and the molar ratio of the reactants.
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INTRODUCTION
The search for new energetic materials (EMs) with economical synthesis, environmentally benign properties, excellent
thermal stability, lower sensitivity and better performance has attracted significant attention worldwide for civilian
and military applications. 1,2 So far, TNT, RDX, PETN and HMX are extensively employed EMs in propellants and
explosive field on account of their ease of synthesis, high density, great stability and good detonation performance.3-4
Until now, vast research has been carried out on energetic salts, nitrogen-rich organic molecules, energetic cocrystals,
metal-organic frameworks and energetic coordination polymers due to their high detonation performance and
remarkable low sensitivity.5-14 In particular, the energetic salts were widely studied as they offer tailorable
physicochemical properties such as crystal apparent density, size of voids, inter or intra-particle porosity, shape and
internal defects with a choice of cations and anions.15-16 Based on their exciting behaviors, the commercial bulk
production of new energetic materials becomes a center of attraction as well as a challenging task for the research
community. So, there is a growing interest in altering the performance of known energetic compounds through the
adaptation of new methodologies, including polymorph purification, amorphous stabilization, particle coating, and
cocrystallization.17 In addition to this, plenty of research has been carried out to investigate the picrate ion-based
various energetic salts, because of its ability to stabilize the salt via the development of strong inter- and intra-
molecular H-bond network, exhibit low vapor pressure, and better density than its atomically similar neutral
derivative.18-23
Picric acid (PA) is known for its sensitive nature towards impact, friction, and reacting with surrounding
metals to give highly sensitive derivatives. In PA, the deprotonation of –OH group forms potential active sites and
enhances its reactivity towards the environment.24 PA is an attractive anionic moiety comprising three powerful
oxidizing groups, which improves the density, oxygen balance (OB), and detonation performance by exploding at
elevated temperature. Substantially, numerous nitrogen-rich aliphatic and aromatic bases with contiguous N–N bonds
are the well-known examples of energetic materials that persuade potential heat of formation and massive energy
release on detonation. The combination of PA with various nitrogen-rich bases can form new salts, which have
remarkable properties for emerging explosives and may consider as a possible replacement of traditional energetic
materials. Although, most of the energetic salts are composed of one or two cations and anions, whereas the
combination of three or four anions with one cation not much investigated.25-28
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Hence, we decided to carry out the study of new PA-based energetic salts combining several nitrogen-bases
namely hexamine, N,N-diethylethanamine, hydrazine hydrate, 1H,1'H-[3,3'-bi-1,2,4-triazole]-5,5'-diamine, and N,N-
bis(2-aminoethyl)ethane-1,2-diamine (see Scheme 1). The role of various amines and the molar-ratio of the PA can
play a major role in tailoring the various energetic properties. Herein we report the systematical investigation for all
the eight energetic salts, including their synthesis strategy, crystal structures, energy content, density, detonation
performance, thermal stability, impact, and friction sensitivity. The crystal structures of six salts (four salts and two
polymorphic forms) have revealed their packing structure, density, and hydrogen bonding interactions among the
respective cations and anions. The energetic properties of the synthesized salts have also been compared with well-
known explosive TNT.
EXPERIMENTAL SECTION
Caution! Working with PA and its salts should always be done carefully. We prepared all of these energetic salts on
the milligram scale, and none of the salt exploded or detonated during this research. Safety shields, safety glasses,
face shields, leather gloves, and protective clothing, such as leather suits and earplugs, must be worn.
Materials and Physical measurements
The reagents were available commercially and were used as purchased without further purification. 1H-NMR
and 13C-NMR spectra were recorded on Bruker AVANCE-III spectrometer operating at 500 MHz with the solvent
resonance as an internal standard (1H-NMR: DMSO-d6 at δ =2.50 and 3.50 ppm; 13C-NMR: DMSO-d6 at δ=44.0 ppm
relative to tetramethyl silane). All 1H and 13C-NMR chemical shifts were reported in ppm relative to tetramethyl silane
(TMS). The IR spectra were obtained as KBr pellets in mid IR region (4000 to 400cm-1) on a Shimadzu FT-IR
spectrometer. Elemental analysis was carried out on a FLASH EA 1112 analyzer. Melting points and decomposition
temperatures (DTA) were determined by using DSC–TGA measurements. The single-crystal X-ray data collection
was carried out at Bruker D8 Quest PHOTON II diffractometer with monochromatic Mo Kα radiation (λ = 0.71073
Å) at 296(2) K operating at 50 kV voltage and 20 mA current by using ω and ϕ scan. The detailed data collection
strategy and crystal structure analysis are given in the supporting information. The impact and friction sensitivity
measurements were carried out with a BAM fall hammer apparatus (BFH-10) and a BAM friction apparatus (FSKM-
10), respectively. Computational calculations were carried out using the B3PW91/6-31G(d,p) level with the Gaussian
09 program package.29 All optimized structures were examined to be the local energy minima on the potential energy
surface with no imaginary frequencies, and the same has been used in the computation of molecular electrostatic
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potential (MESP) using the Multiwfn program.30 The reliable and extensively used computational methods31-35 were
used to calculate the stated energetic properties and summarized in the ESI.
Synthesis of Salt 1: (3r,5r,7r)-1,3,5,7-tetraazaadamantan-1-ium 2,4,6-trinitrophenolate (1)
PA (0.458 g, 2 mmol) was taken in the 20mL methanol and stirred for a few minutes. Then the hexamine
(0.28 g, 2 mmol) was added in the above solution at room temperature. Initially, the suspension was a clear solution
and after a few minutes of stirring, a yellow solid was precipitating out. After stirring for 3h, the precipitate was
obtained by filtration and air-dried to get salt 1 as yellow solid. Yield: 87.4% (0.64 g). 1H-NMR (500 MHz, DMSO-
d6): δ 8.60 (2H), 4.84 (12H). 13C-NMR (126 MHz, DMSO-d6): δ 162.87 (CO), 144.21 (C-NO2), 125.61 (C-NO2),
124.66 (CH), 71.79 (CH2). IR (KBr) υ: 3431, 2916, 2547, 1635, 1568, 1435, 1361, 1159, 1078, 1060, 1008, 979, 906,
867, 819, 709, 657 cm–1. Elemental analysis: (%) calculated for C12H15N7O7 (369.29): C, 39.03; H, 4.09; N, 26.55;
found C, 38.97; H, 4.06; N, 26.50.
Synthesis of Salt 2: Ttriethylammonium 2,4,6-trinitrophenolate (2)
In 20 mL methanolic solution of PA (0.458 g, 2 mmol), N,N-diethylethanamine (0.28 ml, 2 mmol) was added
with the help of micro syringe. Yellow solid was started precipitating out from the reaction mixture after a while. The
precipitate was isolated by filtration after 2 h and air-dried. Yield: 72.8 % (0.48 g). 1H-NMR (500 MHz, DMSO-d6):
δ 8.85 (1H), 8.60 (2H), 3.11(6H), 1.18 (9H). 13C-NMR (126 MHz, DMSO-d6): δ 161.28 (CO), 142.36 (C-NO2), 125.56
(C-NO2), 124.58 (CH), 46.40 (CH2), 8.99 (CH3). IR (KBr) υ: 3086, 2738, 2675, 2490, 1639, 1562, 1496, 1438, 1330,
1273, 1163, 1078, 910, 744, 709 cm–1. Elemental analysis: (%) calculated for C12H18N4O7 (330.12): C, 43.64; H, 5.49;
N, 16.96; found C, 43.62; H, 5.49; N, 16.91.
Synthesis of Salt 3: Hydrazine-1,2-diium 2,4,6-trinitrophenolate (3)
To a solution of PA (0.916 g, 4 mmol) in 20 mL methanol, hydrazine hydrate (0.1 ml, 2 mmol) was added
with the help of microsyringe. After the addition of hydrazine hydrate, the reaction mixture turned into a red color and
slowly converted to yellow color after a few minutes. The resulting solution was stirred for 4 h at room temperature,
and the solvent was evaporated under reduced pressure to yield salt 3 as a yellow solid; yield: 96.6 % (0.94 g). 1H-
NMR (500 MHz, DMSO-d6): δ 8.60 (4H), 7.96 (6H). 13C-NMR (126 MHz, DMSO-d6): δ 161.10 (CO), 142.22 (C-
NO2), 125.62 (C-NO2), 124.99 (CH). IR (KBr) υ: 3103, 1870, 1633, 1556, 1431, 1369, 1265, 1157, 1083, 970, 920,
785, 709, 547 cm–1. Elemental analysis: (%) calculated for C12H10N8O14 (490.25): C, 29.42; H, 2.08; N, 22.84; found
C, 29.38; H, 2.06; N, 22.81.
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Synthesis of Salt 4: 5,5'-diamino-1H,1'H-[3,3'-bi(1,2,4-triazole)]-4,4'-diium 2,4,6-trinitrophenolate (4)
1H,1'H-[3,3'-bi-1,2,4-triazole]-5,5'-diamine (0.167 g, 1 mmol) was added in 20 ml methanol and warmed to
60 °C for obtaining clear solution. PA (0.458 g, 2 mmol) was added in ten portions to this warmed solution. After
complete addition of PA, the reaction mixture was heated at 80 oC for 12 h. The reaction mixture was cooled to room
temperature and solvent was evaporated under reduced pressure to yield salt 4 as a yellow solid. Yield: 86.9 % (0.54
g). 1H-NMR (500 MHz, DMSO-d6): δ 8.60 (4H), 7.02 (4H), 6.25 (2H), 5.51 (6H). 13C-NMR (126 MHz, DMSO-d6):
δ 161.78 (CO), 159.37 (CN), 144.41 (C-NO2), 130.20 (CN), 125.71 (C-NO2), 125.35 (CH). IR (KBr) υ: 3363, 3298,
3086, 1674, 1558, 1483, 1435, 1369, 1338, 1276, 1161, 1082, 937, 746, 709 cm–1. Elemental analysis: (%) calculated
for C16H12N14O14 (624.36): C, 30.78; H, 1.94; N, 31.41; found C, 30.74; H, 1.97; N, 31.32.
Synthesis of Salt 5: mono(2,2'-((2-aminoethyl)azanediyl)bis(ethan-1-aminium)) mono(2,4,6-trinitrophenolate (5)
To a solution of PA (0.458 g, 2 mmol) in 15 mL methanol, N,N-bis(2-aminoethyl)ethane-1,2-diamine (0.3
ml, 2 mmol) was added with the help of microsyringe. The resulting solution was stirred at room temperature for 4 h
and the solvent was evaporated under reduced pressure to collect salt 5 as an orange solid. Yield: 96.8 % (0.73 g).
1H-NMR (500 MHz, DMSO-d6): δ 8.61 (2H), 4.72 (7H), 2.70 (6H), 2.50 (6H). 13C-NMR (126 MHz, DMSO-d6): δ
161.31 (CO), 142.30 (C-NO2), 125.71 (C-NO2), 124.24 (CH), 54.64 (CH2), 38.83 (CH2). IR (KBr) υ 3047, 1631, 1558,
1435, 1369, 1330, 1271, 1163, 1080, 908, 796, 746, 704 cm–1. Elemental analysis: (%) calculated for C12H21N7O7
(375.34): C, 38.40; H, 5.64; N, 26.12; found C, 38.38; H, 5.62; N, 26.09.
Synthesis of Salt 6: 2,2'-((2-aminoethyl)azanediyl)bis(ethan-1-aminium) 2,4,6-trinitrophenolate (6)
Salt 6 was prepared by a similar method as stated above for salt 5. The mixture of PA (0.916 g, 4 mmol),
N,N-bis(2-aminoethyl)ethane-1,2-diamine (0.3 ml, 2 mmol), and methanol (20 mL) was taken to obtain orange solid.
Yield: 93.3 % (1.13 g). 1H-NMR (500 MHz, DMSO-d6): δ 8.61 (4H), 6.31 (8H), 2.89 (6H), 2.59 (6H). 13C-NMR (126
MHz, DMSO-d6): δ 161.34 (CO), 142.28 (C-NO2), 125.70 (C-NO2), 124.92 (CH), 51.10 (CH2), 37.06 (CH2). IR (KBr)
υ 3462, 3049, 1629, 1560, 1483, 1369, 1330, 1269, 1163, 1082, 908, 796, 746, 704 cm–1. Elemental analysis: (%)
calculated for C18H24N10O14 (604.14): C, 35.77; H, 4.00; N, 23.17; found C, 35.74; H, 4.01; N, 23.15.
Synthesis of Salt 7: 2,2',2''-nitrilotris(ethan-1-aminium) 2,4,6-trinitrophenolate (7)
In 20 mL methanolic solution of PA (0.687 g, 3 mmol), N,N-bis(2-aminoethyl)ethane-1,2-diamine (0.15 ml,
1 mmol) was added with the help of micro syringe. Now the PA and the amine ratio for the reaction were increased
to 3:1. The resulting solution was stirred at room temperature for 4 h and the solvent was evaporated under reduced
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pressure to yield salt 7 as a yellow solid. Yield: 91.9 % (0.76 g). 1H-NMR (500 MHz, DMSO-d6): δ 8.61 (6H), 7.54
(9H), 2.92 (6H), 2.51 (6H). 13C-NMR (126 MHz, DMSO-d6): δ 161.28 (CO), 142.04 (C-NO2), 125.56 (C-NO2), 124.77
(CH), 50.57 (CH2), 36.37 (CH2). IR (KBr) υ 3452, 3051, 1629, 1558, 1483, 1436, 1369, 1332, 1269, 1163, 908, 796,
746 cm–1. Elemental analysis: (%) calculated for C24H31N13O23 (869.17): C, 33.15; H, 3.59; N, 20.94; found C, 33.21;
H, 3.46; N, 20.62.
Synthesis of Salt 8: N1,N1-bis(2-ammonioethyl)ethane-1,2-diaminium 2,4,6-trinitrophenolate (8)
The reaction condition for the synthesis of salt 8 was similar as we followed in case of salt 7. Only the amount
of PA (0.916 g, 4 mmol) was increased and the molar ratio of PA and amine was 4:1. The resulting solution was stirred
at room temperature for 4 h and the solvent was evaporated under reduced pressure to collect salt 8 as a yellow solid.
Yield: 94.5 % (1.0 g). 1H-NMR (500 MHz, DMSO-d6): δ 8.61 (8H), 7.54 (9H), 2.61 (6H), 5.51 (6H). 13C-NMR (126
MHz, DMSO-d6): δ 161.25 (CO), 142.25 (C-NO2), 125.73 (C-NO2), 125.02 (CH), 50.92 (CH2), 36.94 (CH2). IR (KBr)
υ 3473, 3080, 1633, 1558, 1435, 1273, 1163, 1082, 914, 746, 711 cm–1. Elemental analysis: (%) calculated for
C30H30N16O28 (1062.65): C, 33.91; H, 2.85; N, 21.09; found C, 33.90; H, 2.85; N, 21.06.
RESULTS AND DISCUSSION
Synthesis and Characterizations
The formation of the energetic picrate salts with different cations is straightforward and synthesized with a
common reaction technique. The reaction of PA with different N-bases (five amine molecules) in methanol at room
temperature except in salt 4 stemmed in the formation of eight picrate salts. Four different amine molecules were
utilized to obtain the salts 1–4, while the same N-base was used to prepare the salts 5–8. Here, PA can act as monoanion
for its single hydroxyl (–OH) and several N-bases are used as variable charged-cations. By increasing the concentration
of PA in the reaction mixture, the degree of protonation of the amine molecules can be enhanced. Hence, PA and the
respective N-bases were added in the preferred molar ratio (cation: anion) i.e., 1:1 ratio for salts 1, 2, and 5; 1:2 ratio
for salts 3, 4, and 6; 1:3 and 1:4 ratio for salts 7 and 8, respectively. All these salts were obtained in high yields, stable
under ambient conditions in the open atmosphere. The structures of the salts 1-8 were supported by IR spectral data,
elemental analysis, 1H- and 13C–NMR spectra (see ESI). The growth of singles crystals also confirmed the structure
of salts 1, 2, 5, and 7. Although we tried to grow the single crystals of each salt with the variation of solvents, we
obtained single crystals for four compounds along with two sets of polymorphs.
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In the 1H-NMR spectra of salts 1–8 (in DMSO-d6), the sharp peak of the two PA protons (=CH) occurs at δ
≈ 8.60 ppm, whereas four signals for carbon atoms of PA are observed at δ =124, 125, 142, and 161 ppm in13C–NMR,
agrees with the previously reported picrate salts.25 The peaks in 1H–, and 13C–NMR spectra of PA-anion are almost
similar for all the salts; instead, the chemical shift values for amine moiety in various salts are different in 1H-NMR
spectra. The –CH2– protons of hexamine in salt 1 resonate at δ = 4.84 ppm, while protons of methylene (CH2) and
methyl (CH3) groups of trimethylamine in salt 2 appears at 3.08 ppm and 1.18 ppm, respectively. A broadened peak
corresponding to –NH protons of hydrazine in salt 3 can be found at δ = 7.96 ppm, whereas 1H,1'H-[3,3'-bi-1,2,4-
triazole]-5,5'-diamine in salt 4 shows the broad resonances at 6.25 ppm and 7.02 ppm for –NH and –NH2 groups. In
salts 5–8, the –CH2– groups of N,N-bis(2-aminoethyl)ethane-1,2-diamine have signals approximately in the range
between 2.49 and 3.17 ppm. 13C-NMR spectrum of salt 1 shows the assignable peak at δ = 71.7 ppm for hexamine.
The resonances for salt 2 are detected at chemical shifts of 46.4 and 8.99 ppm that represent the carbon atom of the
trimethylamine. The resonances at 130.2 and 144.4 ppm in the 13C-NMR spectrum can be attributed to the carbon
atom of the triazole rings in salt 4. The 13C–NMR spectra of the salts 5–8 show a resonance at approximately 36 and
50 ppm corresponding to the carbon atoms of the two CH2 groups in N,N-bis(2-aminoethyl)ethane-1,2-diamine.
Hence, all the structures of the salts are correct as we desired to synthesize. Most of the IR vibrational modes of the
synthesized salts have been described based on previous studies of PA salts.25 All the salts are formed by the proton
transfer from PA to N-base. Hence, IR spectra dominated by a very broad band ranging from 3100 to 3400 cm-1 due
to the N–H‧‧‧O hydrogen bonds and stretching vibrations of –NH, –NH2, and –NH3 groups. In all the salts, the bands
at 3040–3080 cm-1 show aromatic C–H stretching vibrations in the picrate ring, while C–H rocking vibrations can be
observed in the range of 1000 to 1300 cm-1. The bands at 1620 to 1650 cm-1 can be assigned to the C–O stretching
vibrations in PA. The C–C bonds in the aromatic ring show stretching vibrations within the range of 1500–1600 cm-
1. The symmetric stretching in –NO2 group displays characteristic vibration at 1330–1340 cm-1, while the anti-
symmetric stretching are observed near to 1610 cm-1. The C–N stretching vibrations are observed in the region of
1090–1130 cm-1.
Crystal structures and polymorphism
The structures of salts 1, 2, 5, and 7 were verified by using single-crystal X-ray diffraction, and their structural
parameters and refinement details are listed in Table 1. The crystal structures were deposited in the CSD database and
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can be obtained with the CCDC nos. 1972972 (1a), 1972973 (1b), 1972974 (2), 1972975 (5), 1972976 (7a) and
1972977 (7b). Interestingly, the salts 1 and 7 lead to the formation of two different polymorphs in the process of
crystallization in various solvents. The single-crystals of salt 1a (Form I) and 1b (Form II) were obtained at room
temperature by slow evaporation of acetonitrile and ethanol: acetonitrile (1:1), respectively. The single-crystal X-ray
diffraction data revealed that 1a and 1b crystallized in the monoclinic crystal system with P21 and P21/c space groups,
respectively. The resultant structures 1a and 1b are the same with 1:1 combination of PA and amine, whereas other
crystal parameters such as cell lengths, volume, and density parameters are different. Salt 1a possesses two molecules
per unit cell with a density of 1.59 g/cm3, whereas 1b has four molecules per unit cell with a density of 1.63 g/cm3.
The asymmetric unit contains one unit of picrate anion and mono-protonated hexamine (1:1). The molecular structures
of 1a and 1b are shown in Figures 1 and 2, while the packing diagram along the b-axis for both the compounds is the
same and displayed in Figure 3. From the packing diagram of crystal structure, one can easily observe the strong H–
bonding interactions between the oxygen atom of picric acid and nitrogen atoms of hexamine, as presented in Figures
S3 and S4. So, the various kinds of intra- and inter-molecular N–H···O and C–H···O interactions are observed as
listed in Table S4 (see ESI).
The single crystal of the salt 2 was obtained from slow evaporation of acetone at room temperature and it
crystallizes in the orthorhombic cell with Pca21 space group comprising four molecules per unit cell with a density of
1.38 g/cm3. The asymmetric unit contains one protonated N,N-diethylethanamine moiety and one anionic picrate
moiety (Figure 4 ). The closed packing of the structure shows that two picrate anions are placed inside a channel
developed by six amine units, as shown in Figure 5. Extensive N–H···O and C–H···O hydrogen bonding interactions
support the overall three-dimensional packing of the salt 2 (see ESI, Table S5 and Figure S5). Suitable single-crystals
of 5 were obtained by recrystallization with the methanol as solvent. Salt 5 also forms orthorhombic cell with the
space group P212121. The unit cell comprises of 1:1 pair of cationic N,N-bis(2-aminoethyl)ethane-1,2-diamine and
anionic picrate moiety (Figure 6) and the calculated density is 1.42 g/cm3. In the crystal structure, it is observed that
the two terminal amino groups remained as -NH2 while the third one is forming –NH3 group. The observed packing
diagram (Figure 7) is closely similar to the packing diagram of 2. We can observe various N–H···O, N–H···N and C–
H···O hydrogen bonding interactions in the three-dimensional packing structure of 5 (see ESI, Table S6 and Figure
S6).
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Single crystals of salt 7a (Form I of salt 7) and 7b (form II of salt 7) were obtained by slow evaporation of
methanol and ethanol: acetonitrile (1:1) solution. Salt 7a crystallized in the triclinic cell with the space group P-1,
whereas 7b forms monoclinic cell with the space group P21/n. The asymmetric unit of 7a contains three picrate anion,
one tri-protonated N,N-bis(2-aminoethyl)ethane-1,2-diamine moiety and one methanol molecule (Figure 8). Here, all
the three-terminal amine groups of aliphatic N-base are protonated and support for the crystallization forming 1:3 pair
of amine and PA in the salt 7. The crystal 7b possesses three units of picrate anion, one tri-protonated amine and two
water molecules in the asymmetric unit (Figure 9). Thus, both the structures can be considered as solvatomorphs as
the structures are dissimilar due to the presence of solvents in salts. Recently, a similar observation for solvate
formation is also communicated with adamantylamine.36 The calculated densities of both the solvatomorphs are almost
identical to the values of 1.62 g/cm3 for 7a and 1.65 g/cm3 for 7b. But the overall packing diagrams look different for
7a and 7b, as illustrated in Figures 10 and 11, respectively. In both the structures, the N–H···O, O–H···O and C–H···O
H–bonding interactions are observed in greater extent compared to the other salts (see ESI, Tables S8-S9 and Figures
S7–S8). Solvent molecules and tri–protonated amines help to exhibit the highest number of hydrogen bonding
interactions in 7a and 7b. Hirshfield surfaces and related 2D fingerprint plots of the salts 1, 2, 5, and 7 were analyzed
to understand the nature and type of intermolecular interactions in the crystal (see ESI). The percentage contribution
of various intermolecular interactions due to the close contacts experienced by the PA and N-base molecules in the
crystal are summarized in the ESI.
Energetic properties and sensitivity studies
The heat of formation (HOF) is considered as one of the essential parameters in the design of energetic salts.
The HOFs of all ions were predicted using quantum chemical calculations, while HOFs of the salts were calculated
by using Born–Haber energy cycles and Jenkins Equations (see ESI).37,38 The physiochemical properties of salts 1–8
are listed in Table 2. All the salts show negative HOFs (in the range of -93 to -1304 kJ/mol) and tend to decrease with
increasing the carbon content in the synthesized salts. The HOFs of the individual cations and picrate anion (see ESI,
Table S2) reveal that the cations positively influence the energy content while anion has the reverse effect. We observe
that with an increase in the molar ratio of the anion in 8 (4:1) compared to the salt 5 (1:1), HOF significantly decreases
due to the negative HOF value of the picrate ion (-458 kJ/mol).
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Oxygen balance (OB) specifies the oxygen content in the molecular structure and degree to which an
explosive can be oxidized. Even though the present salts possess negative OB values, but the salts 3, 4, and 8 show
better OB than TNT (-74%). Higher % of C and H atoms in the present salts are mainly responsible for the oxygen-
deficient nature of these salts. The calculated densities of salts 1–8 lie in the range of 1.41–1.82 g/cm3, while salts 3,
4, 7, and 8 have higher densities than TNT (1.65 g/cm3). The higher densities are exhibited by salt 3 (1.82 g/cm3) and
4 (1.80 g/cm3) among all the salts confirming the presence of compact and nitrogen-rich cations helps to gain better
densities (Figure 12). In salts 5–8, the addition of picrate anion increases the density by 0.04-0.12 g/cm3. The values
of HOFs and calculated densities of the salts encourage us to evaluate the other energetic properties. The molecular
formulas were used to obtain the detonation velocities and pressures of salts 1 (6.44 km/s, 17.12 GPa), 2 (5.67 km/s,
12.15 GPa), 3 (7.95 km/s, 28.20 GPa), 4 (7.20 km/s, 23.0 GPa), 5 (6.21 km/s, 15.29 GPa), 6 (6.65 km/s, 18.43 GPa),
7 (7.09 km/s, 21.46 GPa), and 8 (7.14 km/s, 22.07 GPa), with the aid of the Kamlet-Jacobs equations.39 Among the
synthesized salts, 3 and 4 show the highest detonation properties owing to their high densities. The salts 3, 4, 7, and 8
have greater predicted performance values than TNT (6.88 km/s, 19.5 GPa).40 A comparison of the OB, densities, and
detonation properties are presented in Figure 12 for all eight salts with TNT.
Here, all the synthesized salts were characterized for their sensitivities toward external stimuli like heat,
impact, and friction. All the salts can be classified as insensitive as they possess sensitivities for impact and friction
higher than 35 J and 350 N, respectively and surpass the requisite criteria to mechanical stimuli (IS≥7.5 J, FS≥120
N).41 The thermal stabilities of all picrate salts were explored by TG-DTA measurements with a heating rate of 5 ˚C
min−1 in a nitrogen atmosphere. TG-DTA curves (see ESI) support the existence of stable picrate salts as they
decomposed between 231 ̊C (7) to 267 ̊C (3), which fall in the range of RDX (210 ̊C) and TNT (295 ̊
C).41,42 The higher
thermal stability and greater insensitivity may be attributed to the strong H-bonding interactions between cations and
anions in the salts.43
The present four salts, 5–8, possess unusual structural variations with single amine [N,N-bis(2-
aminoethyl)ethane-1,2-diamine] molecule as we have altered the molar ratio of the reactants. The degree of
protonation is slowly enhanced with the increase of PA concentration. Interestingly, the energetic properties like
HOFs, OB and detonation velocities are also increased gradually from the salts 5 to 8. It is worthy to compare our
present salts with the earlier reported PA-based energetic salts,44-56 which can assure the present synthesized salts have
their novel structure-performance relationship with the exceptional polymorphic nature. Sabaté et al.46,47 synthesized
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PA salts with 1-cyanomethyl-1,1-dimethylhydrazinium and 1-aminomethylidene-1,4,4-trimethyl-2-tetrazenium
cations, which show thermal decomposition at 194 and 225 C, respectively and resulted in relatively lower detonation
̊
performance (D= 6.90-7.08 km/s, P=15.9-18.0 GPa). Interestingly, PA salt with 1-amino-1,2,3-triazole decomposed
C and resulted in good detonation properties (D= 7.74 km/s, P=25.9 GPa).48 Wu et al.49,50 reported the
at 148.3
̊
combination of 3,4-diamino-1,2,4-triazole (DATr) and 3-hydrazino-4-amino-1,2,4-triazole (HATr) with PA to obtain
mono- and di-valent salts. DATr-PA salt possesses high thermal stability (Td = 287.6 C) and moderate detonation
properties (D= 7.49 km/s, P=23.8 GPa), while HATr-PA salt decomposes at 185 C acquiring better detonation
̊
̊
performance (D= 7.87 km/s, P=27.4 GPa). The combination of nitrogen-rich bases with PA leads to the formation of
dense salts with moderate thermal stability and better detonation performance.48-50 Recently, two salts of PA are also
found with diaminotoluene derivatives which are 80% less impact sensitive than PA.57 Few tetrazolium, triazole, and
bis-triazolium based PA salts are studied with their crystal packing and energetic properties, but the inclusion of
additional amino groups in bis-triazolium ligand related to our present salt 4 is not studied so far.21,24 The multiligand
coordination compounds with transition metals can also form environmental friendly energetic compounds with PA.19
The supramolecular complexes of PA with N-heterocyclic bases suggested that noncovalent interaction rises with an
increase in the number of nitrogen atoms in the heterocyclic base and play the vital role in packing and controlling the
structure of complexes.58 The coordination compounds based on PA and methyl carbazate revealed moderate thermo-
kinetics and catalytic performance.59 Hence, our metal-free PA salts with various organic amines are the new examples
of insensitive energetic materials.
CONCLUSIONS
In this study, eight energetic picrate salts with the different N-base cations have been synthesized and fully
characterized by NMR, IR, elemental analysis, TG-DTA, and single-crystal X-ray structure analysis. The crystal
structure analysis of the four salts revealed the three-dimensional packing and various H–bonding interactions in the
energetic salts. The isolations of polymorphs in salt 1 and solvatomorphs in salt 7 are noteworthy. The variation of the
cationic amines and the molar ratio of anion/cation can produce versatile crystal packing and energetic behavior in the
products. The detonation velocities and pressures of the synthesized salts were ranging from 5.67 to 7.95 km/s, and
12.15 to 28.20 GPa, respectively. Among them, salts 3 and 4 exhibit superior detonation properties than TNT.
Additionally, all the materials can be classified as thermally stable (Td > 200 ˚C) and less sensitive to impact (> 30 J)
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and friction (> 350 N) stimuli. The present salts may have possible applications as energetic materials as they are safe
to handle, easy to synthesize, and moderate performance characteristics. Our design strategy with various amines into
thermally stable energetic salts can be further applicable for synthesizing new energetic materials with the variation
of concentration and modification of amine moieties.
ASSOCIATED CONTENT
Supporting Information summary
The computational details, calculated energetic properties data, X-ray crystallography data, Hirshfield surface
analysis, NMR and TGA data, and checkCIF report are summarized in the Supporting Information.
ACKNOWLEDGMENT
RSM thank Armament Research Board, Defence R&D Organization, DRDO for research fellowship (No.
ARMREB/CDSW/2019/211). AKP and NK gratefully acknowledge to DST (INSPIRE Award No. IFA14-CH-144)
and UGC-DAE-CSR for financial support.
Corresponding Authors:
*E-mail: gvd@nitkkr.ac.in
*E-mail: apaul@nitkkr.ac.in
Conflict of Interest
The authors declare no conflict of interest.
References
1. A. K. Sikder and N. Sikder, J. Hazard. Mater., 2004, 112, 1–15.
2. Y. Shang, R. K. Huang, S. L. Chen, C. T. He, Z. H. Yu, Z. M. Ye, W. X. Zhang and X. M. Chen, Cryst. Growth
Des., 2020, 20, 1891–1897.
3. D. M. Badgujar, M. B. Talawar, S. N. Asthana and P. P. Mahulikar, J. Hazard. Mater., 2008, 151, 289–305.
4. M. Guillevic, V. Pichot, J. Cooper, G. Coquerel, L. Borne and D. Spitze, Cryst. Growth Des., 2020, 20, 130–138.
5. Y. Tang, L. A. Mitchell, G. H. Imler, D. A. Parrish and J. M. Shreeve, Angew. Chem. Int. Ed., 2017, 56, 5894–
5898.
6. G. Zhao, D. Kumar, L. Hu and J. M. Shreeve, ACS Applied Energy Materials, 2019, 2, 6919–6923.
7. Y. Wang, Y. Liu, S. Song, Z. Yang, X. Qi, K. Wang, Y. Liu, Q. Zhang and Y. Tian, Nat. Commun., 2018, 9,
2444.
12

Page 13 of 26
CrystEngComm
View Article Online
DOI: 10.1039/D0CE00772B
8. Y. Qu and S. P. Babailov, J. Mater. Chem. A, 2018, 6, 1915-1940.
9. C. Yang, C. Zhang, Z. Zheng, C. Jiang, J. Luo, Y. Du, B. Hu, C. Sun and K. O. Christe, J. Am. Chem. Soc., 2018,
140, 16488-16494.
10. Y. Xu, Q. Wang, C. Shen, Q. Lin, P. Wang and M. Lu, Nature, 2017, 549, 78–81.
11. C. Zhang, C. Sun, B. Hu, C. Yu and M. Lu, Science, 2017, 355, 374–376.
12. R. V. Kent, R. A. Wiscons, P. Sharon, D. Grinstein, A. Frimer and A. J. Matzger, Cryst. Growth Des., 2017, 18,
219–224.
13. K. B. Landenberger, O. Bolton and A. J. Matzger, J. Am. Chem. Soc., 2015, 137, 5074–5079.
14. X. Ma, C. Cai, W. Sun, W. M. Song, Y. Ma, X. Liu, G. Xie, S. Chen and S. L. Gao, ACS Appl. Mater. Interfaces,
2019, 11, 9233–9238.
15. J. G. Xu, C. Sun, M. J. Zhang, B. W. Liu, X. Z. Li, J. Lu, S. H. Wang, F. K. Zheng and G. C. Guo, Chem. Mater.,
2017, 29, 9725–9733.
16. H. Gao and J. M. Shreeve, Chem. Rev., 2011, 111, 7377–7436.
17. Q. Zhang and J. M. Shreeve, Chem. Rev., 2014, 114, 10527–10574.
18. N. S. Fondren, Z. T. Fondren, D. K. Unruh, A. Maiti, A. F. Cozzolino, Y. J. Lee, L. J. Hope-Weeks and B. L.
Weeks, Cryst. Growth Des., 2020, 20, 116–129.
19. B. D. Wu, J. G. Zhang, T. L. Zhang, L. Yang and Z. N. Zhou, Eur. J. Inorg. Chem., 2012, 2012, 1261–1268.
20. C. M. Jin, C. Ye, C. Piekarski, B. Twamley and J. M. Shreeve, Eur. J. Inorg. Chem., 2005, 2005, 3760–3767.
21. Z. Mi, Y. G. Bi, Y. A. Feng and T. Zhang, Z. Anorg. Allg. Chem., 2016, 642, 317–322.
22. C. M. Sabaté, H. Delalu and E. Jeanneau, Chem. Asian J., 2012, 7, 2080–2089.
23. T. M. Klapötke, F. Mieskes, J. Stierstorfer and M. Weyrauther, Propell. Explos. Pyrotech., 2016, 41, 217–222.
24. T. M. Klapötke and C. M. Sabaté, Eur. J. Inorg. Chem., 2008, 2008, 5350–5366.
25. D. Srinivas, V. D. Ghule and K. Muralidharan, New J. Chem., 2014, 38, 3699–3707.
26. D. Srinivas, V. D. Ghule, K. Muralidharan and H. D. B. Jenkins, Chem. Asian J., 2013, 8, 1023–1028.
27. T. G. Witkowski, P. Richardson, B. Gabidullin, A. Hu and M. Murugesu, ChemPlusChem, 2018, 83, 984–990.
28. P. Peng, B. Hu, F. Lu, Y. Du, C. Zhao, H. Su, P. Zhang, S. H. Li and S. P. Pang, New J. Chem., 2019, 43, 19069–
19074.
13

CrystEngComm
Page 14 of 26
View Article Online
DOI: 10.1039/D0CE00772B
29. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B.
Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F.
Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N.
Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery Jr, J. E. Peralta, F. Ogliaro, M. Bearpark,
J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W.
Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman and D. J. Fox, Gaussian 09, Revision E.01,
Gaussian, Inc., Wallingford, CT, 2013.
30. T. Lu and F. Chen, J. Comput. Chem., 2012, 33, 580–592.
31. V. D. Ghule, J. Phys. Chem. A, 2012, 116, 9391–9397.
32. V. D. Ghule, J. Phys. Chem. C, 2013, 117, 16840−16849.
33. V. D. Ghule, S. Deswal, A. Devi and T. Ram Kumar, Ind. Eng. Chem. Res., 2016, 55, 875–881.
34. A. Devi, S. Dharavath and V. D. Ghule, ChemistrySelect, 2018, 3, 4501–4504.
35. V. D. Ghule, A. Nirwan and A. Devi, J. Mol. Model., 2018, 24, 50.
36. K. Smorkrovic and V. Stilinovic, CrystEngComm., 2020, 22, 1822–1833.
37. L. Glasser and H. D. B. Jenkins, J. Am. Chem. Soc., 2000, 122, 632–638.
38. H. D. B. Jenkins, D. Tudela, and L. Glasser, Inorg. Chem., 2002, 41, 2364–2367.
39. M. J. Kamlet and S. J. J. Chem. Phys., 1968, 48, 23−36.
40. Y. Zhang, D. A. Parrish and J. M. Shreeve, Chem. Eur. J., 2012, 18,987–994.
41. T. M. Klapötke, P. C. Schmid, S. Schnell and J. Stierstorfer, Chem. Eur. J., 2015, 21, 9219–9228.
42. H. Huang, Z. Zhou, J. Song, L. Liang, K. Wang, D. Cao, W. Sun, X. Dong and M. Xue, Chem. Eur. J., 2011, 17,
13593–13602.
43. W. J. Geng, Q. Ma, Y. Chen, W. Yang, Y. F. Jia, J. S. Li, Z. Q. Zhang, G. J. Fan and S. M. Wang, Cryst. Growth
Des., 2020, 20, 2106–2114.
44. P. Y. Chen, L. Zhang, S. G. Zhu, and G. B. Cheng, Crystals 2015, 5, 346–354.
45. L. Liu, C. He, H. Wanga, Z. Li, S. Chang, J. Sun, X. Zhang and S. Zhang, J. Mol. Str. 2011, 989, 136–143.
14

Page 15 of 26
CrystEngComm
View Article Online
DOI: 10.1039/D0CE00772B
46. C. M. Sabaté, H. Delalu and E. Jeanneau, Chem. Asian J. 2012, 7, 1085 – 1095.
47. C. M. Sabaté and H. Delalu, Cent. Eur. J. Energ. Mater. 2014, 11, 515–537.
48. Z. B. Zhang and J. G. Zhang, J. Mol. Str. 2018, 1158, 88–95.
49. J. T. Wu, J. G. Zhang, X. Yin, Z. Y. Cheng and C. X. Xu, New J. Chem. 2015, 39, 5265–5271.
50. J. T. Wu, J. G. Zhang, X. Yin and L. Wu, New J. Chem. 2016, 40, 5414–5419.
51. W. Liu, W. L. Liu and S. P. Pang, RSC Adv. 2017, 7, 3617–3627.
52. N. Szimhardt, M. H. H. Wurzenberger, L. Zeisel, M. S. Gruhne, M. Lommel, T. M. Klapötke and J. Stierstorfer,
Chem. Eur. J. 2019, 25, 1963–1974.
53. X. G. Du, J. Q. Zhou, M. Zhong, X. M. Zhu, F. Yun and C. M. Jin, J. Heterocyclic Chem. 2019, 56, 839–844.
54. T. Li, D. Li, J. Li, G. Zhang, W. Zhang and Z. Gao, Z. Anorg. Allg. Chem. 2016, 642, 1095–1103.
55. N. Szimhardt, M. H. H. Wurzenberger, A. Beringer, L. J. Daumann and J Stierstorfer, J. Mater. Chem. A 2017,
5, 23753–23765.
56. M. H. H. Wurzenberger, B. R. G. Bissinger, M. Lommel, M. S. Gruhne, N. Szimhardt and J. Stierstorfer, New J.
Chem. 2019, 43, 18193–18202
57. N. Şen, H. Nazir, N. Atçeken, K. S. Hope, N. Acar and O. Atakol, J. Mol. Str. 2020, 1205,127580–127592.
58. N. Goel and U. P. Singh, J. Phys. Chem. A 2013, 117, 10428−10437.
59. X. Yang, Y. Wang, Z. Li, J. Du, L. Wang and T. Zhang, New J. Chem. 2019, 43, 14159–14165.
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Table 1. Crystallographic data and structure refinement parameters for salts 1, 2, 5 and 7.
Compound
Salt-1a
Salt-1b
Salt-2
Salt-5
Salt-7a
Salt-7b
Empirical
formula
C12 H15 N7
O7
C12 H15 N7 O7 C24 H36 N8
O14
C12 H21 N7 O7
C25 H31 N13
O22
C24 H31 N13
O23
Formula
weight
369.31
369.31
660.61
375.36
865.63
869.62
Crystal
system
Space
group
a (Å)
Monoclinic
Monoclinic
Orthorhombic Orthorhombic
Triclinic
Monoclinic
P21
P21/c
Pca21
P21 21 21
P -1
P21/n
9.9819(6)
7.1284(4)
11.8414(7)
90.00
12.462(2)
6.7318(11)
18.747(3)
90.00
21.997(8)
6.972(2)
20.770(7)
90.00
6.9949(9)
12.5916(19)
19.969(3)
90.00
8.4362(9)
12.5183(14)
18.3788(19)
72.109(3)
83.298(3)
72.280(3)
1758.9(3)
2
14.1276(6)
10.6978(5)
24.1392(11)
90.00
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
114.070(2)
90.00
107.065(5)
90.00
90.00
90.00
106.656(10)
90.00
90.00
90.00
769.31(8)
2
1503.5(4)
4
3185.2(18)
4
1758.9(4)
4
3495.2(3)
4
D
1.594
1.632
1.378
1.418
1.634
1.653
(calc/gcm-3)
μ (mm-1)
0.133
0.136
0.114
0.117
0.145
0.149
0.71073
0.71073
0.71073
0.71073
0.71073
0.71073
 (Mo
Kα/Å)
θ min (°)
1.88
1.71
1.85
2.60
3.32
1.51
θ max (°)
25.00
7662
25.00
14928
24.49
28692
23.99
10407
25.00
30065
25.00
35849
Total data
collected
Unique data 2705
2637
5275
2646
6066
6153
0.0356
R1 =
Rint
0.0379
0.0545
0.0606
0.0792
0.0399
R indexes [ R1 = 0.0522;
R1 = 0.0519; R1 = 0.0770;
R1 = 0.0686;
R1 = 0.0592;
wR2 =
0.1176
wR2 = 0.1330 wR2 = 0.1751 wR2 = 0.1592
wR2 = 0.1603 0.0495; wR2
= 0.1475
I > 2 (I)]
R indexes
(all data)
R1 = 0.0637;
wR2 =
0.1263
R1 = 0.0979; R1 = 0.1399; R1 = 0.1804;
wR2 = 0.1764 wR2 = 0.2159 wR2 = 0.1967
R1 = 0.0888;
wR2 = 0.1774
R1 =
0.0685; wR2
= 0.1682
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Table 2. Physiochemical properties of salts 1-8 and TNT.
[d]
[i]
OB[a]
(%)
Density[b]
(g/cm3)
HOFsalt
D[e]
(km/s)
6.44
5.67
7.95
7.20
6.21
6.65
7.09
7.14
P[f]
IS[g]
(J)
FS[h]
Td
Salt
(kJ/mol)
-93
(GPa)
17.12
12.15
28.20
23.0
(N)
(˚C)
1
2
3
4
5
6
7
8
-106.2
-126.1
-49.0
-61.5
-117.3
-90.1
-77.8
-70.8
1.60 (1.59)[c]
1.41 (1.38)[c]
1.82
>30
>30
>30
>30
>30
>30
>30
>30
15
>350
>350
>350
>350
>350
>350
>350
>350
267.1
261.8
255.2
238.1
234.2
237.6
231.8
242.2
-453
-257
1.80
-439
1.51 (1.42)[c]
1.63
-263
15.29
18.43
21.46
22.07
-758
1.69 (1.65)[c]
1.73
-727
-1304
1.65
-67
6.88
19.5
353
295.0
TNT
-74.0
(Ref.
42)
(Ref. 42)
(Ref. 42)
(Ref. 42)
(Ref. 42)
(Ref. 42) (Ref. 42)
[a] Oxygen balance. [b] Density calculated using molecular volume approach [Ref. 35], [c] Density obtained from the
X-ray determinations. [d] Heat of formation of salt. [e] Detonation velocity. [f] Detonation pressure. [g] Impact
sensitivity according to BAM method. [h] Friction sensitivity according to BAM method. [i] Decomposition
temperature.
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Scheme 1. Structures of anion and cations selected for the formation of eight energetic salts.
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Fig. 1. Asymmetric unit of 1a with 50% probability displacement ellipsoids of the non-hydrogen atoms.
Fig. 2. Asymmetric unit of 1b with 50% probability displacement ellipsoids of the non-hydrogen atoms.
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Fig. 3. Packing diagram of salt 1a along the b-axis.
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Fig. 4. Asymmetric unit of 2 with 50% probability displacement ellipsoids of the non-hydrogen atoms.
Fig. 5. Packing diagram along the a-axis for crystal 2.
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Fig. 6. Asymmetric unit of 5 with 50% probability displacement ellipsoids of the non-hydrogen atoms.
Fig. 7. Packing diagram of the salt 5 along the a-axis.
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Fig. 8. Asymmetric unit of 7a with 50% probability displacement ellipsoids of the non-hydrogen atoms.
Fig. 9. Asymmetric unit of 7b with 50% probability displacement ellipsoids of the non-hydrogen atoms.
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Fig. 10. Packing diagram of 7a along the a-axis.
Fig. 11. Packing diagram of 7b along the a-axis.
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Fig. 12. Comparisons of calculated values of OB, density, and detonation parameters of 7 salts with TNT.
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Graphical abstract
Eight energetic salts combining N–bases with picrate ion were synthesized in high yields. Salts 1 and 7 exist in
different polymorphic forms and the effect of solvent on polymorphism was examined. The structures and energetic
properties were regulated by the variation of N–base molecules and the concentration of the picric acid in the reaction
mixture.
26