Chelates with π-stacking and hydrogen-bonding interactions as safer and structurally reinforced energetic materials

Article abstract of DOI:10.1016/j.ica.2017.06.071

Three chelating energetic materials (CEM), [Co(SCZ)₂(H₂O)₂](TNR)(H₂O)₂ (1), [Ni(SCZ)₂(H₂O)₂](TNR)(H₂O)₂ (2) and [Zn(SCZ)₂(H₂

Full text of DOI:10.1016/j.ica.2017.06.071

Inorganica Chimica Acta 466 (2017) 405–409
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Chelates with
p-stacking and hydrogen-bonding interactions as safer
and structurally reinforced energetic materials
⇑
⇑
Li Yang , Hongrun Li, Guoying Zhang, Jianchao Liu, Wenchao Tong
State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three chelating energetic materials (CEM), [Co(SCZ)2(H2O)2](TNR)(H2O)2 (1), [Ni(SCZ)2(H2O)2](TNR)
(H2O)2 (2) and [Zn(SCZ)2(H2O)2](TNR)(H2O)2 (3, SCZ = semicarbazide, H2TNR = styphnic acid), were syn-
thesized and characterized by elemental analysis, FTIR spectroscopy and single-crystal X-ray diffraction
analysis. Single-crystal X-ray diffraction analysis revealed that 1 mainly exhibits swathe construction,
whereas 2 and 3 manifest grating structure. Thermal decomposition behaviors of 1–3 were studied by
differential scanning calorimetry (DSC). The critical temperature of thermal explosion, the entropy of
Received 17 March 2017
Received in revised form 31 May 2017
Accepted 28 June 2017
Available online 29 June 2017
Keywords:
Energetic
Chelate
Semicarbazide
Crystal
activation (D D D
S–), the enthalpy of activation ( H–), and the free energy of activation ( G–) were also cal-
culated. Sensitivity tests revealed that 1–3 are insensitive to mechanical stimuli, and that the grating
structure (2 and 3) shows better shock resistance and flame retardant property than the swathe construc-
tion (1) at the molecular level.
Ó 2017 Elsevier B.V. All rights reserved.
Property
1. Introduction
(NO3ꢀ, N(NO2)2ꢀ, ClO4ꢀ, N3ꢀ, and TNR2ꢀ) in the coordination com-
plexes. Inter- and intramolecular interactions in the molecule give
Nowadays, insensitive high-energy-density materials (HEDMs)
remain to be the overriding theme in the field of energetic materi-
als [1–7]. The development of insensitive HEDMs continues to
focus on coordination energetic materials [8–14]. Linear ligands
usually can be obtained commercially with inexpensive price, so
research on linear ligands start early and many achievements have
turned into applications. For instance, zinc tri(carbohydrazide) per-
chlorate, cadmium tri(carbohydrazide) perchlorate and nickel
hydrazine nitrate are all widely used as lead-free primary explo-
sives in industrial detonators [15–17]. Among the linear ligands,
azotic and oxygenic ligand carbohydrazide, 3-amino-1-nitroguani-
dine and SCZ have attracted researcher’s attention, because they
can coordinate to central metal ion to form five-member rings
and the chelate effect can enhance their structural stability
definitely.
rise to compact and stable packing, which are conducive to increas-
ing the density of these energetic materials. In addition, -stacking
in benzene or nitrogen heterocyclic compounds can also enhance
the structural reinforcement and will definitely strengthen the
thermal stability of the complex.
In pursuit of safer and structurally reinforced energetic mate-
rial, we report herein the syntheses, structures and properties of
three CEMs with transition metal as the central ion, SCZ as the
ligand, and TNR2ꢀ as the outside counterion.
p
2. Experimental section
2.1. Materials and physical techniques
All reagents (analytic grade) were obtained from commercial
sources and used without further purification. Elemental analyses
were performed with a Flash EA 1112 full automatic trace element
analyzer. The FT-IR spectra were recorded with a Bruker Equinox
55 infrared spectrometer (KBr pellets) in the range of 4000–
400 cmꢀ1with a resolution of 4 cmꢀ1. DSC measurement were per-
formed with a Pyris-1 differential scanning calorimeter in a dry
nitrogen atmosphere with flowing rate of 20 mLꢁminꢀ1. The condi-
tions for the thermal analyses were as follow: the crystal sample
was powdered and sealed in the aluminum pans with a linear heat-
ing rate of 10 °Cꢁminꢀ1from 50 °C to 500 °C.
SCZ based coordination chelates were reported extensively [18–
21], but its energetic characteristics didn’t arouse attention until
recently [22,23]. Hydrogen bonding, as an interesting interaction
between hydrogen and other atoms, has been found as an effective
methodology for the construction of HEDMs [24–26]. The amino
groups in SCZ can form vast hydrogen bond with counterions
⇑
Corresponding authors.
E-mail addresses: yanglibit@bit.edu.cn (L. Yang), 6120160064@bit.edu.cn (W.
Tong).
http://dx.doi.org/10.1016/j.ica.2017.06.071
0020-1693/Ó 2017 Elsevier B.V. All rights reserved.

406
L. Yang et al. / Inorganica Chimica Acta 466 (2017) 405–409
2.2. Synthesis of SCZ (aq.)
hydrogen atoms were obtained from the difference Fourier map
and subjected to anisotropic refinement by full-matrix least
squares on F2. Detailed information concerning crystallographic
data collection and structure refinement are summarized in
Table 1.
Semicarbazide hydrochloride (30 mmol, 3.33 g) was dissolved
in distilled water. Using solid Na2CO3 adjusted the solution pH
value to 6–7.
2.3. Synthesis of [Co(SCZ)2(H2O)2](TNR)(H2O)2(1)
3. Results and discussion
Cobalt carbonate (10 mmol, 1.19 g) was added to a solution of
2,4,6-trinitroresorcinol (10 mmol, 2.45 g) in deionized water
(40 mL), and the mixture was stirred at 60–65 °C until a clear solu-
tion resulted. A solution containing SCZ (30 mmol) in deionized
water (30 mL) was added and the mixture was kept at 60–65 °C
for 15 min. Then the solution was cooled to room temperature.
The precipitate was collected by filtration, washed with ethanol,
and dried under vacuum in an explosion-proof water-bath dryer.
Yield: 71% (3.72 g). Orange prism single crystals suitable for X-
ray measurements were obtained by recrystallization of the prod-
ucts from deionized water at room temperature over half month.
Anal. Calcd. (%) for C8H19CoN9O14: C, 18.33; H, 3.65; N, 24.07.
Found (%): C, 18.26; H, 3.59; N, 23.99. IR (KBr): 3434, 3375, 3320,
1658, 1578, 1491, 1437, 1345, 1307, 1236, 1182, 1088, 1051,
3.1. Structure description
The molecular structures of 1–3 are illustrated in Figs. 1–3. In
all of these compounds, SCZ exhibits typical bidentate coordina-
tion, which is coordinated with central ion via the carbonyl oxygen
and the terminal nitrogen of hydrazine. Compounds 1–3 all contain
one central metal cation, one TNR2ꢀ, two SCZ groups and four
water molecules. These TNR2- based compounds all contain two
formula units in the unit cell. Compound 1 is structurally more
symmetrical, which crystallized in the monoclinic space group
Cm, while the other two are crystallizing isotypically with a tri-
clinic unit cell in the space group P-1. The central ions are hexaco-
ordinated with two SCZ and two water molecules, composing an
octahedral structure. These selected bond angles obviously deviate
from the ideal angle of 180° and bond lengths mostly are different
from each other, which demonstrate that the central ion is coordi-
nated to form a considerable distorted octahedral configuration.
In all of these compounds, amino groups from SCZ, nitro groups
from TNR2ꢀ and H2O molecules play an important role to construct
intermolecular and intramolecular hydrogen bonds, which are con-
ducive to increasing the molecular density and stability. Selected
hydrogen bonds are shown in Tables S1–S3. In 1, the benzene ring
and the Co-O-C-N-N five-member ring are almost in the same
plane (A or B), linked by N2–H2ꢁ ꢁ ꢁO5, N2–H2ꢁ ꢁ ꢁO6, N3–
H3 Aꢁ ꢁ ꢁO5 and other hydrogen bonds. Plane A is 7.174x ꢀ 0.093y
774, 703, 516 cmꢀ1
.
2.4. Synthesis of [Ni(SCZ)2(H2O)2](TNR)(H2O)2(2)
Nickel carbonate (10 mmol, 1.25 g) was added to a solution of
2,4,6-trinitroresorcinol (10 mmol, 2.45 g) in deionized water (40
mL), and the mixture was stirred at 60–65 °C until a clear solution
resulted. A solution containing SCZ (30 mmol) in deionized water
(30 mL) was added and the mixture was kept at 60–65 °C for
15 min. Then the solution was cooled to room temperature. The
precipitate was collected by filtration, washed with ethanol, and
dried under vacuum in an explosion-proof water-bath dryer. Yield:
68% (3,56 g). Yellow prism single crystals suitable for X-ray mea-
surements were obtained by recrystallization of the products from
deionized water at room temperature over half month. Anal. Calcd.
(%) for C8H19N9NiO14: C, 18.34; H, 3.65; N, 24.06. Found (%): C,
18.26; H, 3.57; N, 23.98. IR (KBr): 3830, 3745, 3463, 3323, 3239,
2423, 1633, 1534, 1387, 1303, 1165, 1086, 932, 787, 746, 688,
+ 2.823z = ꢀ1.8433 (mean deviation 0.2109 Å). Plane
B
is
7.296x ꢀ 0.053y + 2.778z = 1.7118 (mean deviation 0.1829 Å).
Obviously, plane A and plane B are almost parallel to each other
Table 1
Crystallographic data of 1–3.
632, 515 cmꢀ1
.
1–3
1
2
3
CCDC
1010968
C8H19CoN9O14
524.25
153(2)
Monoclinic
Cm
1.2723(4)
1.5900(5)
0.47442(16)
90.00
109.162(4)
90.00
0.9066(5)
2
1.921
1010970
C8H19N9NiO14
524.03
153(2)
Triclinic
P-1
0.7032(3)
0.9727(5)
1.5154(7)
108.346(6)
90.760(4)
108.039(4)
0.9283(7)
2
1013946
C8H19N9ZnO14
527.67
153(2)
Triclinic
P-1
0.7034(2)
0.9730(3)
1.5115(3)
108.302(7)
90.755(3)
108.084(14)
0.9265(4)
2
2.5. Synthesis of [Zn(SCZ)2(H2O)2](TNR)(H2O)2(3)
Empirical formula
Formula weight
T/K
Crystal system
Space group
a/nm
Zinc carbonate (10 mmol, 1.14 g) was added to a solution of
2,4,6-trinitroresorcinol (10 mmol, 2.45 g) in deionized water (40
mL), and the mixture was stirred at 60–65 °C until a clear solution
resulted. A solution containing SCZ (30 mmol) in deionized water
(30 mL) was added and the mixture was kept at 60–65 °C for
15 min. Then the solution was cooled to room temperature. The
precipitate was collected by filtration, washed with ethanol, and
dried under vacuum in an explosion-proof water-bath dryer. Yield:
54% (2.84 g). Brown prism single crystals suitable for X-ray mea-
surements were obtained by recrystallization of the products from
deionized water at room temperature over half month. Anal. Calcd.
(%) for C8H19N9ZnO14: C, 18.11; H, 3.61; N, 23.75. Found (%): C,
18.06; H, 3.50; N, 23.88. IR (KBr): 3430, 3185, 2925, 1635, 1501,
b/nm
c/nm
a
/(°)
b/(°)
c
/(°)
V/nm3
Z
Dc/(gꢁcmꢀ3
)
1.875
1.891
h/(°)
2.56–31.51
ꢀ18–18, ꢀ22–
23,
2.34 ꢂ 29.11
ꢀ9–9, ꢀ13–
13,
2.34 ꢂ 27.99
h, k, l
ꢀ9–9,
ꢀ12 ꢂ 12,
ꢀ19–19
3839
ꢀ6–6
ꢀ20–20
1392, 1325, 1200, 1089, 933, 779, 710, 533 cmꢀ1
.
Reflections
collections
2849
4949
Rint
S
0.0252
1.000
0.0554
1.001
0.0392
0.998
2.6. X-ray data collection and structure refinement
R1,wR2[I > 2
r
(I)]
0.0306, 0.0659
0.1454,
0.3710
0.1617,
0.3780
1.143
0.0898, 0.2373
The X-ray diffraction data collection was performed with a
Rigaku AFC-10/Saturn724+CCD detector diffractometer with gra-
R1,wR2(all data)
)/mmꢀ1
0.0380, 0.0906
0.0968, 0.2405
phite monochromated Mo-K
modes at 153(2) K. The structure was solved by direct methods
using SHELXS-97 and refined with SHELXL-97 [27,28]. All non-
a radiation (k = 0.71073) with u and
m(MoK
a
1.047
538
1.423
538
x
F(0 0 0)
540

L. Yang et al. / Inorganica Chimica Acta 466 (2017) 405–409
407
1.891 g cmꢀ3, so swathe construction is more compact than the
grating structure.
3.2. Thermal decomposition and non–isothermal kinetics analysis
The thermal behavior of 1–3 were investigated by using differ-
ential scanning calorimetry with a linear heating rate of 10 °-
Cꢁminꢀ1 (Fig. 5). In the DSC curves of all the three compounds,
there is one endothermic and multiple exothermic processes,
which manifest that these compounds have the similar response
to the influence of heat. The DSC curves manifest that, owing to
Fig. 1. Molecular moiety of 1. Selected coordination distances (nm): Co1ꢀO1
0.2085(2), Co1ꢀO2 0.2090(3), Co1ꢀO3 0.2071(3), Co1ꢀN1 0.2156(3); angles (deg):
O1ꢀCo1ꢀO2 92.44(9), O1ꢀCo1ꢀN1 77.04(9), O3ꢀCo1ꢀO1 92.27(9), O3ꢀCo1ꢀN1
89.92(10), O3ꢀCo1ꢀO2 173.12(13), O2ꢀCo1ꢀN1 86.25(9). Symmetry codes: (i) x,
ꢀy, z; (ii) x + 1/2, y + 1/2, z; (iii) x + 1/2, ꢀy + 1/2, z.
p-stacking and hydrogen-bonding interactions, these chelates are
all thermally stable with first exothermic peak temperatures above
200 °C. The sensitivity order is as follows: Tp2(246.8 °C)
> Tp3(241.8 °C) > Tp1(222.9 °C), which indicates that strong struc-
tural reinforcement of the grating structure in complexes 2 and 3
is thermally more stable than the swathe construction of chelate 1.
In the present works, Kissinger’s method and Ozawa-Doyle’s
method are widely used to determine the apparent activation
energy (E) and the pre-exponential factor (A) [29–31]. The Kis-
singer and Ozawa-Doyle equations are as follows, respectively.
ln b=T2p
v
¼ ln½RA=Eꢃ ꢀ E=ðRTpÞ
ð1Þ
lg b ¼ lg½AE=RGð Þꢃ ꢀ 2:315 ꢀ 0:4567E=RTp
a
ð2Þ
where Tp is the peak temperature (°C), R is the gas constant (8.314 J
°Cꢀ1 molꢀ1), b is the linear heating rate (°C minꢀ1), and G(
a) is the
reaction mechanism function.
Based on the first exothermic peak temperatures measured at
four different heating rates of 5, 10, 15 and 20 °C minꢀ1, Kissinger’s
method and Ozawa-Doyle’s method were applied to study the
kinetics parameters of 1–3. From the original data, the apparent
activation energy E, pre-exponential factor A, linear coefficient Rc
and standard deviations S were determined and shown in Table 2.
So, the Arrhenius equations of 1–3 can be expressed as follows:
(E is the average of Ek and Eo):
Fig. 2. Molecular moiety of 2. Selected coordination distances (nm): Ni1ꢀO1 0.2077
(8), Ni1ꢀO2 0.2066(9), Ni1ꢀO3 0.2183(7), Ni1ꢀO4 0.2232(9), Ni1ꢀN1 0.2114(9),
Ni1ꢀN4 0.2107(10); angles (deg): O1ꢀNi1ꢀO3 90.6(3), O1ꢀNi1ꢀN1 80.0(3),
O3ꢀNi1ꢀO4 176.6(3), O3ꢀNi1ꢀN1 89.0(3). Symmetry codes: (i) ꢀx, ꢀy, ꢀz.
ln
ln
ln
j
j
j
¼ 52:39 ꢀ 231:1 ꢄ 103=ðRTÞ
¼ 67:90 ꢀ 307:3 ꢄ 103=ðRTÞ
¼ 92:46 ꢀ 406:0 ꢄ 103=ðRTÞ
ð3Þ
ð4Þ
ð5Þ
The equations can be used to estimate the rate constants of the
initial thermal decomposition process of these compounds.
3.3. Calculation of critical temperatures of thermal explosion,
H– and G–
D
S–,
D
D
The values of the peak temperature corresponding to b ? 0
obtained according to the following Eq. (6)[32,33] are shown in
Table 3, where a, b and c are coefficients.
Fig. 3. Molecular moiety of 3. Selected coordination distances (nm): Zn1ꢀO1
0.2068(5), Zn1ꢀO2 0.2076(5), Zn1ꢀO3 0.2181(5), Zn1ꢀO4 0.2229(6), Zn1ꢀN1
0.2098(6), Zn1ꢀN4 0.2116(6); angles (deg): O1ꢀZn1ꢀO3 89.4(2), O1ꢀZn1ꢀN1 80.5
(2), O3ꢀZn1ꢀO4 175.6(2), O3ꢀZn1ꢀN1 91.4(2). Symmetry codes: (i) ꢀx, ꢀy, ꢀz.
Tpi ¼ Tp0
þ
a
b þ bb2 þ cb3
ð6Þ
The corresponding critical temperatures of thermal explosion
(Tb) obtained by the following Eq. (7) [32,33] are shown in Table 3.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
with plane angle 0.7°. And thus, complex 1 is extended into a
swathe structure (Fig. 4). In 2, in one unit cell nickel connected
five-member rings are almost in the same plane (A or B), and the
two planes are almost parallel. The planes (C and D) of benzene
rings are parallel to each other, but vertical to plane A (or B), which
constitutes a grating structure. The coordinating environment of
Tb ¼ ðE ꢀ E2 ꢀ 4ERTP0Þ=2R
ð7Þ
The entropies of activation (
D
S–), enthalpies of activation
(D D
H–), and free energies of activation ( G–) of the decomposition
reaction corresponding to T = Tp0, Ea = EK and A = AK, obtained by
the following Eqs. (8)(10)[32,33] are shown in Table 3.
compound 3 is similar with 2. Beside,
benzene rings can further enhance their structural stability. The
crystal densities of 1–3 are 1.921 g cmꢀ3 1.875 g cmꢀ3 and
p-stacking in these parallel
S–=R
A ¼ ðkBT=hÞðeD
Þ
ð8Þ
,

408
L. Yang et al. / Inorganica Chimica Acta 466 (2017) 405–409
Fig. 4. Hydrogen bonds, planes and topologies of 1 (top), 2 (middle), and 3 (bottom).
3.4. Sensitivity test
Impact sensitivity was determined by a fall hammer apparatus.
The compound (20 mg) was placed between two steel poles and
was hit by a 5.0 kg drop hammer. The tests showed that the 50%
firing heights (h50) was 30.0 cm (=15 J) for 1 and the firing rate
was 0% for the other two at 80 cm height (>40 J). The testing results
were shown in Table 4. So the grating structure possesses better
shock resistance than the swathe construction.
Friction sensitivity was determined using 20 mg sample, which
was placed on a Julius Peter’s machine. 25 tests were done. An
explosion or non-explosion was recorded. The tested compounds
did not fire, which demonstrate that these compounds are struc-
turally abrasion-resistance.
According to the method of flame sensitivity test [34], 20 mg of
1 was compacted to a copper cap under the press of 39.2 MPa and
was ignited by black powder pellet. The test result demonstrated
that the height for 50% explosion probability (h50) of 1 was 6 cm
and less than 6 cm (testing minimum height) for the other two,
which indicate that the grating structure exhibits good flame retar-
dant property.
Fig. 5. DSC curve for 1 with b = 10 °Cꢁminꢀ1 in a nitrogen atmosphere.
D
D
H– ¼ Ea ꢀ RT
ð9Þ
4. Conclusions
Three insensitive CEMs with p-stacking and hydrogen-bonding
G–
¼
D
H– ꢀ T
D
S–
ð10Þ
interactions were synthesized and characterized. Despite all the
three compounds were prepared by the similar reaction route, sin-
gle-crystal X-ray diffraction analysis revealed that complex 1 crys-
tallizes in the monoclinic space group Cm exhibiting swathe
construction, whereas the crystal structures of both 2 and 3 belong
where kB is the Boltzmann constant (1.381 ꢄ 10ꢀ23 J/K) and h is the
Planck constant (6.626 ꢄ 10ꢀ34 Jꢁs).
Table 2
Peak temperatures of the first exotherm at different heating rates and the chemical kinetics parameters.
b (°C minꢀ1
)
Tp(°C)
Parameter
Kissinger’s method
Ozawa’s method
1
2
3
1
2
3
1
2
3
5
218.1
222.4
226.5
229.8
243.3
247.6
250.5
253.2
239.8
242.3
244.4
247.1
E(kJ molꢀ1
lgA
Rc
S
)
232.8
22.78
-0.9892
0.1041
310.8
29.52
-0.9965
0.0597
412.0
40.2
-0.9771
0.1537
229.3
/
-0.9900
0.0452
303.8
/
-0.9967
0.0259
400.0
/
-0.978
0.0667
10
15
20

L. Yang et al. / Inorganica Chimica Acta 466 (2017) 405–409
409
Table 3
Calculation of Tb,
D , D D .
S– H– and G–
Compounds
Tp0 (°C)
Tb (°C)
D
S– (Jꢁ(Kꢁmolꢀ1))
D
H– (kJꢁmolꢀ1
)
D
G– (kJꢁmolꢀ1
)
1
2
3
214.2
236.4
235.9
216.5
237.9
237.1
192.9
321.1
530.4
231.0
308.8
410.0
143.4
248.1
433.7
Table 4
Physicochemical properties of compounds 1–3.
[a]
[b]
Compd
Tm (°C)
Tdec. (°C)
D[c](g cmꢀ3
)
N[d] (%)
N + O[e] (%)
IS[f] (J)
FS[g] (N)
FlS[h] (cm)
1
2
3
128
99
108
200
232
231
1.86
1.90
1.87
24.07
24.06
23.75
66.80
66.81
65.96
15
>40
>40
>360
>360
>360
6
<6
<6
[a]
[b]
[c]
[d]
[e]
[f]
Melting point/DSC endothermic peak.
Thermal decomposition temperature (onset) (DSC, 10 °C minꢀ1).
Measured density.
Nitrogen content.
Nitrogen and oxygen content.
Impact sensitivity, h50 (BAM drophammer).
Friction sensitivity.
[g]
[h]
Flame sensitivity, h50
.
to triclinic P-1 space group manifesting grating structure. DSC
analyses showed that they are thermally stable with onset decom-
position temperatures all above 200 °C. Non-isothermal kinetics
analyses reveal that the Arrhenius equations of 1–3 can be
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expressed
as
follows:
lnk = 52.39 ꢀ 231.1 ꢄ 103/(RT),
lnk = 67.90 ꢀ 307.3 ꢄ 103/(RT) and lnk = 92.46 ꢀ 406.0 ꢄ 103/(RT).
The critical temperature of thermal explosion (Tb), entropy of acti-
vation (
vation
D D
S–), enthalpy of activation ( H–), and free energy of acti-
(D
G–) of the decomposition reaction are 216.5 °C,
192.9 JꢁKꢀ1ꢁmolꢀ1, 231.0 kJꢁmolꢀ1, 143.4 kJꢁmolꢀ1 for 1, 237.9 °C,
321.1 JꢁKꢀ1ꢁmolꢀ1
,
308.8 kJꢁmolꢀ1
,
248.1 kJꢁmolꢀ1 for
2
and
237.1 °C, 530.4 JꢁKꢀ1ꢁmolꢀ1, 410.0 kJꢁmolꢀ1, 433.7 kJꢁmolꢀ1 for 3.
Sensitivity tests indicated that they are all insensitive to mechani-
cal stimuli. In addition, the lightweight grating structure (2 and 3)
shows good thermal stability, shock resistance and flame retardant
property comparing with the swathe construction (1) in a molecu-
lar level. Therefore, chelates with p-stacking and hydrogen-bond-
ing interactions as a package of strategy for designing insensitive
energetic materials is emerging, and the research on safe yet pow-
erful chelates is on the way.
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Acknowledgements
We gratefully acknowledge financial support from the State Key
Laboratory of Explosion Science and Technology (No. YB2016-16)
and the National Natural Science Foundation of China (No.
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CCDC 1010968, 1010970 and 1013946 contains the supplemen-
tary crystallographic data for compounds 1–3. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/re-
trieving. html, or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223–336–033;
or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2017.06.071.